Materials for Orthotic and Prosthetic Applications

Materials for Orthotic and Prosthetic Applications
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About This Resource HOPE Careers Consortium, a partnership of five institutions of higher education, is building exciting new programs which provide valuable career education and training in the Orthotics, Prosthetics, and Pedorthics (O&P) sector. The five institutions are: Baker College – Flint, Michigan; Century College – White Bear Lake, Minnesota; Oklahoma State University Institute of Technology – Okmulgee, Oklahoma; Spokane Falls Community College – Spokane, Washington; and St. Petersburg College – St. Petersburg, Florida. HOPE Careers Consortium is an equal opportunity program, and auxiliary aids and services are available upon request to individuals with disabilities. Click on the following link to visit the HOPE Careers Consortium Web site: LINK: HOPE Careers Consortium. The Web site address is This Open Educational Resource (OER) is provided with the goal of helping learners more fully understand the many types of materials that can be used when selecting, designing, adjusting, and fabricating orthotic and prosthetic devices. This product was funded by a grant awarded by the US Department of Labor’s Employment Training Administration. The product was created by the grantee and does not necessarily reflect the official position of the US Department of Labor. The Department of Labor makes no guarantees, warranties, or assurances of any kind, express or implied, with respect to such information, including any information on linked sites and including, but not limited to, accuracy of the information or its completeness, timeliness, usefulness, adequacy, continued availability, or ownership.

Objectives Upon successful completion of this Open Educational Resource presentation, you will be able to: Evaluate material variables to determine how best to meet a patient’s need; Compare and contrast open-cell and closed-cell foam structures; Describe the purpose of a durometer scale; Describe the purpose of a Mohs scale; Describe the properties and uses of leather in O&P devices; Explain how leather is measured; Describe the properties and uses of cork in O&P devices; Describe the properties and uses of carbon composites; Contrast and compare the key properties and uses of common thermoplastics in the O&P field; Compare and contrast the differences between thermoplastic and thermoset; Describe the properties and uses of foams and gels; Describe the properties and uses of textiles; Compare and contrast the differences between metals that are malleable and metals that are ductile; Compare and contrast the attributes of polyester, vinyl ester, and epoxy resins; and List protective measures to take when working with chemicals and dust.

Introduction: Course Management
MATERIALS FOR ORTHOTIC AND PROSTHETIC APPLICATIONS There was a time when leather, wood, and steel were the primary materials used when designing and fabricating orthotic and prosthetic devices. Not anymore. In the O&P field, thermoplastics and other synthetic materials provide varying combinations of strength, weight, flexibility, and energy return, while composites and metal alloys facilitate lighter, stronger artificial limbs. So, what materials should be selected for any given patient? Factors to consider include the patient’s age, weight, general health, occupation, hobbies and aspirations, where they live (cold or warm climate), and insurance coverage. And because there are so many material choices available and each has its own advantages and disadvantages, decisions must be made to balance material qualities, such as firmness, flexibility, rigidity, adjustability, strength … and so on. This presentation helps to address some of these issues by providing: 1. Information about the considerations to make when working with orthotic and prosthetic materials; 2. Categories and descriptions of materials used in the O&P industry: natural, synthetic, textiles, and metals; 3. Information about the chemicals used in O&P devices; and 4. Helpful, self-assessment sections. Note: Self-assessments sections are provided throughout the presentation. In addition, each materials section and the chemicals section includes a link to Quizlet, which enables further self-assessment. Quizlet is a fun and easy online learning resource featuring “STUDY” tools and “PLAY” tools. Visit the site to further your understanding of the information presented here. The length of time it will take a learner to complete this self-study resource depends greatly on the learner’s style and pace of learning as well as his / her current understanding of the subject matter. However, an estimate has been made that a learner could thoroughly read and review this material, as well as participate in all self-assessment opportunities, in approximately six hours.

Introduction: Orthotic and Prosthetic Terms
ORTHOTIC DEVICES Orthotic devices include: FO—Foot Orthosis; AFO—Ankle Foot Orthosis; KAFO—Knee Ankle Foot Orthosis; HKAFO—Hip Knee Ankle Foot Orthosis; KO—Knee Orthosis; HO—Hip Orthosis; WHO—Wrist Hand Orthosis; EWHO—Elbow Wrist hand Orthosis; SEWHO—Shoulder Elbow Wrist Hand Orthosis; SO—Sacral Orthosis; LSO—Lumbar Sacral Orthosis; TLSO—Thoracolumbosacral Orthosis; and CTLSO—Cervical Thoraco Lumbar Sacral Orthosis. PROSTHESIS TYPES Types of prostheses include: TM—Transmetatarsal Amputation; AD—Ankle Disarticulation; TT—Transtibial; TF—Transfemoral; HD—Hip Disarticulation; HP—Hemipelvectomy; WD—Wrist Disarticulation; TR—Transradial; ED—Elbow Disarticulation; TH—Transhumeral; SD—Shoulder Disarticulation; and IT—Interscapulo Thoracic.

Index Below is a list of terms/product names used in the O&P field as they relate to materials. Note: Registered trademark information can be found at the conclusion of this presentation. A: Acetal, Acrylic, Acrylic Resin, Acrylonitrile Butadiene Styrene (ABS), Aliplast®, Aluminum, and Aramid. B: Basalt Braid, Bidirectional Carbon Fiber, and Birko Cork. C: Carbon, Carbon Composites, Carbon Fiber, Carbon Fiber Braid, Carbon Fiber Reinforced Plastic / Polymer (CFRP), Carboplast®, Closed-Cell Foam, Collagen, Compressive Strength, Co-Polymer, Copper, Corium, Cork, Cork Compounds, and Cushion Cork. D: Dacron Felt, Dacron Strap, Ductility, and Durometer. E: Elasti-CorkTM, Epoxy Resin, Ethyl Vinyl Acetate (EVA), and Evazote®. F: Fiberglass, Fiberglass Tapes and Sleeves, and Foams. G: Gels. I: Impact Strength and Iron. K: Kevlar®, KorexTM, and Kydex®. L: Lamination, Lay-Up, and Leather. M: Malleability, Microcel Puff®, Mohs Scale of Hardness, Molding Temperature, and MulticorkTM. N: Neoprene, Nickelplast-S, Nyglass Stockinette, Nylon, and Nylon Stockinette. O: Open-Cell Foam, OrtholenTM, and Orthoplast®. P: P-CellTM, PPT®, Pe-Lite®, Perlon Stockinette, Plastazote®, Polycarbonate, Polyethylene Terephthalate Glycol (PETG), Polyester Resin, Polyethylene, Polyethylene Foam, Polymer, Polypropylene, Polyurethane, Polyurethane Foam, Polyvinyl Chloride (PVC), Poron®, Pre-Preg, Proflex, and Proflex with Silicone. R: Resins and Rubber. S: Silicone, Spenco®, Stainless Steel, Styrene, SubOrtholen®, and Surlyn®. T: TL-2100, Tensile Strength, Thermo CorkTM, Thermoplastic Elastomers (TPE), Thermoplastics, Thermoset, ThermoSKY®, and Titanium. U: Unidirectional Carbon Fiber. V: Velcro® and Vivak®. Y: Yield Strength.

Section 1: Decision-Making Tools

Decision-Making Tools: Overview Here you will find information that O&P professionals utilize when considering their material options.

Decision-Making Tools: Material Variables Here are variables O&P professionals consider when determining their selection of materials. Note: Additional variables continue on following slides. STRENGTH. Types of strengths measured in the O&P field: (1) Tensile strength: the resistance of a material to break under tension, (2) Compressive strength: the resistance of a material under compression, (3) Yield strength: the lowest stress that produces a permanent deformation in a material, and (4) Impact strength: the ability of the material to support or sustain an applied load. DURABILITY. The ability to withstand wear, pressure, or damage. More specifically, it refers to resistance-to-fatigue failure and repeated ability to withstand loading and unloading cycles. DENSITY. A consideration when determining how to make the O&P device as light as possible without sacrificing strength, stiffness, and durability. Calculation: The material’s weight per unit of volume. Related to density is specific (or relative) gravity, which is the ratio of the density of a substance to the density of a given reference material (usually water). HARDNESS. With rubbers, polyurethane, and plastics, hardness is described as the material’s resistance to permanent indentation and is determined through the use of a durometer (measurement and instrument). With metals, hardness can be determined through the use of a Mohs scale.

Decision-Making Tools: Material Variables, continued
STIFFNESS. The rigidity of a structure; the extent to which it resists deformation, bending, or compression when a material is loaded. The stiffer a structure, the less flexible it is and the less likely that deformation will occur. Calculation: Load divided by deformation. MOLDING TEMPERATURE. The recommended temperature at which materials should be heated for optimal molding. Note: This is typically different from the melting temperature. THICKNESS. “Iron” is a thickness-measurement tool used in the shoe industry and when dealing with leather. Calculation: One iron is equal to 1/48 inch. Synthetic O&P materials, such as thermoplastics and foams, are sold in sheets of varying thicknesses. CORROSION RESISTANCE. The degree to which the material is susceptible to chemical degradation. Contact with body fluids is an important consideration.

Decision-Making Tools: Material Variables, continued
GRINDABILITY. Defines whether or not the material can be used on a grinder. SHEET SIZE. The size and depth to which a given sheet of material is cut –typically available in a full or half sheet, roll, or wheel. MALLEABILITY. The property of a metal that enables it to be hammered, bent, pressed, or rolled into sheets without breaking. DUCTILITY. The property of a metal that enables it to stretch without damage. LAMINATION. The number of layers or materials glued together to form a single sheet. Laminating materials with different characteristics together can often produce better functioning materials.

Decision-Making Tools: Open- versus Closed-Cell Foams
Foamed thermoplastics are formed by forcing nitrogen or some other gas into the plastic during heating. They can be open-cell or closed-cell structures. Below is an overview of the key differences in the two types of cell foams. Open-Cell Foam. Pores are connected to form an interconnected network, which allows air to flow between the cells. When air fills the space, the foam becomes soft. Breathable, soft, spongy. Low Density: ½ to ¾ of a pound per cubic foot. Absorbs moisture. Resistant to compression deformation. One of the most common open-cell foams used in O&P is Poron®. It is a polyurethane foam that is compression-set resistant, fungal resistant, and breathable. Typical applications for Poron in the O&P field include custom and prefabricated orthoses, prosthetic padding, and biomechanical supports. Closed-Cell Foam. Pores are not interconnected, but instead “piled” together. Bubbles of trapped air are surrounded by cell walls, making the foam more rigid. Lightweight and washable. Medium Density: 2 to 3 pounds per cubic foot. Does not absorb fluids/ moisture. Susceptible to compression. One of the most common closed-cell foams used in O&P is Plastazote®. It is a polyethylene foam and is lightweight, non-toxic, odorless, and will not absorb water. Typical applications for Plastazote in the O&P field include custom and prefabricated foot orthoses, soft-touch skin contact material (used in braces, splints, collars, and other supports), and lightweight cosmetic covers for upper and lower limb prostheses.

Decision-Making Tools: Durometer Scales of Hardness
THE DUROMETER. The purpose of a durometer is to identify the hardness of materials—specifically, polymers, elastomers, and rubbers. It helps determine the material’s resistance to permanent indentation. The durometer is both a measurement as well as the gauge instrument used to determine the measurement. Albert Shore defined and developed hardness durometer scales—the three most common being Shore 00, Shore A, and Shore D. The points on the presser foot of the gauges get progressively sharper, from Shore 00 to Shore A to Shore D. Durometer readings should: Have a minimum thickness of ¼ inch; Be measured parallel to the surface; and Be measured within one second of pressing down with the gauge. Note: Additional durometer information follows on the next slide.

Decision-Making Tools: Durometer Scales of Hardness, continued
Here is a snapshot of how Shore scales overlap when identifying the hardness of various materials. All values, ranges, and item examples are approximate and should be used as a general guide only.

Decision-Making Tools: Mohs Scale
The Mohs scale ranks materials—specifically, minerals, gemstones, and metals—on their hardness. The scale was developed by the German geologist Friedrich Mohs. He used a simple guide of scratch resistance to determine the hardness grade of each material—that is, which materials will scratch other materials, and which materials can get scratched by other materials. The scale is considered to be relative in nature and somewhat imprecise yet highly useful. Referring to the scale to the right, zirconium can be scratched by all the materials that have a higher Mohs grade (such as glass, emerald, and diamond). Zirconium, in turn, scratches all the materials with a lower Mohs grade (such as nickel, platinum, and silver.) GRADE/VALUE and SUBSTANCE 1 to 1.5: Tin, Plastic, Pencil Lead; 2: Cadmium; 2.5 to 3: Gold, Silver, Aluminum, Copper, Zinc, Brass, Bronze; 3.5: Platinum; 4 to 4.5: Iron, Nickel, Steel, Platinum, Iron; 5 to 5.5: Zirconium, Glass; 6: Uranium, Titanium; 7: Quartz; 7.5 to 8: Emerald, Hardened Steel; 8: Topaz, Cubic Zirconia; 9: Tungsten Carbide; and 10: Diamond. Here is an example of a Mohs scale. Many variations of the Mohs scale exist. The Mohs scale provides grades based on a material’s pure state; it assumes no other substances have been added.

Decision-Making Tools: Thermoset versus Thermoplastic
Plastics tend to fall into one of two categories: thermosetting plastics or thermoplastics. Below is an overview of the two types. THERMOSET PROCESS: Chemical bonding takes place. Polymers form an irreversible chemical bond when heated. The material will not re-melt when heat is applied. Materials are heat and deformation resistant, and tend to be strong and brittle. Pros: Generally less expensive than thermoplastic; high level of dimensional stability; good for high-heat applications; resistant to high temperatures. Cons: Somewhat difficult to surface finish; cannot be remolded or reshaped; cannot be recycled. THERMOPLASTIC PROCESS: No chemical bonding takes place. Polymers soften when heated but can be remolded and recycled without affecting the material’s properties. Materials tend to be high strength, shrink resistant, chemical resistant, and easily bendable. Pros: Hard crystalline or rubbery surfaces; can be remolded and reshaped to accommodate changes or pressure areas; recyclable. Cons: Generally more expensive than thermoset; can melt if heated.

Decision-Making Tools: Temperature Conversion
Working with orthotic and prosthetic materials requires an understanding of the relationship between Celsius and Fahrenheit temperatures. Below are formulas for converting between the two types of temperatures. Converting Fahrenheit temperatures to Celsius temperatures. 1. Take the Fahrenheit temperature and subtract 32. 2. Multiply that number by 5/9 (or .555). This number is the Celsius temperature equivalent. For example, to convert 95 degrees Fahrenheit to Celsius, subtract 32 from 95, which is 63. Multiply 63 times The answer is The Celsius equivalent is 35. Converting Celsius temperatures to Fahrenheit temperatures. 1. Take the Celsius temperature and multiply by 9/5 (or 1.8). 2. Add 32 to that number. This number is the Fahrenheit temperature equivalent. For example, to convert 50 degrees Celsius to Fahrenheit, multiply 50 times 1.8, which is 90. Add 90 plus 32. The answer is 122. The Fahrenheit equivalent is 122.

Decision-Making Tools: Measurement Conversion
Use this quick reference guide when determining the size, thickness, and density of materials. Length. 1 centimeter equals 10 millimeters 1 inch equals 2.54 centimeters 1 foot equals meters 1 foot equals 12 inches 1 yard equals 3 feet 1 meter equals 100 centimeters 1 meter approximately equals feet 1 furlong equals 660 feet 1 kilometer equals 1,000 meters 1 kilometer approximately equals miles 1 mile equals 5,280 feet 1 mile equals kilometers 1 nautical mile equals kilometers Weight. 1 milligram equals grams 1 gram equals kilograms 1 gram approximately equals ounces 1 ounce equals grams 1 ounce equals pounds 1 pound equals 16 ounces 1 pound equals kilograms 1 kilogram equals 1,000 grams 1 kilogram approximately equals ounces 1 kilogram approximately equals pounds 1 stone equals 14 pounds 1 short ton equals 2,000 pounds 1 metric ton equals 1,000 kilograms

Section 2: Natural Materials

Natural Materials: Overview
This diagram provides an overview of how leather and cork, both natural materials, are categorized in terms of firmness and flexibility. Leather can be used either as a functional or an accommodative material, depending on what casting techniques and other materials are used. Cork, a subset of bark tissue, is lightweight, resilient, and shock absorbent. Cork compounds can be comprised of liquid latex (a type of rubber), nylon, wood, leather shavings, or other materials. Each combination produces a different material with different properties and different uses.

Natural Materials: Leather
Once processed, which includes the steps of pre-tanning, tanning, and finishing, leather provides some highly beneficial properties. Specifically, it is: Firm; Water repellent; Fast and soft drying; Flexible; Durable; Non-compressible; and Breathable. Because it provides both shock absorption and control, leather orthotic devices can help control excessive pronatory forces while limiting excessive vertical stress. For custom orthoses, leather can be used as top and bottom covers. Other uses for leather in the O&P field include the lining of straps, thigh lacer suspensions, T-straps (correction straps), patellar suspension cuffs, knee disarticulate sockets, ankle gauntlets, and wrist-hand orthoses. As with all materials, however, leather does have its drawbacks. Leather devices can be more bulky than thermoplastic/synthetic devices. And while leather has a low-water absorption, it does not hold up well under repeated soaking.

Natural Materials: Leather, continued
To watch a video on how leather is made, click on the following link: Video: How It’s Made: Leather. For a transcript only, click on the following link: Video Transcript— How It’s Made: Leather. LEATHER BASICS. Complex Structure: Corium and Collagen; Multi-directional layers of fibers; and Layers: Upper is the grain, bottom is the flesh side, and the center/inner layer is the Corium (core). The Corium consists of small woven, twisted fibers that join together. The Collagen molecules are long and spiral- like. Together, they can produce a soft, flexible, breathable, tough material. MEASURING LEATHER. Measured in square feet and ounces; Thickness: In ounces; One ounce = 1/64th of an inch. 1 ounce = .75 irons = 1/64 inch = .41 millimeters. 2 ounces = 1.50 irons = 1/32 inch = .78 millimeters. ….and it progresses to … 8 ounces = 6 irons = 1/8 inch = 3.18 millimeters. …and it progresses to … 16 ounces = 12 irons = 1/4 inch = 6.36 millimeters. The “Bend”: Considered the best part of the hide because of its thickness and firmness. The hide is cut down the spine to make two sides of leather. Note: “hide” typically refers to the skin of a large animal while “skin” refers to the skin of a small animal. Image Source: Pixabay.com. Access the site by clicking on the following link: Pixabay.com.

Natural Materials: Cork
Cork is a natural, renewable substance. It is harvested from the bark of cork Oak trees, which are found primarily in southwestern Europe and northwestern Africa. The trees are unharmed by the harvesting process. One of its key components is suberin, a waterproof, waxy substance. This helps make it buoyant, elastic, and fire retardant. Also noteworthy is that cork has a honeycomb-like structure that consists largely of empty spaces. Plus, its density (weight per unit of volume) is one-fourth that of water. These characteristics make cork a highly effective cushioning material. It is also recognized as being flexible and highly resilient. For orthotic devices, cork is often combined with other substances, including rubber, nylon, and thermoplastics.

Natural Materials: Cork, continued
Below are six cork-based products used in manufacturing custom orthotic devices, along with characteristics and properties of each. This list is a representation of materials available to O&P professionals and is not intended to be comprehensive in nature. 1. Birko Cork. Cork granules and nylon blend. Porous, lightweight, flexible, strong, supportive. Available in various thicknesses, as well as soft and hard densities. Grinds easily. Thermoformable. Common uses include arch support, modifications, and repair. 2. Thermo CorkTM. Shredded cork and rubber blend. Strong and flexible; good for shock absorption. Thermoformable. Its density makes it a solid option for those who do not tolerate rigid devices. Often used when a patient’s weight is a factor. Thermocork® Lite is a variation of Thermocork. 3. KorexTM. Cork granules and rubber blend. Flexible, durable. Grindable. Resists compression forces. Not thermoformable. Common uses include accommodations, forefoot extensions, and wedges. 4. Cushion Cork. Cork and rubber blend. Stiff. Not thermoformable but easy to grind and skive (cut off in thin layers or pieces) to shape. Common uses include lifts and wedges. 5. Elasti-CorkTM. Cork and rubber blend. Thermoformable. Grindable. Common uses include base layers for foot orthoses and postings. More rigid than lightweight cork. 6. MulticorkTM. Shredded cork and Ethyl Vinyl Acetate (EVA) blend. Tough, easy to grind, long lasting, good shape retention. Common uses include base layers in foot orthoses and postings, as well as arch fills, postings, and heel lifts.

Natural Materials: Review
You have two options for self-assessment: Visit Quizlet to test your knowledge of natural materials or take the multiple-choice quiz that follows. Quizlet: Click on the following link: LINK to QUIZLET: NATURAL MATERIALS O&P. Once on the site, click on “Test Your Knowledge: Natural Materials O&P.” You will see a list of words/terms and their associated meanings. Give the list a quick review. Choose any or all of the “Study” tools and “Play” tools listed at the top of the page. Test your knowledge in multiple ways, including flashcards, formal tests, spelling, and timed games. Note: With the test option, you can re-format in multiple ways and take as many times as you like. When finished, return to this presentation for more materials information. Quiz: Use the following quiz to test and apply your knowledge. Read the question and possible answers provided. Then, proceed to the next slide for the correct answer. This self-assessment consists of 10 questions.

Review Question 1 The skin of a large animal is commonly referred to as the: A. The hide. B. The bend. C. The suberin. D. The corium.

Answer Question 1 The skin of a large animal is commonly referred to as the: The answer is “A”: The hide.

Review Question 2 (Blank) is a natural, renewable substance.
A. Leather. B. Cork. C. Corium. D. Rubber.

Answer Question 2 (Blank) is a natural, renewable substance.
The answer is “B”: Cork.

Review Question 3 The waterproof, waxy substance found in cork is:
A. Korex. B. Suberin. C. Rubber. D. There is no such substance in cork.

Answer Question 3 The waterproof, waxy substance found in cork is:
The answer is “B”: Suberin.

Review Question 4 The density of cork is: A. One-half that of water.
B. One-fourth that of water. C. Equal to water. D. Two times that of water.

Answer Question 4 The density of cork is:
The answer is “B”: One-fourth that of water.

Review Question 5 As it relates to leather, a tool for measuring thickness is called a/an: A. Corium. B. Collagen. C. Iron. D. Density.

Answer Question 5 As it relates to leather, a tool for measuring thickness is called a/an: The answer is “C”: Iron.

Review Question 6 The skin of a small animal is commonly referred to as: A. The bend. B. The suberin. C. The corium. D. The skin.

Answer Question 6 The skin of a small animal is commonly referred to as: The answer is “D”: The skin.

Review Question 7 The best part of the hide because of its thickness and firmness is the: A. The collagen. B. The corium. C. The irons. D. The bend.

Answer Question 7 The best part of the hide because of its thickness and firmness is the: The answer is “D”: The bend.

Review Question 8 For orthotic devices, cork is often combined with other substances, including: A. Rubber, nylon, and corium. B. Nylon, corium, and thermoplastics. C. Rubber, nylon, and thermoplastics. D. Corium, thermoplastics, and collagen.

Answer Question 8 For orthotic devices, cork is often combined with other substances, including: The answer is “C”: Rubber, nylon, and thermoplastics.

Review Question 9 (Blank) is typically measured in square feet and ounces. A. Leather. B. Corium. C. Collagen. D. Suberin.

Answer Question 9 (Blank) is typically measured in square feet and ounces. The answer is “A”: Leather.

Review Question 10 Leather comprises a complex structure of:
A. Corium and cork. B. Collagen and Korex. C. Korex and fibers. D. Corium and collagen.

Answer Question 10 Leather comprises a complex structure of:
The answer is “D”: Corium and collagen.

Section 3: Synthetic Materials

Synthetic Materials: Overview
This diagram provides an overview of how synthetic materials are categorized in terms of firmness and flexibility. Carbon composites and some plastics are rigid materials designed to control function. Plastics can also be semi-rigid, often constructed by using layers of softer material that are reinforced with more rigid materials. Foams, ethyl vinyl acetates (EVAs), and gels are softer materials designed to provide a higher degree of accommodation and flexibility. These materials are more shock absorbent and help minimize pressure. Note: The softness or rigidness of all materials can vary based on such factors as their thickness or number and types of layers used.

Synthetic Materials: Carbon Composites
A composite material is a combination of two or more materials that, while retaining their respective identities, produce a material with characteristics different from the individual components. The plastic material that surrounds fiber reinforcement is referred to as the matrix. The primary purpose of fibers in a composite is to provide strength and stiffness, but the fiber alone can be brittle—for example, glass. Two basic types of high-strength fiber reinforcements used in prosthetics are glass and carbon. Fiberglass reinforced plastic/polymer (FRP) is commonly referred to as simply fiberglass. It is comprised of fibers and a polymer matrix. The matrix contributes to the material’s strength. Reinforcement of the matrix occurs when the FRP becomes stronger or more elastic as compared to its original strength and elasticity. Carbon fiber reinforced plastic/polymer (CFRP) occurs when carbon fiber bonds with a resin system—usually epoxy or acrylic. The resin works with the carbon fibers to form a “weave” in a geometric arrangement. The chemical bond created by carbon atoms in the resin matrix produce a material that is strong and stiff. If the orthotic or prosthetic device needs to have a strong strength-to-weight ratio, carbon fiber is a great option. For prostheses, these composites can be used for socket reinforcements, transtibial (TT) and transfemoral (TF) sockets, and Symes and Knee Disarticulation Prostheses. For orthotic devices, these composites work well for people who are highly active, overweight, or need specialized orthotic designs.

Synthetic Materials: Carbon Composites, continued
Reinforced composites should be lightweight, durable, flexible, stiff, and strong under both tension and compression. Contrast and compare the key characteristics of the materials below. 1. FIBERGLASS. Heavier than Carbon and Kevlar. Most economical and most common composite. Easy to saturate with resin. Easy to obtain. Durable and flexible. Twice as strong under compression then tension. 2.56 grams of Density 620 kilopounds per square inch (ksi) Tensile Strength 2. CARBON. Almost as light as Kevlar®. Very stiff and able to hold its shape under stress. Strong under tension and compression. Carbon fibers create stiffness and brittleness. Poor resistance to impact. 1.79 grams of Density 800 ksi Tensile Strength A Carbon-Fiberglass BLEND results in a material that is stiff and lightweight (Carbon) as well as flexible and durable (Fiberglass). 3. ARAMID (KEVLAR®). Lightest and most expensive composite. Excellent resistance to fracture under impact. Resistant to chemicals; difficult to saturate with resin. Very poor in maintaining structure or form under load. Five times as strong under compression than tension. 1.44 grams of Density 400 ksi Tensile Strength A Carbon-Kevlar BLEND results in a material that is light and stiff (Carbon) as well as light and impact / torque resistant (Kevlar).

Synthetic Materials: Carbon Composites, continued
Below is additional information about carbon composites/products and the fiber reinforcement process. 1. FIBER. All the available strength and characteristics of a composite fiber are displayed and produced only along the length of the fiber. Fiber comes in two weaves: unidirectional and bidirectional. With unidirectional, all fibers are parallel. In bidirectional, fibers cross at a 90-degree angle. The weave and angle used will determine the material’s strength, flexibility, and best uses. For example, a bidirectional carbon-fiber weave aligned 45 degrees to the line of progression will produce great flexibility and could be used in a device that needs low resistance. 2. TL-2100. TL-2100 is a thermoplastic acrylic-carbon fiber composite laminate. It is thin, lightweight, strong, heat adjustable, and available in various thicknesses and rigidities. 3. CARBOPLAST®. Carboplast® products use high-strength carbon and glass fibers. It is considered to be more flexible than TL It is available in various thicknesses and rigidities. 4. “PRE-PREG.” “Pre-preg” or “pre-preg carbon” refers to composite fabrics that have been pre-impregnated by the manufacturer with thermosetting curable resin. The resin can be polyester, epoxy, or some type of glue. Epoxy is the most common. The amount and type of resin used is based on the customer’s specifications, ensuring the right amount of fiber to resin. Pre-preg composites tend to be more expensive than thermoplastic sheet materials. It is available in unidirectional and bidirectional carbon fiber weaves.

Synthetic Materials: Thermoplastics
Thermoplastics are plastic materials (polymers) that soften when heated and harden when cooled. They can be remolded and reshaped to accommodate changes or pressure areas. Thermoplastics provide many benefits because they are lightweight, durable, easy to fabricate, water resistant, easily adjustable, and recyclable. Typically sold in sheets, thermoplastics are available in many thicknesses, strengths, colors, and finishes. Following is a list of the types of thermoplastics. Within each group of plastics, different levels of performance are available. Acrylic; Polyethylene (PE)—typically categorized by their densities: Low density (LDPE); Medium density (MDPE); High density (HDPE); and Ultra-high density (UHMWPE). Polypropylene (PP)—one of the most rigid thermoplastics; Polyvinyl Chloride (PVC); Co-polymer—a blend of polypropylene and 5% to 10% of LDPE; Polystyrene; Acrylonitrile Butadiene Styrene (ABS); Nylon; Polyethylene terephthalate glycol-modified (PETG); and Proflex/Proflex with Silicone. Key attributes to consider when selecting or comparing thermoplastics include: Sheet size; Sheet thickness; Surface type; Degree of flexibility; Degree of rigidity; Strength (also referred to as impact strength); Color; and Heating (or forming or molding) temperature.

Synthetic Materials: Thermoplastics, continued
Below is an overview of thermoplastic materials/products commonly used in the O&P field, along with some of their key attributes. Polypropylene: Rigid, strong, impact and fatigue resistant, no moisture absorption, self adhesive. Co-polymer: Good formability, rigid yet flexible, self adhesive. LDPE: Soft, flexible, low tensile strength, easy formability. HDPE: Durable, flexible, strong, resistant to impact, lightweight. Modified Polyethylene: In between co-polymer and LDPE. Orthoplast®: Low temperature plastic; once heated, can be molded and applied directly to patient. Thermoplastic Elastomers (TPE): Semi-rigid, flexible, durable. PETG (Vivak®): Transparent color, tough, hard, easy to bond and fabricate. Polycarbonate: High impact strength, durable. Acrylic: Very rigid, bondable. Kydex®: PVC and acrylic blend, rigid, strong. Ortholen®: Tough, corrosion resistant, does not become brittle or absorb perspiration. ABS: Strong, stiff, bondable. Acetal: Strong, stiff, enhanced dimensional stability, low moisture absorption. Proflex: Rubber-like ethylene based, durable, flexible. Proflex with Silicone: Very flexible, minimal rigidity, flexible. Surlyn®: Minimal rigidity, flexible, vacuum formable. SubOrtholen®: High molecular weight HDPE, flexible, tough polymer, more durable than Ortholen.

Synthetic Materials: Thermoplastics, continued
Contrast and compare the key properties of the thermoplastic materials/products listed below. Note: For heating temperatures, always check the manufacturer’s recommendations. 1. Homopolymer Polypropylene. SURFACE: Smooth. FLEXIBILITY: Very little. RIGIDITY: Very rigid. IMPACT STRENGTH: Reasonable to Poor. THICKNESS (IN INCHES): 1/32, 1/16, 3/32, 1/8, 5/32, 3/16, 1/4, 3/8, 1/2, 5/8, 3/4. HEATING TEMPS: 325 to 350 degrees Fahrenheit. COMMON USES IN O&P: Body jackets, ankle foot orthoses (AFOs), definitive sockets. 2. Colyene Co-Polymer. SURFACE: Smooth. FLEXIBILITY: More flexible than Homopolymer Polypropylene. RIGIDITY: Semi-rigid to rigid. IMPACT STRENGTH: Very good. THICKNESS (IN INCHES): 1/32, 1/16, 3/32, 1/8, 5/32, 3/16, 1/4, 3/8, 1/2, 5/8, 3/4. HEATING TEMPS: 300 to 350 degrees Fahrenheit. COMMON USES IN O&P: Helmets, definitive sockets, body jackets, splints. 3. PETG (Vivak®). SURFACE: Smooth. FLEXIBILITY: Minimal. RIGIDITY: Very rigid. IMPACT STRENGTH: Very brittle. THICKNESS (IN INCHES): 1/16, 1/8, 3/16, 1/4, 3/8, 1/2. HEATING TEMPS: 250 to 300 degrees Fahrenheit. COMMON USES IN O&P: Face masks, check sockets, burn management, upper limb static orthoses. 4. Low Density Polyethylene (LDPE). SURFACE: Smooth. FLEXIBILITY: More flexible than Homopolymer Polypropylene. RIGIDITY: Moderate. IMPACT STRENGTH: Very good. THICKNESS (IN INCHES): 1/32, 1/16, 3/32, 1/8, 5/32, 3/16, 1/4, 3/8, 1/2. HEATING TEMPS: 325 to 350 degrees Fahrenheit. COMMON USES IN O&P: Pediatric AFOs, splints, flexible socket interfaces. 5. Modified Polyethylene. SURFACE: Smooth. FLEXIBILITY: More flexible than Homopolymer Polypropylene. RIGIDITY: Semi-rigid. IMPACT STRENGTH: Very good. THICKNESS (IN INCHES): 3/32, 1/8, 5/32, 3/16, 1/4, 3/8, 1/2. HEATING TEMPS: 270 to 330 degrees Fahrenheit. COMMON USES IN O&P: Spinal orthoses, interim type of upper and lower limb orthoses. 6. High Density Polyethylene (HDPE). SURFACE: Smooth. FLEXIBILITY: More flexible than Modified Polyethylene. RIGIDITY: Semi-rigid. IMPACT STRENGTH: Very good. THICKNESS (IN INCHES): 1/8, 3/16, 1/4. HEATING TEMPS: 325 to 350 degrees Fahrenheit. COMMON USES IN O&P: May be used in place of polypropylene; tends to crack under stress.

Synthetic Materials: Thermoplastics
Below is a guide showing which thermoplastics are commonly used in O&P devices as they relate to the human body. NECK and SPINE DEVICES: Polypropylene, Co-polymer, Modified Polyethylene. UPPER LIMB DEVICES: Polypropylene, Co-polymer, LDPE, HDPE, PETG, Proflex, Orthoplast®, Proflex with Silicone. LOWER LIMB DEVICES: Polypropylene, Co-polymer, HDPE, TPE, PETG, Proflex, Proflex with Silicone. KNEE DEVICES: Polypropylene, Co-polymer. HEAD and FACE DEVICES: Polypropylene, Co-polymer, PETG, Polycarbonate. UPPER BODY DEVICES: Polypropylene, Co-polymer, LDPE, HDPE, Modified Polyethylene, Kydex®, ABS. LOWER BODY DEVICES: ANKLE and FOOT DEVICES: Polypropylene, Co-polymer, HDPE, TPE, Acrylic, Acetal.

Synthetic Materials: Foams and Gels
The softer, more supportive and protective devices help to absorb shock, minimize pressure, and improve desirable load-bearing. Devices designed to reach these goals use foam and gel materials. Firmer foams are supportive in nature while the more flexible/compressible foams are more protective. Foams have multiple uses with foot orthoses: Top layers may consist of soft, compressible foam, such as neoprene; they make an orthotic device comfortable and can extend the life of the material; Middle layers often feature polyurethane foams because they are durable, cushioning materials; and Bottom layers can comprise firmer, non-compressible materials, such as cork, dense foam, or thin plastic. Foams are categorized as either open-cell or closed-cell and are typically polyurethane, polyethylene, and/or ethyl vinyl acetates (EVAs). The softness or rigidness of a material can vary based on factors, such as its thickness and the number of layers used. Plastazote®, for example, is a polyethylene, closed-cell foam and is considered a “soft” material when a single layer is used. It would be considered more rigid if laminated, multiple layers were used. A variety of gel elastomers (natural or synthetic polymers having elastic properties), such as composite gels, thermoplastic gels, polyurethane gels, and silicone gels, provides pressure relief and shock absorption. Silicones are classified as fluids, elastomers, or resins. Common uses for silicones in prosthetic devices include distal end pads in sockets, and silicone gel inserts. Gel liners conform to the bony prominence of the residual limb and are used to provide comfort and protection.

Synthetic Materials: Foams and Gels, continued
Below is an overview of the types of synthetic materials/foams used in the O&P field. Within each group, different levels of performance are available. 1. POLYURETHANE (PU) FOAMS. Dense, open-cell, thermosetting structures that do not conform to the shape of the foot. PU foams experience little to no compression over time. PU foams are available in three groups: flexible, rigid, and elastomers; Memory foam, Poron®, Poron® Medical, and PPT® are examples of PU foams; Commonly used in the O&P field for arch support and high-impact applications. 2. POLYETHYLENE (PE) FOAMS. Closed-cell, chemically cross-linked structures that are lightweight, strong, durable, and excellent shock and moisture absorbers. Some are subject to compression with continued wear. PE foams are available in varying sheet sizes, densities, thicknesses, and colors; PE foams are known by such trade names as Plastazote®, Pe-Lite®, and Aliplast®; Commonly used in the O&P field for total-contact orthoses. 3. ETHYL VINYL ACETATES (EVAs). Closed-cell co-polymer (ethylene and vinyl acetate) structures that are lightweight, flexible, and shock absorbent. They tend to compress over time. They are softer and more resilient than PE foams. EVAs are available in a variety of durometers and thicknesses; EVAs are known by such trade names as Evazote®, Microcel Puff®, and ThermoSKY®; Commonly used in the O&P field for insoles, top and bottom covers, wedges, cushioning material, and shell material for accommodative and functional orthoses.

Below is an overview of foam materials/products commonly used in the O&P field, along with some of their key attributes and uses. Note: many products share the same or similar characteristics and compete under different trade names. Additional materials / products continue on the following slide. 1. ThermoSKY®: EVA Foam. Shock absorbing, lightweight, heat formed, various durometers. Uses: Base, middle layer, or top cover; prosthetic liners, orthotic postings, heel lifts, and shoe elevations. 2. Evazote®: EVA Foam. Various durometers, comfortable, resilient. Uses: Depending on durometer chosen, orthotic top cover and base for diabetic and arthritic patients, molded insoles, distal pads, shells, shoe elevations. 3. Microcel Puff®: EVA Foam. Shock absorbing; heat moldable; various durometers, colors, and thicknesses; tends to bottom out when put under pressure- or sore-producing areas. Uses: Top and bottom layers in foot orthoses, body jacket linings, lifts, postings, prosthetic liners, and cones. 4. Poron® and Poron® Medical Polyurethane Foam, Medical Grade. Breathable, odorless, washable, shock absorbing, very durable, lightweight, flexible, not heat moldable, grindable. Similar to PPT. Uses: Custom orthoses, prefabricated orthoses, prosthetic padding, cushioning, metatarsal and heel pads. Commonly used as the middle layer of foot orthoses. 5. P-CellTM: EVA Foam. Grindable, soft, heat-moldable, variety of thicknesses, shock absorbing, durable. Resistance to “pack-out.” Comparable to Plastazote. Uses: Cushioning, coverings, insoles. 6. PPT®, Polyurethane Foam, Medical Grade. Shock absorbing, resilient, lightweight, does not compress. Similar to Poron. Uses: Soft tissue supplement for cushioning, shock absorption, and friction reduction. Also used as self-adhesive components for heel wedges, heel lifts, metatarsal pads and bars, and longitudinal arch pads.

Below is a continuation of an overview of foam materials/products commonly used in the O&P field, along with some of their key attributes and uses. Note: Many products share the same or similar characteristics and compete under different trade names. 7. Nickelplast-S: EVA and Polyethylene Foam. Tough, tear resistant, variety of durometers, resists bottoming out, shock absorbing, resilient and rubbery quality. Uses: Cushioning, postings, sock liner, PTB liners. 8. Pe-Lite®: Expanded Polyethylene Foam. Lightweight, moisture proof, shock absorbing, variety of thicknesses, densities, and durometers. Similar to Plastazote. Uses: Cushioning, commonly used for sockets, pads, AFOs, prosthetic liners. 9. Aliplast®: Polyethylene Foam. Soft, smooth in appearance, variety of densities/durometers. Comparable to Plastazote but the rigid density of the Aliplast XPE is heavier than the rigid durometer of Plastazote. Uses: Direct-molded orthotic fabrication, cushioning, liner material. 10. Neoprene: Closed-Cell Rubber Foam. A synthetic polymer resembling rubber. Medium softness, variety of thicknesses, great compression resistance. Uses: Top cover, inlay for soft foot orthoses, full-length orthotic devices used in athletic and casual shoes with removable insoles. 11. Plastazote® Polyethylene Foam. Lightweight, heat moldable, various densities and durometers, conformable, grindable. Poor shock absorber. Contours easily to the foot. Will compress or “bottom out.” Uses: Top covers in orthoses and AFO interfaces, base layers in foot orthoses and light postings. Also used as liners for prostheses and orthoses. 12. Spenco® Closed-Cell Neoprene Foam. Contains nitrogen gas bubbles. Durable, flexible, compatible with moisture exposure. Has a nylon top cover. Uses: Orthotic arch supports, top cover for plastic orthoses, insoles.

The key information needed to select foam materials includes the durometer, sheet size, composition, molding temperature, grindability, colors, and uses. Below is an example of how this information is typically presented in an O&P materials catalog. Durometer: 35 Shore A. Sheet Size: 37 inches by 30 inches. Composition: Ethyl Vinyl Acetate (EVA). Molding Temperature: degrees to 275 degrees Fahrenheit, 2 to 3 minutes. Grindable: Yes. Available Colors: Blue, Pink, White, Black, Forest Green, Green, Purple, Yellow, Aqua, Blue/Black/Aqua, Yellow/Red/Blue/Green, Green/Purple/White, Pink/Purple/White, Black Ice, Storm. Case Quantities: 1/16 inch thickness: 48 sheets; 1/8 inch thickness: 24 sheets; 3/16 inch thickness: sheets … and so on to … 1 inch thickness: 3 sheets. Uses: Top and bottom layers in orthotics; lifts, postings, and prosthetic liners.

Synthetic Materials: Review
You have two options for self-assessment: Visit Quizlet to test your knowledge of synthetic materials or take the multiple-choice quiz that follows. Quizlet: Click on the following link: LINK to QUIZLET: SYNTHETIC MATERIALS O&P. Once on the site, click on “Test Your Knowledge: Synthetic Materials O&P.” You will see a list of words/terms and their associated meanings. Give the list a quick review. Choose any or all of the “Study” tools and “Play” tools listed at the top of the page. Test your knowledge in multiple ways, including flashcards, formal tests, spelling, and timed games. Note: With the test option, you can re-format in multiple ways and take as many times as you like. When finished, return to this presentation for more materials information. Quiz: Use the following quiz to test and apply your knowledge. Read the question and possible answers provided. Then, proceed to the next slide for the correct answer. This self-assessments consists of 10 questions.

Review Question 1 As it relates to orthotic and prosthetic materials, fiberglass is best described as: A. Heavy, durable, and flexible; easy to saturate with resin; an economical and common composite. B. Very stiff and able to hold its shape under stress. Strong under tension and compression. C. Resistant to chemicals; difficult to saturate with resin. Very poor in maintaining structure or form under load.

Answer Question 1 As it relates to orthotic and prosthetic materials, fiberglass is best described as: The answer is “A”: Heavy, durable, and flexible; easy to saturate with resin; an economical and common composite.

Review Question 2 In the thermoplastic process:
A. Carbon fiber bonds with a resin system. B. No chemical bonding takes place; plastic materials can be remolded and reshaped. C. Chemical bonding takes place; plastic materials cannot be remolded or reshaped.

Answer Question 2 In the thermoplastic process:
The answer is “B”: No chemical bonding takes place; plastic materials can be remolded and reshaped.

Review Question 3 “Pre-preg” or “pre-preg carbon” refers to:
A. Closed-cell, chemically cross-linked structures. B. Composite fabrics that have been pre-impregnated by the manufacturer with thermosetting curable resin. C. Closed-cell, co-polymer structures. D. Materials (polymers) that soften when heated and harden when cooled.

Answer Question 3 “Pre-preg” or “pre-preg carbon” refers to:
The answer is “B”: Composite fabrics that have been pre-impregnated by the manufacturer with thermosetting curable resin.

Review Question 4 Polypropylene is:
A. A high-strength fiber reinforcement. B. A type of elastomer or resin. C. One of the most rigid thermoplastics. D. Is the result of carbon fiber bonding with a resin system.

Answer Question 4 Polypropylene is:
The answer is “C”: One of the most rigid thermoplastics.

Review Question 5 Polyethylene foams are:
A. Dense, open-cell, thermosetting structures that do not conform to the shape of the foot; they experience little to no compression over time. Trade names include Poron® and PPT®. B. Closed-cell co-polymer (ethylene and vinyl acetate) structures that are lightweight, flexible, and shock absorbent; they tend to compress over time. Trade names include Microcel Puff® and ThermoSKY®. C. Closed-cell, chemically cross-linked structures that are lightweight, strong, durable, and excellent shock and moisture absorbers; some are subject to compression with continued wear. Trade names include Plastazote®, Pe-Lite®, and Aliplast®.

Answer Question 5 Polyethylene foams are:
The answer is “C”: Closed-cell, chemically cross-linked structures that are lightweight, strong, durable, and excellent shock and moisture absorbers; some are subject to compression with continued wear. Trade names include Plastazote®, Pe-Lite®, and Aliplast®.

Review Question 6 As it relates to orthotic and prosthetic materials, silicone is classified as: A. Fluids, elastomers, or resins. B. Open- or closed-cell. C. Unidirectional or bidirectional.

Answer Question 6 As it relates to orthotic and prosthetic materials, silicone is classified as: The answer is “A”: Fluids, elastomers, or resins.

Review Question 7 Carbon fiber reinforced plastic/polymer (CFRP):
A. Is one of the most rigid thermoplastics. B. Is typically categorized according to density—low, medium, high, and ultra high. C. Occurs when carbon fiber bonds with a resin system—usually epoxy or acrylic.

Answer Question 7 Carbon fiber reinforced plastic/polymer (CFRP):
The answer is “C”: Occurs when carbon fiber bonds with a resin system—usually epoxy or acrylic.

Review Question 8 As it relates to orthotic and prosthetic materials, foam is classified as: A. Unidirectional or bidirectional. B. Open- or closed-cell. C. A fluid, elastomer, or resin.

Answer Question 8 As it relates to orthotic and prosthetic materials, foam is classified as: The answer is “B”: Open- or closed-cell.

Review Question 9 Kevlar is: A. One of the most rigid thermoplastics.
B. Typically the lightest and most expensive composite; excellent resistance to fracture under impact. C. Typically categorized according to density—low, medium, high, and ultra high.

Answer Question 9 Kevlar is:
The answer is “B”: Typically the lightest and most expensive composite; excellent resistance to fracture under impact.

Review Question 10 Glass and carbon are:
A. Classified as either open- or closed-cell. B. Types of high-strength fiber reinforcements used in prosthetics. C. Typically categorized according to density—low, medium, high, and ultra high.

Answer Question 10 Glass and carbon are:
The answer is “B”: Types of high-strength fiber reinforcements used in prosthetics.

Section 4: Textiles

Textiles: Overview To watch a video on how a prosthesis is made, click on the following link: Video: How Is Your Prosthesis Made? Note: This video is image-based only. No instructional narrative is provided; therefore, no transcript is available. Textiles have numerous uses within the O&P field. The lamination process for orthoses and prostheses, for example, involves the saturation of reinforcement textiles with a resin. A reinforcement textile is a fabric/fiber, such as fiberglass, nylon, cotton, Dacron, carbon, and Kevlar, used to provide strength. The strength of the laminate is determined by the material properties of the fiber and the resin. Important properties to consider include stress, strain, stiffness (Young’s modulus), ultimate tensile strength (UTS), yield strength, brittleness, and ductility. The “lay-up” process includes: Sealing the model (PVA bag, cellulose acetate); Layering the textiles; Applying the outer PVA bag; Saturating the textiles with resin and hardener under vacuum; and Curing.

Textiles: Terms “WHAT IS …”
LAY-UP: Materials AND a Process. The combination of all textiles placed in position over the model. The process of placing successive layers of reinforcing materials in position in the model. ULTIMATE TENSILE STRENGTH (UTS): The maximum force applied before a fiber breaks. YOUNG’S MODULUS: The measure of the stiffness of a solid material.

Textiles: Nylon, Fibers, Braids, Felt, Velcro
Below are examples of textiles/products commonly used in the O&P field, along with some of their key attributes and uses. 1. Perlon® Stockinette: Used for socket laminations, AFOs, KAFOs, KOs; compatible with all types of resins; superior elasticity; smooth appearance. 2. Basalt Braid: Used for composite sockets and AFOs, plastics reinforcement; tough, durable, strong, lightweight, superior resin saturation. 3. Carbon Fiber Braid: Used for strong, lightweight layups, reinforcement for laminated devices, prosthetic sockets; lightweight, strong, conforms to irregular shapes. 4. Nyglass Stockinette: Used for sockets that need to be lightweight and thin, socket laminations, AFOs, KAFOs, KOs; combines the lightweight strength of fiberglass with the elasticity of nylon. 5. Dacron Straps: Used for arm harnesses and as reinforced strapping. Strong, durable. Resists elongation under tension. 6. Fiberglass Tapes and Sleeves: Used for reinforcement and wrapping applications to cover small areas or unique shapes; compatible with polyester, vinyl ester, and epoxy resins. 7. Nylon Stockinette: Used for socket laminations—TF and TT; nylon fibers add durability to artificial limbs and other orthotic devices. 8. Dacron Felt: Used in laminations as “base” layer/inner surface of a lamination, on the outside of the sockets for lining and padding, around trim lines; provides extra material inside of socket for grinding out reliefs without sacrificing integrity of the reinforcement material; provides little strength. 9. Velcro®: As a hook and loop fastener, used for attaching straps or padding to hard-surface materials, such as splints and braces.

You have two options for self-assessment:
Textiles: Review You have two options for self-assessment: Visit Quizlet to test your knowledge of textiles or take the multiple-choice quiz that follows. Quizlet: Click on the following link below: LINK to QUIZLET: TEXTILES O&P. Once on the site, click on “Test Your Knowledge: Textiles O&P.” You will see a list of words/terms and their associated meanings. Give the list a quick review. Choose any or all of the “Study” tools and “Play” tools listed at the top of the page. Test your knowledge in multiple ways, including flashcards, formal tests, spelling, and timed games. Note: With the test option, you can re-format in multiple ways and take as many times as you like. When finished, return to this presentation for more materials information. Quiz: Use the following quiz to test and apply your knowledge. Read the question and possible answers provided. Then, proceed to the next slide for the correct answer. This self-assessment consists of 5 questions.

Review Question 1 Young’s modulus is:
A. The measure of the stiffness of a solid material. B. The maximum force applied before a fiber breaks. C. Determined by the material properties of the fiber and the resin.

Answer Question 1 Young’s modulus is:
The answer is “A”: The measure of the stiffness of a solid material.

Review Question 2 Laminate strength is:
A. Determined by the maximum force applied before a fiber breaks. B. Determined by the material properties of the fiber and the resin. C. Determined by gauging the material’s resistance to permanent indentation.

Answer Question 2 Laminate strength is:
The answer is “B”: Determined by the material properties of the fiber and the resin.

Review Question 3 Ultimate tensile strength is:
A. The measure of the stiffness of a solid material. B. Determined by the material properties of the fiber and the resin. C. The maximum force applied before a fiber breaks. D. Determined by gauging the material’s resistance to permanent indentation.

Answer Question 3 Ultimate tensile strength is:
The answer is “C”: The maximum force applied before a fiber breaks.

Review Question 4 A reinforcement textile is:
A. Fabric or fiber used to provide strength in the lamination process. B. Used when determining a material’s resistance to permanent indentation. C. A closed-cell, chemically cross-linked structure.

Answer Question 4 A reinforcement textile is:
The answer is “A”: Fabric or fiber used to provide strength in the lamination process.

Review Question 5 Lay-up is:
A. The term used to describe the maximum force applied before a fiber breaks. B. Considered to be both materials as well as a process. C. The term used to measure the stiffness of a solid material.

Answer Question 5 Lay-up is:
The answer is “B”: Considered to be both materials as well as a process.

Section 5: Metals

Metals: Overview To watch a video on the physical properties of metals, click on the following link: Video: Physical Properties of Metals: Tensile Strength, Impact Strength, Malleability, Ductility, Melting Point. For a transcript only, click on the following link: Video Transcript—Physical Properties of Metals. Metals are used in the O&P field in many ways: For prosthetic devices, which replace parts of the body; and For orthotic devices, which augment and/or support parts of the body. With the exception of mercury, a liquid element, metals are solids at room temperature and typically have high melting points and high density. They have good electrical and thermal conductivity. One key characteristic of metals is their ability to be deformed without immediately breaking. Alternatives to metals include composite materials because they are strong, lightweight, and often less expensive than some metals. Key attributes to consider when selecting or comparing metals for O&P devices include strength—compressive, tensile, and yield; stiffness; hardness—can be determined in relative terms through use of the Mohs scale; resistance to fatigue; density; bio-compatibility; resistance to corrosion; ease of fabrication; and cost. Examples of specific considerations include: The amount of weight the device has to support—For lower-body prostheses and orthoses, the metals need to have a good resistance to fatigue. The control needed—For devices that need more control, lower density is important. Fatigue—Devices for the lower extremity must be resistant to repetitive loading.

Metals: Malleability versus Ductility
Metals are often evaluated based on their malleability and ductility. Malleability: The property of a metal that enables it to be hammered, bent, pressed, or rolled into sheets without breaking; Can be beaten into sheets. It provides information about a metal’s compressive strength. It measures how much pressure the metal can withstand without breaking. Malleable metals include but are not limited to gold, silver, aluminum, and copper. Ductility: The property of a metal that enables it to stretch without damage; Can be stretched into wires. It provides information about a metal’s tension strength. It measures how much strain a metal can withstand before failing. Ductile metals include but are not limited to gold, silver, platinum, copper, and iron.

Metals: Steel, Aluminum, Titanium, Copper
Below is an overview of four metals commonly used in the O&P field. 1. Stainless Steel: A steel alloy that contains 12% or more of chromium. Martensitic stainless steel is used in the O&P field because it can be hardened by a heat treatment. Stainless steel has a high degree of stiffness and a high resistance to corrosion. Typical applications: Joints, support uprights, washers, fasteners, rivets, screws. 2. Aluminum: The most abundant element in the earth’s crust. It is lightweight, highly conductive, non-toxic, and can be easily machined. It has a higher strength-to-weight ratio than steel, has a low resistance to fatigue, and is susceptible to corrosion from body fluids. Typical applications: Strengthening supports and other structures, rivets, screws. 3. Titanium: Ti-6AI-4v is the most common alloy used. It is stronger than aluminum and is comparable in strength of stainless steel but 60% lighter. It has a very high resistance to corrosion, is difficult to fabricate, and is more expensive than aluminum and stainless steel. Typical applications: Replacement joints, artificial limbs, implants, adapters, connectors, rotating bases. 4. Copper: Pure copper is soft; two alloys are bronze and brass. Copper alloys become stronger and more ductile as temperature goes down. It is both malleable and ductile. It has a good resistance to atmospheric corrosion, is more dense than aluminum, and is one of the best electrical conductors of all metals. Typical applications: Rivets, screws, burrs.

Metals: Review You have two options for self-assessment: Visit Quizlet to test your knowledge of metals or take the multiple- choice quiz that follows. Quizlet: Click on the following link: LINK to QUIZLET: METALS O&P. Once on the site, click on “Test Your Knowledge: Metals O&P.” You will see a list of words/terms and their associated meanings. Give the list a quick review. Choose any or all of the “Study” tools and “Play” tools listed at the top of the page. Test your knowledge in multiple ways, including flashcards, formal tests, spelling, and timed games. Note: With the test option, you can re-format in multiple ways and take as many times as you like. When finished, return to this presentation for more Materials information. Quiz: Use the following quiz to test and apply your knowledge. Read the question and possible answers provided. Then, proceed to the next slide for the correct answer. This self-assessment consists of 10 questions.

Review Question 1 In the O&P field, metals:
A. Are stronger than aluminum, and more expensive than aluminum and stainless steel. B. Can be used to make devices that replace or support parts of the body. C. Are the most abundant element in the earth’s crust and have a higher strength-to-weight ratio than steel.

Answer Question 1 In the O&P field, metals:
The answer is “B”: Can be used to make devices that replace or support parts of the body.

Review Question 2 (Blank) is both malleable and ductile, is more dense than aluminum, and is one of the best electrical conductors of all metals. A. Copper. B. Aluminum. C. Titanium. D. Stainless steel.

Answer Question 2 (Blank) is both malleable and ductile, is more dense than aluminum, and is one of the best electrical conductors of all metals. The answer is “A”: Copper.

Review Question 3 (Blank) have a high melting point, high density, good conductivity, and can be deformed without immediately breaking. A. Composite materials. B. Thermoplastics. C. Metals. D. Closed-cell foams.

Answer Question 3 (Blank) have a high melting point, high density, good conductivity, and can be deformed without immediately breaking. The answer is “C”: Metals.

Review Question 4 (Blank) is a steel alloy that contains 12% or more of chromium, a high degree of stiffness, and a high resistance to corrosion. A. Stainless steel. B. Aluminum. C. Copper. D. Titanium.

Answer Question 4 (Blank) is a steel alloy that contains 12% or more of chromium, a high degree of stiffness, and a high resistance to corrosion. The answer is “A”: Stainless steel.

Review Question 5 (Blank) measures how much pressure the metal can withstand without breaking; can be beaten into sheets. A. Durometer. B. Ductility. C. Mohs scale. D. Malleability.

Answer Question 5 (Blank) measures how much pressure the metal can withstand without breaking; can be beaten into sheets. The answer is “D”: Malleability.

Review Question 6 (Blank) measures how much strain the metal can withstand without failing; can be stretched into wires: A. Durometer. B. Ductility. C. Mohs scale. D. Malleability.

Answer Question 6 (Blank) measures how much strain the metal can withstand without failing; can be stretched into wires: The answer is “B”: Ductility.

Review Question 7 (Blank) is the most abundant element in the earth’s crust and has a higher strength-to-weight ratio than steel. A. Copper. B. Titanium. C. Aluminum. D. Gold.

Answer Question 7 (Blank) is the most abundant element in the earth’s crust and has a higher strength-to-weight ratio than steel. The answer is “C”: Aluminum.

Review Question 8 (Blank) ranks materials—minerals, gemstones, and metals—on their relative hardness. A. The durometer. B. The Mohs scale. C. The tensile meter.

Answer Question 8 (Blank) ranks materials—minerals, gemstones, and metals—on their relative hardness. The answer is “B”: The Mohs scale.

Review Question 9 (Blank) are alternatives to metals because they are strong, lightweight, and often less expensive. A. Foams and gels. B. Co-polymers. C. Composite materials. D. Copper and steel.

Answer Question 9 (Blank) are alternatives to metals because they are strong, lightweight, and often less expensive. The answer is “C”: Composite materials.

Review Question 10 (Blank) is a metal that is stronger than aluminum, and is more expensive than aluminum and stainless steel. A. Copper. B. Cadmium. C. Titanium. D. Stainless steel.

Answer Question 10 (Blank) is stronger than aluminum, and is more expensive than aluminum and stainless steel. The answer is “C”: Titanium.

Section 6: Chemicals

Chemicals: Styrene, Acetone, Toluene, MEK
When choosing chemicals, weigh the advantages and disadvantages of each, and try to use the least hazardous whenever possible. Below is an overview of commonly used chemicals in the O&P field. 1. STYRENE. A colorless liquid consisting of carbon and hydrogen; can have an odor. Primarily a synthetic chemical. Used to make plastics, rubbers, and resins. Also used as a filler or thinner and reactive cross-linker to polyester resins. Regarded as a hazardous material and possibly a carcinogen. Possible irritation to the eyes, nose, respiratory system, central nervous system, liver, reproductive system. 2. ACETONE. A colorless, volatile liquid with a mint-like odor. Moderately aggressive. Used as a solvent for plastics and synthetic fibers, a thinner to polyester and epoxy resins, and to synthesize Bisphenol A (BPA), a chemical found in hard plastics and epoxy resins. Slight toxicity in normal use. Highly flammable. Not regarded as a carcinogen. Possible irritation to the eyes, nose, throat, respiratory system, central nervous system. Considered safer and less toxic than toluene solvents. 3. TOLUENE. A colorless liquid with an aromatic Benzene-like odor. Used as a solvent. Resembles Benzene, a colorless and highly flammable liquid with a sweet smell. Harmful vapor/fumes. Flammable. Possible irritation to the eyes, nose, respiratory system, central nervous system, liver, kidneys. 4. METHYL ETHYL KETONE (MEK). A colorless liquid with a sharp, sweet alcohol-like odor. Also known as Butanone. Used as a thinner for polyester and epoxy resins. Used when an evaporation slower than acetone is desired. Water soluble. Harmful vapors/fumes. Flammable. Possible irritation to the eyes, nose, respiratory system, skin, central nervous system, mucous membranes.

Chemicals: Resins Below is an overview of three types of thermosetting resins commonly used in the O&P field. Attributes to consider when comparing and selecting resins to use in any given situation include ease of use, cost, degree of possible toxicity, strength and flexibility, degree of adhesion, shrinkage, cure time, and shelf life. POLYESTER RESINS. Thermosetting unsaturated synthetic resins combined with hardeners. Contains approximately 60% polyester and 40% styrene. Fractures easily; lacks durability: best suited for lighter-weight objects. Compatible only with fiberglass materials—limited use for lamination, seaming, and repairing. Not water resistant. Poor adhesion. High shrinkage. Shorter cure time than epoxy resins. Less expensive than epoxy resins. ACRYLIC RESINS. Produced from methyl methacrylate (MMA) and dissolved polymethyl methacrylate (PMMA). Hardness can be adjusted for various applications. More water resistant than polyester resins. Bonds to core materials better than polyester resins. Shrinks less than polyester resins on curing. More expensive than polyester resins; less expensive than epoxy resins. EPOXY RESINS. Thermosetting polymer combined with hardeners. Also known as a polyepoxide. High tension strength. Greater flexibility than polyester resins. Better than polyester resins for high-strength bonding. Does not contain styrene. Reinforces glass and carbon materials. Very little shrinkage. Able to bond dissimilar and already cured material. Longer cure time than polyester resins. More expensive than acrylic resins and polyester resins.

Chemicals: Dust Particles
Dust Particles in the Workplace Working with carbon fiber and metals adds dust particles and other abrasive elements into the air. They are by-products of the manufacturing process. Sanding and grinding create more fine dust than cutting. Depending on the material, particle size and concentration, and exposure time, dust can cause a variety of health problems. GOALS: Reduce dust infiltration for health reasons and to minimize/eliminate the possibility of combustion. A cloud of dust can cause an explosion. Even materials that do not burn in larger pieces (such as aluminum or iron) can explode in dust form, given the proper conditions. The risks associated with working around dust particles can be managed/minimized. SOLUTIONS: Proper ventilation and air-purifying systems, proper and frequent training for best practices, proper collection systems, and use of masks and respirators, especially when cutting, grinding, and sanding materials.

Chemicals: Protection
GOOD ADVICE! Wash hands thoroughly at the end of each activity and prior to eating and drinking. Use appropriate personal protective equipment (PPE) and clothing to protect hands, eyes, and the face. Remove/replace any work clothing that becomes contaminated or wet from flammable liquids. Work in a properly ventilated environment. Keep Material Safety Data Sheets (MSDS) available in case of emergencies. They provide a wide range of information, including first aid treatment, reactive elements, and fire-fighting measures. TYPES OF PROTECTION FROM CHEMICALS AND DUST: Rubber or plastic gloves and sleeves protect against heat and abrasion. Consider a heat insulating terrycloth or leather glove. Simple protective glasses can protect against flying dust and small particles. A face shield provides additional coverage and may be necessary when dealing with caustic fluids. Proper ventilation can dramatically control the amount of dust and other particles in and around a work area. A filtration mask/device may be necessary when working close to the source of dust or chemical.

You have two options for self-assessment:
Chemicals: Review You have two options for self-assessment: Visit Quizlet to test your knowledge of chemicals or take the multiple-choice quiz that follows. Quizlet: Click on the following link: LINK to QUIZLET: CHEMICALS O&P. Once on the site, click on “Test Your Knowledge: Chemicals O&P.” You will see a list of words/terms and their associated meanings. Give the list a quick review. Choose any or all of the “Study” tools and “Play” tools listed at the top of the page. Test your knowledge in multiple ways, including flashcards, formal tests, spelling, and timed games. Note: With the test option, you can re-format in multiple ways and take as many times as you like. When finished, return to this presentation for more materials information. Quiz: Use the following quiz to test and apply your knowledge. Read the question and possible answers provided. Then, proceed to the next slide for the correct answer. This self-assessment consists of 10 questions.

Review Question 1 (Blank) is a colorless liquid consisting of carbon and hydrogen, is used to make plastics, rubbers, resins, and is considered hazardous. A. Epoxy resin. B. Toluene. C. Acetone. D. Styrene.

Answer Question 1 (Blank) is a colorless liquid consisting of carbon and hydrogen, is used to make plastics, rubbers, resins, and is considered hazardous. The answer is “D”: Styrene.

Review Question 2 By-products of the manufacturing process include:
A. Acetone and toluene. B. Acrylic and epoxy resins. C. Carbon fiber and metal dust.

Answer Question 2 By-products of the manufacturing process include:
The answer is “C”: Carbon fiber and metal dust.

Review Question 3 (Blank) is a thermosetting unsaturated synthetic resin and contains styrene. A. Epoxy resin. B. Acrylic resin. C. Polyester resin.

Answer Question 3 (Blank) is a thermosetting unsaturated synthetic resin and contains styrene. The answer is “C”: Polyester resin.

Review Question 4 (Blank) provide helpful information about materials in case of emergencies. A. Durometers. B. Material Safety Data Sheets. C. Product catalogs. D. Mohs scales.

Answer Question 4 (Blank) provide helpful information about materials in case of emergencies. The answer is “B”: Material Safety Data Sheets.

Review Question 5 (Blank) is a thermosetting polymer, is also known as polyepoxide, and does not contain styrene. A. Acrylic resin. B. Polyester resin. C. Epoxy resin. D. Methyl Ethyl Ketone. .

Answer Question 5 (Blank) is a thermosetting polymer, is also known as polyepoxide, and does not contain styrene. The answer is “C”: Epoxy resin.

Review Question 6 (Blank) is a highly flammable, colorless, volatile liquid, and can be used as a solvent and thinner. A. Epoxy resin. B. Acrylic resin. C. Acetone. D. Butanone.

Answer Question 6 (Blank) is a highly flammable, colorless, volatile liquid, and can be used as a solvent and thinner. The answer is “C”: Acetone.

Review Question 7 (Blank) is a colorless liquid and is also known as Butanone. A. Methyl ethyl ketone. B. Toluene. C. Styrene. D. Acetone.

Answer Question 7 (Blank) is a colorless liquid and is also known as Butanone. The answer is “A”: Methyl ethyl ketone.

Review Question 8 (Blank) is a colorless, flammable liquid and resembles Benzene. A. Styrene. B. Toluene. C. Acetone. D. Methyl ethyl ketone.

Answer Question 8 (Blank) is a colorless, flammable liquid and resembles Benzene. The answer is “B”: Toluene.

Review Question 9 (Blank) is/are more water resistant than polyester resins and bonds to core materials better than polyester resins; is less expensive than epoxy resins. A. Styrene. B. Acrylic resins. C. Acetone. D. Thermoplastics.

Answer Question 9 (Blank) is/are more water resistant than polyester resins and bonds to core materials better than polyester resins; is less expensive than epoxy resins. The answer is “B”: Acrylic resins.

Review Question 10 Using these will help minimize / manage the risk of dust particles in the workplace. A. Durometers. B. Acetone and styrene. C. Material Safety Data Sheets. D. Masks, respirators, ventilation, and collection systems.

Answer Question 10 Using these will help minimize / manage the risk of dust particles in the workplace. The answer is “D”: Masks, respirators, ventilation, and collection systems.

Full Review Use the following Full Review Section to test and apply your knowledge. The self-assessment included in this section features multiple-choice questions that cover subject matter from the entire presentation. Read the question and determine the answer that most accurately reflects the correct response. Proceed to the next slide for the correct answer. The self-assessment consists of 10 questions.

Review Question 1 Which one of the following represents an example of a soft material that might be used in the fabrication of a foot orthosis? A. Carbon fiber. B. Polypropylene. C. Open-cell polyurethane foam. D. Polyester resins.

The answer is “C”: Open-cell polyurethane foam.
Answer Question 1 Which one of the following represents an example of a soft material that might be used in the fabrication of a foot orthosis? The answer is “C”: Open-cell polyurethane foam.

Review Question 2 The process wherein polymers form an irreversible chemical bond when heated and the material cannot be remolded or reshaped is called: A. Thermoplastic. B. Thermoset. C. Young’s modulus. D. Pre-preg.

The answer is “B”: Thermoset.
Answer Question 2 The process wherein polymers form an irreversible chemical bond when heated and the material cannot be remolded or reshaped is called: The answer is “B”: Thermoset.

Review Question 3 The property of a metal that enables it to be hammered, bent, pressed, or rolled into sheets without breaking is: A. Ductility. B. Grindability. C. Malleability. D. Durability.

The answer is “C”: Malleability.
Answer Question 3 The property of a metal that enables it to be hammered, bent, pressed, or rolled into sheets without breaking is: The answer is “C”: Malleability.

Plastazote, Pe-Lite, and Aliplast are examples of:
Review Question 4 Plastazote, Pe-Lite, and Aliplast are examples of: A. Polyester resins. B. Carbon fiber reinforced plastics. C. Open-cell thermosetting foams. D. Polyethylene foams.

Answer Question 4 Plastazote, Pe-Lite, and Aliplast are examples of:
The answer is “D”: Polyethylene foams.

Acetone and toluene are both:
Review Question 5 Acetone and toluene are both: A. Chemical solvents. B. Steel alloys. C. Polyester resins. D. Lamination materials.

Answer Question 5 Acetone and toluene are both:
The answer is “A”: Chemical solvents.

Review Question 6 Foamed thermoplastics are formed by forcing nitrogen or some other gas into the plastic during heating. They can be: A. Malleable or ductile. B. Open-cell or closed-cell. C. Natural or synthetic. D. Dense or durable.

The answer is “B”: Open-cell or closed-cell.
Answer Question 6 Foamed thermoplastics are formed by forcing nitrogen or some other gas into the plastic during heating. They can be: The answer is “B”: Open-cell or closed-cell.

Density can be calculated:
Review Question 7 Density can be calculated: A. As the load divided by deformation. B. Using the Mohs scale. C. Using a durometer. D. As the material’s weight per unit of volume.

Answer Question 7 Density can be calculated:
The answer is “D”: As the material’s weight per unit of volume.

Review Question 8 The tool that helps determine a material’s resistance to permanent indentation is the: A. Mohs scale. B. Iron. C. Durometer. D. Laminator.

The answer is “C”: Durometer.
Answer Question 8 The tool that helps determine a material’s resistance to permanent indentation is the: The answer is “C”: Durometer.

Review Question 9 The process of placing successive layers of reinforcing materials in position in the model is called: A. Young’s modulus. B. Lay-up. C. Pre-preg. D. Thermosetting.

The answer is “B”: Lay-up.
Answer Question 9 The process of placing successive layers of reinforcing materials in position in the model is called: The answer is “B”: Lay-up.

Review Question 10 In the lamination process, reinforcement textiles are fabric / fibers used to provide: A. Strength. B. Comfort. C. Weight. D. Tension.

The answer is “A”: Strength.
Answer Question 10 In the lamination process, reinforcement textiles are fabric / fibers used to provide: The answer is “A”: Strength.

Attributions Aliplast is a registered trademark of Alimed.
Carboplast is a registered trademark of Aetrex Worldwide, Inc. Dacron is a registered trademark of DuPont. ElastiCork is a registered trademark of Acor Orthopaedic, Inc. Evazote is a registered trademark of Zotefoams, Inc. Kevlar is a registered trademark of DuPont. Kydex is a registered trademark of Kydex LLC. Microcel Puff is a registered trademark of Acor Orthopaedic, Inc. Multicork is a registered trademark of Acor Orthopaedic, Inc. Ortholen is a registered trademark of Teufel Orthopedic / Wilhelm Julius Teufel. Perlon is a registered trademark of Perlon-Monofil GMBH. PPT is a registered trademark of Langer Biomechanics Group, Inc. P-Cell is a registered trademark of Acor Orthopaedic, Inc. Pe-Lite is a registered trademark of Fillauer, LLC. Plastazote is a registered trademark of Zotefoams, Inc. Poron is a registered trademark of Rogers Corporation. Spenco is a registered trademark of Spenco Medical Corporation. SubOrtholen is a registered trademark of Teufel Orthopedic. Surlyn is a registered trademark of DuPont. Thermo Cork is a registered trademark of Aetrex Worldwide, Inc. ThermoSKY is a registered trademark Aetrex Worldwide, Inc. Velcro is a registered trademark of Velcro Industries B.V. VIVAK is a registered trademark of Sheffield Plastics Inc. Although the authoring institution of this educational resource has made every effort to ensure that the information presented is correct, the institution assumes no liability to any party for any loss, damage, or disruption caused by errors or omissions. Additionally, this information is not intended to serve as a substitute for professional medical advice. Produced 2016. Images used from Pixabay are released into the public domain under Creative Commons CC0. Click on the following link for more information: Link: Creative Commons CC0. This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this license, click on the following link: Creative Commons Licenses 4.0.

TRANSCRIPT: How It’s Made: Leather YouTube Video Link: How It's Made: Leather NOTE: The video is closed captioned and provides a transcript. However, some words have been transcribed incorrectly. Below is a revised transcript edited for accuracy. It serves as a companion piece to the video or can be used as a stand-alone resource. The transcript continues to the next slide. BEGINNING Leather production dates back to primitive times when humans rubbed fats into animal skins to preserve them. Times have changed but leather endures. From footwear to furniture, this tough material remains an integral part of our lives. This leather comes from the hides of cows killed for meat. Without tanning, these cowhides would go to waste. Converting them to leather is a kind of recycling. The first step is to cut each hide in half. The hides are draped over a sawhorse, stamped with an identification code, and sliced down the center. Two smaller pieces will be easier to handle in process than one large hide. Hundreds of these hide halves are loaded into a modified cement mixer for some serious hair removal. As the mixer fills with water, a worker dumps in a combination of sodium sulfhydrate and lime. A chemical reaction strips the hair from the hides. The hairless hides now get an acid bath to prepare them for the tanning process. The tanning itself happens inside big wooden drums with prongs to keep the skins from getting tangled. Chrome salts turn the hides a robin’s egg blue as they bind to the collagen fibers of the skins. The hides have now been preserved into leather. Next, the pieces are fed grain-side-up into a machine that slices the leather to an even thickness. The cutoffs won’t be wasted. They’ll be recycled into suede. (Click on the arrow to continue the video transcript)

TRANSCRIPT: How It’s Made: Leather Video, continued
Workers check each piece of leather with a gauge to confirm that the thickness is uniform. Now, it’s back into the wooden drums for a second tanning—this time using a solution of vegetable extract, tree bark, and water. Dye is added along with a chemical that will make the leather water-resistant. The solution binds to the leather, giving it a brownish tone. It’s a gentler process than the first tanning, and it softens the leather. Now, a mixture of starch and water is brushed onto the tanned hides. This paste-like solution allows the hides to be pressed onto big glass frames, which also have been moistened with the same starchy mixture. This process allows the leather to dry flat, prevents it from shrinking, and stops the edges from curling up. After four hours in a dryer, it’s time to remove the leather. It easily peels away from the glass. A revolving paint gun system dyes the leather. And now it’s time for the finishing touches. A glazing jack pulls a glass cylinder over the leather and the abrasive action polishes it. This glass is very strong so it can do this vigorous work without shattering. Finally, huge heated rollers smooth out any wrinkles. It’s the end of the production line for this big pile of leather but just the beginning for so many other products. Fashionable and tough, it’s no wonder this ancient material continues to be one of our favorite products today. CONCLUSION (Click on the arrow to return to the presentation)

TRANSCRIPT: Physical Properties of Metals YouTube Video Link: Physical Properties of Metals NOTE: The video is closed captioned and provides a transcript. However, some words have been transcribed incorrectly. Below is a revised transcript edited for accuracy. It serves as a companion piece to the video or can be used as a stand-alone resource. The transcript continues to the next slide. BEGINNING: TENSILE STRENGTH: Tensile strength is the strength in tension—that is, a pulling force. To test tensile strength, you put a sample into a tensile meter and pull until it breaks. This sample of mild steel broke at about 8 kilonewtons. The cast iron breaks at about 5 kilonewtons. So, although cast iron is harder, it is weaker in tension. On a larger tensile meter, it is possible to see how mild steel behaves under tension. At first it stretches elastically—that is, it will return to its original shape when the load is removed. Then, it passes its elastic limit at the yield point. Any stretching beyond here is permanent. The sample necks and then ruptures. Comparing it to an original bar, you can see how much it has stretched. TOUGHNESS OR IMPACT STRENGTH. Toughness is a measure of how much work it takes to break a steel. If it is strong and also bends a lot before breaking, then it takes a lot of work to break it. This machine allows us to compare the impact strength or toughness of various metals. Mild steel, distorted a little and absorbed the energy of the weighted pendulum, it is very tough. Now, cast iron. It snaps easily and there is even energy left over. So, although it is hard, it is not tough. It can’t absorb energy because it doesn’t stretch before it breaks. Brass is similar to mild steel. (Click on the arrow to continue the video transcript)

TRANSCRIPT: Physical Properties of Metal Video, continued
MALLEABILITY. Malleability is the ability of steel to be distorted by compression or squeezing—how easy it is to be rolled or hammered out into a thin sheet. The malleability of steel varies with its carbon content. It is very malleable when it is red hot. DUCTILITY. When steel sheet is being pressed into shape, it needs to be malleable and it needs to be ductile as well. Ductility is the ability to stretch. MELTING POINT. The melting and softening point of metals varies a lot. A drill point may get hot so it must have a high melting and softening point. CONCLUSION. (Click on the arrow to return to the presentation)

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