Download presentation
Presentation is loading. Please wait.
1
Hydrogels and Their Biomedical Uses
2
Overview Hydrogels Structure Swelling properties Biomedical Uses
3
Common Hydrogels? Can you think of hydrogels in your everyday life?
- Contact Lenses - Jello (a collagen gel ~ 97% water) - Extracellular matrix components - Polysaccharides - DNA/RNA - Blood clot
5
Applications of Hydrogels
Soft contact lenses Pills/capsules Bioadhesive carriers Implant coatings Transdermal drug delivery Electrophoresis gels Wound healing Chromatographic packaging material
6
Hydrogels “Hydrogels are water swollen, cross-linked polymeric structures produced by the simple reaction of one or more monomers or by association of bonds such as hydrogen bonds and strong van der Waals interactions between chains.” -N. A. Peppas in Biomaterials Science (1996)
7
Other definitions Water insoluble, three dimensional network of polymeric chains that are crosslinked by chemical or physical bonding Polymers capable of swelling substantially in aqueous conditions (eg hydrophilic) Polymeric network in which water is dispersed throughout the structure
8
Behavior of Hydrogels No flow when in the steady-state
By weight, gels are mostly liquid, yet they behave like solids They can absorb large quantities of water May absorb up to 1000 times their dry weight Cross linkers within the fluid give a gel its structure (hardness) and contribute to stickiness (tack).
9
Q = actual sample volume in the swollen state
Volume degree of swelling (Q) Q = actual sample volume in the swollen state volume in the dry state
10
= actual sample weight in the swollen state
Weight degree of swelling = actual sample weight in the swollen state weight in the dry state
11
Based on structural features, hydrogels can be classified as...
Amorphous hydrogels Randomly arranged macromolecular chains Semicrystalline hydrogels Dense regions of ordered macromolecular chains (crystallites) Hydrogen bonded hydrogels 3-D network held together by hydrogen bonds Strong hydrophobic/hydrophillic interactions
12
Based on crosslinkers features, hydrogels can be classified as...
Chemical Physical
13
Chemical Covalently crosslinked Absorb water until they reach equilibrium swelling (crosslink density dependent) High stability in harsh environments (high temp, acidic/basic and high stress)
14
Non-covalently crosslinked
Physical Non-covalently crosslinked Disordered networks are held together by associative forces capable of forming non-covalent crosslinks (molecular entanglements, electrostatic interactions, hydrogen bonding, and hydrophobic interactions) Weaker and more reversible forms of chain-chain interaction Respond to physical changes (temperature, pH, ionic strength and stress)
15
Hydrogel Fabrication Chemical hydrogels Physical hydrogels
Covalently crosslinked Noncovalently crosslinked ▪ Hydrogen bonding ▪ hydrophobic interaction ▪ crystallinity ▪ stereocomplex formation ▪ ionic complexation Thermoset hydrogels Thermoplastic hydrogels Reliable shape stability and memory Limited shape stability and memory
17
Physical crosslinking
Cross-linking without chemical reaction ionic interaction, hydrogen bonding, antigen-antibody interaction, supramolecular association • Ionic hydrogel
20
Chemical Hydrogels Methods
Co-polymerization of monomer and crosslinker HEMA and EGDMA (Ethylene glycol dimethacrylate) Crosslinking water soluble polymers Conversion of hydrophobic polymers to hydrophilic polymers plus crosslinking
21
Chemical crosslinking
Hydrogel Fabrication Chemical crosslinking Polymerization of water soluble monomers in the presence of bi- or multifunctional cross-linking agent + Monomer Crosslinker Vinyl group-containing water-soluble polymers Copolymerization Polymerization Hydrogel network
22
EGDMA HEMA
26
An example as Wound Dressing
29
Ref.:
30
poly(acrylic acid) (PAAc)
31
Based on ionic charges, hydrogels can be classified as...
Neutral hydrogels No charge Anionic hydrogels Negatively charged Cationic hydrogels Positively charged Ampholytic hydrogels Capable of behaving either positively or negatively
32
Classes of Hydrogels
33
Hydrogel Forming Polymers
Natural O H 2 C N a n p o l y ( h u r i c d ) s m g t e Synthetic O N H n p o l y ( e t h g c ) a i d - s r m
35
Hydrogel Swelling One or more highly electronegative atoms which results in charge asymmetry favoring hydrogen bonding with water Because of their hydrophilic nature dry materials absorb water By definition, water must constitute at least 10% of the total weight (or volume) for a materials to be a hydrogel When the content of water exceeds 95% of the total weight (or volume), the hydrogel is said to be superabsorbant
36
Important features of hydrogels
Usually comprised of highly polyionic polymers Often exhibit large volumetric changes eg. highly compressed in secretory vesicle and expand rapidly and dramatically on release Can undergo volumetric phase transitions in response to ionic concentrations (Ca++, H+), temperature, ... Volume is determined by combination of attractive and repulsive forces: repulsive electrostatic, hydrophobic attractive, hydrogen binding, cross-linking Secretory غده مترشحه
37
Swelling...Thermodynamically Speaking
Network starts to swell due to the thermodynamic compatibility of the polymer chains and water Swelling in chemical (crosslinked) polymers is dependent on the solvent Swelling force is counterbalanced by the retractive force induced by the crosslinks of the network Swelling equilibrium is reached when these two forces are equal Degree of swelling can be quantified by: ratio of sample volume in the swollen state to volume in the dry state weight degree of swelling: ratio of the weight of swollen sample to that of the dry sample
38
Swelling Properties Gibbs Free Energy Chemical Potential
DG=DGelastic+DGmix Chemical Potential m1-m1,0=Dmelastic+Dmmix Dmmix=RT(ln(1-2v2,s)+v2,s+c1v^22,s) G=Gibbs Free Energy work exchanged by the system with its surroundings minus the work of the pressure forces during a reversible transformation of the system from the same initial state to the same final state DG<0 Spontaneous DG=0 Equilibrium DG>0 Non-spontaneous
39
Swelling Properties Gibbs Free Energy Chemical Potential
DG=DGelastic+DGmix Chemical Potential m1-m1,0=Dmelastic+Dmmix Dmmix=RT(ln(1-2v2,s)+v2,s+c1v^22,s) m= Chemical Potential the chemical potential is the change in a characteristic thermodynamic state function per change in the number of molecules Particles will tend to move from regions of high chemical potential to regions of low chemical potential G=Gibbs Free Energy work exchanged by the system with its surroundings minus the work of the pressure forces during a reversible transformation of the system from the same initial state to the same final state DG<0 Spontaneous DG=0 Equilibrium DG>0 Non-spontaneous Electrophoresis: For example, consider charged particles in a fluid. A concentration gradient in a fluid may promote movement of particles in one direction, and the electric potential gradient may promote movement of the particles in another. The chemical potential would account for both concentration and electric components and describe a potential distribution that determines net particle movement. In hydrogels: accounts for water on outside and inside of polymer network, can be altered by heat formed during mixing and entropy changes during mixing
40
Swelling Properties Gibbs Free Energy DG=DGelastic+DGmix
Chemical Potential m1-m1,0=Dmelastic+Dmmix Dmmix=RT(ln(1-2v2,s)+v2,s+c1v^22,s) v2,s=polymer volume fraction of the gel v2,s= Volume of polymer = vp = 1 __________________ __ __ Volume of swollen gel vgel Q Q= volume degree of swelling c1= polymer-water interaction parameter (look up in a table) R= Universal Gas Constant= 472(15) J K−1 mol−1
41
Some swollen Hydrogels
Highly swollen hydrogels: cellulose derivatives poly(vinyl alcohol) poly(ethylene glycol) What do these all have in common? Lots of OH (or =O) groups to interact with acidic environments hydrophillic swelling Moderately or poorly swollen hydrogels: poly(hydroxyethyl methacrylate), PHEMA and derivatives One may copolymerize a highly hydrophilic monomer with other less hydrophilic monomers to achieve desired swelling properties
42
Contact Angle (wetability)
Hydrophobic – “water hating” Hydrophilic – “water loving” Why is this important to materials selection? Do you want your eyes to be dried out by your contact lenses? Probably not… * Cool fact, fluorinated surfaces have the most hydrophobic properties and are deemed super-hydrophobic.
43
Electrowetting of the surface
Top: charge neutral (grounded) surface with high contact angle Bottom: Allowing voltage between the drop and the electrode changes the distribution of electric charge within the drop and significantly decreases the contact angle. The polarity of voltage in the drawing is arbitrary, and in both directions electrowetting will occur. In a natural environment, this may be electric charge change due to pH changes
44
Other Important Properties
Solute diffusion coefficient through the hydrogel Optical properties Mechanical properties Hydrophilic hydrogel surfaces are poor substrates for Protein adsorption Cell adsorption
45
How biological hydrogels grow
Polymerization/deposition (blood clots) 12/2/2019
46
Environmentally Responsive Hydrogels
Hydrogels that exhibit swelling changes due to the external pH Temperature Ionic Concentration
47
Environmentally Responsive Hydrogels
pH Location in Body pH Gastric Contents 1.0 Urine Intracellular 6.8 Interstitial (also called extravascular compartment or tissue space) 7.0 Blood
48
Environmentally Responsive Hydrogels
Temperature Location in Body Temperature °C Normal Core 37 Deviations During Disease Normal Skin 28 Skin at Extremeties 0-45
49
Environmentally Responsive Hydrogels
Ionic concentration Cations Concentration in Blood (mEq/L) Sodium 142 Pottasium 4 Calcium 5 Magnesium 2 Anions Concentration in Blood (mEq/L) Chlorine 101 Bicarbonate 27 Phosphate 2 Sulfate 1 Proteins 22 Notice they both add up to the same…equillibrium
50
Hydrogel Advantages Non-thrombogenic
Non-ionic hydrogels used for blood contacting applications Heparinized hydrogels show promise Biocompatible Good transport of nutrients to cells and products from cells May be easily modified with cell adhesion ligands Can be injected in vivo as a liquid that gels at body temperature Thrombogenic لخته زا
51
Advantages of Hydrogels
Environment can protect cells and other substances (i.e. drugs, proteins, and peptides) Timed release of growth factors and other nutrients to ensure proper tissue growth Good transport properties Easy to modify
52
Disadvantages of Hydrogels
Low mechanical strength Hard to handle Difficult to load difficult to be sterilized
53
Types of Hydrogels Natural Polymers
Dextran, Chitosan, Collagen, Dextran Sulfate Advantages Generally have high biocompatibility Intrinsic cellular interactions Biodegradable Cell controlled degradability Low toxicity byproducts Disadvantages Mechanical Strength Batch variation Animal derived materials may pass on viruses intrinsic ذاتي، اصلي، باطني، طبيعي، ذهني، روحي، حقيقي، مرتب، شايسته
54
Types of Hydrogels Synthetic Polymers
PEG-PLA-PEG, Poly (vinyl alcohol) Advantages Precise control and mass produced Can be tailored to give a wide range of properties (can be designed to meet specific needs) Low immunogenecity Minimize risk of biological pathogens or contaminants Disadvantages Low biodegradability Can include toxic substances Combination of natural and synthetic Collagen-acrylate, P (PEG-co-peptides)
55
Properties of Hydrogels
Pore Size Fabrication techniques Shape and surface/volume ratio H2O content Strength Swelling activation
56
Why Hydrogels? Tissue Engineering Scaffolds for tissue engineering
Cell Culture Systems Drug Delivery Time released delivery Contact Lenses
57
Biomedical Uses for Hydrogels
Common Scaffolds in tissue engineering. Sustained-release delivery systems Hydrogels that are responsive to specific molecules, such as glucose or antigens can be used as biosensors. Disposable diapers where they "capture" urine, or in sanitary napkins Contact lenses (silicone hydrogels, polyacrylamides) Medical electrodes using hydrogels composed of cross linked polymers (PEO, polyAMPS and polyvinylpyrrolidone) Lubricating surface coating used with catheters, drainage tubes and gloves Hydrogels are non-adherent and can be removed without trauma to the wound. Slough sich häuten (Tiere); sich ablösen; abwerfen (Haut); aufgeben Diaper پارچهء قنداق، گل و بوتهداركردن، گل و بوته كشيدن،كهنهء بچه را عوض كردن PolyAMPS, or poly(2-acrylamido-2-methyl-1-propanesulfonic acid), is an organic polymer. It is water-soluble, forms gels when cross linked, and acts as an anionic polyelectrolyte. It can be used for ion exchange resins. It can form hydrogels.
58
Biomedical Uses for Hydrogels
Less common uses include Breast implants Dressings for healing of burn or other hard-to-heal wounds. Wound gels are excellent for helping to create or maintain a moist environment. Reservoirs in topical drug delivery; particularly ionic drugs Artificial tendon and cartilage Wound healing dressings (Vigilon®, Hydron®, Gelperm®) non-antigenic, flexible wound cover permeable to water and metabolites Artificial kidney membranes Artificial skin Maxillofacial and sexual organ reconstruction materials Vocal cord replacement Butt injections Kidney کليه Butt مقعد
59
Headlines
60
Smart Polymers: Hydrogels and Shape Memory Polymers
Ref.: Smart Polymers: Hydrogels and Shape Memory Polymers Dr. Jenny Amos February 19, 2009
Similar presentations
© 2025 SlidePlayer.com Inc.
All rights reserved.