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Design of a mechanical testing device for ESEM for Bone fracture healing assessment.

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Presentation on theme: "Design of a mechanical testing device for ESEM for Bone fracture healing assessment."— Presentation transcript:

1 Design of a mechanical testing device for ESEM for Bone fracture healing assessment

2 Participants Project Sponsor Dr. Stephen Doty, Hospital of Special Surgery Project Advisors Luis Cardoso, Ph.D and Marom Bikson Ph.D from The Biomedical Engineering Department at City College Stewart Russell, Ph.D Students Rasha Aaskar Gaurav Aggarwal Cristina Alexandrescu, Team Leader Francisco Saenz

3 Table of Contents Introduction –Project Goals –Clinical Need –Physiology of Bone Healing Background –Current Testing Methods for Assessing Healing Concept Development –Design Specifications –Constraints –Existing Products Concept Design –Universal External Testing Stage –Concept 1: Piezo Actuator –Concept 2: DC Electric Motor –Advantages & Disadvantages Conclusion

4 Project Goals Develop a device that is capable to: –Perform mechanical testing on fractured bone during the healing process –Allow placement inside the ESEM for microscopic analysis

5 Clinical Need Understand the mechanisms of fracture healing –Evaluation of the mechanical properties –Microscopic assessment of the tissue composition Analyze the effects of different treatments in the fracture repair process –Increase in rate of healing –Improve the strength of the fracture site Improve patient’s quality of life

6 Physiology of Bone Healing Inflammation –Occurs immediately after fracture –Mechanical stability is achieved by presence of hematoma –Callus forms by bridging the fracture site »Takes 2-3 days Reparation –Callus size increases to unite fracture site and reduce bone motion –Callus begins mineralization and eventually matures into lamellar bone --> bony union occurs »Takes 4-12 weeks Remodeling –Characterized by Wolff’s Law –Fully restore anatomical configuration of bone »Takes 6 months to 1 year in adults

7 Current Testing Methods for Assessing Fracture Healing Qualitative methods –Radiography –Densitometry Quantitative methods –Mechanical testing Three point bending Four point bending Torsion These tests measure: –Stiffness –Ultimate load –Work to failure –Ultimate displacement Hiltunen et al

8 Design Specifications Testing Method –Four point bending inside the ESEM Components –A motor that applies a chosen range of forces –Sensors to measure: Displacement Force Applied Materials –440C Stainless Steel –UHMWPE –Rubber –Copper Tubing Design should allow easy visualizations of bone callus for microscopic analysis The Data Acquisition will initially be done via Lab View and NI DAQ Hardware ParametersValue Workable Area Length 20 cm Depth 8 cm Height 10 cm Internal Environmental Conditions Type of Atmosphere Partial ~ 4000 Pa Temperature 25 Degrees Celsius Measurement Feedback Scales Force 0 ~ 30 newtons Displacement 0 ~ 3 mm Accuracy Force 1 micro-newton Displacement 0.01 mm Force Lost Due to Components (Gears, shafts, couplers, etc.) To The Bone 0.01 newtons

9 Constraints ESEM –Minimal alterations to microscope –Electromagnetic and environmental conditions –Workable space inside the chamber Device Components –Satisfy ESEM constraints –Must be sturdy and secured inside the chamber Testing Conditions –Bone hydration

10 Initial Concepts of Internal Testing System Modification of existing stage gear system –Requires excessive modification of the ESEM Use of the external port of the ESEM –Requires the creation of a Vacuum seal –Modification of the port assembly of the ESEM These two concepts might result in damage of the ESEM and are too expensive to be pursued.

11 Existing Products There exist devices that meet the design criteria and overcome the imposed constraints –Prices range from $10,000-30,000 –Encompass all testing methods –Customized software applications Courtesy of

12 Therefore… Existing commercial devices provide an immediate solution to the original design specifications However these systems are too expensive These challenges can be overcome by building an external device as opposed to an internal one. The external testing system will: –Be a cheaper alternative to commercial devices –Perform the most relevant testing method for fracture healing studies –Specifically designed for testing of mouse bones –Be portable for usage in multiple microscopes –While having a self locking mechanism to maintain deformation –Be used as a prototype for preliminary studies to determine clinical relevance –Be safe for the ESEM No fragmentation of bone No alterations No EMF

13 Concept Designs Test system: –Accommodates motors and linear actuators –Minimizes alterations to the stage design. Criteria: –Cost –Accuracy –Size –Locking Mechanism

14 Universal External Testing Stage Y Z X Interface for bone (consisting of hardened liquid polymer [polyethylene] and metal coupler). Applies four point bending force. Physical stage constructed of Stainless Steel or polyethylene with maximum size of 20 x 8 x 10 cm Motor / Actuator Load Cell LVDT

15 Concept 1 Piezo Actuator Composed of a ceramic material that expands and contracts in response to an applied electrical voltage

16 Piezo Actuator (cont’d) Advantages –Self locking when power is removed –Rapid response –High resolution –Not subject to mechanical tear and wear –Eliminates the need for an external LVDT Disadvantages –Brittle –Repeatability errors due to hysterisis and creep –Higher costs of roughly $500

17 Concept 2 DC Electric Motor An electrical motor converts electrical energy to mechanical energy using principles of magnetism to propel the armature

18 DC Electric Motor (cont’d) Advantages –If operated only outside it would not create EMF inside the ESEM –Very Inexpensive Costs can be less than $100 Disadvantages –Constant power must be applied to maintain load –Special locking clamps would be needed to maintain deformation –Repeatability errors due to hysterisis and creep –Requires external load and displacement sensor –Requires design of gear system for linear displacement

19 External Testing System Advantages –No EMF inside ESEM –No possible damage to the ESEM –No particle creation inside the ESEM from fracturing –External testing system with the possibility to test inside, with appropriate shielding –Cost effective in manufacturing –Less need for shielding Disadvantages –Power needs to be removed while imaging in the ESEM for no EMF generation –Possibility of losing deformation during movement

20 Conclusion The risk of modification with an internal system, and the costs of existing devices has lead to the development of an external testing system Our design will provide an alternative solution to the sponsor’s original design specifications while still meeting the requirements of the device


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