Design of a mechanical testing device for ESEM

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. 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 Table of Contents

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. 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 Physiology of Bone Healing • 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

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. 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 Existing Products Courtesy of www.gatan.com

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

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

16. 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 Piezo Actuator (cont’d)

17. Concept 2 DC Electric Motor • An electrical motor converts electrical energy to mechanical energy using principles of magnetism to propel the armature http://en.wikipedia.org/wiki/Image:Electric_motor_cycle_1.png

18. 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 DC Electric Motor (cont’d)

19. 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 External Testing System

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