Biomechanical Tissue Stimulator Group 1: Matt Brady (BME/EE) Ankeet Choxi (BME) Misha Kotov (CS) Steven Manuel (ME) Adviser: Dr. V. Prasad Shastri

Overview  Design device that mimics physiological cyclic compressive loading to induce growth repair and remodeling mechanisms during tissue culture of articular cartilage

Past Work Ongoing cell-culture research project Prototype of stimulator has been constructed Many problems incurred Much research done for design of new device Range of force Sensors Detection and environment

What are we culturing and stimulating?  Articular cartilage covers human joint surfaces transfers mechanical load to skeletal system makes up ~2% of tissue volume in human body

Why stimulate culturing cartilage?  Hypothesized that mechanically stimulated cartilage will grow more like in vivo cartilage Increased formation of cartilage matrix, stronger  Type II collagen  Glycosaminoglycan (GAG)

Persistent medical problems  Limited ability to self-repair avascular  Osteoarthrosis and related problems very common  100,000 AC injuries annually  Arthritis 2 nd most common US disability $86 billion in medical expenses annually  21% of adults in US diagnosed with arthritis  Very marketable project

Current Work  All parts have arrived Working towards implementation of sensors and motor  Constructing and attaching sensor mounts to device frame Requires high level of precision mounting  Extending functionality of dummy application to control sensors and motor

Design Parameters  Accuracy of 20 microns  Stimulation frequency of 1 Hz max  Max load of 1 MPa or 100 N per sample  12 wells at once  Max in-test stroke of 1 mm  Total sample size of 10 mm  100 percent humidity at 98°F  Use multiple waveforms for stimulation

Resolution and Accuracy  Driving Resolution: 4 microns  Driving Accuracy: variable  Measuring Resolution: 5 microns  Measuring Accuracy: +/- 10 microns

Finite Element Analysis  Completed finite element analysis and finalized fabrication parameters

Contact Sensor  Made significant progress toward an easy to fabricate custom contact sensor

computer DAQ Card Tissue Stimulator Displacement Sensors Driver Power Supply Contact Sensors

Programming objectives  Program an application provide the following: Control the stepper motor Provide movement feedback through displacement and force sensors Gather relevant data

Application considerations  Precise motion control for the motor  Display the baseline displacement where contact is made with all wells; record measurements in reference to this point  Ideally, allow for customized routines, be able to save and repeat procedures  Record experiment figures in real time  Provide exception handling routines  Communication with the DAQ card

Current Work on Programming  Working to modify some pre- programmed modules to control stepper motor  Contacted our assigned application engineer from National Instruments  Set up the DAQ card and installed relevant software  Finished dummy application and working to extend its functionality

DAQ Card  Reads data from the motor and sensors  Keeps timing of device  Outputs the step and direction into the driver which runs the motor  Runs off LabView

Motor Driver  Driver takes inputs from the DAQ card and relays them to the motor  Allows fractional stepping of motor  Provides current limiting to keep motor from getting too hot and drawing too much power

Power Supply  Regulated 27V so motor runs at optimal current  Connects to driver, which in turn powers motor  Powers other components as well, however, resistors need to be used to lower voltage.

Displacement Sensor  Linear Encoder  Will output measurements of displacement  Needed to determine amount of strain applied to each tissue sample  Used as a tilt sensor (3 sensors)

Future Work  Attaching displacement sensors to device  Constructing contact sensors  Programming data acquisition protocols for sensors and motor Control program for motor  Begin phase testing with sensors and other components

Summary  Articular cartilage and problems  Biomechanical tissue stimulator Mechanically stimulates cartilage Promotes growth of tissue  Design, considerations

Cost Breakdown  Frame: $  Linear Actuator: $  Contact Sensors:$10.00  Linear Encoder:$  FlexiForce Sensors (4):$59.00  Strain Gages (5):$44.00  Power Supply:$35.00  Driver:$  DAQ Cards (2):$  Laptop:$ Total:$3,063.00

End Goals  End Goal of Overall Project To develop implantable artificial cartilage to replace damaged articular cartilage in the body.  End Goal of Senior Design Project To develop device that mimics mechanical load placed on growing cartilage through controlled experimental stimulation.

References Aufderheide, Adam C., Athanasiou, Kyriacos A. A Direct Compression Stimulator for Articular Cartilage and Meniscal Explants. (2006) Annals of Biomedical Engineering, Vol Bobic,Vladimir. Current Status of the Articular Cartilage Repair biomed: The Journal of Regenerative Medicine Apr 2000, Vol. 1, No. 4: Mansour JM. Biomechanics of Cartilage. (2004) Kinesiology: The Mechanics & Pathomechanics of Human Movement by Carol Oatis Xia Y, Moody JB, Alhadlaq H. Orientational Dependence of T2 Relaxation in Articular Cartilage: a microscopic MRI study. (2002) Magnetic Resonance in Medicine 48: