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

Overview  Stimulates tissue mechanically  Promotes growth of tissue engineered cartilage

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

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

Why stimulate?  Positive response to mechanical stimulation  Biomechanical stimulator delivers controlled amount of force  Measured results

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

Current Work  Finalizing design specifications Purchasing appropriate hardware/software  Equipment consideration: Motor to drive device and design Controller system for motor Power Supply Multiple sensors Data Acquisition and Device Calibration

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  100 percent humidity at 98°F

Well plate with samples Platen Stepper Actuator Teflon pistons Device Structure Samples

Mechanical End Progress  Completed finite element analysis and finalized fabrication parameters

Mechanical End Progress  Made significant progress toward an easy to fabricate custom contact sensor

Programming objectives  Program an application provide the following: Control the motor(s) Calibrate the sensors Gather relevant data  Help on interface with standalone control unit

LabVIEW!  Acquire, analyze, present data  Graphical development environment  Measurement and control services  Virtual instrumentation

Application considerations  Based on the number of samples, display appropriate distribution pattern  Display where contact was made and with how much force; determine baseline displacement  Allow for customized routines, be able to save and repeat procedures  Update experiment figures in real time  Provide exception handling routines  Communication with standalone control unit

Current Work  Found some pre-programmed modules to control stepper motor  Contacted National Instruments about an assigned application engineer  Looked into interface with displacement sensors

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  Powers individual components of system  Need to know what voltage and current each part runs on to determine what power supply can be used and for which components

Power Supply  Regulated 24V so motor runs at optimal voltage  Connects to driver, which in turn powers motor  Powers other components as well, however, resistors need to be used to lower voltage.

Displacement Sensor  Will output measurements of displacement  Needed to determine amount of strain applied to each tissue sample  Used as a tilt sensor

Future Work  Finalizing the device design  Ordering necessary hardware to begin construction on device prototype  Drawings and sketches of device design.  Begin milling and construction of device frame.  Program common compatibility of motors, sensors, drivers, and power supply.  Begin phase testing

Summary  Articular cartilage and problems  Biomechanical tissue stimulator Mechanically stimulates cartilage Promotes growth of tissue  Design, considerations  End Goal Be able to mechanically stimulate growing cartilage

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: