A drop tower for controlled impact testing of biological tissues

Area of Science:

• Biomechanics
• Biomaterials Science
• Tissue Engineering

Background:

• Impact damage to articular cartilage is a significant cause of morbidity.
• Understanding the mechanical forces and cellular responses to impact is crucial for predicting clinical outcomes.

Purpose of the Study:

• To design and validate an instrumented drop tower for applying controlled impact loads to biological tissues.
• To measure the mechanical properties of articular cartilage under high strain rates.

Main Methods:

• An instrumented drop tower was engineered to deliver controlled impacts to small tissue samples.
• Impact severity was modulated using varying impactor masses and drop heights.
• Force and deceleration were recorded at 50,000 samples s(-1) using a force transducer and accelerometer.
• Repeatability was assessed using rubber washers, yielding coefficients of variation below 8% for dynamic stiffness.

Main Results:

• The system demonstrated high repeatability for dynamic stiffness, stress, and strain measurements.
• Initial tests on human femoral head cartilage at 916 s(-1) yielded a peak dynamic modulus of 59 MPa.
• Bovine cartilage tested at 3380 s(-1) showed a peak dynamic modulus of 130 MPa.

Conclusions:

• The developed instrumented drop tower can apply defined impact energy and velocity to tissue biopsies.
• The equipment accurately measures deformation and load at high loading rates.
• This system provides a valuable tool for investigating the biomechanics of impact damage in articular cartilage and other tissues.