Session: 06-11-03: Biotechnology and General Applications

Paper Number: 145174

145174 - Manufacture and In-Vitro Test of Thin and Flexible Polycarbonate Urethane for Use as Knee Implant 

Millions of people suffer from pain and limiting mobility with the onset of knee osteoarthritis (OA), which can afflict people at any age. Surgical interventions, such as total knee replacements (TKRs), offer a “cure” to knee OA by completely removing the knee joint and replacing it with metal and plastic implants. The surgical procedure is invasive and may result in a painful and slow recovery process. As traditional TKRs erode with prolonged use, plastic and metal wear particles may result in periprosthetic osteolysis, requiring another invasive surgical procedure to remove the particles. Polycarbonate urethanes (PCUs) have shown tremendous potential in applications involving long-term friction and wear. One potential application of PCUs is as a material intended for knee implants, specifically to mitigate the debilitating erosion of articular cartilage and bone prevalent in knee OA. ChronoFlex, an FDA approved PCU, is already used for various human implants, but it has not been applied as a load bearing implant. This study focused on manufacturing ChronoFlex samples for potential use as a knee implant material. Two variations of ChronoFlex were obtained to explore test sample manufacturing techniques: ChronoFlex C (aromatic PCU supplied in pellet form) and ChronoFlex AR (PCU supplied in liquid form with a dimethylacetamide solvent). ChronoFlex C manufacturing trials consisted of melting the pellets in open molds or crucibles to pour in liquid form into molds. The pellets were also extruded into filament for use in a 3D printer. ChronoFlex AR manufacturing trials consisted of building layers set in a furnace to achieve a desired thickness and pouring the liquid solution into open molds to set in a surface. Molding the ChronoFlex AR solution in a furnace produced the best quality samples. To validate ChronoFlex AR as a potential PCU for use as a knee implant material, thin-film rectangular samples 0.25 mm thick were mounted on a custom-built knee simulator’s femoral component to be cyclically worn against an ultra-high molecular weight (UHMW) polyethylene (PE) tibial component. The in-vitro test protocol consisted of 5 thin-film samples axially loaded at 1112 N with a cyclical wear cycle of 0.5 Hz. 1 thin-film sample was only axially loaded as the control specimen. A wear test of 50,000 cycles with wear measurements at 10,000 cycle intervals was defined using ISO 14243 as a testing guideline. ISO 14243, titled “Implants for surgery: Wear of total knee-joint prostheses,” and its sub-chapters -1, -2, and -3, define the long-term wear testing and measurement procedures for validating TKRs. The 5 cyclically loaded samples ruptured with a maximum cycle count of 1860. None of the samples showed statistically significant wear. Future tests with increased sample thickness are proposed to mitigate failure of the test samples and enable long-term wear testing. If validated with long-term wear testing, ChronoFlex AR would provide an alternative biomaterial for knee implants, possibly eliminating periprosthetic osteolysis as the knee implant wears, prolonging a patient’s need for further revision knee surgeries.

Presenting Author: Maria Ramos Gonzalez Massachusetts Institute of Technology

Presenting Author Biography: Maria Ramos Gonzalez, PhD is a Massachusetts Institute of Technology School of Engineering Distinguished Postdoctoral Fellow whose multidisciplinary research covers human-in-the-loop for robotic manipulation tasks and neuroprosthetic feedback control paradigms for upper limb amputees. Maria’s doctoral research included the design and fabrication of a novel biocompatible polycarbonate urethane knee implant. She also designed and fabricated a multi-knee joint implant test apparatus for long-term wear testing and validation of the novel implant. As a postdoctoral fellow, Maria’s innovative work holds great promise for advancing our understanding of human sensation, improving prosthetic design and control, and delivering technologies that improve lives at all levels of integrated human robotics applications. In addition, she aims to make these kinds of life-enhancing engineering solutions accessible to underserved populations.

Authors:

Maria Ramos Gonzalez Massachusetts Institute of Technology
Brendan O'toole University of Nevada, Las Vegas