A main limitation in deployment of prosthetic technology is the integration of the prosthetic device into the body. Using current procedures, effective prosthetic integration often requires 18 months and multiple surgeries. A new technique involves merging tissue engineering and medical imaging technology to directly implant a prosthetic interface that will rapidly and securely integrate with surrounding bone and soft tissue. Through controlled placement of appropriate cells, signaling factors, and scaffold materials, this process will enable the generation of multi-component implants that include a prosthetic interface.
The vision for such technology is the widespread deployment of tissue implants that use CT or MRI scans, and robot-assisted surgery, to guide the direct in vivo generation of composite implants that provide a secure interface for any prosthetic device. This will provide a more functional prosthetic interface in a shorter time, and enable the more rapid development and deployment of advanced prosthetic devices.
The base polymer system used for cell delivery was alginate, a natural biopolymer shown to be successful for encapsulation of over 30 cell types. The cell type chosen for delivery in these applications was chondrocytes isolated from bovine articular cartilage. The bioactive molecule chosen for controlled-release studies was insulin-like growth factor-I (IGFI), a protein shown to be highly anabolic for many cell types including chondrocytes. Data from function studies of chondrocyte metabolism demonstrated that the modified polymer enhanced proteoglycan synthesis, both in the presence and absence of IGF-I, as well as extending the duration of action of the growth factor.
In order to develop an in vitro system for evaluating cells and materials for integrating prosthetic materials with tissues in the body, particularly bone, the interface between cancellous bone harvested from the bovine femur and implant-grade porous stainless steel, were engineered. The material/cell delivery vehicle chosen for this application was collagen, which has a long history as a scaffold to support cell growth. The integration protocol utilized a Plexiglas mold to align cylindrical pieces of cancellous bone and the porous stainless steel. A collagen/ riboflavin mixture was injected between the bone and stainless steel, with excess volume to ensure that the mixture penetrated the pores of both the bone and metal. The mold was then exposed to a 458-nm light source for times up to 160 seconds, and samples were removed from the mold.
To determine enhancement of bone-metal integration, composite samples constructed as described were mounted in a test frame and pulled to failure in tension. From the force-displacement curves, tensile modulus, ultimate tensile strength, strain energy density, and strain at failure were determined. Photocrosslinking did not enhance tensile modulus, but increased tensile strength by -20%, failure strain by -40%, and strain energy density by -65%.
This work was done by Lawrence Bonassar, Hod Lipson, and Ephrahim Garcia of Cornell University for the Air Force Office of Scientific Research. AFRL-0159