Fabrication of biodegradable biopolymer composites for orthopedic applications

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New materials for the manufacture of orthopedic devices are needed in order to aid with the alleviation of problems associated with the materials currently in production. The desire for new materials is due to the disparity between the mechanical properties of metal materials and surrounding tissues, along with the necessity of a second surgery for removal of temporary devices. Orthopedic devices are used to repair problems related to the musculoskeletal system. These devices can be used for permanent applications, such as total knee replacements where the device is essential for the lifetime of the patient, or for temporary applications, such as bone fractures where the device is no longer needed once the patient has healed. This research will introduce a novel composite material design for the fabrication of temporary implanted orthopedic devices. The use of biopolymers for fabrication of orthopedic devices has gained much attention because of the biopolymer’s ability to biodegrade and be replaced by natural tissues. The new composite material design combines the biopolymers polycaprolactone (PCL) and polyglycolide (PGA) to produce miscible 50/50 PCL-PGA blended electrospun fibers with a PCL matrix. Single-walled carbon nanotubes (SWNTs) were purified and wrapped with double stranded deoxyribonucleic acid (dsDNA) and introduced in the fibers to further increase strength. This design utilizes the long degradation rate of PCL while acquiring the strength of PGA. The PCL-PGA blended fibers will increase the interfacial bonding between the fibers and matrix while the dsDNA will aid in improving dispersion of the SWNTs in the fibers, thereby increasing the mechanical properties of the composite. The PCL, PGA, PCL-PGA, and PCL-PGA/dsDNA-SWNT fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) so that the integrity of the fibers could be assessed. Bulk PCL was compression molded to encapsulate the PCL-PGA blended fibers as well as the PCL-PGA/dsDNA-SWNT fibers. Mechanical testing of the composites included tensile testing and three-point bend testing to determine if load transfer occurred. The enzymatic and thermal degradation of the composites was studied using SEM, DSC, and x-ray diffraction (XRD). Incorporation of the PCL-PGA fibers was able to increase the tensile yield strength and Young’s modulus over that of the bulk PCL, while decreasing the percent elongation at break. The incorporation of the PCL-PGA/dsDNA-SWNT fibers was able to increase the bending strength and modulus over that of the bulk PCL and PCL-PGA fibers alone. The use of blended fibers allowed load transfer from dsDNA-SWNT to PCL matrix, thereby creating a stronger biodegradable polymer. The goal of creating a stronger, biocompatible, fully biodegradable composite for use in implanted orthopedic applications was achieved with PCL, PGA, and dsDNA-SWNTs.

Composites, Miscibility, Electrospinning, Carbon Nanotubes, Biopolymers, dsDNA, Enzymatic Degradation