M.S. (Master of Science)
Department of Mechanical Engineering
A biomaterial is a substance that is specifically engineered to take on a role within the body, either alone or in conjunction with other materials, with the purpose of influencing the body. Using Polymers as a biomaterial is an exciting field of study that has the potential to further our abilities to help those in need. Creating composite nanofibrous scaffolds composed of hydrophobic and hydrophilic polymers may outperform structures made of a single polymer in both in vitro and in vivo environments. Hydrophilicity governs the behavior of polymers in the body and has influence over the mechanical properties of the polymer. The polymers of interest in our current work are polycaprolactone (PCL) and Poly(lactic-co-glycolic acid) (PLGA). PCL is a synthetic polymer with hydrophobic properties and a relatively high degradation rate in the body which can be used to make biodegradable scaffolds. PLGA is also a synthetic polymer, but hydrophilic which has excellent bio-adhesion. In current work, polymers have been fabricated by electrospinning method to create fibrous scaffolds. Electrospinning as a fiber production method was first attempted in 1888 and since then has been used to create polymer fibers by controlling the voltage, concentration, feed rate, and plate distance. A composite fibrous scaffold composed of a hydrophobic and hydrophilic polymer may result in better physical and mechanical properties, and improve its performance in biological environment, as compared to non-composite scaffolds. The core-shell method is a composite electrospinning technique that creates a fiber out of two concentric components polymers. In this work the core-shell fabrication technique was used to create a concentric fiber with an outer layer composed of 7.5% w/v PCL and an inner layer composed of 35% w/v (50:50) PLGA. For the core-shell composite fibers PCL was chosen as the shell material as its hydrophobic properties would act as a barrier prolonging drug release and reducing the initial burst. PLGA was used as the core material because its more hydrophilic nature gives it better drug encapsulation efficiency. This was achieved by first optimizing the electrospinning process of the individual polymers. The results are considered optimized by first examining the electrospinning process, especially the Taylor cone, provided that the Taylor cone is stable and consistent. The fibers are then examined under an SEM where the fiber morphology is characterized and any abnormalities such as beading could be seen. The first step taken was optimizing monoaxial PCL fibers. This was done by electrospinning 7.5% (w/v) PCL in HFIP at various feed rates, voltages, and plate distances. Through experimentation it was determined that an applied voltage from 7.0-8.0 kV, a 1.5 mL/h feed rate, and a 10 cm plate distance resulted in the best fibers. Monoaxial PLGA fibers were then optimized using 35% (w/v) PLGA in HFIP and the PCL parameters. Using an applied voltage of 7.0-8.0 kV the feed rate had to be decreased to 1.1 mL/h to improve fiber consistency with a 10 cm plate distance. The production of core-shell composite electrospun fibers with a PLGA core and a PCL shell was successful under a 7.0-8.0 kV applied voltage, a 1.1-1.5 mL/h core-shell feed rate or a 0.9-1.5 mL/h core-shell feed rate, and a 10 cm plate distance. This research did not find a clear relationship between core feed rate and overall core-shell fiber diameter. The impact of voltage outside the optimized range on core-shell fibers was found to increase the range of fiber diameters produced. Increasing relative humidity was studied and found to have a direct impact on core-shell fiber diameter. The core-shell scaffolds produced in this work can be used as drug delivery vehicles in tissue engineering or as composite scaffolds in soft tissue regeneration. Periodontal disease treatment, therapeutic reparation, and bone tissue regeneration have already found improvements using PCL based scaffolds. The successful electrospinning of these core-shell fibers opens future research to investigate the impact electrospinning parameters have on the mechanical, drug release, and degradation properties of PLGA-PCL core-shell fibers.
Kleszynski, Matthew Michael, "Coaxially Electrospun fibrous Polymer Scaffolds for Tissue Regeneration and Drug Delivery" (2021). Graduate Research Theses & Dissertations. 7258.
Northern Illinois University
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