Nanofibrous Scaffolds for Tissue Engineering Application

Abstract

Tissue engineering utilizes the approach whereby biomaterials are designed and engineered to encourage living cells to repair and restore damaged tissues and maintain normal function. In this study, the fields of fiber spinning and textile technology have been integrated with tissue engineering so as to design and produce fibrous scaffold prototypes using different bioresorbable polymers and fabrication techniques. In order to evaluate the performance, functionality and resorption profile of the fibrous prototypes as tissue engineering scaffolds, their morphological, dimensional, physical, chemical, mechanical and biological properties over time have been determined using a variety of polymer and fiber science analytical techniques and biological assays. Elastomeric and bioresorbable small diameter (5 mm) tubular constructs were successfully electrospun with a 50:50 poly(L-lactide-co-[varepsilon]-caprolactone) (PLCL) copolymer using two solvent systems of acetone and hexafluoroisopropanol (HFIP) for vascular tissue engineering applications. Depending on the solvent system, the average fiber diameter and pore size differed but the mechanical properties of both types of tubes demonstrated greater strength and compliance to those of natural arteries of equivalent caliber. Also they both supported the growth of fibroblasts for up to 14 days of culture. HFIP was preferred as a solvent for electrospinning this particular copolymer as it gave a more stable threadline and superior mechanical properties. The HFIP spun tubes were found to be mechanically stable without any significant change in their properties after being exposed to accelerated pulsatile fatigue forces equivalent to one year in the human body. The resorption behavior of PLCL scaffolds electrospun from HFIP has been evaluated under three different types of degradation environments: hydrolytic, enzymatic and cell culture media treatment. Among the three conditions, the enzymatic treatment accelerated surface degradation of the scaffolds, and all the fibers disintegrated and resorbed by Day 21. Significant decreases in mass, molecular weight and mechanical properties were observed in addition to major changes in microstructure. However, no significant changes in physical, chemical or morphological properties were observed from the exposure to pH 7.4 hydrolytic and cell culture media conditions. A novel fibrous scaffold prototype with a high surface area, high total porosity and pore size large enough to facilitate cell infiltration was successfully designed using a poly(L-lactic acid) (PLA) nonwoven fabric with multi-grooved fibers produced by a bi-component spinning technique. The water dispersible sacrificial component (EastOne(TM)) from bi-component spinning was successfully removed by heat-setting the nonwoven fabric and then scouring in deionized water. The complete removal of the EastOne(TM) sacrificial component and the formation of a multi-grooved configuration of PLA component were confirmed by SEM, FTIR and XPS analysis. Experimentally, the surface area for the round cross-sectional nonwoven samples was 0.51 m 2 /g whereas for the grooved samples, it was 2.36 m2 /g, which was in good agreement with the theoretical calculation. Overall, the novel PLA scaffold containing the grooved and fibrillated fibers exhibited enhanced wettability, greater flexibility, a larger surface area and superior initial cellular adhesion compared to its round counterpart. Both fabrics had sufficient bursting pressures that could withstand normal physiological conditions. The stability of the nonwoven PLA fabrics with different cross-sectional fibers has been evaluated for up to 21 days under three different conditioning environments: hydrolytic, enzymatic and cell culture media treatment. There was no statistical significant evidence that these conditioning treatments preferably influenced either fabric during the resorption study. Therefore, it was concluded that PLA fibrous fabrics would successfully serve as a stable scaffold material during the initial period of in vitro culture studies for up to 21 days without losing its dimensional integrity and mechanical properties. Lastly, the two types of PLA nonwoven scaffolds with both round and multi-grooved cross-sectional fibers were successfully cultured with hepatic progenitor cells and mesothelioma cells. The PLA nonwoven with round and grooved fibers both successfully supported the culture of hepatic progenitor cells for up to 7 days, showing homogenous cell distribution throughout the scaffolds. Hepatic progenitor cells maintained their hepatic functionality expressing albumin production only when cultured on the scaffolds but not on 2D monolayer culture, indicating that both scaffolds actively supported hepatic progenitor cell differentiation. The PLA nonwoven scaffolds with different cross-sectional fibers were also cultured with a MS-1 mesothelioma cell line to seek potential use as a barrier membrane for preventing adhesions. Both scaffolds were supportive in facilitating attachment and proliferation of MS-1 cells for up to 4 days. Superior cellular proliferation was found with the scaffold containing round fibers at Day 4 compared to the scaffolds with grooved fibers.