Biodegradable poly (ethylene glycol) diacrylate filled aramid nanofiber hydrogel three dimensional printed tissue engineering scaffold

Abstract

Digital Light Processing (DLP) process is one of the additive manufacturing techniques and has been widely used to fabricate tissue engineering scaffold based on Poly (ethylene glycol) diacrylate (PEGDA) material. However, the existing PEGDA scaffold via DLP 3D printing commonly exhibits poor mechanical and biocompatible properties. The PEGDA 3D scaffolds also have low cells viability which can cause tissue engineering failure. Therefore, this study aims to develop a novel soft tissue engineering scaffold biomaterial, using PEGDA filled with Aramid nanofibers (ANFs), with enhanced mechanical strength and biocompatible properties via DLP 3D printing technique. ANFs was first synthesized from macro size Kevlar fibre (0.2 %wt.) prior to crosslinking with Diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO) photo initiator. The mixing ratio of PEGDA resin to ANFs was fixed to 9:1. During the mixing, the concentration of TPO was varied at 0.5, 1.0 and 1.7% wt., while the resin concentration was fixed at 30% wt. to produce three sets of biomaterials. Preliminary study was conducted prior to the actual printing for the purpose of eliminating unprintable TPO concentration. The final scaffold was printed using a FEMTO3D DLP machine at two different curing times; 70s and 80s to obtain good shape and printable 3D structure. It was found that 1.7%wt of TPO failed to produce a 3D profile shape. It was observed the printed 3D scaffold of 1%wt TPO at 70s curing time produced the most discernible shape of the compression specimen (ASTM D695). Based on the printable photo initiator results, the experiments were expanded further by taking into account the PEGDA concentration, resin to ANFs ratio and DLP curing time. At this stage, both resin-PEGDA/TPO ratio and TPO concentration were fixed at 8:2 and 1.0 %wt. respectively. A two level factorial design involving three factors was used to determine the feasible printing parameter where the response is the Young's Modulus. The resin to ANFs ratio (9:1, 8:2, 7:3), PEGDA concentrations (30, 40, 50 %wt.) and curing time (70, 80, 90s) were varied during the experiments. Response surface method was used to determine the optimum setting for maximizing the Young’s Modulus. The synthesized ANFs have shown a nano diameter size distributions ranging from 20 nm to 80 nm. The optimum condition was found at 7:3 resin to ANFs ratio, PEGDA concentration at 50 %wt. and at 100s curing time, which recorded the highest Young’s modulus (0.55 MPa). 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay showed a weak condition of the cells viability at a ratio of 10:0 (61.4 %) after 3 days of incubation. Increased ratio of ANFs enhanced the cell viability where 81.6%, 89.3 % and 96.3 % of cells viability were recorded at the ratios of 9:1, 8:2 and 7:3, respectively. Fourier Transform Infrared Spectroscopy and Diffraction Scanning Calorimetry analyses also proved that the presence of Aramid functional group in the printed PEGDA/ANFs scaffold. The optimized dried sample after freeze-drying process for 24 hours confirmed that their physical reliability with minimal volume shrinkage (30%) and 80% water content remained in the final scaffold with high interconnected internal porous structure. The mechanical strength of the optimized printed scaffold also increased at 69.1% (0.93 MPa) after the freeze dried. Overall, the mechanical and biocompatibility properties of the fabricated PEGDA filled with ANFs exhibits significant improvement as compared to PEGDA without ANFs. It has proved that the newly developed PEGDA-ANFs scaffold has a great potential to be used as an articular cartilage in soft tissue engineering applications.