Drug release kinetics of poly(glycerol sebacate urethane) scaffolds for soft tissue engineering

Abstract

In this study, three different poly(glycerol sebacate urethane), (PGSU) scaffolds were fabricated with an anisotropic microstructure and characterized their drug release kinetics (DRK). PGSU scaffolds with different ratios of hexamethyl diisocyanate (HDI) and polymer poly(glycerol sebacate urethane), pre-(PGS) concentration, were fabricated and investigated for their aforementioned physical properties. PGSU was synthesized with pre-PGS at concentrations 10% and 15% w/v% and HDI was added at molar concentrations (glycerol:HDI) 1:0.8 and 1:1.0. Freeze-drying with custom made moulds and ice templating, were used to form an anisotropic PGSU scaffold. The nomenclature of the samples is PGSU X-Y% where X refers to HDI ratio (0.8 or 1.0) and Y to polymer concentration (w/v%) (10% or 15%). The aim of this study was to study the DRK therefore the PGSU scaffolds were characterized for their microstructure, hydrophilicity (water contact angle and swelling rate), their drug loading efficiency, degradation rate and finally the DRK. PGSU scaffolds were characterized for their microstructure SEM and were found to exhibit an anisotropic open pore microstructure. The hydrophilicity was tested using contact angle and swelling ratio and were found to exhibit a fairly hydrophilic surface with a linear swelling rate. DRK were studied by loading BSA in scaffolds, using an in-house derived dynamic loading method which used vacuum/ventilation cycles. It resulted to a 75% drug loading efficiency, which is considered very good especially for non-hydrophilic materials. Then bovine serum albumin (BSA) was released by soaking the scaffold in phosphate buffer solution (PBS) solution on a rocker at 100 rpm for 28 days. The samples collected at different time points were analyzed using bicinchoninic acid (BCA), to determine the amount of protein released over time. A linear release rate was found and almost all samples withheld and released the protein over a period of at least 19 days. Finally, the degradation rate was studied by soaking the PGSU scaffolds in lipase enzyme and enzyme free PBS solution for 42 days in a shaker incubator, at 37oC and 100 rpm. The mass of the scaffolds was taken at multiple time points and compared with the initial mass to derive the degradation rate, the degradation rate was considered to be too slow. These results demonstrate that the glycerol:HDI molar ratio and polymer concentration affect the properties of the scaffold, the DRK technique developed by our group was successful and the fabricated PGSU scaffolds can be used in soft TE.