The manufacture of three dimensional polymeric scaffolds for the regeneration of tissues and the materials that these structures are constructed from is an area of intense research.
In this study, a preliminary investigation into the phase separation behaviour and suitability of a novel polyurethane (PU), poly(lactic-co-glycolic acid) (PLGA) and dimethylsulphoxide (DMSO) solvent system for the fabrication of biocompatible scaffolds was carried out. This involved carrying out a cloud point analysis for the PU-DMSO system; analysing the thermodynamic properties of the polymer- solvent solutions by differential scanning calorimetery (DSC); fabricating pure polymer (PU and PLGA), blended polymer (50/50 PU/PLGA) and layered scaffolds (PU outer layer with 50/50 PU/PLGA blend core); the analysis of the morphology of these scaffolds by scanning electron microscope (SEM) and an elemental analysis of this morphology by energy dispersive spectroscopy (EDS).
For concentrations of PU between 0.5%-2% the cloud point temperature was 59°C. For concentrations between 2%-6% it was 66°C. A 10 times increase in concentration only altered the temperature by 7°C. Unlike PU-DMSO, PLGA- DMSO does not exhibit liquid-liquid phase separation, so no cloud point analysis was performed. However, the freezing point of a 5% PLGA-DMSO solution was found to be 11°C, some 7.4°C lower than that of pure DMSO, indicating some super-cooling occurs in the presence of PLGA.
The DSC thermodynamic analysis turned out to be inconclusive due to a contaminant in the analysis cell, and later the malfunctioning of the equipment. However, while no firm conclusions could be drawn, no noticeable liquid-liquid phase change was observed in a PU-DMSO system at the cooling rate of 10°C/min, which may have been due to the machines in ability to detect a change due to the small quantities of polymer in the DSC pan.
Concentrations lower than 5% polymer do not produce scaffolds that are mechanically sound - a concentration of 1% results in total disintegration of the structure, regardless of polymer (PU, PU-PLGA blend or PLGA) when the solvent is leached. At a polymer concentration of 2% there was a marked improvement in the structural integrity of the PU-PLGA blend scaffold, but it only retained a very basic shape of the mould and was fairly fragile. The pure PU scaffold was a Polymeric Scaffolds for Tissue Engineering loosely connected clump of polymer that broke apart when moved. Only the pure PLGA scaffold retained its shape, but was still fragile. At concentrations of 5% all three polymer systems were structurally sound. Qualitatively, the mechanical characteristics of the scaffolds varied - the pure PU scaffolds were rubbery, and quite elastic; the pure PLGA scaffolds were hard and brittle; the 50/50 PU-PLGA blend demonstrated mechanical characteristics somewhere in-between those of the pure polymer scaffolds: slightly more rigid than pure PU, but not brittle, and not quite as elastic as pure PU. The layered scaffold demonstrated approximately the same mechanical characteristics as the PU-PLGA blend, however, it should be noted that PU was used as the outer layer and a PU-PLGA blend was used as the core so on physical inspection, the scaffold felt quite elastic.
SEM analysis showed the pure PLGA structures to be open and fibrous, where as the pure PU scaffolds were much more densely packed. While the PU-PLGA blended scaffold possessed a morphology that was a combination of the two pure morphologies, it also possessed some unique structures - bundles of PU channels. The exact cause of this morphology is not known. A layered scaffold with an outer layer of PU and an inner core of a 50/50 PU-PLGA blend had a fair degree of cross layer interconnectivity, however, the boundary between the two layers was clearly evident.
The blended PU/PLGA system appears promising as a potential polymer blend from which to fabricate biomedical scaffolds due to its large surface area, open nature, fibrous interconnected pore networks, and combined mechanical properties of the two individual polymers. Further work needs to be performed in order to ascertain the mechanical strength, cell-scaffold interactions, biocompatibility and biostability of scaffolds manufactured from the PU-PLGA-DMSO system.