Mechanical characterisation of directionally frozen polycaprolactone scaffolds using 1,4-dioxane and glacial acetic acid for articular cartilage tissue engineering

Abstract

Polymer scaffolds have shown promising results in bone and cartilage repair when the underlying property being designed for is morphological. Despite their ability to mimic the morphology of the native extracellular matrix, current studies have not managed to find a polymer-solvent-method combination that provides sufficient mechanical strength. This study performs a comparison of the strength, stiffness and structure of different biomedical scaffolds created using a thermally-induced phase separation (directional freezing) method with different solvents and polymer concentrations. 1,4-dioxane and glacial acetic acid are used with polycaprolactone, a combination which has not been studied before using the directional freezing method. Strength tests are performed with an Instron compression/tension tester and structural comparisons made using Scanning Electron Microscopy. It is found that higher polymer concentrations create stiffer and stronger scaffolds and that using 1,4-dioxane as a solvent creates substantially stiffer scaffolds than using glacial acetic acid. The 15 w/v% 1,4-dioxane scaffold had a maximum tensile strength of 840.7 ± 117.3 kPa compared to 93.5 ± 26.2 kPa for glacial acetic acid. The 1,4-dioxane scaffolds display significant cross-linking compared to glacial acetic acid scaffolds and also showed a porous structure similar to that of a cartilage extracellular matrix. This method produced scaffolds with a distinctive bi-phasic polymer structure, similar in morphology to cartilage which requires load bearing properties and lubricating properties. The study shows that thermally-induced phase separation can create porous scaffolds which mimic the physiological properties of the native extracellular matrix.