Does increasing PLA scaffold porosity using supercritical CO2 strategies enhance the characteristics for use as an alternative to allograft in impaction bone grafting?

Aims

Disease transmission, availability and economic costs of allograft have resulted in significant efforts into finding an allograft alternative for use in impaction bone grafting (IBG). Biotechnology offers the combination of skeletal stem cells (SSC) with biodegradable polymers as a potential solution. Recently polymers have been identified with both structural strength and SSC compatibility that offer the potential for clinical translation.

The aim of this study was to assess whether increasing the porosity of one such polymer via super critical CO₂ fluid foaming (SCF) enhanced the mechanical and cellular compatibility characteristics for use as an osteogenic alternative to allograft in IBG.

Methods

High molecular weight PLA scaffolds were produced via traditional (solid block) and SCF (porous) techniques, and the differences characterised using scanning electron microscopy (SEM). The polymers were milled, impacted, and mechanical comparison between traditional vs SCD created scaffolds and allograft controls was made using a custom shear testing rig, as well as a novel agitation test to assess cohesion. Cellular compatibility tests for cell number, viability and osteogenic differentiation using WST-1 assays, fluorostaining and ALP assays were determined following 14 day culture with SSC's.

Results

SEM showed increased porosity of the SCF produced PLA scaffolds, with pores between 50–100µm. Shear testing showed the SCF polymer exceeded the shear strength of allograft controls (P< 0.001). Agitation testing showed greater cohesion between the particles of the SCF polymer (P< 0.05). Cellular studies showed increased cell number, viability and osteogenic differentiation on the SCF polymer compared to traditional polymer (P< 0.05) and allograft (P< 0.001).

Conclusions

The use of supercritical C0₂ to generate PLA scaffolds significantly improves the cellular compatibility and cohesion compared to traditional non-porous PLA, without substantial loss of mechanical shear strength. The improved characteristics are critical for clinical translation as a potential osteogenic composite for use in IBG.