Novel Fabricating Process for Porous Polyglycolic Acid Scaffolds by Melt-Foaming Using Supercritical Carbon Dioxide

Polyglycolic acid (PGA) is a biocompatible and biodegradable polymer with high crystallinity. It is difficult to obtain PGA porous scaffolds with controllable morphology as well as outstanding mechanical properties without toxic solvents. The current study thus aimed to develop a novel melt-foaming strategy to prepare porous PGA scaffolds through the interaction between PGA molecules and supercritical carbon dioxide (scCO₂). Before the design of foaming strategy, rheological properties of PGA were first studied by a Haake rheometer, whereas the effect of scCO₂ on PGA was investigated by high-pressure differential scanning calorimetry (DSC). It was revealed that the elasticity and viscosity could be greatly improved by a temperature regulation operation to withstand the growth of bubbles at the initial depressurization. Meanwhile, the melting and crystallization temperatures of PGA were reduced because of the plasticization effect of scCO₂. Through the dissolution of compressed CO₂ into PGA melt and subsequent rapid depressurization at a relatively low temperature with high PGA melt strength, PGA scaffolds with porosity of 39-74%, average pore sizes ranging from 5 to 50 μm, and interconnectivity greater than 90% could be controllably fabricated. The effect of foaming temperature and pressure on morphology of PGA foams were then examined in detail. Special nanoscale morphology on the pore surface of resultant porous PGA foams was observed. These PGA foams also exhibited attractive compressive modulus of 68-116 MPa. The PGA foams with 74% porosity and average pore size of 38 μm, prepared at 208 °C and 20 MPa were then used as scaffolds for in vitro cellular evaluation. Fibroblasts seeded on the scaffold exhibited excellent spreading shape and good proliferation ability and in vivo implantation of PGA foams manifested as the notable tissue ingrowth and neovascularization process within the foams, ascertaining its potential applications for tissue engineering and regenerative medicine. This work presents a breakthrough to fabricate highly crystalline PGA into porous scaffolds instead of traditional fibrous ones.