Hua-Mo Yin

Engineering Porous Poly(lactic acid) Scaffolds with High Mechanical Performance via a Solid State Extrusion/Porogen Leaching Approach

A knotty issue concerning the poor mechanical properties exists in the porogen leaching approach to porous scaffolds, despite its advantage in tuning pore structure. To address this hurdle, solid state extrusion (SSE) combined with porogen leaching was utilized to engineer porous scaffolds of poly(lactic acid) (PLA). Advances introduced by poly(ethylene glycol) (PEG) caused the PLA ductile to be processed and, on the other hand, enabled the formation of interconnected pores. Thus, a well-interconnected porous architecture with high connectivity exceeding 97% and elevated porosity over 60% was obtained in the as-prepared PLA scaffolds with the composition of NaCl higher than 75.00 wt % and PEG beyond 1.25 wt %. More strikingly, the pore walls of macropores encompassed countless micropores and rough surface topography, in favor of transporting nutrients and metabolites as well as cell attachment. The prominent compressive modulus of the PLA scaffolds was in the range of 85.7–207.4 MPa, matching the normal modulus of human trabecular bone (50–250 MPa). By means of alkaline modification to improve hydrophilicity, biocompatible porous PLA scaffolds exhibited good cell attachment. These results suggest that the SSE/porogen leaching approach provides an eligible clue for fabricating porous scaffolds with high mechanical performance for use as artificial extracellular matrices.

Effects of extrusion draw ratio on the morphology, structure and mechanical properties of poly(L-lactic acid) fabricated using solid state ram extrusion

Solid state ram extrusion (SSRE) was utilized to fabricate poly(L-lactic acid) (PLLA) and the effects of extrusion draw ratios (EDRs) on its morphology, structure, and properties were investigated. Scanning electron microscopy observation indicated that the original spherulites gradually transformed into microfibrils aligned along the extrusion direction with an increase of the EDR. The molecular orientation of SSRE PLLA proceeded with EDRs in both the sheath and core region as detected by wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering characterization. Interestingly, on the basis of the WAXD curves, the β form of PLLA was found to appear in the bulk extrudates when the EDR was beyond 4.0, where the crystal transformation from the primary α form to the β form occurred between (203)α and (131)β. Meanwhile, the sheath region contained a much higher amount of the β form than the core region, contributing to the existence of a larger deformation in the sheath region. A multiple melting phenomenon of PLLA consisting of α and β mixture crystals was revealed by on-line WAXD and differential scanning calorimetry (DSC) measurements, which was explained by the melting, recrystallization and remelting. Formation of the fibrous crystals and the melting re-crystallization may lead to the increase of the melting point of SSRE PLLA. Additionally, the flexural strength and flexural modulus showed a monotonic rise with the EDR, achieving 4 and 13 times higher for the specimen at an EDR of 8.2 relative to the sample at an EDR of 1.0, respectively.