The effect of fabrication methods on the mechanical and thermal properties of poly(lactide-co-glycolide) scaffolds

Magnesium ion stimulation of bone marrow stromal cells enhances osteogenic activity, simulating the effect of magnesium alloy degradation

Magnesium alloys are being investigated for load-bearing bone fixation devices due to their initial mechanical strength, modulus similar to native bone, biocompatibility and ability to degrade in vivo. Previous studies have found Mg alloys to support bone regeneration in vivo, but the mechanisms have not been investigated in detail. In this study, we analyzed the effects of Mg(2+) stimulation on intracellular signaling mechanisms of human bone marrow stromal cells (hBMSCs). hBMSCs were cultured in medium containing 0.8, 5, 10, 20 and 100mM MgSO4, either with or without osteogenic induction factors. After 3weeks, mineralization of extracellular matrix (ECM) was analyzed by Alizarin red staining, and gene expression was analyzed by quantitative polymerase chain reaction array. Mineralization of ECM was enhanced at 5 and 10mM MgSO4, and collagen type X mRNA (COL10A1, an ECM protein deposited during bone healing) expression was increased at 10mM MgSO4 both with and without osteogenic factors. We also confirmed the increased production of collagen type X protein by Western blotting. Next, we investigated the mechanisms of intracellular signaling by analyzing the protein production of hypoxia-inducible factor (HIF)-1α and 2α (transcription factors of COL10A1), vascular endothelial growth factor (VEGF) (activated by HIF-2α) and peroxisome proliferator-activated receptor gamma coactivator (PGC)-1α (transcription coactivator of VEGF). We observed that 10mM MgSO4 stimulation enhanced COL10A1 and VEGF expression, possibly via HIF-2α in undifferentiated hBMSCs and via PGC-1α in osteogenic cells. These data suggest possible ECM proteins and transcription factors affected by Mg(2+) that are responsible for the enhanced bone regeneration observed around degradable Mg orthopedic/craniofacial devices.

The influence of side group modification in polyphosphazenes on hydrolysis and cell adhesion of blends with PLGA

Polyphosphazenes have been synthesized with tris(hydroxymethyl)amino methane (THAM) side groups and with co-substituents glycine ethyl ester and alanine ethyl ester. The THAM side group was linked to the polyphosphazene backbone via the amino function. The three pendent hydroxyl functions on each THAM side group were utilized for hydrogen bonding association with poly(glycolic-lactic acid) (PLGA). Co-substitution of the polyphosphazene with both THAM and glycine or alanine ethyl esters was employed to avoid the insolubility of the single-substituent THAM-substituted polyphosphazenes. Both poly[(tris(hydroxymethyl)aminomethane)(ethyl glycinato)phosphazene] and poly[(tris(hydroxymethyl)aminomethane)(ethyl alanato)phosphazene] (1:1 ratio of side groups) were blended with PLGA (50:50) or PLGA (85:15). DSC analysis indicated miscible blend formation, irrespective of the detailed molecular structure of the polyphosphazene or the composition of PLGA in the blend. Hydrolysis studies of the polyphosphazene:PLGA (50:50) blends indicated that the PLGA component hydrolyzed more rapidly than the polyphosphazene. Primary osteoblast cell studies showed good cell adhesion to the polymer blends during 14 days, but subsequent limited cell spreading due to increased surface roughness as the two polymers eroded at different rates.