Effect of Hydrolysis Pretreatment on the Formation of Bone-like Apatite on Poly(L-lactide) by Mineralization in Simulated Body Fluids

A bone-like apatite-coated surface that mediates a positive interaction between materials and bone is key to the development of desirable bone substitute materials. To incorporate apatite-coating on poly(L-lactide) (PLLA) surfaces, the effect of the hydrolysis of PLLA surfaces on the formation ability of bone-like apatite was investigated in this study.PLLA films and porous PLLA scaffolds were hydrolyzed for different time periods in alkaline solution and the hydrolyzed PLLA surfaces were characterized with X-ray photoelectron spectroscopy, atomic force microscopy, contact angle, and the measurement of carboxyl density. An apatite coating was formed by mineralizing the hydrolyzed PLLA in simulated body fluids (SBF) for 3 weeks and characterized. The hydrolyzed PLLA surfaces were rich in COOH and OH; the hydrophilicity, surface roughness, and carboxyl density increased with the hydrolysis time. After the incubation in SBF, a bone-like apatite layer with different morphology and composition was formed on the PLLA surfaces. The apatite formation on PLLA surfaces was promoted by the hydrolysis pretreatment and this increases with hydrolysis time. In addition, the compression module of the apatite-coated PLLA scaffolds increased compared with the pure PLLA scaffolds and increased with the hydrolysis time. The hydrolysis pretreatment was important in functionalizing the PLLA surfaces, facilitating subsequent apatite nucleation and apatite growth.

In Vitro Evaluation of Drug Solubility and Gamma Irradiation on the Release of Betamethasone under Simulated In Vivo Conditions

In situ—forming biodegradable polymeric systems loaded with betamethasone (BTM) and betamethasone acetate (BTMA) (5, 7, and 10% (w/w)) were prepared using poly(DL-lactide-co-glycolide) (33% (w/w)), ethyl heptanoate (5% (w/w)), and N-methyl-2-pyrrolidone as biodegradable material, additive, and solvent, respectively. The effects of gamma irradiation, drug loading, and solvent removal on release profiles were evaluated. The drug release in phosphate-buffered solution (pH = 7.4, 37°C) was measured using high-performance liquid chromatography. The release profiles of irradiated and nonirradiated formulations based on BTMA showed a three-phase release pattern, whereas the pattern for BTM was biphasic. Gamma irradiation had no significant effect on the BTMA release profiles ( p>0.05). Unexpectedly, irradiation had a significant effect on release behavior of BTM ( p<0.05); also, the rate of BTM release was decreased with an increase in drug loading up to 10%. The amount of BTM that was released in the burst phase decreased by about 1.4 and 1.5 times for 7 and 10% BTM loading, respectively. The duration of BTM release was more than that of BTMA. Changes in hydrophobicity and hydrogen bonding had a strong effect on the release behavior of the two forms of BTM from the in situ—forming systems.

Bone Regeneration with BMP-2 Gene-modified Mesenchymal Stem Cells Seeded on Nano-hydroxyapatite/Collagen/ Poly(L-Lactic Acid) Scaffolds

In this study, the capacity of bone morphogenetic protein 2 (BMP-2) gene-transfected bone marrow-derived mesenchymal stem cells (MSCs) in combination with nano-hydroxyapatite/collagen/poly(L-lactic acid) (nHAC/ PLA) to improve the repair of bone defects in rabbit was explored. MSCs from New Zealand White rabbits were cultured and injected with pIRES2-EGFPhBMP-2 or pIRES2-EGFP by electroporation. After the transfer efficiency was determined through the expression of EGFP, the MSCs were seeded on scaffolds to generate an in vitro 3D cell/scaffold construct. The adhesion and proliferation of the MSCs cultured in the scaffold was assessed by SEM. The cellular constructs obtained were allografted into the 15 mm critical-sized segmental bone defects in the radius of New Zealand White rabbits for 12 weeks. The bone regeneration was assessed by radiographical and histological analyses. In vitro, nHAC/PLA facilitated MSC adhesion and proliferation on the scaffold, and gene transfer efficiency reached a maximum of 35.5 ± 3.8%. In vivo, the implantation of BMP-2 transfected MSCs/nHAC/PLA construct significantly enhanced the formation of new bone in the segmental defect, compared to the control groups. This novel 3D BMP-2 transfected MSCs/nHAC/PLA construct has the potential for bone repair by genetic tissue engineering approach.

Multilevel Posterior Lumbar Interlaminar Fusion in Rabbits Using Bovine Bone Protein Extract Delivered by a RP-synthesized 3D Biopolymer Construct

Rapid prototyping (RP)-based highly porous poly(DL-lactic-co-glycolic acid)/tricalcium phosphate (PLGA/TCP(RP)) scaffolds were fabricated. PLGA/TCP constructs (PLGA/TCP(TS)) were also made via thermally induced phase separation with solvent casting and by particulate leaching approach. Both scaffolds were loaded with bovine bone protein extract (BBPE). Sixty-four New Zealand white rabbits were randomized into four groups (groups of A, B, C, and D) and unilaterally underwent posterior lumbar interlaminar fusion at L2—L4 level. Spinal fusions were systematically evaluated. In groups of A (PLGA/TCP (RP)/BBPE constructs) and C (autogenous iliac bone grafts), good bone fusions occurred in vivo. Histological analyses indicated that endochondral ossification played an essential role in initiation of bone fusions in group A, whereas in group B (PLGA/TCP(TS)/BBPE constructs), few bone fusions were observed. In group D (PLGA/TCP(RP) scaffolds alone), the scaffolds were biocompatible and biodegradable; however, no newly formed bone mass or bone fusion was found. Twelve weeks after surgery, the fusion was significantly higher in groups of A and C compared with groups B and D (p<0.01). The PLGA/ TCP(RP)/BBPE biomaterials have potential as grafting substitutes for bone healing and spinal fusion.