Poly(lactic-co-glycolic acid)-based composite bone-substitute materials

Research and development of the ideal artificial bone-substitute materials to replace autologous and allogeneic bones for repairing bone defects is still a challenge in clinical orthopedics. Recently, poly(lactic-co-glycolic acid) (PLGA)-based artificial bone-substitute materials are attracting increasing attention as the benefit of their suitable biocompatibility, degradability, mechanical properties, and capabilities to promote bone regeneration. In this article, we comprehensively review the artificial bone-substitute materials made from PLGA or the composites of PLGA and other organic and inorganic substances, elaborate on their applications for bone regeneration with or without bioactive factors, and prospect the challenges and opportunities in clinical bone regeneration.

Evaluation of the in vitro biodegradation and biological behavior of poly(lactic-co-glycolic acid)/nano-fluorhydroxyapatite composite microsphere-sintered scaffold for bone tissue engineering

The objective of this research was to study the degradation and biological characteristics of the three-dimensional porous composite scaffold made of poly(lactic- co-glycolic acid)/nano-fluorhydroxyapatite microsphere using sintering method for potential bone tissue engineering. Our previous experimental results demonstrated that poly(lactic- co-glycolic acid)/nano-fluorhydroxyapatite composite scaffold with a ratio of 4:1 sintered at 90ºC for 2 h has the greatest mechanical properties and a proper pore structure for bone repair applications. The weight loss percentage of both poly(lactic- co-glycolic acid)/nano-fluorhydroxyapatite and poly(lactic- co-glycolic acid) scaffolds demonstrated a monotonic trend with increasing degradation time, that is, the incorporation of nano-fluorhydroxyapatite into polymeric scaffold could lead to weight loss in comparison with that of pure poly(lactic- co-glycolic acid). The pH change for composite scaffolds showed that there was a slight decrease until 2 weeks after immersion in simulated body fluid, followed by a significant increase in the pH of simulated body fluid without a scaffold at the end of immersion time. The mechanical properties of composite scaffold were higher than that of poly(lactic- co-glycolic acid) scaffold at total time of incubation in simulated body fluid; however, it should be noted that the incorporation of nano-fluorhydroxyapatite into composite scaffold leads to decline in the relatively significant mechanical strength and modulus during hydrolytic degradation. In addition, MTT assay and alkaline phosphatase activity results defined that a general trend of increasing cell viability was seen for poly(lactic- co-glycolic acid)/nano-fluorhydroxyapatite scaffold sintered by time when compared to control group. Eventually, experimental results exhibited poly(lactic- co-glycolic acid)/nano-fluorhydroxyapatite microsphere-sintered scaffold is a promising scaffold for bone repair.

Bioelectric effect of a chitosan bioelectret membrane on bone regeneration in rabbit cranial defects

In this study, the effects of a chitosan bioelectret membrane on bone regeneration in a rabbit cranial defect model were examined. The bioelectret was fabricated by film casting and polarized by grid-controlled corona charging (−1 kV). In vitro, the equivalence surface charge density of the bioelectret gradually reduced under both wet and dry conditions. In vivo, two rectangular transosseous defects of 8 mm × 10 mm were created symmetrically on each rabbit cranial bone. The defects were treated with the bioelectret membrane, with unpolarized membrane, and no membrane, respectively. The rabbits were killed at 4, 8, and 12 weeks postoperatively, and specimens were examined by micro-computed tomography and histological analysis. The bioelectret membrane recipients had a significantly higher volume of newly formed bone and greater rate of material degradation than the unpolarized membrane. Furthermore, the bioelectret membrane induced new bone formation not only around the host bone but also in the center of the defects. The chitosan bioelectret membrane application has an apparent potential in guided bone regeneration applications.

Nano-hydroxyapatite/chitosan sponge-like biocomposite for repairing of rat calvarial critical-sized bone defect

A three-dimensional porous nano-hydroxyapatite (nHA)/chitosan (CS) biocomposite was synthesized. The rod-like nHA grains of 15—30 × 5—10 nm in size were observed by TEM and confirmed by characteristic XRD patterns. The diameters of the interconnecting pores of the nHA/CS biocomposite, determined by SEM, were 120—300 μm. Standard critical-sized calvarial bone defect ( = 6.5 mm) was created in Sprague-Dawley (SD) rats. In group 1, nHA/CS was implanted and in group 2, no implant was made in the defect. After 1 week, the histological assessment of group 1 clearly showed that a large number of living cells were anchored in the pores of the nHA/CS implants. New bone formation, both at the edge and in the center of implants, was found as early as 2 weeks. Histological assays confirmed that the newly formed bone tissue was bioactive and neovascularized. After 5 weeks, the mineral content and volume of the newly formed bone tissue in the defects were significantly greater in group 1 than in group 2 (p < 0.01). These results indicate that implantation of the nHA/CS enhanced the repair of bone defect and confirm the potential of this biocomposite as a bioactive bone grafting substitute.

A 6-month in vivo study of polymer/mesenchymal stem cell constructs for cranial defects

Two biodegradable polymers, poly(L-lactide) and poly(ε-caprolactone) were blended (50/50) and used to produce polymeric scaffolds by the dual porogen approach using a salt leaching technique to create pores within the matrix, while supercritical-CO 2 treatment was used to enhance the interconnectivity and to remove impurities from synthesis steps. The scaffolds were highly porous (porosity >90%) with interconnected pore morphologies. These biodegradable scaffolds were evaluated in Sprague Dawley rats for osteoconductive properties over a 6-month period. Bone specimens were analyzed after 1, 3, and 6 months, for bone healing and tissue response. The cortical bone remodeling by controlled osteoblastic and osteoclastic activities as well as the bone marrow elements recovery were semi-quantitatively examined for each group. Excellent integration and biocompatibility behavior was observed in all groups. No adverse tissue responses were observed.

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.

Customized Ca-P/PHBV nanocomposite scaffolds for bone tissue engineering: design, fabrication, surface modification and sustained release of growth factor

Integrating an advanced manufacturing technique, nanocomposite material and controlled delivery of growth factor to form multifunctional tissue engineering scaffolds was investigated in this study. Based on calcium phosphate (Ca-P)/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocomposite microspheres, three-dimensional Ca-P/PHBV nanocomposite scaffolds with customized architecture, controlled porosity and totally interconnected porous structure were successfully fabricated using selective laser sintering (SLS), one of the rapid prototyping technologies. The cytocompatibility of sintered Ca-P/PHBV nanocomposite scaffolds, as well as PHBV polymer scaffolds, was studied. For surface modification of nanocomposite scaffolds, gelatin was firstly physically entrapped onto the scaffold surface and heparin was subsequently immobilized on entrapped gelatin. The surface-modification improved the wettability of scaffolds and provided specific binding site between conjugated heparin and the growth factor recombinant human bone morphogenetic protein-2 (rhBMP-2). The surface-modified Ca-P/PHBV nanocomposite scaffolds loaded with rhBMP-2 significantly enhanced the alkaline phosphatase activity and osteogenic differentiation markers in gene expression of C3H10T1/2 mesenchymal stem cells. Together with osteoconductive nanocomposite material and controlled growth factor delivery strategies, the use of SLS technique to form complex scaffolds will provide a promising route towards individualized bone tissue regeneration.

Posterolateral Spinal Fusion in Rabbits Using a RP-based PLGA/ TCP/Col/BMSCs-OB Biomimetic Grafting Material

Three-dimensional highly porous poly(DL-lactic-co-glycolic acid)/ tricalcium phosphate (PLGA/TCP) scaffolds were fabricated using a rapid prototyping technique (RP). The 3D rhombic lamellar PLGA/TCP carriers (20 mm × 20 mm × 3 mm) subsequently were coated with collagen type I (Col) to produce PLGA/TCP/Col composites. Both the RP-based PLGA/TCP scaffolds and the PLGA/TCP/Col composites were observed by scanning electron microscopy. Forty New Zealand white rabbits were equally randomized into 2 groups (group A and group B) and bilaterally underwent posterolateral intertransverse process arthrodesis at the L4—L5 level using the following graft materials: In group A, PLGA/TCP/Col/BMSCs-OB composites (on the right side, group A1, n = 20) and autogenous iliac bone grafts (on the left side, group A2, n = 20) were used; In group B, PLGA/TCP scaffolds plus fresh autogenous bone marrow (on the right side, group B1, n = 20) and PLGA/TCP scaffolds alone (on the left side, group B2, n = 20) were utilized. In group A1, rabbit bone marrow stromal cells (BMSCs) were isolated and cultured under the osteogenic conditions (BMSCs-OB). Structural PLGA/TCP/Col composites then were efficiently loaded with BMSCs-OB and cultured 5 days to make PLGA/TCP/ Col/BMSCs-OB biomaterials. Rabbits were sacrificed after 12-week follow-up and the spinal fusion were evaluated by a general observation, a manual palpation test, histological analyses and radiography. As a result, RP established PLGA/TCP scaffolds with appropriate biomaterial properties including satisfactory microstructure, inter-connectivity and porosity. Modifications to the structural highly porous PLGA/TCP scaffolds with Col (PLGA/TCP/Col) essentially increased the affinity of the carriers to seeding cells. In group A1, radiological evaluation revealed strong ability of new bone formation and bony fusion in the implanted sites and histological analyses showed highly cellular bone marrow between the newly formed trabecular bone was present in the fusion mass. In group A2, there was a reduced amount of newly formed bone. In group B1, only a few bony fusions were obtained. In group B2, PLGA/TCP scaffolds were biocompatible and biodegradable; whereas, no newly formed bone or bony fusion was found. Twelve weeks after surgery, spinal fusion rates in groups of A1, A2, B1, and B2 were 70.0%(14/20), 45.0%(9/20), 15.8%(3/19), and 0%(0/19), respectively. The rates of fusion were significantly higher in groups of A1 and A2 compared with groups of B1 and B2 (p<0.01), and there was no significant difference of fusion rate between group A1 and group A2 (p>0.05). Therefore, RP-based 3D PLGA/TCP/Col/BMSCs-OB biomaterial holds promise as a bone grafting substitute for spinal fusion. Our attempts may provide a novel method for biofabrication of the bionic construct.