Dual Delivery of BMP2 and IGF1 Through Injectable Hydrogel Promotes Cranial Bone Defect Healing.

Critical-sized cranial bone defect remains a great clinical challenge. With advantages in regenerative medicine, injectable hydrogels incorporated with bioactive molecules show great potential in promoting cranial bone repair. Recently, we developed a dual delivery system by sequential release of bone morphogenetic protein 2 (BMP2) followed by insulin-like growth factor 1 (IGF1) in microparticles (MPs), and an injectable alginate/collagen (alg/col)-based hydrogel. In this study, we aim to evaluate the effect of dual delivery of BMP2 and IGF1 in MPs through the injectable hydrogel in critical-sized cranial bone defect healing. The gelatin MPs loaded with BMP2 and poly(lactic-co-glycolic acid)-poly(ethylene glycol)-carboxyl (PLGA-PEG-COOH) MPs loaded with IGF1 were prepared, respectively. The encapsulation efficiency and release profile of growth factors in MPs were measured. A cranial defect model was applied to evaluate the efficacy of the dual delivery system in bone regeneration. Adult Sprague Dawley rats were subjected to osteotomy to make an ⌀8-mm cranial defect. The injectable hydrogel containing MPs loaded with BMP2 (2 µg), IGF1 (2 µg), or a combination of BMP2 (1 µg) and IGF1 (1 µg) were injected to the defect site. New bone formation was evaluated by microcomputed tomography, histological analysis, and immunohistochemistry after 4 or 8 weeks. Data showed that dual delivery of the low-dose BMP2 and IGF1 in MPs through alg/col-based hydrogel successfully restored cranial bone as early as 4 weeks after implantation, whose effect was comparable to the single delivery of high-dose BMP2 in MPs. In conclusion, this study suggests that dual delivery of BMP2 and IGF1 in MPs in alg/col-based hydrogel achieves early bone regeneration in critical-sized bone defect, with advantage in reducing the dose of BMP2. Impact Statement Sequential release of bone morphogenetic protein 2 (BMP2) followed by insulin-like growth factor 1 (IGF1) in two different microparticles promotes critical-sized bone defect healing. This dual delivery system reduces the dose of BMP2 by supplementing IGF1, which may diminish the potential side effects of BMP2.

Lyophilization to improve drug delivery for chitosan-calcium phosphate bone scaffold construct: a preliminary investigation.

Lyophilization was evaluated in chitosan-calcium phosphate microspheres and scaffolds to improve drug delivery of growth factors and antibiotics for orthopedic applications. The dual delivery of an antibiotic and a growth factor from a composite scaffold would be beneficial for treatment of complex fracture sites, such as comminuted fractures and segmental bone defects. The aim of this investigation was to increase the loading capacity of the composite by taking advantage of the increased porosity, due to lyophilization, and to produce an extended elution profile using a secondary chitosan-bead coating. The physiochemical properties of the composite were investigated, and loading and elution studies were performed with alkaline phosphatase (ALP), bone morphogenetic protein-2 (BMP-2), and amikacin. Lyophilization was found to increase the surface area of scaffolds by over 400% and the porosity of scaffolds by 50%. Using ALP as a model protein, the loading capacity was increased by lyophilization from 4.3 +/- 2.5 to 24.6 +/- 3.6 microg ALP/mg microspheres, and the elution profile was extended by a supplemental chitosan coating. The loading capacity of BMP-2 for composite microspheres was increased from 74.4 +/- 3.7 to 102.1 +/- 8.0 microg BMP-2/g microspheres with lyophilization compared with nonlyophilized microspheres. The elution profiles of BMP-2 and the antibiotic amikacin were not extended with the supplemental coating. Additional investigations are planned to improve these elution characteristics for growth factors and antibiotics.

Protein adsorption and osteoblast precursor cell attachment to hydroxyapatite of different crystallinities.

PURPOSE: The effect of hydroxyapatite (HA) crystallinity on protein adsorption and osteoblast precursor cell attachment to HA was investigated. MATERIALS AND METHODS: Different weight ratios of 100% crystalline HA and 100% amorphous calcium phosphate powders were mixed and pressed into disks (0.5 g) of different crystallinities--either 0% (HAO), 30% (HA30), 50% (HA50), 70% (HA70), or 100% (HA100). RESULTS: X-ray diffraction indicated differences in HA crystallinities. In addition, dissolution of the HA was dependent on its crystallinity, with an increase in phosphorus dissolution as the degree of crystallinity was decreased. No significant difference in albumin adsorption and initial osteoblast precursor cell attachment was observed in the range of HA0 to HA70 surfaces. However, a significantly lower albumin adsorption and initial osteoblast precursor cell attachment were observed on HA100. DISCUSSION: It was suggested that changes in ionic interactions as a result of a change in crystallinity affect the amount of calcium ion ligands readily available to electrostatically bind to proteins. CONCLUSION: It was thus concluded from this study that HA crystallinity affects the amount of albumin adsorbed and initial osteoblast attachment.