Bone inductive properties of rhBMP-2 loaded porous calcium phosphate cement implants in cranial defects in rabbits

Humidity-Responsive Amorphous Calcium-Magnesium Pyrophosphate/Cassava Starch Scaffold for Enhanced Neurovascular Bone Regeneration

Developing a neurovascular bone repair scaffold with an appropriate mechanical strength remains a challenge. Calcium phosphate (CaP) is similar to human bone, but its scaffolds are inherently brittle and inactive, which require recombination with active ions and polymers for bioactivity and suitable strength. This work discussed the synthesis of amorphous magnesium-calcium pyrophosphate (AMCP) and the subsequent development of a humidity-responsive AMCP/cassava starch (CS) scaffold. The scaffold demonstrated enhanced mechanical properties by strengthening the intermolecular hydrogen bonds and ionic bonds between AMCP and CS during the gelatinization and freeze-thawing processes. The release of active ions was rapid initially and stabilized into a long-term stable release after 3 days, which is well-matched with new bone growth. The release of pyrophosphate ions endowed the scaffold with antibacterial properties. At the cellular level, the released active ions simultaneously promoted the proliferation and mineralization of osteoblasts, the proliferation and migration of endothelial cells, and the proliferation of Schwann cells. At the animal level, the scaffold was demonstrated to promote vascular growth and peripheral nerve regeneration in a rat skull defect experiment, ultimately resulting in the significant and rapid repair of bone defects. The construction of the AMCP/CS scaffold offers practical suggestions and references for neurovascular bone repair.

In Vitro and In Vivo Evaluation of Injectable Strontium-Modified Calcium Phosphate Cement for Bone Defect Repair in Rats

Calcium phosphate cement (CPC) has been widely studied, but its lack of osteoinductivity and inadequate mechanical properties limit its application, while strontium is able to promote bone formation and inhibit bone resorption. In this study, different proportions of tristrontium silicate were introduced to create a novel strontium-modified calcium phosphate cement (SMPC). The physicochemical properties of SMPC and CPC were compared, and the microstructures of the bone cements were characterized with scanning electron microscopy assays. Then, the effect of SMPC on cell proliferation and differentiation was examined. Furthermore, local inflammatory response and osteogenesis after SMPC implantation were also confirmed in the study. Finally, a rat model of isolated vertebral defects was used to test the biomechanical properties of the cements. The results showed that SMPC has better injectability and a shorter setting time than CPC. Meanwhile, the addition of tristrontium silicate promoted the mechanical strength of calcium phosphate cement, and the compressive strength of 5% SMPC increased to 6.00 ± 0.74 MPa. However, this promotion effect gradually diminished with an increase in tristrontium silicate, which was also found in the rat model of isolated vertebral defects. Furthermore, SMPC showed a more preferential role in promoting cell proliferation and differentiation compared to CPC. Neither SMPC nor CPC showed significant inflammatory responses in vivo. Histological staining suggested that SMPCs were significantly better than CPC in promoting new bone regeneration. Importantly, this osteogenesis effect of SMPC was positively correlated with the ratio of tristrontium silicate. In conclusion, 5% SMPC is a promising substitute material for bone repair with excellent physicochemical properties and biological activity.

Repair of alveolar cleft bone defects in rabbits by active bone particles containing modified rhBMP-2

Objective: A model of alveolar cleft phenotype was established in rabbits to evaluate the effect of active bone particles containing modified rhecombinant human BMP-2 on the repair of the alveolar cleft. Methods: 2-month-old Japanese white rabbits were selected and randomly divided into four groups: normal, control, material and BMP groups. Blood biochemical analysis, skull tomography (microfocus computerized tomography), and histological and immunohistochemical staining analysis of paraffin sections were performed 3  and 6 months after operation. Results: Both types of collagen particles showed good biocompatibility and promoted bone regeneration. The effect of active bone particles on bone repair and regeneration was better than that of bone collagen particles. Conclusions: Active bone particles containing modified rhecombinant human BMP-2 can be used for incisors regeneration.

Active bone material containing modified recombinant human bone morphogenetic protein 2 induces bone regeneration in the alveolar process cleft in rabbits

The clinical application of most materials used to fill severe bone defects is limited owing to the insufficient ability of such materials to induce bone regeneration over a long repair period. The purpose of this study was to establish a model for the alveolar process cleft in rabbits to evaluate the effect of active bone material in bone defect repair. The active bone material used in this study is a new bone repair material composed of a heterogeneous collagen membrane implanted with modified recombinant human bone morphogenetic protein 2. This proposed active bone material can specifically bind to collagen. Twenty-four young Japanese white rabbits (JWRs) were selected and randomly divided into four groups (normal, control, material, and bone morphogenetic protein groups). The alveolar process cleft model was established by removing an equal volume bone at the left maxillary position. Blood samples were collected from the JWRs 3 and 6 months after the surgery to evaluate the biocompatibility of the active bone materials. Subsequently, the skull model was established, and the appearance was observed. Imaging methods (including X-ray examination and micro-computerized tomography scanning), tissue staining, and immunohistochemistry were employed for the evaluation. The bone collagen material and active bone material exhibited high biocompatibility. In addition, the ability of the active bone material to induce bone repair and regeneration was higher than that of the bone collagen material. The active bone material exhibited satisfactory bone regeneration performance in rabbits, indicating its potential as an active material for repairing congenital alveolar process clefts in humans.

Comparative study of photoinitiators for the synthesis and 3D printing of a light-curable, degradable polymer for custom-fit hard tissue implants

Three-dimensional (3D) printing enhances the production of on-demand fabrication of patient-specific devices, as well as anatomically fitting implants with high complexity in a cost-effective manner. Additive systems that employ vat photopolymerisation such as stereolithography (SLA) and digital light projection are used widely in the field of biomedical science and engineering. However, additive manufacturing methods can be limited by the types of materials that can be used. In this study, we present an isosorbide-based formulation for a polymer resin yielding a range of elastic moduli between 1.7 and 3 GN mm^-2 dependent on the photoinitiator system used as well as the amount of calcium phosphate filler added. The monomer was prepared and enhanced for 3D-printing using an SLA technique that delivered stable and optimized 3D-printed models. The resin discussed could potentially be used following major surgery for the correction of congenital defects, the removal of oral tumours and the reconstruction of the head and neck region. The surgeon is usually limited with devices available to restore both function and appearance and with the ever-increasing demand for low-priced and efficient facial implants, there is an urgent need to advance new manufacturing approaches and implants with a higher osseointegration performance.

Incorporation of nanosized calcium silicate improved osteointegration of polyetheretherketone under diabetic conditions

Diabetes can impair osteoblastic functions and negatively interfere with osteointegration at the bone/implant interface. Previously, we prepared a nanosized calcium silicate (CS) incorporated-polyetheretherketone (PK) biocomposite (CS/PK) and found that the CS/PK composite exhibited enhanced osteoblast functions in vitro and osteointegration in vivo, but its bioperformance under diabetic conditions remained elusive. In this study, MC3T3-E1 cells incubated on CS/PK and PK samples were subjected to diabetic serum (DS) and normal serum (NS); cell attachment, morphology, spreading, proliferation, and osteogenic differentiation were compared to assess in vitro osteoblastic functions on the surfaces of different materials. An in vivo test was performed on diabetic rabbits implanted with CS/PK or PK implants into the cranial bone defect to assess the osteointegration ability of the implants. In vitro results showed that diabetes inhibited osteoblastic functions evidenced by impaired morphology and spreading, and decreased attachment, proliferation, and osteogenic differentiation compared with the findings under normal conditions. Notably, CS/PK ameliorated osteoblastic disfunction under diabetic conditions in vitro. In vivo results from micro-CT and histologic examinations revealed that rabbits with CS/PK implants exhibited improved osteointegration at the bone/implant interface under diabetic conditions compared with PK. Therefore, the CS/PK composite improved the impaired osteointegration induced by diabetes and is a promising orthopedic or craniofacial implant material that may obtain good clinical performance in diabetic patients.

Human periodontal ligament stem cells on calcium phosphate scaffold delivering platelet lysate to enhance bone regeneration

Human periodontal ligament stem cells (hPDLSCs) are promising for tissue engineering applications but have received relatively little attention. Human platelet lysate (HPL) contains a cocktail of growth factors. To date, there has been no report on hPDLSC seeding on scaffolds loaded with HPL. The objectives of this study were to develop a calcium phosphate cement (CPC)-chitosan scaffold loaded with HPL and investigate their effects on hPDLSC viability, osteogenic differentiation and bone mineral synthesis for the first time. hPDLSCs were harvested from extracted human teeth. Scaffolds were formed by mixing CPC powder with a chitosan solution containing HPL. Four groups were tested: CPC-chitosan + 0% HPL (control); CPC-chitosan + 2.66% HPL; CPC-chitosan + 5.31% HPL; CPC-chitosan + 10.63% HPL. Scanning electron microscopy, live/dead staining, CCK-8, qRT-PCR, alkaline phosphatase and bone minerals assay were applied for hPDLSCs on scaffolds. hPDLSCs attached well on CPC-chitosan scaffold. Adding 10.63% HPL into CPC increased cell proliferation and viability (p < 0.05). ALP gene expression of CPC-chitosan + 10.63% HPL was 7-fold that of 0% HPL at 14 days. Runx2, OSX and Coll1 of CPC-chitosan + 10.63% HPL was 2-3 folds those at 0% HPL (p < 0.05). ALP activity of CPC-chitosan + 10.63% HPL was 2-fold that at 0% HPL (p < 0.05). Bone minerals synthesized by hPDLSCs for CPC-chitosan + 10.63% HPL was 3-fold that at 0% HPL (p < 0.05). This study showed that CPC-chitosan scaffold was a promising carrier for HPL delivery, and HPL in CPC exerted excellent promoting effects on hPDLSCs for bone tissue engineering for the first time. The novel hPDLSC-CPC-chitosan-HPL construct has great potential for orthopedic, dental and maxillofacial regenerative applications.

Bone repair scaffold coated with bone morphogenetic protein-2 for bone regeneration in murine calvarial defect model: Systematic review and quality evaluation

To systematically assess the effects of hydroxyapatite bone repair scaffold coated with bone morphogenetic protein-2 on murine calvarial defect models and to determine the quality of studies according to the Animal Research Reporting in In Vivo Experiments guidelines. Internet search was performed in duplicate using PubMed, MEDLINE, Ovid and Embase databases (without restrictions on publication date). The Animal Research Reporting in In Vivo Experiments guidelines were used to evaluate the quality of selected studies. Following screening, 12 studies were eligible for the review. Studies with average quality coefficients predominated (66.67%), followed by poor (25%) and excellent (8.33%) quality coefficients. Minimum quality scores were assigned to the Animal Research Reporting in In Vivo Experiments guideline items: housing and husbandry (9), allocation (11), outcomes (12), interpretation (18) and generalizability (19). Sprague–Dawley rats were the most frequently used (50%) species, and most studies had a sample size of more than 30 (58.33%). A defect dimension of 5 mm was the most common (33.33%). The biological hydroxyapatite composite scaffold was common (50%), and the bioactive factors were bone morphogenetic protein-2 (50%) and recombinant human bone morphogenetic protein-2 (50%). Histomorphometric results showed that bone morphogenetic protein-2 enhanced the capacity to regenerate bone considerably. In addition, scaffolds with bone morphogenetic protein-2 resulted in a significant increase in the blood vessel in the new bone. The findings suggested that data on animal experiments of hydroxyapatite scaffold coated with bone morphogenetic protein-2 in murine calvarial defect models lack homogeneity. Animal experiment should follow the Animal Research Reporting in In Vivo Experiments guidelines to promote the high quality, integrity and reproducibility. This systematic review suggested that bone morphogenetic protein-2 enhanced the capacity to regenerate bone and the angiogenesis in the new bone.

Improving osteogenesis of calcium phosphate bone cement by incorporating with lysine: An in vitro study

Calcium phosphate bone cement (CPC) has attracted extensive interests from surgeons and material scientists. However, its actual application is still limited because of its poor osteogenesis. In this work, lysine, one of the essential components of proteins, was incorporated into the CPC to improve its osteogenesis ability. Effects of lysine on the phase, morphology, physicochemical properties, protein adsorption, lysine release and cytocompatibility of CPC were investigated. Results showed that lysine had no significant influence on the phase and morphology of the hydrated cements, but evidently raised the compressive strength, apparent porosity and setting time of the cements in a content-dependent manner of lysine. In contrast to the control, the lysine-incorporated CPCs had notably enhanced in vitro osteogenesis capability. It was supposed to be synergistically attributed to the improvements of fibronectin (FN) anchoring and bone mesenchymal stem cells (BMSCs) adhesion on the hydrated cements as well as the sustained release of bioactive amino acid molecules. Hence, lysine was expected to be applied as a novel bioactive admixture in the development of CPC with the improved osteogenesis ability and physicochemical properties for numerous orthopedic applications.

Concentration-dependent osteogenic and angiogenic biological performances of calcium phosphate cement modified with copper ions

Development of multifunctional bone grafting biomaterials with both osteogenesis and angiogenesis properties have earned increasing interest in the field of regenerative medicine. In the present investigation, copper-doped β-tricalcium phosphate (Cu-TCP) powders were successfully synthesized. And Cu-containing calcium phosphate cement (Cu-CPC) was acquired through uniformly mixing CPC and Cu-TCP powders, with Cu-TCP serving as the donor of Cu²⁺. Cu-CPC exhibited suitable setting time, and the incorporation of Cu-TCP aggregating into CPC exhibited positive effect on the compressive strength while Cu²⁺ was in lower concentration. Investigation results showed that Cu-CPC had relatively low releasing amount of Cu²⁺, which was attributed to the re-bonding of Cu²⁺ into the newly formed HA crystals on surface. In vitro osteogenesis and angiogenesis properties of Cu-CPC were systematically evaluated through co-culture with mouse bone marrow stromal cells (mBMSCs) and human umbilical vein endothelial cells (HUVECs) respectively. The results indicated dose-dependent biological functions of Cu²⁺ in Cu-CPCs. The mBMSCs and HUVECs showed well activity and attachment morphology on TCP/CPC, 0.05 Cu-TCP/CPC, 0.1 Cu-TCP/CPC. The upregulated osteogenic-related genes expression and angiogenic-related genes expression were detected with lower Cu²⁺ content. Taken together, Cu-containing CPC is of great potential for the regeneration of vascularized new bone.

Novel Calcium Phosphate Cement with Metformin-Loaded Chitosan for Odontogenic Differentiation of Human Dental Pulp Cells

Metformin is an old and widely accepted first-line drug for treating type 2 diabetes. Our previous studies demonstrate that metformin can stimulate the osteo/odontogenic differentiation of human-induced pluripotent stem cell-derived mesenchymal stem cells and human dental pulp cells (DPCs). Due to the rapid dilution of metformin from the defect area, the aim of this study was to develop a drug delivery system with controlled release of metformin to promote cell viability and odontogenic differentiation of DPCs favoring dentin regeneration. Calcium phosphate cement (CPC) containing chitosan and metformin as a scaffold was synthesized. DPCs were seeded onto the scaffold, and the viability and proliferation were evaluated at several time points. For osteogenic differentiation analysis, alkaline phosphatase (ALP) activity was tested, cells were stained with Alizarin Red, and the expression of odontogenic markers was evaluated by real-time polymerase chain reaction. DPCs remained viable and attached well to the CPC-chitosan composite scaffold. Moreover, the addition of metformin to the CPC-chitosan composite did not adversely affect cell proliferation, compared to that of CPC control. Our data further revealed that the novel CPC-chitosan-metformin composite enhanced the odontogenic differentiation of DPCs, as evidenced by higher ALP activity, elevated expression of odontoblastic markers, and strong mineral deposition. These results suggest that the new CPC-chitosan-metformin composite is a highly promising scaffold with the potential for tissue engineering applications including dentin regeneration.

Histological and structural evaluation of growth hormone and PLGA incorporation in macroporous scaffold of α-tricalcium phosphate cement

An in vivo study was conducted to evaluate the effects of the incorporation of fibers of poly(lactic acid-co-glycolic acid, PLGA) and poly(isoprene) blend and recombinant human growth hormone (rhGH) in a macroporous scaffold of α-tricalcium phosphate cement (α-TCP) samples inserted into calvarial defects (8 mm in diameter) of 48 Wistar rats. The samples of α-TCP + PLGA/poly(isoprene) blend fibers were also submitted to a mechanical test of flexural strength. The animals of the different experimental groups [1] α-TCP (n = 6); [2] α-TCP + PLGA/poly(isoprene) blend fibers (n = 6); [3] α-TCP + rhGH, (n = 6) and [4] α-TCP + PLGA/poly(isoprene) blend fibers + rhGH, (n = 6) (the numbers within square brackets identify the experimental groups), after two weeks (subdivision "a") and four weeks (subdivision "b"), were euthanized and the implants removed for histological analysis. There was no statistical difference (p > 0.05) between the samples with and without fibers in the mechanical test. Light microscopy revealed good integration of the material in the host tissue, represented by tissue penetration into the macropores and adequate angiogenesis. In the two-week period, the groups [3a] and [4a] were significantly superior (p < 0.05) to the other groups with regard to angiogenesis and bone neoformation. In the four-week period, the group [3b] was significantly superior (p < 0.05) to the other groups with regard to bone neoformation. We conclude that the macroporous α-TCP scaffold used in this study has low mechanical resistance, is biocompatible and has significantly improved the osteoconductive capacity when rhGH is incorporated into its structure.

A comparison of the bone regeneration and soft-tissue-formation capabilities of various injectable-grafting materials in a rabbit calvarial defect model

Restoring adequate blood supply is essential to the success of bone repair and augmentation procedures in craniofacial surgery. Nevertheless, the manner by which the incorporation of collagen gels (which can potentially induce angiogenesis), particulated deproteinized bovine bone grafts, or a combination of both can accelerate or delay bone regeneration in a clinical setting remains controversial. The objective of this study was to evaluate radiographically and histologically the capacity and functionality of particulated bone grafts and collagen gels on bone ossification and soft tissue formation in a rabbit calvarial defect. Bilateral calvarial defects in adult white New Zealand rabbits were filled or left either unfilled with bone grafts (DBBM), collagen gels (Gel), or a combination of both (DBBM + Gel). The defects were allowed to heal for 1, 2, and 6 months postoperatively before termination. Healing and regeneration patterns were assessed by 3D µCT and histological methods, and the biomechanical properties of regenerated tissue constructs were investigated and compared with autogenous calvarial bone. Results show that implanted DBBM and DBBM + Gel significantly enhanced immature bone formation compared with the empty and Gel groups; the latter treatment improved soft tissue formation and impeded immature bone formation but yielded no significant effect on mature bone formation. Implantation of DBBM not only effectively reconstructed 188.83 ± 25.25% of the tissue volume of the original defect, but it also regenerated bone tissue with similar tissue composition and biomechanical properties as the original autogenous bone. We also show that implanting different biomaterials can control the composition of soft and hard tissue in reconstructed tissue constructs in calvarial bone defects. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 529-544, 2019.

A collagen membrane containing osteogenic protein-1 facilitates bone regeneration in a rat mandibular bone defect

OBJECTIVES

Osteogenic protein-1 (OP-1) has shown osteoinductive activities and is useful for clinical treatments, including bone regeneration. Regenerative procedures using a bioabsorbable collagen membrane (BCM) are well established in periodontal and implant dentistry. We evaluated the subsequent effects of the BCM in combination with OP-1 on bone regeneration in a rat mandibular circular critical-sized bone defect in vivo.

DESIGN

We used 8 rats that received surgery in both sides of the mandible, and created the total 16 defects which were divided into 4 groups: Group 1; no treatment, as a control, Group 2; BCM alone, Group 3; BCM containing low dose 0.5μg of OP-1 (L-OP-1), and Group 4; BCM containing high dose 2.0μg of OP-1 (H-OP-1). Newly formed bone was evaluated by micro computed tomography (micro-CT) and histological analyses at 8 weeks postoperatively. In quantitative and qualitative micro-CT analyses of the volume of new bone formation, bone density, and percentage of new bone area was evaluated.

RESULTS

BCM with rhOP-1 significantly increased and accelerated bone volume, bone mineral density, and percentage of new bone area compared to control and BCM alone at 8 weeks after surgery; these enhancements in bone regeneration in the OP-1-treated groups were dose-dependent.

CONCLUSIONS

OP-1 delivered with a BCM may have effective osteoinductive potency and be a good combination for bone regeneration. The use of such a combination device for osteogenesis may result in safer and more predictable bone regenerative outcomes in the future.

Osseointegration of nanohydroxyapatite- or nano-calcium silicate-incorporated polyetheretherketone bioactive composites in vivo

Polyetheretherketone (PEEK) exhibits appropriate biomechanical strength as well as good biocompatibility and stable chemical properties but lacks bioactivity and cannot achieve highly efficient osseointegration after implantation. Incorporating bioceramics into the PEEK matrix is a feasible approach for improving its bioactivity. In this study, nanohydroxyapatite (n-HA) and nano-calcium silicate (n-CS) were separately incorporated into PEEK to prepare n-HA/PEEK and n-CS/PEEK biocomposites, respectively, using a compounding and injection-molding technique, and the in vitro degradation characteristics were evaluated. Discs with a diameter of 8 mm were inserted in 8 mm full-thickness cranial defects in rabbits for 4 and 8 weeks, and implantation of pure PEEK was used as the control. Three-dimensional microcomputed tomography, histological analysis, fluorescence microscopy of new bone formation, and scanning electron microscopy were used to evaluate the osseointegration performance at the bone/implant interface. The results of the in vitro degradation study demonstrated that degradation of n-CS on the surface of n-CS/PEEK could release Ca and Si ions and form a porous structure. In vivo tests revealed that both n-CS/PEEK and n-HA/PEEK promoted osseointegration at the bone/implant interface compared to PEEK, and n-CS/PEEK exhibited higher bone contact ratio and more new bone formation compared with those of n-HA/PEEK, implying that n-CS/PEEK possessed a stronger ability to promote osseointegration. These two PEEK biocomposites are promising materials for the preparation of orthopedic or craniofacial implants.

Escherichia coli-derived recombinant human bone morphogenetic protein-2 combined with bone marrow-derived mesenchymal stromal cells improves bone regeneration in canine segmental ulnar defects

BACKGROUND

Large bone defects in canines usually require assistance to achieve healing. Implantation of osteoinductive factors can promote bone healing, while transplantation of osteoprogenitor cells can enhance bone regeneration. We hypothesized that implantation of an osteoinductive factor, recombinant human bone morphogenetic protein-2 (rhBMP-2), combined with osteoprogenitor cells, bone marrow-derived mesenchymal stromal cells (BMSCs), would synergistically promote bone healing. In this study, we examined the combined effects of Escherichia coli-derived rhBMP-2 and BMSCs on bone healing after implantation into canine ulnar defects.

RESULTS

Critical-sized osteoperiosteal segmental defects (2.5 cm) were created in the ulnae of healthy female beagle dogs, and implanted with combinations of E. coli-derived rhBMP-2 (560 or 140 μg) and autologous BMSCs (10(7), 10(5), or 0 cells). In the present study,18 forelimbs of nine healthy purpose-bred female beagles were used. All six treatment groups contained three forelimbs, and the animals were euthanized after 12 weeks. The control groups (560 and 140 μg/0 cells) were cited from our previous study to reduce the number of experimental animals. Radiographically, the regenerated bone width was significantly increased in the 560 or 140 μg with 10(7) and 10(5) cells groups compared with the 0 cells groups. By quantitative CT, the bone mineral density was higher in the 560 μg with 10(7) and 10(5) cells groups, while non-uniformity of the bone mineral density was improved in the 560 μg with 10(7) and 10(5) cells groups and 140 μg/10(7) cells group. Mechanically, the maximum loads at failure were significantly higher in the 560 μg with 10(7) and 10(5) cells groups. Histologically, the regenerated bone was well-developed and contained osteocyte-like cells marrow cavities, and vessels. However, the osteoclasts and osteoblasts were hardly observed. The osteocyte-like cell numbers were significantly higher in the 560 μg with 10(7) and 10(5) cells and 140 μg with 10(7) and 10(5) cells groups.

CONCLUSIONS

Implantation of E. coli-derived rhBMP-2 and BMSCs led to significantly enhanced bone formation, with improved bone mineral density and reduced non-uniformity of the regenerated bone. Combined implantation of rhBMP-2 and BMSCs may be useful for promotion of bone healing in critical-sized defects in canines.

Preparation of resorbable carbonate-substituted hollow hydroxyapatite microspheres and their evaluation in osseous defects in vivo

Hollow hydroxyapatite (HA) microspheres, with a high-surface-area mesoporous shell, can provide a unique bioactive and osteoconductive carrier for proteins to stimulate bone regeneration. However, synthetic HA has a slow resorption rate and a limited ability to remodel into bone. In the present study, hollow HA microspheres with controllable amounts of carbonate substitution (0-12 wt.%) were created using a novel glass conversion route and evaluated in vitro and in vivo. Hollow HA microspheres with ~12 wt.% of carbonate (designated CHA12) showed a higher surface area (236 m(2) g(-1)) than conventional hollow HA microspheres (179 m(2)g(-1)) and a faster degradation rate in a potassium acetate buffer solution. When implanted for 12 weeks in rat calvarial defects, the CHA12 and HA microspheres showed a limited capacity to regenerate bone but the CHA12 microspheres resorbed faster than the HA microspheres. Loading the microspheres with bone morphogenetic protein-2 (BMP2) (1 μg per defect) stimulated bone regeneration and accelerated resorption of the CHA12 microspheres. At 12 weeks, the amount of new bone in the defects implanted with the CHA12 microspheres (73±8%) was significantly higher than the HA microspheres (59±2%) while the amount of residual CHA12 microspheres (7±2% of the total defect area) was significantly lower than the HA microspheres (21±3%). The combination of these carbonate-substituted HA microspheres with clinically safe doses of BMP2 could provide promising implants for healing non-loaded bone defects.

A review on carrier systems for bone morphogenetic protein-2

Bone morphogenetic protein-2 (BMP-2) has unique bone regeneration property. The powerful osteoinductive nature makes it considered as second line of therapy in nonunion bone defect. A large number of carriers and delivery systems made up of different materials have been investigated for controlled and sustained release of BMP-2. The delivery systems are in the form of hydrogel, microsphere, nanoparticles, and fibers. The carriers used for the delivery are made up of metals, ceramics, polymers, and composites. Implantation of these protein-loaded carrier leads to cell adhesion, degradation which eventually releases the drug/protein at site specific. But, problems like ectopic growth, lesser protein delivery, inactivation of the protein are reported in the available carrier systems. Therefore, it is need of an hour to modify the available carrier systems as well as explore other biomaterials with desired properties. In this review, all the reported carrier systems made of metals, ceramics, polymers, composites are evaluated in terms of their processing conditions, loading capacity and release pattern of BMP-2. Along with these biomaterials, the attempts of protein modification by adding some functional group to BMP-2 or extracting functional peptides from the protein to achieve the desired effect, is also evaluated. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 904-925, 2017.

Covalently immobilised type I collagen facilitates osteoconduction and osseointegration of titanium coated implants

Background/Objective

Plasma-sprayed titanium coating (TC) with rough surfaces has been successfully applied in hip or knee prostheses. This study aimed to investigate the osteoconduction and osseointegration of Type I collagen covalently immobilised on TC (TC-AAC) compared with those of TC.

Methods

In vitro, the migration of human mesenchymal stem cells (hMSCs) on TC and TC-AAC was observed by scanning electron microscopy and visualised fluorescent live/dead assay. In vivo, a rabbit model with femur condyle defect was employed, and implants of TC and TC-AAC were embedded into the femur condyles.

Results

Collagen immobilised on TC could promote hMSCs' migration into the porous structure of the TC. Micro computed tomography images showed that bone trabeculae were significantly more abundant around TC-AAC implants than around TC implants. Fluorescence micrographs indicated more active new-bone formation around implants in the TC-AAC group than in the TC group. The measurement of bone–implant contact on histological sections indicated significantly greater osteointegration around TC-AAC implants than around TC ones.

Conclusion

Immobilised Type I collagen could improve the osteoconduction and osseointegration of TC implants.

A novel controlled-release system for antibacterial enzyme lysostaphin delivery using hydroxyapatite/chitosan composite bone cement

In this work, a lysostaphin-loaded, control-released, self-setting and injectable porous bone cement with efficient protein delivery was prepared by a novel setting method using hydroxyapatite/chitosan (HA/CS) composite scaffold. The cement samples were made through cementitious reactions by mixing solid powder, a mixture of HA/CS composite particles, lysostaphin, Ca(OH)2, CaCO3 and NaHCO3, with setting liquid containing citric acid, acetic acid, NaH2PO4, CaCl2 and poloxamer. The setting parameters of the cement samples were determined. The results showed that the final setting time was 96.6±5.2 min and the pH value increased from approximately 6.2 to nearly 10 during the setting process and the porosity was 34% at the end. And the microstructure and composition were detected by scanning electron microscopy (SEM), x-ray diffraction and Fourier transform-infrared spectroscopy. For the release behavior of lysostaphin loaded in the cement sample, the in vitro cement extract experiment indicated that about 94.2±10.9% of the loaded protein was released before day 8 and the in vivo Qdot 625 fluorescence tracking experiment showed that the loaded protein released slower than the free one. Then the biocompatibility of the cement samples was evaluated using the methylthiazol tetrazolium assay, SEM and hematoxylin-eosin staining, which suggested good biocompatibility of cement samples with MC 3T3-E1 cells and subcutaneous tissues of mice. Finally the antibacterial activity assay indicated that the loaded lysostaphin had good release ability and strong antibacterial enzymatic activity against methicillin-resistant Staphylococcus aureus. Collectively, all the results suggested that the lysostaphin-loaded self-setting injectable porous bone cement released the protein in a controlled and effective way and the protein activity was well retained during the setting and releasing process. Thus this bone cement can be potentially applied as a combination of artificial bone substitute and controlled-release system for delivery of lysostaphin to treat bone defects and infections.

BMP-functionalised coatings to promote osteogenesis for orthopaedic implants

The loss of bone integrity can significantly compromise the aesthetics and mobility of patients and can be treated using orthopaedic implants. Over the past decades; various orthopaedic implants; such as allografts; xenografts and synthetic materials; have been developed and widely used in clinical practice. However; most of these materials lack intrinsic osteoinductivity and thus cannot induce bone formation. Consequently; osteoinductive functionalisation of orthopaedic implants is needed to promote local osteogenesis and implant osteointegration. For this purpose; bone morphogenetic protein (BMP)-functionalised coatings have proven to be a simple and effective strategy. In this review; we summarise the current knowledge and recent advances regardingBMP-functionalised coatings for orthopaedic implants.

Biocomposite cryogels as tissue-engineered biomaterials for regeneration of critical-sized cranial bone defects

Analysis of the in vivo regeneration capability of any tissue-engineered biomaterial is necessary once it shows potential characteristics during in vitro studies. Thus, we applied polyvinyl alcohol-tetraethylorthosilicate-alginate-calcium oxide (PTAC) biocomposite cryogel on critical-sized cranial bone defects in wistar rats for examining the comparative bone regeneration of cryogel-treated and nontreated defects over a period of 4 weeks. An in-depth analysis was performed from macroscopic level till the gene level. Bone regeneration in cryogel-treated defects was clearly evident from the results, whereas the nontreated group did not show any defect healing except at few peripheral areas. At the macroscopic level, micro-computed tomography analysis revealed new bone formation. This was further confirmed at the cellular level, wherein, new bone formation was demonstrated by hematoxylin and eosin staining. Osteoblastic differentiation was further validated by immunohistological staining of runt-related transcription factor-2 (Runx-2) protein and via calcium-phosphate crystal formation after 2 weeks through scanning electron microscopy and energy dispersive X-ray spectroscopy. Finally, at the gene level, real-time PCR analysis confirmed the mRNA expression of osteoblastic markers, that is, runx-2, collagen type I (Col I), alkaline phosphatase (ALP), and osteocalcin (OCN). Therefore, the results of in vivo cranial defect model studies suggest that PTAC biocomposite cryogels can show suitable potential for human bone regeneration.

Self-setting calcium orthophosphate formulations

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are bioactive and biodegradable grafting bioceramics in the form of a powder and a liquid. After mixing, both phases form pastes, which set and harden forming either a non-stoichiometric calcium deficient hydroxyapatite or brushite. Since both of them are remarkably biocompartible, bioresorbable and osteoconductive, self-setting calcium orthophosphate formulations appear to be promising bioceramics for bone grafting. Furthermore, such formulations possess excellent molding capabilities, easy manipulation and nearly perfect adaptation to the complex shapes of bone defects, followed by gradual bioresorption and new bone formation. In addition, reinforced formulations have been introduced, which might be described as calcium orthophosphate concretes. The discovery of self-setting properties opened up a new era in the medical application of calcium orthophosphates and many commercial trademarks have been introduced as a result. Currently such formulations are widely used as synthetic bone grafts, with several advantages, such as pourability and injectability. Moreover, their low-temperature setting reactions and intrinsic porosity allow loading by drugs, biomolecules and even cells for tissue engineering purposes. In this review, an insight into the self-setting calcium orthophosphate formulations, as excellent bioceramics suitable for both dental and bone grafting applications, has been provided.

Hollow hydroxyapatite microspheres: a novel bioactive and osteoconductive carrier for controlled release of bone morphogenetic protein-2 in bone regeneration

The regeneration of large bone defects is a common and significant clinical problem. Limitations associated with existing treatments such as autologous bone grafts and allografts have increased the need for synthetic bone graft substitutes. The objective of this study was to evaluate the capacity of novel hollow hydroxyapatite (HA) microspheres to serve as a carrier for controlled release of bone morphogenetic-2 (BMP2) in bone regeneration. Hollow HA microspheres (106-150 μm) with a high surface area (>100 m2 g(-1)) and a mesoporous shell wall (pore size 10-20 nm) were created using a glass conversion technique. The release of BMP2 from the microspheres into a medium composed of diluted fetal bovine serum in vitro was slow, but it occurred continuously for over 2 weeks. When implanted in rat calvarial defects for 3 or 6 weeks, the microspheres loaded with BMP2 (1 μg per defect) showed a significantly better capacity to regenerate bone than those without BMP2. The amount of new bone in the defects implanted with the BMP2-loaded microspheres was 40% and 43%, respectively, at 3 and 6 weeks, compared to 13% and 17%, respectively, for the microspheres without BMP2. Coating the BMP2-loaded microspheres with a biodegradable polymer, poly(lactic-co-glycolic acid), reduced the amount of BMP2 released in vitro and, above a certain coating thickness, significantly reduced bone regeneration in vivo. The results indicate that these hollow HA microspheres could provide a bioactive and osteoconductive carrier for growth factors in bone regeneration.

Evaluation of bone response to various anorganic bovine bone xenografts: an experimental calvaria defect study

This in vivo study investigated the in vivo performance of two newly developed synthetic bone substitutes and compared them to commercially available xenografts (Bio-Oss, Geistlich Pharma AG, Switzerland; OsteoGraf, Dentsply, USA). The materials were tested in a rabbit calvaria model, and the bone forming properties were observed at 4 and 8 weeks after implantation by means of histomorphometry and micro computed tomography (micro-CT). Defects without any graft material were used as negative controls. Micro-CT showed that all materials tested presented new bone formation that filled the defects at both time points, whereas the negative control presented less bone formation, with soft tissue infiltration into the defects. Comparable bone fill percentages were observed for histomorphometric and micro-CT results. Even though no statistically significant difference was found quantitatively between all of the bone graft substitute groups, a higher mean decrease in graft material filling the defects, along with higher remodelling activity, was evident for the experimental materials compared to the commercially available xenografts at 8 weeks. The results indicate that the experimental materials possess high degradability, along with osteoconduction comparable to commercially available xenografts.

The effect of rhBMP-2 and PRP delivery by biodegradable β-tricalcium phosphate scaffolds on new bone formation in a non-through rabbit cranial defect model

This study evaluated whether the combination of biodegradable β-tricalcium phosphate (β-TCP) scaffolds with recombinant human bone morphogenetic protein-2 (rhBMP-2) or platelet-rich plasma (PRP) could accelerate bone formation and increase bone height using a rabbit non-through cranial bone defect model. Four non-through cylindrical bone defects with a diameter of 8-mm were surgically created on the cranium of rabbits. β-TCP scaffolds in the presence and absence of impregnated rhBMP-2 or PRP were placed into the defects. At 8 and 16 weeks after implantation, samples were dissected and fixed for analysis by microcomputed tomography and histology. Only defects with rhBMP-2 impregnated β-TCP scaffolds showed significantly enhanced bone formation compared to non-impregnated β-TCP scaffolds (P < 0.05). Although new bone was higher than adjacent bone at 8 weeks after implantation, vertical bone augmentation was not observed at 16 weeks after implantation, probably due to scaffold resorption occurring concurrently with new bone formation.

Evaluation of bone regeneration in implants composed of hollow HA microspheres loaded with transforming growth factor β1 in a rat calvarial defect model

Implants that serve simultaneously as an osteoconductive matrix and as a device for local growth factor delivery may be required for optimal bone regeneration in some applications. In the present study, hollow hydroxyapatite (HA) microspheres (106-150μm) in the form of three-dimensional (3-D) scaffolds or individual (loose) microspheres were created using a glass conversion process. The capacity of the implants, with or without transforming growth factor β1 (TGF-β1), to regenerate bone in a rat calvarial defect model was compared. The 3-D scaffolds supported the proliferation and alkaline phosphatase activity of osteogenic MLO-A5 cells in vitro, showing their cytocompatibility. Release of TGF-β1 from the 3-D scaffolds into phosphate-buffered saline ceased after 2-3 days when ∼30% of the growth factor was released. Bone regeneration in the 3-D scaffolds and the individual microspheres increased with time from 6 to 12 weeks, but it was significantly higher (23%) in the individual microspheres than in the 3-D scaffolds (15%) after 12 weeks. Loading with TGF-β1 (5μg per defect) enhanced bone regeneration in the 3-D scaffolds and individual microspheres after 6 weeks, but had little effect after 12 weeks. 3-D scaffolds and individual microspheres with larger HA diameter (150-250μm) showed better ability to regenerate bone. Based on these results, implants composed of hollow HA microspheres show promising potential as an osteoconductive matrix for local growth factor delivery in bone regeneration.

Trehalose maintains bioactivity and promotes sustained release of BMP-2 from lyophilized CDHA scaffolds for enhanced osteogenesis in vitro and in vivo

Calcium phosphate (Ca-P) scaffolds have been widely employed as a supportive matrix and delivery system for bone tissue engineering. Previous studies using osteoinductive growth factors loaded Ca-P scaffolds via passive adsorption often experience issues associated with easy inactivation and uncontrolled release. In present study, a new delivery system was fabricated using bone morphogenetic protein-2 (BMP-2) loaded calcium-deficient hydroxyapatite (CDHA) scaffold by lyophilization with addition of trehalose. The in vitro osteogenesis effects of this formulation were compared with lyophilized BMP-2/CDHA construct without trehalose and absorbed BMP-2/CDHA constructs with or without trehalose. The release characteristics and alkaline phosphatase (ALP) activity analyses showed that addition of trehalose could sufficiently protect BMP-2 bioactivity during lyophilization and achieve sustained BMP-2 release from lyophilized CDHA construct in vitro and in vivo. However, absorbed BMP-2/CDHA constructs with or without trehalose showed similar BMP-2 bioactivity and presented a burst release. Quantitative real-time PCR (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA) demonstrated that lyophilized BMP-2/CDHA construct with trehalose (lyo-tre-BMP-2) promoted osteogenic differentiation of bone marrow stromal cells (bMSCs) significantly and this formulation could preserve over 70% protein bioactivity after 5 weeks storage at 25°C. Micro-computed tomography, histological and fluorescent labeling analyses further demonstrated that lyo-tre-BMP-2 formulation combined with bMSCs led to the most percentage of new bone volume (38.79% ± 5.32%) and area (40.71% ± 7.14%) as well as the most percentage of fluorochrome stained bone area (alizarin red S: 2.64% ± 0.44%, calcein: 6.08% ± 1.37%) and mineral apposition rate (4.13 ± 0.62 µm/day) in critical-sized rat cranial defects healing. Biomechanical tests also indicated the maximum stiffness (118.17 ± 15.02 Mpa) and load of fracture (144.67 ± 16.13 N). These results lay a potential framework for future study by using trehalose to preserve growth factor bioactivity and optimize release profile of Ca-P based delivery system for enhanced bone regeneration.

Physical and chemical characterization of adsorbed protein onto gold electrode functionalized with Tunisian coral and nacre

Bone substitutes are more and more used in bone surgery because of their biologic safety, clinic efficiency and facility to synthesize. Bone substitutes with active osteogenic properties, associating biomaterials with organic macromolecule components of the extracellular matrix (protein, GAG) are recommended. Nevertheless, we should have a simple technique to control interactions between proteins and the material. Natural coral and nacre have been found to be impressive bone graft substitutes. In this work, we characterize nacre and coral powder using energy dispersive X-ray analysis (EDX). We used electrochemical impedance spectroscopy (EIS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to evaluate bovine serum albumin (BSA) as model protein, adsorbed to these biomaterial surfaces. In order to understand the nacre/coral-protein interfacial compatibility, it is necessary to investigate the wettability.

Controlling the biological function of calcium phosphate bone substitutes with drugs

There is a growing interest in bone tissue engineering for bone repair after traumatic, surgical or pathological injury, such as osteolytic tumor or osteoporosis. In this regard, calcium phosphate (CaP) bone substitutes have been used extensively as bone-targeting drug-delivery systems. This localized approach improves the osteogenic potential of bone substitutes by delivering bone growth factors, thus extending their biofunctionality to any pathological context, including infection, irradiation, tumor and osteoporosis. This review briefly describes the physical and chemical processes implicated in the preparation of drug-delivering CaPs. It also describes the impact of these processes on the intrinsic properties of CaPs, especially in terms of the drug-release profile. In addition, this review focuses on the potential influence of drugs on the resorption rate of CaPs. Interestingly, by modulating the resorption parameters of CaP biomaterials, it should be possible to control the release of bone-stimulating ions, such as inorganic phosphate, in the vicinity of bone cells. Finally, recent in vitro and in vivo evaluations are extensively reported.

Calcium phosphate cements as drug delivery materials

Calcium phosphate cements are used as synthetic bone grafts, with several advantages, such as their osteoconductivity and injectability. Moreover, their low-temperature setting reaction and intrinsic porosity allow for the incorporation of drugs and active principles in the material. It is the aim of the present work to: a) provide an overview of the different approaches taken in the application of calcium phosphate cements for drug delivery in the skeletal system, and b) identify the most significant achievements. The drugs or active principles associated to calcium phosphate cements are classified in three groups, i) low molecular weight drugs; ii) high molecular weight biomolecules; and iii) ions.

Local delivery of small and large biomolecules in craniomaxillofacial bone

Current state of the art reconstruction of bony defects in the craniomaxillofacial (CMF) area involves transplantation of autogenous or allogenous bone grafts. However, the inherent drawbacks of this approach strongly urge clinicians and researchers to explore alternative treatment options. Currently, a wide interest exists in local delivery of biomolecules from synthetic biomaterials for CMF bone regeneration, in which small biomolecules are rapidly emerging in recent years as an interesting adjunct for upgrading the clinical treatment of CMF bone regeneration under compromised healing conditions. This review highlights recent advances in the local delivery small and large biomolecules for the clinical treatment of CMF bone defects. Further, it provides a perspective on the efficacy of biomolecule delivery in CMF bone regeneration by reviewing presently available reports of pre-clinical studies using various animal models.

Processing and in vivo evaluation of multiphasic calcium phosphate cements with dual tricalcium phosphate phases

Calcium phosphate cements (CPCs) use the simultaneous presence of several calcium phosphates phases. This is done to generate specific bulk and in vivo properties. This work has processed and evaluated novel multiphasic CPCs containing dual tricalcium phosphate (TCPs) phases. Dual TCPs containing α- and β-TCP phases were obtained by thermal treatment. Standard CPC (S-CPC) was composed of α-TCP, anhydrous dicalcium phosphate and precipitated hydroxyapatite, while modified CPC (DT-CPC) included both α- and β-TCP. Physicochemical characterization of these CPCs was based on scanning electron microscopy, X-ray diffraction, specific surface area (SSA) and particle size (PS) analysis and mechanical properties. This characterization allowed the selection of one DT-CPC for setting time, cohesion and biological assessment compared with S-CPC. Biological assessment was carried out using a tibial intramedullary cavity model and subcutaneous pouches in guinea pigs. Differences in the surface morphology and crystalline phases of the treated TCPs were detected, although PS analysis of the milled CPC powders produced similar results. SSA analysis was significantly higher for DT-CPC with α-TCP treated at 1100°C for 5h. Poorer mechanical properties were found for DT-CPC with α-TCP treated at 1000°C. Setting time and cohesion, as well as the in vivo performance, were similar in the selected DT-CPC and the S-CPC. Both CPCs created the desired host reactions in vivo.

Differential loading methods for BMP-2 within injectable calcium phosphate cement

Clinical application of calcium phosphate cement (CPC; with incorporated polymeric porogens) in an injectable form implicates that loading methods for growth factors are limited. In view of this, the current study evaluated the in vitro and in vivo release kinetics of bone morphogenetic protein-2 (BMP-2) loaded on poly(d,l-lactic-co-glycolic acid) (PLGA) microparticles (CPC/PLGA), BMP-2 incorporation into the liquid phase of CPC (CPC/liquid), and BMP-2 absorbed to the surface of preset, porous CPC (CPC/surface) as a control via an in vitro release experiment and in vivo using microSPECT imaging with (125)I-labeled BMP-2. In addition, the osteoinductive capacity of scaffolds generated via the different BMP-2 loading methods was assessed in a subcutaneous rat model. Additional controls consisted of porous CPC scaffolds (CPC/porous) and CPC/PLGA (CPC/control) without BMP-2 loading. The results revealed that it is feasible to load BMP-2 into CPC via adsorption to PLGA-microparticles or the liquid phase of CPC, which resulted in a similar release profile over the course of 28 days, despite distinct protein distribution patterns. Compared to CPC-scaffolds with surface-loaded BMP-2, these loading methods showed a similar release profile, except for a significantly decreased burst release. As such, the observed osteoinductive capacity for only CPC-scaffolds with surface-loaded BMP-2 is likely to be related to this difference in burst release. It remains unclear to what extent the differential BMP-2 loading methods for injectable CPC can affect the biological response in a bone environment.

Simvastatin-loaded macroporous calcium phosphate cement: preparation, in vitro characterization, and evaluation of in vivo performance

The aim of our study was to construct macroporous calcium phosphate bone cements (CPCs) with enhanced osteogenic potential. For this purpose, 300 mM sodium dodecyl sulfate (SDS) as an air-entraining agent was added to the liquid phase and 1, 5, and 10% simvastatin (SIM) was homogenized with the solid phase. The physical and mechanical characteristics of the test samples were investigated. Biological properties of the new CPCs were examined after intramuscular and endosteal implantation in rabbits. The introduction of SDS produced interconnected macropores and did not significantly affect initial setting time, transformation of solid phase to hydroxyapatite, and biocompatibility of CPCs. Large amounts (10 wt %) of SIM could decrease the compressive strength and induce severe muscular necrosis and inflammatory reaction. Small amounts (1 wt %) of SIM were compatible with the CPCs did not affect the physico-chemical properties or biocompatibility and were sufficient to enhance the osteogenic potential of macroporous CPCs.