Application of bone growth factors--the potential of different carrier systems

Investigations into the effects of scaffold microstructure on slow-release system with bioactive factors for bone repair

In recent years, bone tissue engineering (BTE) has played an essential role in the repair of bone tissue defects. Although bioactive factors as one component of BTE have great potential to effectively promote cell differentiation and bone regeneration, they are usually not used alone due to their short effective half-lives, high concentrations, etc. The release rate of bioactive factors could be controlled by loading them into scaffolds, and the scaffold microstructure has been shown to significantly influence release rates of bioactive factors. Therefore, this review attempted to investigate how the scaffold microstructure affected the release rate of bioactive factors, in which the variables included pore size, pore shape and porosity. The loading nature and the releasing mechanism of bioactive factors were also summarized. The main conclusions were achieved as follows: i) The pore shapes in the scaffold may have had no apparent effect on the release of bioactive factors but significantly affected mechanical properties of the scaffolds; ii) The pore size of about 400 μm in the scaffold may be more conducive to controlling the release of bioactive factors to promote bone formation; iii) The porosity of scaffolds may be positively correlated with the release rate, and the porosity of 70%-80% may be better to control the release rate. This review indicates that a slow-release system with proper scaffold microstructure control could be a tremendous inspiration for developing new treatment strategies for bone disease. It is anticipated to eventually be developed into clinical applications to tackle treatment-related issues effectively.

Effects of Calcium Carbonate Microcapsules and Nanohydroxyapatite on Properties of Thermosensitive Chitosan/Collagen Hydrogels

Thermosensitive chitosan/collagen hydrogels are osteoconductive and injectable materials. In this study, we aimed to improve these properties by adjusting the ratio of nanohydroxyapatite particles to calcium carbonate microcapsules in a β-glycerophosphate-crosslinked chitosan/collagen hydrogel. Two hydrogel systems with 2% and 5% nanohydroxyapatite particles were studied, each of which had varying microcapsule content (i.e., 0%, 1%, 2%, and 5%). Quercetin-incorporated calcium carbonate microcapsules were prepared. Calcium carbonate microcapsules and nanohydroxyapatite particles were then added to the hydrogel according to the composition of the studied system. The properties of the hydrogels, including cytotoxicity and biocompatibility, were investigated in mice. The calcium carbonate microcapsules were 2-6 µm in size, spherical, with rough and nanoporous surfaces, and thus exhibited a burst release of impregnated quercetin. The 5% nanohydroxyapatite system is a solid particulate gel that supports homogeneous distribution of microcapsules in the three-dimensional matrix of the hydrogels. Calcium carbonate microcapsules increased the mechanical and physical strength, viscoelasticity, and physical stability of the nanohydroxyapatite hydrogels while decreasing their porosity, swelling, and degradation rates. The calcium carbonate microcapsules-nanohydroxyapatite hydrogels were noncytotoxic and biocompatible. The properties of the hydrogel can be tailored by adjusting the ratio of calcium carbonate microcapsules to the nanohydroxyapatite particles. The 1% calcium carbonate microcapsules containing 5% nanohydroxyapatite particle-chitosan/collagen hydrogel exhibited mechanical and physical strength, permeability, and prolonged release profiles of quercetin, which were superior to those of the other studied systems and were optimal for promoting bone regeneration and delivering natural flavonoids.

Regenerative Medicine Technologies to Treat Dental, Oral, and Craniofacial Defects

Additive manufacturing (AM) is the automated production of three-dimensional (3D) structures through successive layer-by-layer deposition of materials directed by computer-aided-design (CAD) software. While current clinical procedures that aim to reconstruct hard and soft tissue defects resulting from periodontal disease, congenital or acquired pathology, and maxillofacial trauma often utilize mass-produced biomaterials created for a variety of surgical indications, AM represents a paradigm shift in manufacturing at the individual patient level. Computer-aided systems employ algorithms to design customized, image-based scaffolds with high external shape complexity and spatial patterning of internal architecture guided by topology optimization. 3D bioprinting and surface modification techniques further enhance scaffold functionalization and osteogenic potential through the incorporation of viable cells, bioactive molecules, biomimetic materials and vectors for transgene expression within the layered architecture. These computational design features enable fabrication of tissue engineering constructs with highly tailored mechanical, structural, and biochemical properties for bone. This review examines key properties of scaffold design, bioresorbable bone scaffolds produced by AM processes, and clinical applications of these regenerative technologies. AM is transforming the field of personalized dental medicine and has great potential to improve regenerative outcomes in patient care.

Human stem cell response to layered zirconium phosphate

This study aims to evaluate the in vitro cytocompatibility of layered zirconium phosphate (ZP) and its derivative material that was organically modified using glycerophosphate (ZGP). The ZP and ZGP particles were prepared via a reflux method in an aqueous solution containing phosphoric acid. The field emission scanning electron microscopy showed the prepared samples were fine particles with 70–100 nm diameter. X-ray diffraction and Raman spectrometry indicated the presence of a layered crystal structure. The interlayer distance of ZP was estimated to be 0.76 nm from the 002 diffraction. Modification of ZP with β-glycerophosphate, lead to expansion of the interlayer distance of 0.85 nm. Grazing incidence X-ray diffraction and Raman spectrometry showed that the crystal structures of ZP and ZGP were maintained even after the samples were coated onto polyethylene (PE) substrates via hot pressing. The water droplet contact angles on the PE substrates coated with the ZP and ZGP particles (ZP/PE and ZGP/PE) were 2 ∼ 6° lesser than that on the uncoated PE substrate. After human adipose-derived stem cells (hASCs) were cultured on the substrates, 2.5–3.5 times higher numbers of adhered cells were observed on the substrates coated with ZP and ZGP than on the uncoated PE substrates and 1.1–1.6 times higher than on the substrate coated with hydroxyapatite particles (HAp/PE). Increasing cell numbers were observed after culturing for 24 h, indicating that the ZP/PE and ZGP/PE showed low cytotoxicity to the hASCs. Furthermore, the ZP/PE showed the highest area of hASC adhesion among all the samples. These results highlight the possibility that layered zirconium phosphate and its organically modified substances can be applied to biomaterials for tissue repair.

This study aims to evaluate the in vitro cytocompatibility of layered zirconium phosphate (ZP) and its derivative material that was organically modified using glycerophosphate (ZGP).

Enhanced selective cellular proliferation by multi-biofunctionalization of medical implant surfaces with heterodimeric BMP-2/6, fibronectin, and FGF-2

Increasing cell adhesion on implant surfaces is an issue of high biomedical importance. Early colonization with endogenous cells reduces the risk of bacterial contamination and enhances the integration of an implant into the diverse cellular tissues surrounding it. In vivo integration of implants is controlled by a complex spatial and temporal interplay of cytokines and adhesive molecules. The concept of a multi-biofunctionalized TiO₂ surface for stimulating bone and soft tissue growth is presented here. All supramolecular architectures were built with a biotin-streptavidin coupling system. Biofunctionalization of TiO₂ with immobilized FGF-2 and heparin could be shown to selectively increase the proliferation of fibroblasts while immobilized BMP-2 only stimulated the growth of osteoblasts. Furthermore, TiO₂ surfaces biofunctionalized with either the BMP-2 or BMP-2/6 growth factor and the cell adhesion-enhancing protein fibronectin showed higher osteoblast adhesion than a TiO₂ surface functionalized with only one of these proteins. In conclusion, the presented immobilization strategy is applicable in vivo for a selective surface coating of implants in both hard and connective tissue. The combined immobilization of different extracellular proteins on implants has the potential to further influence cell-specific reactions. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2910-2922, 2018.

Porous PolyHIPE microspheres for protein delivery from an injectable bone graft

Delivery of osteoinductive factors such as bone morphogenetic protein 2 (BMP-2) has emerged as a prominent strategy to improve regeneration in bone grafting procedures. However, it remains challenging to identify a carrier that provides the requisite loading efficiency and release kinetics without compromising the mechanical properties of the bone graft. Previously, we reported on porous, polymerized high internal phase emulsion (polyHIPE) microspheres fabricated using controlled fluidics. Uniquely, this solvent-free method provides advantages over current microsphere fabrication strategies including in-line loading of growth factors to improve loading efficiency. In the current study, we utilized this platform to fabricate protein-loaded microspheres and investigated the effect of particle size (∼400 vs ∼800 μm) and pore size (∼15 vs 30 μm) on release profiles. Although there was no significant effect of these variables on the substantial burst release profile of the microspheres, the incorporation of the protein-loaded microspheres within the injectable polyHIPE resulted in a sustained release of protein from the bulk scaffold over a two-week period with minimal burst release. Bioactivity retention of encapsulated BMP-2 was confirmed first using a genetically-modified osteoblast reporter cell line. A functional assay with human mesenchymal stem cells established that the BMP-2 release from microspheres induced osteogenic differentiation. Finally, microsphere incorporation had minimal effect on the cure and compressive properties of an injectable polyHIPE bone graft. Overall, this work demonstrates that these microsphere-polyHIPE composites have strong potential to enhance bone regeneration through controlled release of BMP-2 and other growth factors. STATEMENT OF SIGNIFICANCE: This manuscript describes a method for solvent-free fabrication of porous microspheres from high internal phase emulsions using a controlled fluids setup. The principles of emulsion templating and fluid dynamics provide exceptional control of particle size and pore architecture. In addition to the advantage of solvent-free fabrication, this method provides in-line loading of protein directly into the pores of the microspheres with high loading efficiencies. The incorporation of the protein-loaded microspheres within an injectable polyHIPE scaffold resulted in a sustained release of protein over a two-week period with minimal burst release. Retention of BMP-2 bioactivity and incorporation of microspheres with minimal effect on scaffold compressive properties highlights the potential of these new bone grafts.

Adsorption and release kinetics of growth factors on barrier membranes for guided tissue/bone regeneration: A systematic review

OBJECTIVES

Guided bone / tissue regeneration (GBR/GTR) procedures are necessary to improve conditions for implant placement. These techniques in turn can be enhanced by using growth factors (GFs) such as bone morphogenetic protein (BMP-2) and platelet-derived growth factor (PDGF) to accelerate regeneration. The aim of the present systematic review was to evaluate the GF loading and release kinetics of barrier membranes.

STUDY DESIGN

A total of 138 articles were screened in PubMed databases, and 31 meeting the inclusion criteria were included in the present systematic review.

RESULTS

All the articles evaluated bio-resorbable membranes, especially collagen or polymer-based membranes. In most studies, the retention and release kinetics of osteogenic GFs such as BMP-2 and PDGF were widely investigated. Growth factors were incorporated to the membranes by soaking and incubating the membranes in GF solution, followed by lyophilization, or mixing in the polymers before evaporation. Adsorption onto the membranes depended upon the membrane materials and additional reagents such as heparin, cross-linkers and GF concentration. Interestingly, most studies showed two phases of GF release from the membranes: a first phase comprising a burst release (about 1 day), followed by a second phase characterized by slower release. Furthermore, all the studies demonstrated the controlled release of sufficient concentrations of GFs from the membranes for bioactivities.

CONCLUSIONS

The adsorption and release kinetics varied among the different materials, forms and GFs. The combination of membrane materials, GFs and manufacturing methods should be considered for optimizing GBR/GTR procedures.

Vertical bone regeneration using rhBMP-2 and VEGF

Background

Sufficient vertical and lateral bone supply and a competent osteogenic healing process are prerequisities for the successful osseointegration of dental implants in the alveolar bone. Several techniques including autologous bone grafts and guided bone regeneration are applied to improve quality and quantity of bone at the implantation site. Depending on the amount of lacking bone one- or two-stage procedures are required. Vertical bone augmentation has proven to be a challenge particularly in terms of bone volume stability. This study focuses on the three dimensional vertical bone generation in a one stage procedure in vivo. Therefore, a collagenous disc-shaped scaffold (ICBM = Insoluble Collagenous Bone Matrix) containing rhBMP-2 (Bone Morphogenetic Protein-2) and/or VEGF (Vascular Endothelial Growth Factor) was applied around the coronal part of a dental implant during insertion. RhBMP-2 and VEGF released directly at the implantation site were assumed to induce the generation of new vertical bone around the implant.

Methods

One hundred eight titanium implants were inserted into the mandible and the tibia of 12 mini pigs. Four experimental groups were formed: Control group, ICBM, ICBM + BMP-2, and ICBM + BMP-2 + VEGF.

After 1, 4 and 12 weeks the animals were sacrificed and bone generation was investigated histologically and histomorphometrically.

Results

After 12 weeks the combination of ICBM + rhBMP2 + VEGF showed significantly more bone volume density (BVD%), a higher vertical bone gain (VBG) and more vertical bone gain around the implant (PVBG) in comparison to the control group.

Conclusion

By using collagenous disc-shaped matrices in combination with rhBMP-2 and VEGF vertical bone can be generated in a one stage procedure without donor site morbidity. The results of the presenting study suggest that the combination of rhBMP-2 and VEGF applied locally by using a collagenous carrier improves vertical bone generation in vivo. Further research is needed to establish whether this technique is applicable in clinical routines.

Enhanced osteogenesis of multilayered pore-closed microsphere-immobilized hydroxyapatite scaffold via sequential delivery of osteogenic growth peptide and BMP-2

Accelerated bone regeneration of a novel microsphere-immobilized hydroxyapatite scaffold based on a sequence of steps regulated by two biofactors; this regeneration occurs through an orchestrated sequence of spatial changes.

Comparison of growth & function of endothelial progenitor cells cultured on deproteinized bovine bone modified with covalently bound fibronectin and bound vascular endothelial growth factor

OBJECTIVES

The objective of this study was to assess and compare the growth and function of Endothelial Progenitor Cells (EPCs) cultured on covalently bonded Vascular Endothelial Growth Factor (VEGF) and covalently bonded Fibronectin (FN) coating on deproteinized bovine bone (DBB) (test samples), compared to non-modified DBB blocks (control sample).

MATERIALS AND METHODS

The test samples were prepared by plasma polymerization of allylamine onto DBB blocks. Group1 of test samples were prepared with VEGF coating (VEGF-DBB) where as the Group2 test samples were coated with FN (FN-DBB). Non-modified DBB blocks served as a Control. EPCs were isolated and cultivated from buffy coats of peripheral blood of healthy volunteers and cultivated in the different samples and examined at time intervals of 24 h, 3 days, and 7 days. Evaluation of growth by cell count and cell morphology was done using Confocal Laser Scanning Electron Microscopy; vitality and function of cells was assessed using MTT assay and RT-PCR and ELISA for eNOS and iNOS respectively.

RESULTS

The results of the study show that both VEGF and FN could be successfully immobilized by plasma polymerization onto a complex, porous, three-dimensional structure of DBB. When comparing vital cell coverage, proliferation and function of EPCs, FN-DBB provided more positive values followed by VEGF-DBB as compared to DBB samples. eNOS level were significant higher in VEGF-DBB and FN-DBB when compared to DBB (P = 0.019 and P = 0.002). The difference between VEGF-DBB and FN-DBB was not significant.

CONCLUSIONS

Biomimetic coatings of Fibronectin may clinically relate to faster angiogenesis and earlier healing potential.

Current and future options of regeneration methods and reconstructive surgery of the facial skeleton

Musculoskeletal defects attributable to trauma or infection or as a result of oncologic surgery present a common challenge in reconstructive maxillofacial surgery. The autologous vascularized bone graft still represents the gold standard for salvaging these situations. Preoperative virtual planning offers great potential and provides assistance in reconstructive surgery. Nevertheless, the applicability of autologous bone transfer might be limited within the medically compromised patient or because of the complexity of the defect and the required size of the graft to be harvested. The development of alternative methods are urgently needed in the field of regenerative medicine to enable the regeneration of the original tissue. Since the first demonstration of de novo bone formation by regenerative strategies and the application of bone growth factors some decades ago, further progress has been achieved by tissue engineering, gene transfer, and stem cell application concepts. This review summarizes recent approaches and current developments in regenerative medicine.

Influence of synthetic polyethylene glycol hydrogels on new bone formation during mandibular augmentation procedures in Goettingen minipigs

Polyethylene glycol hydrogels (PEG) have been used as slow release carrier for osteoinductive growth factors in order to achieve a retarded delivery. However, there have been concerns about negative effects on bone regeneration. This study aims to test whether PEG hydrogels themselves affect new bone formation (NBF), when used as a carrier during mandibular augmentation procedures. In a randomized split-mouth design, bilateral mandibular bone defects were surgically created in 12 Goettingen minipigs, and subsequently augmented, using PEG hydrogel on one side of the mandible. The contralateral sides, without PEG, served as controls. After 4 and 12 weeks, bone formation was evaluated in six animals each. A comparison of the data, using a three-way analysis of variance (ANOVA), revealed a significant effect of the healing time and the region of the graft on the distribution and enhancement of NBF (P < .0001, respectively). Although a 0.3% (95%-CI [-5.5; 4.8]) lower volume density of newly formed bone could be observed over all PEG hydrogel sections, in contrast to the contralateral controls, the analysis revealed no clinically significant effects of the PEG hydrogel treatment on the total level (P = 0.90), and the distribution of NBF (P = 0.54). In conclusion, PEG hydrogels do not affect NBF when used as a carrier for osteoinductive growth factors during mandibular augmentation procedures.

Time-dependent periimplant bone reaction of acidic monomer-treated injection molded zirconia implants in rabbit tibiae

PURPOSE

The aim of this study was to evaluate and compare the osseointegration of zirconia implants in rabbit tibiae with and without 10-methacryloyloxydecyl dihydrogen phosphate (MDP) treatment.

MATERIALS AND METHODS

Twenty-eight rabbits received a total of 112 external hex-type implants made by the powder injection molding technique with and without MDP treatment before installation in the tibiae. The contact angles on the zirconia implants and zirconia discs before and after MDP application were evaluated. Removal torque (RT) and bone-implant contact (BIC) ratios were measured.

RESULTS

The MDP treatment markedly enhanced the hydrophilicity and seemed to alter the topography and chemical composition of the implant and disc surface. As the healing time increases, the BIC and RT were increased in both groups. The MDP-treated implants exhibited higher BIC values than the control implants after 2 and 4 weeks of healing. The RT was higher in MDP-treated implants after 2 weeks of healing but not after 4 weeks of healing.

CONCLUSION

The 10-MDP treatments made the surface more hydrophilic and enhanced the osseointegration of the implants in the early healing phase.

Antigen-extracted xenogeneic cancellous bone graft with recombinant human bone morphogenetic protein-2 enhances bone regeneration in repair of mandibular defect in rabbits

The effects of a large-piece of xenogeneic bone that was separated from healthy pigs as a scaffold for the repair of a mandibular defect was investigated, and the applicability of antigen-extracted xenogeneic cancellous bone (AXCB) soaked with recombinant human bone morphogenetic protein-2 (rhBMP-2) in bone defect repair was assessed. Mandibular defects were created in 48 New Zealand rabbits, and the animals were randomly divided into four groups, in which the mandibular defects were grafted with AXCB, AXCB soaked with rhBMP-2, and autograft bone, or left blank. An equal number of animals from each group were classified into three time points (4, 8, and 12 weeks) after surgery for gross pathological observation, hematoxylin and eosin (H and E) staining, radiographic examination, and bone density measurement. H and E staining revealed that the area percentage of bone regeneration in the group of the AXCB/rhBMP-2 graft was 27.72 ± 4.68, 53.90 ± 21.92, and 77.35 ± 9.83 at 4 weeks, 8 weeks, and 12 weeks, respectively. These results were better than those of the autogenous bone graft, suggesting that the group of the AXCB/rhBMP-2 graft achieved a good osteogenic effect. With regard to the AXCB graft without rhBMP-2, the area percentage of bone regeneration was only 14.03 ± 5.02, 28.49 ± 11.35, and 53.90 ± 21.92. Therefore, the osteogenic effect of the AXCB/rhBMP-2 graft was demonstrated to have the best effect. In the group of the AXCB/rhBMP-2 graft, the area percentage of bone regeneration increased, and the implanted materials were gradually degraded and replaced by autogenous bone regeneration over time. We conclude that the AXCB graft soaked with rhBMP-2 showed good osteogenic effect in the repair of bone defects and good biocompatibility. AXCB serves as a good carrier of rhBMP-2, which promotes bone formation.

Growth factor conjugation: strategies and applications

Growth factors, first known for their essential role in the initiation of mitosis, are required for a variety of cellular processes and their localized delivery is considered as a rational approach in their therapeutic application to assure a safe and effective treatment while avoiding unwanted adverse effects. Noncovalent immobilization of growth factors as well as their covalent conjugation is amongst the most common strategies for localized delivery of growth factors. Today, immobilized and covalently conjugated growth factors are considered as a promising drug design and are widely used for protein reformulation and material design to cover the unwanted characteristics of growth factors as well as improving their functions. Selection of a suitable conjugation technique depends on the substrate chemistry and the availability of functional reactive groups in the structure of growth factor, the position of reactive groups in growth factor molecules and its relation with the receptor binding area, and the intention of creating either patterned or unpatterned conjugation. Various approaches for growth factor reformulation have been reported. This review provides an overview on chemical conjugation of growth factors and covers the relevant studies accomplished for bioconjugation of growth factors and their related application.

Strategies for controlled delivery of growth factors and cells for bone regeneration

The controlled delivery of growth factors and cells within biomaterial carriers can enhance and accelerate functional bone formation. The carrier system can be designed with pre-programmed release kinetics to deliver bioactive molecules in a localized, spatiotemporal manner most similar to the natural wound healing process. The carrier can also act as an extracellular matrix-mimicking substrate for promoting osteoprogenitor cellular infiltration and proliferation for integrative tissue repair. This review discusses the role of various regenerative factors involved in bone healing and their appropriate combinations with different delivery systems for augmenting bone regeneration. The general requirements of protein, cell and gene therapy are described, with elaboration on how the selection of materials, configurations and processing affects growth factor and cell delivery and regenerative efficacy in both in vitro and in vivo applications for bone tissue engineering.

Osteoinduction in the palatal submucosa by injecting BMP-2 on 2 different carriers

In this work, we investigated the ability of injected recombinant human bone morphogenetic protein 2 (rhBMP-2) on brushite cement (a β-tricalcium phosphate-based biomaterial) and collagen gel as carriers to induce osteogenic differentiation in the palatal submucosa of 10-day-old rats. This was part of a broader study aiming to create bone in the palatal submucosa at cleft palate edges in the search for a minimally invasive treatment. Thirteen treated animals, 7 with rhBMP-2/brushite cement and 6 with rhBMP-2/collagen gel, were injected with 5 to 10 μL of each biomaterial in the right palatal submucosa at the level between the second and third rugae. The contralateral site was uninjected and served as the control. Six weeks after injection, both brushite cement and collagen gel were histologically unrecognizable in all treated animals. New bone structures such as ossicles of woven bone were not detected. However, an augmentation in the thickness of the palatal fibromucosa was observed at the injection site of all palates. In addition, immunolabeling for osteopontin, proliferating cell nuclear antigen, and TUNEL revealed intense osteogenic induction at the injection site with both constructs, which was negative in the control site from the same specimens; no differences regarding cell proliferation and death were observed. The present study confirms the feasibility of generating osteogenic cells in the palatal submucosa by injecting low doses of rhBMP-2 in these 2 biomaterials, together with their inability to form bone.

Osseointegration: the slow delivery of BMP-2 enhances osteoinductivity

Although the placement of dental and orthopedic implants is now generally a safe, reliable and successful undertaking, the functional outcome is less assured in patients whose bone-healing capacity is compromised. To enhance peri-implant osteogenesis in these individuals, BMP-2 could be locally administered. However, neither a free suspension nor an implant-adsorbed depot of the agent is capable of triggering sustained bone formation. We hypothesize that this end could be achieved by incorporating BMP-2 into the three-dimensional crystalline latticework of a bone-mineral like, calcium-phosphate implant coating, where from it would be liberated gradually - as the inorganic layer undergoes osteoclast-mediated degradation - not rapidly, as from an implant-adsorbed (two-dimensional) depot. To test this postulate, we compared the osteoinductive efficacies of implant coatings bearing either an incorporated, an adorbed, or an incorporated and an adsorbed depot of BMP-2 at a maxillary site in miniature pigs. The implants were retrieved 1, 2 and 3 weeks after surgery for the histomorphometric analysis of bone formation within a defined 'osteoinductive' space. At each juncture, the volume of newly-formed bone within the osteoinductive space was greatest around implants that bore a coating-incorporated depot of BMP-2, peak osteogenic activity being attained during the first week and sustained thereafter. In the other groups, the temporal course of bone formation was variable, and the peak levels were not sustained. The findings of this study confirm our hypothesis: they demonstrate that we now have at our disposal a means of efficaciously augmenting and expediting peri-implant bone formation. Clinically, this possibility would render the process of implant placement a safer and a more reliable undertaking in patients whose bone-healing capacity is compromised, and would also permit a curtailment of the postoperative recovery period by a forestallment of the mechanical-loading phase.

Strategies for stimulation of new bone formation: a critical review

Large bone defects, congenital or caused by diseases, trauma or surgery, do not heal spontaneously and are usually a clinical challenge in the orthopedic and dental practices. A critical review concerning strategies to substitute lost bone or stimulate osteogenesis was undertaken. Pivotal concepts ranging from traditional bone grafting and use of biomaterials to local application of growth factors and gene therapy were addressed, including critical comments on the efficacy and safety, difficulties, advantages and disadvantages of each method. The most predictable results are still obtained with autogenous bone graft, despite the inconveniences of morbidity and limited availability of graft material. Satisfactory results have been reported for recombinant bone morphogenetic proteins (rhBMPs)-2 and -7, which distinguish for their osteoinductive property, the difficulty being the need for a degradable carrier that allows its continuous release in a rate compatible to that of new bone formation. Other bone growth factors are currently under evaluation in preclinical models of bone defects; however their efficacy is also dependent on the competence of a delivery strategy and on an appropriate delineation of “which one”, “which dose” and “when”. Parameters of efficiency and safety for gene therapy are still being established. In conclusion, given the variety of growth factors involved in the complex cascade of bone repair and the biological interactions between them, it remains a challenge to accomplish the ideal strategy to stimulate reparational bone formation in specific conditions of the medical as in the dental practices.