Bone regeneration of porous β-tricalcium phosphate (Conduit™ TCP) and of biphasic calcium phosphate ceramic (Biosel®) in trabecular defects in sheep

Beta tricalcium phosphate, either alone or in combination with antimicrobial photodynamic therapy or doxycycline, prevents medication-related osteonecrosis of the jaw

Surgical trauma in those under a prolonged use of bisphosphonates, can lead to mediation-related osteonecrosis of the jaw (MRONJ). This study aimed to evaluate the preventive therapies for MRONJ. Following four cycles of zoledronic acid administration, Wistar rats had their molar extracted, and were organized into nine treatment groups: negative control group (NCG), treated with saline solution and blood-clot in the alveolus; positive control group (PCG), with blood-clot in the alveolus; BG, β-tricalcium phosphate-based biomaterial; DG, 10% doxycycline gel; aG, antimicrobial photodynamic therapy; and DBG, aBG, aDG, and aDBG, using combination therapy. After 28 days, the lowest bone volume (BV/TV) was reported in PCG (42.17% ± 2.65), and the highest in aDBG (69.85% ± 6.25) (p < 0.05). The higher values of daily mineral apposition rate were recorded in aDBG (2.64 ± 0.48) and DBG (2.30 ± 0.37) (p < 0.001). Moreover, aDBG presented with the highest neoformed bone area (82.44% ± 2.69) (p < 0.05). Non-vital bone was reported only in the PCG (37.94 ± 18.70%). Owing to the key role of the biomaterial, the combination approach (aDBG) was the most effective in preventing MRONJ following tooth extraction.

A Mini-Pig Mandibular Defect Model for Evaluation of Craniomaxillofacial Bone Regeneration

Craniomaxillofacial bone defects represent a clinical challenge in the fields of maxillofacial surgery and (implant) dentistry. Regeneration of these bone defects requires the application of bone graft materials that facilitate new bone formation in a safe, reliable, and predictive manner. In addition to autologous bone graft, several types of (synthetic) bone substitute materials have become clinically available, and still major efforts are focused on improving such bone substitute materials by optimizing their properties. Given the regulatory necessity to evaluate the performance of new bone substitute materials for craniomaxillofacial bone regeneration in a large animal model with similarity to human bone before clinical application, we here describe a mini-pig mandibular bone defect model that allows for the creation of multiple (critical-size) bone defects within the mandibular body of a single animal. As examples of bone substitute materials, we utilize both the clinically used BioOss granules and an experimental calcium phosphate cement for filling the created defects. Regarding the latter, its advantages are the injectable application within the defect site, in which the material rapidly sets, and the tailorable degradation properties via the inclusion of hydrolytically degrading polymeric particles. For both bone substitute materials, we show the suitability of the bone defect model to assess bone regeneration via histology and micro-computed tomography. Impact statement Given the regulatory necessity to evaluate the performance of new bone substitute materials for craniomaxillofacial bone regeneration in a large animal model with similarity to the human bone before clinical application, we here describe a mini-pig mandibular bone defect model that allows for the creation of multiple (critical-size) bone defects within the mandibular body of a single animal that can be used for the evaluation of the bone regenerative capacity of new bone grafting materials as well as tissue-engineered products for alveolar bone regeneration.

High-performance bilayer composites for the replacement of osteochondral defects

Two novel bilayer constructs for the repair of osteochondral defects were developed from nanofibers and ceramic particles embedded into PVA matrices, exhibiting multiple promising properties similar to those of corresponding natural tissues.

Evaluation of Osteoconduction of a Synthetic Hydroxyapatite/β-Tricalcium Phosphate Block Fixed in Rabbit Mandibles

(1) Background: This study aimed to evaluate the incorporation of hydroxyapatite/β-tricalcium phosphate blocks grafted in rabbit mandibles. (2) Methods: Topographic characterization of biomaterial was performed through scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). Ten rabbits randomly received autogenous bone graft harvested from the tibia (Autogenous Group—AG) or synthetic biomaterial manufactured in β-tricalcium phosphate (Biomaterial Group—BG) at their right and left mandibular angles. Euthanasia was performed at 30 and 60 postoperative days; (3) Results: SEM-EDX showed a surface with the formation of crystals clusters. Histological analyses in BG at 30 days showed a slower process of incorporation than AG. At 60 days, BG showed remnants of biomaterial enveloped by bone tissue in the anabolic modeling phase. Histometric analysis showed that mean values of newly formed bone-like tissue in the AG (6.56%/9.70%) were statistically higher compared to BG (3.14%/6.43%) in both periods, respectively. Immunohistochemical analysis demonstrated early bone formation and maturation in the AG with more intense osteopontin and osteocalcin staining. (4) Conclusions: The biomaterial proved to be a possible bone substitute, being incorporated into the receiving bed; however, it showed delayed bone incorporation compared to autogenous bone.

Preparation and evaluation of BCP-CSD-agarose composite microsphere for bone tissue engineering

Composite microspheres have been widely investigated over the years in order to achieve a sound scaffold with suitable combinations of biodegradable polymers and bioactive ceramics/glasses for bone tissue engineering. In our present study, composite microspheres were prepared for the first time by agarose (1 wt %) enforcement with combination of biphasic calcium phosphate (BCP; 20 wt %) and calcium sulfate dehydrate (CSD; 20 wt %), and analyzed for use in bone regeneration. The one-step fabrication process revealed spheres of sizes ranging from 50 to 1000 μm of BCP-CSD contents effectively formed by natural solidification of agarose matrix, which is very simple, time and cost-effective, and could allow for large scale production. Furthermore, the BCP-CSD-agarose composite microspheres were tested in in vitro and in vivo for bone-forming properties in order to assess their biocompatibility. The rapid diffusion of Ca ²⁺ ions from CSD of the composite microspheres through agarose matrix potentially increased interactivity with microenvironment and gave support for cell adhesion and proliferation. Moreover, in vivo result demonstrated that fabricated microspheres promoted neovascularization, stimulated fibroblast cell proliferation, and host cell migration occurred throughout the defects and within microspheres, ultimately guided to new bone formation. The developed composite microspheres with novel approach could have potential for bone regeneration application. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2263-2272, 2019.

Human Bone Marrow Mesenchymal Stromal Cells Promote Bone Regeneration in a Xenogeneic Rabbit Model: A Preclinical Study

Significant research efforts have been undertaken during the last decades to treat musculoskeletal disorders and improve patient's mobility and quality of life. The goal is the return of function as quickly and completely as possible. Cellular therapy has been increasingly employed in this setting. The design of this study was focused on cell-based alternatives. The present study aimed at investigating the bone regeneration capacity of xenogeneic human bone marrow-derived mesenchymal stromal cell (hMSC) implantation with tricalcium phosphate (TCP) granules in an immunocompetent rabbit model of critical-size bone defects at the femoral condyles. Two experimental groups, TCP and hMSC + TCP, were compared. Combination of TCP and hMSC did not affect cell viability or osteogenic differentiation. We also observed significantly higher bone regeneration in vivo in the hMSC + TCP group, which also displayed better TCP osteointegration. Also, evidence of hMSC contribution to a better TCP osteointegration was noticed. Finally, no inflammatory reaction was detected, besides the xenotransplantation of human cells into an immunocompetent recipient. In summary, hMSC combined with TCP granules is a potential combination for bone regeneration purposes that provides better preclinical results compared to TCP alone.

Functional self-assembled neocartilage as part of a biphasic osteochondral construct

Bone-to-bone integration can be obtained by osteoconductive ceramics such as hydroxyapatite (HAp) and beta-tricalcium phosphate (β-TCP), but cartilage-to-cartilage integration is notoriously difficult. Many cartilage repair therapies, including microfracture and mosaicplasty, capitalize on the reparative aspects of subchondral bone due to its resident population of stem cells and vascularity. A strategy of incorporating tissue engineered neocartilage into a ceramic to form an osteochondral construct may serve as a suitable alternative to achieve cartilage graft fixation. The use of a tissue engineered osteochondral construct to repair cartilage defects may also benefit from the ceramic’s proximity to underlying bone and abundant supply of progenitor cells and nutrients. The objective of the first study was to compare HAp and β-TCP ceramics, two widely used ceramics in bone regeneration, in terms of their ability to influence neocartilage interdigitation at an engineered osteochondral interface. Additional assays quantified ceramic pore size, porosity, and compressive strength. The compressive strength of HAp was six times higher than that of β-TCP due to differences in porosity and pore size, and HAp was thus carried forward in the second study as the composition with which to engineer an osteochondral construct. Importantly, it was shown that incorporation of the HAp ceramic in conjunction with the self-assembling process resulted in functionally viable neocartilage. For example, only collagen/dry weight and ultimate tensile strength of the chondral control constructs remained significantly greater than the neocartilage cut off the osteochondral constructs. By demonstrating that the functional properties of engineered neocartilage are not negatively affected by the inclusion of an HAp ceramic in culture, neocartilage engineering strategies may be directly applied to the formation of an osteochondral construct.

The use of a biphasic calcium phosphate in a maxillary sinus floor elevation procedure: a clinical, radiological, histological, and histomorphometric evaluation with 9- and 12-month healing times

Background

This study evaluates the clinical, radiological, histological, and histomorphometric aspects of a fully synthetic biphasic calcium phosphate (BCP) (60% hydroxyapatite and 40% ß-tricalcium phosphate), used in a human maxillary sinus floor elevation (MSFE) procedure with 9- and 12-month healing time.

Methods

A unilateral MSFE procedure, using 100% BCP, was performed in two series of five patients with healing times of 9 and 12 months respectively. Clinical and radiological parameters were measured up to 5 years postoperatively. Biopsy retrieval was carried out during dental implants placement. Histology and histomorphometry were performed on 5-μm sections of undecalcified bone biopsies.

Results

The MSFE procedure with BCP showed uneventful healing in all cases. All dental implants appeared to be well osseointegrated after 3 months. Radiological evaluation showed less than 1 mm tissue height loss from MSFE to the 5-year follow-up examination. No signs of inflammation were detected on histological examination. Newly formed mineralized tissue was found cranially from the native bone. The BCP particles were surrounded by connective tissue, osteoid islands, and newly formed bone. Mineralized bone tissue was in intimate contact with the BCP particles. After 12 months, remnants of BCP were still present. The newly formed bone had a trabecular structure. Bone maturation was demonstrated by the presence of lamellar bone. Histomorphometric analysis showed at 9 and 12 months respectively an average vital bone volume/total volume of 35.2 and 28.2%, bone surface/total volume of 4.2 mm²/mm³ and 8.3 mm²/mm³, trabecular thickness of 224.7 and 66.7 μm, osteoid volume/bone volume of 8.8 and 3.4%, osteoid surface/bone surface (OS/BS) of 42.4 and 8.2%, and osteoid thickness of 93.9 and 13.6 μm.

Conclusions

MFSE with BCP resulted in new bone formation within the augmented sinus floor and allowed the osseointegration of dental implants in both groups. From a histological and histomorphometric perspective, a 9-month healing time for this type of BCP may be the optimal time for placement of dental implants.

Guangxi cobra venom-derived NGF promotes the osteogenic and therapeutic effects of porous BCP ceramic

Neuro-osteological interactions have an important role in the regulation of bone metabolism and regeneration. Neuropeptides combined with porous biphasic calcium phosphates (BCP) using protein adsorption may contribute to the acceleration of bone formation. In the present study, we investigated the effect of BCP combined with nerve growth factor (NGF) on the growth of osteoblasts in vitro and the combinational therapeutic effect on the repair of calvarial defects in vivo. NGF was separated and purified from Chinese cobra venom using a simplified three-step chromatography method. BCP combined with NGF exerted a potent effect on osteoblast differentiation, as evidenced by enhanced cell proliferation, increased ALP activity and the up-regulated expression of osteogenesis-related genes and proteins. Further, combinational therapy with BCP and NGF improved calvarial regeneration, which was superior to treatment with therapy alone, as observed using imageological and morphological examination and histological and immunohistochemical staining. The results confirmed the effect of neuro-osteological interactions through combinatorial treatment with NGF and BCP to promote osteogenesis and bone formation, which may provide an effective and economical strategy for clinical application.

Biphasic calcium phosphates bioceramics (HA/TCP): Concept, physicochemical properties and the impact of standardization of study protocols in biomaterials research

Biphasic calcium phosphates (BCP) bioceramics have become the materials of choice in various orthopedic and maxillofacial bone repair procedures. One of their main advantages is their biodegradation rate that can be modified by changing the proportional ratio of the composition phases. For enhanced bone tissue regeneration, the bioactivity of BCP should be increased by optimizing their physicochemical properties. To date, the ideal physicochemical properties of BCP for bone applications have not been defined. This is mostly related to lack of standard study protocols in biomaterial science especially with regards to their characterizations and clinical applications. In this paper we provided a review on BCP and their physicochemical properties relevant to clinical applications. In addition, we summarized the available literature on their use in animal models and evaluated the influences of different composition ratios on bone healing. Controversies in literature with regards to ideal composition ratio of BCP have also been discussed in detail. We illustrated the discrepancies in study protocols among researchers in animal studies and emphasized the need to develop and follow a set of generally accepted standardized guidelines. Finally; we provided general recommendations for future pre-clinical studies that allow better standardization of study protocols. This will allow better comparison and contrast of newly developed bone substitute biomaterials that help further progress in the field of biomaterial science.

Remodeling of injectable, low-viscosity polymer/ceramic bone grafts in a sheep femoral defect model

Ceramic/polymer composite bone grafts offer the potential advantage of combining the osteoconductivity of ceramic component with the ductility of polymeric component, resulting in a graft that meets many of the desired properties for bone void fillers (BVF). However, the relative contributions of the polymer and ceramic components to bone healing are not well understood. In this study, we compared remodeling of low-viscosity (LV) ceramic/poly(ester urethane) composites to a ceramic BVF control in a sheep femoral condyle plug defect model. LV composites incorporating either ceramic (LV/CM) or allograft bone (LV/A) particles were evaluated. We hypothesized that LV/CM composites which have the advantageous handling properties of injectability, flowability, and settability would heal comparably to the CM control, which was evaluated for up to 2 years to study its long-term degradation properties. Remodeling of LV/CM was comparable to that observed for the CM control, as evidenced by new bone formation on the surface of the ceramic particles. At early time points (4 months), LV/CM composites healed similar to the ceramic clinical control, while LV/A components showed more variable healing due to osteoclast-mediated resorption of the allograft particles. At longer time points (12-15 months), healing of LV/CM composites was more variable due to the nonhomogeneous distribution and lower concentration of the ceramic particles compared to the ceramic clinical control. Resorption of the ceramic particles was almost complete at 2 years. This study highlights the importance of optimizing the loading and distribution of ceramic particles in polymer/ceramic composites to maximize bone healing. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2333-2343, 2017.

Needle-like ion-doped hydroxyapatite crystals influence osteogenic properties of PCL composite scaffolds

Surface topography and chemistry both play a crucial role on influencing cell response in 3D porous scaffolds in terms of osteogenesis. Inorganic materials with peculiar morphology and chemical functionalities may be proficiently used to improve scaffold properties-in the bulk and along pore surface-promoting in vitro and in vivo osseous tissue in-growth. The present study is aimed at investigating how bone regenerative properties of composite scaffolds made of poly(Ɛ-caprolactone) (PCL) can be augmented by the peculiar properties of Mg(2+) ion doped hydroxyapatite (dHA) crystals, mainly emphasizing the role of crystal shape on cell activities mediated by microstructural properties. At the first stage, the study of mechanical response by crossing experimental compression tests and theoretical simulation via empirical models, allow recognizing a significant contribution of dHA shape factor on scaffold elastic moduli variation as a function of the relative volume fraction. Secondly, the peculiar needle-like shape of dHA crystals also influences microscopic (i.e. crystallinity, adhesion forces) and macroscopic (i.e. roughness) properties with relevant effects on biological response of the composite scaffold: differential scanning calorimetry (DSC) analyses clearly indicate a reduction of crystallization heat-from 66.75 to 43.05 J g(-1)-while atomic force microscopy (AFM) ones show a significant increase of roughness-from (78.15  ±  32.71) to (136.13  ±  63.21) nm-and of pull-off forces-from 33.7% to 48.7%. Accordingly, experimental studies with MG-63 osteoblast-like cells show a more efficient in vitro secretion of alkaline phosphatase (ALP) and collagen I and a more copious in vivo formation of new bone trabeculae, thus suggesting a relevant role of dHA to support the main mechanisms involved in bone regeneration.

In situ comparison of varying composite tibial tunnel interference screws used for ACL soft tissue graft fixation

PURPOSE

This mechanical study using an in vitro porcine model compared composite interference screw fixation of soft tissue ACL grafts in tibial tunnels.

METHODS

Forty-eight porcine profundus tendons and tibiae were divided into four groups of 12 closely matched specimens. Equivalent diameter grafts were assigned to each group. Tibial bone tunnels were drilled to 0.5mm greater than graft diameter. Grafts were fixed in tunnels using one 10 × 35 mm composite interference screw designed by four different manufacturers. Maximal insertion torque and perceived within group mechanical testing outcome predictions were recorded. Constructs were potted and loaded into a six degrees of freedom clamp that placed the servohydraulic device tensile loading vector in direct tunnel alignment. Constructs were pre-loaded to 25 N, pre-conditioned between 0 and 50 N for 10 cycles (0.5 Hz), submaximally tested between 50 and 250 N for 500 cycles (one hertz) and load to failure tested at 20mm/min.

RESULTS

Statistically significant differences were not observed between groups for displacement during submaximal cyclic loading, yield load, displacement at yield load, stiffness, ultimate load at failure and displacement at ultimate load. One composite screw group displayed a slightly greater proportion of specimens that required use of more than one screw during insertion.

CONCLUSIONS

Under highly controlled conditions groups displayed comparable fixation.

Bioactivity and bone healing properties of biomimetic porous composite scaffold: in vitro and in vivo studies

Tissue engineering (TE) represents a valid alternative to traditional surgical therapies for the management of bone defects that do not regenerate spontaneously. Scaffolds, one of the most important component of TE strategy, should be biocompatible, bioactive, osteoconductive, and osteoinductive. The aim of this study was to evaluate the biological properties and bone regeneration ability of a porous poly(ɛ-caprolactone) (PCL) scaffold, incorporating MgCO3 -doped hydroxyapatite particles, uncoated (PCL_MgCHA) or coated by apatite-like crystals via biomimetic treatment (PCL_MgCHAB). It was observed that both scaffolds are not cytotoxic and, even if cell viability was similar on both scaffolds, PCL_MgCHAB showed higher alkaline phosphatase and collagen I (COLL I) production at day 7. PCL_MgCHA induced more tumor necrosis factor-α release than PCL_MgCHAB, while osteocalcin was produced less by both scaffolds up to 7 days and no significant differences were observed for transforming growth factor-β synthesis. The percentage of new bone trabeculae growth in wide defects carried out in rabbit femoral distal epiphyses was significantly higher in PCL_MgCHAB in comparison with PCL_MgCHA at 4 weeks and even more at 12 weeks after implantation. This study highlighted the role of a biomimetic composite scaffold in bone regeneration and lays the foundations for its future employment in the clinical practice.

Bioactivity of porous biphasic calcium phosphate enhanced by recombinant human bone morphogenetic protein 2/silk fibroin microsphere

To prepare a bioactive bone substitute, which integrates biphasic calcium phosphate (BCP) and rhBMP-2/silk fibroin (SF) microsphere, and to evaluate its characteristics. Hydroxyapatite and β-tricalcium phosphate were integrated with a ratio of 60–40%. RhBMP-2/SF (0.5 μg/1 mg) microsphere was prepared, and its rhBMP-2-release kinetics was assed. After joining pore-forming agent (Sodium chloride, NaCl), porous BCP/rhBMP-2/SF were manufactured, and its characteristics and bioactivity in vitro were evaluated. Mean diameter of rhBMP-2/SF microsphere was 398.7 ± 99.86 nm, with a loading rate of 4.53 ± 0.08%. RhBMP-2 was released in a dual-phase pattern, of which fast-release (nearly half of protein released) focused on the initial 3 days, and slow-release sustained more than 28 days. With the increase in concentration of NaCl, greater was porosity and pore size, but smaller mechanical strength of BCP/rhBMP-2/SF. Material with 150% (w/v) NaCl had an optimal performance, with a porosity of 78.83%, pore size of 293.25 ± 42.77μm and mechanical strength of 31.03 MPa. Proliferation of human placenta-derived mesenchymal stem cells (hPMSCs) on leaching extract medium was similar to the normal medium (P = 0.89), which was better than that on control group (P = 0.03). Activity of alkaline phosphatase on BCP/rhBMP-2/SF surface was higher than on pure BCP at each time point except at 1 day (P < 0.05). RhBMP-2 has a burst release on early times and a sustaining release on later times. BCP/rhBMP-2/SF with 150% (w/v) pore-forming agent has excellent porosity, pore size and mechanical strength. The biomaterial induces proliferation and differentiation hPMSCs effectively.

Avaliação histológica de hidroxiapatita sintética associada a fosfato de cálcio (?-TCP) utilizados em levantamento de assoalho de seio maxilar

Introdução: Quando a altura do osso alveolar residual é insuficiente na região posterior da maxila, a elevação do assoalho do seio maxilar visando a viabilizar a instalação de implantes dentários é um procedimento indicado. O enxerto autógeno (EA) de regiões intra ou extraorais é considerado o padrão ouro para esse procedimento. Novas opções de substitutos ósseos vêm surgindo, como o Straumann(r) BoneCeramic (BC) - 60% constituído de hidroxiapatita e 40% de β tricálcio fosfato, 100% sintético -, sendo o material utilizado no presente trabalho. Objetivo: Avaliar e comparar histologicamente o comportamento deste substituto ósseo com o enxerto ósseo autógeno. Material e método: Dez pacientes saudáveis e parcialmente desdentados na região posterior da maxila foram submetidos à elevação do assoalho do seio maxilar previamente à instalação de implantes dentários osseointegráveis, sendo, destes, cinco com EA e cinco com BC. Após seis meses do tempo de integração do enxerto ósseo, as amostras foram coletadas por uma trefina e coradas em hematoxilina e eosina para microscopia. Resultado: Todos os implantes osseointegráveis apresentaram boa estabilidade primária. A análise histológica demonstrou tecido ósseo neoformado viável em quatro das cinco amostras do BC, além de um íntimo contato do tecido ósseo mineralizado recém-formado com as partículas do BC. Em uma amostra do BC, não foi observada formação de osso viável. O tecido ósseo formado a partir do EA e do BC apresentou uma característica histológica similar. Conclusão: O BC se mostrou um material adequado para a elevação do assoalho do seio maxilar previamente à instalação de implantes dentários osseointegráveis.

Osteoinductive activity of ErhBMP-2 after anterior cervical diskectomy and fusion with a ß-TCP interbody cage in a goat model

Bone morphogenetic protein (BMP)-2 induces bone and cartilage tissue formation. Large amounts of BMP-2 are difficult to purify or to produce in vitro using eukaryotic cells. The goal of the present study was to assess the clinical use of Escherichia coli-derived recombinant human BMP-2 (ErhBMP-2) on bone fusion after cervical and lumbar spine surgery in a goat model, compared with the standard autogenous iliac bone grafting. Thirty-six goats were randomized to 3 groups: (A) autogenous iliac bone grafting, (B) cervical interbody fusion cage containing ß-tricalcium phosphate (ß-TCP), or (C) cervical interbody fusion cage containing ß-TCP+ErhBMP-2 (2.5 mg). Cervical bone repair was evaluated using radiographs and computed tomography scans at 0, 3, and 6 months. Histological analyses were performed on cervical samples. Two goats died from infection. The differences in intervertebral height among the groups were not significant 3 months postoperatively but became significant after 6 months between groups A vs B and C (P=.04); there was no difference between groups B and C at 6 months. Adding ErhBMP-2 significantly increased cervical fusion at 6 months (P=.04). Histological examinations showed that ß-TCP+ErhBMP-2 increased new bone area, material degradation rate, and depth of tissue penetration and decreased residual material area, all in a time-dependent manner. Escherichia coli-derived rhBMP-2 combined with an enhanced fusion cage containing ß-TCP induced bone formation in a goat model. Furthermore, its ability to promote bone fusion was similar to autogenous iliac bone grafting.

The association of hydrogel and biphasic calcium phosphate in the treatment of dehiscence-type peri-implant defects: an experimental study in dogs

Hydrogel polymers have many applications in regenerative medicine. The aim of this study in dogs was to investigate bone regeneration in dehiscence-type peri-implant defects created surgically and treated with (i) biphasic calcium phosphate (BCP) granules alone; (ii) a composite putty hydroxypropyl methylcellulose (HPMC)/BCP (MBCP/putty); and (iii) a polymer crosslinked membrane of silanized-HPMC (Si-HPMC/BCP) compared with empty controls. At 3 months, new bone formation was significantly more important in defects filled with HPMC/BCP or Si-HPMC/BCP compared with spontaneous healing in control (P = 0.032 and P = 0.046 respectively) and more substantial compared with BCP alone. Furthermore, new bone formation in direct contact with the implant surface was observed in all three groups treated with BCP. The addition of HPMC to the BCP granules may have enhanced the initial stability of the material within the blood clot in these large and complex osseous defects. The Si-HPMC hydrogel may also act as an occlusive membrane covering the BCP, which could improve the stability of the granules in the defect area. However, the crosslinking time of the Si-HPMC is too long for easy handling and the mechanical properties remain to be improved. The composite MBCP/putty appears to be a valuable bone-graft material in complex defects in periodontology and implantology. These encouraging results should now be confirmed in clinical studies.

Multiple silk coatings on biphasic calcium phosphate scaffolds: effect on physical and mechanical properties and in vitro osteogenic response of human mesenchymal stem cells

Ceramic scaffolds such as biphasic calcium phosphate (BCP) have been widely studied and used for bone regeneration, but their brittleness and low mechanical strength are major drawbacks. We report the first systematic study on the effect of silk coating in improving the mechanical and biological properties of BCP scaffolds, including (1) optimization of the silk coating process by investigating multiple coatings, and (2) in vitro evaluation of the osteogenic response of human mesenchymal stem cells (hMSCs) on the coated scaffolds. Our results show that multiple silk coatings on BCP ceramic scaffolds can achieve a significant coating effect to approach the mechanical properties of native bone tissue and positively influence osteogenesis by hMSCs over an extended period. The silk coating method developed in this study represents a simple yet effective means of reinforcement that can be applied to other types of ceramic scaffolds with similar microstructure to improve osteogenic outcomes.

Engineering axially vascularized bone in the sheep arteriovenous-loop model

Treatment of complex bone defects in which vascular supply is insufficient is still a challenge. To overcome the limitations from autologous grafts, a sheep model has been established recently, which is characterized by the development of an independent axial vascularization of a bioartificial construct, permitting microsurgical transplantation. To engineer independently axially vascularized bone tissue in the sheep arteriovenous (AV)-loop model, mesenchymal stem cells (MSCs), without and in combination with recombinant human bone morphogenetic protein-2 (rhBMP-2), were harvested and directly autotransplanted in combination with β-tricalcium phosphate-hydroxyapatite (β-TCP-HA) granules into sheep in this study. After explantation after 12 weeks, histological and immunohistochemical evaluation revealed newly formed bone in both groups. An increased amount of bone area was obtained using directly autotransplanted MSCs with rhBMP-2 stimulation. Osteoblastic and osteoclastic cells were detected adjacent to the newly formed bone, revealing an active bone remodelling process. Directly autotransplanted MSCs can be found close to the β-TCP-HA granules and are contributing to bone formation. Over time, magnetic resonance imaging (MRI) and micro-computed tomography (μCT) imaging confirmed the dense vascularization arising from the AV-loop. This study shows de novo engineering of independently axially vascularized transplantable bone tissue in clinically significant amounts, using directly autotransplanted MSCs and rhBMP-2 stimulation in about 12 weeks in the sheep AV-loop model. This strategy of engineering vascularized transplantable bone tissue could be possibly transferred to the clinic in the future in order to augment current reconstructive strategies.

The association of human primary bone cells with biphasic calcium phosphate (βTCP/HA 70:30) granules increases bone repair

This work evaluates the suitability of biphasic calcium phosphate (BCP) granules (β-TCP/HA 70:30) as potential carriers for cell-guided bone therapy. The BCP granules were obtained by synthesis in the presence of wax, thermal treatment, crushing and sieving and characterized by scanning electron microscopy (SEM), X-ray diffraction and Fourier transform infrared spectroscopy. The cytocompatibility of the BCP granules was confirmed by a multiparametric cytotoxicity assay. SEM analysis showed human bone cell adhesion and migration after seeding onto the material. Rat subcutaneous xenogeneic grafting of granules associated to human bone cells revealed a more accentuated moderate chronic inflammatory infiltrate, without signs of a strong xenoreactivity. Histomorphometrical analysis of bone repair of defects in rat skulls (∅ = 5 mm) has shown that bone cell associated-BCP and autograft promoted a two- and threefold increase, respectively, on new bone formation after 45 days, as compared to BCP alone and blood clot. The increase in bone repair supports the suitability the biocompatible (70:30) BCP granules as injectable and mouldable scaffolds for human cells in bone bioengineering.

Biphasic, triphasic and multiphasic calcium orthophosphates

Biphasic, triphasic and multiphasic (polyphasic) calcium orthophosphates have been sought as biomaterials for reconstruction of bone defects in maxillofacial, dental and orthopedic applications. In general, this concept is determined by advantageous balances of more stable (frequently hydroxyapatite) and more resorbable (typically tricalcium orthophosphates) phases of calcium orthophosphates, while the optimum ratios depend on the particular applications. Therefore, all currently known biphasic, triphasic and multiphasic formulations of calcium orthophosphate bioceramics are sparingly soluble in water and, thus, after being implanted they are gradually resorbed inside the body, releasing calcium and orthophosphate ions into the biological medium and, hence, seeding new bone formation. The available formulations have already demonstrated proven biocompatibility, osteoconductivity, safety and predictability in vitro, in vivo, as well as in clinical models. More recently, in vitro and in vivo studies have shown that some of them might possess osteoinductive properties. Hence, in the field of tissue engineering biphasic, triphasic and multiphasic calcium orthophosphates represent promising biomaterials to construct various scaffolds capable of carrying and/or modulating the behavior of cells. Furthermore, such scaffolds are also suitable for drug delivery applications. This review summarizes the available information on biphasic, triphasic and multiphasic calcium orthophosphates, including their biomedical applications. New formulations are also proposed.

Regeneration of periodontal tissues in non-human primates with rhGDF-5 and beta-tricalcium phosphate

The application of growth factors has been advocated in support of periodontal regeneration. Recombinant human growth and differentiation factor-5 (rhGDF-5), a member of the bone morphogenetic protein family, has been used to encourage periodontal tissue regeneration. This study evaluated the dose response of rhGDF-5 lyophilized onto beta-tricalcium phosphate (bTCP) granules for periodontal tissue regeneration in a baboon model. Periodontal defects were created bilaterally in 12 baboons by a split-mouth design. Plaque was allowed to accumulate around wire ligatures to create chronic disease. After 2 mos, the ligatures were removed, and a notch was placed at the base of the defect. Two teeth on each side of the mouth were randomly treated with bTCP only, 0.5, 1.0, or 2.0 mg rhGDF-5/g bTCP. Animals were sacrificed 5 mos post-treatment, with micro-CT and histomorphometric analysis performed. After 5 mos, analysis showed alveolar bone, cementum, and periodontal ligament formation in all treatment groups, with a dose-dependent increase in rhGDF-5-treated groups. Height of periodontal tissues also increased with the addition of rhGDF-5, and the amount of residual graft material decreased with rhGDF-5 treatment. Therefore, rhGDF-5 delivered on bTCP demonstrated effective regeneration of all 3 tissues critical for periodontal repair.

Positive effect on bone fusion by the combination of platelet-rich plasma and a gelatin β-tricalcium phosphate sponge: a study using a posterolateral fusion model of lumbar vertebrae in rats

We developed a novel method for bone fusion by combining platelet-rich plasma (PRP) and a gelatin β-tricalcium phosphate (β-TCP) sponge. The PRP is an autologous concentration of platelets that includes several growth factors. The gelatin β-TCP sponge comprises gelatin and β-TCP, thus enabling the sustained release of growth factors and osteoconduction. To evaluate this method, we generated a posterolateral fusion model of lumbar vertebrae in rats and divided it into five groups by implanting the following materials between transverse processes of vertebrae, (1) the gelatin β-TCP sponge with PRP (PRP sponge), (2) the gelatin β-TCP sponge with platelet-poor plasma, (3) gelatin hydrogel with PRP, (4) autologous iliac bone (autograft), and (5) no material was implanted as a control. The assessment of bone fusion by a radiographic assessment, a biomechanical test, microcomputed tomography, and histological evaluations demonstrated that there were no significant differences between the PRP sponge and the autograft groups regarding the osteogenic effect. Subsequent examinations revealed that no significant differences existed between the PRP sponge and the autograft groups in either biomechanical stiffness or the bone volume over time; whereas the radiographic and histological composition underwent similar changes in the fusion process. These results indicate that the PRP sponge could, therefore, be potentially useful as an attractive and less invasive method for bone fusion.

How bone forms in large cancellous defects: critical analysis based on experimental work and literature

The behaviour of physiological biomaterials, β-tricalciumphosphate and hydroxyapatite, is analysed based on current literature and our own experimental work. The properties of graft substitutes based on ceramic materials are clearly defined according to their scientific efficiency. The strength of the materials and their biodegradability are still not fully evaluated. Strength and degradability have a direct proportional relationship and are considered the most efficient way to be adapted by their properties to the needs for the treatment of bone defects. New technologies for the manufacturing process are presented that increase those properties and thus open up new indications and easier application of the ceramic materials. The implantation process as well is carefully validated by animal experiments to avoid failures. Based on the experiments, a completely new approach is defined as to how primary bone formation with osteoconductive ceramics can be achieved. The milestones in that approach comprise a synthetically manufactured replica of the bone marrow spaces as osteoconductive ladder, whereas the bead is defined as bone-forming element. As a result, materials are available with high strength if the ceramic is solid or highly porous and possesses a micro-structure. The injection moulding process allows for the combination of high strength of the material with high porosity. Based on the strong capillary forces, micro-chambered beads fulfil most expectations for primary bone formation in cancellous bone defects, including drug delivery, mechanical strengthening if necessary, and stable implantation in situ by coagulation of the blood and bone marrow suctioned in.

Macroporous bioceramics: A remarkable material for bone regeneration

This review summarises the major developments of macroporous bioceramics used mainly for repairing bone defects. Porous bioceramics have been receiving attention ever since their larger surface area was reported to be beneficial for the formation of more rigid bonds with host tissues. The study of porous bioceramics is important to overcome the less favourable bonds formed between dense bioceramics and host tissues, especially in healing bone defects. Macroporous bioceramics, which have been studied extensively, include hydroxyapatite, tricalcium phosphate, alumina, and zirconia. The pore size and interconnections both have significant effects on the growth rate of bone tissues. The optimum pore size of hydroxyapatite scaffolds for bone growth was found to be 300 µm. The existence of interconnections between pores is critical during the initial stage of tissue ingrowth on porous hydroxyapatite scaffolds. Furthermore, pore formation on β-tricalcium phosphate scaffolds also allowed the impregnation of growth factors and cells to improve bone tissues growth significantly. The formation of vascularised tissues was observed on macroporous alumina but did not take place in the case of dense alumina due to its bioinert nature. A macroporous alumina coating on scaffolds was able to improve the overall mechanical properties, and it enabled the impregnation of bioactive materials that could increase the bone growth rate. Despite the bioinertness of zirconia, porous zirconia was useful in designing scaffolds with superior mechanical properties after being coated with bioactive materials. The pores in zirconia were believed to improve the bone growth on the coated system. In summary, although the formation of pores in bioceramics may adversely affect mechanical properties, the advantages provided by the pores are crucial in repairing bone defects.

Bone formation with two types of grafting materials: a histologic and histomorphometric study

BACKGROUND

Although autogenous bone grafts are considered the gold standard for bone regeneration, they have certain limitations, including patient morbidity at the harvest site. Synthetic bone substitutes have been developed to overcome some of these limitations. The present study aimed to compare the osteogenic properties of Straumann Bone Ceramic (SBC), which is a biphasic calcium phosphate, with Bio-Oss, an inorganic bovine bone material, in an animal model.

METHODS

Thirteen rabbits were included in this study. In each rabbit, four 6.5-mm-diameter identical defects were prepared on the calvarium. One site was filled with Bio-Oss, the second site was treated with small-particle SBC, the third site was treated with large-particle SBC, and the fourth site was left as an untreated control. After 4 and 8 weeks, the animals were sacrificed, and histologic and histomorphometric examinations were performed. The data were analyzed using Friedman and multiple-comparison Mann-Whitney U tests.

RESULTS

There were no statistically significant differences in the amount of bone fill between the four groups. L-SBC showed more inflammation and foreign-body reactions than the other bone substitutes.

CONCLUSION

No statistically significant differences were found between groups. Further studies on this issue seem necessary.

Treatment of periodontal defects in dogs using an injectable composite hydrogel/biphasic calcium phosphate

An injectable composite silanized hydroxypropyl methyl cellulose/biphasic calcium phosphate (Si-HPMC/BCP) has been investigated in humans with promising results. The aim of this study was to evaluate his efficacy for treating periodontal defects (canine fenestration and premolar furcation) in dog models. At 3 months, we observed that bone formation around BCP particles in furcation model is more discernible but not statistically significant in defects filled with Si-HPMC/BCP compared to healing in control. We suggest that BCP particles sustain the bone healing process by osteoconduction, while the Si-HPMC hydrogel enhances intergranular cohesion and acts as an exclusion barrier. Furthermore, bone ingrowth is not so distinctive in superficial defects where the biomaterial appears unstable. These results with Si-HPMC/BCP are encouraging. In addition, this biomaterial is easy to use and simplifies the process of filling periodontal lesions. However, more researches are needed to improve the viscosity and hardness to adjust the material to the specificities of periodontal defects.

A glass-reinforced hydroxyapatite and surgical-grade calcium sulfate for bone regeneration: In vivo biological behavior in a sheep model

A glass-reinforced hydroxyapatite (HA) composite (Bonelike®) was developed for bone grafting. This biomaterial is composed of a modified HA matrix with α- and β-tricalcium phosphate secondary phases, resulting in higher solubility than single HA type of materials. Several in vitro and in vivo studies demonstrated that Bonelike® has a highly bioactive behavior, which was also confirmed by employing granular forms of this biomaterial in orthopedics and dental applications. However, a fast consolidation vehicle was needed to promote the fixation of Bonelike® granules if applied in larger defects or in unstable sites. Surgical-grade calcium sulfate (CS), which is widely recognized as a well-tolerated and inexpensive bone graft material, was the chosen vehicle to improve the handling characteristics of Bonelike® as it can be used in the form of a powder that is mixed with a liquid to form a paste that sets in situ. After application in non-critical monocortical defects in sheep, histological, and scanning electron microscopy evaluations demonstrated that Bonelike® associated to CS functioned as a very satisfactory scaffold for bone regeneration as it achieved synchronization of the ingrowing bone with biomaterial resorption and subsequent preservation of the bone graft initial volume. Therefore, our results indicate that CS is an effective vehicle for Bonelike® granules as it facilitates their application and does not interfere with their proven highly osteoconductive properties. In the opposite way, the incorporation of Bonelike® improves the bone regeneration capabilities of CS.

Osteogenic differentiation of miniature pig mesenchymal stem cells in 2D and 3D environment

Mesenchymal stem cells (MSCs) have been repeatedly shown to be able to repair bone defects. The aim of this study was to characterize the osteogenic differentiation of miniature pig MSCs and markers of this differentiation in vitro. Flow-cytometrically characterized MSCs were seeded on cultivation plastic (collagen I and vitronectin coated/uncoated) or plasma clot (PC)/plasma-alginate clot (PAC) scaffolds and differentiated in osteogenic medium. During three weeks of differentiation, the formation of nodules and deposition of calcium were visualized by Alizarin Red Staining. In addition, the production of alkaline phosphatase (ALP) activity was quantitatively detected by fluorescence. The expression of osteopontin, osteonectin and osteocalcin were assayed by immunohistochemistry and Western Blot analysis. We revealed a decrease of osteopontin expression in 2D and 3D environment during differentiation. The weak initial osteonectin signal, culminating on 7(th) or 14(th) day of differentiation, depends on collagen I and vitronectin coating in 2D system. The highest activity of ALP was detected on 21(th) day of osteogenic differentiation. The PC scaffolds provided better conditions for osteogenic differentiation of MSCs than PAC scaffolds in vitro. We also observed expected effects of collagen I and vitronectin on the acceleration of osteogenic differentiation of miniature pig MSC. Our results indicate similar ability of miniature pig MSCs osteogenic differentiation in 2D and 3D environment, but the expression of osteogenic markers in scaffolds and ECM coated monolayers started earlier than in the monolayers without ECM.

Compression behaviour of biphasic calcium phosphate and biphasic calcium phosphate-agarose scaffolds for bone regeneration

There is an acknowledged need for shaping 3-D scaffolds with adequate porosity and mechanical properties for biomedical applications. The mechanical properties under static and cyclic compressive testing of dense and designed porous architecture bioceramic scaffolds based on the biphasic calcium phosphate (BCP) systems and BCP-agarose systems have been evaluated. The dense and designed porous architecture scaffolds in BCP systems exhibited a brittle behaviour. Agarose, a biocompatible and biodegradable hydrogel, has been used to shape designed architecture ceramic-agarose scaffolds following a low-temperature shaping method. Agarose conferred toughness, ductility and a rubbery consistency for strains of up to 60% of in ceramic BCP-agarose systems. This combination of ceramic and organic matrix helps to avoid the inherent brittleness of the bioceramic and enhances the compression resistance of hydrogel. The presence of mechanical hysteresis, permanent deformation after the first cycle and recovery of the master monotonous curve indicate a Mullins-like effect such as that observed in carbon-filled rubber systems. We report this type of mechanical behaviour, the Mullins effect, for the first time in bioceramics and bioceramic-agarose systems.

Calcium orthophosphates as bioceramics: state of the art

In the late 1960s, much interest was raised in regard to biomedical applications of various ceramic materials. A little bit later, such materials were named bioceramics. This review is limited to bioceramics prepared from calcium orthophosphates only, which belong to the categories of bioactive and bioresorbable compounds. There have been a number of important advances in this field during the past 30-40 years. Namely, by structural and compositional control, it became possible to choose whether calcium orthophosphate bioceramics were biologically stable once incorporated within the skeletal structure or whether they were resorbed over time. At the turn of the millennium, a new concept of calcium orthophosphate bioceramics-which is able to promote regeneration of bones-was developed. Presently, calcium orthophosphate bioceramics are available in the form of particulates, blocks, cements, coatings, customized designs for specific applications and as injectable composites in a polymer carrier. Current biomedical applications include artificial replacements for hips, knees, teeth, tendons and ligaments, as well as repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jawbone, spinal fusion and bone fillers after tumor surgery. Exploratory studies demonstrate potential applications of calcium orthophosphate bioceramics as scaffolds, drug delivery systems, as well as carriers of growth factors, bioactive peptides and/or various types of cells for tissue engineering purposes.

Healing of bone defects in the goat mandible, using COLLOSS E and beta-tricalciumphosphate

COLLOSS E, an equine extracellular matrix product containing native transforming growth factor beta1 and several bone morphogenetic proteins, has shown osteoinductive properties in ectopic sites. This study was set up to examine its properties in an orthotoptic site in conjunction with a beta-tricalciumphosphate (beta-TCP) scaffolding material. Thirty-two 17-mm circular defects in goat mandibles were filled with COLLOSS E, beta-TCP, COLLOSS E + beta-TCP, or left empty. After 9 weeks the results were quantified by micro-computed tomography and histology. The empty defects contained the highest percentage of new bone (62%). The beta-TCP scaffold resulted in 38% (p = 0.0029), the mixture of beta-TCP/COLLOSS E resulted in 36% (p = 0.0057), while the use of COLLOSS E alone resulted in 55% (not significant p = 0.34). These results show that addition of TCP did not result in the expected synergy with regard to the healing of the defect and seemed even to inhibit the healing process. On the other hand, the addition of COLLOSS E induced the formation of small islands of new bone, not connected to the defect edges. This was not observed in the specimens not containing COLLOSS E (4.61% of bone formation centrally in the defect vs. 0.56%; p = 0.042). In conclusion, the results of the present study are somewhat unexpected in that the empty defects showed the most bone ingrowth; however, this ingrowth was always connected to the defect edges. In contrast, the application of COLLOSS E with or without beta-TCP induced bone formation in the center of the defects also.

The influence hydroxyapatite nanoparticle shape and size on the properties of biphasic calcium phosphate scaffolds coated with hydroxyapatite-PCL composites

We developed a composite biphasic calcium phosphate (BCP) scaffold by coating a nanocomposite layer, consisting of hydroxyapatite (HA) nanoparticles and polycaprolactone (PCL), over the surface of BCP. The effects of HA particle size and shape in the coating layer on the mechanical and biological properties of the BCP scaffold were examined. Micro-computerized tomography studies showed that the prepared scaffolds were highly porous (approximately 91%) with large pore size (400-700 microm) and an interconnected porous network of approximately 100%. The HA nanoparticle (needle shape)-composite coated scaffolds displayed the highest compressive strength (2.1 +/- 0.17 MPa), compared to pure HA/beta-TCP (0.1 +/- 0.05 MPa) and to the micron HA - composite coated scaffolds (0.29 +/- 0.07 MPa). These needle shaped scaffolds also showed enhanced elasticity and similar stress-strain profile to natural bone. Needle shaped coated HA/PCL particles induced the differentiation of primary human bone derived cells, with significant upregulation of osteogenic gene expression (Runx2, collagen type I, osteocalcin and bone sialoprotein) and alkaline phosphatase activity compared to other groups. These properties are essential for enhancing bone ingrowth in load-bearing applications. The developed composite scaffolds possessed superior physical, mechanical, elastic and biological properties rendering them potentially useful for bone tissue regeneration.

Bone regeneration potential of a soybean-based filler: experimental study in a rabbit cancellous bone defects

Autologous and allogenic bone grafts are considered as materials of choice for bone reconstructive surgery, but limited availability, risks of transmittable diseases and inconsistent clinical performances have prompted the development of alternative biomaterials. The present work compares the bone regeneration potential of a soybean based bone filler (SB bone filler) in comparison to a commercial 50:50 poly(D: ,L: lactide-glycolide)-based bone graft (Fisiograft((R)) gel) when implanted into a critical size defect (6-mm diameter, 10-mm length) in rabbit distal femurs. The histomorphometric and microhardness analyses of femoral condyles 4, 8, 16 and 24 weeks after surgery showed that no significant difference was found in the percentage of both bone repair and bone in-growth in the external, medium and inner defect areas. The SB filler-treated defects showed significantly higher outer bone formation and microhardness results at 24 weeks than Fisiograft((R)) gel (P < 0.05). Soybean-based biomaterials clearly promoted bone repair through a mechanism of action that is likely to involve both the scaffolding role of the biomaterial for osteoblasts and the induction of their differentiation.

The use of Straumann Bone Ceramic in a maxillary sinus floor elevation procedure: a clinical, radiological, histological and histomorphometric evaluation with a 6-month healing period

OBJECTIVES

In this study, we evaluated the quality and quantity of bone formation in maxillary sinus floor elevation procedure using a new fully synthetic biphasic calcium phosphate (BCP) consisting of a mixture of 60% hydroxyapatite and 40% of beta-tricalcium phosphate (Straumann Bone Ceramic).

MATERIAL AND METHODS

A unilateral maxillary sinus floor elevation procedure was performed in six patients using 100% BCP. Biopsy retrieval for histological and histomorphometric analysis was carried out before implant placement after a 6-month healing period.

RESULTS

In this study, the maxillary sinus floor elevation procedure with the use of BCP showed uneventful healing. Radiological evaluation after 6 months showed maintenance of vertical height gained immediately after surgery. Primary stability was achieved with all Straumann SLA dental implants of 4.1 mm diameter and 10 or 12 mm length. The implants appeared to be osseointegrated well after a 3-month healing period. Histological investigation showed no signs of inflammation. Cranial from the native alveolar bone, newly formed mineralized tissue was observed. Also, osteoid islands as well as connective tissue were seen around the BCP particles, cranial from the front of newly formed mineralized tissue. Close bone-to-substitute contact was observed. Histomorphometric analysis showed an average bone volume/total volume (BV/TV) of 27.3% [standard deviation (SD) 4.9], bone surface/total volume (BS/TV) 4.5 mm(2)/mm(3) (SD 1.1), trabecula-thickness (TbTh) 132.1 mum (SD 38.4), osteoid-volume/bone volume (OV/BV) 7.5% (SD 4.3), osteoid surface/bone surface (OS/BS) 41.3% (SD 28.5), osteoid thickness (O.Th) 13.3 mum (SD 4.7) and number of osteoclasts/total area (N.Oc/Tar) 4.4 1/mm (SD 5.7).

CONCLUSIONS

Although a small number of patients were treated, this study provides radiological and histological evidence in humans confirming the suitability of this new BCP for vertical augmentation of the atrophied maxilla by means of a maxillary sinus floor elevation procedure allowing subsequent dental implant placement after a 6-month healing period. The newly formed bone had a trabecular structure and was in intimate contact with the substitute material, outlining the osteoconductive properties of the BCP material. Bone maturation was evident by the presence of lamellar bone.

Macroscopic and histologic analyses of de novo bone in the posterior spine at time of spinal implant removal

STUDY DESIGN

Case series report.

OBJECTIVE

To evaluate the macroscopic and histologic appearance of bone after implantation of bone marrow aspirate on mineralized collagen fiber (Healos) at 12 to 24 months postoperative.

SUMMARY OF BACKGROUND DATA

Numerous bone graft substitutes are currently used for spinal fusion. The success of these technologies is usually determined by radiographic visualization at 1-year or 2-year follow-up. Although x-rays and computed tomography scans are among the best tools to identify bone, interpretation of these images can still lead to error.

METHODS

Six subjects with prior spinal fusion were reoperated for spinal implant removal. All subjects had reached at least 11-month follow-up from their initial spinal surgery. The graft material used in all fusion sites was bone marrow aspirate with Healos (BMA-H), except in a case where autograft was used on one side and BMA-H on the other. At implant removal, macroscopic appearances of the fusion sites were manually tested, photographed, and biopsies were taken and processed for routine histology.

RESULTS

Macroscopic observations were critical to determine presence of mineralized or fibrous tissue. In the site implanted with autograft, fibrous tissue was observed macroscopically. This finding was confirmed by histology. In all sites implanted with BMA-H, solid bone was observed macroscopically. In 1 particular case, the newly formed fusion masses had a rectangular shape, reminiscent of that of the implanted strips. Histologically, BMA-H biopsies revealed mature cortico-cancellous bone.

CONCLUSIONS

Published accounts of histologic evaluations of bone graft materials are uncommon, due to ethical and clinical limitations to harvesting tissue samples. Reoperations for instrumentation removal present rare occurrences when biopsies can be performed. In all cases, BMA-H implants resulted in solid, mature bone. These findings provide additional data on the effectiveness of BMA-H as a bone graft substitute for posterolateral fusion.

A comparative assessment of synthetic ceramic bone substitutes with different composition and microstructure in rabbit femoral condyle model

Various bone substitutes with improved biocompatibility have been developed. Because these products vary in composition and microstructure, it is difficult to understand each feature and make an appropriate selection. Three recently developed highly porous ceramic bone substitutes were evaluated, including two made of hydroxyapatite with different structures (Apaceram-AX: 85%-porosity with micropores, NEOBONE: 75%-porosity without micropores) and one composed of beta-tricalcium phosphate (OSferion: 75%-porosity with micropores) in a rabbit model. Apaceram-AX showed gradual degradation, while NEOBONE remaining intact. OSferion was almost completely degraded at 24 weeks. Numerous osteoclasts were detected in materials with micropores, whether Apaceram-AX or OSferion, but not in NEOBONE. These differences of biodegradability seemed to be related to the presence of micropores. The compressive strength of OSferion increased for several weeks and decreased at a level of cancellous bone. The strength of NEOBONE gradually increased and remained at the highest level among three. The strength of Apaceram-AX increased two to three times that of cancellous bone. Surprisingly, the strength of all materials declined during the initial 1 week, suggesting that great care should be taken in the early period after implantation. These findings may help surgeons to select an appropriate porous substitute based on understanding of their features.

Comparative study of biphasic calcium phosphates with different HA/TCP ratios in mandibular bone defects. A long-term histomorphometric study in minipigs

Three biphasic calcium phosphate (BCP) bone substitute materials with hydroxyapatite (HA)/tricalcium phosphate (TCP) ratios of 20/80, 60/40, and 80/20 were compared to coagulum, particulated autogenous bone, and deproteinized bovine bone mineral (DBBM) in membrane-protected bone defects. The defects were prepared in the mandibles of 24 minipigs that were divided into four groups of six with healing times of 4, 13, 26, and 52 weeks, respectively. The histologic and histomorphometric evaluation focused on differences in amount and pattern of bone formation, filler degradation, and the interface between bone and filler. Collapse of the expanded polytetrafluoroethylene barrier membrane into the coagulum defects underlined the necessity of a filler material to maintain the augmented volume. Quantitatively, BCP 20/80 showed bone formation and degradation of the filler material similar to autografts, whereas BCP 60/40 and BCP 80/20 rather equaled DBBM. Among the three BCP's, the amount of bone formation and degradation of filler material seemed to be inversely proportional to the HA/TCP ratio. The fraction of filler surface covered with bone was highest for autografts at all time points and was higher for DBBM than BCP 80/20 and 60/40 at the early healing phase. TRAP-positive multinucleated cells were identified on BCP and DBBM surfaces without showing typical signs of resorption lacunae.

Magnetic resonance imaging analysis of the bioabsorbable Milagro interference screw for graft fixation in anterior cruciate ligament reconstruction

Ligament graft fixation with bioabsorbable interference screws is a standard procedure in cruciate ligament replacement. Previous screw designs may resorb incompletely, and can cause osteolysis and sterile cysts despite being implanted for several years. The aim of this study was to examine the in vivo degradation and biocompatibility of the new Milagro™ interference screw (Mitek, Norderstedt, Germany). The Milagro™ interference screw is made of 30% ß-TCP (TriCalcium phosphate) and 70% PLGA (Poly-lactic-co-glycolic acid). In the period between June 2005 and February 2006, 38 patients underwent graft fixation with Milagro™ screws in our hospital. Arthroscopic ACL reconstruction was performed using hamstring tendon grafts in all the patients. MR imaging was performed on 12 randomly selected patients out of the total of 38 at 3, 6 and 12 months after surgery. During the examination, the volume loss of the screw, tunnel enlargement, presence of osteolysis, fluid lines, edema and postoperative screw replacement by bone tissue were evaluated. There was no edema or signs of inflammation around the bone tunnels. At 3, 6 and 12 months, the tibial screws showed an average volume loss of 0, 8.1% (±7.9%) and 82.6% (±17.2%, P < 0.05), respectively. The femoral screws showed volume losses of 2.5% (±2.1%), 31.3% (±21.6%) and 92.02% (±6.3%, P < 0.05), respectively. The femoral tunnel enlargement was 47.4% (±43.8%) of the original bone tunnel volume after 12 months, and the mean tunnel volume of the tibial tunnel was −9.5% (±58.1%) compared to the original tunnel. Bone ingrowth was observed in all the patients. In conclusion, the resorption behaviour of the Milagro™ screw is closely linked to the graft healing process. The screws were rapidly resorbed after 6 months and, at 12 months, only the screw remnants were detectable. Moreover, the Milagro™ screw is biocompatible and osteoconductive, promoting bone ingrowth during resorption. Tunnel enlargement is not prevented in the first months but is reduced by bone ingrowth after 12 months.