Coralline bone graft substitutes

Effect of a synthetic hydroxyapatite-based bone grafting material compared to established bone substitute materials on regeneration of critical-size bone defects in the ovine scapula

Lately, the potential risk of disease transmission due to the use of bovine-derived bone substitutes has become obvious, demonstrating the urgent need for a synthetic grafting material with comparable bioactive behaviour and properties. Therefore, the effect of a synthetic hydroxyapatite (HA) (Osbone®) bone grafting material on bone regeneration was evaluated 2 weeks, 1 month, and 3, 6, 12 and 18 months after implantation in critical-size bone defects in the ovine scapula and compared to that of a bovine-derived HA (Bio-Oss®) and β-tricalcium phosphate (TCP) (Cerasorb® M). New bone formation and the biodegradability of the bone substitutes were assessed histomorphometrically. Hard tissue histology and immunohistochemical analysis were employed to characterize collagen type I, alkaline phosphatase, osteocalcin, as well as bone sialoprotein expression in the various cell and matrix components of the bone tissue to evaluate the bioactive properties of the bone grafting materials. No inflammatory tissue response was detected with any of the bone substitute materials studied. After 3 and 6 months, β-TCP (Cerasorb® M) showed superior bone formation when compared to both HA-based materials (3 months: β-TCP 55.65 ± 2.03% vs. SHA 49.05 ± 3.84% and BHA 47.59 ± 1.97%; p ≤ 0.03; 6 months: β-TCP 62.03 ± 1.58%; SHA: 55.83 ± 2.59%; BHA: 53.44 ± 0.78%; p ≤ 0.04). Further, after 12 and 18 months, a similar degree of bone formation and bone-particle contact was noted for all three bone substitute materials without any significant differences. The synthetic HA supported new bone formation, osteogenic marker expression, matrix mineralization and good bone-bonding behaviour to an equal and even slightly superior degree compared to the bovine-derived HA. As a result, synthetic HA can be regarded as a valuable alternative to the bovine-derived HA without the potential risk of disease transmission.

Joint Surface Lesions in the Knee Treated with an Acellular Aragonite-Based Scaffold: A 3-Year Follow-Up Case Series

OBJECTIVE

The study aimed to evaluate the clinical outcome and repair capacity of a cell-free aragonite-based scaffold in patients with an isolated symptomatic joint surface lesion (JSL) of the knee.

DESIGN

Thirteen patients (age 33.5 ± 8.9; female 23%; body mass index 25.3 ± 3.4, K/L [Kellgren-Lawrence] 1.8) with a JSL (2.6 ± 1.7 cm² [1.0-7.5 cm²]) of the distal femur were enrolled in a single-center prospective case series. Safety and clinical outcome was assessed by the KOOS (Knee Injury and Osteoarthritis Outcome Score), IKDC (International Knee Documentation Committee), Lysholm, and Tegner activity scale at baseline and 6, 12, 18, 24, and 36 months follow-up. The MOCART 2.0 and scaffold integration were evaluated on magnetic resonance imaging at 12, 24, and 36 months postoperatively.

RESULTS

Primary outcome (KOOS pain) improved with 36.5 ± 14.7 points at 12 months (P = 0.002) and 41.2 ± 14.7 points at 36 months (P = 0.002) follow-up. Similar increasing trends were observed for the other KOOS subscales, IKDC, and Lysholm score, which were significantly better at each follow-up time point relative to baseline (P < 0.05). Activity level increased from 2.75 ± 1.6 to 4.6 ± 2.2 points at final follow-up (P = 0.07). The MOCART was 61.7 ± 12.6 at 12 months and 72.9 ± 13.0 at 36 months postoperatively. Sixty-six to 100% implant integration and remodeling was observed in 73.3% cases at 36 months. No serious adverse events were reported.

CONCLUSION

The study demonstrated that the biphasic aragonite-based scaffold is a safe and clinically effective implant for treating small-medium sized JSLs of the distal femur in a young and active patient cohort. The implant showed satisfying osteointegration and restoration of the osteochondral unit up to 3 years postimplantation.

Osseointegration Improvement of Co-Cr-Mo Alloy Produced by Additive Manufacturing

Cobalt-base alloys (Co-Cr-Mo) are widely employed in dentistry and orthopedic implants due to their biocompatibility, high mechanical strength and wear resistance. The osseointegration of implants can be improved by surface modification techniques. However, complex geometries obtained by additive manufacturing (AM) limits the efficiency of mechanical-based surface modification techniques. Therefore, plasma immersion ion implantation (PIII) is the best alternative, creating nanotopography even in complex structures. In the present study, we report the osseointegration results in three conditions of the additively manufactured Co-Cr-Mo alloy: (i) as-built, (ii) after PIII, and (iii) coated with titanium (Ti) followed by PIII. The metallic samples were designed with a solid half and a porous half to observe the bone ingrowth in different surfaces. Our results revealed that all conditions presented cortical bone formation. The titanium-coated sample exhibited the best biomechanical results, which was attributed to the higher bone ingrowth percentage with almost all medullary canals filled with neoformed bone and the pores of the implant filled and surrounded by bone ingrowth. It was concluded that the metal alloys produced for AM are biocompatible and stimulate bone neoformation, especially when the Co-28Cr-6Mo alloy with a Ti-coated surface, nanostructured and anodized by PIII is used, whose technology has been shown to increase the osseointegration capacity of this implant.

ZnO-mesoporous glass scaffolds loaded with osteostatin and mesenchymal cells improve bone healing in a rabbit bone defect

The use of 3D scaffolds based on mesoporous bioactive glasses (MBG) enhanced with therapeutic ions, biomolecules and cells is emerging as a strategy to improve bone healing. In this paper, the osteogenic capability of ZnO-enriched MBG scaffolds loaded or not with osteostatin (OST) and human mesenchymal stem cells (MSC) was evaluated after implantation in New Zealand rabbits. Cylindrical meso-macroporous scaffolds with composition (mol %) 82.2SiO₂-10.3CaO-3.3P₂O₅-4.2ZnO (4ZN) were obtained by rapid prototyping and then, coated with gelatin for easy handling and potentiating the release of inorganic ions and OST. Bone defects (7.5 mm diameter, 12 mm depth) were drilled in the distal femoral epiphysis and filled with 4ZN, 4ZN + MSC, 4ZN + OST or 4ZN + MSC + OST materials to evaluate and compare their osteogenic features. Rabbits were sacrificed at 3 months extracting the distal third of bone specimens for necropsy, histological, and microtomography (µCT) evaluations. Systems investigated exhibited bone regeneration capability. Thus, trabecular bone volume density (BV/TV) values obtained from µCT showed that the good bone healing capability of 4ZN was significantly improved by the scaffolds coated with OST and MSC. Our findings in vivo suggest the interest of these MBG complete systems to improve bone repair in the clinical practice.

Injectable BMP-2 gene-activated scaffold for the repair of cranial bone defect in mice

Tissue engineering using adult human mesenchymal stem cells (MSCs) seeded within biomaterial scaffolds has shown the potential to enhance bone healing. Recently, we have developed an injectable, biodegradable methacrylated gelatin‐based hydrogel, which was especially effective in producing scaffolds in situ and allowed the delivery of high viable stem cells and gene vehicles. The well‐demonstrated benefits of recombinant adeno‐associated viral (rAAV) vector, including long‐term gene transfer efficiency and relative safety, combination of gene and cell therapies has been developed in both basic and translational research to support future bone tissue regeneration clinical trials. In this study, we have critically assessed the applicability of single‐step visible light (VL) photocrosslinking fabrication of gelatin scaffold to deliver rAAV encoding human bone morphogenetic protein‐2 (BMP‐2) gene to address the need for sustained BMP‐2 presence localized within scaffolds for the repair of cranial bone defect in mouse model. In this method, rAAV‐BMP‐2 and human bone marrow‐derived MSCs (hBMSCs) were simultaneously included into gelatin scaffolds during scaffold formation by VL illumination. We demonstrated that the subsequent release of rAAV‐BMP‐2 constructs from the scaffold matrix, which resulted in efficient in situ expression of BMP‐2 gene by hBMSCs seeded within the scaffolds, and thus induced their osteogenic differentiation without the supplement of exogenous BMP‐2. The reparative capacity of this novel stem cell‐seeded and gene‐activated scaffolds was further confirmed in the cranial defect in the severe combined immunodeficiency mice, revealed by imaging, histology, and immunohistochemistry at 6 weeks after cranial defect treatment.

Hair follicle stem cells differentiation into bone cells on collagen scaffold

The hair follicle is a dynamic structure which contains different niches for stem cells, therefore; it has been considered as valuable and rich sources of stem cells, due to easy access, multipotency and non-oncogenic properties. In the present study, the differentiation capacities of hair follicle stem cells into bone cells on the natural collagen scaffolds were investigated. The stem cells were extracted from the hair follicle bulge area of male Wistar rats' whisker and cultured until 3rd passage, then osteogenic differentiations were induced by culturing the cells in the specific osteogenic medium. After 3 weeks, the differentiation parameters, including morphological changes, levels of calcification and expression of the bone specific genes were detected. The hydrogel preparation and scaffold fabrication was carried out using the extracted collagen and was studied by scanning electron microscope. Comparison of the stem cells' growth and changes on the scaffold and non-scaffold conditions showed that, in the both situation, the cells revealed differentiation signs of osteocytes, including large and cubic morphology with a star-shaped nucleus. Staining by Alizarin-red and Von-Kossa methods showed the presence of red and black calcium mass on the scaffold. Expression of the osteopontin and alkaline phosphatase genes confirmed the differentiation. Considerable porosity in the surface of the scaffold was recorded by scanning electron microscopy, which made it convenient for cells' attachment and growth. The data showed that the bulge stem cells possess significant capacity for osteoblastic differentiation and collagen scaffolds were found to be an appropriate matrix for growth and differentiation of the cell.

Hydroxylapatite-collagen hybrid scaffold induces human adipose-derived mesenchymal stem cells to osteogenic differentiation in vitro and bone regrowth in patients

Tissue engineering-based bone graft is an emerging viable treatment modality to repair and regenerate tissues damaged as a result of diseases or injuries. The structure and composition of scaffolds should modulate the classical osteogenic pathways in human stem cells. The osteoinductivity properties of the hydroxylapatite-collagen hybrid scaffold named Coll/Pro Osteon 200 were investigated in an in vitro model of human adipose mesenchymal stem cells (hASCs), whereas the clinical evaluation was carried out in maxillofacial patients. Differentially expressed genes (DEGs) induced by the scaffold were analyzed using the Osteogenesis RT² PCR Array. The osteoinductivity potential of the scaffold was also investigated by studying the alkaline phosphatase (ALP) activity, matrix mineralization, osteocalcin (OCN), and CLEC3B expression protein. Fifty patients who underwent zygomatic augmentation and bimaxillary osteotomy were evaluated clinically, radiologically, and histologically during a 3-year follow-up. Among DEGs, osteogenesis-related genes, including BMP1/2, ALP, BGLAP, SP7, RUNX2, SPP1, and EGFR, which play important roles in osteogenesis, were found to be upregulated. The genes to cartilage condensation SOX9, BMPR1B, and osteoclast cells TNFSF11 were detected upregulated at every time point of the investigation. This scaffold has a high osteoinductivity revealed by the matrix mineralization, ALP activity, OCN, and CLEC3B expression proteins. Clinical evaluation evidences that the biomaterial promotes bone regrowth. Histological results of biopsy specimens from patients showed prominent ossification. Experimental data using the Coll/Pro Osteon 200 indicate that clinical evaluation of bone regrowth in patients, after scaffold implantation, was supported by DEGs implicated in skeletal development as shown in "in vitro" experiments with hASCs.

Efficient in vivo bone formation by BMP-2 engineered human mesenchymal stem cells encapsulated in a projection stereolithographically fabricated hydrogel scaffold

Background

Stem cell-based bone tissue engineering shows promise for bone repair but faces some challenges, such as insufficient osteogenesis and limited architecture flexibility of the cell-delivery scaffold.

Methods

In this study, we first used lentiviral constructs to transduce ex vivo human bone marrow-derived stem cells with human bone morphogenetic protein-2 (BMP-2) gene (BMP-hBMSCs). We then introduced these cells into a hydrogel scaffold using an advanced visible light-based projection stereolithography (VL-PSL) technology, which is compatible with concomitant cell encapsulation and amenable to computer-aided architectural design, to fabricate scaffolds fitting local physical and structural variations in different bones and defects.

Results

The results showed that the BMP-hBMSCs encapsulated within the scaffolds had high viability with sustained BMP-2 gene expression and differentiated toward an osteogenic lineage without the supplement of additional BMP-2 protein. In vivo bone formation efficacy was further assessed using an intramuscular implantation model in severe combined immunodeficiency (SCID) mice. Microcomputed tomography (micro-CT) imaging indicated rapid bone formation by the BMP-hBMSC-laden constructs as early as 14 days post-implantation. Histological examination revealed a mature trabecular bone structure with considerable vascularization. Through tracking of the implanted cells, we also found that BMP-hBMSC were directly involved in the new bone formation.

Conclusions

The robust, self-driven osteogenic capability and computer-designed architecture of the construct developed in this study should have potential applications for customized clinical repair of large bone defects or non-unions.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1350-6) contains supplementary material, which is available to authorized users.

Autograft, Allograft, and Bone Graft Substitutes: Clinical Evidence and Indications for Use in the Setting of Orthopaedic Trauma Surgery

Bone grafts are the second most common tissue transplanted in the United States, and they are an essential treatment tool in the field of acute and reconstructive traumatic orthopaedic surgery. Available in cancellous, cortical, or bone marrow aspirate form, autogenous bone graft is regarded as the gold standard in the treatment of posttraumatic conditions such as fracture, delayed union, and nonunion. However, drawbacks including donor-site morbidity and limited quantity of graft available for harvest make autograft a less-than-ideal option for certain patient populations. Advancements in allograft and bone graft substitutes in the past decade have created viable alternatives that circumvent some of the weak points of autografts. Allograft is a favorable alternative for its convenience, abundance, and lack of procurement-related patient morbidity. Options include structural, particulate, and demineralized bone matrix form. Commonly used bone graft substitutes include calcium phosphate and calcium sulfate synthetics-these grafts provide their own benefits in structural support and availability. In addition, different growth factors including bone morphogenic proteins can augment the healing process of bony defects treated with grafts. Autograft, allograft, and bone graft substitutes all possess their own varying degrees of osteogenic, osteoconductive, and osteoinductive properties that make them better suited for different procedures. It is the purpose of this review to characterize these properties and present clinical evidence supporting their indications for use in the hopes of better elucidating treatment options for patients requiring bone grafting in an orthopaedic trauma setting.

Development of Phosphatized Calcium Carbonate Biominerals as Bioactive Bone Graft Substitute Materials, Part I: Incorporation of Magnesium and Strontium Ions

Synthetic materials based on calcium phosphate (CaP) are frequently used as bone graft substitutes when natural bone grafts are not available or not suitable. Chemical similarity to bone guarantees the biocompatibility of synthetic CaP materials, whereas macroporosity enables their integration into the natural bone tissue. To restore optimum mechanical performance after the grafting procedure, gradual resorption of CaP implants and simultaneous replacement by natural bone is desirable. Mg and Sr ions released from implants support osteointegration by stimulating bone formation. Furthermore, Sr ions counteract osteoporotic bone loss and reduce the probability of related fractures. The present study aimed at developing porous Ca carbonate biominerals into novel CaP-based, bioactive bone implant materials. Macroporous Ca carbonate biominerals, specifically skeletons of corals (aragonite) and sea urchins (Mg-substituted calcite), were hydrothermally converted into pseudomorphic CaP materials with their natural porosity preserved. Sr ions were introduced to the mineral replacement reactions by temporarily stabilizing them in the hydrothermal phosphate solutions as Sr-EDTA complexes. In this reaction system, Na, Mg, and Sr ions favored the formation of correspondingly substituted β-tricalcium phosphate over hydroxyapatite. Upon dissolution, the incorporated functional ions became released, endowing these CaP materials with bioactive and potentially osteoporotic properties.

Development of Phosphatized Calcium Carbonate Biominerals as Bioactive Bone Graft Substitute Materials, Part II: Functionalization with Antibacterial Silver Ions

Porous calcium phosphate (CaP) materials as bone graft substitutes can be prepared from Ca carbonate biomineral structures by hydrothermal conversion into pseudomorphic CaP scaffolds. The present study aims at furnishing such phosphatized Ca carbonate biomineral (PCCB) materials with antibacterial Ag ions in order to avoid perisurgical wound infections. Prior to this study, PCCB materials with Mg and/or Sr ions incorporated for stimulating bone formation were prepared from coral skeletons and sea urchin spines as starting materials. The porous PCCB materials were treated with aqueous solutions of Ag nitrate with concentrations of 10 or 100 mmol/L, resulting in the formation of Ag phosphate nanoparticles on the sample surfaces through a replacement reaction. The materials were characterized using scanning electron microscopy (SEM) energy-dispersive X-ray spectroscopy (EDS) and X-ray diffractometry (XRD). In contact with Ringer`s solution, the Ag phosphate nanoparticles dissolved and released Ag ions with concentrations up to 0.51 mg/L, as shown by atomic absorption spectroscopy (AAS) analyses. In tests against Pseudomonas aeruginosa and Staphylococcus aureus on agar plates, antibacterial properties were similar for both types of Ag-modified PCCB materials. Concerning the antibacterial performance, the treatment with AgNO₃ solutions with 10 mmol/L was almost as effective as with 100 mmol/L.

Mesenchymal Stem Cells of Different Origin-Seeded Bioceramic Construct in Regeneration of Bone Defect in Rabbit

BACKGROUND

Stem cell is currently playing a major role in the treatment of number of incurable diseases via transplantation therapy. The objective of this study was to determine the osteogenic potential of allogenic and xenogenic bone-derived MSC seeded on a hydroxyapatite (HA/TCP) bioceramic construct in critical size bone defect (CSD) in rabbits.

METHODS

A 15 mm long radial osteotomy was performed unilaterally in thirty-six rabbits divided equally in six groups. Bone defects were filled with bioscaffold seeded with autologous, allogenic, ovine, canine BMSCs and cell free bioscaffold block in groups A, B, C, D and E respectively. An empty defect served as the control group.

RESULTS

The radiological, histological and SEM observations depicted better and early signs of new bone formation and bridging bone/implant interfaces in the animals of group A followed by B. Both xenogenous MSC-HA/TCP construct also accelerated the healing of critical sized bone defect. There was no sign of any inflammatory reaction in the xenogenic composite scaffold group of animals confirmed their well acceptance by the host body.

CONCLUSION

In vivo experiments in rabbit CSD model confirmed that autogenous, allogenous and xenogenous BMSC seeded on bioscaffold promoted faster healing of critical size defects. Hence, we may suggest that BMSCs are suitable for bone formation in fracture healing and non-union.

The hydroxyapatite Turkish Delight: a technical note

Nasal dorsum augmentation is commonly performed using autologous cartilage grafts, also in the Turkish Delight technique. The aim of this study was to describe a modification of the Turkish Delight technique for dorsal augmentation consisting of small hydroxyapatite-calcium carbonate granules (0.5-1 mm) that were wrapped in layers of oxidized cellulose and glued with 1-2-cm3 fibrin sealant and to compare its utility with that of other techniques. Clinically stable and satisfactory results were achieved in the four cases examined. Cone-beam computerized tomography (CBCT) imaging revealed that there was no degradation of the graft up to 2 years after surgery. The use of a modified Turkish Delight method using hydroxyapatite granules promises to be a valuable option for the correction of nasal dorsum deficiency.

Delayed Tibial Osteomyelitis after Anterior Cruciate Ligament Reconstruction with Hamstrings Autograft and Bioabsorbable Interference Screw: A Case Report and Review of the Literature

Osteomyelitis following arthroscopically assisted anterior cruciate ligament (ACL) reconstruction has rarely been reported in the literature. We report a case of a 20-year-old female who had delayed tibial osteomyelitis and a pretibial cyst with culture-positive, oxacillin sensitive Staphylococcus epidermidis 15 months after an ACL reconstruction with hamstring autograft. Soft tissue fixation within the tibial tunnel was with a poly-L-D-lactic acid (PLDLA) bioabsorbable interference screw. The patient underwent surgical treatment with curettage, debridement, hardware removal, and bone grafting of the tibial tunnel followed by a course of intravenous antibiotics. Arthroscopic evaluation demonstrated an intact ACL graft without any evidence of intra-articular infection. The patient returned to collegiate athletics without any complications. While the most common biologic complications include pretibial cysts, granuloma formation, tunnel widening, and inflammatory reactions, infection is exceedingly rare. Late infection and osteomyelitis are also rare but can occur and should be considered in the differential diagnosis.

The healing of alveolar bone defects with novel bio-implants composed of Ad-BMP9-transfected rDFCs and CHA scaffolds

Cells, scaffolds, and growth factors play important roles in bone regeneration. Bone morphogenetic protein 9 (BMP9), a member of BMP family, could facilitate osteogenesis by regulating growth factors and promoting angiogenesis. Similar to other stem cells, rat dental follicle stem cells (rDFCs), the precursor cells of cementoblasts, osteoblasts and periodontal ligament cells, can self-renew and exhibit multipotential capacity. Coralline hydroxyapatite (CHA) has good biocompatibility and conductivity required for bone tissue engineering. Here, we reported that BMP9 could enhance the osteogenic differentiation of rDFCs in cell culture. Moreover, our results suggested that BMP9 acted through the Smad1/5/8 signaling pathway. We also produced a novel scaffold that encompasses bio-degradable CHA seeded with recombinant adenoviruses expressing BMP9-transfected rDFCs (Ad-BMP9-transfected rDFCs). With this implant, we achieved more alveolar bone regeneration in the alveolar bone defect compared to blank group, CHA group and rDFCs group. Our results provided a novel bio-implants composed of Ad-BMP9-transfected rDFCs and CHA scaffolds and its mechanism is regarding the activation of Smad1/5/8 signaling pathway in BMP9-induced rDFCs osteogenesis.

In Vitro Investigation of Cell Compatibility of Pure β-TCP Granules

In this study, osteoblastic cells were isolated from rat bone marrow and characterized. The cells were cultured on β-TCP granules and the osteoblast/ β-TCP constructs. For this purpose, bone marrow was harvested under sterile conditions. Cell aggregates were broken up by pipetting and a cell suspension was cultured in DMEM/F12. After three days, the cells that adhered to the surface of the flask were cultured in osteoblast medium. When the cells became confluent, they were passaged and cultured in 24-well polystyrene cell culture dishes. Characterization of the osteoblasts, cell proliferation and alkaline phosphatase activity were measured on days 1, 7, 14, 21 and 30. To investigate the cell compatibility of the β-TCP granules, osteoblastic cells were cultured on β-TCP granules and a polystyrene cell culture dish (control group). Cell proliferation and alkaline phosphatase (ALP) activity were measured on days 1, 7, 14, 21 and 30 in both groups. Cell growth significantly increased at each time point, but on day 30 a decrease was observed. The ALP activity also increased at each time point and also decreased on day 30. This study may be regarded as the first step leading to a therapy for various bone defects.

Tissue segregation restores the induction of bone formation by the mammalian transforming growth factor-β(3) in calvarial defects of the non-human primate Papio ursinus

A diffusion molecular hypothesis from the dura and/or the leptomeninges below that would control the induction of calvarial membranous bone formation by the recombinant human transforming growth factor-β3 (hTGF-β3) was investigated. Coral-derived calcium carbonate-based macroporous constructs (25 mm diameter; 3.5/4 mm thickness) with limited hydrothermal conversion to hydroxyapatite (7% HA/CC) were inserted into forty calvarial defects created in 10 adult Chacma baboons Papio ursinus. In 20 defects, an impermeable nylon foil membrane (SupraFOIL(®)) was inserted between the cut endocranial bone and the underlying dura mater. Twenty of the macroporous constructs were preloaded with hTGF-β3 (125 μg in 1000 μl 20 mM sodium succinate, 4% mannitol pH4.0), 10 of which were implanted into defects segregated by the SupraFOIL(®) membrane, and 10 into non-segregated defects. Tissues were harvested on day 90, processed for decalcified and undecalcified histology and quantitative real-time polymerase chain reaction (qRT-PCR). Segregated untreated macroporous specimens showed a reduction of bone formation across the macroporous spaces compared to non-segregated constructs. qRT-PCR of segregated untreated specimens showed down regulation of osteogenic protein-1 (OP-1), osteocalcin (OC), bone morphogenetic protein-2 (BMP-2), RUNX-2 and inhibitor of DNA binding-2 and -3 (ID2,ID3) and up regulation of TGF-β3, a molecular signalling pathway inhibiting the induction of membranous bone formation. Non-segregated hTGF-β3/treated constructs also showed non-osteogenic expression profiles when compared to non-segregated untreated specimens. Segregated hTGF-β3/treated 7% HA/CC constructs showed significantly greater induction of bone formation across the macroporous spaces and, compared to non-segregated hTGF-β3/treated constructs, showed up regulation of OP-1, OC, BMP-2, RUNX-2, ID2 and ID3. Similar up-regulated expression profiles were seen for untreated non-segregated constructs. TGF-β signalling via ID genes creates permissive or refractory micro-environments that regulate the induction of calvarial bone formation which is controlled by the exogenous hTGF-β3 upon segregation of the calvarial defects. The dura is the common regulator of the induction of calvarial bone formation modulated by the presence or absence of the SupraFOIL(®) membrane with or without hTGF-β3.

Parathyroid hormone-related protein (107-111) improves the bone regeneration potential of gelatin-glutaraldehyde biopolymer-coated hydroxyapatite

Biopolymer-coated nanocrystalline hydroxyapatite (HA) made as macroporous foams which are degradable and flexible are promising candidates as orthopaedic implants. The C-terminal (107-111) epitope of parathyroid hormone-related protein (PTHrP) exhibits osteogenic properties. The main aim of this study was to evaluate whether PTHrP (107-111) loading into gelatin-glutaraldehyde biopolymer-coated HA (HAGlu) scaffolds would produce an optimal biomaterial for tissue engineering applications. HAGlu scaffolds with and without PTHrP (107-111) were implanted into a cavitary defect performed in both distal tibial metaphysis of adult rats. Animals were sacrificed after 4 weeks for histological, microcomputerized tomography and gene expression analysis of the callus. At this time, bone healing occurred only in the presence of PTHrP (107-111)-containing HAGlu implant, related to an increase in bone volume/tissue volume and trabecular thickness, cortical thickness and gene expression of osteocalcin and vascular cell adhesion molecule 1, but a decreased gene expression of Wnt inhibitors, SOST and dickkopf homolog 1. The autonomous osteogenic effect of the PTHrP (107-111)-loaded HAGlu scaffolds was confirmed in mouse and human osteoblastic cell cultures. Our findings demonstrate the advantage of loading PTHrP (107-111) into degradable HAGlu scaffolds for achieving an optimal biomaterial that is promising for low load bearing clinical applications.

Advanced nanocomposites for bone regeneration

The field of orthopedic tissue engineering is quickly expanding with the development of novel materials and strategies designed for rapid bone regeneration. While autologous bone grafts continue to be the standard of care, drawbacks include donor-site morbidity and short tissue supplies. Herein we report a novel nanocomposite sponge composed of poly(1,8-octanediol-co-citrate) (POC) and the bioactive ceramic β-tricalcium phosphate (TCP). We show that these nanocomposite sponges can be used as a depot for bone-producing (a.k.a. osteogenic) growth factors. In vitro bioactivity is demonstrated by significant upregulation of osteogenic genes, osteopontin (∼3 fold increase), osteocalcin (∼22 fold increase), alkaline phosphatase (∼10 fold increase), and transcription factor, RUNX2 (∼5 fold increase) over basal expression levels in mesenchymal stem cells. In vivo osteogenicity and biocompatibility is demonstrated in a standard subcutaneous implant model in rat. Results show that the nanocomposite sponge supports complete cell infiltration, minimal adverse foreign body response, positive cellular proliferation, and cellular expression of osteogenic markers in subcutaneous tissue. The results shown herein are encouraging and support the use of this sponge for future bone tissue engineering efforts.

Osteochondral regeneration using a novel aragonite-hyaluronate bi-phasic scaffold in a goat model

PURPOSE

The objective of this study was to examine whether different mechanical modifications and/or impregnation of hyaluronic acid (HA) might enhance aragonite-based scaffold properties for the regeneration of cartilage and bone in an animal model.

METHODS

Bi-phasic osteochondral scaffolds were prepared using coralline aragonite with different modifications, including 1- to 2-mm-deep drilled channels in the cartilage phase (Group 1, n = 7) or in the bone phase (Group 2, n = 8), and compared with unmodified coral cylinders (Group 3, n = 8) as well as empty control defects (Group 4, n = 4). In each group, four of the implants were impregnated with HA to the cartilage phase. Osteochondral defects (6 mm diameter, 8 mm depth) were made in medial and lateral femoral condyles of 14 goats, and the scaffolds were implanted according to a randomization chart. After 6 months, cartilage and bone regeneration were evaluated macroscopically and histologically by an external laboratory.

RESULTS

Group 1 implants were replaced by newly formed hyaline cartilage and subchondral bone (combined histological evaluation according to the ICRS II-2010 and O'Driscoll et al. 34 ± 4 n = 7). In this group, the cartilaginous repair tissue showed a smooth contour and was well integrated into the adjacent native cartilage, with morphological evidence of hyaline cartilage as confirmed by the marked presence of proteoglycans, a marked grade of collagen type II and the absence of collagen type I. The average scores in other groups were significantly lower (Group 2 (n = 8) 28.8 ± 11, Group 3 (n = 8) 23 ± 9 and Group 4 (empty control, n = 4) 19.7 ± 15).

CONCLUSIONS

The implants with the mechanical modification and HA impregnation in the cartilage phase outperformed all other types of implant. Although native coral is an excellent material for bone repair, as a stand-alone material implant, it does not regenerate hyaline cartilage. Mechanical modification with drilled channels and impregnation of HA within the coral pores enhanced the scaffold's cartilage regenerative potential. The modified implant shows young hyaline cartilage regeneration. This implant might be useful for the treatment of both chondral and osteochondral defects in humans.

Strontium Incorporated Coralline Hydroxyapatite for Engineering Bone

Goniopora was hydrothermally converted to coralline hydroxyapatite (CHA) and incorporated with Sr (Sr-CHA). The pore size of Goniopora was in the range of 40–300 μm with a porosity of about 68%. Surface morphologies of the coral were modified to flake-like hydroxyapatite structures on CHA and the addition of Sr detected on Sr-CHA as confirmed by SEM and EDX. As the first report of incorporating Sr into coral, about 6%–14% Sr was detected on Sr-CHA. The compressive strengths of CHA and Sr-CHA were not compromised due to the hydrothermal treatments. Sr-CHA was studied in vitro using MC3T3-E1 cells and in vivo with an ovariectomized rat model. The proliferation of MC3T3-E1 cells was significantly promoted by Sr-CHA as compared to CHA. Moreover, higher scaffold volume retention (+40%) was reported on the micro-CT analysis of the Sr-CHA scaffold. The results suggest that the incorporation of Sr in CHA can further enhance the osteoconductivity and osteoinductivity of corals. Strontium has been suggested to stimulate bone growth and inhibit bone resorption. In this study, we have successfully incorporated Sr into CHA with the natural porous structure remained and explored the idea of Sr-CHA as a potential scaffolding material for bone regeneration.

Calcium ions and osteoclastogenesis initiate the induction of bone formation by coral-derived macroporous constructs

Coral-derived calcium carbonate/hydroxyapatite macroporous constructs of the genus Goniopora with limited hydrothermal conversion to hydroxyapatite (7% HA/CC) initiate the induction of bone formation. Which are the molecular signals that initiate pattern formation and the induction of bone formation? To evaluate the role of released calcium ions and osteoclastogenesis, 7% HA/CC was pre-loaded with either 500 μg of the calcium channel blocker, verapamil hydrochloride, or 240 μg of the osteoclast inhibitor, biphosphonate zoledronate, and implanted in the rectus abdominis muscle of six adult Chacma baboons Papio ursinus. Generated tissues on days 15, 60 and 90 were analysed by histomorphometry and qRT-PCR. On day 15, up-regulation of type IV collagen characterized all the implanted constructs correlating with vascular invasion. Zoledronate-treated specimens showed an important delay in tissue patterning and morphogenesis with limited bone formation. Osteoclastic inhibition yielded minimal, if any, bone formation by induction. 7% HA/CC pre-loaded with the Ca⁺⁺ channel blocker verapamil hydrochloride strongly inhibited the induction of bone formation. Down-regulation of bone morphogenetic protein-2 (BMP-2) together with up-regulation of Noggin genes correlated with limited bone formation in 7% HA/CC pre-loaded with either verapamil or zoledronate, indicating that the induction of bone formation by coral-derived macroporous constructs is via the BMPs pathway. The spontaneous induction of bone formation is initiated by a local peak of Ca⁺⁺ activating stem cell differentiation and the induction of bone formation.

Randomized controlled trial of osteoconductive fixation screws for anterior cruciate ligament reconstruction: a comparison of the Calaxo and Milagro screws

PURPOSE

To compare the outcome of 2 bioabsorbable screws for tibial interference fixation in anterior cruciate ligament reconstruction with reference to rate of absorption, osteoconductive properties, and clinical outcome.

METHODS

Patients undergoing primary anterior cruciate ligament reconstruction with hamstring autograft in a single unit were invited to participate in this study. Patients were randomized to receive either the Calaxo screw (Smith & Nephew, Andover, MA) or Milagro screw (DePuy Mitek, Raynham, MA) for tibial fixation. Patients were reviewed with subjective and objective evaluation by use of the International Knee Documentation Committee form, Lysholm score, KT-1000 arthrometry (MEDmetric, San Diego, CA), and clinical examination. Magnetic resonance imaging was performed at 1 year and computed tomography scanning at 1 week and at 6, 12, and 24 months.

RESULTS

Sixty patients agreed to participate in the study, with 32 patients randomized to the Calaxo screw and 28 to the Milagro screw for tibial fixation. There was no significant difference in subjective or objective clinical outcome between the 2 groups. At 24 months, 88% of Calaxo screws showed complete screw resorption compared with 0% of Milagro screws (P < .001). Tibial cysts were present in 88% of the Calaxo group and 7% of the Milagro group (P = .001). At 24 months, the mean volume of new bone formation for the Calaxo group was 21% of original screw volume. Ossification of the Milagro screw was unable to be accurately assessed as a result of incomplete screw resorption.

CONCLUSIONS

Both screws showed similar favorable objective and subjective outcomes at 2 years. The Calaxo screw resorbed completely over a period of 6 months and was associated with a high incidence of intra-tunnel cyst formation. The Milagro screw increased in volume over a period of 6 months, followed by a gradual resorption, which was still ongoing at 2 years. Both screws were associated with tunnel widening, and neither showed evidence of significant tunnel ossification. We conclude that, despite satisfactory clinical outcomes, the addition of "osteoconductive" materials to bioabsorbable screws is not associated with bone formation at the screw site at 2 years.

LEVEL OF EVIDENCE

Level I, randomized controlled trial.

In vivo osteointegration of three-dimensional crosslinked gelatin-coated hydroxyapatite foams

The main requirement of bone regenerative scaffolds is to enhance the chemical reactions leading to the formation of new bone while providing a proper surface for tissue in-growth as well as a suitable degradation rate. Calcium phosphate ceramics are conformed by different shaping methods. One requirement is to design implants and scaffolds with suitable shapes and sizes, but also with interconnected porosity to ensure bone oxygenation and angiogenesis. In this work we present the in vivo performance of hierarchically arranged glutaraldehyde crosslinked, gelatin-coated nanocrystalline hydroxyapatite (HABP) scaffolds (1-400 μm), with high potential as bone regenerators and excellent osteointegration performance, as well as an appropriate bioresorption rate. 6×10 mm bone defects were made in the lateral aspect of both distal femoral epiphysis of 15 mature (9 months old) male New Zealand rabbits. The bone defect in the left femur was then filled by using HABP foam cylinders, allowing the surgeon to carve the appropriate shape for a particular bone defect with high stability intra-operatively. The foam becomes swollen with body fluid and fills the cavity, ensuring good fixation without the need for a cement. Histological and radiographical studies after 4 months implantation showed healing of all treated bone defects, with bone integration of the HABP foam cylinders and bone conduction over the surface. This in vivo behaviour offers promising results as a scaffold for clinical applications, mainly in orthopaedics and dentistry.

A Macroporous Bioreactor Super Activated by the Recombinant Human Transforming Growth Factor-β(3)

Macroporous single phase hydroxyapatite (HA) and biphasic HA/β-tricalcium phosphate with 33% post-sinter hydroxyapatite (HA/β-TCP) were combined with 25 or 125 μg recombinant human transforming growth factor-β3 (hTGF-β₃) to engineer a super activated bioreactor implanted in orthotopic calvarial and heterotopic rectus abdominis muscle sites and harvested on day 30 and 90. Coral-derived calcium carbonate fully converted (100%) and partially converted to 5 and 13% hydroxyapatite/calcium carbonate (5 and 13% HA/CC) pre-loaded with 125 and 250 μg hTGF-β₃, and 1:5 and 5:1 binary applications of hTGF-β₃: hOP-1 by weight, were implanted in the rectus abdominis and harvested on day 20 and 30, respectively, to monitor spatial/temporal morphogenesis by high doses of hTGF-β₃. Bone formation was assessed on decalcified paraffin-embedded sections by measuring the fractional volume of newly formed bone. On day 30 and 90, single phase HA implants showed greater amounts of bone when compared to biphasic specimens; 5 and 13% HA/CC pre-loaded with 125 and 250 μg hTGF-β₃ showed substantial induction of bone formation; 250 μg hTGF-β₃ induced as yet unreported massive induction of bone formation as early as 20 days prominently outside the profile of the macroporous constructs. The induction of bone formation is controlled by the implanted ratio of the recombinant morphogens, i.e., the 1:5 hTGF-β₃:hOP-1 ratio by weight was greater than the inverse ratio. The unprecedented tissue induction by single doses of 250 μg hTGF-β₃ resulting in rapid bone morphogenesis of vast mineralized ossicles with multiple trabeculations surfaced by contiguous secreting osteoblasts is the novel molecular and morphological frontier for the induction of bone formation in clinical contexts.

In vitro cytotoxic evaluation of processed natural coral in human osteoblasts

This study aimed to evaluate the in vitro cytotoxic effects of locally produced processed natural coral (PNC) using human osteoblasts (HOS). Cytotoxicity was not observed when HOS cells were cultured with PNC, as assessed by (3-(4,5-dimethylthiazol-2-yl)-2-5-diphenyl tetrazolium bromide; MTT) and Neutral Red (NR) assays at concentration up 200 mg/mL for up to 72 hours. Flow cytometry (FCM) analysis showed that PNC (200 mg/mL) did not decrease viability of HOS cells after 48 and 72 hours of treatment. In a cell attachment study, the HOS cells attached to the edge of the PNC disc, and later grew into the pores of the PNC disc. All results from these studies indicate that locally produced PNC material is noncytotoxic and favors the growth of HOS cells.

Flow perfusion culture of human mesenchymal stem cells on coralline hydroxyapatite scaffolds with various pore sizes

Bone grafts are widely used in orthopaedic reconstructive surgery, but harvesting of autologous grafts is limited due to donor site complications. Bone tissue engineering is a possible alternative source for substitutes, and to date, mainly small scaffold sizes have been evaluated. The aim of this study was to obtain a clinically relevant substitute size using a direct perfusion culture system. Human bone marrowderived mesenchymal stem cells were seeded on coralline hydroxyapatite scaffolds with 200 μm or 500 μm pores, and resulting constructs were cultured in a perfusion bioreactor or in static culture for up to 21 days and analysed for cell distribution and osteogenic differentiation using histological stainings, alkaline phosphatase activity assay, and real-time RT-PCR on bone markers. We found that the number of cells was higher during static culture at most time points and that the final number of cells was higher in 500 μm constructs as compared with 200 μm constructs. Alkaline phosphatase enzyme activity assays and real time RT-PCR on seven osteogenic markers showed that differentiation occurred primarily and earlier in statically cultured constructs with 200 μm pores compared with 500 μm ones. Adhesion and proliferation of the cells was seen on both scaffold sizes, but the vitality and morphology of cells changed unfavorably during perfusion culture. In contrast to previous studies using spinner flask that show increased cellularity and osteogenic properties of cells when cultured dynamically, the perfusion culture in our study did not enhance the osteogenic properties of cell/scaffold constructs. The statically cultured constructs showed increasing cell numbers and abundant osteogenic differentiation probably because of weak initial cell adhesion due to the surface morphology of scaffolds. Our conclusion is that the specific scaffold surface microstructure and culturing system flow dynamics has a great impact on cell distribution and proliferation and on osteogenic differentiation, and the data presented warrant careful selection of in vitro culture settings to meet the specific requirements of the scaffolds and cells, especially when natural biomaterials with varying morphology are used.

Osteogenic differentiation influences stem cell migration out of scaffold-free microspheres

Complete bone regeneration of critical-size defects frequently fail because of the use of acellular bone substitutes and because of partially negative influences of artificial scaffolds. However, the supply of cells to critical-size defects is essential for the regeneration. Therefore, engineered scaffold-free tissues, with outgrowing cells that fill up spaces in the bony defect, are promising candidates for bone regeneration approaches. Here, we demonstrate such a scaffold-free tissue construct (microspheres) that, if osteogenic differentiated, mineralizes while maintaining the capability to let cells grow out of the united cell structure. A superior outgrowth capability of microspheres composed of human cord blood-derived unrestricted somatic stem cells compared with murine embryonic stem cells was found and a time-dependent reduction in outgrowth was evident in vitro. Even after 5 days of osteoinduction and strong mineralization, the cells migrate out of the microsphere. As migration of cells out of unrestricted somatic stem cell microspheres was also found in extracellular matrix gel, we suggest that cells would migrate also in vivo. Thus, microspheres could serve as the scaffold and the source of osteogenic cells in future bone regeneration approaches. Further, microspheres permit the precise administration of large amount of cells into an area of interest.

Antibacterial effects of sol-gel-derived bioactive glass nanoparticle on aerobic bacteria

The aim of this work was to evaluate the antibacterial effect of bioactive glass nanopowders. The 58S, 63S, and 72S compositions were prepared via the sol-gel technique. Characterization techniques such as X-ray diffraction, transmission electron microscopy (TEM), Zetasizer, and X-ray fluorescent were used. The antibacterial activity was studied using Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, and Staphylococcus aureus. Cytotoxicity of the samples was evaluated using mouse fibroblast L929 cell line. The chemical compositions of the prepared samples were as predicted, and the particle size of the samples with an amorphous structure mainly ranged over 20-90 nm. At broth concentrations below 50 mg/mL, they showed no antibacterial activity. The 58S showed the highest antibacterial activity with the minimum bactericidal concentrations of 50 and 100 mg/mL for E. coli plus S. aureus and for P. aeruginosa, respectively. The 63S exhibited bactericidal and bacteriostatic effects on E. coli and S. aureus at concentrations of 100 and 50 mg/mL, respectively, at an minimum bactericidal concentrations of 100 mg/mL. However, 72S bioactive glass nanopowder showed no antibacterial effect. They showed no cytotoxicity. It was concluded that bioactive glass nanopowders could be considered as good candidates for the treatment of oral bone defects and root canal disinfection. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

Synergistic induction of bone formation by hOP-1, hTGF-beta3 and inhibition by zoledronate in macroporous coral-derived hydroxyapatites

Thirty coral-derived calcium carbonate-based macroporous constructs with limited hydrothermal conversion to hydroxyapatite (7% HA/CC) were implanted in the rectus abdominis of three adult non-human primate Papio ursinus to investigate the intrinsic induction of bone formation. Macroporous constructs with 125 microg human recombinant osteogenic protein-1 (hOP-1) or 125 microg human recombinant transforming growth factor-beta(3) (hTGF-beta(3)) were also implanted. The potential synergistic interaction between morphogens was tested by implanting binary applications of hOP-1 and hTGF-beta(3) 5:1 by weight, respectively. To evaluate the role of osteoclastic activity on the implanted macroporous surfaces, coral-derived constructs were pre-loaded with 0.24 mg of bisphosphonate zoledronate (Zometa). To correlate the morphology of tissue induction with osteogenic gene expression and activation, harvested specimens on day 90 were analyzed for changes in OP-1 and TGF-beta(3) mRNA synthesis by quantitative real-time polymerase chain reaction (qRT-PCR). The induction of bone formation in 7% HA/CC solo correlated with OP-1 expression. Massive bone induction formed by binary applications of the recombinant morphogens. Single applications of hOP-1 and hTGF-beta(3) also resulted in substantial bone formation, not comparable however to synergistic binary applications. Zoledronate-treated macroporous constructs showed limited bone formation and in two specimens bone formation was altogether absent; qRT-PCR showed a prominent reduction of OP-1 gene expression whilst TGF-beta(3) expression was far greater than OP-1. The lack of bone formation by zoledronate-treated specimens indicates that osteoclastic activity on the implanted coral-derived constructs is critical for the spontaneous induction of bone formation. Indirectly, zoledronate-treated samples showing lack of OP-1 gene expression and absent or very limited bone formation by induction confirm that the spontaneous induction of bone formation by coral-derived macroporous constructs is initiated by secreted BMPs/OPs, in context the OP-1 isoform.

Coralline hydroxyapatite is a suitable bone graft substitute in an intra-articular goat defect model

Intra-articular defects can be filled with an autologous bone graft taken from the iliac crest. This can be indicated after trauma or following correcting osteotomy. Patients may encounter donor site morbidity after this procedure. In this in vivo study, we studied if coralline hydroxyapatite (CHA) is a suitable material to replace autologous bone graft to fill a defect in the femoral trochlea of goats. CHA did not evoke any negative reaction in the synovium, and the articular cartilage was comparable to controls. In the bone graft group, we found scattered areas of (enchondral formed) bone. Most bone graft had been resorbed or remodeled, and the scarce remnants were incorporated into new bone. Resorption of CHA was limited or absent and most CHA was surrounded by new bone. In areas with fragmented CHA, close to the joint surface, numerous giant cells were found. The study shows that in this animal model, CHA inserted in a defect that directly communicates with the joint space incorporates into bone. This study did not show any negative effects of CHA in a joint environment.

Injectable biomaterials for regenerating complex craniofacial tissues

Engineering complex tissues requires a precisely formulated combination of cells, spatiotemporally released bioactive factors, and a specialized scaffold support system. Injectable materials, particularly those delivered in aqueous solution, are considered ideal delivery vehicles for cells and bioactive factors and can also be delivered through minimally invasive methods and fill complex 3D shapes. In this review, we examine injectable materials that form scaffolds or networks capable of both replacing tissue function early after delivery and supporting tissue regeneration over a time period of weeks to months. The use of these materials for tissue engineering within the craniofacial complex is challenging but ideal as many highly specialized and functional tissues reside within a small volume in the craniofacial structures and the need for minimally invasive interventions is desirable due to aesthetic considerations. Current biomaterials and strategies used to treat craniofacial defects are examined, followed by a review of craniofacial tissue engineering, and finally an examination of current technologies used for injectable scaffold development and drug and cell delivery using these materials.

Next generation calcium phosphate-based biomaterials

It has been close to a century since calcium phosphate materials were first used as bone graft substitutes. Numerous studies conducted in the last two decades have produced a wealth of information on the chemistry, in vitro properties, and biological characteristics of granular calcium phosphates and calcium phosphate cement biomaterials. An in depth analysis of several key areas of calcium phosphate cement properties is presented with the aim of developing strategies that could lead to break-through improvements in the functional efficacies of these materials.

The induction of bone formation by coral-derived calcium carbonate/hydroxyapatite constructs

The spontaneous induction of bone formation in heterotopic rectus abdominis and orthotopic calvarial sites by coral-derived biomimetic matrices of different chemical compositions was investigated in a long-term study in the non-human primate Papio ursinus. Coral-derived calcium carbonate constructs were converted to hydroxyapatite by hydrothermal exchange. Limited conversion produced hydroxyapatite/calcium carbonate (HA/CC) constructs of 5% and 13% hydroxyapatite. Rods of 20 mm in length and 7 mm in diameter were implanted in heterotopic rectus abdominis sites; discs 25 mm in diameter were implanted in orthotopic calvarial defects of six adult non-human primates P. ursinus. Heterotopic samples also included fully converted hydroxyapatite replicas sintered at 1100 degrees C. To further enhance spontaneous osteoinductive activity, fully converted hydroxyapatite replicas were coated with the synthetic peptide P15 known to increase the adhesion of fibroblasts to anorganic bovine mineral. Bone induction was assessed at 60, 90 and 365 days by histological examination, alkaline phosphatase and osteocalcin expression, as well as by the expression of BMP-7, GDF-10 and collagen type IV mRNAs. Induction of bone occurred in the concavities of the matrices at all time points. At 365 days, bone marrow was evident in the P15-coated and uncoated implants. Resorption of partially converted calcium carbonate/hydroxyapatite was apparent, as well as remodeling of the newly formed bone. Northern blot analyses of samples from heterotopic specimens showed high levels of expression of BMP-7 and collagen type IV mRNA in all specimen types at 60 days, correlating with the induction of the osteoblastic phenotype in invading fibrovascular cells. Orthotopic specimens showed prominent bone formation across the different implanted constructs. The concavities of the matrices biomimetize the remodeling cycle of the osteonic primate cortico-cancellous bone and promote the ripple-like cascade of the induction of bone formation. This study demonstrates for the first time that partially converted HA/CC constructs also induce spontaneous differentiation of bone, albeit only seen one year post-implantation.

Efficacy of nano-hydroxyapatite prepared by an aqueous solution combustion technique in healing bone defects of goat

The present study was undertaken to evaluate porous hydroxyapatite (HAp), the powder of which was prepared by a novel aqueous solution combustion technique, as a bone substitute in healing bone defects in vivo, as assessed by radiologic and histopathologic methods, oxytetracycline labeling, and angiogenic features in Bengal goat. Bone defects were created in the diaphysis of the radius and either not filled (group I) or filled with a HAp strut (group II). The radiologic study in group II showed the presence of unabsorbed implants which acted as a scaffold for new bone growth across the defect, and the quality of healing of the bone defect was almost indistinguishable from the control group, in which the defect was more or less similar, although the newly formed bony tissue was more organized when HAp was used. Histologic methods showed complete normal ossification with development of Haversian canals and well-defined osteoblasts at the periphery in group II, whereas the control group had moderate fibro-collagenization and an adequate amount of marrow material, fat cells, and blood vessels. An oxytetracycline labeling study showed moderate activity of new bone formation with crossing-over of new bone trabeculae along with the presence of resorption cavities in group II, whereas in the control group, the process of new bone formation was active from both ends and the defect site appeared as a homogenous non-fluoroscent area. Angiograms of the animals in the control group showed uniform angiogenesis in the defect site with establishment of trans-transplant angiogenesis, whereas in group II there was complete trans-transplant shunting of blood vessel communication. Porous HAp ceramic prepared by an aqueous combustion technique promoted bone formation over the defect, confirming their biologic osteoconductive property.

Composites of poly(DL-lactide-co-glycolide) and calcium carbonate: in vitro evaluation for use in orthopedic applications

Biodegradable materials utilized in current orthopedic sports medicine fixation devices are required to maintain mechanical properties for at least 12 weeks to facilitate tissue healing and then ideally degrade with eventual replacement by surrounding tissue (bone). Current materials exhibit excessive longevity, which limit the potential for bone replacement, an ideal outcome in clinical procedures where revisions are a possibility. This study investigates material property modification of poly(DL-lactide-co-glycolide) (PLGA) by calcium carbonate. Modification of the degradation rate of PLGA by calcium carbonate (16, 36, 51% w/w) was demonstrated and the percentage of calcium carbonate within the polymer optimized at 36% (w/w). The optimized formulation was molded into a fixation screw and in vitro degradation demonstrated a gradual loss in molecular weight but with a pull-out strength retention beyond 12 weeks. Significant mass loss then occurred after 26 weeks. Physical testing, insertion torque, and failure torque indicated that this composite also had sufficient initial mechanical properties required for screw in type fixation devices. The combination of mechanical properties and degradation behavior suggests that this material may have potential to be utilized in orthopedic fixation devices that are placed in bone.

Bone differentiation of marrow-derived mesenchymal stem cells using beta-tricalcium phosphate-alginate-gelatin hybrid scaffolds

The aim of the present study was to establish a 3D culture system for bone differentiation of mesenchymal stem cells (MSCs), using a new hybrid sponge. To manufacture the scaffold, a composite of beta-tricalcium phosphate-alginate-gelatin was prepared and cast as pellets of 1 cm diameter. The sponge was then fabricated by drying in freeze-dryer for 12 h. The porosity, mean pore size, compressive modulus and strength of the composite sponge fabricated in this study were 89.7%, 325.3 microm, 1.82 and 0.196 MPa, respectively. To establish a 3D culture system, the rat bone marrow-derived MSCs were suspended in 500 microl diluted collagen gel, loaded into the porous sponge and provided with medium with or without osteogenic supplements for 3 weeks. The day after loading, the cells appeared in the scaffold's internal spaces, where later some of them from either culture survived by anchoring on the surfaces. At the end of cultivation period, individually adhered cells from both cultures were observed to be replaced by cell aggregates, in which mineralized matrix was detected by alizarin red staining. Furthermore, RT-PCR analysis indicated that the bone-specific gene osteocalcin was expressed in cultures in both the presence and absence of the osteogenic supplements. Taken together, it seems that the studied scaffolds are cell-compatible and, more importantly, possess some osteo-inductive properties.

Apoptosis in bone for tissue engineering

Bone loss due to congenital defects, trauma, improper fracture fixation, metabolic disturbances, infections, or after tumor resection represents a major clinical problem in head and neck surgery. To address these issues, different types of scaffolds, growth factors and cell sources -- alone or in various combinations -- have been applied for development of bioartificial bone tissues. Although these applications have received increasing interest, use of autologous bone grafts is still considered as the gold standard for tissue repair. Despite progress in some areas of tissue regeneration, significant translation into clinical practice has not been achieved. Reasons for this impass include rejection of engineered tissue implants by the immune system, limited blood supply, or morbidity of the donor site. During the process of bone regeneration, approximately 50-70% of osteoblasts undergo apoptosis. Apoptosis is a naturally occurring cell death pathway induced in a variety of cell types and is associated with caspase activation or caspase mediation. It is recognized as an important component of embryogenesis and tissue morphogenesis and, in adult skeletons, it contributes substantially to physiological bone turnover, repair, and regeneration. Intracellular mechanisms are orchestrated by a variety of proteins, the interplay of which seems to vary, depending on the differentiation state of the cell or the current status of the tissue. Closing gaps in current knowledge of the apoptosis of bone and understanding the mechanisms of cell death in tissue engineered bone will improve results in the translation from bench to bedsite. This review aims to provide a broad overview of the current general concepts in apoptosis with a special focus on its regulation in osteoblasts and its significance for bone tissue engineering.

Coralline hydroxyapatite in complex acetabular reconstruction

This retrospective study examined whether a coralline hydroxyapatite bone graft substitute adequately repaired bone defects during complex acetabular reconstructions. Seventeen patients who underwent acetabular revision using Pro Osteon 500 were assessed to determine whether any cups required re-revision, whether bone had incorporated into the coralline hydroxyapatite grafts, and whether the coralline hydroxyapatite grafts resorbed with time. At latest follow-up, no cups required re-revision, but 1 had failed. Radiographic evidence of bone incorporation was observed in every coralline hydroxyapatite graft. Graft resorption was not observed.