Differential effects of bone graft substitutes on regeneration of bone marrow

The intensity of subacute local biological effects after the implantation of ALBO-OS dental material based on hydroxyapatite and poly(lactide-co-glycolide): in vivo evaluation in rats

OBJECTIVES

This study aimed to evaluate the intensity of the subacute local biological effects after implantation and osseoconductive potential of novel hydroxyapatite-based bone substitute coated with poly (lactide-co-glycolide), named ALBO-OS, in comparison to Bio-Oss®.

METHODS

Fifteen male Wistar rats, randomly assigned into groups: 10, 20, and 30 days (n꞊5), were subcutaneously implanted with ALBO-OS and Bio-Oss®. Furthermore, artificially made bone defects on both rat's tibias were implanted with experimental materials. Unimplanted defects represented negative control. After the animals' euthanizing, tissue samples were prepared and analyzed histologically and histomorphometrically.

RESULTS

Normal healing of the epithelial tissue was observed, with no signs of infection or necrosis. Minimal vascular congestion was noted immediately around the graft, with no signs of tissue oedema, with a minimal capsule thickness. The applied material did not cause an inflammatory response (IR) of significant intensity, and 20 days after implantation, the IR was mainly assessed as minimal. The tibial specimen showed that ALBO-OS has good osseoconductive potential, similar to Bio-Oss®, as well as low levels of acute and subacute inflammation.

CONCLUSIONS

The tested material exhibits satisfying biocompatibility, similar to Bio-Oss®.

Bicalcium Phosphate as an Asset in Regenerative Therapy

After a loss of a tooth, alveolar bone resorption is immutable, leaving the area devoid of sufficient bone quality and mass for a successful and satisfactory implant or any other dental treatment. To treat this problem of irreversible bone loss, bone grafting is the primary solution and a well-accepted technique. The use of bone grafting procedures has increased in recent years. This review is about the various bone grafting techniques and best-situated material available currently along with their trump cards and limitations. In the thorough discussion regarding bone grafting materials and their substitutes, one alloplastic material has shown unbeaten and the most satisfactory properties than any other material, "bicalcium phosphate" (BCP). BCP is a mixture of hydroxyapatite (HA) and beta-tricalcium phosphate (B-TCP) usually obtained through sintering calcium-deficient apatite (CDA) at or above 700°C or by other methods such as hydrolysis or precipitation. The review also shows comparative studies done to understand the effect, most adequate balance, and impact of ratios of HA/B-TCP on the properties, structure, and success rate of this material. The objective of the review is to enlighten the principal characteristic of the most likely used bone graft material presently, i.e., BCP. The most impeccable characteristic of BCP is its capability to osteointegrate, which results in a superior interface. This interface depicts a dynamic process that includes physicochemical reactions, crystal-protein interactions, cell and tissue colonization, and bone remodeling. BCP has certain essential properties that could be put forth as its advantage over any other substitute. These properties include bioactivity, osteointegration, osteoinduction, osteogenesis, and biodegradation, which are mostly governed by modifying the HA/B-TCP ratio. Other applications of BCP are feasible, such as in drug administration and scaffolds for tissue engineering.

Bone Grafts in Dental Medicine: An Overview of Autografts, Allografts and Synthetic Materials

This review provides an overview of various materials used in dentistry and oral and maxillofacial surgeries to replace or repair bone defects. The choice of material depends on factors such as tissue viability, size, shape, and defect volume. While small bone defects can regenerate naturally, extensive defects or loss or pathological fractures require surgical intervention and the use of substitute bones. Autologous bone, taken from the patient's own body, is the gold standard for bone grafting but has drawbacks such as uncertain prognosis, surgery at the donor site, and limited availability. Other alternatives for medium and small-sized defects include allografts (from human donors), xenografts (from animals), and synthetic materials with osteoconductive properties. Allografts are carefully selected and processed human bone materials, while xenografts are derived from animals and possess similar chemical composition to human bone. Synthetic materials such as ceramics and bioactive glasses are used for small defects but may lack osteoinductivity and moldability. Calcium-phosphate-based ceramics, particularly hydroxyapatite, are extensively studied and commonly used due to their compositional similarity to natural bone. Additional components, such as growth factors, autogenous bone, and therapeutic elements, can be incorporated into synthetic or xenogeneic scaffolds to enhance their osteogenic properties. This review aims to provide a comprehensive analysis of grafting materials in dentistry, discussing their properties, advantages, and disadvantages. It also highlights the challenges of analyzing in vivo and clinical studies to select the most suitable option for specific situations.

Osseointegration and Remodeling of Mineralized Bone Graft Are Negatively Impacted by Prior Treatment with Bisphosphonates

BACKGROUND

Bisphosphonates limit resorption by inhibiting osteoclast formation and activation. They are removed during preparation of demineralized bone matrix (DBM) particles, but it is not known if osteogenesis and incorporation of mineralized bone allografts from patients treated with oral bisphosphonates are affected in vivo.

METHODS

Human block allografts from 3 bisphosphonate-treated donors and 3 age and sex-matched control donors who had not received bisphosphonates were obtained (Musculoskeletal Transplant Foundation); one-half from each donor was demineralized. In the first study, 3 × 2-mm mineralized and demineralized cylindrical grafts were implanted bilaterally in the femoral metaphysis of 56 rats. In the second study, samples from each group were pooled, prepared as particles, and implanted bilaterally in the femoral marrow canal of 24 rats. Osseointegration, defined as native bone in contact with allograft, was assessed at 10 weeks by micro-computed tomography (CT) and histomorphometry.

RESULTS

Micro-CT showed greater bone volume in sites treated with demineralized samples compared with the control mineralized and bisphosphonate-exposed mineralized samples. More new bone was generated along the cortical-endosteal interface compared with mineralized samples. Histology showed significantly less new bone in contact with the mineralized bisphosphonate-exposed allograft (10.4%) compared with mineralized samples that did not receive bisphosphonates (22.8%) and demineralized samples (31.7% and 42.8%). A gap was observed between native bone and allograft in the bisphosphonate-exposed mineralized samples (0.50 mm 2 ). The gap area was significantly greater compared with mineralized samples that did not receive bisphosphonates (0.16 mm 2 ) and demineralized samples (0.10 and 0.03 mm 2 ).

CONCLUSIONS

Mineralized allografts were osseointegrated, but not remodeled or replaced by living bone, preventing full regeneration of the bone defect. Prior treatment of the donor with bisphosphonates affected osteogenesis, preventing osteointegration and remodeling of the allograft into the regenerating bone.

CLINICAL RELEVANCE

Clinical use of mineralized allografts from patients who had received bisphosphonate therapy needs to be evaluated; in this animal model, such grafts were not integrated into the host bone or remodeled, and full regeneration of the bone defects was prevented.

The surgical management of the cavity and bone defects in enchondroma cases: A prospective randomized trial

BACKGROUND

We compared the curettage/bone grafting and the curettage/bone graft substitutes surgical techniques in their relation to functional outcomes, oncologic outcome (recurrence, malignant transformation), the rate of postsurgical complications, durations of surgery and of postsurgical immobilization for hand-localized cases of solitary and multiple enchondromas.

METHODS

The current prospective randomized trial analyzed 200 adult patients (2012-2017) with enchondroma who underwent surgical intervention. The cases were randomly divided into Group 1 (n = 100; F 56, M 44) for surgeries with curettage and autogenous bone grafting, and Group 2 (n = 100; F 55, M 45) for surgeries with curettage and bone graft substitutes. The placebo control Group 3 consisted of cases operated by curettage only (n = 56; F 31, M 25). The follow-up period was set at 30 months.

RESULTS

The duration of surgery was 51 ± 4 min in Group 1 and 27 ± 1 min in Group 2 (p = 0.008). In Group 1, the rate of recurrence was 6% against 1% in Group 2 (p = 0.005). No other statistically significant differences in postsurgical outcomes between three involved groups were noted.

CONCLUSION

In cases of enchondroma of the hand, postsurgical functional outcomes, the rate of postsurgical complications, the duration of immobilization, and the time to complete recovery are not influenced by the type of chosen grafting material. The implementation of HAp-collagen bone substitutes in granules instead of autogenous bone grafting reduces the duration of surgery. The implementation of autogenous bone grafting may increase the rate of tumor recurrence.

Continuous microfluidic encapsulation of single mesenchymal stem cells using alginate microgels as injectable fillers for bone regeneration

The encapsulation of cells in microscale hydrogels can provide a mimic of a three-dimensional (3D) microenvironment to support cell viability and functions and to protect cells from the environmental stress, which have been widely used in tissue regeneration and cell therapies. Here, a microfluidics-based approach is developed for continuous encapsulation of mesenchymal stem cells (MSCs) at the single-cell level using alginate microgels. This microfluidic technique integrated on-chip encapsulation, gelation, and de-emulsification into a one-step fabrication process, which enables scalable cell encapsulation while retaining the viability and functionality of loaded cells. Remarkably, we observed MSCs encapsulated in Ca-alginate microgels at the single-cell level showed significantly enhanced osteogenesis and accelerated mineralization of the microgels which occurred only after 7 days of induction. Furthermore, MSCs laden in alginate microgels displayed significantly enhanced bone formation compared to MSCs mixed with microgels and acellular microgels in a rat tibial ablation model. To conclude, the current microfluidic technique represents a significant step toward continuous single cell encapsulation, fabrication, and purification. These microgels can boost bone regeneration by providing a controlled osteogenic microenvironment for encapsulated MSCs and facilitate stem cell therapy in the treatment of bone defects in a minimally invasive delivery way. STATEMENT OF SIGNIFICANCE: The biological functions and therapeutic activities of single cells laden in microgels for tissue engineering remains less investigated. Here, we reported a microfluidic-based method for continuous encapsulation of single MSCs with high viability and functionality by integrating on-chip encapsulation, gelation, and de-emulsification into a one-step fabrication process. More importantly, MSCs encapsulated in alginate microgels at the single-cell level showed significantly enhanced osteogenesis, remarkably accelerated mineralization in vitro and bone formation capacity in vivo. Therefore, this single-cell encapsulation technique can facilitate stem cell therapy for bone regeneration and be potentially used in a variety of tissue engineering applications.

Evaluation of the osteogenic potential of growth factor-rich demineralized bone matrix in vivo

BACKGROUND

The study evaluates the osteogenic properties and biocompatibility of growth factor-rich demineralized bone matrix (GDBM) by comparing with cancellous mineralized bone matrix (CMBM) and anorganic bovine bone matrix (ABBM).

METHODS

Thirty-six Sprague-Dawley rats were used (n = 6/group/time point). To assess biocompatibility and osteoinductivity, the respective bone matrices were randomly placed in subcutaneous pouches for 7 and 28 days and evaluated by histology and osteopontin expression. Osteoconductivity was assessed by randomly implanting respective bone matrices in osteotomies on femurs for 14 and 28 days and evaluated by microcomputed tomography and histology.

RESULTS

Neither acute inflammation nor mineralized tissue was noted in any of the subcutaneous specimens, whereas expression of osteopontin was more prominent in the GDBM group. Among the femoral specimens, the greatest relative bone volume (bone volume [BV] divided by trabecular volume [TV]) and trabecular thickness was noted in the ABBM group at both time points, whereas less BV/TV was noted in GDBM group at day 14. Residual matrix particles were noted in all examined groups at both time points, without significant differences regarding defect fill between groups. The GDBM group presented similar levels of newly formed bone compartment and marrow space to those of the ABBM group.

CONCLUSIONS

GDBM demonstrated acceptable biocompatibility and osteogenic potential comparable to ABBM in vivo. Further investigations in a more clinically relevant model are warranted.

BIOMATERIAL IMPLANTS IN BONE FRACTURES PRODUCED IN RATS FIBULAS

To evaluate the importance of collagen and hydroxyapatite in the regeneration of fractures experimentally induced in the fibulas of rats. Method: 15 rats were used. These were subjected to surgery to remove a fragment from the fibula. This site then received a graft consisting of a silicone tubes filled with hydroxyapatite and collagen. Results: Little bone neoformation occurred inside the tubes filled with the biomaterials. There was more neoformation in the tubes with collagen. Conclusion: The biomaterials used demonstrated biocompatibility and osteoconductive capacity that was capable of stimulating osteogenesis, even in bones with secondary mechanical and morphological functions such as the fibula of rats.

Bone repair is influenced by different particle sizes of anorganic bovine bone matrix: a histologic and radiographic study in vivo

PURPOSE

The aim of this study was to analyze histologically and radiographically the influence of particle size of anorganic bovine bone matrix (ABBM) on bone repair.

MATERIALS AND METHODS

Four calvarial defects of 8 mm each were prepared in 18 adult New Zealand rabbits. The defects were then filled with either particulate autogenous bone (control group) or ABBM of large, medium, and small size granules. The animals were sacrificed at 15, 30, and 60 days after surgery. The samples were radiographically examined before being submitted to histological processing.

RESULTS

Autogenous bone showed a slight radiopacity at the beginning, which was increased at the final period, being very similar to the adjacent bone tissue. The large and medium size ABBM particles maintained the same radiographic behavior, showing a radiolucent area in the central portion of the defect at 60 days. ABBM of small size granules showed a slight radiolucity at the initial period, which was increased at the subsequent periods. More intense bone formation occurred in the control group (autogenous bone). All 3 particle sizes of the biomaterial resulted in inflammatory infiltration at 15 and 30 days. ABBM of small size granules lead to a greater amount of osteoid tissue, and the particles were almost totally reabsorbed within 60 days of implantation.

CONCLUSIONS

Autogenous bone graft lead to the best result in terms of bone defect repair; ABBM of large and medium size granules are not totally reabsorbed at the observed period; ABBM of small size granules was more intensively reabsorbed and led to a greater osteoid tissue formation when compared to the medium and large ABBM granules.

Osteogenic embryoid body-derived material induces bone formation in vivo

The progressive loss of endogenous regenerative capacity that accompanies mammalian aging has been attributed at least in part to alterations in the extracellular matrix (ECM) composition of adult tissues. Thus, creation of a more regenerative microenvironment, analogous to embryonic morphogenesis, may be achieved via pluripotent embryonic stem cell (ESC) differentiation and derivation of devitalized materials as an alternative to decellularized adult tissues, such as demineralized bone matrix (DBM). Transplantation of devitalized ESC materials represents a novel approach to promote functional tissue regeneration and reduce the inherent batch-to-batch variability of allograft-derived materials. In this study, the osteoinductivity of embryoid body-derived material (EBM) was compared to DBM in a standard in vivo ectopic osteoinduction assay in nude mice. EBM derived from EBs differentiated for 10 days with osteogenic media (+β-glycerophosphate) exhibited similar osteoinductivity to active DBM (osteoinduction score = 2.50 ± 0.27 vs. 2.75 ± 0.16) based on histological scoring, and exceeded inactive DBM (1.13 ± 0.13, p < 0.005). Moreover, EBM stimulated formation of new bone, ossicles, and marrow spaces, similar to active DBM. The potent osteoinductivity of EBM demonstrates that morphogenic factors expressed by ESCs undergoing osteogenic differentiation yield a novel devitalized material capable of stimulating de novo bone formation in vivo.

Evaluation of the effect of a gamma irradiated DBM-pluronic F127 composite on bone regeneration in Wistar rat

Demineralized bone matrix (DBM) is widely used for bone regeneration. Since DBM is prepared in powder form its handling properties are not optimal and limit the clinical use of this material. Various synthetic and biological carriers have been used to enhance the DBM handling. In this study we evaluated the effect of gamma irradiation on the physical-chemical properties of Pluronic and on bone morphogenetic proteins (BMPs) amount in DBM samples. In vivo studies were carried out to investigate the effect on bone regeneration of a gamma irradiated DBM-Pluronic F127 (DBM-PF127) composite implanted in the femur of rats. Gamma irradiation effects (25 kGy) on physical-chemical properties of Pluronic F127 were investigated by rheological and infrared analysis. The BMP-2/BMP-7 amount after DBM irradiation was evaluated by ELISA. Bone regeneration capacity of DBM-PF127 containing 40% (w/w) of DBM was investigated in transcortical holes created in the femoral diaphysis of Wistar rat. Bone porosity, repaired bone volume and tissue organization were evaluated at 15, 30 and 90 days by Micro-CT and histological analysis. The results showed that gamma irradiation did not induce significant modification on physical-chemical properties of Pluronic, while a decrease in BMP-2/BMP-7 amount was evidenced in sterilized DBM. Micro-CT and histological evaluation at day 15 post-implantation revealed an interconnected trabeculae network in medullar cavity and cellular infiltration and vascularization of DBM-PF127 residue. In contrast a large rate of not connected trabeculae was observed in Pluronic filled and unfilled defects. At 30 and 90 days the DBM-PF127 samples shown comparable results in term of density and thickness of the new formed tissue respect to unfilled defect. In conclusion a gamma irradiated DBM-PF127 composite, although it may have undergone a significant decrease in the concentration of BMPs, was able to maintains bone regeneration capability.

Avaliação histomorfométrica da associação entre biovidro e osso bovino liofilizado no tratamento de defeitos ósseos críticos criados em calvárias de ratos. Estudo piloto

OBJETIVO: Avaliar histomorfometricamente o efeito de biovidro (B), osso bovino liofilizado (OB) ou da mistura desses dois biomateriais (B/OB - 1:1) no reparo de defeitos ósseos críticos em calvária de ratos. MATERIAL E MÉTODO: Defeitos ósseos (8 mm Ø) foram criados cirurgicamente na calvária de 24 ratos, distribuídos em 4 grupos com 6 animais, de acordo com o tipo de biomaterial: coágulo sanguíneo (GC), biovidro (GB), osso bovino liofilizado (GOB) e a mistura desses dois biomateriais (GB/OB). Os animais foram eutanasiados após 15 e 60 dias do procedimento cirúrgico (3 animais por período). A avaliação histológica foi baseada na descrição da morfologia dos tecidos neoformados, enquanto para a avaliação histomorfométrica foi realizada quantificação da porcentagem de tecido ósseo, de tecido conjuntivo fibroso neoformados e de biomaterial remanescente no defeito ósseo. RESULTADO: Nos dois períodos experimentais, a análise histológica apresentou neoformação óssea, principalmente nas bordas dos defeitos, e ao redor de partículas de biomateriais remanescentes. A avaliação histomorfométrica demonstrou que no período de 15 dias o grupo GC apresentou maior percentagem de tecido ósseo em relação aos demais grupos estudados, enquanto que aos 60 dias o grupo GOB apresentou maior porcentagem de tecido ósseo em relação ao grupo GB. CONCLUSÃO: O osso bovino liofilizado apresentou maior formação óssea em relação ao biovidro, mas nenhum dos biomateriais foi superior ao coágulo. A associação do biovidro e osso bovino liofilizado não adicionou vantagem à formação óssea.

An in vivo swine study for xeno-grafts of calcium sulfate-based bone grafts with human dental pulp stem cells (hDPSCs)

The purpose of this in vivo study was to evaluate the effect of human dental pulp stem cells (hDPSCs) on various resorbable calcium sulfate/calcium phosphate bone grafts in bone regeneration. Granular particles of calcium sulfate dehydrate (CSD), α-calcium sulfate hemihydrate/amorphous calcium phosphate (α-CSH/ACP), and CSD/β-tricalcium phosphates (β-TCP) were prepared for in vitro dissolution and implantation test. The chemical compositions of specimen residues after dissolution test were characterized by XRD. The ratios of new bone formation for implanted grafts/hDPSCs were evaluated using mandible bony defect model of Lanyu pig. All the graft systems exhibited a similar two-stage dissolution behavior and phase transformation of poor crystalline HAp. Eight weeks post-operation, the addition of hDPSCs to various graft systems showed statistically significant increasing in the ratio of new bone formation (p<0.05). Null hypothesis of hDPSCs showing no scaffold dependence in bone regeneration was rejected. The results suggest that the addition of hDPSCs to calcium sulfate based xenografts could enhance the bone regeneration in the bony defect.

Bone marrow-on-a-chip replicates hematopoietic niche physiology in vitro

Current in vitro hematopoiesis models fail to demonstrate the cellular diversity and complex functions of living bone marrow; hence, most translational studies relevant to the hematologic system are conducted in live animals. Here we describe a method for fabricating 'bone marrow-on-a-chip' that permits culture of living marrow with a functional hematopoietic niche in vitro by first engineering new bone in vivo, removing it whole and perfusing it with culture medium in a microfluidic device. The engineered bone marrow (eBM) retains hematopoietic stem and progenitor cells in normal in vivo-like proportions for at least 1 week in culture. eBM models organ-level marrow toxicity responses and protective effects of radiation countermeasure drugs, whereas conventional bone marrow culture methods do not. This biomimetic microdevice offers a new approach for analysis of drug responses and toxicities in bone marrow as well as for study of hematopoiesis and hematologic diseases in vitro.

Size matters: effects of PLGA-microsphere size in injectable CPC/PLGA on bone formation

The aim of this study was to evaluate the effect of PLGA microsphere dimensions on bone formation after injection of calcium phosphate cement (CPC)/PLGA in a guinea pig tibial intramedullarly model. To this end, injectable CPC/PLGA formulations were prepared using PLGA microspheres with either a small (~25 µm) or large (~100 µm) diameter, which were incorporated at a 20:80 ratio (wt%) within apatite CPC. Both CPC/PLGA formulations were injected into a marrow-ablated tibial intramedullary cavity and, after an implantation period of 12 weeks, histology and histomorphometry were used to address bone formation. The results demonstrated bone ingrowth throughout the entire scaffold material for both CPC/PLGA formulations upon PLGA microsphere degradation. More importantly, bone formation within the CPC matrix was > two-fold higher for CPC-PLGA with 25 µm PLGA microspheres. Additionally, the pattern of bone and marrow formation showed distinct differences related to PLGA microsphere dimension. In general, this study demonstrates that PLGA microsphere dimensions of ~25 µm, leading to pores of ~25 µm within CPC, are sufficient for bone ingrowth and allow substantial bone formation. Further, the results demonstrate that PLGA microsphere dimensions provide a tool to control bone formation for injectable CPC/PLGA bone substitutes. Copyright © 2013 John Wiley & Sons, Ltd.

Application of stem-cell media to explant culture of human periosteum: An optimal approach for preparing osteogenic cell material

As part of our clinical tests on bone regeneration using cultured periosteal sheets, here, we prepared cultured periosteal sheets in two types of stem-cell culture media, STK1 and STK3. Human periosteum was expanded either in 1% human serum–supplemented STK1 for 28 days, in 1% human serum–supplemented STK1 for 14 days followed by 1% human serum–supplemented STK3 for 14 days (1% human serum–supplemented STK1+3), or in 10% fetal bovine serum–supplemented Medium 199 for 28 days (control). Cultured periosteal sheet diameter and DNA content were significantly higher, and the multilayer structure was prominent in 1% human serum–supplemented STK1 and 1% human serum–supplemented STK1+3. The messenger RNA of osteoblastic markers was significantly upregulated in 1% human serum–supplemented STK1+3. Osteopontin-immunopositive staining and mineralization were evident across a wide area of the cultured periosteal sheet in 1% human serum–supplemented STK1+3. Subcutaneous implantation in nude mice following expansion in 1% human serum–supplemented STK1+3 produced the highest cultured periosteal sheet osteogenic activity. Expansion in 1% human serum–supplemented STK1+3 successfully induced cultured periosteal sheet growth while retaining osteogenic potential, and subsequent osteoblastic induction promoted the production of homogeneous cell material.

Subcutaneous tissue response and osteogenic performance of calcium phosphate nanoparticle-enriched hydrogels in the tibial medullary cavity of guinea pigs

In the current study, oligo(poly(ethylene glycol) fumarate) (OPF)-based hydrogels were tested for the first time as injectable bone substitute materials. The primary feature of the material design was the incorporation of calcium phosphate (CaP) nanoparticles within the polymeric matrix in order to compare the soft tissue response and bone-forming capacity of plain OPF hydrogels with CaP-enriched OPF hydrogel composites. To that end, pre-set scaffolds were implanted subcutaneously, whereas flowable polymeric precursor solutions were injected in a tibial ablation model in guinea pigs. After 8 weeks of implantation, histological and histomorphometrical evaluation of the subcutaneous scaffolds confirmed the biocompatibility of both types of hydrogels. Nevertheless, OPF hydrogels presented a loose structure, massive cellular infiltration and extensive material degradation compared to OPF-CaP hydrogels that were more compact. Microcomputed tomography and histological and histomorphometrical analyses showed comparable amounts of new trabecular bone in all tibias and some material remnants in the medial and distal regions. Particularly, highly calcified areas were observed in the distal region of OPF-CaP-treated tibias, which indicate a heterogeneous distribution of the mineral phase throughout the hydrogel matrix. This phenomenon can be attributed to either hindered gelation under highly perfused in vivo conditions or a faster degradation rate of the polymeric hydrogel matrix compared to the nanostructured mineral phase, resulting in loss of entrapment of the CaP nanoparticles and subsequent sedimentation.

Porous ceramic titanium dioxide scaffolds promote bone formation in rabbit peri-implant cortical defect model

Titanium oxide (TiO₂) scaffolds have previously been reported to exhibit very low mechanical strength. However, we have been able to produce a scaffold that features a high interconnectivity, a porosity of 91% and a compressive strength above 1.2 MPa. This study analyzed the in vivo performance of the porous TiO₂ scaffolds in a peri-implant cortical defect model in the rabbit. After 8 weeks of healing, morphological microcomputed tomography analyses of the defects treated with the TiO₂ scaffolds had significantly higher bone volume, bone surface and bone surface-to-volume ratio when compared to sham, both in the cortical and bone marrow compartment. No adverse effects, i.e. tissue necrosis or inflammation as measured by lactate dehydrogenase activity and real-time reverse transcription polymerase chain reaction analysis, were observed. Moreover, the scaffold did not hinder bone growth onto the adjacent cortical titanium implant. Histology clearly demonstrated new bone formation in the cortical sections of the defects and the presence of newly formed bone in close proximity to the scaffold surface and the surface of the adjacent Ti implant. Bone-to-material contact between the newly formed bone and the scaffold was observed in the histological sections. Islets of new bone were also present in the marrow compartment albeit in small amounts. In conclusion, the present investigation demonstrates that TiO₂ scaffolds osseointegrate well and are a suitable scaffold for peri-implant bone healing and growth.

Osteoblast maturation and new bone formation in response to titanium implant surface features are reduced with age

The surface properties of materials contribute to host cellular response and play a significant role in determining the overall success or failure of an implanted biomaterial. Rough titanium (Ti) surface microtopography and high surface free energy have been shown to enhance osteoblast maturation in vitro and increase bone formation in vivo. Whereas the surface properties of Ti are known to affect osteoblast response, host bone quality also plays a significant role in determining successful osseointegration. One factor affecting host bone quality is patient age. We examined both in vitro and in vivo whether response to Ti surface features was affected by animal age. Calvarial osteoblasts isolated from 1-, 3-, and 11-month-old rats all displayed a reduction in cell number and increases in alkaline phosphatase-specific activity and osteocalcin in response to increasing Ti surface microtopography and surface energy. Further, osteoblasts from the three ages examined displayed increased production of osteocalcin and local factors osteoprotegerin, vascular endothelial growth factor (VEGF)-A, and active transforming growth factor (TGF)-β1 in response to increasing Ti surface roughness and surface energy. Latent TGF-β1 only increased in cultures of osteoblasts from 1- and 3-month-old rats. Treatment with the systemic osteotropic hormone 1α,25(OH)(2)D(3) further enhanced the response of osteoblasts to Ti surface features for all three age groups. However, osteoblasts derived from 11-month-old animals had a reduced response to 1α,25(OH)(2)D(3) compared to osteoblasts derived from 1- or 3-month-old animals. These results were confirmed in vivo. Ti implants placed in the femoral intramedullary canal of old (9-month-old) mice yielded lower bone-to-implant contact and neovascularization in response to Ti surface roughness and energy compared to younger (2-month-old) mice. These results show that rodent osteoblast maturation in vitro as well as new bone formation in vivo is reduced with age. Whether comparable age differences exist in humans needs to be determined.

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.

Stem cell-biomaterial interactions for regenerative medicine

The synergism of stem cell biology and biomaterial technology promises to have a profound impact on stem-cell-based clinical applications for tissue regeneration. Biomaterials development is rapidly advancing to display properties that, in a precise and physiological fashion, could drive stem-cell fate both in vitro and in vivo. Thus, the design of novel materials is trying to recapitulate the molecular events involved in the production, clearance and interaction of molecules within tissue in pathologic conditions and regeneration of tissue/organs. In this review we will report on the challenges behind translating stem cell biology and biomaterial innovations into novel clinical therapeutic applications for tissue and organ replacements (graphical abstract).

The influence of hyperbaric oxygen treatment on the healing of experimental defects filled with different bone graft substitutes

To assess potential effects of hyperbaric oxygen (HBOT) on artificial bone grafts, β - Tricalcium phosphate (β-TCP) and calcium phosphate coated bovine bone (CPCBB) substitutes were applied to standard bone defects in rat tibiae. The control defects were left empty. Half of the animals received 60 minutes of 2.4 atmosphere absolute (ATA) of HBOT. Rats were sacrificed at one, two and four weeks. Bone healing was assessed histologically and histomorphometrically using light microscopy. The periosteum over the bone defects was examined ultrastructurally. Cardiac blood was collected to determine the serum osteocalcin levels. The HBOT increased new bone formation in the unfilled controls and β-TCP groups and significantly decreased cartilage matrix and fibrous tissue formations in all groups. Active osteoblasts and highly organized collagen fibrils were prominent in the periosteum of β-TCP and control groups. Serum osteocalcin levels also increased with HBOT. The healing of defects filled with CPCBB was similar to the controls and it did not respond to HBOT. These findings suggested that the HBOT had beneficial effects on the healing of unfilled bone defects and those filled with β-TCP bone substitute but not with CPCBB, indicating a material-specific influence pattern of HBOT.

Hyaluronic acid stimulates neovascularization during the regeneration of bone marrow after ablation

Restoration of vasculature is a critical component for successful integration of implants in musculoskeletal tissue. Sodium hyaluronate (NaHY) has been used as a carrier for demineralized bone matrix (DBM). DBM is osteoinductive and osteoconductive, but whether NaHY by itself has an effect is not known. NaHY has been reported to promote neovascularization, suggesting it may increase neovasculature when used with DBM as well. To test this, we used a rat tibial marrow ablation model to assess neovascularization during bone formation and regeneration of marrow with different combinations of NaHY alone and NaHY+DBM. To assess neovascularization during normal healing, animals were euthanized at 3-, 6-, 14-, 21-, and 28-days post-ablation, and the vasculature perfused using a radio-opaque contrast agent. Vascular morphology was assessed using μCT and histology. Peak vessel volume within the marrow cavity was observed on day-14 post-ablation. Test materials were injected into the ablated marrow space as follows: (A) empty defect controls; (B) high MW (700-800 kDa) NaHY + heat inactivated DBM; (C) DBM in PBS; (D) low MW NaHY (35 kDa) + DBM; (E) high MW NaHY + DBM; (F) D:E 50:50; (G) low MW NaHY; (H) high MW NaHY; and (I) G:H 50:50. Neovascularization varied with bone substitute formulation. μCT results revealed that addition of NaHY resulted in an increase in vessel number compared to empty defects. Total blood vessel volume in all NaHY only groups were similar to DBM alone. Histomorphometry of sagittal sections showed that all three formulations of NaHY increased blood vessel number within the marrow cavity, confirming that NaHY promotes neovascularization.

Regeneration of bone marrow after tibial ablation in immunocompromised rats is age dependent

Injuries to the marrow cavity result in rapid endosteal bone formation followed by remodeling and regeneration of the marrow. It is not known whether this process is affected by age, although marrow quality is markedly different in young and old animals. To test if marrow regeneration differs with age, we used a bone marrow ablation model that has been used to examine calcification, osteointegration of metal implants, and remodeling of bone graft substitutes. Marrow was ablated in the left tibia of seven immunocompromised rats (rNu/rNu) per time point. At 0, 7, 14, 21, 28, 35 and 42 days post-surgery, treated and contralateral tibias were harvested and fixed in buffered formalin. Both tibias were scanned using microCT and trabecular and cortical BVF calculated. Mid-sagittal histological sections of the treated limbs were stained with haematoxylin and eosin and BV/TV calculated. MicroCT and histomorphometry showed the greatest increase in bone formation was in young animals and was seen on day 7. Remodeling also occurred at an earlier time point in young rats. Bone formation peaked on day 7 in adult rats, but remodeling was slower than in young rats. Aged animals showed a delay in bone formation. Moreover, aged rats produced less primary bone than younger animals and remodeling was initiated later. These results show that response to injury in immunocompromised rats is reduced in aging and restoration of normal tissue quality is age-dependent.

In vitro proliferation of human osteogenic cells in presence of different commercial bone substitute materials combined with enamel matrix derivatives

BACKGROUND

Cellular reactions to alloplastic bone substitute materials (BSM) are a subject of interest in basic research. In regenerative dentistry, these bone grafting materials are routinely combined with enamel matrix derivatives (EMD) in order to additionally enhance tissue regeneration.

MATERIALS AND METHODS

The aim of this study was to evaluate the proliferative activity of human osteogenic cells after incubation over a period of seven days with commercial BSM of various origin and chemical composition. Special focus was placed on the potential additional benefit of EMD on cellular proliferation.

RESULTS

Except for PerioGlas, osteogenic cell proliferation was significantly promoted by the investigated BSM. The application of EMD alone also resulted in significantly increased cellular proliferation. However, a combination of BSM and EMD resulted in only a moderate additional enhancement of osteogenic cell proliferation.

CONCLUSION

The application of most BSM, as well as the exclusive application of EMD demonstrated a positive impact on the proliferation of human osteogenic cells in vitro. In order to increase the benefit from substrate combination (BSM + EMD), further studies on the interactions between BSM and EMD are needed.

Fracture healing in India: Available therapies, indications, and protocols

The availability of fracture healing therapies to the general public is limited in India. The infrastructure of the health system in India, involving both public and private sectors, does not provide adequate opportunity for rural and low-income inhabitants to access needed care. Also the lack of funding from the government and the overall lack of physicians place a large strain on the system. This paper will take an in-depth look at the state of the current health care system and how it affects bone stimulation therapy in India. The Indian Journal of Orthopaedics was used as a reference for the bone stimulation therapies currently utilized in India. A general search of the therapies and technologies was performed to determine protocols and indications. A table of fracture healing therapies and technologies was composed which provides a description of each therapy, as well as its specific indications and protocols. This information was then used by the authors to hypothesize the most feasible methods of fracture healing to meet the Indian demographic. Based on an assessment of the health system of India, the most practical methods of bone stimulation therapy were determined. It was also determined that nearly all forms of therapy could be made available if sufficient resources were set aside for it. Bone stimulation therapy in India remains a large void in the health care system.