Small-sized granules of biphasic bone substitutes support fast implant bed vascularization

Biphasic bone substitutes coated with PLGA incorporating therapeutic ions Sr2+ and Mg2+: cytotoxicity cascade and in vivo response of immune and bone regeneration

The incorporation of bioactive ions into biomaterials has gained significant attention as a strategy to enhance bone tissue regeneration on the molecular level. However, little knowledge exists about the effects of the addition of these ions on the immune response and especially on the most important cellular regulators, the macrophages. Thus, this study aimed to investigate the in vitro cytocompatibility and in vivo regulation of bone remodeling and material-related immune responses of a biphasic bone substitute (BBS) coated with metal ions (Sr2+/Mg2+) and PLGA, using the pure BBS as control group. Initially, two cytocompatible modified material variants were identified according to the in vitro results obtained following the DIN EN ISO 10993-5 protocol. The surface structure and ion release of both materials were characterized using SEM-EDX and ICP-OES. The materials were then implanted into Wistar rats for 10, 30, and 90 days using a cranial defect model. Histopathological and histomorphometrical analyses were applied to evaluate material degradation, bone regeneration, osteoconductivity, and immune response. The findings revealed that in all study groups comparable new bone formation were found. However, during the early implantation period, the BBS_Sr2+ group exhibited significantly faster regeneration compared to the other two groups. Additionally, all materials induced comparable tissue and immune responses involving high numbers of both pro-inflammatory macrophages and multinucleated giant cells (MNGCs). In conclusion, this study delved into the repercussions of therapeutic ion doping on bone regeneration patterns and inflammatory responses, offering insights for the advancement of a new generation of biphasic calcium phosphate materials with potential clinical applicability.

A comparative analysis of particulate bovine bone substitutes for oral regeneration: a narrative review

PURPOSE

Particulate bovine bone substitutes (BS) are commonly used in oral regeneration. However, more literature is needed focusing on comparative analyses among various particulate bovine BS. This study evaluates pre-clinical and clinical data of different particulate bovine BS in oral regeneration.

METHODS

A narrative review was conducted by screening the PubMed database Included in the review were pre-clinical and clinical studies until 2024 comparing a minimum of two distinct particulate bovine BS. In addition to examining general data concerning manufacturing and treatment processes, biological safety, physical and chemical characteristics, and graft resorption, particular emphasis was placed on assessing pre-clinical and clinical data related to ridge preservation, sinus floor elevation, peri-implant defects, and various forms of alveolar ridge augmentation utilizing particulate bovine BS.

RESULTS

Various treatment temperatures ranging from 300 to 1,250 °C and the employment of chemical cleaning steps were identified for the manufacturing process of particulate bovine BS deemed to possess biosecurity. A notable heterogeneity was observed in the physical and chemical characteristics of particulate bovine BS, with minimal or negligible graft resorption. Variations were evident in particle and pore sizes and the porosity of particulate bovine BS. Pre-clinical assessments noted a marginal inclination towards favorable outcomes for particulate bovine BS subjected to higher treatment temperatures. However, clinical data are insufficient. No distinctions were observed regarding ridge preservation, while slight advantages were noted for high-temperature treated particulate bovine BS in sinus floor elevation.

CONCLUSIONS

Subtle variances in both pre-clinical and clinical outcomes were observed in across various particulate bovine BS. Due to inadequate data, numerous considerations related to diverse particulate bovine BS, including peri-implant defects, must be more conclusive. Additional clinical studies are imperative to address these knowledge gaps effectively.

Comparison of Particulate, Block and Putty Forms of β-tricalcium Phosphate-Based Synthetic Bone Grafts on Rat Calvarium Model

Purpose

Bone augmentation is a necessity for atrophied alveolar ridge prior to dental implant placement. Various bone graft types and forms with different characteristics are available in the market for alveolar augmentation. Beta tricalcium phosphate (β-TCP) is a synthetic biomaterial known as the oldest type of calcium phosphate. Studies comparing particulate, block or putty grafts are very limited. The aim of this study was to compare the particulate, block and putty forms of the same β-TCP bone graft and analyze the efficiency in critical size calvarium defects.

Material and Methods

Twenty male Wistar-Albino rats were employed for the study. Four bicortical bone defects with 5 mm diameter were created on each rat calvarium, and three defects were filled with particulate, block or putty β-TCP graft and one defect was left empty. The animals were killed after 8 weeks. New bone formation, residual graft, loose connective tissue, condensed mesenchyme, alkaline phosphatase, proliferating cell nuclear antigen, osteocalcin were measured on the specimens.

Results

Compared to block and putty forms, significantly higher new bone formation and least residual graft were observed in the particulate graft group. The residual graft was significantly higher in the block graft group than both the particulate and the putty groups. The cellular immunoreactivity of the samples in the particulate graft group was significantly higher. There was no significant difference between putty and block graft groups.

Conclusion

Bone regeneration is significantly affected by the form of β-TCP bone graft, and the particulate form was the most successful in our study.

Analyses of the Cellular Interactions between the Ossification of Collagen-Based Barrier Membranes and the Underlying Bone Defects

Barrier membranes are an essential tool in guided bone Regeneration (GBR), which have been widely presumed to have a bioactive effect that is beyond their occluding and space maintenance functionalities. A standardized calvaria implantation model was applied for 2, 8, and 16 weeks on Wistar rats to test the interactions between the barrier membrane and the underlying bone defects which were filled with bovine bone substitute materials (BSM). In an effort to understand the barrier membrane’s bioactivity, deeper histochemical analyses, as well as the immunohistochemical detection of macrophage subtypes (M1/M2) and vascular endothelial cells, were conducted and combined with histomorphometric and statistical approaches. The native collagen-based membrane was found to have ossified due to its potentially osteoconductive and osteogenic properties, forming a “bony shield” overlying the bone defects. Histomorphometrical evaluation revealed the resorption of the membranes and their substitution with bone matrix. The numbers of both M1- and M2-macrophages were significantly higher within the membrane compartments compared to the underlying bone defects. Thereby, M2-macrophages significantly dominated the tissue reaction within the membrane compartments. Statistically, a correlation between M2-macropahges and bone regeneration was only found at 2 weeks post implantationem, while the pro-inflammatory limb of the immune response correlated with the two processes at 8 weeks. Altogether, this study elaborates on the increasingly described correlations between barrier membranes and the underlying bone regeneration, which sheds a light on the understanding of the immunomodulatory features of biomaterials.

Barrier Membranes for Guided Bone Regeneration (GBR): A Focus on Recent Advances in Collagen Membranes

Guided bone regeneration (GBR) has become a clinically standard modality for the treatment of localized jawbone defects. Barrier membranes play an important role in this process by preventing soft tissue invasion outgoing from the mucosa and creating an underlying space to support bone growth. Different membrane types provide different biological mechanisms due to their different origins, preparation methods and structures. Among them, collagen membranes have attracted great interest due to their excellent biological properties and desired bone regeneration results to non-absorbable membranes even without a second surgery for removal. This work provides a comparative summary of common barrier membranes used in GBR, focusing on recent advances in collagen membranes and their biological mechanisms. In conclusion, the review article highlights the biological and regenerative properties of currently available barrier membranes with a particular focus on bioresorbable collagen-based materials. In addition, the advantages and disadvantages of these biomaterials are highlighted, and possible improvements for future material developments are summarized.

In Vivo Analysis of the Regeneration Capacity and Immune Response to Xenogeneic and Synthetic Bone Substitute Materials

Although various studies have investigated differences in the tissue reaction pattern to synthetic and xenogeneic bone substitute materials (BSMs), a lack of knowledge exists regarding the classification of both materials based on the DIN ISO 10993-6 scoring system, as well as the histomorphometrical measurement of macrophage subtypes within their implantation beds. Thus, the present study was conducted to analyze in vivo responses to both xenogeneic and synthetic bone substitute granules. A standardized calvaria implantation model in Wistar rats, in combination with established scoring, histological, histopathological, and histomorphometrical methods, was conducted to analyze the influence of both biomaterials on bone regeneration and the immune response. The results showed that the application of the synthetic BSM maxresorb^® induced a higher pro-inflammatory tissue response, while the xenogeneic BSM cerabone^® induced a higher anti-inflammatory reaction. Additionally, comparable bone regeneration amounts were found in both study groups. Histopathological scoring revealed that the synthetic BSM exhibited non-irritant scores at all timepoints using the xenogeneic BSM as control. Overall, the results demonstrated the biocompatibility of synthetic BSM maxresorb^® and support the conclusion that this material class is a suitable alternative to natural BSM, such as the analyzed xenogeneic material cerabone^®, for a broad range of indications.

Effect of Photobiomodulation Therapy Associated With Biphasic Phosphate Calcium on Bone Repair: A Histomorphometric Study in Rats

Introduction: This study aimed to investigate the effects of photobiomodulation (PBM) therapy associated with biphasic calcium phosphate on calvaria critical defects in rats. Methods: Forty-eight (90 days old) adult male rats (Rattus norvegicus, Albinus variation, Wistar) received critical defects of 5 mm in diameter, which were made on their skull, and they were randomly assigned into the following groups: C-blood clot, B-biphasic calcium phosphate, L-photobiomodulation therapy, and B + L-biphasic calcium phosphate + photobiomodulation therapy. A low-level a gallium aluminum arsenide (GaAlAs) laser was applied in a single dose during surgery, in a wavelength of 660 nm and total energy density of 45 J/cm². On 30^th and 60^th days, the animals from each group were euthanized. Histological and histomorphometric analyses were performed. Results:In 30 days, almost all specimens (C, L, B and B + L) showed bone neoformation areas in regions near the borders of the surgical defect. In 60 days, in many specimens (C, L, B, B + L), it was possible to see a narrow neoformed bone structure along almost the whole extension of the surgical defect, though it was thinner than the original calvary bone. Data were recorded as mean ± standard deviation, and after normality was tested, a suitable statistical test was applied (α = 5%). On day 60, there was a statistically significant difference when comparing the proportion of neoformation area between group L (0.52%±0.13) and group B+L (0.20%±0.08). Group L showed a difference compared with all the groups when we compared the remaining distance between the edges of neoformed bone (C×L, P=0.0431; B × L, P=0.0386; L×B+L, P=0.0352), demonstrating a great defect closure. Conclusion: Our findings suggest that although biphasic calcium phosphate exerts some osteogenic activity during bone repair, PBM therapy is not able to modulate this process.

Lyophilized Human Bone Allograft as an Antibiotic Carrier: An In Vitro and In Vivo Study

Background: Antibiotics delivered from implanted bone substitute materials (BSM) can potentially be used to prevent acute infections and biofilm formation, providing high concentrations of antibiotics at the surgical site without systemic toxicity. In addition, BSM should allow osteoconductivity supporting bone healing without further surgery. Promising results have been achieved using lyophilized bone allografts mixed with antibiotics. Methods: In this study specially prepared human bone allografts were evaluated as an antibiotic carrier in vitro and in vivo. The efficacy of different antibiotic-impregnated bone allografts was measured by drug release tests in vitro and in vivo and bacterial susceptibility tests using four bacterial species usually responsible for implant-associated infections. Results: The loading procedures of allograft bone substitutes with antibiotics were successful. Some of the antibiotic concentrations exceeded the MIC90 for up to 7 days in vitro and for up to 72 h in vivo. The susceptibility tests showed that S. epidermidis ATCC 12228 was the most susceptible bacterial species in comparison to the other strains tested for all antibiotic substances. Vancomycin and rifampicin showed the best results against standard and patient-isolated strains in vitro. In vivo, new bone formation was comparable in all study groups including the control group without antibiotic loading. Conclusions: Human bone allografts showed the capacity to act as customized loaded antibiotic carriers to prevent acute infections and should be considered in the management of bone infections in combination with systemic antimicrobial therapy.

In Vivo Biocompatibility Analysis of a Novel Barrier Membrane Based on Bovine Dermis-Derived Collagen for Guided Bone Regeneration (GBR)

Collagen-based barrier membranes are nowadays the prevalent option for Guided Bone Regeneration (GBR) procedures. Xenogeneic collagen is highly biocompatible as it shares a similar structure to native human collagen, which prevents it from eliciting an exaggerated host immune response. Most commercially available collagen barrier membranes are porcine-derived, while bovine-derived alternatives are still rarely available. The aim of the present study was to investigate the tissue responses and the barrier functionality of a novel GBR membrane composed of bovine collagen type I (BM). Therefore, the subcutaneous implantation model in Wistar rats was performed to compare the novel medical device with two already clinically used native porcine-based barrier membranes, i.e., Jason^® membrane (JM) and Bio-Gide^® (BG), at 10-, 30-, 60-, and 90-days post implantationem. Histochemical and immunohistochemical stains were used for histopathological evaluation including a biocompatibility scoring according to the DIN EN ISO 10993-6 norm as well as histomorphometrical analyses of the occurrence of M1 and M2 macrophages and the transmembraneous vascularization. The bovine membrane exhibited a host tissue reaction that was comparable to both control materials, which was verified by the scoring results and the histomorphometrical macrophage measurements. Moreover, the novel membrane exhibited an integration pattern without material fragmentation up to day 60. At day 90, material fragmentation was observable that allowed for “secondary porosity” including transmembrane vascularization. The results of this study suggest that the novel bovine barrier membrane is fully biocompatible and suitable for indications that require GBR as a suitable alternative to porcine-sourced barrier membranes.

In Vivo Biocompatibility Investigation of an Injectable Calcium Carbonate (Vaterite) as a Bone Substitute including Compositional Analysis via SEM-EDX Technology

Injectable bone substitutes (IBS) are increasingly being used in the fields of orthopedics and maxillofacial/oral surgery. The rheological properties of IBS allow for proper and less invasive filling of bony defects. Vaterite is the most unstable crystalline polymorph of calcium carbonate and is known to be able to transform into hydroxyapatite upon contact with an organic fluid (e.g., interstitial body fluid). Two different concentrations of hydrogels based on poly(ethylene glycol)-acetal-dimethacrylat (PEG-a-DMA), i.e., 8% (w/v) (VH-A) or 10% (w/v) (VH-B), were combined with vaterite nanoparticles and implanted in subcutaneous pockets of BALB/c mice for 15 and 30 days. Explants were prepared for histochemical staining and immunohistochemical detection methods to determine macrophage polarization, and energy-dispersive X-ray analysis (EDX) to analyze elemental composition was used for the analysis. The histopathological analysis revealed a comparable moderate tissue reaction to the hydrogels mainly involving macrophages. Moreover, the hydrogels underwent a slow cellular infiltration, revealing a different degradation behavior compared to other IBS. The immunohistochemical detection showed that M1 macrophages were mainly found at the material surfaces being involved in the cell-mediated degradation and tissue integration, while M2 macrophages were predominantly found within the reactive connective tissue. Furthermore, the histomorphometrical analysis revealed balanced numbers of pro- and anti-inflammatory macrophages, demonstrating that both hydrogels are favorable materials for bone tissue regeneration. Finally, the EDX analysis showed a stepwise transformation of the vaterite particle into hydroxyapatite. Overall, the results of the present study demonstrate that hydrogels including nano-vaterite particles are biocompatible and suitable for bone tissue regeneration applications.

The Granule Size Mediates the In Vivo Foreign Body Response and the Integration Behavior of Bone Substitutes

The physicochemical properties of synthetically produced bone substitute materials (BSM) have a major impact on biocompatibility. This affects bony tissue integration, osteoconduction, as well as the degradation pattern and the correlated inflammatory tissue responses including macrophages and multinucleated giant cells (MNGCs). Thus, influencing factors such as size, special surface morphologies, porosity, and interconnectivity have been the subject of extensive research. In the present publication, the influence of the granule size of three identically manufactured bone substitute granules based on the technology of hydroxyapatite (HA)-forming calcium phosphate cements were investigated, which includes the inflammatory response in the surrounding tissue and especially the induction of MNGCs (as a parameter of the material degradation). For the in vivo study, granules of three different size ranges (small = 0.355-0.5 mm; medium = 0.5-1 mm; big = 1-2 mm) were implanted in the subcutaneous connective tissue of 45 male BALB/c mice. At 10, 30, and 60 days post implantationem, the materials were explanted and histologically processed. The defect areas were initially examined histopathologically. Furthermore, pro- and anti-inflammatory macrophages were quantified histomorphometrically after their immunohistochemical detection. The number of MNGCs was quantified as well using a histomorphometrical approach. The results showed a granule size-dependent integration behavior. The surrounding granulation tissue has passivated in the groups of the two bigger granules at 60 days post implantationem including a fibrotic encapsulation, while a granulation tissue was still present in the group of the small granules indicating an ongoing cell-based degradation process. The histomorphometrical analysis showed that the number of proinflammatory macrophages was significantly increased in the small granules at 60 days post implantationem. Similarly, a significant increase of MNGCs was detected in this group at 30 and 60 days post implantationem. Based on these data, it can be concluded that the integration and/or degradation behavior of synthetic bone substitutes can be influenced by granule size.

Multinucleated Giant Cells Induced by a Silk Fibroin Construct Express Proinflammatory Agents: An Immunohistological Study

Multinucleated giant cells (MNGCs) are frequently observed in the implantation areas of different biomaterials. The main aim of the present study was to analyze the long-term polarization pattern of the pro- and anti-inflammatory phenotypes of macrophages and MNGCs for 180 days to better understand their role in the success or failure of biomaterials. For this purpose, silk fibroin (SF) was implanted in a subcutaneous implantation model of Wistar rats as a model for biomaterial-induced MNGCs. A sham operation was used as a control for physiological wound healing. The expression of different inflammatory markers (proinflammatory M1: CCR-7, iNos; anti-inflammatory M2: CD-206, CD-163) and tartrate-resistant acid phosphatase (TRAP) and CD-68 were identified using immunohistochemical staining. The results showed significantly higher numbers of macrophages and MNGCs within the implantation bed of SF-expressed M1 markers, compared to M2 markers. Interestingly, the expression of proinflammatory markers was sustained over the long observation period of 180 days. By contrast, the control group showed a peak of M1 macrophages only on day 3. Thereafter, the inflammatory pattern shifted to M2 macrophages. No MNGCs were observed in the control group. To the best of our knowledge, this is study is the first to outline the persistence of pro-inflammatory MNGCs within the implantation bed of SF and to describe their long-term kinetics over 180 days. Clinically, these results are highly relevant to understand the role of biomaterial-induced MNGCs in the long term. These findings suggest that tailored physicochemical properties may be a key to avoiding extensive inflammatory reactions and achieving clinical success. Therefore, further research is needed to elucidate the correlation between proinflammatory MNGCs and the physicochemical characteristics of the implanted biomaterial.

Ex Vivo and In Vivo Analysis of a Novel Porcine Aortic Patch for Vascular Reconstruction

(1) Background: The aim of the present study was the biocompatibility analysis of a novel xenogeneic vascular graft material (PAP) based on native collagen won from porcine aorta using the subcutaneous implantation model up to 120 days post implantationem. As a control, an already commercially available collagen-based vessel graft (XenoSure®) based on bovine pericardium was used. Another focus was to analyze the (ultra-) structure and the purification effort. (2) Methods: Established methodologies such as the histological material analysis and the conduct of the subcutaneous implantation model in Wistar rats were applied. Moreover, established methods combining histological, immunohistochemical, and histomorphometrical procedures were applied to analyze the tissue reactions to the vessel graft materials, including the induction of pro- and anti-inflammatory macrophages to test the immune response. (3) Results: The results showed that the PAP implants induced a special cellular infiltration and host tissue integration based on its three different parts based on the different layers of the donor tissue. Thereby, these material parts induced a vascularization pattern that branches to all parts of the graft and altogether a balanced immune tissue reaction in contrast to the control material. (4) Conclusions: PAP implants seemed to be advantageous in many aspects: (i) cellular infiltration and host tissue integration, (ii) vascularization pattern that branches to all parts of the graft, and (iii) balanced immune tissue reaction that can result in less scar tissue and enhanced integrative healing patterns. Moreover, the unique trans-implant vascularization can provide unprecedented anti-infection properties that can avoid material-related bacterial infections.

In Vivo Analysis of the Biocompatibility and Bone Healing Capacity of a Novel Bone Grafting Material Combined with Hyaluronic Acid

The present in vivo study analyses both the inflammatory tissue reactions and the bone healing capacity of a newly developed bone substitute material (BSM) based on xenogeneic bone substitute granules combined with hyaluronate (HY) as a water-binding molecule. The results of the hyaluronate containing bone substitute material (BSM) were compared to a control xenogeneic BSM of the same chemical composition and a sham operation group up to 16 weeks post implantationem. A major focus of the study was to analyze the residual hyaluronate and its effects on the material-dependent healing behavior and the inflammatory tissue responses. The study included 63 male Wistar rats using the calvaria implantation model for 2, 8, and 16 weeks post implantationem. Established and Good Laboratory Practice (GLP)-conforming histological, histopathological, and histomorphometrical analysis methods were conducted. The results showed that the new hyaluronate containing BSM was gradually integrated within newly formed bone up to the end of the study that ended in a condition of complete bone defect healing. Thereby, no differences to the healing capacity of the control BSM were found. However, the bone formation in both groups was continuously significantly higher compared to the sham operation group. Additionally, no differences in the (inflammatory) tissue response that was analyzed via qualitative and (semi-) quantitative methods were found. Interestingly, no differences were found between the numbers of pro- and anti-inflammatory macrophages between the three study groups over the entire course of the study. No signs of the HY as a water-binding part of the BSM were histologically detectable at any of the study time points, altogether the results of the present study show that HY allows for an optimal material-associated bone tissue healing comparable to the control xenogeneic BSM. The added HY seems to be degraded within a very short time period of less than 2 weeks so that the remaining BSM granules allow for a gradual osteoconductive bone regeneration. Additionally, no differences between the inflammatory tissue reactions in both material groups and the sham operation group were found. Thus, the new hyaluronate containing xenogeneic BSM and also the control BSM have been shown to be fully biocompatible without any differences regarding bone regeneration.

Exploring the Biomaterial-Induced Secretome: Physical Bone Substitute Characteristics Influence the Cytokine Expression of Macrophages

In addition to their chemical composition various physical properties of synthetic bone substitute materials have been shown to influence their regenerative potential and to influence the expression of cytokines produced by monocytes, the key cell-type responsible for tissue reaction to biomaterials in vivo. In the present study both the regenerative potential and the inflammatory response to five bone substitute materials all based on β-tricalcium phosphate (β-TCP), but which differed in their physical characteristics (i.e., granule size, granule shape and porosity) were analyzed for their effects on monocyte cytokine expression. To determine the effects of the physical characteristics of the different materials, the proliferation of primary human osteoblasts growing on the materials was analyzed. To determine the immunogenic effects of the different materials on human peripheral blood monocytes, cells cultured on the materials were evaluated for the expression of 14 pro- and anti-inflammatory cytokines, i.e., IL-6, IL-10, IL-1β, VEGF, RANTES, IL-12p40, I-CAM, IL-4, V-CAM, TNF-α, GM-CSF, MIP-1α, Il-8 and MCP-1 using a Bio-Plex^® Multiplex System. The granular shape of bone substitutes showed a significant influence on the osteoblast proliferation. Moreover, smaller pore sizes, round granular shape and larger granule size increased the expression of GM-CSF, RANTES, IL-10 and IL-12 by monocytes, while polygonal shape and the larger pore sizes increased the expression of V-CAM. The physical characteristics of a bone biomaterial can influence the proliferation rate of osteoblasts and has an influence on the cytokine gene expression of monocytes in vitro. These results indicate that the physical structure of a biomaterial has a significant effect of how cells interact with the material. Thus, specific characteristics of a material may strongly affect the regenerative potential in vivo.

Critical-size Defect Augmentation Using Sintered and Non-Sintered Bovine Bone Matrix - An Experimental Controlled Study in Minipigs

PURPOSE

Xenogeneic bone substitute materials are often used for augmentation of larger bone defects. Purification methods for these materials vary, mainly in terms of temperature. The aim of this study was to determine in vivo how sintering affects quantitative and qualitative bone regeneration of 2 bovine augmentation materials.

METHODS

A total of 56 critical size defects were set at the frontal bone of 14 domestic pigs (4 each) and filled randomly with either bovine, sintered hydroxyapatite (BO), bovine, non-sintered hydroxyapatite (BOS), local autologous bone (AB) or left empty. All defects were additionally covered with a collagen membrane. Specimens were harvested after 4 and 8 weeks and were evaluated histologically and histomorphometrically.

RESULTS

Histologically new bone could be seen in every group. Significantly highest new bone formation was found in AB. No significant difference could be detected between BO and BOS.

CONCLUSIONS

According to the results of this study, sintered bone substitute material remains histologically distinguishable but does not affect quantitative and qualitative bone regeneration.

The Early Fragmentation of a Bovine Dermis-Derived Collagen Barrier Membrane Contributes to Transmembraneous Vascularization-A Possible Paradigm Shift for Guided Bone Regeneration

Collagen-based barrier membranes are an essential component in Guided Bone Regeneration (GBR) procedures. They act as cell-occlusive devices that should maintain a micromilieu where bone tissue can grow, which in turn provides a stable bed for prosthetic implantation. However, the standing time of collagen membranes has been a challenging area, as native membranes are often prematurely resorbed. Therefore, consolidation techniques, such as chemical cross-linking, have been used to enhance the structural integrity of the membranes, and by consequence, their standing time. However, these techniques have cytotoxic tendencies and can cause exaggerated inflammation and in turn, premature resorption, and material failures. However, tissues from different extraction sites and animals are variably cross-linked. For the present in vivo study, a new collagen membrane based on bovine dermis was extracted and compared to a commercially available porcine-sourced collagen membrane extracted from the pericardium. The membranes were implanted in Wistar rats for up to 60 days. The analyses included well-established histopathological and histomorphometrical methods, including histochemical and immunohistochemical staining procedures, to detect M1- and M2-macrophages as well as blood vessels. Initially, the results showed that both membranes remained intact up to day 30, while the bovine membrane was fragmented at day 60 with granulation tissue infiltrating the implantation beds. In contrast, the porcine membrane remained stable without signs of material-dependent inflammatory processes. Therefore, the bovine membrane showed a special integration pattern as the fragments were found to be overlapping, providing secondary porosity in combination with a transmembraneous vascularization. Altogether, the bovine membrane showed comparable results to the porcine control group in terms of biocompatibility and standing time. Moreover, blood vessels were found within the bovine membranes, which can potentially serve as an additional functionality of barrier membranes that conventional barrier membranes do not provide.

Physical characterization of biphasic bioceramic materials with different granulation sizes and their influence on bone repair and inflammation in rat calvaria

Biphasic calcium phosphate bioceramics (BCP) consist of a mixture of hydroxyapatite (HA) and beta-tricalcium phosphate (β-TCP) within the same particle. Due to their osteoconductive properties, biocompatibility and resemblance to natural bone, these materials have become a promising and suitable alternative to autologous bone grafting. First, the topography characteristics, specific surface area, and total pore volume of BCP were evaluated using scanning electron microscopy and the BET and BJH methods. Next, this study aimed to evaluate the intensity of the inflammatory process and the bone neoformation capacity of various particle sizes of BCP in the repair of critical defects in the calvaria of rats. A xenogeneic biomaterial was used in the control group. After 30, 60, and 90 days, the animals were euthanized, followed by the processing of the samples to measure the intensity of inflammatory infiltrates and the areas of bone neoformation. Our results indicate that no considerable differences were observed in the inflammatory scores in sites treated with distinct BCP grain sizes. A greater area of bone neoformation was measured in the xenogeneic group at all analysis times, with no substantial differences in bone formation between the BCP particle size in the range of 250-500 µm and 500-1000 µm.

The Condensation of Collagen Leads to an Extended Standing Time and a Decreased Pro-inflammatory Tissue Response to a Newly Developed Pericardium-based Barrier Membrane for Guided Bone Regeneration

BACKGROUND/AIM

A new manufacturing process has been established for the condensation of collagen derived from porcine pericardium to develop a new dental barrier membrane (CPM) that can provide a long barrier functionality. A native collagen membrane (PM) was used as control.

MATERIALS AND METHODS

Established in vitro procedures using L929 and MC3T3 cells were used for cytocompatibility analyses. For the in vivo study, subcutaneous implantation of both membrane types in 40 BALB/c mice and established histological, immuno histochemical and histomorphometrical methods were conducted.

RESULTS

Both the in vitro and in vivo results revealed that the CPM has a biocompatibility profile comparable to that of the control membrane. The new CPM induced a tissue reaction including more M2-macrophages.

CONCLUSION

The CPM is fully biocompatible and seems to support the early healing process. Moreover, the new biomaterial seems to prevent cell ingrowth for a longer period of time, making it ideally suited for GBR procedures.

Implantation of an Injectable Bone Substitute Material Enables Integration Following the Principles of Guided Bone Regeneration

BACKGROUND/AIM

The present study investigates the in vivo tissue reaction and the integration behavior of an injectable bone substitute material (IBS) composed of a water-based gel combined with nano hydroxyapatite particles and biphasic calcium phosphate granules. The results of the IBS were compared to biphasic bone substitute granules (BBSM) of the same chemical composition.

MATERIALS AND METHODS

The subcutaneous implantation model in 40 female 5-week-old CD-1 mice up to 60 days after implantation was used for conduction of the in vivo experiments. Moreover, established histological, histopathological and histomorphometrical methods were applied.

RESULTS

The results showed that the IBS was gradually invaded by cells and complex tissue elements. Thus, the implant bed could be distinguished in two areas, i.e. an outer and inner region. While the outer region started to interact with the peri-implant tissue by evoking multinucleated giant cells and at earlier time points by undergoing a continuous high vascularization, the inner part was free of peri-implant cells for at least 30 days, starting to undergo a similar tissue reaction at a later time point. The bone substitute granules allowed for a fast tissue influx between the interspaces of the granules starting at day 10. While the vessel density did not differ in both groups up to the end of the study, the amount of vascularization was significantly higher over the entire observation period in the BBSM group. Moreover, the amount of biomaterial-associated multinucleated giant cells (BMGCs) was significantly higher in the IBS group in the period of between 15 to 30 days after implantation, while comparable BMGC numbers were found in both groups towards the end of the study.

CONCLUSION

IBS can build a barrier-like structure that is able to control the soft tissue influx into the central regions of the implantation bed, which could not be observed in other bone substitute granules of the same chemical composition. This directed integration behavior is assumed to be in accordance with the concept of Guided Bone Regeneration (GBR). Furthermore, BMGCs can significantly influence the process of angiogenesis within an implant bed of a biomaterial but not the maturity of blood vessels.

Specialized Histological and Histomorphometrical Analytical Methods for Biocompatibility Testing of Biomaterials for Maxillofacial Surgery in (Pre-) Clinical Studies

Both preclinical in vivo experiments and clinical trials are indispensable for analysis of tissue reactions in evaluating the compatibility of biomaterials or medical devices, i.e. the cell types interacting with the material, integration or degradation behavior, implant bed vascularization and immunological response. In particular, both the histological workup (including the processes such as embedding, cutting, histochemical and immunohistochemical staining methods), as well as qualitative and quantitative analysis are crucial steps enabling the final evaluation of biocompatibility. We present a short overview of the most important steps of the different workup and analytical methods used in preclinical and clinical biopsies for both novice and experienced researchers in the field of biomaterial science.

The Biomaterial-Induced Cellular Reaction Allows a Novel Classification System Regardless of the Biomaterials Origin

Several different biomaterials are being introduced for clinical applications. However, no current material-specific systematic studies define parameters for evaluating these materials. The aim of this retrospective animal study is to classify biomaterials according to the in vivo induced cellular reaction and outline the clinical consequence of the biomaterial-specific cellular reaction for the regeneration process. A retrospective histologic analysis was performed for 13 polymeric biomaterials and 19 bone substitute materials (BSMs) (of various compositions and origins) that were previously implanted in a standardized subcutaneous model. Semiquantitative analyses were performed at days 3, 15, and 30 after implantation according to a standardized score for the induction of multinucleated giant cells (MNGCs) and vascularization rate. The induced cellular reaction in response to different polymeric materials allowed their classification according to the MNGC score in the following groups: class I induced no MNGCs at any time point, class II induced and maintained a constant number of MNGCs over 30 days, and class III induced MNGCs and provided an increasing number over 30 days. All BSMs induced MNGCs to varying extents. Therefore, the resultant BSM classifications are as follows: class I induced MNGCs with a decreasing number, class II induced and maintained constant MNGCs over 30 days, and class III induced MNGCs with increasing number over 30 days. These observations were mostly related to the biomaterial physicochemical properties and were independent of the biomaterial origin. Consequently, the induction of MNGCs and their increase over 30 days resulted in disintegration of the biomaterial. By contrast, the absence of MNGCs resulted in an integration of the biomaterial within the host tissue. This novel classification provides clinicians a tool to assess the capacity and suitability of biomaterials in the intended clinical indication for bone and soft tissue implantations.

In Vivo Analysis of the Biocompatibility and Immune Response of Jellyfish Collagen Scaffolds and its Suitability for Bone Regeneration

Jellyfish collagen, which can be defined as "collagen type 0" due to its homogeneity to the mammalian types I, II, III, V, and IX and its batch-to-batch consistent producibility, is of special interest for different medical applications related to (bone) tissue regeneration as an alternative to mammalian collagen-based biomaterials. However, no in vivo studies regarding the induction of M1- and M2-macrophages and their time-dependent ration as well as the analysis of the bone regeneration capacity of jellyfish collagen scaffolds have been conducted until now. Thus, the goal of this study was to determine the nature of the immune response to jellyfish collagen scaffolds and their bone healing capacities. Two in vivo studies using established implantation models, i.e., the subcutaneous and the calvarian implantation model in Wistar rats, were conducted. Furthermore, specialized histological, histopathological, and histomorphometrical methods have been used. As a control biomaterial, a collagen scaffold, originating from porcine pericardium, which has already been stated as biocompatible, was used for the subcutaneous study. The results of the present study show that jellyfish collagen scaffolds are nearly completely resorbed until day 60 post implantation by stepwise integration within the subcutaneous connective tissue mediated mainly by macrophages and single multinucleated giant cells. Interestingly, the degradation process ended in a vessel rich connective tissue that is understood to be an optimal basis for tissue regeneration. The study results showed an overall weaker immune response to jellyfish collagen than to porcine pericardium matrices by the induction of significantly lower numbers of macrophages together with a more balanced occurrence of M1- and M2-macrophages. However, both collagen-based biomaterials induced balanced numbers of both macrophage subtypes, which supports their good biocompatibility. Moreover, the histomorphometrical results for the calvarial implantation of the jellyfish scaffolds revealed an average of 46.20% de novo bone formation at day 60, which was significantly higher compared to the control group. Thereby, the jellyfish collagen scaffolds induced also significantly higher numbers of anti-inflammatory macrophages within the bony implantation beds. Altogether, the results show that the jellyfish collagen scaffolds allowed for a directed integration behavior, which is assumed to be in accordance with the concept of Guided Bone Regeneration (GBR). Furthermore, the jellyfish collagen scaffolds induced a long-term anti-inflammatory macrophage response and an optimal vascularization pattern within their implant beds, thus showing excellent biocompatibility and (bone) tissue healing properties.

Albumin-impregnated bone granules modulate the interactions between mesenchymal stem cells and monocytes under in vitro inflammatory conditions

Bone regeneration around newly implanted biomaterials is a complex process, which in its early phases involves the interactions between Mesenchymal Stem Cells (MSCs) and immune cells. The response of these cells to the biomaterial depends both on the local microenvironment and on the characteristics of the inserted bone substitute. In this work, bone allografts impregnated with albumin are loaded with a co-culture of human MSCs and monocytes; bone granules without albumin are used for comparison. Co-cultures are contextually treated with pro-inflammatory cytokines to simulate the inflammatory milieu naturally present during the bone regeneration process. As revealed by microscopic images, albumin-impregnated bone granules promote adhesion and interactions between cells populations. Compared to control granules, albumin coating diminishes reactive species production by cells. This reduced oxidative stress may be attributable to antioxidant properties of albumin, and it is also reflected in the mitigated gene expression of mitochondrial electron transport chain complexes, where most intracellular reactive molecules are generated. MSCs-monocytes co-cultured onto albumin-impregnated bone granules additionally release higher amounts of immunomodulatory cytokines and growth factors. In summary, this work demonstrates that impregnation of bone granules with albumin positively modulates the interactions between MSCs and immune cells, consequently influencing their mutual activities and immunomodulatory functions.

Balancing Purification and Ultrastructure of Naturally Derived Bone Blocks for Bone Regeneration: Report of the Purification Effort of Two Bone Blocks

The present publication reports the purification effort of two natural bone blocks, that is, an allogeneic bone block (maxgraft^®, botiss biomaterials GmbH, Zossen, Germany) and a xenogeneic block (SMARTBONE^®, IBI S.A., Mezzovico-Vira, Switzerland) in addition to previously published results based on histology. Furthermore, specialized scanning electron microscopy (SEM) and in vitro analyses (XTT, BrdU, LDH) for testing of the cytocompatibility based on ISO 10993-5/-12 have been conducted. The microscopic analyses showed that both bone blocks possess a trabecular structure with a lamellar subarrangement. In the case of the xenogeneic bone block, only minor remnants of collagenous structures were found, while in contrast high amounts of collagen were found associated with the allogeneic bone matrix. Furthermore, only island-like remnants of the polymer coating in case of the xenogeneic bone substitute seemed to be detectable. Finally, no remaining cells or cellular remnants were found in both bone blocks. The in vitro analyses showed that both bone blocks are biocompatible. Altogether, the purification level of both bone blocks seems to be favorable for bone tissue regeneration without the risk for inflammatory responses or graft rejection. Moreover, the analysis of the maxgraft^® bone block showed that the underlying purification process allows for preserving not only the calcified bone matrix but also high amounts of the intertrabecular collagen matrix.

An introduction to bone tissue engineering

Bone tissue has the capability to regenerate itself; however, defects of a critical size prevent the bone from regenerating and require additional support. To aid regeneration, bone scaffolds created out of autologous or allograft bone can be used, yet these produce problems such as fast degradation rates, reduced bioactivity, donor site morbidity or the risk of pathogen transmission. The development of bone tissue engineering has been used to create functional alternatives to regenerate bone. This can be achieved by producing bone tissue scaffolds that induce osteoconduction and integration, provide mechanical stability, and either integrate into the bone structure or degrade and are excreted by the body. A range of different biomaterials have been used to this end, each with their own advantages and disadvantages. This review will introduce the requirements of bone tissue engineering, beginning with the regeneration process of bone before exploring the requirements of bone tissue scaffolds. Aspects covered include the manufacturing process as well as the different materials used and the incorporation of bioactive molecules, growth factors and cells.

The Addition of High Doses of Hyaluronic Acid to a Biphasic Bone Substitute Decreases the Proinflammatory Tissue Response

Biphasic bone substitutes (BBS) are currently well-established biomaterials. Through their constant development, even natural components like hyaluronic acid (HY) have been added to improve both their handling and also their regenerative properties. However, little knowledge exists regarding the consequences of the addition of HY to their biocompatibility and the inflammatory tissue reactions. Thus, the present study was conducted, aiming to analyze the influence of two different amounts of high molecular weight HY (HMWHY), combined with a BBS, on in vitro biocompatibility and in vivo tissue reaction. Established in vitro procedures, using L929 cells, were used for cytocompatibility analyses under the test conditions of DIN EN:ISO 10993-5. For the in vivo part of the study, calvarial defects were created in 20 Wistar rats and subsequently filled with BBS, and BBS combined with two different HMWHY amounts, i.e., BBS + HY(L) and BBS + HY(H). As controls, empty defects were used. Established histological, immunohistochemical, and histomorphometrical methods were applied to analyze the tissue reactions to the three different materials, including the induction of pro- and anti-inflammatory macrophages and multinucleated giant cells (BMGCs). The in vitro results showed that none of the materials or compositions caused biological damage to the L929 cells and can be considered to be non-toxic. The in vivo results showed that only the addition of high doses of HY to a biphasic bone substitute significantly decreases the occurrence of pro-inflammatory macrophages (* p < 0.05), comparable to the numbers found in the control group, while no significant differences within the three study groups for M2-macrophages nor BMGCs were detected. In conclusion, the addition of different amounts of HMWHY does not seem to affect the inflammation response to BBS, while improving the material handling properties.

The Role of Strontium Enriched Hydroxyapatite and Tricalcium Phosphate Biomaterials in Osteoporotic Bone Regeneration

Background: Strontium (Sr) enriched biomaterials have been used to improve bone regeneration in vivo. However, most studies provide only two experimental groups. The aim of our study was to compare eleven different bone sample groups from osteoporotic and healthy rabbits’ femoral neck, as it is the most frequent osteoporotic fracture in humans. Methods: Osteoporotic bone defects were filled with hydroxyapatite 30% (HA) and tricalcium phosphate 70% (TCP), 5% Sr-enriched HA30/TCP70, HA70/TCP30, or Sr-HA70/TCP30 granules and were compared with intact leg, sham surgery and healthy non-operated bone. Expression of osteoprotegerin (OPG), nuclear factor kappa beta 105 (NFkB-105), osteocalcin (OC), bone morphogenetic protein 2/4 (BMP-2/4), collagen I (Col-1α), matrix metalloproteinase 2 (MMP-2), tissue inhibitor of matrix metalloproteinase 2 (TIMP-2), interleukin 1 (IL-1) and interleukin 10 (IL-10) was analyzed by histomorphometry and immunohistochemistry. Results: Our study showed that Sr-HA70/TCP30 induced higher expression of all above-mentioned factors compared to intact leg and even higher expression of OC, MMP-2 and NFkB-105 compared to Sr-HA30/TCP70. HA70/TCP30 induced higher level of NFkB-105 and IL-1 compared to HA30/TCP70. Conclusion: Sr-enriched biomaterials improved bone regeneration at molecular level in severe osteoporosis and induced activity of the factors was higher than after pure ceramic, sham or even healthy rabbits.

In Vivo Analysis of the Biocompatibility and Macrophage Response of a Non-Resorbable PTFE Membrane for Guided Bone Regeneration

The use of non-resorbable polytetrafluoroethylene (PTFE) membranes is indicated for the treatment of large, non-self-containing bone defects, or multi-walled defects in the case of vertical augmentations. However, less is known about the molecular basis of the foreign body response to PTFE membranes. In the present study, the inflammatory tissue responses to a novel high-density PTFE (dPTFE) barrier membrane have preclinically been evaluated using the subcutaneous implantation model in BALB/c mice by means of histopathological and histomorphometrical analysis methods and immunohistochemical detection of M1- and M2-macrophages. A collagen membrane was used as the control material. The results of the present study demonstrate that the tissue response to the dPTFE membrane involves inflammatory macrophages, but comparable cell numbers were also detected in the implant beds of the control collagen membrane, which is known to be biocompatible. Although these data indicate that the analyzed dPTFE membrane is not fully bioinert, but its biocompatibility is comparable to collagen-based membranes. Based on its optimal biocompatibility, the novel dPTFE barrier membrane may optimally support bone healing within the context of guided bone regeneration (GBR).

Cellular Mechanisms Responsible for Success and Failure of Bone Substitute Materials

Bone grafts, i.e., autologous, allogeneic or synthetic bone substitute materials play an increasing role in reconstructive orthopedic surgery. While the indications and materials differ, it is important to understand the cellular mechanisms regarding their integration and remodeling, which are discussed in this review article. Osteoconductivity describes the new bone growth on the graft, while osteoinductivity represents the differentiation of undifferentiated cells into bone forming osteoblasts. The best case is that both mechanisms are accompanied by osteogenesis, i.e., bone modeling and remodeling of the graft material. Graft incorporation is mediated by a number of molecular pathways that signal the differentiation and activity of osteoblasts and osteoclasts (e.g., parathyroid hormone (PTH) and receptor activator of nuclear factor κβ ligand (RANKL), respectively). Direct contact of the graft and host bone as well as the presence of a mechanical load are a prerequisite for the successful function of bone grafts. Interestingly, while bone substitutes show good to excellent clinical outcomes, their histological incorporation has certain limits that are not yet completely understood. For instance, clinical studies have shown contrasting results regarding the complete or incomplete resorption and remodeling of allografts and synthetic grafts. In this context, a foreign body response can lead to complete material degradation via phagocytosis, however it may also cause a fibrotic reaction to the bone substitute. Finally, the success of bone graft incorporation is also limited by other factors, including the bone remodeling capacities of the host, the material itself (e.g., inadequate resorption, toxicity) and the surgical technique or preparation of the graft.

Purification processes of xenogeneic bone substitutes and their impact on tissue reactions and regeneration

Xenogeneic bone substitute materials are widely used in oral implantology. Prior to their clinical use, purification of the former bone tissue has to be conducted to ensure the removal of immunogenic components and pathogens. Different physicochemical methods are applied for purification of the donor tissue, and temperature treatment is one of these methods. Differences in these methods and especially the application of different temperatures for purification may lead to different material characteristics, which may influence the tissue reactions to these materials and the related (bone) healing process. However, little is known about the different material characteristics and their influences on the healing process. Thus, the aim of this mini-review is to summarize the preparation processes and the related material characteristics, safety aspects, tissue reactions, resorbability and preclinical and clinical data of two widely used xenogeneic bone substitutes that mainly differ in the temperature treatment: sintered (cerabone^®) and non-sintered (Bio-Oss^®) bovine-bone materials. Based on the summarized data from the literature, a connection between the material-induced tissue reactions and the consequences for the healing processes are presented with the aim of translation into their clinical application.

Analysis of the in vitro degradation and the in vivo tissue response to bi-layered 3D-printed scaffolds combining PLA and biphasic PLA/bioglass components - Guidance of the inflammatory response as basis for osteochondral regeneration

The aim of the present study was the in vitro and in vivo analysis of a bi-layered 3D-printed scaffold combining a PLA layer and a biphasic PLA/bioglass G5 layer for regeneration of osteochondral defects in vivo Focus of the in vitro analysis was on the (molecular) weight loss and the morphological and mechanical variations after immersion in SBF. The in vivo study focused on analysis of the tissue reactions and differences in the implant bed vascularization using an established subcutaneous implantation model in CD-1 mice and established histological and histomorphometrical methods. Both scaffold parts kept their structural integrity, while changes in morphology were observed, especially for the PLA/G5 scaffold. Mechanical properties decreased with progressive degradation, while the PLA/G5 scaffolds presented higher compressive modulus than PLA scaffolds. The tissue reaction to PLA included low numbers of BMGCs and minimal vascularization of its implant beds, while the addition of G5 lead to higher numbers of BMGCs and a higher implant bed vascularization. Analysis revealed that the use of a bi-layered scaffold shows the ability to observe distinct in vivo response despite the physical proximity of PLA and PLA/G5 layers. Altogether, the results showed that the addition of G5 enables to reduce scaffold weight loss and to increase mechanical strength. Furthermore, the addition of G5 lead to a higher vascularization of the implant bed required as basis for bone tissue regeneration mediated by higher numbers of BMGCs, while within the PLA parts a significantly lower vascularization was found optimally for chondral regeneration. Thus, this data show that the analyzed bi-layered scaffold may serve as an ideal basis for the regeneration of osteochondral tissue defects. Additionally, the results show that it might be able to reduce the number of experimental animals required as it may be possible to analyze the tissue response to more than one implant in one experimental animal.

Multinucleated Giant Cells: Good Guys or Bad Guys?

Multinucleated giant cells (MNGCs) are a special class of giant cell formed by the fusion of monocytes/macrophages abundantly found in human tissues. While historically their role around certain classes of biomaterials have been directly linked to a foreign body reaction leading to material rejection, recent accumulating evidence has put into question their role around certain classes of bone biomaterials. It was once thought that specifically in bone tissues, all giant cells were considered osteoclasts characterized by their ability to resorb and replace bone grafts with newly formed native bone. More recently, however, a special subclass of bone biomaterials has been found bordered by large MNGCs virtually incapable of resorbing bone substitutes even years after their implantation yet surrounded by stable bone. Interestingly, research from the field of cardiovascular disease has further shown how a shift in macrophage polarization from M1 "tissue-inflammatory" macrophages toward M2 "wound-healing" macrophages in atherosclerotic plaque may lead to MNGC formation and ectopic calcification of arteries. Despite the growing observation that MNGC formation occurs around certain bone biomaterials, their role in these tissues remains extremely poorly understood and characterized. In summary, four central aspects of this review are discussed with a focus on (1) the role of MNGCs in bone/tissue biology, and their ability to induce vascularization/new bone formation, their role around, (2) bone substitutes for bone augmentation, (3) dental implants, as well as (4) during peri-implant infection. The authors express the necessity to no longer refer to MNGCs as "good" or "bad" cells, but instead point toward the necessity to more specifically characterize them scientifically and appropriately as M1-MNGC and M2-MNGC accordingly. Future research investigating the factors influencing their polarization as a "center of control" is also likely to act as a key factor in the progression/resolution of various diseases.

Variant Purification of an Allogeneic Bone Block

Objective

This short communication reports on a histological analysis of the composition of the commercially available Maxgraft® allogeneic bone block.

Materials and Methods

Based on previously published, easily applicable histological methods, blanc samples of the Maxgraft® allogeneic bone block ^have been decalcified, dehydrated and embedded in paraffin before histological and histochemical staining. Afterwards, the slides were evaluated for their material characteristics, such as the bone matrix structure and other components, including collagen or cells/cell remnants.

Results

The results show that this bone block exhibits a trabecular structure with lamellar sub-organization. Additionally, cellular remnants within the osteocyte lacunae and at the outer trabecular surfaces reside together with remnants of the former inter-trabecular fatty and connective tissue, i.e., collagenous structures and connective tissue cells or cell remnants.

Conclusion

Consistent with a previous study on this topic, the data presented here demonstrate that some of the certified purification techniques might not allow for the production of allogeneic materials free of organic cell and tissue components.

Multinucleated giant cells in the implant bed of bone substitutes are foreign body giant cells-New insights into the material-mediated healing process

In addition to macrophages, multinucleated giant cells (MNGCs) are involved in the tissue reaction to a variety of biomaterials. Especially in the case of bone substitute materials it has been assumed that the MNGCs are osteoclasts, based on the chemical and physical similarity of many materials to the calcified matrix and the bony environment in which they are used. However, many studies indicate that these cells belong to the cell line of the foreign body giant cells (FBGCs), which are of "inflammatory origin", although they have been shown to possess both a pro- and also anti-inflammatory phenotype. Moreover, no information is available about their role in the tissue reaction to bone substitute materials. The present study was conducted to analyze the origin of MNGCs in the implant beds of a synthetic and a xenogeneic bone substitute and focused on the application of immunohistochemical methods. Two antibodies against integrin molecules specific for osteoclasts (β-3 integrin) or FBGCs (β-2 integrin) were used to distinguish both giant cell types. The results of the present study indicate that the MNGCs induced by both kinds of bone substitutes are FBGCs, as they express only β-2 integrin in contrast to the osteoclasts outside of the immediate implantation areas, which only demonstrate β-3 integrin expression. These data give new insight into the tissue reaction to both xenogeneic and synthetic bone substitutes. Based on this new knowledge further research concerning the proteomic profile of the FBGCs especially based on the different physicochemical properties of bone substitutes is necessary. This may show that specific characteristics of bone substitutes may exhibit a substantial influence on the regeneration process via the expression of anti-inflammatory molecules by FBGCs. Based on this information it may be possible to formulate and choose bone substitutes that can guide the process of bone tissue regeneration on the molecular level. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1105-1111, 2017.

Giant cells around bone biomaterials: Osteoclasts or multi-nucleated giant cells?

Recently accumulating evidence has put into question the role of large multinucleated giant cells (MNGCs) around bone biomaterials. While cells derived from the monocyte/macrophage lineage are one of the first cell types in contact with implanted biomaterials, it was originally thought that specifically in bone tissues, all giant cells were bone-resorbing osteoclasts whereas foreign body giant cells (FBGCs) were found associated with a connective tissue foreign body reaction resulting in fibrous encapsulation and/or material rejection. Despite the great majority of bone grafting materials routinely found with large osteoclasts, a special subclass of bone biomaterials has more recently been found surrounded by large giant cells virtually incapable of resorbing bone grafts even years after their implantation. While original hypotheses believed that a 'foreign body reaction' may be taking place, histological data retrieved from human samples years after their implantation have put these original hypotheses into question by demonstrating better and more stable long-term bone volume around certain bone grafts. Exactly how or why this 'special' subclass of giant cells is capable of maintaining long-term bone volume, or methods to scientifically distinguish them from osteoclasts remains extremely poorly studied. The aim of this review article was to gather the current available literature on giant cell markers and differences in expression patterns between osteoclasts and MNGCs utilizing 19 specific markers including an array of CD-cell surface markers. Furthermore, the concept of now distinguishing between pro-inflammatory M1-MNGCs (previously referred to as FBGCs) as well as wound-healing M2-MNGCs is introduced and discussed.

STATEMENT OF SIGNIFICANCE

This review article presents 19 specific cell-surface markers to distinguish between osteoclasts and MNGCs including an array of CD-cell surface markers. Furthermore, the concept of now distinguishing between pro-inflammatory M1-MNGCs (often previously referred to as FBGCs) as well as wound-healing M2-MNGCs is introduced and discussed. The proposed concepts and guidelines aims to guide the next wave of research facilitating the differentiation between osteoclast/MNGCs formation, as well as provides the basis for increasing our understanding of the exact function of MNGCs in bone tissue/biomaterial homeostasis.

Monocyte preseeding leads to an increased implant bed vascularization of biphasic calcium phosphate bone substitutes via vessel maturation

The present study analyzes the influence of the addition of monocytes to a biphasic bone substitute with two granule sizes (400-700 μm and 500-1000 μm). The majority of the added monocytes was detectable as mononuclear cells, while also low amounts of (chimeric) multinucleated giant cells (MNGCs) were found. No increase in the total number of MNGCs was established, but a significantly increased percent vascularization. Altogether, the results show that the added monocytes become involved in the tissue response to a biomaterial without marked changes in the overall reaction. Monocyte addition enables an increased implant bed vascularization especially via induction of vessel maturation and, thus intervenes positively in the healing reaction to a biomaterial. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2928-2935, 2016.