Influence of biomaterial surface chemistry on the apoptosis of adherent cells

Additive manufacturing of wet-spun chitosan/hyaluronic acid scaffolds for biomedical applications

Additive manufacturing (AM) holds great potential for processing natural polymer hydrogels into 3D scaffolds exploitable for tissue engineering and in vitro tissue modelling. The aim of this research activity was to assess the suitability of computer-aided wet-spinning (CAWS) for AM of hyaluronic acid (HA)/chitosan (Cs) polyelectrolyte complex (PEC) hydrogels. A post-printing treatment based on HA chemical cross-linking via transesterification with poly(methyl vinyl ether-alt-maleic acid) (PMVEMA) was investigated to enhance the structural stability of the developed scaffolds in physiological conditions. PEC formation and the esterification reaction were investigated by infrared spectroscopy, thermogravimetric analysis, evolved gas analysis-mass spectrometry, and differential scanning calorimetry measurements. In addition, variation of PMVEMA concentration in the cross-linking medium was demonstrated to strongly influence scaffold water uptake and its stability in phosphate buffer saline at 37 °C. The in vitro cytocompatibility of the developed hydrogels was demonstrated by employing the murine embryo fibroblast Balb/3T3 clone A31 cell line, highlighting that PMVEMA cross-linking improved scaffold cell colonization. The results achieved demonstrated that the developed hydrogels represent suitable 3D scaffolds for long term cell culture experiments.

Angiogenic and immunomodulation role of ions for initial stages of bone tissue regeneration

It is widely known that bone has intrinsic capacity to self-regenerate after injury. However, the physiological regeneration process can be impaired when there is an extensive damage. One of the main reasons is due to the inability to establish a new vascular network that ensures oxygen and nutrient diffusion, leading to a necrotic core and non-junction of bone. Initially, bone tissue engineering (BTE) emerged to use inert biomaterials to just fill bone defects, but it eventually evolved to mimic bone extracellular matrix and even stimulate bone physiological regeneration process. In this regard, the stimulation of osteogenesis has gained a lot of attention especially in the proper stimulation of angiogenesis, being critical to achieve a successful osteogenesis for bone regeneration. Besides, the immunomodulation of a pro-inflammatory environment towards an anti-inflammatory one upon scaffold implantation has been considered another key process for a proper tissue restoration. To stimulate these phases, growth factors and cytokines have been extensively used. Nonetheless, they present some drawbacks such as low stability and safety concerns. Alternatively, the use of inorganic ions has attracted higher attention due to their higher stability and therapeutic effects with low side effects. This review will first focus in giving fundamental aspects of initial bone regeneration phases, focusing mainly on inflammatory and angiogenic ones. Then, it will describe the role of different inorganic ions in modulating the immune response upon biomaterial implantation towards a restorative environment and their ability to stimulate angiogenic response for a proper scaffold vascularization and successful bone tissue restoration. STATEMENT OF SIGNIFICANCE: The impairment of bone tissue regeneration when there is excessive damage has led to different tissue engineered strategies to promote bone healing. Significant importance has been given in the immunomodulation towards an anti-inflammatory environment together with proper angiogenesis stimulation in order to achieve successful bone regeneration rather than stimulating only the osteogenic differentiation. Ions have been considered potential candidates to stimulate these events due to their high stability and therapeutic effects with low side effects compared to growth factors. However, up to now, no review has been published assembling all this information together, describing individual effects of ions on immunomodulation and angiogenic stimulation, as well as their multifunctionality or synergistic effects when combined together.

Immunomodulatory Biomaterials and Emerging Analytical Techniques for Probing the Immune Micro-Environment

After implantation of a biomaterial, both the host immune system and properties of the material determine the local immune response. Through triggering or modulating the local immune response, materials can be designed towards a desired direction of promoting tissue repair or regeneration. High-throughput sequencing technologies such as single-cell RNA sequencing (scRNA-seq) emerging as a powerful tool for dissecting the immune micro-environment around biomaterials, have not been fully utilized in the field of soft tissue regeneration. In this review, we first discussed the procedures of foreign body reaction in brief. Then, we summarized the influences that physical and chemical modulation of biomaterials have on cell behaviors in the micro-environment. Finally, we discussed the application of scRNA-seq in probing the scaffold immune micro-environment and provided some reference to designing immunomodulatory biomaterials. The foreign body response consists of a series of biological reactions. Immunomodulatory materials regulate immune cell activation and polarization, mediate divergent local immune micro-environments and possess different tissue engineering functions. The manipulation of physical and chemical properties of scaffolds can modulate local immune responses, resulting in different outcomes of fibrosis or tissue regeneration. With the advancement of technology, emerging techniques such as scRNA-seq provide an unprecedented understanding of immune cell heterogeneity and plasticity in a scaffold-induced immune micro-environment at high resolution. The in-depth understanding of the interaction between scaffolds and the host immune system helps to provide clues for the design of biomaterials to optimize regeneration and promote a pro-regenerative local immune micro-environment.

Medical Applications of Porous Biomaterials: Features of Porosity and Tissue-Specific Implications for Biocompatibility

Porosity is an important material feature commonly employed in implants and tissue scaffolds. The presence of material voids permits the infiltration of cells, mechanical compliance, and outward diffusion of pharmaceutical agents. Various studies have confirmed that porosity indeed promotes favorable tissue responses, including minimal fibrous encapsulation during the foreign body reaction (FBR). However, increased biofilm formation and calcification is also described to arise due to biomaterial porosity. Additionally, the relevance of host responses like the FBR, infection, calcification, and thrombosis are dependent on tissue location and specific tissue microenvironment. In this review, the features of porous materials and the implications of porosity in the context of medical devices is discussed. Common methods to create porous materials are also discussed, as well as the parameters that are used to tune pore features. Responses toward porous biomaterials are also reviewed, including the various stages of the FBR, hemocompatibility, biofilm formation, and calcification. Finally, these host responses are considered in tissue specific locations including the subcutis, bone, cardiovascular system, brain, eye, and female reproductive tract. The effects of porosity across the various tissues of the body is highlighted and the need to consider the tissue context when engineering biomaterials is emphasized.

Immuno-modulatory biomaterials as anti-inflammatory therapeutics

Biocompatible and biodegradable biomaterials are used extensively in regenerative medicine and serve as a tool for tissue replacement, as a platform for regeneration of injured tissue, and as a vehicle for delivery of drugs. One of the key factors that must be addressed in developing successful biomaterial-based therapeutics is inflammation. Whilst inflammation is initially essential for wound healing; bringing about clearance of debris and infection, prolonged inflammation can result in delayed wound healing, rejection of the biomaterial, further tissue damage and increased scarring and fibrosis. In this context, the choice of biomaterial must be considered carefully to minimise further induction of inflammation. Here we address the ability of the biomaterials themselves to modulate inflammatory responses and outline how the physico-chemical properties of the materials impact on their pro and anti-inflammatory properties (Fig. 1).

Covalent linkage of sulfated hyaluronan to the collagen scaffold Mucograft® enhances scaffold stability and reduces proinflammatory macrophage activation in vivo

Sulfated glycosaminoglycans (sGAG) show interaction with biological mediator proteins. Although collagen-based biomaterials are widely used in clinics, their combination with high-sulfated hyaluronan (sHA3) is unexplored. This study aims to functionalize a collagen-based scaffold (Mucograft®) with sHA3 via electrostatic (sHA3/PBS) or covalent binding to collagen fibrils (sHA3+EDC/NHS). Crosslinking without sHA3 was used as a control (EDC/NHS Ctrl). The properties of the sHA3-functionalized materials were characterized. In vitro growth factor and cytokine release after culturing with liquid platelet-rich fibrin was performed by means of ELISA. The cellular reaction to the biomaterials was analyzed in a subcutaneous rat model. The study revealed that covalent linking of sHA3 to collagen allowed only a marginal release of sHA3 over 28 days in contrast to electrostatically bound sHA3. sHA3+EDC/NHS scaffolds showed reduced vascular endothelial growth factor (VEGF), transforming growth factor beta 1 (TGF-β1) and enhanced interleukin-8 (IL-8) and epithelial growth factor (EGF) release in vitro compared to the other scaffolds. Both sHA3/PBS and EDC/NHS Ctrl scaffolds showed a high proinflammatory reaction (M1: CD-68+/CCR7+) and induced multinucleated giant cell (MNGC) formation in vivo. Only sHA3+EDC/NHS scaffolds reduced the proinflammatory macrophage M1 response and did not induce MNGC formation during the 30 days. SHA3+EDC/NHS scaffolds had a stable structure in vivo and showed sufficient integration into the implantation region after 30 days, whereas EDC/NHS Ctrl scaffolds underwent marked disintegration and lost their initial structure. In summary, functionalized collagen (sHA3+EDC/NHS) modulates the inflammatory response and is a promising biomaterial as a stable scaffold for full-thickness skin regeneration in the future.

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Covalent linking of high-sulfated hyaluronan (sHA3) to collagen allows a sustained release of sHA3.

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Covalent linking of sHA3 to collagen modulates the release of growth factor and cytokines in vitro.

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Covalent linking of sHA3 to collagen suppresses the induction of multinucleated giant cells in vivo.

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Covalent linking of sHA3 to collagen reduces the proinflammatory macrophage M1 response in vivo.

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Functionalized collagen with sHA3 is promising for full-thickness skin regeneration.

Cytotoxicity Study of UV-Laser-Irradiated PLLA Surfaces Subjected to Bio-Ceramisation: A New Way towards Implant Surface Modification

In this research we subjected samples of poly(L-lactide) (PLLA) extruded film to ultraviolet (193 nm ArF excimer laser) radiation below the ablation threshold. The modified film was immersed in Simulated Body Fluid (SBF) at 37 °C for 1 day or 7 days to obtain a layer of apatite ceramic (CaP) coating on the modified PLLA surface. The samples were characterized by means of optical profilometry, which indicated an increase in average roughness (Ra) from 25 nm for the unmodified PLLA to over 580 nm for irradiated PLLA incubated in SBF for 1 day. At the same time, the water contact angle decreased from 78° for neat PLLA to 35° for irradiated PLLA incubated in SBF, which suggests its higher hydrophilicity. The obtained materials were investigated by means of cell response fibroblasts (3T3) and macrophage-like cells (RAW 264.7). Properties of the obtained composites were compared to the unmodified PLLA film as well as to the UV-laser irradiated PLLA. The activation of the PLLA surface by laser irradiation led to a distinct increase in cytotoxicity, while the treatment with SBF and the deposition of apatite ceramic had only a limited preventive effect on this harmful impact and depended on the cell type. Fibroblasts were found to have good tolerance for the irradiated and ceramic-covered PLLA, but macrophages seem to interact with the substrate leading to the release of cytotoxic products.

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.

Nonspecific Binding-Fundamental Concepts and Consequences for Biosensing Applications

Nature achieves differentiation of specific and nonspecific binding in molecular interactions through precise control of biomolecules in space and time. Artificial systems such as biosensors that rely on distinguishing specific molecular binding events in a sea of nonspecific interactions have struggled to overcome this issue. Despite the numerous technological advancements in biosensor technologies, nonspecific binding has remained a critical bottleneck due to the lack of a fundamental understanding of the phenomenon. To date, the identity, cause, and influence of nonspecific binding remain topics of debate within the scientific community. In this review, we discuss the evolution of the concept of nonspecific binding over the past five decades based upon the thermodynamic, intermolecular, and structural perspectives to provide classification frameworks for biomolecular interactions. Further, we introduce various theoretical models that predict the expected behavior of biosensors in physiologically relevant environments to calculate the theoretical detection limit and to optimize sensor performance. We conclude by discussing existing practical approaches to tackle the nonspecific binding challenge in vitro for biosensing platforms and how we can both address and harness nonspecific interactions for in vivo systems.

Biocompatibility Evolves: Phenomenology to Toxicology to Regeneration

The word "biocompatibility," is inconsistent with the observations of healing for so-called biocompatible biomaterials. The vast majority of the millions of medical implants in humans today, presumably "biocompatible," are walled off by a dense, avascular, crosslinked collagen capsule, hardly suggestive of life or compatibility. In contrast, one is now seeing examples of implant biomaterials that lead to a vascularized reconstruction of localized tissue, a biological reaction different from traditional biocompatible materials that generate a foreign body capsule. Both the encapsulated biomaterials and the reconstructive biomaterials qualify as "biocompatible" by present day measurements of biocompatibility. Yet, this new generation of materials would seem to heal "compatibly" with the living organism, where older biomaterials are isolated from the living organism by the dense capsule. This review/perspective article will explore this biocompatibility etymological conundrum by reviewing the history of the concepts around biocompatibility, today's standard methods for assessing biocompatibility, a contemporary view of the foreign body reaction and finally, a compendium of new biomaterials that heal without the foreign body capsule. A new definition of biocompatibility is offered here to address advances in biomaterials design leading to biomaterials that heal into the body in a facile manner.

Collagen analogs with phosphorylcholine are inflammation-suppressing scaffolds for corneal regeneration from alkali burns in mini-pigs

The long-term survival of biomaterial implants is often hampered by surgery-induced inflammation that can lead to graft failure. Considering that most corneas receiving grafts are either pathological or inflamed before implantation, the risk of rejection is heightened. Here, we show that bioengineered, fully synthetic, and robust corneal implants can be manufactured from a collagen analog (collagen-like peptide-polyethylene glycol hybrid, CLP-PEG) and inflammation-suppressing polymeric 2-methacryloyloxyethyl phosphorylcholine (MPC) when stabilized with the triazine-based crosslinker 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride. The resulting CLP-PEG-MPC implants led to reduced corneal swelling, haze, and neovascularization in comparison to CLP-PEG only implants when grafted into a mini-pig cornea alkali burn model of inflammation over 12 months. Implants incorporating MPC allowed for faster nerve regeneration and recovery of corneal sensation. CLP-PEG-MPC implants appear to be at a more advanced stage of regeneration than the CLP-PEG only implants, as evidenced by the presence of higher amounts of cornea-specific type V collagen, and a corresponding decrease in the presence of extracellular vesicles and exosomes in the corneal stroma, in keeping with the amounts present in healthy, unoperated corneas.

Host Response to Biomaterials for Cartilage Tissue Engineering: Key to Remodeling

Biomaterials play a core role in cartilage repair and regeneration. The success or failure of an implanted biomaterial is largely dependent on host response following implantation. Host response has been considered to be influenced by numerous factors, such as immune components of materials, cytokines and inflammatory agents induced by implants. Both synthetic and native materials involve immune components, which are also termed as immunogenicity. Generally, the innate and adaptive immune system will be activated and various cytokines and inflammatory agents will be consequently released after biomaterials implantation, and further triggers host response to biomaterials. This will guide the constructive remolding process of damaged tissue. Therefore, biomaterial immunogenicity should be given more attention. Further understanding the specific biological mechanisms of host response to biomaterials and the effects of the host-biomaterial interaction may be beneficial to promote cartilage repair and regeneration. In this review, we summarized the characteristics of the host response to implants and the immunomodulatory properties of varied biomaterial. We hope this review will provide scientists with inspiration in cartilage regeneration by controlling immune components of biomaterials and modulating the immune system.

Improved in vivo stability of silicon-containing polyurethane by fluorocarbon side chain modulation of the surface structure

As a class of widely used biomedical materials, polyurethanes suffer from their insufficient stability in vivo. Although the commercialized silicone-polyetherurethanes (SiPEUs) have demonstrated excellent biostability compared with polyetherurethanes (PEUs) for long-term implantation, the usage of polydimethylsiloxane (PDMS) inevitably decreased the mechanical properties and unexpected breaches were observed. In this study, we introduced a fluorinated diol (FDO) into SiPEU to modulate the molecular interactions and micro-separated morphology. The fluorinated silicon-containing polyurethane (FSiPEU) was achieved with desirable silicone- and fluorine-enriched surfaces and mechanical properties at a low silicon content. As evidenced by in vitro culture of macrophages and in vivo hematoxylin-eosin (H&E) staining, FSiPEU demonstrated a minimized inflammatory response. After implantation in mice for 6 months, the material was devoid of significant surface degradation and had the least chain cleavage of soft segments. The results indicate that FSiPEU could be promising candidates for long-term implantation considering the combination of biostability, biocompatibility and mechanical performances.

Thermal treatment at 500 °C significantly reduces the reaction to irregular tricalcium phosphate granules as foreign bodies: An in vivo study

Evaporation of phosphate species during thermal treatment (> 400 °C) of calcium phosphates leads to the formation of an alkaline layer on their surface. The aim of this study was to evaluate the hypothesis that the biological response of thermally treated calcium phosphates is modified by the presence of such an alkaline layer on their surface. For this purpose, 0.125-0.180 mm α- and β-tricalcium phosphate (TCP) granules were obtained by crushing and size classification, with some being subjected to thermal treatment at 500 °C. The four types of granules (α-TCP, β-TCP, α-TCP-500 °C, and β-TCP-500 °C) were implanted subcutaneously and orthotopically in rats. Sham operations served as control. Subcutaneously, α-TCP and β-TCP induced significantly more multinucleated giant cells (MNGCs) than calcined granules. Most of the induced MNGCs were TRAP-negative, CD-68 positive and cathepsin K-negative, reflecting a typical indication of a reaction with a foreign body. The vessel density was significantly higher in the α-TCP and β-TCP groups than it was in the α-TCP-500 °C and β-TCP-500 °C groups. In the femur model, β-TCP-500 °C induced significantly more new bone formation than that induced by β-TCP. The granule size was also significantly larger in the β-TCP-500 °C group, making it more resistant to degradation than β-TCP. The MNGC density was higher in the α-TCP and β-TCP groups than in the α-TCP-500 °C and β-TCP-500 °C groups, including cathepsin-positive, CD-68 positive, TRAP-positive and TRAP-negative MNGCs. In conclusion, this study confirms that the biological response of calcium phosphates was affected by the presence of an alkaline layer on their surface. Thermally-treated α-TCP and β-TCP granules produced significantly fewer MNGCs and were significantly less degraded than non-thermally-treated α-TCP and β-TCP granules. Thermally treating α-TCP and β-TCP granules shifts the reaction from a foreign body reaction towards a physiological reaction by downregulating the number of induced MNGCs and enhancing degradation resistance.

Switch of macrophage fusion competency by 3D matrices

Foreign body reaction reflects the integration between biomaterials and host cells. At the implantation microenvironment, macrophages usually fuse into multinuclear cells, also known as foreign body giant cells, to respond to the biomaterial implants. To understand the biomaterial-induced macrophage fusion, we examined whether biomaterial alone can initiate and control the fusion rate without exogenous cytokines and chemicals. We introduced a collagen-based 3D matrix to embed Raw264.7 cell line and primary rat bone marrow-derived macrophages. We found the biomaterial-stimuli interacted regional macrophages and altered the overall fusogenic protein expressions to regulate the macrophage fusion rate. The fusion rate could be altered by modulating the cell-matrix and cell-cell adhesions. The fused macrophage morphologies, the nuclei number in the fused macrophage, and the fusion rates were matrix dependent. The phenomena were also observed in the in vivo models. These results suggest that the biomaterial-derived stimuli exert similar functions as cytokines to alter the competency of macrophage fusion as well as their drug sensitivity in the biomaterial implanted tissue environment. Furthermore, this in vitro 3D-matrix model has the potential to serve as a toolbox to predict the host tissue response on implanted biomaterials.

Multinucleated giant cells within the in vivo implantation bed of a collagen-based biomaterial determine its degradation pattern

Objectives

The aim of the present study was to characterize the cellular reaction to a xenogeneic resorbable collagen membrane of porcine origin using a subcutaneous implantation model in Wistar rats over 30 days.

Materials and methods

Ex vivo, liquid platelet-rich fibrin (PRF), a leukocyte and platelet-rich cell suspension, was used to evaluate the blood cell membrane interaction. The material was implanted subcutaneously in rats. Sham-operated rats without biomaterial displayed physiological wound healing (control group). Histological, immunohistological, and histomorphometric analyses were focused on the inflammatory pattern, vascularization rate, and degradation pattern.

Results

The membrane induced a large number of mononuclear cells over the observation period, including lymphocytes, macrophages, and fibroblasts. After 15 days, multinucleated giant cells (MNGCs) were observed on the biomaterial surface. Their number increased significantly, and they proceeded to the center of the biomaterial on day 30. These cells highly expressed CD-68, calcitonin receptor, and MMP-9, but not TRAP or integrin-ß3. Thus, the membrane lost its integrity and underwent disintegration as a consequence of the induction of MNGCs. The significant increase in MNGC number correlated with a high rate of vascularization, which was significantly higher than the control group. Physiological wound healing in the control group did not induce any MNGCs at any time point. Ex vivo blood cells from liquid-PRF did not penetrate the membrane.

Conclusion

The present study suggests a potential role for MNGCs in biomaterial degradation and questions whether it is beneficial to accept them in clinically approved biomaterials or focus on biomaterials that induce only mononuclear cells. Thus, further studies are necessary to identify the function of biomaterial-induced MNGCs.

Clinical relevance

Understanding the cellular reaction to biomaterials is essential to assess their suitability for specific clinical indications and outline the potential benefit of specific group of biomaterials in the respective clinical indications.

The inflammatory response to bone infection - a review based on animal models and human patients

Bone infections are difficult to diagnose and treat, especially when a prosthetic joint replacement or implant is involved. Bone loss is a major complication of osteomyelitis, but the mechanism behind has mainly been investigated in cell cultures and has not been confirmed in human settings. Inflammation is important in initiating an appropriate immune response to invading pathogens. However, many of the signaling molecules used by the immune system can also modulate bone remodeling and contribute to bone resorption during osteomyelitis. Our current knowledge of the inflammatory response relies heavily on animal models as research based on human samples is scarce. Staphylococcus aureus is one of the most common causes of bone infections and is the pathogen of choice in animal models. The regulation of inflammatory genes during prosthetic joint infections and implant-associated osteomyelitis has only been studied in rodent models. It is important to consider the validity of an animal model when results are extrapolated to humans, and both bone composition and the immune system of pigs has been shown to be more similar to humans, than to rodents. Here in vivo studies on the inflammatory response to prosthetic joint infections and implant-associated osteomyelitis are reviewed.

Roxatidine inhibits fibrosis by inhibiting NF‑κB and MAPK signaling in macrophages sensing breast implant surface materials

Capsular contracture is an important complication after silicone mammary implant surgery. Fibroblasts and macrophages play critical roles in the pathogenesis of capsular contracture, making these two cell types therapeutic targets. It has been reported that inhibiting histamine receptors results attenuates fibrosis, but the role of roxatidine (a histamine receptor 2 inhibitor) in preventing fibrosis caused by breast implant materials remains unknown. The aim of the present study was to assess the hypothesis that roxatidine might have a prophylactic effect in capsular contracture induced by implant material. Inflammation induced by breast implant materials was mimicked by co-culturing macrophages or fibroblasts with these materials in vitro. Capsular contracture was modeled in mice by planting breast implant materials in a subcutaneous pocket. Roxatidine was added in the culture medium or administered to mice bearing breast implant materials. By co-culturing macrophages or fibroblasts with common breast implant materials (micro-textured or smooth breast implants), the present study demonstrated that macrophages respond to these materials by producing pro-inflammatory cytokines, a process that was abolished by addition of roxatidine to the culture medium. Although fibroblasts did not respond to implant surface materials in the same way as macrophages, the conditioned media of macrophages induced proliferation of fibroblasts. Mechanistically, administration of roxatidine inhibited activation of NF-κB and p38/mitogen-activated protein kinase (MAPK) signaling in macrophages. Furthermore, treatment with roxatidine in implant-bearing mice reduced serum concentrations of transforming growth factor-β and the abundance of fibroblasts around the implant. The present study concluded that roxatidine plays an important role in preventing fibrosis by inhibiting activation of NF-κB and p38/MAPK signaling in macrophages.

Analyzing the scaffold immune microenvironment using flow cytometry: practices, methods and considerations for immune analysis of biomaterials

The immune system has evolved as a powerful tool for our body to combat infections, and is being engineered for new treatments in cancer and autoimmune disease. More recently, the complex role of the immune system is being recognized in tissue repair, regenerative medicine and biomaterial responses. From these combined interests, the field of immunoengineering is rapidly growing. However, bridging immunology with engineering poses numerous challenges including the biological complexity, language of immunology and accurately leveraging the powerful techniques of immunology to new applications. Elucidating the identity and function of immune cell populations responding to engineering systems will be required for continued advancement. Multi-color flow cytometry is a central technique used by immunologists for this purpose that requires careful control of variables, data acquisition, and interpretation. Here, we present methods for multi-color flow cytometry experimental design and analysis focused on characterizing the scaffold immune microenvironment in regenerative medicine research.

Comparison of different cell culture plates for the enrichment of non-adherent human mononuclear cells

While tissue-resident monocytes and macrophages are considered to be vital players in the in vivo interaction between biomaterials and surrounding tissue, their isolation is limited. In order to establish in vitro models elucidating implant and tissue interactions, peripheral blood mononuclear cells (PBMCs) represent a viable source for bone marrow-derived monocytes and an alternative to tissue-resident cells. The aim of present study was to analyse different adhesion-preventing tissue culture plates for their potential to facilitate the culture of monocytes without differentiation into macrophages. Freshly isolated PBMCs were seeded into four commercially available tissue culture plates with different adhesive properties and were tested for surface CD14 and CD68 expression using flow cytometry following 7 days in culture. When PBMCs were cultivated in RPMI on Cellstar^® Cell culture plates with Cell-Repellent Surface, a significant increase in CD14-positive cells was observed compared with cultivation in standard tissue culture-treated plates. This was accompanied by elevated cytokine production of interleukin-6 (IL6) and interleukin-8 (IL8); however, overall cell growth was not affected. When PBMCs were pre-cultured in cell-repellent plates, there was a higher yield of adherent cells after subsequent transfer into standard tissue culture-treated plates. Cultivation of PBMCs on cell-repellent culture plates favoured a monocytic phenotype and thus, represents an alternative to increase the fraction of monocytes yielded from PBMCs.

Inflammatory responses to micro/nano-structured titanium surfaces with silver nanoparticles in vitro

The fabricated AgPD-MNT exhibited potent antibacterial activity and mediated the inflammatory response.

Cell Density Detector Based on Light Beam Focusing

Although the lab-on-a-chip system has been successfully applied in a wide variety of fields, the goal of achieving a cell counter with simple operation, low cost, and high accuracy still attracts continuous research efforts. In this paper, the authors explore a cell counter based on light beam focusing to measure the density of adherent cells. In this sensor, the light emitted from the optical fibers is collimated by the collimating lens formed in polydimethylsiloxane (PDMS). The uniformly attached adherent cells act as a convex lens, focusing the collimated light propagated through them. The intensity of the focused light indicates the density of the adherent cells. For Hela cells, a detection limit of 8.3 × 10⁴ cells/mL with a detection range from 0.1 × 10⁶ cells/mL to 1.0 × 10⁶ cells/mL is achieved. This sensor is particularly useful for drug screening, cell pathology analysis, and cancer pre-diagnosis.

Fabrication of a blood compatible composite membrane from chitosan nanoparticles, ethyl cellulose and bacterial cellulose sulfate

A heparin-like composite membrane was fabricated through electrospinning chitosan nanoparticles (CN) together with an ethylcellulose (EC) ethanol solution onto a bacterial cellulose sulfate membrane (BCS). Scanning electron microscopy images revealed that there were no chitosan particles in the obtained composite CN-EC/BCS membranes (CEB), indicating CN had been stretched to nanofibers. X-ray photoelectron spectroscopy verified the existence of –NH₂ from chitosan and –SO₃⁻ from BCS on the surface of CEB membranes. Positively charged CN in the electrospinning solution and negatively charged BCS on the collector increased the electrostatic force and the electrospinning ability of the EC was increased. The membrane was hydrophobic, with a water contact angle higher than 120°. CEB membranes expressed good blood compatibility according to the results of coagulation time and platelet adhesion experiments. No platelets adhered on the surface of the CEB membranes. An inflammatory response was investigated according to activation of the macrophages seeded onto the membranes. Macrophages seeded on CEB membranes are not activated after 24 h incubation.

A blood compatible membrane was fabricated through electrospinning a solution of chitosan nanoparticles and ethylcellulose onto a bacterial cellulose sulfate membrane to mimic heparin's structure.

Influence of diabetes on the foreign body response to nitric oxide-releasing implants

The foreign body response (FBR) to nitric oxide (NO)-releasing subcutaneous implants was compared between healthy and streptozotocin-induced diabetic swine by evaluating inflammation, collagen capsule formation, and angiogenesis. Steel wire substrates were first modified with polyurethane membranes capable of diverse NO-release kinetics (NO fluxes and release durations of 0.8-630.0 pmol cm^-2 s^-1 and 2-13 d, respectively). The NO-releasing materials were implanted in the subcutis for 3, 10, or 25 d for histological and immunohistochemical evaluation of the FBR. A delayed, more severe inflammatory response to control (i.e., non-NO-releasing) implants was observed in diabetic pigs relative to healthy swine. Regardless of the animal disease state, each NO-releasing implant tested elicited reduced inflammation compared to controls at both 3 and 10 d. However, only the NO-release materials capable of releasing low NO fluxes (0.8-3.3 pmol cm^-2 s^-1) for 7-13 d durations mitigated the inflammatory response at 25 d. Using immunohistochemical staining for the endothelial cell surface marker CD-31, we also observed poor blood vessel development at non-NO-releasing implants in diabetic swine. Relative to controls, NO-releasing implants with the longest NO-release duration (13 d) increased blood vessel densities by 47.1 and 70.4% in the healthy and diabetic pigs, respectively. In the healthy model, tissues surrounding the long NO-release materials contained sparse amounts of collagen, whereas implants with shorter NO-release durations (2, 3, and 7 d) were characterized with a dense collagen encapsulation layer, similar to controls. Collagen deposition in diabetic swine was inhibited, and unaffected by NO. These results emphasize several key differences in the FBR in the setting of acute onset diabetes. The observation that NO release counteracts the more severe FBR in diabetic swine while simultaneously promoting tissue integration may help guide the design of medical implants (e.g., glucose sensors) with improved performance for diabetes management.

Macrophage interactions with polylactic acid and chitosan scaffolds lead to improved recruitment of human mesenchymal stem/stromal cells: a comprehensive study with different immune cells

Despite the importance of immune cell-biomaterial interactions for the regenerative outcome, few studies have investigated how distinct three-dimensional biomaterials modulate the immune cell-mediated mesenchymal stem/stromal cells (MSC) recruitment and function. Thus, this work compares the response of varied primary human immune cell populations triggered by different model scaffolds and describes its functional consequence on recruitment and motility of bone marrow MSC. It was found that polylactic acid (PLA) and chitosan scaffolds lead to an increase in the metabolic activity of macrophages but not of peripheral blood mononuclear cells (PBMC), natural killer (NK) cells or monocytes. PBMC and NK cells increase their cell number in PLA scaffolds and express a secretion profile that does not promote MSC recruitment. Importantly, chitosan increases IL-8, MIP-1, MCP-1 and RANTES secretion by macrophages while PLA stimulates IL-6, IL-8 and MCP-1 production, all chemokines that can lead to MSC recruitment. This secretion profile of macrophages in contact with biomaterials correlates with the highest MSC invasion. Furthermore, macrophages enhance stem cell motility within chitosan scaffolds by 44% but not in PLA scaffolds. Thus, macrophages are the cells that in contact with engineered biomaterials become activated to secrete bioactive molecules that stimulate MSC recruitment.

Differential apoptotic response of MC3T3-E1 pre-osteoblasts to biodegradable magnesium alloys in an in vitro direct culture model

The biodegradable magnesium-based implants have been widely utilized in medical orthopedic applications in recent years. We have recently shown that direct culture on Pure Mg and Mg2Ag alloys lead to a progressive differentiation impairment of MC3T3-E1 pre-osteoblasts. In this study, we aimed to analyze the apoptotic reaction of MC3T3-E1 cells in response to the direct culture on Pure Mg, Mg2Ag and Extreme High Pure Mg (XHP Mg) alloy samples. Our results demonstrated that long-term culturing of MC3T3-E1 cells on Pure Mg and Mg2Ag alloys induce time-dependent expression of active caspase-3 (active casp-3) and cleaved PARP-1 (cl. PARP-1), the hallmark of apoptosis reactions concomitant with a significant increase in the number of dead cells. However, direct culture on XHP Mg material results in a lower number of dead cells in comparison to Pure Mg and Mg2Ag alloys. Furthermore, XHP Mg materials influence expression of apoptotic markers in a process resembles that of observed in osteogenic condition apparently indicative of MC3T3-E1 osteodifferentiation. This study indicates that Mg alloy samples mediated differential apoptotic reactions of MC3T3-E1 cells can be ascribed to factors such as distinct topography and hydrophobicity features of Mg material surfaces, contrasting nature/composition of corrosion products as well as different impurities of these materials. Therefore, initial Mg alloys surface preparation, controlling the growth and composition of corrosion products and Mg alloys purity enhancement are necessary steps towards optimizing the Mg alloys usage in medical orthopedic applications.

The control of stem cell morphology and differentiation using three-dimensional printed scaffold architecture

In this work, we investigated the interactions of human mesenchymal stem cells (hMSCs) with three-dimensional (3D) printed scaffolds displaying different scaffold architectures. Pressure-assisted microsyringe system was used to fabricate scaffolds with square (SQR), hexagonal (HEX), and octagonal (OCT) architectures defined by various degrees of curvatures. OCT represents the highest degree of curvature followed by HEX, and SQR is composed of linear struts without curvature. Scaffolds were fabricated from poly(L-lactic acid) and poly(tyrosol carbonate). We found that hMSCs attached and spread by taking the shape of the individual struts, exhibiting high aspect ratios (ARs) and mean cell area when cultured on OCT scaffolds as compared with those cultured on HEX and SQR scaffolds. In contrast, cells appeared bulkier with low AR on SQR scaffolds. These significant changes in cell morphology directly correlate with the stem cell lineage commitment, such that 80 ± 1% of the hMSCs grown on OCT scaffolds differentiated into osteogenic lineage, compared with 70 ± 4% and 62 ± 2% of those grown on HEX and SQR scaffolds, respectively. Cells on OCT scaffolds also showed 2.5 times more alkaline phosphatase activity compared with cells on SQR scaffolds. This study demonstrates the importance of scaffold design to direct stem cell differentiation, and aids in the development of novel 3D scaffolds for bone regeneration.

Biological responses to M13 bacteriophage modified titanium surfaces in vitro

Phage-based materials have showed great potential in tissue engineering application. However, it is unknown what inflammation response will happen to this kind of materials. This work is to explore the biological responses to M13 bacteriophage (phage) modified titanium surfaces in vitro from the aspects of their interaction with macrophages, osteoblasts and mineralization behavior. Pretreated Ti surface, Ti surfaces with noncrosslinked phage film (APP) and crosslinked phage film (APPG) were compared. Phage films could limit the macrophage adhesion and activity due to inducing adherent-cell apoptosis. The initial inflammatory activity (24h) caused by phage films was relatively high with more production of TNF-α, but in the later stage (7-10days) inflammatory response was reduced with lower TNF-α, IL-6 and higher IL-10. In addition, phage films improved osteoblast adhesion, differentiation, and hydroapatite (HA)-forming via a combination of topographical and biochemcial cues. The noncrosslinked phage film displayed the best immunomodulatory property, osteogenic activity and HA mineralization ability. This work provides better understanding of inflammatory and osteogenetic activity of phage-based materials and contributes to their future application in tissue engineering.

STATEMENT OF SIGNIFICANCE

In vivo, the bone and immune cells share a common microenvironment, and are being affected by similar cytokines, signaling molecules, transcription factors and membrane receptors. Ideal implants should cause positive biological response, including adequate and appropriate inflammatory reaction, well-balanced bone formation and absorption. Phage-based materials have showed great potential in tissue engineering application. However, at present it is unknown what inflammation response will happen to this kind of materials. A good understanding of the immune response possibly induced by phage-based materials is needed. This work studied the osteoimmunomodulation property of phage films on titanium surface, involving inflammatory response, osteogenic activity and biomineralization ability. It provides more understanding of the phage-based materials and contributes to their future application in tissue engineering.

Foreign Body Response to Silicone in Cochlear Implant Electrodes in the Human

HYPOTHESIS

Silicone as part of a cochlear implant electrode may be responsible for a foreign body response in the human.

BACKGROUND

Clinical evidence of a foreign body response to a cochlear implant has been reported. In a previous study, particulate material found within the fibrous sheath and within macrophages surrounding a cochlear implant has been identified as being consistent with platinum. However, to date, there has been no histologic evidence of a role for silicone in this cellular immune response.

METHODS

A total of 44 temporal bone specimens from 36 patients were reviewed by light microscopy for evidence of presumed platinum and/or silicone foreign bodies in an extracellular or intracellular location. Identification of cell type involved in phagocytosis of foreign body material was accomplished using CD163 immunostaining. The identity and source of the foreign body material was confirmed using energy-dispersive X-ray spectroscopy and scanning electron microscopy.

RESULTS

Evidence for both platinum and silicone was found in all 44 specimens. In three patients, anti-CD 163 immunostaining demonstrated phagocytized platinum and silicone foreign bodies. In five specimens, energy-dispersive X-ray spectroscopy demonstrated that the birefringent foreign bodies were consistent with silicone. Scanning electron microscopy of two electrodes removed from temporal bones demonstrated small cracks, fragmentation, and small circular defects in the silicone carrier.

CONCLUSION

Histologic evidence of a foreign body response to the presence of platinum and silicone in a cochlear implant has been demonstrated and may be responsible for some reported delayed failures or extrusion.

Functional biocompatibility testing of silicone breast implants and a novel classification system based on surface roughness

PURPOSE

Increasing numbers of women undergo breast implantation for cosmetic and reconstructive purposes. Contracture of the fibrous capsule, which encases the implant leads to significant pain and reoperation. Texture, wettability and the cellular reaction to implant surfaces are poorly understood determinants of implant biocompatibility. The aim of this study was to evaluate the in-vitro characteristics of a range of commercial available implants using a macrophage based assay of implant biocompatibility and a quantitative assessment of wettability and texture.

METHODS

Thirteen commercially available surfaces were subjected to wettability and texture characterisation using scanning and laser confocal microscopy. THP-1 macrophages were cultured on their surfaces and assessed using Integrin αV immunocytochemistry, SEM and RT-PCR for the expression of TNF-Alpha, IL-6, IL-10 and a cytokine array for the production of TNF-alpha, IL-10, IL-1RA and IL1β; important indicators of inflammation and macrophage polarization.

RESULTS

Textured surfaces can be accurately sub-categorized dependent upon roughness and re-entrant features into four main types (macro, micro, meso and nano-textured surfaces). Significant (P < 0.0001) differences in implant hydrophobicity and texture exist. Certain surfaces promoted poor macrophage polarization and an innate potential to foster a proinflammatory response. A subgroup analysis showed that texture had a variable effect on markers of inflammation in these surfaces.

CONCLUSIONS

We propose a classification of implant surfaces based on roughness and present a macrophage based assay of breast implant biocompatibility with a quantitative assessment of implant wettability and texture. The breast implant surface-cell interaction is variable and sufficient to alter healing response and capsular contracture fate in-vivo.

Effects of age-related shifts in cellular function and local microenvironment upon the innate immune response to implants

The host macrophage response is now well recognized as a predictor of the success or failure of biomaterial implants following placement. More specifically, shifts from an "M1" pro-inflammatory towards a more "M2-like" anti-inflammatory macrophage polarization profile have been shown to result in enhanced material integration and/or tissue regeneration downstream. As a result, a number of biomaterials-based approaches to controlling macrophage polarization have been developed. However, the ability to promote such activity is predicated upon an in-depth, context-dependent understanding of the host response to biomaterials. Recent work has shown the impacts of both tissue location and tissue status (i.e. underlying pathology) upon the host innate immune response to implants, representing a departure from a focus upon implant material composition and form. Thus, the ideas of "biocompatibility," the host macrophage reaction, and ideal material requirements and modification strategies may need to be revisited on a patient, tissue, and disease basis. Immunosenescence, dysregulation of macrophage function, and delayed resolution of immune responses in aged individuals have all been demonstrated, suggesting that the host response to biomaterials in aged individuals should differ from that in younger individuals. However, despite the increasing usage of implantable medical devices in aged patients, few studies examining the effects of aging upon the host response to biomaterials and the implications of this response for long-term integration and function have been performed. The objective of the present manuscript is to review the putative effects of aging upon the host response to implanted materials and to advance the hypothesis that age-related changes in the local microenvrionement, with emphasis on the extracellular matrix, play a previously unrecognized role in determining the host response to implants.

Combinatorial Therapies After Spinal Cord Injury: How Can Biomaterials Help?

Traumatic spinal cord injury (SCI) results in an immediate loss of motor and sensory function below the injury site and is associated with a poor prognosis. The inhibitory environment that develops in response to the injury is mainly due to local expression of inhibitory factors, scarring and the formation of cystic cavitations, all of which limit the regenerative capacity of endogenous or transplanted cells. Strategies that demonstrate promising results induce a change in the microenvironment at- and around the lesion site to promote endogenous cell repair, including axonal regeneration or the integration of transplanted cells. To date, many of these strategies target only a single aspect of SCI; however, the multifaceted nature of SCI suggests that combinatorial strategies will likely be more effective. Biomaterials are a key component of combinatorial strategies, as they have the potential to deliver drugs locally over a prolonged period of time and aid in cell survival, integration and differentiation. Here we summarize the advantages and limitations of widely used strategies to promote recovery after injury and highlight recent research where biomaterials aided combinatorial strategies to overcome some of the barriers of spinal cord regeneration.

Long term performance evaluation of small-diameter vascular grafts based on polyvinyl alcohol hydrogel and dextran and MSCs-based therapies using the ovine pre-clinical animal model

The functional and structural performance of a 5cm synthetic small diameter vascular graft (SDVG) produced by the copolymerization of polyvinyl alcohol hydrogel with low molecular weight dextran (PVA/Dx graft) associated to mesenchymal stem cells (MSCs)-based therapies and anticoagulant treatment with heparin, clopidogrel and warfarin was tested using the ovine model during the healing period of 24 weeks. The results were compared to the ones obtained with standard expanded polyetetrafluoroethylene grafts (ePTFE graft). Blood flow, vessel and graft diameter measurements, graft appearance and patency rate (PR), thrombus, stenosis and collateral vessel formation were evaluated by B-mode ultrasound, audio and color flow Doppler. Graft and regenerated vessels morphologic evaluation was performed by scanning electronic microscopy (SEM), histopathological and immunohistochemical analysis. All PVA/Dx grafts could maintain a similar or higher PR and systolic/diastolic laminar blood flow velocities were similar to ePTFE grafts. CD14 (macrophages) and α-actin (smooth muscle) staining presented similar results in PVA/Dx/MSCs and ePTFE graft groups. Fibrosis layer was lower and endothelial cells were only detected at graft-artery transitions where it was added the MSCs. In conclusion, PVA/Dx graft can be an excellent scaffold candidate for vascular reconstruction, including clinic mechanically challenging applications, such as SDVGs, especially when associated to MSCs-based therapies to promote higher endothelialization and lower fibrosis of the vascular prosthesis, but also higher PR values.

Effects of aging upon the host response to implants

Macrophage polarization during the host response is now a well-accepted predictor of outcomes following material implantation. Immunosenescence, dysregulation of macrophage function, and delayed resolution of immune responses in aged individuals have all been demonstrated, suggesting that host responses to materials in aged individuals should differ from those in younger individuals. However, few studies examining the effects of aging upon the host response have been performed. The present work sought to elucidate the impacts of aging upon the host response to polypropylene mesh implanted into 8-week-old and 18-month-old mice. The results showed that there are significant differences in macrophage surface marker expression, migration, and polarization during the early host macrophage response and delayed resolution of the host response in 18-month-old versus 8-week-old mice. These differences could not be attributed to cell-intrinsic defects alone, suggesting that the host macrophage response to implants is likely also dictated to a significant degree by the local tissue microenvironment. These results raise important questions about the design and testing of materials and devices often intended to treat aged individuals and suggest that an improved understanding of patient- and context-dependent macrophage responses has the potential to improve outcomes in aged individuals. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1281-1292, 2017.

Electrospun poly-ε-caprolactone scaffold modified with catalytic nitric oxide generation and heparin for small-diameter vascular graft

Vascular grafts are significantly needed in peripheral vascular surgery; however, small diameter grafts are not always available, and synthetic grafts perform poorly because of acute thrombosis and neointimal proliferation after implantation.

Activation of Macrophages in Response to Biomaterials

Macrophages are the initial biologic responders to biomaterials. These highly plastic immune sentinels control and modulate responses to materials, foreign or natural. The responses may vary from immune stimulatory to immune suppressive. Several parameters have been identified that influence macrophage response to biomaterials, specifically size, geometry, surface topography, hydrophobicity, surface chemistry, material mechanics, and protein adsorption. In this review, the influence of these parameters is supported with examples of both synthetic and naturally derived materials and illustrates that a combination of these parameters ultimately influences macrophage responses to the biomaterial. Having an understanding of these properties may lead to highly efficient design of biomaterials with desirable biologic response properties.

Carbon Nanostructures in Bone Tissue Engineering

BACKGROUND

Recent advances in developing biocompatible materials for treating bone loss or defects have dramatically changed clinicians' reconstructive armory. Current clinically available reconstructive options have certain advantages, but also several drawbacks that prevent them from gaining universal acceptance. A wide range of synthetic and natural biomaterials is being used to develop tissue-engineered bone. Many of these materials are currently in the clinical trial stage.

METHODS

A selective literature review was performed for carbon nanostructure composites in bone tissue engineering.

RESULTS

Incorporation of carbon nanostructures significantly improves the mechanical properties of various biomaterials to mimic that of natural bone. Recently, carbon-modified biomaterials for bone tissue engineering have been extensively investigated to potentially revolutionize biomaterials for bone regeneration.

CONCLUSION

This review summarizes the chemical and biophysical properties of carbon nanostructures and discusses their functionality in bone tissue regeneration.

The pathology of the foreign body reaction against biomaterials

The healing process after implantation of biomaterials involves the interaction of many contributing factors. Besides their in vivo functionality, biomaterials also require characteristics that allow their integration into the designated tissue without eliciting an overshooting foreign body reaction (FBR). The targeted design of biomaterials with these features, thus, needs understanding of the molecular mechanisms of the FBR. Much effort has been put into research on the interaction of engineered materials and the host tissue. This elucidated many aspects of the five FBR phases, that is protein adsorption, acute inflammation, chronic inflammation, foreign body giant cell formation, and fibrous capsule formation. However, in practice, it is still difficult to predict the response against a newly designed biomaterial purely based on the knowledge of its physical-chemical surface features. This insufficient knowledge leads to a high number of factors potentially influencing the FBR, which have to be analyzed in complex animal experiments including appropriate data-based sample sizes. This review is focused on the current knowledge on the general mechanisms of the FBR against biomaterials and the influence of biomaterial surface topography and chemical and physical features on the quality and quantity of the reaction. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 927-940, 2017.

A Different Approach for Usage of the Implant Materials: The Composite Graft Prefabrication

With all implanted materials, a certain sequence of biological events occurs following the implantation. This process is destructive to the implant and peri-implant tissues. The aforementioned sequence of biological events may be responsible for the complications. In this study, the natural biologic process following implantation was completed in an area other than the final implantation area. The aim was to keep the peri-implant tissues in the final implantation area away from the process. In the control group, the porous polyethylene discs were implanted to subcutaneous area on the frontal bone of the rats. A month after the implantation, macroscopic and microscopic examinations were performed. In the study group, the discs were implanted primarily above the rectus abdominis muscle of the rats. It was named as "the composite graft prefabrication." Twenty-one days after the first implantation, the discs were removed from the rectus muscle and implanted to subcutaneous area on the frontal bone of the rats. A month after the final implantation, macroscopic and microscopic examinations were performed. In macroscopic examination, all possible complications were evaluated. In microscopic examination, apoptosis, fibrosis, inflammation, and fibrovascular in-growing were evaluated. In the control group, implant exposure was observed in 3 of the rats. In the study group, no complications were observed. Although there was no statistical difference between 2 groups in the microscopic findings, at first glance, the inflammation seemed to be the factor responsible for the complication in the control group. According to the macroscopic results, the composite graft prefabrication seemed to be effective in preventing complications.