A review on macrophage responses to biomaterials

Surface immobilized α-1 acid glycoprotein and collagen VI modulate mouse macrophage polarization and reduce the foreign body capsule

Macrophages are widely recognized in modulating the foreign body response, and the manner in which they do so largely depends on their activation state, often referred to as their polarization. This preliminary study demonstrates that surface immobilized α-1 acid glycoprotein (AGP), as well as collagen VI (Col6) in conjunction with AGP, can direct macrophages towards the M2 polarization state in vitro and modify the foreign body response in vivo. AGP and Col6 are immobilized onto poly(2-hydroxyethyl methacrylate) (pHEMA) surfaces using carbonyl diimidazole chemistry. Mouse bone marrow derived macrophages are cultured on modified surfaces with or without lipopolysaccharide stimulation. Surface modified pHEMA discs are implanted subcutaneously into mice to observe differences in the foreign body response. After stimulation with lipopolysaccharide, macrophages cultured on AGP or Col6 modified surfaces showed a reduction in TNF-α expression compared to controls. Arg1 expression was also increased in macrophages cultured on modified surfaces. Explanted tissues showed that the foreign body capsule around implants with AGP or AGP and Col6 modification had reduced thickness, while also being more highly vascularized. These data demonstrate that α-1 acid glycoprotein and collagen VI could potentially be used for the surface modification of medical devices to influence macrophage polarization leading to a reduced and modulated foreign body response.

Chitosan-based biomaterials promote bone regeneration by regulating macrophage fate

The development of various osteogenic biomaterials has not only promoted the development of bone tissue engineering but also provided more possibilities for bone defect repair. However, most previous studies have focused on the interaction of biomaterials on endogenous or exogenous stem cells involved in the bone regeneration process while neglecting the effect of changes in the immune microenvironment of bone defect sites on bone regeneration after biomaterial implantation into the host. With the development of bone immunology, the role of various immune cells, especially macrophages, in bone regeneration has gradually attracted the attention of researchers. An increasing number of studies have begun to target macrophages to better promote bone regeneration by modulating the fate of macrophages in a spatiotemporally ordered manner to mimic the changes in the immune microenvironment of bone defect sites during the natural repair process of bone tissue. Chitosan is one of the most abundant natural polysaccharides in the world. In recent years, various chitosan-based biomaterials have been widely used in macrophage fate modulation and bone regeneration. In this review, we review the interaction between macrophages and scaffold materials, general information about chitosan, the modulation of macrophage fate by chitosan-based biomaterials, and their application in bone regeneration.

Materials Strategies to Overcome the Foreign Body Response

The foreign body response (FBR) is an immune-mediated reaction that can occur with most biomaterials and biomedical devices. The FBR initiates a deterioration in the performance of implantable devices, representing a longstanding challenge that consistently hampers their optimal utilization. Over the last decade, significant strides are achieved based on either hydrogel design or surface modifications to mitigate the FBR. This review delves into recent material strategies aimed at mitigating the FBR. Further, the authors look forward to future novel anti-FBR materials from the perspective of clinical translation needs. Such prospective materials hold the potential to attenuate local immune responses, thereby significantly enhancing the overall performance of implantable devices.

Unraveling and Harnessing the Immune Response at the Cell-Biomaterial Interface for Tissue Engineering Purposes

Biomaterials are defined as "engineered materials" and include a range of natural and synthetic products, designed for their introduction into and interaction with living tissues. Biomaterials are considered prominent tools in regenerative medicine that support the restoration of tissue defects and retain physiologic functionality. Although commonly used in the medical field, these constructs are inherently foreign toward the host and induce an immune response at the material-tissue interface, defined as the foreign body response (FBR). A strong connection between the foreign body response and tissue regeneration is suggested, in which an appropriate amount of immune response and macrophage polarization is necessary to trigger autologous tissue formation. Recent developments in this field have led to the characterization of immunomodulatory traits that optimizes bioactivity, the integration of biomaterials and determines the fate of tissue regeneration. This review addresses a variety of aspects that are involved in steering the inflammatory response, including immune cell interactions, physical characteristics, biochemical cues, and metabolomics. Harnessing the advancing knowledge of the FBR allows for the optimization of biomaterial-based implants, aiming to prevent damage of the implant, improve natural regeneration, and provide the tools for an efficient and successful in vivo implantation.

Titanium corrosion products from dental implants and their effect on cells and cytokine release: A review

INTRODUCTION

Titanium is considered to be an inert material owing to the ability of the material to form a passive titanium oxide layer. However, once the titanium oxide layer is lost, it can lead to exposure of the underlying titanium substructure and can undergo corrosion.

SUMMARY

The article explores the role of titanium ions and particles from dental implants on cells, cytokine release, and on the systemic redistribution of these particles as well as theories proposed to elucidate the effects of these particles on peri-implant inflammation based on evidence from in-vitro, human, and animal studies. Titanium particles and ions have a pro-inflammatory and cytotoxic effect on cells and promote the release of pro-inflammatory mediators like cytokines. Three theories to explain etiopathogenesis have been proposed, one based on microbial dysbiosis, the second based on titanium particles and ions and the third based on a synergistic effect between microbiome and titanium particles on the host.

CONCLUSION

There is clear evidence from in-vitro and limited human and animal studies that titanium particles released from dental implants have a detrimental effect on cells directly and through the release of pro-inflammatory cytokines. Future clinical and translational studies are required to clarify the role of titanium particles and ions in peri-implant inflammation and the etiopathogenesis of peri-implantitis.

Challenges and Pitfalls of Research Designs Involving Magnesium-Based Biomaterials: An Overview

Magnesium-based biomaterials hold remarkable promise for various clinical applications, offering advantages such as reduced stress-shielding and enhanced bone strengthening and vascular remodeling compared to traditional materials. However, ensuring the quality of preclinical research is crucial for the development of these implants. To achieve implant success, an understanding of the cellular responses post-implantation, proper model selection, and good study design are crucial. There are several challenges to reaching a safe and effective translation of laboratory findings into clinical practice. The utilization of Mg-based biomedical devices eliminates the need for biomaterial removal surgery post-healing and mitigates adverse effects associated with permanent biomaterial implantation. However, the high corrosion rate of Mg-based implants poses challenges such as unexpected degradation, structural failure, hydrogen evolution, alkalization, and cytotoxicity. The biocompatibility and degradability of materials based on magnesium have been studied by many researchers in vitro; however, evaluations addressing the impact of the material in vivo still need to be improved. Several animal models, including rats, rabbits, dogs, and pigs, have been explored to assess the potential of magnesium-based materials. Moreover, strategies such as alloying and coating have been identified to enhance the degradation rate of magnesium-based materials in vivo to transform these challenges into opportunities. This review aims to explore the utilization of Mg implants across various biomedical applications within cellular (in vitro) and animal (in vivo) models.

Electrospun nanofiber mats caged the mammalian macrophages on their surfaces and prevented their inflammatory responses independent of the fiber diameter

Poly-ε-caprolactone (PCL) has been widely used as biocompatible materials in tissue engineering. They have been used in mammalian cell proliferation to polarization and differentiation. Their modified versions had regulatory activities on mammalian macrophages in vitro. There are also studies suggesting different nanofiber diameters might alter the biological activities of these materials. Based on these cues, we examined the inflammatory activities and adherence properties of mammalian macrophages on electrospun PCL nanofibrous scaffolds formed with PCL having different nanofiber diameters. Our results suggest that macrophages could easily attach and get dispersed on the scaffolds. Macrophages lost their inflammatory cytokine TNF and IL6 production capacity in the presence of LPS when they were incubated on nanofibers. These effects were independent of the mean fiber diameters. Overall, the scaffolds have potential to be used as biocompatible materials to suppress excessive inflammatory reactions during tissue and organ transplantation by caging and suppressing the inflammatory cells.

Macrophages in guided bone regeneration: potential roles and future directions

Guided bone regeneration (GBR) is one of the most widely used and thoroughly documented alveolar bone augmentation surgeries. However, implanting GBR membranes inevitably triggers an immune response, which can lead to inflammation and failure of bone augmentation. It has been shown that GBR membranes may significantly improve in vivo outcomes as potent immunomodulators, rather than solely serving as traditional barriers. Macrophages play crucial roles in immune responses and participate in the entire process of bone injury repair. The significant diversity and high plasticity of macrophages complicate our understanding of the immunomodulatory mechanisms underlying GBR. This review provides a comprehensive summary of recent findings on the potential role of macrophages in GBR for bone defects in situ. Specifically, macrophages can promote osteogenesis or fibrous tissue formation in bone defects and degradation or fibrous encapsulation of membranes. Moreover, GBR membranes can influence the recruitment and polarization of macrophages. Therefore, immunomodulating GBR membranes are primarily developed by improving macrophage recruitment and aggregation as well as regulating macrophage polarization. However, certain challenges remain to be addressed in the future. For example, developing more rational and sophisticated sequential delivery systems for macrophage activation reagents; addressing the interference of bone graft materials and dental implants; and understanding the correlations among membrane degradation, macrophage responses, and bone regeneration.

Emerging factors affecting peri-implant bone metabolism

Implant dentistry has evolved to the point that standard implant osseointegration is predictable. This is attributed in part to the advancements in material sciences that have led toward improvements in implant surface technology and characteristics. Nonetheless, there remain several cases where implant therapy fails (specifically at early time points), most commonly attributed to factors affecting bone metabolism. Among these patients, smokers are known to have impaired bone metabolism and thus be subject to higher risks of early implant failure and/or late complications related to the stability of the peri-implant bone and mucosal tissues. Notably, however, emerging data have unveiled other critical factors affecting osseointegration, namely, those related to the metabolism of bone tissues. The aim of this review is to shed light on the effects of implant-related factors, like implant surface or titanium particle release; surgical-related factors, like osseodensification or implanted biomaterials; various drugs, like selective serotonin reuptake inhibitors, proton pump inhibitors, anti-hypertensives, nonsteroidal anti-inflammatory medication, and statins, and host-related factors, like smoking, diet, and metabolic syndrome on bone metabolism, and aseptic peri-implant bone loss. Despite the infectious nature of peri-implant biological complications, these factors must be surveyed for the effective prevention and management of peri-implantitis.

Mechanical force increases tooth movement and promotes remodeling of alveolar bone defects augmented with bovine bone mineral

BACKGROUND

Orthodontic tooth movement (OTM) in a region containing alveolar bone defects with insufficient height and width is hard to achieve. Bovine bone mineral (Bio-Oss) is available to restore the alveolar defect; however, whether the region augmented with a bovine bone mineral graft (BG) is feasible for OTM, and the mechanisms by which macrophages remodel the BG material, is uncertain under the mechanical force induced by OTM.

MATERIAL AND METHODS

Rats were divided into three groups: OTM (O), OTM + BG material (O + B), and Control (C). First molars were extracted to create bone defects in the O and O + B groups with bovine bone mineral grafting in the latter. Second molars received OTM towards the bone defects in both groups. After 28 days, maxillae were analyzed using microfocus-computed tomography (μCT) and scanning-electron-microscopy (SEM); and macrophages (M1/M2) were stained using immunofluorescence. THP-1 cell-induced macrophages were cultured under mechanical force (F), BG material (B), or both (F + B). Phagocytosis-related signaling molecules (cAMP/PKA/RAC1) were analyzed, and conditioned media was analyzed for MMP-9 and cytokines (IL-1β, IL-4).

RESULTS

Our study demonstrated that alveolar defects grafted with BG materials are feasible for OTM, with significantly increased OTM distance, bone volume, and trabecular thickness in this region. SEM observation revealed that the grafts served as a scaffold for cells to migrate and remodel the BG materials in the defect during OTM. Moreover, the population of M2 macrophages increased markedly both in vivo and in cell culture, with enhanced phagocytosis via the cAMP/PKA/RAC1 pathway in response to mechanical force in combination with BG particles. By contrast, M1 macrophage populations were decreased under the same circumstances. In addition, M2 macrophage polarization was also indicated by elevated IL-4 levels, reduced IL-1β levels, and less active MMP-9 in cell culture.

CONCLUSION

This study explored the mechanisms of mechanical force-induced alveolar bone remodeling with bovine bone mineral grafts during OTM. The results might provide molecular insights into the related clinical problems of whether we can move teeth into the grafted materials; and how these materials become biologically remodeled and degraded under mechanical force.

Effects of glass-ceramic produced by the sol-gel route in macrophages recruitment and polarization into bone tissue regeneration

Effective bone substitute biomaterials remain an important challenge in patients with large bone defects. Glass ceramics produced by different synthesis routes may result in changes in the material physicochemical properties and consequently affect the success or failure of the bone healing response. To investigate the differences in the orchestration of the inflammatory and healing process in bone grafting and repair using different glass-ceramic routes production. Thirty male Wistar rats underwent surgical unilateral parietal defects filled with silicate glass-ceramic produced by distinct routes: BS - particulate glass-ceramic produced via the fusion/solidification route, and BG - particulate glass-ceramic produced via the sol-gel route. After 7, 14, and 21 days from biomaterial grafting, parietal bones were removed to be analyzed under H&E and Massons' Trichome staining, and immunohistochemistry for CD206, iNOS, and TGF-β. Our findings demonstrated that the density of lymphocytes and plasma cells was significantly higher in the BS group at 45, and 7 days compared to the BG group, respectively. Furthermore, a significant increase of foreign body giant cells (FBGCs) in the BG group at day 7, compared to BS was found, demonstrating early efficient recruitment of FBGCs against sol-gel-derived glass-ceramic particulate (BS group). According to macrophage profiles, CD206+ macrophages enhanced at the final periods of both groups, being significantly higher at 45 days of BS compared to the BG group. On the other hand, the density of transformation growth factor beta (TGF-β) positive cells on 21 days were the highest in BG, and the lowest in the BS group, demonstrating a differential synergy among groups. Noteworthy, TGF-β+ cells were significantly higher at 21 days of BG compared to the BS group. Glass-ceramic biomaterials can act differently in the biological process of bone remodeling due to their route production, being the sol-gel route more efficient to activate M2 macrophages and specific FBGCs compared to the traditional route. Altogether, these features lead to a better understanding of the effectiveness of inflammatory response for biomaterial degradation and provide new insights for further preclinical and clinical studies involved in bone healing.

Effect of unsoluble corrosion products of WE43 alloys in vitro on macrophages

Magnesium alloys have been used to manufacture biodegradable implants, bone graft substitutes, and cardiovascular stents. WE43 was the most widely used magnesium alloy. The degradation process begins when the magnesium alloy stent is implanted in the body and comes into contact with body fluid. The degradation products include hydrogen, Mg2+ , local alkaline environment, and unsoluble products. A large number of studies focused on Mg2+ and pH in vitro, and in vivo of magnesium alloys, but few studies on unsoluble corrosion products (UCPs). In this study, UCPs of WE43 alloy were prepared by immersion in vitro, and their effects on macrophages were investigated. The results showed that the unsoluble corrosion products were Mg24Y5, Mg12YNd, and MgCO3 ·3H2 O, which were dose-dependent on the apoptosis and necrosis of macrophages. After phagocytosis of UCPs, macrophages mainly metabolize in lysosome, and autophagy also participates in the metabolism of UCPs. It also decreases mitochondrial membrane potential and increases lysosomes, endoplasmic reticulum stress, and P2X7 receptor activation. These will increase reactive oxygen species (ROS) in cells, activating NLRP3 inflammatory corpuscles, activating the downstream pro-IL18 and pro-IL1β, and converting it to IL-18, and IL-1β. However, its pro-inflammatory effect is far lower than that of the classical Lipopolysaccharide (LPS) pro-inflammatory pathway. This work has increased our understanding of magnesium alloy metabolism and provides new ideas for the clinical application of magnesium alloys.

Injectable polyisocyanide hydrogel as healing supplement for connective tissue regeneration in an abdominal wound model

In pelvic organ prolapse (POP) patients, the uterus, bladder and/or rectum descends into vagina due to weakened support tissues. High recurrence rates after POP surgery suggest an urgent need for improved surgical outcomes. Our aim is to promote connective tissue healing that results in stimulated tissue support functions by surgically applying a hydrogel functionalized with biological cues. We used known vaginal wound healing promoting factors (basic fibroblast growth factor, β-estradiol, adipose-derived stem cells) in the biomimetic and injectable polyisocyanide (PIC) hydrogel, which in itself induces regenerative vaginal fibroblast behavior. The regenerative capacity of injected PIC hydrogel, and the additional pro-regenerative effects of these bioactive factors was evaluated in abdominal wounds in rabbits. Assessment of connective tissue healing (tensile testing, histology, immunohistochemistry) revealed that injection with all PIC formulations resulted in a statistically significant stiffness and collagen increase over time, in contrast to sham. Histological evaluation indicated new tissue growth with moderate to mild immune activity at the hydrogel - tissue interface. The results suggest that PIC injection in an abdominal wound improves healing towards regaining load-bearing capacity, which encourages us to investigate application of the hydrogel in a more translational vaginal model for POP surgery in sheep.

Generation of Haploid Spermatids on Silk Fibroin-Alginate-Laminin-Based Porous 3D Scaffolds

In vitro production of sperm is a desirable idea for fertility preservation in azoospermic men and prepubertal boys suffering from cancer. In this study, a biocompatible porous scaffold based on a triad mixture of silk fibroin (SF), alginate (Alg), and laminin (LM) is developed to facilitate the differentiation of mouse spermatogonia stem cells (SSCs). Following SF extraction, the content is analyzed by SDS-PAGE and stable porous 3D scaffolds are successfully prepared by merely Alg, SF, and a combination of Alg-SF, or Alg-SF-LM through freeze-drying. Then, the biomimetic scaffolds are characterized regarding the structural and biological properties, water absorption capacity, biocompatibility, biodegradability, and mechanical behavior. Neonatal mice testicular cells are seeded on three-dimensional scaffolds and their differentiation efficiency is evaluated using real-time PCR, flow cytometry, immunohistochemistry. Blend matrices showed uniform porous microstructures with interconnected networks, which maintained long-term stability and mechanical properties better than homogenous structures. Molecular analysis of the cells after 21 days of culture showed that the expression of differentiation-related proteins in cells that are developed in composite scaffolds is significantly higher than in other groups. The application of a composite system can lead to the differentiation of SSCs, paving the way for a novel infertility treatment landscape in the future.

Safety of terminally gamma-ray-sterilized screws coated with fibroblast growth factor 2-calcium phosphate composite layers in non-human primates

Screws coated with fibroblast growth factor 2 (FGF-2)-calcium phosphate (CP) composite layers exhibit enhanced soft tissue and bone formation and angiogenesis because of the biological activity of FGF-2. Furthermore, the mitogenic activity of the FGF-2 within the composite layers remains unchanged after gamma-ray sterilization, which may improve the storage stability prior to clinical use. However, the in vivo safeties of these screws as spinal implants remain unknown. Here, a randomized controlled trial, involving non-human primates, investigated the safety of using FGF-2-CP composite layer-coated screws after either gamma-ray sterilization or aseptic processing. Titanium alloy screws coated with FGF-2-CP composite layers and subjected to either gamma-ray sterilization at 25 kGy (GS group) or aseptic storage (AS group) were implanted into the vertebral bodies of two cynomolgus monkeys exceeding 12 weeks (day 99). Physiological, histological, and radiographic investigations were performed to evaluate the safeties of the screws. There were no serious adverse events, such as surgical site infection, significant loss of body weight, or abnormal blood test results. No radiolucent areas were observed around the screws from the GS or AS group throughout the study. In the intraosseous region, no significant differences were observed in bone and fibrous tissue apposition rates and rate of bone formation between the two groups (p = 0.49, 0.77, and 0.11, respectively). Neither tumor lesions nor accumulation of lymphocytes and neutrophils were observed in either group. Our data suggest that FGF-2-CP composite layer-coated screws subjected to terminal gamma-ray sterilization are as safe as those fabricated in aseptic processing.

3D-printed placental-derived bioinks for skin tissue regeneration with improved angiogenesis and wound healing properties

Extracellular matrix (ECM)-based bioinks has attracted much attention in recent years for 3D printing of native-like tissue constructs. Due to organ unavailability, human placental ECM can be an alternative source for the construction of 3D print composite scaffolds for the treatment of deep wounds. In this study, we use different concentrations (1.5%, 3% and 5%w/v) of ECM derived from the placenta, sodium-alginate and gelatin to prepare a printable bioink biomimicking natural skin. The printed hydrogels' morphology, physical structure, mechanical behavior, biocompatibility, and angiogenic property are investigated. The optimized ECM (5%w/v) 3D printed scaffold is applied on full-thickness wounds created in a mouse model. Due to their unique native-like structure, the ECM-based scaffolds provide a non-cytotoxic microenvironment for cell adhesion, infiltration, angiogenesis, and proliferation. In contrast, they do not show any sign of immune response to the host. Notably, the biodegradation, swelling rate, mechanical property, cell adhesion and angiogenesis properties increase with the increase of ECM concentrations in the construct. The ECM 3D printed scaffold implanted into deep wounds increases granulation tissue formation, angiogenesis, and re-epithelialization due to the presence of ECM components in the construct, when compared with printed scaffold with no ECM and no treatment wound. Overall, our findings demonstrate that the 5% ECM 3D scaffold supports the best deep wound regeneration in vivo, produces a skin replacement with a cellular structure comparable to native skin.

Long-Term Degradation Assessment of a Polyurethane-Based Surgical Adhesive-Assessment and Critical Consideration of Preclinical In Vitro and In Vivo Testing

Tissue adhesives constitute a great possibility to improve conventional wound closure. In contrast to sutures, they enable nearly immediate hemostasis and can prevent fluid or air leaks. In the present study, a poly(ester)urethane-based adhesive was investigated which already proved to be suitable for different indications, such as reinforcing vascular anastomosis and sealing liver tissue. Using in vitro and in vivo setups, the degradation of the adhesives was monitored over a period of up to 2 years, to evaluate long-term biocompatibility and determine degradation kinetics. For the first time, the complete degradation of the adhesive was documented. In subcutaneous locations, tissue residues were found after 12 months and in intramuscular locations, tissue degradation was complete after about 6 months. A detailed histological evaluation of the local tissue reaction revealed good biocompatibility throughout the different degradation stages. After full degradation, complete remodeling to physiological tissue was observed at the implant locations. In addition, this study critically discusses common issues related to the assessment of biomaterial degradation kinetics in the context of medical device certification. This work highlighted the importance and encouraged the implementation of biologically relevant in vitro degradation models to replace animal studies or at least reduce the number of animals in preclinical testing prior to clinical studies. Moreover, the suitability of frequently used implantation studies based on ISO 10993-6 at standard locations was critically discussed, especially in light of the associated lack of reliable predictions for degradation kinetics at the clinically relevant site of implantation.

Vorinostat decrease M2 macrophage polarization through ARID1A6488delG/HDAC6/IL-10 signaling pathway in endometriosis-associated ovarian carcinoma

Endometriosis is a common disease in women and may be one of the factors that induces malignant epithelial ovarian tumors. Previous studies suggested that endometriosis is related to ARID1A mutation mediating the expression of HDAC6, but the detailed pathogenic mechanism is still unclear. First, we collected endometriosis-associated ovarian carcinoma (EAOC) clinical samples and examined the expression of HDAC6. Our results found that the high HDAC6 expression group was positively correlated with EAOC histology (P = 0.015), stage (P < 0.000), and tumor size (P < 0.000) and inversely correlated with survival (P < 0.000). We also found that ARID1A^6488delG/HDAC6 induced M2 polarization of macrophages through IL-10. In addition, the HDAC inhibitor (HDACi) vorinostat inhibited cell growth and blocked the effect of HDAC6. Tomographic microscopy was used to monitor the live cell morphology of these treated cells, and we found that vorinostat treatment resulted in substantial cell apoptosis by 3 h 42 min. Next, we established a transgenic mouse model of EAOC and found that vorinostat significantly reduced the size of ovarian tumors by inhibiting M2 macrophage polarization in mice. Together, these data demonstrate that the signaling pathway of E4F1/ARID1A^6488delG/HDAC6/GATA3 mediates macrophage polarization and provides a novel immune cell-associated therapeutic strategy targeting IL-10 in EAOC.

Holistic View on the Structure of Immune Response: Petri Net Model

The simulation of immune response is a challenging task because quantitative data are scarce. Quantitative theoretical models either focus on specific cell-cell interactions or have to make assumptions about parameters. The broad variation of, e.g., the dimensions and abundance between lymph nodes as well as between individual patients hampers conclusive quantitative modeling. No theoretical model has been established representing a consensus on the set of major cellular processes involved in the immune response. In this paper, we apply the Petri net formalism to construct a semi-quantitative mathematical model of the lymph nodes. The model covers the major cellular processes of immune response and fulfills the formal requirements of Petri net models. The intention is to develop a model taking into account the viewpoints of experienced pathologists and computer scientists in the field of systems biology. In order to verify formal requirements, we discuss invariant properties and apply the asynchronous firing rule of a place/transition net. Twenty-five transition invariants cover the model, and each is assigned to a functional mode of the immune response. In simulations, the Petri net model describes the dynamic modes of the immune response, its adaption to antigens, and its loss of memory.

Antimicrobial-Loaded Polyacrylamide Hydrogels Supported on Titanium as Reservoir for Local Drug Delivery

Arthroplasty is a highly successful treatment to restore the function of a joint. The contamination of the implant via bacterial adhesion is the first step toward the development of device-associated infections. The emerging concern about antimicrobial resistance resulted in a growing interest to develop alternative therapeutic strategies. Thus, the increment in the incidence of bacterial periprosthetic infections, the complexity of treating infections caused by organisms growing in biofilms, together with the rise in antibiotic resistant bacteria, expose the need to design novel surfaces that provide innovative solutions to these rising problems. The aim of this work is to develop a coating on titanium (Ti) suitable for inhibiting bacterial adhesion and proliferation, and hence, biofilm formation on the surface. We have successfully prepared polyacrylamide hydrogels containing the conventional antibiotic ampicillin (AMP), silver nanoparticles (AgNPs), and both, AMP and AgNPs. The release of the antibacterial agents from the gelled to aqueous media resulted in an excellent antibacterial action of the loaded hydrogels against sessile S. aureus. Moreover, a synergic effect was achieved with the incorporation of both AMP and AgNPs in the hydrogel, which highlights the importance of combining antimicrobial agents having different targets. The polyacrylamide hydrogel coating on the Ti surface was successfully achieved, as it was demonstrated by FTIR, contact angle, and AFM measurements. The modified Ti surfaces having the polyacrylamide hydrogel film containing AgNPs and AMP retained the highest antibacterial effect against S. aureus as it was found for the unsupported hydrogels. The modified surfaces exhibit an excellent cytocompatibility, since healthy, flattened MC3T3-E1 cells spread on the surfaces were observed. In addition, similar macrophage RAW 264.7 adhesion was found on all the surfaces, which could be related to a low macrophage activation. Our results indicate that AMP and AgNP-loaded polyacrylamide hydrogel films on Ti are a good alternative for designing efficient antibacterial surfaces having an excellent cytocompatibility without inducing an exacerbated immune response. The approach emerges as a superior alternative to the widely used direct adsorption of therapeutic agents on surfaces, since the antimicrobial-loaded hydrogel coatings open the possibility of modulating the concentration of the antimicrobial agents to enhance bacterial killing, and then, reducing the risk of infections in implantable materials.

Macrophages: From Simple Phagocyte to an Integrative Regulatory Cell for Inflammation and Tissue Regeneration-A Review of the Literature

The understanding of macrophages and their pathophysiological role has dramatically changed within the last decades. Macrophages represent a very interesting cell type with regard to biomaterial-based tissue engineering and regeneration. In this context, macrophages play a crucial role in the biocompatibility and degradation of implanted biomaterials. Furthermore, a better understanding of the functionality of macrophages opens perspectives for potential guidance and modulation to turn inflammation into regeneration. Such knowledge may help to improve not only the biocompatibility of scaffold materials but also the integration, maturation, and preservation of scaffold-cell constructs or induce regeneration. Nowadays, macrophages are classified into two subpopulations, the classically activated macrophages (M1 macrophages) with pro-inflammatory properties and the alternatively activated macrophages (M2 macrophages) with anti-inflammatory properties. The present narrative review gives an overview of the different functions of macrophages and summarizes the recent state of knowledge regarding different types of macrophages and their functions, with special emphasis on tissue engineering and tissue regeneration.

Exposure of Cyprinus carpio var. larvae to PVC microplastics reveals significant immunological alterations and irreversible histological organ damage

Microplastics have become pervasive in ambient aquatic ecosystems over the last decade and are currently a serious global scale concern. To evaluate the potential toxic effects of PVC (polyvinyl chloride) microplastics on the immune functions of freshwater fish, this study undertook a conducted chronic 60-day dietary exposure experiment with Cyprinus carpio var. larvae. We exposed the fish to four microplastic treatments of different concentrations (food rationed diets): no-plastic (control), 10%, 20% and 30%. At the end of the experimental period the impacts of microplastics on the histology, biochemistry, ROS (reactive oxygen species) levels and gene transcription of immune organs were investigated. The results revealed that PVC microplastics induced cytoplasmic vacuolation in the liver, damaged villi in the intestine, inflammatory cell infiltration, hemosiderosis and vacuolar degeneration in the spleen, glomeruli tuft shrinkage and aggregation of melanin macrophage cells in the kidney. Moreover, following PVC microplastics exposure, ROS levels in the liver and protein levels of pro-inflammatory cytokines including IL-6, IL-8, and TNFα in the liver and serum were increased. Furthermore, modifications in the activities of non-specific immunoenzyme ACP (Acid phosphatase), AKP (alkaline phosphatase), LZM (lysozyme), and expression levels of a range of immune-related genes were observed. Using various techniques at the histological, biochemical and molecular levels, our findings demonstrated the effects of PVC microplastics on changes and imbalances in the immune status of carp. The results of this study provide basic toxicological data toward elucidating and quantifying the impacts of microplastics immunotoxicity on aquatic organisms.

Advances in surface modifications of the silicone breast implant and impact on its biocompatibility and biointegration

Silicone breast implants are commonly used for cosmetic and oncologic surgical indications owing to their inertness and being nontoxic. However, complications including capsular contracture and anaplastic large cell lymphoma have been associated with certain breast implant surfaces over time. Novel implant surfaces and modifications of existing ones can directly impact cell-surface interactions and enhance biocompatibility and integration. The extent of foreign body response induced by breast implants influence implant success and integration into the body. This review highlights recent advances in breast implant surface technologies including modifications of implant surface topography and chemistry and effects on protein adsorption, and cell adhesion. A comprehensive online literature search was performed for relevant articles using the following keywords silicone breast implants, foreign body response, cell adhesion, protein adsorption, and cell-surface interaction. Properties of silicone breast implants impacting cell-material interactions including surface roughness, wettability, and stiffness, are discussed. Recent studies highlighting both silicone implant surface activation strategies and modifications to enhance biocompatibility in order to prevent capsular contracture formation and development of anaplastic large cell lymphoma are presented. Overall, breast implant surface modifications are being extensively investigated in order to improve implant biocompatibility to cater for increased demand for both cosmetic and oncologic surgeries.

Biocompatibility and degradation comparisons of four biodegradable copolymeric osteosynthesis systems used in maxillofacial surgery: A goat model with four years follow-up

Applying biodegradable osteosyntheses avoids the disadvantages of titanium osteosyntheses. However, foreign-body reactions remain a major concern and evidence of complete resorption is lacking. This study compared the physico-chemical properties, histological response and radiographs of four copolymeric biodegradable osteosynthesis systems in a goat model with 48-months follow-up. The systems were implanted subperiosteally in both tibia and radius of 12 Dutch White goats. The BioSorb FX [poly(70LLA-co-30DLLA)], Inion CPS [poly([70–78.5]LLA-co-[16–24]DLLA-co-4TMC)], SonicWeld Rx [poly(DLLA)], LactoSorb [poly(82LLA-co-18GA)] systems and a negative control were randomly implanted in each extremity. Samples were assessed at 6-, 12-, 18-, 24-, 36-, and 48-month follow-up. Surface topography was performed using scanning electron microscopy (SEM). Differential scanning calorimetry and gel permeation chromatography were performed on initial and explanted samples. Histological sections were systematically assessed by two blinded researchers using (polarized) light microscopy, SEM and energy-dispersive X-ray analysis. The SonicWeld Rx system was amorphous while the others were semi-crystalline. Foreign-body reactions were not observed during the complete follow-up. The SonicWeld Rx and LactoSorb systems reached bone percentages of negative controls after 18 months while the BioSorb Fx and Inion CPS systems reached these levels after 36 months. The SonicWeld Rx system showed the most predictable degradation profile. All the biodegradable systems were safe to use and well-tolerated (i.e., complete implant replacement by bone, no clinical or histological foreign body reactions, no [sterile] abscess formation, no re-interventions needed), but nanoscale residual polymeric fragments were observed at every system's assessment.

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Foreign-body reactions are a major concern of biodegradable osteosyntheses.

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Amorphous poly(DLLA) showed the most predictable degradation profile.

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Nanoscale residual polymeric fragments could still be observed after 4 years.

Dysfunction of macrophages leads to diabetic bone regeneration deficiency

Insufficient bone matrix formation caused by diabetic chronic inflammation can result in bone nonunion, which is perceived as a worldwide epidemic, with a substantial socioeconomic and public health burden. Macrophages in microenvironment orchestrate the inflammation and launch the process of bone remodeling and repair, but aberrant activation of macrophages can drive drastic inflammatory responses during diabetic bone regeneration. In diabetes mellitus, the proliferation of resident macrophages in bone microenvironment is limited, while enhanced myeloid differentiation of hematopoietic stem cells (HSCs) leads to increased and constant monocyte recruitment and thus macrophages shift toward the classic pro-inflammatory phenotype, which leads to the deficiency of bone regeneration. In this review, we systematically summarized the anomalous origin of macrophages under diabetic conditions. Moreover, we evaluated the deficit of pro-regeneration macrophages in the diabetic inflammatory microenvironment. Finally, we further discussed the latest developments on strategies based on targeting macrophages to promote diabetic bone regeneration. Briefly, this review aimed to provide a basis for modulating the biological functions of macrophages to accelerate bone regeneration and rescue diabetic fracture healing in the future.

Macrophage-extracellular matrix interactions: Perspectives for tissue engineered heart valve remodeling

In situ heart valve tissue engineering approaches have been proposed as promising strategies to overcome the limitations of current heart valve replacements. Tissue engineered heart valves (TEHVs) generated from in vitro grown tissue engineered matrices (TEMs) aim at mimicking the microenvironmental cues from the extracellular matrix (ECM) to favor integration and remodeling of the implant. A key role of the ECM is to provide mechanical support to and attract host cells into the construct. Additionally, each ECM component plays a critical role in regulating cell adhesion, growth, migration, and differentiation potential. Importantly, the immune response to the implanted TEHV is also modulated biophysically via macrophage-ECM protein interactions. Therefore, the aim of this review is to summarize what is currently known about the interactions and signaling networks occurring between ECM proteins and macrophages, and how these interactions may impact the long-term in situ remodeling outcomes of TEMs. First, we provide an overview of in situ tissue engineering approaches and their clinical relevance, followed by a discussion on the fundamentals of the remodeling cascades. We then focus on the role of circulation-derived and resident tissue macrophages, with particular emphasis on the ramifications that ECM proteins and peptides may have in regulating the host immune response. Finally, the relevance of these findings for heart valve tissue engineering applications is discussed.

In Vivo Comparison of Synthetic Macroporous Filamentous and Sponge-like Skin Substitute Matrices Reveals Morphometric Features of the Foreign Body Reaction According to 3D Biomaterial Designs

Synthetic macroporous biomaterials are widely used in the field of skin tissue engineering to mimic membrane functions of the native dermis. Biomaterial designs can be subclassified with respect to their shape in fibrous designs, namely fibers, meshes or fleeces, respectively, and porous designs, such as sponges and foams. However, synthetic matrices often have limitations regarding unfavorable foreign body responses (FBRs). Severe FBRs can result in unfavorable disintegration and rejection of an implant, whereas mild FBRs can lead to an acceptable integration of a biomaterial. In this context, comparative in vivo studies of different three-dimensional (3D) matrix designs are rare. Especially, the differences regarding FBRs between synthetically derived filamentous fleeces and sponge-like constructs are unknown. In the present study, the FBRs on two 3D matrix designs were explored after 25 days of subcutaneous implantation in a porcine model. Cellular reactions were quantified histopathologically to investigate in which way the FBR is influenced by the biomaterial architecture. Our results show that FBR metrics (polymorph-nucleated cells and fibrotic reactions) were significantly affected according to the matrix designs. Our findings contribute to a better understanding of the 3D matrix tissue interactions and can be useful for future developments of synthetically derived skin substitute biomaterials.

Recent advances in nanomedicines for regulation of macrophages in wound healing

Macrophages are essential immune cells and play a major role in the immune response as pro-inflammatory or anti-inflammatory agents depending on their plasticity and functions. Infiltration and activation of macrophages are usually involved in wound healing. Herein, we first described macrophage polarization and their critical functions in wound healing process. It is addressed how macrophages collaborate with other immune cells in the wound microenvironment. Targeting macrophages by manipulating or re-educating macrophages in inflammation using nanomedicines is a novel and feasible strategy for wound management. We discussed the design and physicochemical properties of nanomaterials and their functions for macrophages activation and anti-inflammatory signaling during wound therapy. The mechanism of action of the strategies and appropriate examples are also summarized to highlight the pros and cons of those approaches. Finally, the potential of nanomedicines to modulate macrophage polarization for skin regeneration is discussed.

An in vivo toxicity assessment of piezoelectric sodium potassium niobate [NaxK1-xNbO3 (x = 0.2-0.8)] nanoparticulates towards bone tissue engineering approach

One of the recent challenges in the design/development of prosthetic orthopedic implants is to address the concern of local/systemic toxicity of debris particles, released due to wear or degradation. Such debris particles often lead to inflammation at the implanted site or aseptic loosening of the prosthesis which results in failure of the implant during long run. Several in vitro studies demonstrated the potentiality of piezoelectric sodium potassium niobate [Na_xK_1-xNbO₃ (x = 0.2, 0.5, 0.8), NKN] as an emerging next-generation polarizable orthopedic implant. In this perspective, we performed an in vivo study to examine the local and systemic toxicity of NKN nanoparticulates, as a first report. In the present study, male Wistar rats were intra-articularly injected to the knee joint with 100 μl of NKN nanoparticulates (25 mg/ml in normal saline). After 7 days of exposure, the histopathological analyses demonstrate the absence of any inflammation or dissemination of nanoparticulates in vital organs such as heart, liver, kidney and spleen. The anti-inflammatory cytokines (IL-4 and IL-10) profile analyses suggest the increased anti-inflammatory response in the treated rats as compared to non-injected (control) rats, preferably for the sodium and potassium rich NKN i.e., Na_0.8K_0.2NbO₃ and Na_0.2K_0.8NbO₃. The biochemical analyses revealed no pathological changes in the liver and kidney of particulate treated rats. The present study is the first proof to confirm the non-toxic nature of NKN nanoparticulates which provides a step forward towards the development of prosthetic orthopedic implants using biocompatible piezoelectric NKN ceramics.

Contextual fear conditioning regulates synapse-related gene transcription in mouse microglia

Microglia have been suggested to be involved in the underlying mechanism of conditional fear memory formation by regulating inflammatory cytokines. However, the mechanism linking microglia and neuronal activity related to fear conditioning remains unclear. This study characterized the transcription profile of microglia in a fear memory conditional mouse model. Compared with those in control mice microglia, the most significantly induced genes were synapse-related, whereas immune-related genes were reduced due to fear memory consolidation. Whilst the increased expression of synapse-related genes was reversed after fear memory extinction, that of immunological genes was not, strongly suggesting a connection between microglia, neurons, and a dysregulated immune response following contextual fear conditioning. Furthermore, in the hippocampal microglia, we found that the expression of neurotransmitter release regulators, γ-aminobutyric acid (GABA) receptor GABRB3 and synapsin 1/2, increased under fear memory consolidation and restored (decreased) after extinction. In addition, compared with the transcription profile in peripheral monocytes, few overlapping genes were not enriched in biological processes. Taken together, the identified conditional fear stress-induced changes in mouse microglial transcription profiles suggest that microglia-neuron communication mediates contextual fear conditioning.

Two-Photon Polymerization of 2.5D and 3D Microstructures Fostering a Ramified Resting Phenotype in Primary Microglia

Microglia are the resident macrophages of the central nervous system and contribute to maintaining brain’s homeostasis. Current 2D “petri-dish” in vitro cell culturing platforms employed for microglia, are unrepresentative of the softness or topography of native brain tissue. This often contributes to changes in microglial morphology, exhibiting an amoeboid phenotype that considerably differs from the homeostatic ramified phenotype in healthy brain tissue. To overcome this problem, multi-scale engineered polymeric microenvironments are developed and tested for the first time with primary microglia derived from adult rhesus macaques. In particular, biomimetic 2.5D micro- and nano-pillar arrays (diameters = 0.29–1.06 µm), featuring low effective shear moduli (0.25–14.63 MPa), and 3D micro-cages (volume = 24 × 24 × 24 to 49 × 49 × 49 μm³) with and without micro- and nano-pillar decorations (pillar diameters = 0.24–1 µm) were fabricated using two-photon polymerization (2PP). Compared to microglia cultured on flat substrates, cells growing on the pillar arrays exhibit an increased expression of the ramified phenotype and a higher number of primary branches per ramified cell. The interaction between the cells and the micro-pillar-decorated cages enables a more homogenous 3D cell colonization compared to the undecorated ones. The results pave the way for the development of improved primary microglia in vitro models to study these cells in both healthy and diseased conditions.

Fucoidan-derived carbon dots against Enterococcus faecalis biofilm and infected dentinal tubules for the treatment of persistent endodontic infections

Enterococcus faecalis (E. faecalis) biofilm-associated persistent endodontic infections (PEIs) are one of the most common tooth lesions, causing chronic periapical periodontitis, root resorption, and even tooth loss. Clinical root canal disinfectants have the risk of damaging soft tissues (e.g., mucosa and tongue) and teeth in the oral cavity, unsatisfactory to the therapy of PEIs. Nanomaterials with remarkable antibacterial properties and good biocompatibility have been developed as a promising strategy for removing pathogenic bacteria and related biofilm. Herein, carbon dots (CDs) derived from fucoidan (FD) are prepared through a one-pot hydrothermal method for the treatment of PEIs. The prepared FDCDs (7.15 nm) with sulfate groups and fluorescence property are well dispersed and stable in water. Further, it is found that in vitro FDCDs display excellent inhibiting effects on E. faecalis and its biofilm by inducing the formation of intracellular and extracellular reactive oxygen species and altering bacterial permeability. Importantly, the FDCDs penetrated the root canals and dentinal tubules, removing located E. faecalis biofilm. Moreover, the cellular assays show that the developed FDCDs have satisfactory cytocompatibility and promote macrophage recruitment. Thus, the developed FDCDs hold great potential for the management of PEIs.

Titanium or Biodegradable Osteosynthesis in Maxillofacial Surgery? In Vitro and In Vivo Performances

Osteosynthesis systems are used to fixate bone segments in maxillofacial surgery. Titanium osteosynthesis systems are currently the gold standard. However, the disadvantages result in symptomatic removal in up to 40% of cases. Biodegradable osteosynthesis systems, composed of degradable polymers, could reduce the need for removal of osteosynthesis systems while avoiding the aforementioned disadvantages of titanium osteosyntheses. However, disadvantages of biodegradable systems include decreased mechanical properties and possible foreign body reactions. In this review, the literature that focused on the in vitro and in vivo performances of biodegradable and titanium osteosyntheses is discussed. The focus was on factors underlying the favorable clinical outcome of osteosyntheses, including the degradation characteristics of biodegradable osteosyntheses and the host response they elicit. Furthermore, recommendations for clinical usage and future research are given. Based on the available (clinical) evidence, biodegradable copolymeric osteosyntheses are a viable alternative to titanium osteosyntheses when applied to treat maxillofacial trauma, with similar efficacy and significantly lower symptomatic osteosynthesis removal. For orthognathic surgery, biodegradable copolymeric osteosyntheses are a valid alternative to titanium osteosyntheses, but a longer operation time is needed. An osteosynthesis system composed of an amorphous copolymer, preferably using ultrasound welding with well-contoured shapes and sufficient mechanical properties, has the greatest potential as a biocompatible biodegradable copolymeric osteosynthesis system. Future research should focus on surface modifications (e.g., nanogel coatings) and novel biodegradable materials (e.g., magnesium alloys and silk) to address the disadvantages of current osteosynthesis systems.

Upcycling Compact Discs for Flexible and Stretchable Bioelectronic Applications

Electronic waste is a global issue brought about by the short lifespan of electronics. Viable methods to relieve the inundated disposal system by repurposing the enormous amount of electronic waste remain elusive. Inspired by the need for sustainable solutions, this study resulted in a multifaceted approach to upcycling compact discs. The once-ubiquitous plates can be transformed into stretchable and flexible biosensors. Our experiments and advanced prototypes show that effective, innovative biosensors can be developed at a low-cost. An affordable craft-based mechanical cutter allows pre-determined patterns to be scored on the recycled metal, an essential first step for producing stretchable, wearable electronics. The active metal harvested from the compact discs was inert, cytocompatible, and capable of vital biopotential measurements. Additional studies examined the material’s resistive emittance, temperature sensing, real-time metabolite monitoring performance, and moisture-triggered transience. This sustainable approach for upcycling electronic waste provides an advantageous research-based waste stream that does not require cutting-edge microfabrication facilities, expensive materials, and high-caliber engineering skills.

Electronic waste is a global issue brought about by the short lifespan of electronics. Here, the authors report a process to upcycle compact discs into flexible and stretchable bio-electronics.

From hurdle to springboard: The macrophage as target in biomaterial-based bone regeneration strategies

The past decade has seen a growing appreciation for the role of the innate immune response in mediating repair and biomaterial directed tissue regeneration. The long-held view of the host immune/inflammatory response as an obstacle limiting stem cell regenerative activity, has given way to a fresh appreciation of the pivotal role the macrophage plays in orchestrating the resolution of inflammation and launching the process of remodelling and repair. In the context of bone, work over the past decade has established an essential coordinating role for macrophages in supporting bone repair and sustaining biomaterial driven osteogenesis. In this review evidence for the role of the macrophage in bone regeneration and repair is surveyed before discussing recent biomaterial and drug-delivery based approaches that target macrophage modulation with the goal of accelerating and enhancing bone tissue regeneration.

Macrophage-like Cells Are Responsive to Titania Nanotube Intertube Spacing-An In Vitro Study

With the introduction of a new interdisciplinary field, osteoimmunology, today, it is well acknowledged that biomaterial-induced inflammation is modulated by immune cells, primarily macrophages, and can be controlled by nanotopographical cues. Recent studies have investigated the effect of surface properties in modulating the immune reaction, and literature data indicate that various surface cues can dictate both the immune response and bone tissue repair. In this context, the purpose of the present study was to investigate the effects of titanium dioxide nanotube (TNT) interspacing on the response of the macrophage-like cell line RAW 264.7. The cells were maintained in contact with the surfaces of flat titanium (Ti) and anodic TNTs with an intertube spacing of 20 nm (TNT20) and 80 nm (TNT80), under standard or pro-inflammatory conditions. The results revealed that nanotube interspacing can influence macrophage response in terms of cell survival and proliferation, cellular morphology and polarization, cytokine/chemokine expression, and foreign body reaction. While the nanostructured topography did not tune the macrophages’ differentiation into osteoclasts, this behavior was significantly reduced as compared to flat Ti surface. Overall, this study provides a new insight into how nanotubes’ morphological features, particularly intertube spacing, could affect macrophage behavior.

Early Immune Response in Foreign Body Reaction Is Implant/Material Specific

The design of novel biomaterials should directly influence the host-immune system and steer it towards high biocompatibility. To date, new implants/materials have been tested for biocompatibility in vitro in cell cultures and in vivo in animal models. The current methods do not reflect reality (cell cultures) or are very time-consuming and deliver results only after weeks (animal model). In this proof-of-concept study, the suitability of a Whole Blood Stimulation Assay (WBSA) in combination with a Protein Profiler Array (PPA), as a readily available and cost-effective screening tool, was investigated. Three different biomaterials based on poly(lactic-co-glycolic acid (PLGA), calcium sulphate/-carbonate (CS) and poly(methyl methacrylate) (PMMA) were exposed to native whole blood from three volunteers and subsequently screened with a PPA. Individual reproducible protein profiles could be detected for all three materials after 24 h of incubation. The most intense reaction resulted from the use of PLGA, followed by CS. If even marginal differences in implants can be reflected in protein profiles, the combination of WBSA and PPA could serve as an early biocompatibility screening tool in the development of novel biomaterials. This may also lead to a reduction in costs and the amount of animal testing required.

Foreign body response to synthetic polymer biomaterials and the role of adaptive immunity

Implanted biomaterials elicit a series of distinct immune and repair-like responses that are collectively known as the foreign body reaction (FBR). These include processes involving innate immune inflammatory cells and wound repair cells that contribute to the encapsulation of biomaterials with a dense collagenous and largely avascular capsule. Numerous studies have shown that the early phase is dominated by macrophages that fuse to form foreign body giant cells that are considered a hallmark of the FBR. With the advent of more precise cell characterization techniques, specific macrophage subsets have been identified and linked to more or less favorable outcomes. Moreover, studies comparing synthetic- and natural-based polymer biomaterials have allowed the identification of macrophage subtypes that distinguish between fibrotic and regenerative responses. More recently, cells associated with adaptive immunity have been shown to participate in the FBR to synthetic polymers. This suggests the existence of cross-talk between innate and adaptive immune cells that depends on the nature of the implants. However, the exact participation of adaptive immune cells, such as T and B cells, remains unclear. In fact, contradictory studies suggest either the independence or dependence of the FBR on these cells. Here, we review the evidence for the involvement of adaptive immunity in the FBR to synthetic polymers with a focus on cellular and molecular components. In addition, we examine the possibility that such biomaterials induce specific antibody responses resulting in the engagement of adaptive immune cells.

Bioinspired ultra-low fouling coatings on medical devices to prevent device-associated infections and thrombosis

Addressing thrombosis and biofouling of indwelling medical devices within healthcare institutions is an ongoing problem. In this work, two types of ultra-low fouling surfaces (i.e., superhydrophobic and lubricant-infused slippery surfaces) were fabricated to enhance the biocompatibility of commercial medical grade silicone rubber (SR) tubes that are widely used in clinical care. The superhydrophobic (SH) coatings on the tubing substrates were successfully created by dip-coating in superhydrophobic paints consisting of polydimethylsiloxane (PDMS), perfluorosilane-coated hydrophobic zinc oxide (ZnO) and copper (Cu) nanoparticles (NPs) in tetrahydrofuran (THF). The SH surfaces were converted to lubricant-infused slippery (LIS) surfaces through the infusion of silicone oil. The anti-biofouling properties of the coatings were investigated by adsorption of platelets, whole blood coagulation, and biofilm formation in vitro. The results revealed that the LIS tubes possess superior resistance to clot formation and platelet adhesion than uncoated and SH tubes. In addition, bacterial adhesion was investigated over 7 days in a drip-flow bioreactor, where the SH-ZnO-Cu tube and its slippery counterpart significantly reduced bacterial adhesion and biofilm formation of Escherichia coli relative to control tubes (>5 log10 and >3 log10 reduction, respectively). The coatings also demonstrated good compatibility with fibroblast cells. Therefore, the proposed coatings may find potential applications in high-efficiency on-demand prevention of biofilm and thrombosis formation on medical devices to improve their biocompatibility and reduce the risk of complications from medical devices.

Immunological Risk Assessment of Xenogeneic Dural Patch by Comparing with Raw Material via GTKO Mice

OBJECTIVE

In this study, α-Gal epitope-deficient (GGTA1 knockout (GTKO)) mice were used to assess the immunological risks of xenogeneic dural patch by comparing with raw material.

METHODS

The xenogeneic dural patch (T2) was prepared from bovine pericardium (T1, raw material) through decellularization and carboxymethyl chitosan (CMCS) coating. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to characterize the collagen fibers and surface microstructural changes in the T1 and T2 samples. The remnant α-Gal epitopes and DNA of implants were detected by standardized method. T1 and T2 were implanted subcutaneously into GTKO mice for 4 and 12 weeks, respectively, and the negative control group (Con) was only performed sham operation. The total serum antibody, anti-Gal antibody, and splenic lymphocyte subtypes were analyzed by ELISA or flow cytometry, and histological analysis of implant-tissue was performed by H&E and Masson stain.

RESULTS

TEM and Sirius red staining showed that the collagen fibers in the dural patch were closely arranged, and SEM showed that a loose three-dimensional structure was successfully constructed on the surface of the dural patch after CMCS coating. The remnant DNA in T2 was 24.64 ± 8.73 ng/mg (dry weight), and clearance of α-Gal epitope was up to 99.83% compared to T1. The significant increases in serum total IgM, anti-Gal IgG, and anti-Gal IgM at 4 weeks and the significant changes in anti-Gal IgG and spleen lymphocyte at 12 weeks were observed in the T1 group, but no significant change was observed in the T2 group, compared to the control group. Histological semiquantitative analysis showed severe cell and tissue responses at 4 weeks and a moderate response at 12 weeks in the T1 group, while a moderate response at 4 weeks and a slight response at 12 weeks in the T2 group.

CONCLUSIONS

The results demonstrated that the xenogeneic dural patch has a lower and acceptable immunological risk compared to the raw material and control, respectively. On the other hand, it was suggested that GTKO mice are useful experimental model for immunological risk assessment of animal tissue-derived biomaterials.

A prospective study on long-term trace metal accumulation in hair: Is there any difference between minimally invasive repair of pectus excavatum and carinatum?

BACKGROUND

To date, there is no study about trace metal level increases in hair after stainless steel pectus bar implantation. We aimed to determine whether there was any significant increase in the levels of trace metals in the hair of children who underwent minimally invasive repair of pectus excavatum (MIRPE) and minimally invasive repair of pectus carinatum (MIRPC).

MATERIALS AND METHODS

In this prospective study, we collected the data of 223 patients who underwent MIRPE and MIRPC between November 2013 and August 2020. The levels of main components of the stainless steel pectus bar ("PES", Medxpert GmbH, Escbach, Germany) namely Cr, Fe, Ni, and Mo in hair were analyzed. The study involved two study groups: A group of patients who underwent MIRPE with a single bar (n = 112) and a group of patients who underwent MIRPC (n = 71). Both groups were analyzed in two different timelines: A group of consecutive patients prior to bar implantation and a group of the same patients who underwent bar removal after a mean time of 34.6 ± 5.1 months.

RESULTS

Statistically significant increases in all studied trace metal levels were observed in the single-bar MIRPE group. In the MIRPC group, the accumulation of studied trace metals was no statistically significant. The double-bar MIRPE group had higher trace metal increase rates compared to single-bar MIRPE group (p>0.05).

CONCLUSION

In our study; increases in iron, chrome, nickel and molybdenum levels were observed in both MIRPE and MIRPC patients by hair trace metal analysis; but these increases were statistically significant in only MIRPE group.

NanoZnO-modified titanium implants for enhanced anti-bacterial activity, osteogenesis and corrosion resistance

Titanium (Ti) implants are widely used in dentistry and orthopedics owing to their excellent corrosion resistance, biocompatibility, and mechanical properties, which have gained increasing attention from the viewpoints of fundamental research and practical applications. Also, numerous studies have been carried out to fine-tune the micro/nanostructures of Ti and/or incorporate chemical elements to improve overall implant performance. Zinc oxide nanoparticles (nano-ZnO) are well-known for their good antibacterial properties and low cytotoxicity along with their ability to synergize with a variety of substances, which have received increasingly widespread attention as biomodification materials for implants. In this review, we summarize recent research progress on nano-ZnO modified Ti-implants. Their preparation methods of nano-ZnO modified Ti-implants are introduced, followed by a further presentation of the antibacterial, osteogenic, and anti-corrosion properties of these implants. Finally, challenges and future opportunities for nano-ZnO modified Ti-implants are proposed.

Insights into oxidative stress in bone tissue and novel challenges for biomaterials

The presence of Reactive Oxygen Species (ROS) in bone can influence resident cells behaviour as well as the extra-cellular matrix composition and the tissue architecture. Aging, in addition to excessive overloads, unbalanced diet, smoking, predisposing genetic factors, lead to an increase of ROS and, if it is accompanied with an inappropriate production of scavengers, promotes the generation of oxidative stress that encourages bone catabolism. Furthermore, bone injuries can be triggered by numerous events such as road and sports accidents or tumour resection. Although bone tissue possesses a well-known repair and regeneration capacity, these mechanisms are inefficient in repairing large size defects and bone grafts are often necessary. ROS play a fundamental role in response after the implant introduction and can influence its success. This review provides insights on the mechanisms of oxidative stress generated by an implant in vivo and suitable ways for its modulation. The local delivery of active molecules, such as polyphenols, enhanced bone biomaterial integration evidencing that the management of the oxidative stress is a target for the effectiveness of an implant. Polyphenols have been widely used in medicine for cardiovascular, neurodegenerative, bone disorders and cancer, thanks to their antioxidant and anti-inflammatory properties. In addition, the perspective of new smart biomaterials and molecular medicine for the oxidative stress modulation in a programmable way, by the use of ROS responsive materials or by the targeting of selective molecular pathways involved in ROS generation, will be analysed and discussed critically.

Macrophages, the main marker in biocompatibility evaluation of new hydrogels after subcutaneous implantation in rats

Biocompatibility of materials is one of the most important conditions for their successful application in tissue regeneration and repair. Cell-surface interactions stimulate adhesion and activation of macrophages whose acquaintance can assist in designing novel biomaterials that promote favorable macrophage-biomaterial surface interactions for clinical application. This study is designed to determine the distribution and number of macrophages as a means of biocompatibility evaluation of two newly synthesized materials [silver/poly(vinyl alcohol) (Ag/PVA) and silver/poly(vinyl alcohol)/graphene (Ag/PVA/Gr) nanocomposite hydrogels] in vivo, with approval of the Ethics Committee of the Faculty of Veterinary Medicine, University of Belgrade. Macrophages and giant cells were analyzed in tissue sections stained by routine H&E and immunohistochemical methods (CD68⁺). Statistical relevance was determined in the statistical software package SPSS 20 (IBM corp). The results of the study in terms of the number of giant cells localized around the implant showed that their number was highest on the seventh postoperative day (p.o.d.) in the group implanted with Ag/PVA hydrogels, and on the 30th p.o.d. in the group implanted with Ag/PVA/Gr. Interestingly, the number of macrophages measured in the capsular and pericapsular space was highest in the group implanted with the commercial Suprasorb^© material. The increased macrophage number, registered around the Ag/PVA/Gr implant on 60th p.o.d. indicates that the addition of graphene can, in a specific way, modulate different biological responses of tissues in the process of wound healing, regeneration, and integration.

T lymphocytes as critical mediators in tissue regeneration, fibrosis, and the foreign body response

Research on the foreign body response (FBR) to biomaterial implants has been focused on the roles that the innate immune system has on mediating tolerance or rejection of implants. However, the immune system also involves the adaptive immune response and it must be included in order to form a complete picture of the response to biomaterials and medical implants. In this review, we explore recent understanding about the roles of adaptive immune cells, specifically T cells, in modulating the immune response to biomaterial implants. The immune response to implants elicits a delicate balance between tissue repair and fibrosis that is mainly regulated by three types of T helper cell responses -T helper type 1, T helper type 2, and T helper type 17- and their crosstalk with innate immune cells. Interestingly, many T cell response mechanisms to implants overlap with the process of fibrosis or repair in different tissues. This review explores the fibrotic and regenerative T cell biology and draws parallels to T cell responses to biomaterials. Additionally, we also explore the biomedical engineering advancements in biomaterial applications in designing particle and scaffold systems to modulate T cell activity for therapeutics and devices. Not only do the deliberate engineering design of physical and chemical material properties and the direct genetic modulation of T cells not only offer insights to T cell biology, but they also present different platforms to develop immunomodulatory biomaterials. Thus, an in-depth understanding of T cells' roles can help to navigate the biomaterial-immune interactions and reconsider the long-lasting adaptive immune response to implants, which, in the end, contribute to the design of immunomodulatory medical implants that can advance the next generation of regenerative therapy. STATEMENT OF SIGNIFICANCE: This review article integrates knowledge of adaptive immune responses in tissue damage, wound healing, and medical device implantation. These three fields, often not discussed in conjunction, are important to consider when evaluating and designing biomaterials. Through incorporation of basic biological research alongside engineering research, we provide an important lens through which to evaluate adaptive immune contributions to regenerative medicine and medical device development.

Targeted ToF-SIMS Analysis of Macrophage Content from a Human Cranial Triphasic Calcium Phosphate Implant

Macrophages play a key role in determining the fate of implanted biomaterials, especially for biomaterials such as calcium phosphates (CaPs) where these cells play a vital role in material resorption and osteogenesis, as shown in different models, including clinical samples. Although substantial consideration is given to the design and validation of different CaPs, relatively little is known about their material-cell interaction. Specifically, the intracellular content of different CaP phases remains to be assessed, even though CaP-filled macrophages have been observed in several studies. In this study, 2D/3D ToF-SIMS imaging and multivariate analysis were directly applied on the histology samples of an explant to reveal the content of macrophages. The cellular content of the macrophages was analyzed to distinguish three CaP phases, monetite, beta-tricalcium phosphate, and pyrophosphate, which are all part of the monetite-based CaP implant composition under study. ToF-SIMS combined with histology revealed that the content of the identified macrophages was most similar to that of the pyrophosphate phase. This study is the first to uncover distinct CaP phases in macrophages from a human multiphasic CaP explant by targeted direct cell content analysis. The uncovering of pyrophosphate as the main phase found inside the macrophages is of great importance to understand the impact of the selected material in the process of biomaterial-instructed osteogenesis.

A pH-driven genipin gelator to engineer decellularized extracellular matrix-based tissue adhesives

Decellularized extracellular matrix (dECM) derived from natural ECM is receiving considerable interest as a promising component of tissue adhesives because of its high biocompatibility and tissue regenerative ability. However, the availability of dECM as a tissue adhesive is limited because of the lack of a gelator that can crosslink low concentrations of dECM to form hydrogels. Here, we report dECM-based tissue adhesives using a genipin gelator. Based on the pH-dependent reactivity of genipin, genipin-terminated 4 arm-poly(ethylene glycol) (GeniPEG) was synthesized. dECM-based hydrogels were formed within a few seconds of mixing GeniPEG and dECM at an optimum pH through crosslinking of dECM and self-crosslinking between GeniPEG molecules. The hydrogels crosslinked with GeniPEG exhibited greater tissue adhesive strength to porcine-derived aorta tissue than those crosslinked with genipin. Moreover, GeniPEG can be applied to various dECMs, including those from the urinary bladder, heart, liver, pancreas, and small intestine. In vivo implantation experiments demonstrated biocompatibility and biodegradability of the dECM-GeniPEG hydrogels. Therefore, this dECM-based hydrogel may extend the possibility and availability of dECM as an organ-specific tissue adhesive and contribute to successful minimally invasive surgery. STATEMENT OF SIGNIFICANCE: There is a strong need to develop highly functional tissue adhesives with high biocompatibility, tissue adhesive strength, and tissue regenerative ability. In this report, dECM-based tissue adhesives were reported using a pH-driven genipin-gelator. Focusing on the pH-dependent reactivity of genipin, genipin-based gelators were synthesized to form dECM-based hydrogels in response to pH changes. The crosslinking reaction proceeded within a few seconds to form hydrogels. The hydrogels obtained had greater tissue adhesion to aorta tissue than that of the free genipin crosslinker. This gelator can be applied to various types of dECMs. This dECM-based hydrogel had high biocompatibility and tissue adhesive properties and is useful for sealing wounds and preventing postoperative complications.

Functionalization of Silicone Surface with Drugs and Polymers for Regulation of Capsular Contracture

Breast reconstruction is achieved using silicone implants, which are currently associated with major complications. Several strategies have been considered to overcome the existing limitations as well as to improve their performance. Recently, surface modification has proved to be an effective clinical approach to prevent bacterial adhesion, reduce capsular thickness, prevent foreign body reactions, and reduce other implant-associated problems. This review article summarizes the ongoing strategies for the surface modification of silicone implants in breast reconstruction applications. The article mostly discusses two broad categories of surface modification: drug-mediated and polymer-based. Different kinds of drugs have been applied with silicone that are associated with breast reconstruction. Initially, this article discusses studies related to drugs immobilized on silicone implants, focusing on drug-loading methods and their effects on capsule contracture. Moreover, the pharmacological action of drugs on fibroblast cells is considered in this section. Next, the polymeric modification of the silicone surface is introduced, and we discuss its role in reducing capsule thickness at the cellular and biological levels. The polymeric modification techniques, their chemistry, and their physical properties are described in detail. Notably, polymer activities on macrophages and inflammation are also briefly discussed. Each of the reviewed articles is summarized, highlighting their discussion of capsular thickness, foreign body reactions, and bacterial attachment. The aim of this review is to provide the main points of some research articles regarding the surface modification of silicon, which can lead to a decrease in capsular thickness and provides better patient compliance.

In Vivo Biological Evaluation of Biodegradable Nanofibrous Membranes Incorporated with Antibiofilm Compounds

Guided bone regeneration involves excluding non-osteogenic cells from the surrounding soft tissues and allowing osteogenic cells originating from native bone to inhabit the defect. The aim of this work was to fabricate, analyze antibiofilm activity and evaluate in vivo biological response of poly (lactic-co-glycolic acid) (PLGA) electrospun membranes incorporated with tea tree oil and furan-2(5H)-one. Samples were exposed to Streptococcus mutans culture and after 48 h incubation, biofilm was evaluated by colony forming units (CFU/mL) followed by scanning electron microscopy. Additionally, seventy-five Balb-C mice were divided into five experimental groups for subcutaneous implantation: tea tree oil loaded PLGA electrospun fiber membrane, furanone loaded PLGA electrospun fiber membrane, neat PLGA electrospun fiber membrane, a commercially available PLGA membrane –Pratix^® and Sham (no-membrane implantation). Post implantation period of each experimental group (1, 3 and 9 weeks), samples were collected and processed for by histological descriptive and semiquantitative evaluation. Results showed a significant reduction of bacterial attachment on tea tree oil and furan-2(5H)-one incorporated membranes. Macrophage counts were significant found in all the materials implanted, although giant cells were predominantly associated with electrospun fiber membranes. The incorporation of antibiofilm compounds in nanofibers membranes did not incite inflammatory response significantly different in comparison with pure PLGA electrospun membranes, indicating its potential for development of novel functionalized membranes targeting the inhibition of bacterial biofilms on membrane-grafting materials.

Implementation of a Dynamic Co-Culture Model Abated Silver Nanoparticle Interactions and Nanotoxicological Outcomes In Vitro

The incorporation of engineered nanoparticles (NPs) into everyday consumer goods, products, and applications has given rise to the field of nanotoxicology, which evaluates the safety of NPs within biological environments. The unique physicochemical properties of NPs have made this an insurmountable challenge, as their reactivity and variable behavior have given rise to discrepancies between standard cell-based in vitro and animal in vivo models. In this study, enhanced in vitro models were generated that retained the advantages of traditional cell cultures, but incorporated the modifications of (1) inclusion of an activated immune element and (2) the presence of physiologically-relevant dynamic flow. Following verification that the human alveolar epithelial and macrophage (A549/U937) co-culture could be successfully sustained under both static and dynamic conditions, these cultures, in addition to a standard A549 static model, were challenged with 10 nm citrate coated silver NPs (AgNPs). This work identified a reshaping of the AgNP-cellular interface and differential biological responses following exposure. The presence of dynamic flow modified cellular morphology and reduced AgNP deposition by approximately 20% over the static exposure environments. Cellular toxicity and stress endpoints, including reactive oxygen species, heat shock protein 70, and secretion of pro-inflammatory cytokines, were found to vary as a function of both cellular composition and flow conditions; with activated macrophages and fluid flow both mitigating the severity of AgNP-dependent bioeffects. This work highlights the possibility of enhanced in vitro systems to assess the safety of engineered NPs and demonstrates their effectiveness in elucidating novel NP-cellular interactions and toxicological profiles.