Effects of biomaterial-induced inflammation on fibrosis and rejection

Bone Regeneration Facilitated by Autologous Bioscaffold Material: Liquid Phase of Concentrated Growth Factor with Dental Follicle Stem Cell Loading

The application of bioengineering techniques for achieving bone regeneration in the oral environment is an increasingly prominent field. However, the clinical use of synthetic materials carries certain risks. The liquid phase of concentrated growth factor (LPCGF), as a biologically derived material, exhibits superior biocompatibility. In this study, LPCGF was employed as a tissue engineering scaffold, hosting dental follicle cells (DFCs) to facilitate bone regeneration. Both in vivo and in vitro experimental results demonstrate that this platform significantly enhances the expression of osteogenic markers in DFCs, such as alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2), and type I collagen (Col1a1). Simultaneously, it reduces the expression of inflammation-related genes, particularly interleukin-6 (IL-6) and interleukin-8 (IL-8), thereby alleviating the negative impact of the inflammatory microenvironment on DFCs. Further investigation into potential mechanisms reveals that this process is regulated over time by the WNT pathway. Our research results demonstrate that LPCGF, with its favorable physical characteristics, holds great potential as a scaffold. It can effectively carry DFCs, thereby providing an optimal initial environment for bone regeneration. Furthermore, LPCGF endeavors to closely mimic the mechanisms of bone healing post-trauma to facilitate bone formation. This offers new perspectives and insights into bone regeneration engineering.

New approaches to second-degree burn healing: Polyvinyl alcohol membrane loaded to arnica combined to laser therapy

Second-degree burns require greater care, as the damage is more extensive and worrisome and the use of a biomaterial can help in the cell repair process, with better planning, low cost, and better accessibility. Arnica has anti-inflammatory and analgesic properties in skin lesions treatments and laser therapy is another therapeutic alternative for burns. Evaluate the effects of arnica incorporated into PVA associated or not with low intensity laser on burns in rats. PVA and PVA with arnica (PVA+A) were obtained and characterized physicochemically. Through in vivo studies, the effects of PVA and PVA+A with or without the application of laser on the lesions allowed histological and immunohistochemical analyzes. PVA+A was biocompatible and with sustained release of the active, being a promising pharmacological tool and confirmed that laser therapy was effective in accelerating the healing process, due to its potential biomodulator, improving inflammatory aspects, promoting rapid healing in skin lesions.

Uncovering the relationship between macrophages and polypropylene surgical mesh

Currently, in vitro testing examines the cytotoxicity of biomaterials but fails to consider how materials respond to mechanical forces and the immune response to them; both are crucial for successful long-term implantation. A notable example of this failure is polypropylene mid-urethral mesh used in the treatment of stress urinary incontinence (SUI). The mesh was largely successful in abdominal hernia repair but produced significant complications when repurposed to treat SUI. Developing more physiologically relevant in vitro test models would allow more physiologically relevant data to be collected about how biomaterials will interact with the body. This study investigates the effects of mechanochemical distress (a combination of oxidation and mechanical distention) on polypropylene mesh surfaces and the effect this has on macrophage gene expression. Surface topology of the mesh was characterised using SEM and AFM; ATR-FTIR, EDX and Raman spectroscopy was applied to detect surface oxidation and structural molecular alterations. Uniaxial mechanical testing was performed to reveal any bulk mechanical changes. RT-qPCR of selected pro-fibrotic and pro-inflammatory genes was carried out on macrophages cultured on control and mechanochemically distressed PP mesh. Following exposure to mechanochemical distress the mesh surface was observed to crack and craze and helical defects were detected in the polymer backbone. Surface oxidation of the mesh was seen after macrophage attachment for 7 days. These changes in mesh surface triggered modified gene expression in macrophages. Pro-fibrotic and pro-inflammatory genes were upregulated after macrophages were cultured on mechanochemically distressed mesh, whereas the same genes were down-regulated in macrophages exposed to control mesh. This study highlights the relationship between macrophages and polypropylene surgical mesh, thus offering more insight into the fate of an implanted material than existing in vitro testing.

Mitochondria as a therapeutic: a potential new frontier in driving the shift from tissue repair to regeneration

Fibrosis, or scar tissue development, is associated with numerous pathologies and is often considered a worst-case scenario in terms of wound healing or the implantation of a biomaterial. All that remains is a disorganized, densely packed and poorly vascularized bundle of connective tissue, which was once functional tissue. This creates a significant obstacle to the restoration of tissue function or integration with any biomaterial. Therefore, it is of paramount importance in tissue engineering and regenerative medicine to emphasize regeneration, the successful recovery of native tissue function, as opposed to repair, the replacement of the native tissue (often with scar tissue). A technique dubbed 'mitochondrial transplantation' is a burgeoning field of research that shows promise in in vitro, in vivo and various clinical applications in preventing cell death, reducing inflammation, restoring cell metabolism and proper oxidative balance, among other reported benefits. However, there is currently a lack of research regarding the potential for mitochondrial therapies within tissue engineering and regenerative biomaterials. Thus, this review explores these promising findings and outlines the potential for mitochondrial transplantation-based therapies as a new frontier of scientific research with respect to driving regeneration in wound healing and host-biomaterial interactions, the current successes of mitochondrial transplantation that warrant this potential and the critical questions and remaining obstacles that remain in the field.

Bioactive glass in the treatment of ulcerative colitis to regulate the TLR4 / MyD88 / NF-κB pathway

Ulcerative colitis (UC) is a chronic and recurrent intestinal disease of unknown aetiology, and the few treatments approved for UC have serious side effects. In this study, a new type of uniformly monodispersed calcium-enhanced radial mesoporous micro-nano bioactive glass (HCa-MBG) was prepared for UC treatment. We established cellular and rat UC models to explore the effects and mechanism of HCa-MBG and traditional BGs (45S5, 58S) on UC. The results showed that BGs significantly reduced the cellular expression of several inflammatory factors, such as IL-1β, IL-6, TNF-α and NO. In the animal experiments, BGs were shown to repair the DSS-damaged colonic mucosa. Moreover, BGs downregulated the mRNA levels of the inflammatory factors IL-1β, IL-6, TNF-α and iNOS, which were stimulated by DSS. BGs were also found to manage the expression of key proteins in NF-kB signal pathway. However, HCa-MBG was more effective than traditional BGs in terms of improving UC clinical manifestations and reducing the expression of inflammatory factors in rats. This study confirmed for the first time that BGs can be used as an adjuvant drug in UC treatment, thereby preventing UC progression.

Histological and Histomorphometric Evaluation of Implanted Photodynamic Active Biomaterials for Periodontal Bone Regeneration in an Animal Study

Recently, our group developed two different polymeric biomaterials with photodynamic antimicrobial surface activity for periodontal bone regeneration. The aim of the present study was to analyze the biocompatibility and osseointegration of these materials in vivo. Two biomaterials based on urethane dimethacrylate (BioM1) and tri-armed oligoester-urethane methacrylate (BioM2) that additionally contained ß-tricalcium phosphate and the photosensitizer mTHPC (meso-tetra(hydroxyphenyl)chlorin) were implanted in non-critical size bone defects in the femur (n = 16) and tibia (n = 8) of eight female domestic sheep. Bone specimens were harvested and histomorphometrically analyzed after 12 months. BioM1 degraded to a lower extent which resulted in a mean remnant square size of 17.4 mm², while 12.2 mm² was estimated for BioM2 (p = 0.007). For BioM1, a total percentage of new formed bone by 30.3% was found which was significant higher compared to BioM2 (8.4%, p < 0.001). Furthermore, BioM1 was afflicted by significant lower soft tissue formation (3.3%) as compared to BioM2 (29.5%). Additionally, a bone-to-biomaterial ratio of 81.9% was detected for BioM1, while 8.5% was recorded for BioM2. Implantation of BioM2 caused accumulation of inflammatory cells and led to fibrous encapsulation. BioM1 (photosensitizer-armed urethane dimethacrylate) showed favorable regenerative characteristics and can be recommended for further studies.

A microfluidic-based approach to investigate the inflammatory response of macrophages to pristine and drug-loaded nanostructured hydroxyapatite

The in vitro biological characterization of biomaterials is largely based on static cell cultures. However, for highly reactive biomaterials such as calcium-deficient hydroxyapatite (CDHA), this static environment has limitations. Drastic alterations in the ionic composition of the cell culture medium can negatively affect cell behavior, which can lead to misleading results or data that is difficult to interpret. This challenge could be addressed by a microfluidics-based approach (i.e. on-chip), which offers the opportunity to provide a continuous flow of cell culture medium and a potentially more physiologically relevant microenvironment. The aim of this work was to explore microfluidic technology for its potential to characterize CDHA, particularly in the context of inflammation. Two different CDHA substrates (chemically identical, but varying in microstructure) were integrated on-chip and subsequently evaluated. We demonstrated that the on-chip environment can avoid drastic ionic alterations and increase protein sorption, which was reflected in cell studies with RAW 264.7 macrophages. The cells grown on-chip showed a high cell viability and enhanced proliferation compared to cells maintained under static conditions. Whereas no clear differences in the secretion of tumor necrosis factor alpha (TNF-α) were found, variations in cell morphology suggested a more anti-inflammatory environment on-chip. In the second part of this study, the CDHA substrates were loaded with the drug Trolox. We showed that it is possible to characterize drug release on-chip and moreover demonstrated that Trolox affects the TNF-α secretion and morphology of RAW 264.7 ​cells. Overall, these results highlight the potential of microfluidics to evaluate (bioactive) biomaterials, both in pristine form and when drug-loaded. This is of particular interest for the latter case, as it allows the biological characterization and assessment of drug release to take place under the same dynamic in vitro environment.

Micro/Nanostructured Topography on Titanium Orchestrates Dendritic Cell Adhesion and Activation via β2 Integrin-FAK Signals

Background and Purpose

In clinical application of dental implants, the functional state of dendritic cells (DCs) has been suggested to have a close relationship with the implant survival rate or speed of osseointegration. Although microscale surfaces have a stable osteogenesis property, they also incline to trigger unfavorable DCs activation and threaten the osseointegration process. Nanoscale structures have an advantage in regulating cell immune response through orchestrating cell adhesion, indicating the potential of hierarchical micro/nanostructured surface in regulation of DCs’ activation without sacrificing the advantage of microscale topography.

Materials and Methods

Two micro/nanostructures were fabricated based on microscale rough surfaces through anodization or alkali treatment, the sand-blasted and acid-etched (SA) surface served as control. The surface characteristics, in vitro and in vivo DC immune reactions and β2 integrin-FAK signal expression were systematically investigated. The DC responses to different surface topographies after FAK inhibition were also tested.

Results

Both micro/nano-modified surfaces exhibited unique composite structures, with higher hydrophilicity and lower roughness compared to the SA surface. The DCs showed relatively immature functional states with round morphologies and significantly downregulated β2 integrin-FAK levels on micro/nanostructures. Implant surfaces with micro/nano-topographies also triggered lower levels of DC inflammatory responses than SA surfaces in vivo. The inhibited FAK activation effectively reduced the differences in topography-caused DC activation and narrowed the differences in DC activation among the three groups.

Conclusion

Compared to the SA surface with solely micro-scale topography, titanium surfaces with hybrid micro/nano-topographies reduced DC inflammatory response by influencing their adhesion states. This regulatory effect was accompanied by the modulation of β2 integrin-FAK signal expression. The β2 integrin-FAK-mediated adhesion plays a critical role in topography-induced DC activation, which represents a potential target for material–cell interaction regulation.

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.

Substratum interactions determine immune response to allogeneic transplants of endothelial cells

Endothelial cells (ECs) are central to vascular health but also interact with and regulate the immune system. Changes in endothelial state enable immune cells to migrate into the tissue to facilitate repair and fight infection. ECs modulate the function of immune cells through the expression of adhesion molecules, chemokines, major histocompatibility complex (MHC), and an array of co-stimulatory and inhibitor molecules. These interactions allow ECs to act as antigen presenting cells (APCs) and influence the outcome of immune recognition. This study elucidates how EC microenvironment, vascular cell biology, and immune response are not only connected but interdependent. More specifically, we explored how cell-substratum interactions influence EC antigen presentation and co-stimulation, and how these differences affect allorecognition in animal models of cell transplantation. Investigation of EC state was carried out using RNA sequencing while assessment of the allogeneic response includes measurements of immune cell cytotoxic ability, T cell proliferation, cytokine release, serum antibodies, and histological staining. Differences in substratum led to divergent EC phenotypes which in turn influenced immune response to transplanted cells, both due to the physical barrier of matrix-adhesion and differences in expression of surface markers. ECs grown in 2D on tissue culture plastic or in 3D on collagen scaffolds had significantly different basal levels of MHC expression, co-stimulatory and adhesion molecules. When treated with cytokines to mimic an inflammatory state, ECs did not converge to a single phenotype but rather responded differently based on their substratum. Generally, 3D ECs were more responsive to inflammatory stimuli than 2D ECs. These unique expression patterns measured in vitro also influence immune recognition in vivo. ECs grown in 2D were more likely to provoke a cytotoxic response while 3D ECs induced T cell proliferation. ECs are uniquely configured to sense not only local flow and mechanical forces but a range of markers related to systemic state, including immune function. ECs interact with immune cells with differing results depending on the environment in which the EC-lymphocyte interaction occurs. Therefore, understanding this relationship is essential to predicting and modifying the outcome of EC-immune interacts. We specifically examined the relationship between EC substratum and allorecognition.

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.

Modified foreign body reaction to silicone imbedded in subcutaneous tissues by different mouse systemic immune conditions

Foreign body reaction (FBR) causes unexpected adverse effects due to implanted materials in humans and animals. Inflammation and subsequent fibrosis during FBR seems to be affected by recipient immunity, such as the balance of T helper (Th) response that has the potential to regulate FBR-related macrophage function. Here, the immunological effects of FBR on subcutaneously imbedded silicone tubes (ST) at 8 weeks were investigated histologically by comparing Th1-biased C57BL/6N, Th2-biased MRL/MpJ, and autoimmune disease-prone MRL/MpJ-Fas^lpr/lpr . Tissue surrounding ST (TSS) was analyzed at day (D) 7 and 14 (reaction phase) or D35 (stability phase) after surgery. In all strains, the TSS was composed of a thin layer (TL) containing fibrous tissues and loose connective tissues formed outside the TL. Few lymphocytes and mast cells, several neutrophils, and numerous macrophages infiltrated the TSS. Active vascularization was observed at D14 in all strains. For the examined indices, M1-type macrophage density in the TSS of C57BL/6N mice was significantly higher at D14 compared to other strains. No significant strain difference relating to M2-type macrophages was detected, suggesting the effects of Th1-biased immunity on FBR-related inflammation. Collagen fibers in the TSS increased in density and became stable with age in all strains. In particular, MRL/MpJ-Fas^lpr/lpr showed progressive fibrotic features. Serum autoantibody levels in MRL/MpJ-Fas^lpr/lpr mice were inversely correlated with M1-type macrophage density. These data from MRL/MpJ-Fas^lpr/lpr mice suggested modifications of FBR-related inflammation and fibrosis by autoimmune abnormalities. The results provide crucial insights into the pathological modification of FBR by recipient immunity and emphasize its clinicopathological importance in humans and animals.

Challenges in delivering therapeutic peptides and proteins: A silk-based solution

Peptide- and protein-based therapeutics have drawn significant attention over the past few decades for the treatment of infectious diseases, genetic disorders, oncology, and many other clinical needs. Yet, protecting peptide- and protein-based drugs from degradation and denaturation during processing, storage and delivery remain significant challenges. In this review, we introduce the properties of peptide- and protein-based drugs and the challenges associated with their stability and delivery. Then, we discuss delivery strategies using synthetic polymers and their advantages and limitations. This is followed by a focus on silk protein-based materials for peptide/protein drug processing, storage, and delivery, as a path to overcome stability and delivery challenges with current systems.

MXenes Quantum Dots for Biomedical Applications: Recent Advances and Challenges

MXenes have aroused widespread interest in the biomedical field owing to their remarkable photo-thermal conversion capabilities combined with large specific surface areas. MXenes quantum dots (MQDs) have been synthesized either by the physical or chemical methods based on MXenes as precursors, which possess smaller size, higher photoluminescence, coupled with low cytotoxicity and many beneficial properties of MXenes, thereby having potential biomedical applications. Given this, this review summarized the synthesis methods, optical, surface and biological properties of MQDs along with their practical applications in the field of biomedicine. Finally, the authors make an outlook towards the synthesis, properties and applications of MQDs in the future biomedicine field.

Bioclickable Mussel-Derived Peptides With Immunoregulation for Osseointegration of PEEK

Polyether ether ketone (PEEK)–based biomaterials have been widely used in the field of spine and joint surgery. However, lack of biological activity limits their further clinical application. In this study, we synthesized a bioclickable mussel-derived peptide Azide-DOPA₄ as a PEEK surface coating modifier and further combined bone morphogenetic protein 2 functional peptides (BMP2p) with a dibenzylcyclooctyne (DBCO) motif through bio-orthogonal reactions to obtain DOPA₄@BMP2p-PEEK. As expected, more BMP2p can be conjugated on PEEK after Azide-DOPA₄ coating. The surface roughness and hydrophilicity of DOPA₄@BMP2p-PEEK were obviously increased. Then, we optimized the osteogenic capacity of PEEK substrates. In vitro, compared with the BMP2p-coating PEEK material, DOPA₄@BMP2p-PEEK showed significantly higher osteogenic induction capability of rat bone marrow mesenchymal stem cells. In vivo, we constructed a rat calvarial bone defect model and implanted PEEK materials with a differently modified surface. Micro-computed tomography scanning displayed that the DOPA₄@BMP2p-PEEK implant group had significantly higher new bone volume and bone mineral density than the BMP2p-PEEK group. Histological staining of hard tissue further confirmed that the DOPA₄@BMP2p-PEEK group revealed a better osseointegrative effect than the BMP2p-PEEK group. More importantly, we also found that DOPA₄@BMP2p coating has a synergistic effect with induced Foxp3+ regulatory T (iTreg) cells to promote osteogenesis. In summary, with an easy-to-perform, two-step surface bioengineering approach, the DOPA₄@BMP2p-PEEK material reported here displayed excellent biocompatibility and osteogenic functions. It will, moreover, offer insights to engineering surfaces of orthopedic implants.

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.

Poly(amino acid) based fibrous membranes with tuneable in vivo biodegradation

In this work two types of biodegradable polysuccinimide-based, electrospun fibrous membranes are presented. One contains disulfide bonds exhibiting a shorter (3 days) in vivo biodegradation time, while the other one has alkyl crosslinks and a longer biodegradation time (more than 7 days). According to the mechanical measurements, the tensile strength of the membranes is comparable to those of soft the connective tissues and visceral tissues. Furthermore, the suture retention test suggests, that the membranes would withstand surgical handling and in vivo fixation. The in vivo biocompatibility study demonstrates how membranes undergo in vivo hydrolysis and by the 3rd day they become poly(aspartic acid) fibrous membranes, which can be then enzymatically degraded. After one week, the disulfide crosslinked membranes almost completely degrade, while the alkyl-chain crosslinked ones mildly lose their integrity as the surrounding tissue invades them. Histopathology revealed mild acute inflammation, which diminished to a minimal level after seven days.

Silicone Implants Immobilized with Interleukin-4 Promote the M2 Polarization of Macrophages and Inhibit the Formation of Fibrous Capsules

Breast augmentations with silicone implants can have adverse effects on tissues that, in turn, lead to capsular contracture (CC). One of the potential ways of overcoming CC is to control the implant/host interaction using immunomodulatory agents. Recently, a high ratio of anti-inflammatory (M2) macrophages to pro-inflammatory (M1) macrophages has been reported to be an effective tissue regeneration approach at the implant site. In this study, a biofunctionalized implant was coated with interleukin (IL)-4 to inhibit an adverse immune reaction and promoted tissue regeneration by promoting polarization of macrophages into the M2 pro-healing phenotype in the long term. Surface wettability, nitrogen content, and atomic force microscopy data clearly showed the successful immobilization of IL-4 on the silicone implant. Furthermore, in vitro results revealed that IL-4-coated implants were able to decrease the secretion of inflammatory cytokines (IL-6 and tumor necrosis factor-α) and induced the production of IL-10 and the upregulation of arginase-1 (mannose receptor expressed by M2 macrophage). The efficacy of this immunomodulatory implant was further demonstrated in an in vivo rat model. The animal study showed that the presence of IL-4 diminished the capsule thickness, the amount of collagen, tissue inflammation, and the infiltration of fibroblasts and myofibroblasts. These results suggest that macrophage phenotype modulation can effectively reduce inflammation and fibrous CC on a silicone implant conjugated with IL-4.

Biological sealing and integration of a fibrinogen-modified titanium alloy with soft and hard tissues in a rat model

Percutaneous or transcutaneous devices are important and unique, and the corresponding biological sealing at the skin-implant interface is the key to their long-term success. Herein, we investigated the surface modification to enhance biological sealing, using a metal sheet and screw bonded by biomacromolecule fibrinogen mediated via pre-deposited synthetic macromolecule polydopamine (PDA) as a demonstration. We examined the effects of a Ti-6Al-4V titanium alloy modified with fibrinogen (Ti-Fg), PDA (Ti-PDA) or their combination (Ti-PDA-Fg) on the biological sealing and integration with skin and bone tissues. Human epidermal keratinocytes (HaCaT), human foreskin fibroblasts (HFF) and preosteoblasts (MC3T3-E1), which are closely related to percutaneous implants, exhibited better adhesion and spreading on all the three modified sheets compared with the unmodified alloy. After three-week subcutaneous implantation in Sprague-Dawley (SD) rats, the Ti-PDA-Fg sheets could significantly attenuate the soft tissue response and promote angiogenesis compared with other groups. Furthermore, in the model of percutaneous tibial implantation in SD rats, the Ti-PDA-Fg screws dramatically inhibited epithelial downgrowth and promoted new bone formation. Hence, the covalent immobilization of fibrinogen through the precoating of PDA is promising for enhanced biological sealing and osseointegration of metal implants with soft and hard tissues, which is critical for an orthopedic percutaneous medical device.

Biomaterial-based approaches to engineering immune tolerance

The development of biomaterial-based therapeutics to induce immune tolerance holds great promise for the treatment of autoimmune diseases, allergy, and graft rejection in transplantation. Historical approaches to treat these immunological challenges have primarily relied on systemic delivery of broadly-acting immunosuppressive agents that confer undesirable, off-target effects. The evolution and expansion of biomaterial platforms has proven to be a powerful tool in engineering immunotherapeutics and enabled a great diversity of novel and targeted approaches in engineering immune tolerance, with the potential to eliminate side effects associated with systemic, non-specific immunosuppressive approaches. In this review, we summarize the technological advances within three broad biomaterials-based strategies to engineering immune tolerance: nonspecific tolerogenic agent delivery, antigen-specific tolerogenic therapy, and the emergent area of tolerogenic cell therapy.

Enhancing islet transplantation using a biocompatible collagen-PDMS bioscaffold enriched with dexamethasone-microplates

Islet transplantation is a promising approach to enable type 1 diabetic patients to attain glycemic control independent of insulin injections. However, up to 60% of islets are lost immediately following transplantation. To improve this outcome, islets can be transplanted within bioscaffolds, however, synthetic bioscaffolds induce an intense inflammatory reaction which can have detrimental effects on islet function and survival. In the present study, we first improved the biocompatibility of polydimethylsiloxane (PDMS) bioscaffolds by coating them with collagen. To reduce the inflammatory response to PDMS bioscaffolds, we then enriched the bioscaffolds with dexamethasone-loaded microplates (DEX-µScaffolds). These DEX-microplates have the ability to release DEX in a sustained manner over 7 weeks within a therapeutic range that does not affect the glucose responsiveness of the islets but which minimizes inflammation in the surrounding microenvironment. The bioscaffold showed excellent mechanical properties that enabled it to resist pore collapse thereby helping to facilitate islet seeding and its handling for implantation, and subsequent engraftment, within the epididymal fat pad (EFP). Following the transplantation of islets into the EFP of diabetic mice using DEX-µScaffolds there was a return in basal blood glucose to normal values by day 4, with normoglycemia maintained for 30 days. Furthermore, these animals demonstrated a normal dynamic response to glucose challenges with histological evidence showing reduced pro-inflammatory cytokines and fibrotic tissue surrounding DEX-µScaffolds at the transplantation site. In contrast, diabetic animals transplanted with either islets alone or islets in bioscaffolds without DEX microplates were not able to regain glycemic control during basal conditions with overall poor islet function. Taken together, our data show that coating PDMS bioscaffolds with collagen, and enriching them with DEX-microplates, significantly prolongs and enhances islet function and survival.

Preclinical biological and physicochemical evaluation of two-photon engineered 3D biomimetic copolymer scaffolds for bone healing

A major challenge in orthopedics is the repair of large non-union bone fractures. A promising therapy for this indication is the use of biodegradable bioinspired biomaterials that stabilize the fracture site, relieve pain and initiate bone formation and healing. This study uses a multidisciplinary evaluation strategy to assess immunogenicity, allergenicity, bone responses and physicochemical properties of a novel biomaterial scaffold. Two-photon stereolithography generated personalized custom-built scaffolds with a repeating 3D structure of Schwarz Primitive minimal surface unit cell with a specific pore size of ∼400 μm from three different methacrylated poly(d,l-lactide-co-ε-caprolactone) copolymers with lactide to caprolactone monomer ratios of 16 : 4, 18 : 2 and 9 : 1. Using in vitro and in vivo assays for bone responses, immunological reactions and degradation dynamics, we found that copolymer composition influenced the scaffold physicochemical and biological properties. The scaffolds with the fastest degradation rate correlated with adverse cellular effects and mechanical stiffness correlated with in vitro osteoblast mineralization. The physicochemical properties also correlated with in vivo bone healing and immune responses. Overall these observations provide compelling support for these scaffolds for bone repair and illustrate the effectiveness of a promising multidisciplinary strategy with great potential for the preclinical evaluation of biomaterials.

Biological responses to physicochemical properties of biomaterial surface

Biomedical scientists use chemistry-driven processes found in nature as an inspiration to design biomaterials as promising diagnostic tools, therapeutic solutions, or tissue substitutes. While substantial consideration is devoted to the design and validation of biomaterials, the nature of their interactions with the surrounding biological microenvironment is commonly neglected. This gap of knowledge could be owing to our poor understanding of biochemical signaling pathways, lack of reliable techniques for designing biomaterials with optimal physicochemical properties, and/or poor stability of biomaterial properties after implantation. The success of host responses to biomaterials, known as biocompatibility, depends on chemical principles as the root of both cell signaling pathways in the body and how the biomaterial surface is designed. Most of the current review papers have discussed chemical engineering and biological principles of designing biomaterials as separate topics, which has resulted in neglecting the main role of chemistry in this field. In this review, we discuss biocompatibility in the context of chemistry, what it is and how to assess it, while describing contributions from both biochemical cues and biomaterials as well as the means of harmonizing them. We address both biochemical signal-transduction pathways and engineering principles of designing a biomaterial with an emphasis on its surface physicochemistry. As we aim to show the role of chemistry in the crosstalk between the surface physicochemical properties and body responses, we concisely highlight the main biochemical signal-transduction pathways involved in the biocompatibility complex. Finally, we discuss the progress and challenges associated with the current strategies used for improving the chemical and physical interactions between cells and biomaterial surface.

Evaluation of Fibrin-Agarose Tissue-Like Hydrogels Biocompatibility for Tissue Engineering Applications

Generation of biocompatible and biomimetic tissue-like biomaterials is crucial to ensure the success of engineered substitutes in tissue repair. Natural biomaterials able to mimic the structure and composition of native extracellular matrices typically show better results than synthetic biomaterials. The aim of this study was to perform an in vivo time-course biocompatibility analysis of fibrin-agarose tissue-like hydrogels at the histological, imagenological, hematological, and biochemical levels. Tissue-like hydrogels were produced by a controlled biofabrication process allowing the generation of biomechanically and structurally stable hydrogels. The hydrogels were implanted subcutaneously in 25 male Wistar rats and evaluated after 1, 5, 9, and 12 weeks of in vivo follow-up. At each period of time, animals were analyzed using magnetic resonance imaging (MRI), hematological analyses, and histology of the local area in which the biomaterials were implanted, along with major vital organs (liver, kidney, spleen, and regional lymph nodes). MRI results showed no local or distal alterations during the whole study period. Hematology and biochemistry showed some fluctuation in blood cells values and in some biochemical markers over the time. However, these parameters were progressively normalized in the framework of the homeostasis process. Histological, histochemical, and ultrastructural analyses showed that implantation of fibrin-agarose scaffolds was followed by a progressive process of cell invasion, synthesis of components of the extracellular matrix (mainly, collagen) and neovascularization. Implanted biomaterials were successfully biodegraded and biointegrated at 12 weeks without any associated histopathological alteration in the implanted zone or distal vital organs. In summary, our in vivo study suggests that fibrin-agarose tissue-like hydrogels could have potential clinical usefulness in engineering applications in terms of biosafety and biocompatibility.

Pro-Fibrotic CD26-Positive Fibroblasts Are Present in Greater Abundance in Breast Capsule Tissue of Irradiated Breasts

BACKGROUND

Breast capsular contracture is a major problem following implant-based breast reconstruction, particularly in the setting of radiation therapy. Recent work has identified a fibrogenic fibroblast subpopulation characterized by CD26 surface marker expression.

OBJECTIVES

This work aimed to investigate the role of CD26-positive fibroblasts in the formation of breast implant capsules following radiation therapy.

METHODS

Breast capsule specimens were obtained from irradiated and nonirradiated breasts of 10 patients following bilateral mastectomy and unilateral irradiation at the time of expander-implant exchange, under institutional review board approval. Specimens were processed for hematoxylin and eosin staining as well as for immunohistochemistry and fluorescence activated cell sorting for CD26-positive fibroblasts. Expression of fibrotic genes and production of collagen were compared between CD26-positive, CD26-negative, and unsorted fibroblasts.

RESULTS

Capsule specimens from irradiated breast tissue were thicker and had greater CD26-postive cells on immunofluorescence imaging and on fluorescence activated cell sorting analysis than did capsule specimens from the nonirradiated breast. Compared with CD26-negative fibroblasts, CD26-positive fibroblasts produced more collagen and had increased expression of the profibrotic genes IL8, TGF-β1, COL1A1, and TIMP4.

CONCLUSIONS

CD26-positive fibroblasts were found in a significantly greater abundance in capsules of irradiated compared with nonirradiated breasts and demonstrated greater fibrotic potential. This fibrogenic fibroblast subpopulation may play an important role in the development of capsular contracture following irradiation, and its targeted depletion or moderation may represent a potential therapeutic option.

LEVEL OF EVIDENCE: 2

J, McAllister TN, L'Heureux N. Human textiles: A cell-synthesized yarn as a truly "bio" material for tissue engineering applications

In the field of tissue engineering, many groups have come to rely on the extracellular matrix produced by cells as the scaffold that provides structure and strength to the engineered tissue. We have previously shown that sheets of Cell-Assembled extracellular Matrix (CAM), which are entirely biological yet robust, can be mass-produced for clinical applications using normal, adult, human fibroblasts. In this article, we demonstrate that CAM yarns can be generated with a range of physical and mechanical properties. We show that this material can be used as a simple suture to close a wound or can be assembled into fully biological, human, tissue-engineered vascular grafts (TEVGs) that have high mechanical strength and are implantable. By combining this truly "bio" material with a textile-based assembly, this original tissue engineering approach is highly versatile and can produce a variety of strong human textiles that can be readily integrated in the body. STATEMENT OF SIGNIFICANCE: Yarn of synthetic biomaterials have been turned into textiles for decades because braiding, knitting and weaving machines can mass-produce medical devices with a wide range of shapes and mechanical properties. Here, we show that robust, completely biological, and human yarn can be produced by normal cells in vitro. This yarn can be used as a simple suture material or to produce the first human textiles. For example, we produced a woven tissue-engineered vascular grafts with burst pressure, suture retention strength and transmural permeability that surpassed clinical requirements. This novel strategy holds the promise of a next generation of medical textiles that will be mechanically strong without any foreign scaffolding, and will have the ability to truly integrate into the host's body.

Elastic net of polyurethane strands for sustained delivery of triamcinolone around silicone implants of various sizes

We propose an elastic net made of a biocompatible polymer to wrap silicone implants of various sizes, which also allows for the sustained release of an anti-inflammatory drug, triamcinolone, to prevent fibrosis. For this, we first prepared a strand composed of a mixture of polyurethane and triamcinolone via electrospinning, which was then assembled to prepare the elastic drug-delivery net (DDN). The DDN was prepared to just fit for wrapping the small silicone implant sample herein, but was also able to wrap a sample 7 times as large at 72% strain due to the elastic property of polyurethane. The DDN exhibited sustained drug release for 4 weeks, the profile of which was not very different between the intact and strained DDNs. When implanted in a subcutaneous pocket in living rats, the DDN-wrapped silicone implant samples showed an obvious antifibrotic effect due to the sustained release of triamcinolone. Importantly, this effect was similar for the small and large silicone samples, both wrapped with the same DDN. Therefore, we conclude that this drug-loaded net made of an elastic, biocompatible polymer has high potential for sustained drug delivery around silicone implants manufactured in various sizes.

Shape-Depended Biological Properties of Ag3PO4 Microparticles: Evaluation of Antimicrobial Properties and Cytotoxicity in In Vitro Model-Safety Assessment of Potential Clinical Usage

Implant-related infections are an emerging clinical and economic problem. Therefore, we decided to assess potential clinical usefulness and safety of silver orthophosphate microparticles (SOMPs) regarding their shape. We synthesized and then assessed antimicrobial properties and potential cytotoxicity of six shapes of SOMPs (tetrapod, cubes, spheres, tetrahedrons, branched, and rhombic dodecahedron). We found that SOMPs had a high antimicrobial effect; they were more efficient against fungi than bacteria. SOMPs exerted an antimicrobial effect in concentrations not toxic to mammalian cells: human fetal osteoblast (hFOB1.19), osteosarcoma (Saos-2), mouse preosteoblasts (MC3T3-E1), skin fibroblast (HDF), and mouse myoblast (C2C12). At higher concentration SOMPs, induced shape- and concentration-dependent cytotoxicity (according to MTT and BrdU assays). Tetrapod SOMPs had the smallest effect, whereas cubical SOMPs, the highest on cell viability. hFOB1.19 were the most resistant cells and C2C12, the most susceptible ones. We have proven that the induction of oxidative stress and inflammation is involved in the cytotoxic mechanism of SOMPs. After treatment with microparticles, we observed changes in levels of reactive oxygen species, first-line defense antioxidants-superoxide dismutase (SOD1, SOD3), and glutathione peroxidase (GPX4), metalloproteinase (MMP1, MMP3), and NF-κB protein. Neither cell cycle distribution nor ultrastructure was altered as determined by flow cytometry and transmission electron microscopy, respectively. In conclusion, silver orthophosphate may be a safe and effective antimicrobial agent on the implant surface. Spherical-shaped SOMPs are the most promising for biomedical application.

In vitro and in vivo biocompatibility assessment of free radical scavenging nanocomposite scaffolds for bone tissue regeneration

Bone is the second most transplanted tissue in the world, resulting in increased demand for bone grafts leading to the fabrication of synthetic scaffold grafting alternatives. Fracture sites are under increased oxidative stress after injuries, affecting osteoblast function and hindering fracture healing and remodeling. To counter oxidative stress, free radical scavenging agents, such as cerium oxide nanoparticles, have gained traction in tissue engineering. Toward the goal of developing a functional synthetic system for bone tissue engineering, we characterized the biocompatibility of a porous, bioactive, free radical scavenging nanocomposite scaffold composed of poly(1,8 octanediol-co-citrate), beta-tricalcium phosphate, and cerium oxide nanoparticles. We studied cellular and tissue compatibility utilizing in vitro and in vivo models to assess nanocomposite interactions with both human osteoblast cells and rat subcutaneous tissue. We found the scaffolds were biocompatible in both models and supported cell attachment, proliferation, mineralization, and infiltration. Using hydrogen peroxide, we simulated oxidative stress to study the protective properties of the nanocomposite scaffolds via a reduction in cytotoxicity and recovered mineralization of osteoblast cells in vitro. We also found after implantation in vivo the scaffolds exhibited biocompatible properties essential for successful scaffolds for bone tissue engineering. Cells were able to infiltrate through the scaffolds, the surrounding tissues elicited a minimal immune response, and there were signs of scaffold degradation after 30 days of implantation. After the array of biological characterization, we had confirmed the development of a nanocomposite scaffold system capable of supporting bone-remodeling processes while providing a protective free radical scavenging effect.

Immune responses towards bioengineered tissues and strategies to control them

PURPOSE OF REVIEW

Research into development of artificial tissues and bioengineered organs to replace physiological functions of injured counterparts has highlighted a previously underestimated challenge for its clinical translatability: the immune response against biomaterials. Herein, we will provide an update and review current knowledge regarding this important barrier to regenerative medicine.

RECENT FINDINGS

Although a clear understanding of the immune reactivity against biomaterials remains elusive, accumulating evidence indicates that innate immune cells, primarily neutrophils and macrophages, play a key role in the initial phases of the immune response. More recently, data have shown that in later phases, T and B cells are also involved. The use of physicochemical modifications of biomaterials and cell-based strategies to modulate the host inflammatory response is being actively investigated for effective biomaterial integration.

SUMMARY

The immune response towards biomaterials and bioengineered organs plays a crucial role in determining their utility as transplantable grafts. Expanding our understanding of these responses is necessary for developing protolerogenic strategies and delivering on the ultimate promise of regenerative medicine.

Application of Ti3 C2 MXene Quantum Dots for Immunomodulation and Regenerative Medicine

Inflammation is tightly linked to tissue injury. In regenerative medicine, immune activation plays a key role in rejection of transplanted stem cells and reduces the efficacy of stem cell therapies. Next-generation smart biomaterials are reported to possess multiple biologic properties for tissue repair. Here, the first use of 0D titanium carbide (Ti₃ C₂ ) MXene quantum dots (MQDs) for immunomodulation is presented with the goal of enhancing material-based tissue repair after injury. MQDs possess intrinsic immunomodulatory properties and selectively reduce activation of human CD4⁺ IFN-γ⁺ T-lymphocytes (control 87.1 ± 2.0%, MQDs 68.3 ± 5.4%) while promoting expansion of immunosuppressive CD4⁺ CD25⁺ FoxP3⁺ regulatory T-cells (control 5.5 ± 0.7%, MQDs 8.5 ± 0.8%) in a stimulated lymphocyte population. Furthermore, MQDs are biocompatible with bone marrow-derived mesenchymal stem cells and induced pluripotent stem cell-derived fibroblasts. Finally, Ti₃ C₂ MQDs are incorporated into a chitosan-based hydrogel to create a 3D platform with enhanced physicochemical properties for stem cell delivery and tissue repair. This composite hydrogel demonstrates increased conductivity while maintaining injectability and thermosensitivity. These findings suggest that this new class of biomaterials may help bridge the translational gap in material and stem cell-based therapies for tissue repair and treatment of inflammatory and degenerative diseases.

Activation of dendritic cells by crosslinked collagen hydrogels (artificial corneas) varies with their composition

Activated T cells are known to promote fibrosis, a major complication limiting the range of polymeric hydrogels as artificial corneal implants. As T cells are activated by dendritic cells (DC), minimally activating hydrogels would be optimal. In this study, we evaluated the ability of a series of engineered (manufactured/fabricated) and natural collagen matrices to either activate DC or conversely induce DC apoptosis in vitro. Bone marrow DC were cultured on a series of singly and doubly crosslinked hydrogels (made from recombinant human collagen III [RHCIII] or collagen mimetic peptide [CMP]) or on natural collagen-containing matrices, Matrigel^TM and de-cellularised mouse corneal stroma. DC surface expression of major histocompatibility complex Class II and CD86 as well as apoptosis markers were examined. Natural matrices induced low levels of DC activation and maintained a "tolerogenic" phenotype. The same applied to singly crosslinked CMP-PEG gels. RHCIII gels singly crosslinked using either N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide with the coinitiator N-hydroxy succinimide (EDC-NHS) or N-cyclohexyl-N-(2-morpholinoethyl)carbodiimide metho-p-toulenesulfonate with NHS (CMC-NHS) induced varying levels of DC activation. In contrast, however, RHCIII hydrogels incorporating an additional polymeric network of 2-methacryloyloxyethyl phosphorylcholine did not activate DC but instead induced DC apoptosis, a phenomenon observed in natural matrices. This correlated with increased DC expression of leukocyte-associated immunoglobulin-like receptor-1. Despite low immunogenic potential, viable tolerogenic DC migrated into and through both natural and manufactured RHCIII gels. These data show that the immunogenic potential of RHCIII gels varies with the nature and composition of the gel. Preclinical evaluation of hydrogel immunogenic/fibrogenic potential is recommended.

Keratin scaffolds with human adipose stem cells: Physical and biological effects toward wound healing

Keratin, a natural biomaterial derived from wool or human hair, has the intrinsic ability to interact with different types of cells and the potential to serve as a controllable extracellular matrix that can be used a scaffold for tissue engineering. In this study, we demonstrated a simple and fast technique to construct 3D keratin scaffolds for accelerated wound healing using a lyophilization method based on extraction of keratin from human hair. The physical properties of the keratin scaffolds such as water uptake, pore size, and porosity can be adjusted by changing the protein concentrations during the fabrication process. The keratin scaffolds supported human adipose stem cells (hASCs) adhesion, proliferation, and differentiation. In vivo study performed on ICR mice showed that keratin scaffolds with hASCs shortened skin wound healing time, accelerated epithelialization, and promoted wound remodeling. Therefore, keratin scaffolds alone or together with hASCs may serve as therapeutic agents for repairing wounded tissue.

In vitro evaluation of anti-fibrotic effects of select cytokines for vocal fold scar treatment

Scarring of the vocal fold lamina propria (LP) can cause considerable voice disorders due to reduced pliability in scar tissue, attributed in part to abnormal extracellular matrix (ECM) deposition produced by the fibrotic vocal fold fibroblast (fVFF). Cytokines with anti-fibrotic potential have been investigated to limit abnormal LP ECM, but are limited by the need for repeat injections. Moreover, the potentially significant role played by activated macrophages (AMOs) is usually not considered even though the interaction between AMO and fibrotic fibroblasts is known to regulate scar formation across different tissues. AMO are also regulated by cytokines that are used for LP scar removal, but little is known about AMO behaviors in response to these cytokines within the context of LP scar. In the present study, we evaluated anti-fibrotic effects of hepatocyte growth factor (HGF), interleukin-10 (IL-10) and interleukin-6 (IL-6) in a 3D, in vitro fVFF-AMO co-culture system using poly(ethylene glycol) diacrylate (PEGDA) hydrogels. Data from all cytokines was synthesized into a heat-map that enabled assessment of specific associations between AMO and fVFF phenotypes. Cumulatively, our results indicated that both HGF and IL-10 are potentially anti-fibrotic (reduction in fibrotic markers and enhancement in normal, anti-fibrotic VFF markers), while IL-6 displays more complex, marker specific effects. Possible associations between AMO and fVFF phenotypes were found and may highlight a potential desirable macrophage phenotype. These data support the therapeutic potential of HGF and IL-10 for LP scar treatment, and shed light on future strategies aimed at targeting specific AMO phenotypes. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1056-1067, 2019.

Polymer scaffold architecture is a key determinant in mast cell inflammatory and angiogenic responses

Implanted polymer scaffolds can induce inflammation leading to the foreign body response (FBR), fibrosis, and implant failure. Thus, it is important to understand how immune cells interact with scaffolds to mitigate inflammation and promote a regenerative response. We previously demonstrated that macrophage phenotype is modulated by fiber and pore diameters of an electrospun scaffold. However, it is unclear if this effect is consistent among other innate immune cells. Mast cells are inflammatory sentinels that play a vital role in the FBR of implanted biomaterials, as well as angiogenesis. We determined if altering electrospun scaffold architecture modulates mast cell responses, with the goal of promoting regenerative cell-scaffold interactions. Polydioxanone (PDO) scaffolds were made from 60 mg/mL or 140 mg/mL PDO solutions, yielding structures with divergent fiber and pore diameters. Mouse mast cells plated on these scaffolds were activated with IL-33 or lipopolysaccharide (LPS). Relative to the 60 mg/mL scaffold, 140 mg/mL scaffolds yielded less IL-6 and TNF, and greater VEGF secretion. Pores >4-6 μm elicited less IL-6 and TNF secretion. IL-33-induced VEGF regulation was more complex, showing effects of both pore size and fiber diameter. These data indicate parameters that can predict mast cell responses to scaffolds, informing biomaterial design to increase wound healing and diminish implant rejection. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 884-892, 2019.

The summary of the most important cell-biomaterial interactions that need to be considered during in vitro biocompatibility testing of bone scaffolds for tissue engineering applications

Tissue engineered products (TEPs), which mean biomaterials containing either cells or growth factors or both cells and growth factors, may be used as an alternative to the autografts taken directly from the bone of the patients. Nevertheless, the use of TEPs needs much more understanding of biointeractions between biomaterials and eukaryotic cells. Despite the possibility of the use of in vitro cellular models for initial evaluation of the host response to the implanted biomaterial, it is observed that most researchers use cell cultures only for the evaluation of cytotoxicity and cell proliferation on the biomaterial surface, and then they proceed to animal models and in vivo testing of bone implants without fully utilizing the scientific potential of in vitro models. In this review, the most important biointeractions between eukaryotic cells and biomaterials were discussed, indicating molecular mechanisms of cell adhesion, proliferation, and biomaterial-induced activation of immune cells. The article also describes types of cellular models which are commonly used for biomaterial testing and highlights the possibilities and drawbacks of in vitro tests for biocompatibility evaluation of novel scaffolds. Finally, the review summarizes recent findings concerning the use of adult mesenchymal stem cells for TEP generation and compares the potential of bone marrow- and adipose tissue-derived stem cells in regenerative medicine applications.

Toll-like Receptor 2-Dependent NF-κB/AP-1 Activation by Damage-Associated Molecular Patterns Adsorbed on Polymeric Surfaces

The foreign body reaction is a chronic inflammatory response to an implanted biomaterial that ultimately leads to fibrous encapsulation of the implant. It is widely accepted that the host response to implanted biomaterials is largely dependent on the species and conformations of proteins adsorbed onto the material surface due to the adsorbate's role in mediating cellular interactions with the implanted material. While the cellular response to adsorbed serum-derived proteins has been studied extensively, the presence of endogenous, matrix- and cell-derived mediators of inflammation within the adsorbed protein layer and their impact on cell-material interactions is not well-understood. Damage associated molecular patterns (DAMPs) are endogenous ligands released by stressed or damaged tissues to stimulate sterile inflammatory responses via Toll-like receptors (TLRs) and other pattern recognition receptors. The present study investigated the potential role of tissue-derived, pro-inflammatory stimuli in macrophage responses to biomaterials using cell lysate as a complex source of cell-derived DAMPs and poly(methyl methacrylate) (PMMA) and polydimethylsiloxane (PDMS) films as model biomaterials. We show that lysate-adsorbed PMMA and PDMS surfaces strongly induced NF-κB/AP-1 transcription factor activity and pro-inflammatory cytokine secretion in the RAW-Blue macrophage cell line compared to serum-adsorbed surfaces. Lysate-dependent NF-κB/AP-1 activation and cytokine expression were strongly attenuated by TLR2 neutralizing antibodies, while TLR4 inhibition resulted in a modest reduction. These data suggest that DAMPs, in their adsorbed conformations on material surfaces, may play a significant role in macrophage activation through TLR signaling, and that TLR pathways, particularly TLR2, merit further investigation as potential therapeutic targets to modulate host responses to implanted biomaterials.

Combining Calcium Phosphates with Polysaccharides: A Bone-Inspired Material Modulating Monocyte/Macrophage Early Inflammatory Response

The use of inorganic calcium/phosphate supplemented with biopolymers has drawn lots of attention in bone regenerative medicine. While inflammation is required for bone healing, its exacerbation alters tissue regeneration/implants integration. Inspired by bone composition, a friendly automated spray-assisted system was used to build bioactive and osteoinductive calcium phosphate/chitosan/hyaluronic acid substrate (CaP-CHI-HA). Exposing monocytes to CaP-CHI-HA resulted in a secretion of pro-healing VEGF and TGF-β growth factors, TNF-α, MCP-1, IL-6 and IL-8 pro-inflammatory mediators but also IL-10 anti-inflammatory cytokine along with an inflammatory index below 1.5 (versus 2.5 and 7.5 following CaP and LPS stimulation, respectively). Although CD44 hyaluronic acid receptor seems not to be involved in the inflammatory regulation, results suggest a potential role of chemical composition and calcium release from build-up substrates, in affecting the intracellular expression of a calcium-sensing receptor. Herein, our findings indicate a great potential of CaP-CHI-HA in providing required inflammation-healing balance, favorable for bone healing/regeneration.

Dual surface modification of PDMS-based silicone implants to suppress capsular contracture

In this study, we report a new physicochemical surface on poly(dimethylsiloxane) (PDMS)-based silicone implants in an effort to minimize capsular contracture. Two different surface modification strategies, namely, microtexturing as a physical cue and multilayer coating as a chemical cue, were combined to achieve synergistic effects. The deposition of uniformly sized microparticles onto uncured PDMS surfaces and the subsequent removal after curing generated microtextured surfaces with concave hemisphere micropatterns. The size of the individual micropattern was controlled by the microparticle size. Micropatterns of three different sizes (37.16, 70.22, and 97.64 μm) smaller than 100 μm were produced for potential application to smooth and round-shaped breast implants. The PDMS surface was further chemically modified by layer-by-layer (LbL) deposition of poly-l-lysine and hyaluronic acid. Short-term in vitro experiments demonstrated that all the PDMS samples were cytocompatible. However, lower expression of TGF-β and α-SMA, the major profibrotic cytokine and myofibroblast marker, respectively, was observed in only multilayer-coated PDMS samples with larger size micropatterns (70.22 and 97.64 μm), thereby confirming the synergistic effects of physical and chemical cues. An in vivo study conducted for 8 weeks after implantation in rats also indicated that PDMS samples with larger size micropatterns and multilayer coating most effectively inhibited capsular contracture based on analyses of tissue inflammation, number of macrophage, fibroblast and myofibroblast, TGF-β expression, collagen density, and capsule thickness.

STATEMENT OF SIGNIFICANCE

Although poly(dimethylsiloxane) (PDMS)-based silicone implants have been widely used for various applications including breast implants, they usually cause typical side effects called as capsular contracture. Prior studies have shown that microtexturing and surface coating could reduce capsular contracture. However, previous methods are limited in their scope for application, and it is difficult to obtain FDA approval because of the large and nonuniform size of the microtexture as well as the use of toxic chemical components. Herein, those issues could be addressed by creating a microtexture of size less than 100 m, with a narrow size distribution and using layer-by-layer deposition of a biocompatible polymer without using any toxic compounds. Furthermore, this is the first attempt to combine microtexture with multilayer coating to obtain synergetic effects in minimizing the capsular contracture.

Early fragmentation of polyester urethane sheet neither causes persistent oxidative stress nor alters the outcome of normal tissue healing in rat skin

Silicone breast implant is associated with complications inherent to the surgical procedure. Prosthesis coating with polyurethane, however, commonly reduces the incidence of such complications. In this paper, the authors evaluated the inflammatory histomorphometric profile and oxidative damage associated to the implant of polyester urethane sheets. Forty-eight Wistar rats were divided into Sham or polyester urethane groups (n = 8/group) and underwent a polyester urethane implant in the dorsal skinfold. Tissue samples were collected on days seven, 30, and 90 after surgery and subjected to histomorphometric analysis and biochemical tests. Results were analyzed by one-way ANOVA (p ≤ 0.05). Peri-implant tissue samples exhibited characteristic inflammatory response associated with the biomaterial, with increased vascularization on day seven and augmented levels of IL1-b and TNF-a after 30 days. Peri-implant fibrocystic population was small on day seven, but increased considerably after 90 days. A rise in the carbonyl group levels of skin samples in the polyester urethane group was observed on day seven. Findings suggest that polyester urethane sheets undergo biodegradation at an early stage after implantation, followed by increased vascularity and microencapsulation of biomaterial fragments, without persistent oxidative damage. Fiber arrangement inside the collagen matrix results in a fibrotic scar because of polyester urethane degradation.

Silk fibroin/amniotic membrane 3D bi-layered artificial skin

Burn injuries have been reported to be an important cause of morbidity and mortality and they are still considered as unmet clinical need. Although there is a myriad of effective stem cells that have been suggested for skin regeneration, there is no one ideal scaffold. The aim of this study was to develop a three-dimensional (3D) bi-layer scaffold made of biological decellularized human amniotic membrane (AM) with viscoelastic electrospun nanofibrous silk fibroin (ESF) spun on top. The fabricated 3D bi-layer AM/ESF scaffold was submerged in ethanol to induce β-sheet transformation as well as to get a tightly coated and inseparable bi-layer. The biomechanical and biological properties of the 3D bi-layer AM/ESF scaffold were investigated. The results indicate significantly improved mechanical properties of the AM/ESF compared with the AM alone. Both the AM and AM/ESF possess a variety of suitable adhesion cells without detectable cytotoxicity against adipose tissue-derived mesenchymal stem cells (AT-MSCs). The AT-MSCs show increased expression of two main pro-angiogenesis factors, vascular endothelial growth factor and basic fibroblast growth factor, when cultured on the AM/ESF for 7 days, when comparing with AM alone. The results suggest that the AM/ESF scaffold with autologous AT-MSCs has excellent cell adhesion and proliferation along with production of growth factors which serves as a possible application in a clinical setting for skin regeneration.

Systematic in vivo evaluation of the time-dependent inflammatory response to steel and Teflon insulin infusion catheters

Continuous subcutaneous insulin infusion (CSII) catheters are considered the weak link of insulin pump therapy. Wear-time considerably varies between patients and the choice of catheter material is based on personal preferences rather than scientific facts. Therefore, we systematically assessed and quantified the inflammatory tissue response to steel versus Teflon CSII catheters over a maximum wear-time of 7 days in swine. Tissue surrounding catheters was analysed using histopathology and quantitative real-time PCR. The area of inflammation increased significantly over time independent of material which was confirmed by an increase in CD68 expression and an increase in mononuclear and neutrophil cell infiltrate around the catheters. We observed substantially higher fibrin deposition (p < 0.05) around steel on day 4 of wear-time. IL-6 gene expression increased within 24 hours after insertion, returned to normal levels around Teflon (p < 0.05) but remained high around steel (p < 0.05). IL-10 and TGF-β levels did not resolve over time, indicating impaired wound healing. In conclusion, there was a major temporal effect in the acute inflammatory response to CSII catheters but we found little difference between materials. This study setup presents a robust tool for the systematic analysis of the tissue response to CSII catheters.

Immunological challenges associated with artificial skin grafts: available solutions and stem cells in future design of synthetic skin

The repair or replacement of damaged skins is still an important, challenging public health problem. Immune acceptance and long-term survival of skin grafts represent the major problem to overcome in grafting given that in most situations autografts cannot be used. The emergence of artificial skin substitutes provides alternative treatment with the capacity to reduce the dependency on the increasing demand of cadaver skin grafts. Over the years, considerable research efforts have focused on strategies for skin repair or permanent skin graft transplantations. Available skin substitutes include pre- or post-transplantation treatments of donor cells, stem cell-based therapies, and skin equivalents composed of bio-engineered acellular or cellular skin substitutes. However, skin substitutes are still prone to immunological rejection, and as such, there is currently no skin substitute available to overcome this phenomenon. This review focuses on the mechanisms of skin rejection and tolerance induction and outlines in detail current available strategies and alternatives that may allow achieving full-thickness skin replacement and repair.