Biomolecular strategies to modulate the macrophage response to implanted materials

Pro-endothelialization of nitinol alloy cardiovascular stents enhanced by the programmed assembly of exosomes and endothelial affinity peptide

Stent implantation is one of the most effective methods for the treatment of atherosclerosis. Nitinol stent is a type of stent with good biocompatibility and relatively mature development; however, it cannot effectively achieve long-term anticoagulation and early endothelialization. In this study, nitinol surfaces with the programmed assembly of heparin, exosomes from endothelial cells, and endothelial affinity peptide (REDV) were fabricated through layer-by-layer assembly technology and click-chemistry, and then exosomes/REDV-modified nitinol interface (ACC-Exo-REDV) was prepared. ACC-Exo-REDV could promote the rapid proliferation and adhesion of endothelial cells and achieve anticoagulant function in the blood. Besides, ACC-Exo-REDV had excellent anti-inflammatory properties and played a positive role in the transformation of macrophage from the pro-inflammatory to anti-inflammatory phenotype. Ex vivo and in vivo experiments demonstrated the effectiveness of ACC-Exo-REDV in preventing thrombosis and hyperplasia formation. Hence, the programmed assembly of exosome interface could contribute to endothelialization and have potential application on the cardiovascular surface modification to prevent stent thrombosis and restenosis.

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.

Silicone cryogel skeletons enhance the survival and mechanical integrity of hydrogel-encapsulated cell therapies

The transplantation of engineered cells that secrete therapeutic proteins presents a promising method for addressing a range of chronic diseases. However, hydrogels used to encase and protect non-autologous cells from immune rejection often suffer from poor mechanical properties, insufficient oxygenation, and fibrotic encapsulation. Here, we introduce a composite encapsulation system comprising an oxygen-permeable silicone cryogel skeleton, a hydrogel matrix, and a fibrosis-resistant polymer coating. Cryogel skeletons enhance the fracture toughness of conventional alginate hydrogels by 23-fold and oxygen diffusion by 2.8-fold, effectively mitigating both implant fracture and hypoxia of encapsulated cells. Composite implants containing xenogeneic cells engineered to secrete erythropoietin significantly outperform unsupported alginate implants in therapeutic delivery over 8 weeks in immunocompetent mice. By improving mechanical resiliency and sustaining denser cell populations, silicone cryogel skeletons enable more durable and miniaturized therapeutic implants.

Biomaterials for immunomodulation in wound healing

The substantial economic impact of non-healing wounds, scarring, and burns stemming from skin injuries is evident, resulting in a financial burden on both patients and the healthcare system. This review paper provides an overview of the skin's vital role in guarding against various environmental challenges as the body's largest protective organ and associated developments in biomaterials for wound healing. We first introduce the composition of skin tissue and the intricate processes of wound healing, with special attention to the crucial role of immunomodulation in both acute and chronic wounds. This highlights how the imbalance in the immune response, particularly in chronic wounds associated with underlying health conditions such as diabetes and immunosuppression, hinders normal healing stages. Then, this review distinguishes between traditional wound-healing strategies that create an optimal microenvironment and recent peptide-based biomaterials that modulate cellular processes and immune responses to facilitate wound closure. Additionally, we highlight the importance of considering the stages of wounds in the healing process. By integrating advanced materials engineering with an in-depth understanding of wound biology, this approach holds promise for reshaping the field of wound management and ultimately offering improved outcomes for patients with acute and chronic wounds.

Fibrous capsule-resistant, controllably degradable and functionalizable zwitterion-albumin hybrid hydrogels

Foreign body response (FBR) represents an immune-mediated cascade reaction capable of inducing the rejection of foreign implants, thereby compromising their in vivo performance. Pure zwitterionic hydrogels have demonstrated the ability to resist long-term FBR, owing to their outstanding antifouling capabilities. However, achieving such a robust anti-FBR effect necessitates stringent requirements concerning the purity of zwitterionic materials, which constrains their broader functional applications. Herein, we present a biocompatible, controllably degradable, and functionalizable zwitterion-albumin hybrid hydrogel. The zwitterionic hydrogel crosslinked with serum albumin exhibits controllable degradation and excels in preventing the adsorption of various proteins and adhesion of cells and bacteria. Moreover, the hydrogel significantly alleviates the host's FBR compared with PEG hydrogels and particularly outperforms PEG-based cross-linker crosslinked zwitterionic hydrogels in reducing collagen encapsulation when subcutaneously implanted into mice. The zwitterion-albumin hybrid hydrogel shows potential as a functionalizable anti-FBR material in the context of implantable materials and biomedical devices.

Reducing Peri-implant Capsule Thickness in Submuscular Rodent Model of Breast Reconstruction With Delayed Radiotherapy

INTRODUCTION

Capsular contracture remains the most common complication following device-based breast reconstruction, occurring in up to 50% of women who also undergo adjuvant radiotherapy either before or after device-based reconstruction. While certain risk factors for capsular contracture have been identified, there remains no clinically effective method of prevention. The purpose of the present study is to determine the effect of coating the implant with the novel small molecule Met-Z2-Y12, with and without delayed, targeted radiotherapy, on capsule thickness and morphologic change around smooth silicone implants placed under the latissimus dorsi in a rodent model.

METHODS

Twenty-four female Sprague Dawley rats each had 2 mL smooth round silicone breast implants implanted bilaterally under the latissimus dorsi muscle. Twelve received uncoated implants and twelve received implants coated with Met-Z2-Y12. Half of the animals from each group received targeted radiotherapy (20 Gray) on postoperative day ten. At three and 6 months after implantation, the tissue surrounding the implants was harvested for analysis of capsular histology including capsule thickness. Additionally, microCT scans were qualitatively analyzed for morphologic change.

RESULTS

Capsules surrounding Met-Z2-Y12-coated implants were significantly thinner (P = 0.006). The greatest difference in capsule thickness was seen in the irradiated 6-month groups, where mean capsule thickness was 79.1 ± 27.3 μm for uncoated versus 50.9 ± 9.6 μm for Met-Z2-Y12-coated implants (P = 0.038). At the time of explant, there were no capsular morphologic differences between the groups either grossly or per microCT.

CONCLUSIONS

Met-Z2-Y12 coating of smooth silicone breast implants significantly reduces capsule thickness in a rodent model of submuscular breast reconstruction with delayed radiotherapy.

An Antifibrotic Breast Implant Surface Coating Significantly Reduces Periprosthetic Capsule Formation

BACKGROUND

The body responds to prosthetic materials with an inflammatory foreign body response and deposition of a fibrous capsule, which may be deleterious to the function of the device and cause significant discomfort for the patient. Capsular contracture (CC) is the most common complication of aesthetic and reconstructive breast surgery. The source of significant patient morbidity, it can result in pain, suboptimal aesthetic outcomes, implant failure, and increased costs. The underlying mechanism remains unknown. Treatment is limited to reoperation and capsule excision, but recurrence rates remain high. In this study, the authors altered the surface chemistry of silicone implants with a proprietary anti-inflammatory coating to reduce capsule formation.

METHODS

Silicone implants were coated with Met-Z2-Y12, a biocompatible, anti-inflammatory surface modification. Uncoated and Met-Z2-Y12-coated implants were implanted in C57BL/6 mice. After 21, 90, or 180 days, periprosthetic tissue was removed for histologic analysis.

RESULTS

The authors compared mean capsule thickness at three time points. At 21, 90, and 180 days, there was a statistically significant reduction in capsule thickness of Met-Z2-Y12-coated implants compared with uncoated implants ( P < 0.05).

CONCLUSIONS

Coating the surface of silicone implants with Met-Z2-Y12 significantly reduced acute and chronic capsule formation in a mouse model for implant-based breast augmentation and reconstruction. As capsule formation obligatorily precedes CC, these results suggest contracture itself may be significantly attenuated. Furthermore, as periprosthetic capsule formation is a complication without anatomical boundaries, this chemistry may have additional applications beyond breast implants, to a myriad of other implantable medical devices.

CLINICAL RELEVANCE STATEMENT

Coating of the silicone implant surface with Met-Z2-Y12 alters the periprosthetic capsule architecture and significantly reduces capsule thickness for at least 6 months postoperatively in a murine model. This is a promising step forward in the development of a therapy to prevent capsular contracture.

Soft robot-mediated autonomous adaptation to fibrotic capsule formation for improved drug delivery

The foreign body response impedes the function and longevity of implantable drug delivery devices. As a dense fibrotic capsule forms, integration of the device with the host tissue becomes compromised, ultimately resulting in device seclusion and treatment failure. We present FibroSensing Dynamic Soft Reservoir (FSDSR), an implantable drug delivery device capable of monitoring fibrotic capsule formation and overcoming its effects via soft robotic actuations. Occlusion of the FSDSR porous membrane was monitored over 7 days in a rodent model using electrochemical impedance spectroscopy. The electrical resistance of the fibrotic capsule correlated to its increase in thickness and volume. Our FibroSensing membrane showed great sensitivity in detecting changes at the abiotic/biotic interface, such as collagen deposition and myofibroblast proliferation. The potential of the FSDSR to overcome fibrotic capsule formation and maintain constant drug dosing over time was demonstrated in silico and in vitro. Controlled closed loop release of methylene blue into agarose gels (with a comparable fold change in permeability relating to 7 and 28 days in vivo) was achieved by adjusting the magnitude and frequency of pneumatic actuations after impedance measurements by the FibroSensing membrane. By sensing fibrotic capsule formation in vivo, the FSDSR will be capable of probing and adapting to the foreign body response through dynamic actuation changes. Informed by real-time sensor signals, this device offers the potential for long-term efficacy and sustained drug dosing, even in the setting of fibrotic capsule formation.

CaP-coated Zn-Mn-Li alloys regulate osseointegration via influencing macrophage polarization in the osteogenic environment

Immune response is an important factor in determining the fate of bone replacement materials, in which macrophages play an important role. It is a new idea to design biomaterials with immunomodulatory function to reduce inflammation and promote bone integration by regulating macrophages polarization. In this work, the immunomodulatory properties of CaP Zn-Mn-Li alloys and the specific mechanism of action were investigated. We found that the CaP Zn0.8Mn0.1Li alloy promoted the polarization of macrophages toward M2 and reduced inflammation, which could effectively upregulate osteogenesis-related factors and promote new bone formation, indicating the important role of macrophages polarization in biomaterial induction of osteogenesis. In vivo studies further demonstrated that CaP Zn0.8Mn0.1Li alloy could stimulate osteogenesis better than other Zn-Mn-Li alloys implantations by regulating macrophages polarization and reducing inflammation. In addition, transcriptome results showed that CaP Zn0.8Mn0.1Li played an important regulatory role in the life process of macrophages, activating Toll-like receptor signaling pathway, which participated in the activation and attenuation of inflammation, and accelerated bone integration. Thus, by preparing CaP coatings on the surface of Zn-Mn-Li alloys and combining the bioactive ingredient with controlled release, the biomaterial will be imbibed with beneficial immunomodulatory properties that promote bone integration.

Robust Neural Interfaces with Photopatternable, Bioadhesive, and Highly Conductive Hydrogels for Stable Chronic Neuromodulation

A robust neural interface with intimate electrical coupling between neural electrodes and neural tissues is critical for stable chronic neuromodulation. The development of bioadhesive hydrogel neural electrodes is a potential approach for tightly fixing the neural electrodes on the epineurium surface to construct a robust neural interface. Herein, we construct a photopatternable, antifouling, conductive (∼6 S cm-1), bioadhesive (interfacial toughness ∼100 J m-2), soft, and elastic (∼290% strain, Young's modulus of 7.25 kPa) hydrogel to establish a robust neural interface for bioelectronics. The UV-sensitive zwitterionic monomer can facilitate the formation of an electrostatic-assembled conductive polymer PEDOT:PSS network, and it can be further photo-cross-linked into elastic polymer network. Such a semi-interpenetrating network endows the hydrogel electrodes with good conductivity. Especially, the photopatternable feature enables the facile microfabrication processes of multifunctional hydrogel (MH) interface with a characteristic size of 50 μm. The MH neural electrodes, which show improved performance of impedance, charge storage capacity, and charge injection capability, can produce effective electrical stimulation with high current density (1 mA cm-2) at ultralow voltages (±25 mV). The MH interface could realize high-efficient electrical communication at the chronic neural interface for stable recording and stimulation of a sciatic nerve in the rat model.

In Vitro and In Vivo Cell-Interactions with Electrospun Poly (Lactic-Co-Glycolic Acid) (PLGA): Morphological and Immune Response Analysis

Random electrospun three-dimensional fiber membranes mimic the extracellular matrix and the interfibrillar spaces promotes the flow of nutrients for cells. Electrospun PLGA membranes were analyzed in vitro and in vivo after being sterilized with gamma radiation and bioactivated with fibronectin or collagen. Madin-Darby Canine Kidney (MDCK) epithelial cells and primary fibroblast-like cells from hamster’s cheek paunch proliferated over time on these membranes, evidencing their good biocompatibility. Cell-free irradiated PLGA membranes implanted on the back of hamsters resulted in a chronic granulomatous inflammatory response, observed after 7, 15, 30 and 90 days. Morphological analysis of implanted PLGA using light microscopy revealed epithelioid cells, Langhans type of multinucleate giant cells (LCs) and multinucleated giant cells (MNGCs) with internalized biomaterial. Lymphocytes increased along time due to undegraded polymer fragments, inducing the accumulation of cells of the phagocytic lineage, and decreased after 90 days post implantation. Myeloperoxidase⁺ cells increased after 15 days and decreased after 90 days. LCs, MNGCs and capillaries decreased after 90 days. Analysis of implanted PLGA after 7, 15, 30 and 90 days using transmission electron microscope (TEM) showed cells exhibiting internalized PLGA fragments and filopodia surrounding PLGA fragments. Over time, TEM analysis showed less PLGA fragments surrounded by cells without fibrous tissue formation. Accordingly, MNGC constituted a granulomatous reaction around the polymer, which resolves with time, probably preventing a fibrous capsule formation. Finally, this study confirms the biocompatibility of electrospun PLGA membranes and their potential to accelerate the healing process of oral ulcerations in hamsters’ model in association with autologous cells.

New Horizons of Macrophage Immunomodulation in the Healing of Diabetic Foot Ulcers

Diabetic foot ulcers (DFUs) are one of the most costly and troublesome complications of diabetes mellitus. The wound chronicity of DFUs remains the main challenge in the current and future treatment of this condition. Persistent inflammation results in chronic wounds characterized by dysregulation of immune cells, such as M1 macrophages, and impairs the polarization of M2 macrophages and the subsequent healing process of DFUs. The interactive regulation of M1 and M2 macrophages during DFU healing is critical and seems manageable. This review details how cytokines and signalling pathways are co-ordinately regulated to control the functions of M1 and M2 macrophages in normal wound repair. DFUs are defective in the M1-to-M2 transition, which halts the whole wound-healing machinery. Many pre-clinical and clinical innovative approaches, including the application of topical insulin, CCL chemokines, micro RNAs, stem cells, stem-cell-derived exosomes, skin substitutes, antioxidants, and the most recent Phase III-approved ON101 topical cream, have been shown to modulate the activity of M1 and M2 macrophages in DFUs. ON101, the newest clinically approved product in this setting, is designed specifically to down-regulate M1 macrophages and further modulate the wound microenvironment to favour M2 emergence and expansion. Finally, the recent evolution of macrophage modulation therapies and techniques will improve the effectiveness of the treatment of diverse DFUs.

In situ regeneration of nasal septal defects using acellular cartilage enhanced with platelet-derived growth factor

Nasal septum defects can currently only be reconstructed using autologous cartilage grafts. In this study, we examine the reconstruction of septal cartilage defects in a rabbit model using porcine decellularized nasal septal cartilage (DNSC) functionalized with recombinant platelet-derived growth factor-BB (PDFG-BB). The supportive function of the transplanted DNSC was estimated by the degree of septum deviation and shrinkage using magnetic resonance imaging (MRI). The biocompatibility of the transplanted scaffolds was evaluated by histology according to international standards. A study group with an autologous septal transplant was used as a reference. In situ regeneration of cartilage defects was assessed by histological evaluation 4 and 16 weeks following DNSC transplantation. A study group with non-functionalized DNSC was introduced for estimation of the effects of PDFG-BB functionalization. DNSC scaffolds provided sufficient structural support to the nasal septum, with no significant shrinkage or septal deviations as evaluated by the MRI. Biocompatibility analysis after 4 weeks revealed an increased inflammatory reaction of the surrounding tissue in response to DNSC as compared to the autologous transplants. The inflammatory reaction was, however, significantly attenuated after 16 weeks in the PDGF-BB group whereas only a slight improvement of the biocompatibility score was observed in the untreated group. In situ regeneration of septal cartilage, as evidenced by the degradation of the DNSC matrix and production of neocartilage, was observed in both experimental groups after 16 weeks but was more pronounced in the PDFG-BB group. Overall, DNSC provided structural support to the nasal septum and stimulated in situ regeneration of the cartilage tissue. Furthermore, PDFG-BB augmented the regenerative potential of DNSC and enhanced the healing process, as demonstrated by reduced inflammation after 16 weeks.

Temporal Control over Macrophage Phenotype and the Host Response via Magnetically Actuated Scaffolds

Cyclic strain generated at the cell-material interface is critical for the engraftment of biomaterials. Mechanosensitive immune cells, macrophages regulate the host-material interaction immediately after implantation by priming the environment and remodeling ongoing regenerative processes. This study investigated the ability of mechanically active scaffolds to modulate macrophage function in vitro and in vivo. Remotely actuated magnetic scaffolds enhance the phenotype of murine classically activated (M1) macrophages, as shown by the increased expression of the M1 cell-surface marker CD86 and increased secretion of multiple M1 cytokines. When scaffolds were implanted subcutaneously into mice and treated with magnetic stimulation for 3 days beginning at either day 0 or day 5 post-implantation, the cellular infiltrate was enriched for host macrophages. Macrophage expression of the M1 marker CD86 was increased, with downstream effects on vascularization and the foreign body response. Such effects were not observed when the magnetic treatment was applied at later time points after implantation (days 12-15). These results advance our understanding of how remotely controlled mechanical cues, namely, cyclic strain, impact macrophage function and demonstrate the feasibility of using mechanically active nanomaterials to modulate the host response in vivo.

Cerium Oxide Nanoparticles with Entrapped Gadolinium for High T 1 Relaxivity and ROS-Scavenging Purposes

Gadolinium chelates are employed worldwide today as clinical contrast agents for magnetic resonance imaging. Until now, the commonly used linear contrast agents based on the rare-earth element gadolinium have been considered safe and well-tolerated. Recently, concerns regarding this type of contrast agent have been reported, which is why there is an urgent need to develop the next generation of stable contrast agents with enhanced spin-lattice relaxation, as measured by improved T ₁ relaxivity at lower doses. Here, we show that by the integration of gadolinium ions in cerium oxide nanoparticles, a stable crystalline 5 nm sized nanoparticulate system with a homogeneous gadolinium ion distribution is obtained. These cerium oxide nanoparticles with entrapped gadolinium deliver strong T ₁ relaxivity per gadolinium ion (T ₁ relaxivity, r ₁ = 12.0 mM^-1 s^-1) with the potential to act as scavengers of reactive oxygen species (ROS). The presence of Ce³⁺ sites and oxygen vacancies at the surface plays a critical role in providing the antioxidant properties. The characterization of radial distribution of Ce³⁺ and Ce⁴⁺ oxidation states indicated a higher concentration of Ce³⁺ at the nanoparticle surfaces. Additionally, we investigated the ROS-scavenging capabilities of pure gadolinium-containing cerium oxide nanoparticles by bioluminescent imaging in vivo, where inhibitory effects on ROS activity are shown.

Physical Confinement in Alginate Cryogels Determines Macrophage Polarization to a M2 phenotype by Regulating a STAT-Related mRNA Transcription Pathway

The immunologic response is considered to play a pivotal role in the application of biomaterial implants, and intrinsic properties of biomaterials can significantly modulate the anti-inflammatory effects. However, how physical...

Organic and Inorganic Template-Assisted Synthesis of Silica Nanotubes and Evaluation of Their Properties

Mesoporous silica network nanotubes were fabricated using both organic and inorganic templates such as citric acid (CA), cetyltrimethylammonium bromide (CTAB), and sodium bicarbonate (SBC). The phase analysis of synthesized silica network was confirmed by X-ray diffractometer (XRD) analysis, and the present functional groups were revealed by Fourier Transform Infrared Spectroscopy (FTIR) and the formation of tubular morphology was analyzed by transmission electron microscopy (TEM). The mesoporous nature of each template sample was studied using Brunauer-Emmett-Teller (BET) instrument. The surface area and porous size were calculated successfully for fabricated silica network nanotubes.

Light-induced dynamic RGD pattern for sequential modulation of macrophage phenotypes

Due to the critical roles of macrophage in immune response and tissue repair, harnessing macrophage phenotypes dynamically to match the tissue healing process on demand attracted many attentions. Although there have developed many advanced platforms with dynamic features for cell manipulation, few studies have designed a dynamic chemical pattern to sequentially polarize macrophage phenotypes and meet the immune requirements at various tissue repair stages. Here, we propose a novel strategy for spatiotemporal manipulation of macrophage phenotypes by a UV-induced dynamic Arg-Gly-Asp (RGD) pattern. By employing a photo-patterning technique and the specific interaction between cyclodextrin (CD) and azobenzene-RGD (Azo-RGD), we prepared a polyethylene glycol-dithiol/polyethylene glycol-norbornene (PEG-SH/PEG-Nor) hydrogel with dynamic RGD-patterned surface. After irradiation with 365-nm UV light, the homogeneous RGD surface was transformed to the RGD-patterned surface which induced morphological transformation of macrophages from round to elongated and subsequent phenotypic transition from pro-inflammation to anti-inflammation. The mechanism of phenotypic polarization induced by RGD pattern was proved to be related to Rho-associated protein kinase 2 (ROCK2). Sequential modulation of macrophage phenotypes by the dynamic RGD-patterned surface provides a remote and non-invasive strategy to manipulate immune reactions and achieve optimized healing outcomes.

Electronic Drugs: Spatial and Temporal Medical Treatment of Human Diseases

Recent advances in diagnostics and medicines emphasize the spatial and temporal aspects of monitoring and treating diseases. However, conventional therapeutics, including oral administration and injection, have difficulties meeting these aspects due to physiological and technological limitations, such as long-term implantation and a narrow therapeutic window. As an innovative approach to overcome these limitations, electronic devices known as electronic drugs (e-drugs) have been developed to monitor real-time body signals and deliver specific treatments to targeted tissues or organs. For example, ingestible and patch-type e-drugs could detect changes in biomarkers at the target sites, including the gastrointestinal (GI) tract and the skin, and deliver therapeutics to enhance healing in a spatiotemporal manner. However, medical treatments often require invasive surgical procedures and implantation of medical equipment for either short or long-term use. Therefore, approaches that could minimize implantation-associated side effects, such as inflammation and scar tissue formation, while maintaining high functionality of e-drugs, are highly needed. Herein, the importance of the spatial and temporal aspects of medical treatment is thoroughly reviewed along with how e-drugs use cutting-edge technological innovations to deal with unresolved medical challenges. Furthermore, diverse uses of e-drugs in clinical applications and the future perspectives of e-drugs are discussed.

Predicting the In Vivo Performance of Cardiovascular Biomaterials: Current Approaches In Vitro Evaluation of Blood-Biomaterial Interactions

The therapeutic efficacy of a cardiovascular device after implantation is highly dependent on the host-initiated complement and coagulation cascade. Both can eventually trigger thrombosis and inflammation. Therefore, understanding these initial responses of the body is of great importance for newly developed biomaterials. Subtle modulation of the associated biological processes could optimize clinical outcomes. However, our failure to produce truly blood compatible materials may reflect our inability to properly understand the mechanisms of thrombosis and inflammation associated with biomaterials. In vitro models mimicking these processes provide valuable insights into the mechanisms of biomaterial-induced complement activation and coagulation. Here, we review (i) the influence of biomaterials on complement and coagulation cascades, (ii) the significance of complement-coagulation interactions for the clinical success of cardiovascular implants, (iii) the modulation of complement activation by surface modifications, and (iv) in vitro testing strategies.

Macrophage phenotypes in tissue repair and the foreign body response: Implications for biomaterial-based regenerative medicine strategies

Macrophages are a highly heterogeneous and plastic population of cells that are crucial for tissue repair and regeneration. This has made macrophages a particularly attractive target for biomaterial-directed regenerative medicine strategies. However, macrophages also contribute to adverse inflammatory and fibrotic responses to implanted biomaterials, typically related to the foreign body response (FBR). The traditional model in the field asserts that the M2 macrophage phenotype is pro-regenerative and associated with positive wound healing outcomes, whereas the M1 phenotype is pro-inflammatory and associated with pathogenesis. However, recent studies indicate that both M1 and M2 macrophages play different, but equally vital, roles in promoting tissue repair. Furthermore, recent technological developments such as single-cell RNA sequencing have allowed for unprecedented insights into the heterogeneity within the myeloid compartment, related to activation state, niche, and ontogenetic origin. A better understanding of the phenotypic and functional characteristics of macrophages critical to tissue repair and FBR processes will allow for rational design of biomaterials to promote biomaterial-tissue integration and regeneration. In this review, we discuss the role of temporal and ontogenetic macrophage heterogeneity on tissue repair processes and the FBR and the potential implications for biomaterial-directed regenerative medicine applications. STATEMENT OF SIGNIFICANCE: This review outlines the contributions of different macrophage phenotypes to different phases of wound healing and angiogenesis. Pathological outcomes, such as chronic inflammation, fibrosis, and the foreign body response, related to disruption of the macrophage inflammation-resolution process are also discussed. We summarize recent insights into the vast heterogeneity of myeloid cells related to their niche, especially the biomaterial microenvironment, and ontogenetic origin. Additionally, we present a discussion on novel tools that allow for resolution of cellular heterogeneity at the single-cell level and how these can be used to build a better understanding of macrophage heterogeneity in the biomaterial immune microenvironment to better inform immunomodulatory biomaterial design.

The Foreign Body Response to an Implantable Therapeutic Reservoir in a Diabetic Rodent Model

Advancements in type 1 diabetes mellitus treatments have vastly improved in recent years. The move toward a bioartificial pancreas and other fully implantable systems could help restore patient's glycemic control. However, the long-term success of implantable medical devices is often hindered by the foreign body response. Fibrous encapsulation "walls off" the implant to the surrounding tissue, impairing its functionality. In this study we aim to examine how streptozotocin-induced diabetes affects fibrous capsule formation and composition surrounding implantable drug delivery devices following subcutaneous implantation in a rodent model. After 2 weeks of implantation, the fibrous capsule surrounding the devices were examined by means of Raman spectroscopy, micro-computed tomography (μCT), and histological analysis. Results revealed no change in mean fibrotic capsule thickness between diabetic and healthy animals as measured by μCT. Macrophage numbers (CCR7 and CD163 positive) remained similar across all groups. True component analysis also showed no quantitative difference in the alpha-smooth muscle actin and extracellular matrix proteins. Although principal component analysis revealed significant secondary structural difference in collagen I in the diabetic group, no evidence indicates an influence on fibrous capsule composition surrounding the device. This study confirms that diabetes did not have an effect on the fibrous capsule thickness or composition surrounding our implantable drug delivery device. Impact Statement Understanding the impact diabetes has on the foreign body response (FBR) to our implanted material is essential for developing an effective drug delivery device. We used several approaches (Raman spectroscopy and micro-computed tomography imaging) to demonstrate a well-rounded understanding of the diabetic impact on the FBR to our devices, which is imperative for its clinical translation.

Surface modification strategies to improve titanium hemocompatibility: a comprehensive review

Titanium and its alloys are widely used in different biomaterial applications due to their remarkable mechanical properties and bio-inertness. However, titanium-based materials still face some challenges, with an emphasis on hemocompatibility. Blood-contacting devices such as stents, heart valves, and circulatory devices are prone to thrombus formation, restenosis, and inflammation due to inappropriate blood-implant surface interactions. After implantation, when blood encounters these implant surfaces, a series of reactions takes place, such as protein adsorption, platelet adhesion and activation, and white blood cell complex formation as a defense mechanism. Currently, patients are prescribed anticoagulant drugs to prevent blood clotting, but these drugs can weaken their immune system and cause profound bleeding during injury. Extensive research has been done to modify the surface properties of titanium to enhance its hemocompatibility. Results have shown that the modification of surface morphology, roughness, and chemistry has been effective in reducing thrombus formation. The main focus of this review is to analyze and understand the different modification techniques on titanium-based surfaces to enhance hemocompatibility and, consequently, recognize the unresolved challenges and propose scopes for future research.

Inducing Immunomodulatory Effects on Human Macrophages by Multifunctional NCO-sP(EO-stat-PO)/Gelatin Hydrogel Nanofibers

Endowing materials and scaffolds with immunomodulatory properties has evolved into a very active field of research. However, combining such effects with multifunctionality regarding cell adhesion and manipulation is still challenging due to the intricate nature of cell-substrate interactions that require fine-tuning of scaffold properties. Here, we reported electrospinning of a well-known biopolymer, gelatin, together with six-arm star-shaped poly(ethylene oxide-stat-propylene oxide) prepolymer with isocyanate end groups (NCO-sP(EO-stat-PO)) as a reactive prepolymer cross-linker. Covalent coupling of two components during and after processing yielded a network of hydrogel fibers that was remarkably stable under aqueous and also proteolytic conditions without the need for extra cross-linking, with a significant increase in stability with increasing NCO-sP(EO-stat-PO) content. When seeded with human macrophages, cells adhered and spread on the fibers and were found highly viable after 7 days of culture across all scaffolds. Furthermore, hybrid fibrous meshes upregulated the expression of a prohealing gene, CD206, while downregulating proinflammatory genes, IL-1β and IL-8. Markedly, NCO-sP(EO-stat-PO)-rich samples induced a significantly reduced release of proinflammatory cytokines, IL-1β, IL-6, and IL-8. Finally, we successfully conjugated IL-4 to NCO-sP(EO-stat-PO) that effectively steered macrophages into a prohealing M2 type, demonstrating additional and robust control over the immunomodulatory feature of the scaffolds.

Biomaterial design strategies to address obstacles in craniomaxillofacial bone repair

Biomaterial design to repair craniomaxillofacial defects has largely focused on promoting bone regeneration, while there are many additional factors that influence this process. The bone microenvironment is complex, with various mechanical property differences between cortical and cancellous bone, a unique porous architecture, and multiple cell types that must maintain homeostasis. This complex environment includes a vascular architecture to deliver cells and nutrients, osteoblasts which form new bone, osteoclasts which resorb excess bone, and upon injury, inflammatory cells and bacteria which can lead to failure to repair. To create biomaterials able to regenerate these large missing portions of bone on par with autograft materials, design of these materials must include methods to overcome multiple obstacles to effective, efficient bone regeneration. These obstacles include infection and biofilm formation on the biomaterial surface, fibrous tissue formation resulting from ill-fitting implants or persistent inflammation, non-bone tissue formation such as cartilage from improper biomaterial signals to cells, and voids in bone infill or lengthy implant degradation times. Novel biomaterial designs may provide approaches to effectively induce osteogenesis and new bone formation, include design motifs that facilitate surgical handling, intraoperative modification and promote conformal fitting within complex defect geometries, induce a pro-healing immune response, and prevent bacterial infection. In this review, we discuss the bone injury microenvironment and methods of biomaterial design to overcome these obstacles, which if unaddressed, may result in failure of the implant to regenerate host bone.

Biohybrid Nanosystems for Cancer Treatment: Merging the Best of Two Worlds

During the last 20+ years, research into the biomedical application of nanotechnology has helped in reshaping cancer treatment. The clinical use of several passively targeted nanosystems resulted in improved quality of care for patients. However, the therapeutic efficacy of these systems is not superior to the original drugs. Moreover, despite extensive investigations into actively targeted nanocarriers, numerous barriers still remain before their successful clinical translation, including sufficient bloodstream circulation time and efficient tumor targeting. The combination of synthetic nanomaterials with biological elements (e.g., cells, cell membranes, and macromolecules) is presently the cutting-edge research in cancer nanotechnology. The features provided by the biological moieties render the particles with prolonged bloodstream circulation time and homotopic targeting to the tumor site. Moreover, cancer cell membranes serve as sources of neoantigens, useful in the formulation of nanovaccines. In this chapter, we will discuss the advantages of biohybrid nanosystems in cancer chemotherapy, immunotherapy, and combined therapy, as well as highlight their preparation methods and clinical translatability.

A modular, injectable, non-covalently assembled hydrogel system features widescale tunable degradability for controlled release and tissue integration

Biomaterials with attenuated adverse host tissue reactions, and meanwhile, combining biocompatibility with mimicry of mechanical and biochemical cues of native extracellular matrices (ECM) to promote integration and regeneration of tissues are important for many biomedical applications. Further, the materials should also be tailorable to feature desired application-related functions, like tunable degradability, injectability, or controlled release of bioactive molecules. Herein, a non-covalently assembled, injectable hydrogel system based on oligopeptides interacting with sulphated polysaccharides is reported, showing high tolerability and biocompatibility in immunocompetent hairless mice. Altering the peptide or polysaccharide component considerably varies the in vivo degradation rate of the hydrogels, ranging from a half-life of three weeks to no detectable degradation after three months. The hydrogel with sulphated low molecular weight hyaluronic acid exhibits sustained degradation-mediated release of heparin-binding molecules in vivo, as shown by small animal magnetic resonance imaging and fluorescence imaging, and enhances the expression of vascular endothelial growth factor in hydrogel surrounding. In vitro investigations indicate that M2-macrophages could be responsible for the moderate difference in pro-angiogenic effects. The ECM-mimetic and injectable hydrogels represent tunable bioactive scaffolds for tissue engineering, also enabling controlled release of heparin-binding signalling molecules including many growth factors.

Metal-Specific Biomaterial Accumulation in Human Peri-Implant Bone and Bone Marrow

Metallic implants are frequently used in medicine to support and replace degenerated tissues. Implant loosening due to particle exposure remains a major cause for revision arthroplasty. The exact role of metal debris in sterile peri-implant inflammation is controversial, as it remains unclear whether and how metals chemically alter and potentially accumulate behind an insulating peri-implant membrane, in the adjacent bone and bone marrow (BM). An intensively focused and bright synchrotron X-ray beam allows for spatially resolving the multi-elemental composition of peri-implant tissues from patients undergoing revision surgery. In peri-implant BM, particulate cobalt (Co) is exclusively co-localized with chromium (Cr), non-particulate Cr accumulates in the BM matrix. Particles consisting of Co and Cr contain less Co than bulk alloy, which indicates a pronounced dissolution capacity. Particulate titanium (Ti) is abundant in the BM and analyzed Ti nanoparticles predominantly consist of titanium dioxide in the anatase crystal phase. Co and Cr but not Ti integrate into peri-implant bone trabeculae. The characteristic of Cr to accumulate in the intertrabecular matrix and trabecular bone is reproducible in a human 3D in vitro model. This study illustrates the importance of updating the view on long-term consequences of biomaterial usage and reveals toxicokinetics within highly sensitive organs.

Sequential release of immunomodulatory cytokines binding on nano-hydroxyapatite coated titanium surface for regulating macrophage polarization and bone regeneration

Inflammation occurs when the material is implanted into the body. As one of the important immune cells in the regulation of inflammation, macrophages are able to remove pathogens and necrotic cells, and polarize to different phenotypes to regulate inflammatory response for tissue regeneration. Therefore, it is known that the sequential release of immunomodulatory cytokines from the surface of titanium (Ti) implants can regulate the polarization of macrophages and promote osseointegration of implants. In order to control the switch of macrophage phenotypes at desired time, we fabricated hydroxyapatite (HAp) nanotube arrays coating on Ti surface, by acid-etching, alkali-heating and HAp coating sequentially. Then we loaded the interleukin-4 (IL-4) encapsulated by poly (lactic-co-glycolic acid) (PLGA) on the bottom of the nanotube and the interferon-γ (IFN-γ) encapsulated by sodium hyaluronate (SH) on the top of the nanotube. Based on the physical and chemical properties of PLGA and SH and the spatial distribution of loaded cytokines, we hypothesized that the programmed release of IFN-γ and IL-4, which made the phenotypic transition of macrophages at a specific time, so as to regulate inflammation and promote osteogenic repair. Our hypothesis created a new type of drug sustained release system, which has high research value for improving the osseointegration of implants.

Mineralized collagen scaffolds fabricated with amniotic membrane matrix increase osteogenesis under inflammatory conditions

Defects in craniofacial bones occur congenitally, after high-energy impacts, and during the course of treatment for stroke and cancer. These injuries are difficult to heal due to the overwhelming size of the injury area and the inflammatory environment surrounding the injury. Significant inflammatory response after injury may greatly inhibit regenerative healing. We have developed mineralized collagen scaffolds that can induce osteogenic differentiation and matrix biosynthesis in the absence of osteogenic media or supplemental proteins. The amniotic membrane is derived from placentas and has been recently investigated as an extracellular matrix to prevent chronic inflammation. Herein, we hypothesized that a mineralized collagen–amnion composite scaffold could increase osteogenic activity in the presence of inflammatory cytokines. We report mechanical properties of a mineralized collagen–amnion scaffold and investigated osteogenic differentiation and mineral deposition of porcine adipose-derived stem cells within these scaffolds as a function of inflammatory challenge. Incorporation of amniotic membrane matrix promotes osteogenesis similarly to un-modified mineralized collagen scaffolds, and increases in mineralized collagen–amnion scaffolds under inflammatory challenge. Together, these findings suggest that a mineralized collagen–amnion scaffold may provide a beneficial environment to aid craniomaxillofacial bone repair, especially in the course of defects presenting significant inflammatory complications.

mRNA Transfection-Induced Activation of Primary Human Monocytes and Macrophages: Dependence on Carrier System and Nucleotide Modification

Monocytes and macrophages are key players in maintaining immune homeostasis. Identifying strategies to manipulate their functions via gene delivery is thus of great interest for immunological research and biomedical applications. We set out to establish conditions for mRNA transfection in hard-to-transfect primary human monocytes and monocyte-derived macrophages due to the great potential of gene expression from in vitro transcribed mRNA for modulating cell phenotypes. mRNA doses, nucleotide modifications, and different carriers were systematically explored in order to optimize high mRNA transfer rates while minimizing cell stress and immune activation. We selected three commercially available mRNA transfection reagents including liposome and polymer-based formulations, covering different application spectra. Our results demonstrate that liposomal reagents can particularly combine high gene transfer rates with only moderate immune cell activation. For the latter, use of specific nucleotide modifications proved essential. In addition to improving efficacy of gene transfer, our findings address discrete aspects of innate immune activation using cytokine and surface marker expression, as well as cell viability as key readouts to judge overall transfection efficiency. The impact of this study goes beyond optimizing transfection conditions for immune cells, by providing a framework for assessing new gene carrier systems for monocyte and macrophage, tailored to specific applications.

Near-Infrared-Triggered Dynamic Surface Topography for Sequential Modulation of Macrophage Phenotypes

Immune response is critical to tissue repair. Designing biomaterials with immunomodulatory functions has become a promising strategy to facilitate tissue repair. Considering the key roles of macrophages in tissue repair and the significance of the balance of M1 and M2, smart biomaterials, which can harness macrophage phenotypes dynamically to match the tissue healing process on demand, have attracted a lot of attention to be set apart from the traditional anti-inflammatory biomaterials. Here, we prepare a gold nanorod-contained shape memory polycaprolactone film with dynamic surface topography, which has the ability to be transformed from flat to microgrooved under near-infrared (NIR) irradiation. Based on the close relationships between the morphologies and the phenotypes of macrophages, the NIR-triggered surface transformation induces the elongation of macrophages, and consequently the upregulated expressions of arginase-1 and IL-10 in vitro, indicating the change of macrophage phenotypes. The sequential modulation of macrophage phenotypes by dynamic surface topography is further confirmed in an in vivo implantation test. The healing-matched modulation of macrophage phenotypes by dynamic surface topography without the stimuli of cytokines offers an effective and noninvasive strategy to manipulate tissue regenerative immune reactions to achieve optimized healing outcomes.

Bijel-templated implantable biomaterials for enhancing tissue integration and vascularization

Mitigation of the foreign body response (FBR) and successful tissue integration are essential to ensuring the longevity of implanted devices and biomaterials. The use of porous materials and coatings has been shown to have an impact, as the textured surfaces can mediate macrophage interactions with the implant and influence the FBR, and the pores can provide space for vascularization and tissue integration. In this study, we use a new class of implantable porous biomaterials templated from bicontinuous interfacially jammed emulsion gels (bijels), which offer a fully percolating, non-constricting porous network with a uniform pore diameter on the order of tens of micrometers, and surfaces with consistent curvature. We demonstrate that these unique morphological features, inherent to bijel-templated materials (BTMs), can enhance tissue integration and vascularization, and reduce the FBR. Cylindrical polyethylene glycol diacrylate (PEGDA) BTMs, along with PEGDA particle-templated materials (PTMs), and non-templated materials (NTMs), were implanted into the subcutaneous space of athymic nude mice. After 28 days, implants were retrieved and analyzed via histological techniques. Within BTMs, blood vessels of increased size and depth, changes in collagen deposition, and increased presence of pro-healing macrophages were observed compared to that of PTM and NTM implants. Bijel templating offers a new route to biomaterials that can improve the function and longevity of implantable devices. STATEMENT OF SIGNIFICANCE: All implanted biomaterials are subject to the foreign body response (FBR) which can have a detrimental effect on their efficacy. Altering the surface chemistry can decrease the FBR by limiting the amount of proteins adsorbed to the implant. This effect can be enhanced by including pores in the biomaterial to allow new tissue growth as the implant becomes integrated in the body. Here, we introduce a new class of self-assembled biomaterials comprising a fully penetrating, non-constricting pore phase with hyperbolic (saddle) surfaces for enhanced tissue integration. These unique morphological characteristics result in dense blood vessel formation and favorable tissue response properties demonstrated in a four-week implantation study.

Electrochemical Co-deposition of Polydopamine/Hyaluronic Acid for Anti-biofouling Bioelectrodes

Bioelectrodes are key components of electronic devices that efficiently mediate electrical signals in biological systems. However, conventional bioelectrodes often undergo biofouling associated with non-specific proteins and cell adhesion on the electrode surfaces, which leads to seriously degraded electrical and/or electrochemical properties. Hence, a facile and effective method to modify the surface of bioelectrodes is required to introduce anti-biofouling properties and improve performance. Here, we report an electrochemical surface modification of a bioelectrode via co-deposition of hyaluronic acid (HA) and polydopamine (PDA). The electrochemical polymerization and deposition of PDA offered simple and effective incorporation of highly hydrophilic and anti-fouling HA to the electrode surfaces, with no substantial increase in impedance. HA-incorporated PDA (PDA/HA)-modified electrodes displayed significant resistance to non-specific protein adsorption and the adhesion of fibroblasts. In addition, 4-week subcutaneous implantation studies revealed that the modified electrodes attenuated scar tissue formation compared with that induced by unmodified bare electrodes. This simple and effective electrochemical surface modification could be further employed for various implantable bioelectrodes (e.g., prosthetics and biosensors) and could extend their bioelectronic applications.

In-Vivo Corrosion Characterization and Assessment of Absorbable Metal Implants

Absorbable metals have been introduced as materials to fabricate temporary medical implants. Iron, magnesium and zinc have been considered as major base elements of such metals. The metallurgical characterization and in-vitro corrosion assessment of these metals have been covered by the new ASTM standards F3160 and F3268. However, the in-vivo corrosion characterization and assessment of absorbable metal implants are not yet well established. The corrosion of metals in the in-vivo environment leads to metal ion release and corrosion product formation that may cause excessive toxicity. The aim of this work is to introduce the techniques to assess absorbable metal implants and their in-vivo corrosion behavior. This contains the existing approaches, e.g., implant retrieval and histological analysis, ultrasonography and radiography, and the new techniques for real-time in-vivo corrosion monitoring.

Periprosthetic Capsule Formation and Contracture in a Rodent Model of Implant-Based Breast Reconstruction With Delayed Radiotherapy

INTRODUCTION

Capsular contracture (CC) is the most common complication of breast implantation, with an incidence of nearly 50% in patients undergoing breast reconstruction with subsequent radiotherapy. Although the move toward submuscular (SM) device placement led to a decreased incidence of CC, subcutaneous (SQ) implantation has seen a resurgence. The purpose of this study was to use a rodent model of breast reconstruction with smooth silicone implants and delayed radiotherapy to assess the occurrence of CC in SQ versus SM implantation.

METHODS

Custom 2 mL smooth round silicone implants were placed bilaterally into 12 female Sprague Dawley rats that were randomized into 4 groups of 3, with each group differing by implantation plane (SQ vs SM) and irradiation status (irradiated vs nonirradiated). Rats from the SQ group received implants bilaterally underlying the skin on the flank. Rats in the SM groups received implants bilaterally under the latissimus dorsi muscle. Irradiated rats received 20 Gy localized to each implant on postoperative day 10. One rat from each group was imaged with a micro-computed tomography scanner at baseline and at explant 3 months later, whereupon capsules from all rats were examined histologically.

RESULTS

Rats in the SQ group showed evidence of contracture on gross examination and greater evidence of morphologic disruption per micro-computed tomography scan. There was no evidence of contracture or morphologic disruption in either SM group. Mean ± SD capsule thickness was 39.0 ± 9.0 μm in the SQ versus 37.6 ± 9.8 μm in the SM nonirradiated groups and 43.9 ± 14.9 μm in the SQ versus 34.3 ± 8.3 μm in the SM irradiated groups (all P > 0.05).

CONCLUSIONS

In a rodent model of smooth silicone breast implantation and delayed radiotherapy, although there did not appear to be differences in capsule thickness regardless of device placement plane, SQ implants demonstrated gross evidence of CC. These data indicate that capsule thickness is only part of a larger pathogenetic picture, which should take into consideration the contribution from all peri-implant tissue.

Towards smart self-clearing glaucoma drainage device

For patients who are unresponsive to pharmacological treatments of glaucoma, an implantable glaucoma drainage devices (GDD) are often used to manage the intraocular pressure. However, the microscale channel that removes excess aqueous humor from the anterior chamber often gets obstructed due to biofouling, which necessitates additional surgical intervention. Here we demonstrate the proof-of-concept for smart self-clearing GDD by integrating magnetic microactuators inside the drainage tube of GDD. The magnetic microactuators can be controlled using externally applied magnetic fields to mechanically clear biofouling-based obstruction, thereby eliminating the need for surgical intervention. In this work, our prototype magnetic microactuators were fabricated using low-cost maskless photolithography to expedite design iteration. The fabricated devices were evaluated for their static and dynamic mechanical responses. Using transient numerical analysis, the fluid-structure interaction of our microactuator inside a microtube was characterized to better understand the amount of shear force generated by the device motion. Finally, the anti-biofouling performance of our device was evaluated using fluorescein isothiocyanate labeled bovine serum albumin. The microactuators were effective in removing proteinaceous film deposited on device surface as well as on the inner surface of the microchannel, which supports our hypothesis that a smart self-clearing GDD may be possible by integrating microfabricated magnetic actuators in chronically implanted microtubes.

Sortase A as a cross-linking enzyme in tissue engineering

The bacterial ligase Sortase A (SA) and its mutated variants have become increasingly popular over the last years for post-translational protein modifications due to their unparalleled specificity and efficiency. The aim of this work was to study SA as a cross-linking enzyme for hydrogel-based tissue engineering. For this, we optimized SA pentamutant production and purification from E. coli to achieve high yields and purity. Then using hyaluronan (HA) as a model biopolymer and modifying it with SA-substrate peptides, we studied the cross-linking kinetics obtained with SA, the enzyme stability, cytocompatibility, and immunogenicity, and compared those to state-of-the-art standards. The transglutaminase activated factor XIII (FXIIIa) was used as the reference cross-linking enzyme, and the clinical collagen scaffold Chondro-Gide (CG) was used as a reference biocompatible material for in vivo studies. We found SA could be produced in large amounts in the lab without special equipment, whereas the only viable source of FXIIIa is currently a prescription medicine purified from donated blood. SA was also remarkably more stable in solution than FXIIIa, and it could provide even much faster gelation, making it possible to achieve nearly-instantaneous gel formation upon delivery with a double-barrel syringe. This is an interesting improvement for in vivo work, to allow in situ gel formation in a wet environment, and could also be useful for applications like bioprinting where very fast gelation is needed. The cytocompatibility and lack of immunogenicity were still uncompromised. These results support the use of SA as a versatile enzymatic cross-linking strategy for 3D culture and tissue engineering applications.

STATEMENT OF SIGNIFICANCE

Enzymatic crosslinking has immense appeal for tissue engineers as one of the most biocompatible methods of hydrogel crosslinking. Sortase A has a number of unique advantages over previous systems. We show an impressive and tunable range of crosslinking kinetics, from almost instantaneous gelation to several minutes. We also demonstrate that Sortase A crosslinked hydrogels have good cytocompatibility and cause no immune reaction when implanted in vivo. With its additional benefits of excellent stability in solution and easy large-scale synthesis available to any lab, we believe this novel crosslinking modality will find multiple applications in high throughput screening, tissue engineering, and biofabrication.

Calcium phosphate altered the cytokine secretion of macrophages and influenced the homing of mesenchymal stem cells

Immune cells such as macrophages play an important role in tissue regeneration. In this study, an in vivo mouse intramuscular implantation model was applied to demonstrate the gradual infiltration of macrophages, followed by homing of mesenchymal stem cells (MSCs) during the early phase of biphasic calcium phosphate (BCP)-induced ectopic bone formation. Then, a novel real-time cell analysis (RTCA) system was used to continuously monitor cell migration in vitro, suggesting the positive roles of BCP-mediated macrophage secretion in MSC recruitment. A Proteome Profiler cytokine array was also applied to investigate the BCP-stimulated secretion pattern of macrophages by simultaneously screening 111 cytokines, indicating that Raw 264.7 macrophages released a pronounced amount of chemokines (CCL2, 3, 4, 5 and CXCL2, 10, 16) and non-chemokine molecules (OPN, VEGF, CD14, Cystatin C and PAI-1), which are involved in cell homing and bone regeneration. Among them, osteoinductive BCP ceramics significantly promoted the secretion of CCL2, 3, 4 and Cystatin C in macrophages, which was consistent with the up-regulated expression of chemokine genes (Ccl2, 3, 4). Considering their previously-reported chemotactic functions, the effects of CCL2/MCP-1 and CCL3/MIP-1α on MSC recruitment were further evaluated by the RTCA system. It was found that exogenous CCL2/MCP-1 and CCL3/MIP-1α dramatically accelerated MSC migration, while their neutralizing antibodies reduced MSC motility. Moreover, BCP-mediated macrophage secretion up-regulated the gene expression of chemokine receptors (Ccr1 and Ccr2) in MSCs, but the blockage of CCR1 and CCR2 exerted inhibitory effects on MSC chemotaxis. RTCA results showed that compared to CCL3/CCR1, the CCL2/CCR2 axis might exert a predominant chemotactic effect for MSC recruitment. These findings indicated that osteoinductive BCP ceramics might regulate macrophage secretion via an ERK signaling pathway, and the increased release of chemokines in macrophages would accelerate MSC homing to facilitate bone formation. These findings might deepen our understanding of biomaterial-mediated immune response and help to design orthopedic implants with desired immunomodulatory abilities to recruit host stem cells endogenously for bone regeneration.

Updates on the research and development of absorbable metals for biomedical applications

Absorbable metals, metals that corrode in physiological environment, constitute a new class of biomaterials intended for temporary medical implant applications. The introduction of these metals has shifted the established paradigm of metal implants from preventing corrosion to its direct application. Interest toward absorbable metals has been growing in the past decade. This is proved by the rapid increase in scientific publication, progressive development of standards, and launching the first commercial products. Iron, magnesium, zinc, and their alloys are the current three absorbable metals families. Magnesium-based metals are the most progressing family with a large data set obtained from both basic and translational research. Iron-based metals are still facing a major challenge of low in vivo corrosion rate despite the significant efforts that have been put to overcome its weakness. Zinc-based metals are the new alternative absorbable metals with moderate corrosion rates that fall between those of iron and magnesium. This manuscript provides a brief review on the latest progress in the research and development of absorbable metals, the most important findings, the remaining challenges, and the perspective on the future direction.

Cell membrane coating for reducing nanoparticle-induced inflammatory responses to scaffold constructs

The controlled release of therapeutics from micro or nanoparticles has been well-studied. Incorporation of these particles inside biomaterial scaffolds is promising for tissue regeneration and immune modulation. However, these particles may induce inflammatory and foreign body responses to scaffold constructs, limiting their applications. Here we show that widely used poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) formed by double emulsion dramatically increased neutrophil infiltration and pro-inflammatory cytokines in alginate scaffolds 1 day after the subcutaneous injection of the scaffolds into mice. The coating of red blood cell (RBC) membranes on PLGA NPs completely eliminated these short-term inflammatory responses. For a longer term of 10 days, neither PLGA NPs nor RBC membrane-coated nanoparticles exerted a significant effect on the infiltration of neutrophils or macrophages in alginate scaffolds possibly due to the degradation and/or clearance of nanoparticles by infiltrating cells by that time. Despite the extensive exploration of cell membrane-coated nanoparticles, our study is the first to investigate the effects of cell membrane coating on foreign body reaction to nanoparticles. Harnessing the natural biocompatibility of cell membranes, our strategy of anti-inflammatory protection for scaffolds may be pivotal for many applications, such as those relying on the recruitment of stem cells and/or progenitor cells to scaffolds.

Promoting proliferation and differentiation of BMSCs by green tea polyphenols functionalized porous calcium phosphate

In this article, we proposed a facile protocol to functionalize porous calcium phosphate ceramics (PCPC) using dietary tea polyphenols (TP). TP molecules was attracted and anchored by Ca2+ ions from the surface of CPC. These TP molecules modulated the nucleation and crystallization of calcium phosphate nanorods assemblies on the surface of PCPC. Our results prove that these calcium phosphate nanorods assemblies accompanies functional groups of TP make PCPC/TP effectively promote proliferation and differentiation of bone mesenchymal stem cells (BMSCs). We inferred that these calcium phosphate nanorods assemblies might change the surface microenvironment of PCPC, which is critical to promote the proliferation and differentiation of BMSCs. Compared with naked PCPC, PCPC/TP obviously increased BMP2, ErK/MAPK and JNK/MAPK level and mineralization capacity of cells (ALP level).

Role of biphasic calcium phosphate ceramic-mediated secretion of signaling molecules by macrophages in migration and osteoblastic differentiation of MSCs

The inflammatory reaction initiates fracture healing and could play a role in the osteoinductive effect of calcium phosphate (CaP) ceramics, which has been widely confirmed; however, the underlying mechanism has not been fully elucidated. In this study, various signaling molecules from macrophages under the stimulation of osteoinductive biphasic calcium phosphate (BCP) ceramic and its degradation products were examined and evaluated for their influence on the migration and osteoblastic differentiation of mesenchymal stem cells (MSCs). The results of cellular experiments confirmed that the gene expression of most inflammatory factors (IL-1, IL-6 and MCP-1) and growth factors (VEGF, PDGF and EGF) by macrophages were up-regulated to varying degrees by BCP ceramic and its degradation products. Cell migration tests demonstrated that the conditioned media (CMs), which contained abundant signaling molecules secreted by macrophages cultured on BCP ceramic and its degradation products, promoted the migration of MSCs. qRT-PCR analysis indicated that CMs promoted the gene expression of osteogenic markers (ALP, COL-I, OSX, BSP and OPN) in MSCs. ALP activity and mineralization staining further confirmed that CMs promoted the osteoblastic differentiation of MSCs. The present study confirmed the correlation between the inflammatory reaction and osteoinductive capacity of BCP ceramic. The ceramic itself and its degradation products can induce macrophages to express and secrete various signaling molecules, which then recruit and promote the MSCs to differentiate into osteoblasts. Compared with BCP conditioned media, degradation particles played a more substantial role in this process. Thus, inflammation initiated by BCP ceramic and its degradation products could be necessary for osteoinduction by the ceramic.

STATEMENT OF SIGNIFICANCE

It is known that the inflammatory reaction initiates fracture healing. The aim of this study was to examine whether osteoinductive BCP ceramics could cause macrophages to change their secretion patterns and whether the secreted cytokines could affect migration and osteoblastic differentiation of MSCs. Moreover, the duration of inflammation could be influenced by the local ionic environment and the degradation products of the implant. Our experimental results revealed the correlation between the inflammatory reaction and osteoinductive capacity of BCP ceramic. The ceramic itself and its degradation products can induce macrophages to express and secrete various signaling molecules, which then recruit and promote the MSCs to differentiate into osteoblasts. Compared with ionic microenvironment, degradation particles played a more substantial role in this process. Therefore, the appropriate inflammation initiated by BCP ceramic and its degradation products could be essential for osteoinduction by the ceramic. We believe that the present study improves the understanding of the effect of biomaterial-mediated inflammation on MSC migration and differentiation and established a preliminary correlation between the immune system and osteoinduction by biomaterials.