Material surfaces affect the protein expression patterns of human macrophages: A proteomics approach

Response of human peripheral blood monocyte-derived macrophages (PBMM) to demineralized and decellularized bovine bone graft substitutes

The performance of apparently biocompatible implanted bovine bone grafts may be compromised by unresolved chronic inflammation, and poor graft incorporation leading to implant failure. Monitoring the intensity and duration of the inflammatory response caused by implanted bone grafts is crucial. In this study, the ability of demineralized (DMB) and decellularized (DCC) bovine bone substitutes in initiating inflammatory responses to peripheral blood monocyte-derived macrophages (PBMMs) was investigated. The response of PBMMs to bone substitutes was evaluated by using both direct and indirect cell culture, reactive oxygen species (ROS) generation, apoptosis, immunophenotyping, and cytokine production. Analysis of DMB and DCC substitutes using scanning electron microscope (SEM) showed a roughened surface with a size ranging between 500 and 750 μm. PBMMs treated with DMB demonstrated cell aggregation and clumping mimicking lipopolysaccharide (LPS) treated PBMMs and a higher proliferation ability (166.93%) compared to control (100%) and DCC treatments (115.64%; p<0.001) at 24h. This was associated with a significantly increased production of intracellular ROS in PBMMs exposed to DMB substitutes than control (3158.5 vs 1715.5; p<0.001) and DCC treatment (2117.5). The bone substitute exposure also caused an increase in percentage apoptosis which was significantly (p<0.0001) higher in both DMB (27.85) and DCC (29.2) treatment than control (19.383). A significant increase in proinflammatory cytokine expression (TNF-α: 3.4 folds; p<0.05) was observed in DMB substitute-treated PBMMs compared to control. Notably, IL-1β mRNA was significantly higher in DMB (21.75 folds; p<0.0001) than control and DCC (5.01 folds). In contrast, DCC substitutes exhibited immunoregulatory effects on PBMMs, as indicated by the expression for CD86, CD206, and HLDR surface markers mimicking IL-4 treatments. In conclusion, DMB excites a higher immunological response compared to DCC suggesting decellularization process of tissues dampen down inflammatory reactions when exposed to PBMM.

Biomaterial mediated immunomodulation: An interplay of material environment interaction for ameliorating wound regeneration

Chronic wounds are the outcome of an imbalanced inflammatory response caused by sustenance of immune microenvironment. In this context, tissue engineered graft played great role in healing wounds but faced difficulty in scar remodelling, immune rejection and poor vascularization. All the limitations faced are somewhere linked with the immune cells involved in healing. In this consideration, immunomodulatory biomaterials bridge a large gap with the delivery of modulating factors for triggering key inflammatory cells responsible towards interplay in the wound micro-environment. Inherent physico-chemical properties of biomaterials substantially determine the nature of cell-materials interaction thereby facilitating differential cytokine gradient involved in activation or suppression of inflammatory signalling pathways, and followed by surface marker expression. This review aims to systematically describe the interplay of immune cells involved in different phases in the wound microenvironment and biomaterials. Additionally, it also focuses on modulating innate immune cell responses in the context of triggering the halted phase of the wound healing, i.e., inflammatory phase. The various strategies are highlighted for modulation of wound microenvironment towards wound regeneration including stem cells, cytokines, growth factors, vitamins, and anti-inflammatory agents to induce interactive ability of biomaterials with immune cells. The last section focuses on prospective approaches and current potential strategies for wound regeneration. This includes the development of different models to bridge the gap between mouse models and human patients. Emerging new tools to study inflammatory response owing to biomaterials and novel strategies for modulation of monocyte and macrophage behaviour in the wound environment are also discussed.

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

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

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.

Rational Design of Immunomodulatory Hydrogels for Chronic Wound Healing

With all the advances in tissue engineering for construction of fully functional skin tissue, complete regeneration of chronic wounds is still challenging. Since immune reaction to the tissue damage is critical in regulating both the quality and duration of chronic wound healing cascade, strategies to modulate the immune system are of importance. Generally, in response to an injury, macrophages switch from pro-inflammatory to an anti-inflammatory phenotype. Therefore, controlling macrophages' polarization has become an appealing approach in regenerative medicine. Recently, hydrogels-based constructs, incorporated with various cellular and molecular signals, have been developed and utilized to adjust immune cell functions in various stages of wound healing. Here, the current state of knowledge on immune cell functions during skin tissue regeneration is first discussed. Recent advanced technologies used to design immunomodulatory hydrogels for controlling macrophages' polarization are then summarized. Rational design of hydrogels for providing controlled immune stimulation via hydrogel chemistry and surface modification, as well as incorporation of cell and molecules, are also dicussed. In addition, the effects of hydrogels' properties on immunogenic features and the wound healing process are summarized. Finally, future directions and upcoming research strategies to control immune responses during chronic wound healing are highlighted.

Local Immunomodulatory Strategies to Prevent Allo-Rejection in Transplantation of Insulin-Producing Cells

Islet transplantation has shown promise as a curative therapy for type 1 diabetes (T1D). However, the side effects of systemic immunosuppression and limited long-term viability of engrafted islets, together with the scarcity of donor organs, highlight an urgent need for the development of new, improved, and safer cell-replacement strategies. Induction of local immunotolerance to prevent allo-rejection against islets and stem cell derived β cells has the potential to improve graft function and broaden the applicability of cellular therapy while minimizing adverse effects of systemic immunosuppression. In this mini review, recent developments in non-encapsulation, local immunomodulatory approaches for T1D cell replacement therapies, including islet/β cell modification, immunomodulatory biomaterial platforms, and co-transplantation of immunomodulatory cells are discussed. Key advantages and remaining challenges in translating such technologies to clinical settings are identified. Although many of the studies discussed are preliminary, the growing interest in the field has led to the exploration of new combinatorial strategies involving cellular engineering, immunotherapy, and novel biomaterials. Such interdisciplinary research will undoubtedly accelerate the development of therapies that can benefit the whole T1D population.

The Role of Biodegradable Poly-(L-lactide)-Based Polymers in Blood Cell Activation and Platelet-Monocyte Interaction

The main purpose of new stent technologies is to overcome unfavorable material-related incompatibilities by producing bio- and hemo-compatible polymers with anti-inflammatory and anti-thrombogenic properties. In this context, wettability is an important surface property, which has a major impact on the biological response of blood cells. However, the influence of local hemodynamic changes also influences blood cell activation. Therefore, we investigated biodegradable polymers with different wettability to identify possible aspects for a better prediction of blood compatibility. We applied shear rates of 100 s⁻¹ and 1500 s⁻¹ and assessed platelet and monocyte activation as well as the formation of CD62P+ monocyte-bound platelets via flow cytometry. Aggregation of circulating platelets induced by collagen was assessed by light transmission aggregometry. Via live cell imaging, leukocytes were tracked on biomaterial surfaces to assess their average velocity. Monocyte adhesion on biomaterials was determined by fluorescence microscopy. In response to low shear rates of 100 s⁻¹, activation of circulating platelets and monocytes as well as the formation of CD62P+ monocyte-bound platelets corresponded to the wettability of the underlying material with the most favorable conditions on more hydrophilic surfaces. Under high shear rates, however, blood compatibility cannot only be predicted by the concept of wettability. We assume that the mechanisms of blood cell-polymer interactions do not allow for a rule-of-thumb prediction of the blood compatibility of a material, which makes extensive in vitro testing mandatory.

Thrombogenic and Inflammatory Reactions to Biomaterials in Medical Devices

Blood-contacting medical devices of different biomaterials are often used to treat various cardiovascular diseases. Thrombus formation is a common cause of failure of cardiovascular devices. Currently, there are no clinically available biomaterials that can totally inhibit thrombosis under the more challenging environments (e.g., low flow in the venous system). Although some biomaterials reduce protein adsorption or cell adhesion, the issue of biomaterial associated with thrombosis and inflammation still exists. To better understand how to develop more thrombosis-resistant medical devices, it is essential to understand the biology and mechano-transduction of thrombus nucleation and progression. In this review, we will compare the mechanisms of thrombus development and progression in the arterial and venous systems. We will address various aspects of thrombosis, starting with biology of thrombosis, mathematical modeling to integrate the mechanism of thrombosis, and thrombus formation on medical devices. Prevention of these problems requires a multifaceted approach that involves more effective and safer thrombolytic agents but more importantly the development of novel thrombosis-resistant biomaterials mimicking the biological characteristics of the endothelium and extracellular matrix tissues that also ameliorate the development and the progression of chronic inflammation as part of the processes associated with the detrimental generation of late thrombosis and neo-atherosclerosis. Until such developments occur, engineers and clinicians must work together to develop devices that require minimal anticoagulants and thrombolytics to mitigate thrombosis and inflammation without causing serious bleeding side effects.

Scaffold strategies for modulating immune microenvironment during bone regeneration

Implanted bone scaffolds often fail to successfully integrate with the host tissue because they do not elicit a favorable immune reaction. Properties of bone scaffold not only provide mechanical and chemical signals to support cell adhesion, migration, proliferation and differentiation, but also play a pivotal role in determining the extent of immune response during bone regeneration. Appropriate design parameters of bone scaffold are of great significance in the process of developing a new generation of bone implants. Herein, this article addresses the recent advances in the field of bone scaffolds for immune response, particularly focusing on the physical and chemical properties of bone scaffold in manipulating the host response. Furthermore, incorporation of bioactive molecules and cells with immunoregulatory function in bone scaffolds are also presented. Finally, continuing challenges and future directions of scaffold-based strategies for modulating immune microenvironment are discussed.

Toxicity-Attenuated Glycol Chitosan Adhesive Inspired by Mussel Adhesion Mechanisms

Chitosan-catechol, inspired from mussel-adhesive-proteins, is characterized by the formation of an adhesive membrane complex through instant bonding with serum proteins not found in chitosan. Using this intrinsic property, chitosan-catechol is widely applied for hemostatic needles, general hemostatic materials, nanoparticle composites, and 3D printing. Despite its versatility, the practical use of chitosan-catechol in the clinic is limited due to its undesired immune responses. Herein, a catechol-conjugated glycol chitosan is proposed as an alternative hemostatic hydrogel with negligible immune responses enabling the replacement of chitosan-catechol. Comparative cellular toxicity and in vivo skin irritation between chitosan-catechol and glycol chitosan-catechol are evaluated. Their immune responses are also assessed using histological analysis after subcutaneous implantation into mice. The results show that glycol chitosan-catechol significantly attenuates the immune response compared with chitosan-catechol; this finding is likely due to the antibiofouling effect of ethylene glycol groups and the reduced adhesion of immune cells. Finally, the tissue adhesion and hemostatic ability of glycol chitosan-catechol hydrogels reveal that these ethylene glycol groups do not dramatically modify the adhesiveness and hemostatic ability compared with nonglycol chitosan-catechol. This study suggests that glycol chitosan-catechol can be a promising alternative to chitosan-catechol in various biomedical fields such as hemostatic agents.

Material stiffness influences the polarization state, function and migration mode of macrophages

Biomaterial implantation is followed by an inflammatory cascade dominated by macrophages, which determine implant acceptance or rejection through pro- and anti-inflammatory polarization states (Anderson et al., 2008; Brown and Badylak, 2013). It is known that chemical signals such as bacterial endotoxins and cytokines (IL4) can direct macrophage polarization (Mantovani et al., 2004); however, recent evidence implicates biophysical cues in this process (McWhorter et al., 2015; Patel et al., 2012). Here we report that THP-1 derived macrophages cultured on collagen-coated polyacrylamide gels of varying stiffness adapt their polarization state, functional roles and migration mode according to the stiffness of the underlying substrate. Through gene expression and protein secretion analysis, we show that stiff polyacrylamide gels (323 kPa) prime macrophages towards a pro-inflammatory phenotype with impaired phagocytosis in macrophages, while soft (11 kPa) and medium (88 kPa) stiffness gels prime cells towards an anti-inflammatory, highly phagocytic phenotype. Furthermore, we show that stiffness dictates the migration mode of macrophages; on soft and medium stiffness gels, cells display Rho-A kinase (ROCK)-dependent, podosome-independent fast amoeboid migration and on stiff gels they adopt a ROCK-independent, podosome-dependent slow mesenchymal migration mode. We also provide a mechanistic insight into this process by showing that the anti-inflammatory property of macrophages on soft and medium gels is ROCK-dependent and independent of the ligand presented to them. Together, our results demonstrate that macrophages adapt their polarization, function and migration mode in response to the stiffness of the underlying substrate and suggest that biomaterial stiffness is capable of directing macrophage behaviour independent of the biochemical cues being presented to them. The results from this study establish an important role for substrate stiffness in directing macrophage behaviour, and will lead to the design of immuno-informed biomaterials that are capable of modulating the macrophage response after implantation. STATEMENT OF SIGNIFICANCE: Biomaterial implantation is followed by an inflammatory cascade dominated by macrophages, which determine implant acceptance or rejection through pro- and anti-inflammatory polarization states. It is known that chemical signals can direct macrophage polarization; however, recent evidence implicates biophysical cues in this process. Here we report that macrophages cultured on gels of varying stiffness adapt their polarization state, functional roles and migration mode according to the stiffness of the underlying substrate. The results from this study establish an important role for substrate stiffness in directing macrophage behaviour, and will lead to the design of immuno-informed biomaterials that are capable of modulating the macrophage response after implantation.

Immune Regulation of Skin Wound Healing: Mechanisms and Novel Therapeutic Targets

Significance: The immune system plays a central role in orchestrating the tissue healing process. Hence, controlling the immune system to promote tissue repair and regeneration is an attractive approach when designing regenerative strategies. This review discusses the pathophysiology of both acute and chronic wounds and possible strategies to control the immune system to accelerate chronic wound closure and promote skin regeneration (scar-less healing) of acute wounds. Recent Advances: Recent studies have revealed the key roles of various immune cells and immune mediators in skin repair. Thus, immune components have been targeted to promote chronic wound repair or skin regeneration and several growth factors, cytokines, and biomaterials have shown promising results in animal models. However, these novel strategies are often struggling to meet efficacy standards in clinical trials, partly due to inadequate drug delivery systems and safety concerns. Critical Issues: Excess inflammation is a major culprit in the dysregulation of normal wound healing, and further limiting inflammation effectively reduces scarring. However, current knowledge is insufficient to efficiently control inflammation and specific immune cells. This is further complicated by inadequate drug delivery methods. Future Directions: Improving our understanding of the molecular pathways through which the immune system controls the wound healing process could facilitate the design of novel regenerative therapies. Additionally, better delivery systems may make current and future therapies more effective. To promote the entry of current regenerative strategies into clinical trials, more evidence on their safety, efficacy, and cost-effectiveness is also needed.

Recent progress on magnetic nanoparticles for magnetic hyperthermia

Recent advances in nanomaterials science contributed to develop new micro- and nano-devices as potential diagnostic and therapeutic tools in the field of oncology. The synthesis of superparamagnetic nanoparticles (SPMNPs) has been intensively studied, and the use of these particles in magnetic hyperthermia therapy has demonstrated successes in treatment of cancer. However, some physical limitations have been found to impact the heating efficiency required to kill cancer cells. Moreover, the bio-safety of NPs remains largely unexplored. The primary goals of this review are to summarize the recent progress in the development of magnetic nanoparticles (MNPs) for hyperthermia, and discuss the limitations and advances in the synthesis of these particles. Based on this knowledge, new perspectives on development of new biocompatible and biofunctional nanomaterials for magnetic hyperthermia are discussed.

Controlling the dynamics of cell transition in heterogeneous cultures using surface chemistry

Developing materials that can preferentially select defined cancer cell populations for biological characterization will greatly enhance our understanding of cancer cell growth, differentiation, and invasion. The transitional events between epithelial and mesenchymal phenotypes are particularly crucial, as primary tumors and secondary metastasis are generally epithelial in nature, whereas circulating mesenchymal cells derived from primary epithelial cells appear to facilitate the spread of disease and its resistance to therapy. This study describes an amino-functionalized material, which promotes the enrichment of an epithelial phenotype from a single cell line containing both epithelial and mesenchymal subpopulations of cancer cells. The isolation and transitional control of such subpopulations using functional materials will advance understanding of the disease process, have a significant impact on the downstream development of new targeted cancer therapeutics, and also be applicable to tissue engineering and regenerative medicine.

Improved implant osseointegration of a nanostructured titanium surface via mediation of macrophage polarization

The use of endosseous implanted materials is often limited by undesirable effects that may be due to macrophage-related inflammation. The purpose of this study was to fabricate a nanostructured surface on a titanium implant to regulate the macrophage inflammatory response and improve the performance of the implant. Anodization at 5 and 20 V as well as UV irradiation were used to generate hydrophilic, nanostructured TiO2 surfaces (denoted as NT5 and NT20, respectively). Their surface characteristics and in vivo osseointegration as well as the inflammatory response they elicit were analyzed. In addition, the behavior of macrophages in vitro was evaluated. Although the in vitro osteogenic activity on the two surfaces was similar, the NT5 surface was associated with more bone formation, less inflammation, and a reduced CD68(+) macrophage distribution in vivo compared to the NT20 and polished Ti surfaces. Consistently, further experiments revealed that the NT5 surface induced healing-associated M2 polarization in vitro and in vivo. By contrast, the NT20 surface promoted the pro-inflammatory M1 polarization, which could further impair bone regeneration. The results demonstrate the dominant role of macrophage-related inflammation in bone healing around implants and that surface nanotopography can be designed to have an immune-regulating effect in support of the success of implants.

The Effect of Platelet Proteins Released in Response to Titanium Implant Surfaces on Macrophage Pro-Inflammatory Cytokine Gene Expression

BACKGROUND AND PURPOSE

Platelets are one of the earliest cell types to interact with surgically inserted titanium implants. This in vitro study investigated the effect of titanium surface-induced platelet releasate on macrophage cytokine gene expression.

MATERIALS AND METHODS

To mimic the in vivo temporal sequence of platelet arrival and protein production at the implant surface and the subsequent effect of these proteins on mediators of the immune response, the levels of platelet attachment and activation in response to culture on smooth polished, sandblasted and acid-etched (SLA), and hydrophilic-modified SLA (modSLA) titanium surfaces were first determined by microscopy and protein assay. The subsequent effect of the platelet-released proteins on human THP-1 macrophage cytokine gene expression was determined by polymerase chain reaction array after 1 and 3 days of macrophage culture on the titanium surfaces in platelet-releasate conditioned media.

RESULTS

Platelet attachment was surface dependent with decreased attachment observed on the hydrophilic (modSLA) surface. The platelet releasate, when considered independently of the surface effect, elicited an overall pro-inflammatory response in macrophage cytokine gene expression, that is, the expression of typical pro-inflammatory cytokine genes such as TNF, IL1a, IL1b, and CCL1 was significantly up-regulated whereas the expression of anti-inflammatory cytokine genes such as IL10, CxCL12, and CxCL13 was significantly down-regulated. However, following platelet exposure to different surface modifications, the platelet releasate significantly attenuated the macrophage pro-inflammatory response to microrough (SLA) titanium and hastened an anti-inflammatory response to hydrophilic (modSLA) titanium.

CONCLUSIONS

Theses results demonstrate that titanium surface topography and chemistry are able to influence the proteomic profile released by platelets, which can subsequently influence macrophage pro-inflammatory cytokine expression. This immunomodulation may be an important mechanism via which titanium surface modification influences osseointegration.

The molecular mechanism for effects of TiN coating on NiTi alloy on endothelial cell function

The aim of this study is to systematically investigate the molecular mechanism of different effects of nickel titanium (NiTi) alloy surface and titanium nitride (TiN) coating on endothelial cell function. Release of nickel (Ni) ion from bare and TiN-coated NiTi alloys and proliferation of endothelial cells on the two materials were evaluated, and then influence of the two materials on cellular protein expression profiles was investigated by proteomic technology. Subsequently, proteomic data were analyzed with bioinformatics analyses and further validated using a series of biological experiments. Results showed that although the two materials did not affect cell proliferation, the Ni ions released from bare NiTi alloy generated inhibition on pathways associated with actin cytoskeleton, focal adhesion, energy metabolism, inflammation, and amino acid metabolism. In comparison, TiN coating not only effectively prevented release of Ni ions from NiTi alloy, but also promoted actin cytoskeleton and focal adhesion formation, increased energy metabolism, enhanced regulation of inflammation, and promoted amino acid metabolism. Furthermore, the two processes, "the initial mediation of adsorbed serum protein layer to endothelial cell adhesion and growth on the two materials" from our previous study, and "the following action of the two materials on cellular protein expression profile", were linked up and comprehensively analyzed. It was found that in stage of cell adhesion (within 4 h), release of Ni ions from bare NiTi alloy was very low, and the activation of adsorbed proteins to cell adhesion and growth related biological pathways (such as regulation of actin cytoskeleton, and focal adhesion pathways) was almost as same as TiN-coated NiTi alloy. This indicated that the released Ni ions did not affect the mediation of adsorbed proteins to endothelial cell adhesion. However, in stage of cell growth and proliferation, the release of Ni ions from bare NiTi alloy increased with time and reached a higher level, which inhibited endothelial cell function at molecular level, whereas TiN coating improved endothelial cell function.

Monocyte/macrophage proteomics: recent findings and biomedical applications

Macrophages, originating from the migration and differentiation of circulating monocytes into virtually all tissues, are extremely flexible and plastic cells that play vital homeostatic roles, but also contribute to the pathophysiology of many human diseases. For these reasons, they are intensively studied by different approaches, recently including proteomics. Macrophage cells can be taken from a range of different sources, including blood monocytes and macrophages from tissues. Macrophages can also be generated by in vitro culture from blood monocytes, and cell lines derived from this lineage can be used. Similarly, many different proteomic techniques can be used, ranging from classic approaches based on 2D gel electrophoresis to more recent high-throughput gel-free techniques essentially based on mass spectrometry. Here, we review the application of such techniques to the study of monocytes/macrophages, and summarize some results potentially relevant to two paradigmatic conditions - atherosclerosis and disorders of iron metabolism.

Glucose sensor membranes for mitigating the foreign body response

Continuous glucose monitoring devices remain limited in their duration of use due to difficulties presented by the foreign body response (FBR), which impairs sensor functionality immediately following implantation via biofouling and leukocyte infiltration. The FBR persists through the life of the implant, culminating with fibrous encapsulation and isolation from normal tissue. These issues have led researchers to develop strategies to mitigate the FBR and improve tissue integration. Studies have often focused on abating the FBR using various outer coatings, thereby changing the chemical or physical characteristics of the sensor surface. While such strategies have led to some success, they have failed to fully integrate the sensor into surrounding tissue. To further address biocompatibility, researchers have designed coatings capable of actively releasing biological agents (e.g., vascular endothelial growth factor, dexamethasone, and nitric oxide) to direct the FBR to induce tissue integration. Active release approaches have proven promising and, when combined with biocompatible coating materials, may ultimately improve the in vivo lifetime of subcutaneous glucose biosensors. This article focuses on strategies currently under development for mitigating the FBR.

Immune responses to implants - a review of the implications for the design of immunomodulatory biomaterials

A key for long-term survival and function of biomaterials is that they do not elicit a detrimental immune response. As biomaterials can have profound impacts on the host immune response the concept emerged to design biomaterials that are able to trigger desired immunological outcomes and thus support the healing process. However, engineering such biomaterials requires an in-depth understanding of the host inflammatory and wound healing response to implanted materials. One focus of this review is to outline the up-to-date knowledge on immune responses to biomaterials. Understanding the complex interactions of host response and material implants reveals the need for and also the potential of "immunomodulating" biomaterials. Based on this knowledge, we discuss strategies of triggering appropriate immune responses by functional biomaterials and highlight recent approaches of biomaterials that mimic the physiological extracellular matrix and modify cellular immune responses.

Fetal bovine serum xenoproteins modulate human monocyte adhesion and protein release on biomaterials in vitro

Monocyte-derived macrophages are critical in the host-foreign body response to biomaterials and have been studied extensively in various culture conditions in vitro, such as medium supplemented with fetal bovine serum (FBS) or autologous human serum (AHS). Since monocyte maturation into macrophages is highly plastic and may vary considerably depending on the surface, isolation procedures and in vitro culture conditions, we hypothesize that variations in protein adsorption and serum type will greatly impact monocyte behavior in a surface-dependent manner. The impact of xenoproteins on monocyte-surface interactions has not been well studied methodically and the use of AHS rather than FBS for macrophage-biomaterials studies in vitro is far from universal. The commonly used reference materials - tissue culture polystyrene (TCPS), polyethylene glycol (PEG) and polydimethylsiloxane (PDMS) - were employed in this study and we found a 3-fold higher adherent monocyte density on TCPS when AHS was used vs. FBS-supplemented medium. On PEG hydrogels, an 8- to 10-fold higher adhesion density was observed when AHS was employed vs. FBS, while on PDMS no difference in adhesion density was observed between the two sera conditions. Additionally, the presence of lipopolysaccharide abrogated the serum-dependent effect on cell adhesion on TCPS. Significantly different variations in protein release were observed between the serum conditions on these surfaces; in particular, there was a 100-fold higher concentration of growth-related oncogene for the AHS condition on PDMS even though the adhesion levels were comparable between the two serum conditions. These results emphasize the combined impact of the surface type and FBS xenoproteins in mediating the observed monocyte response to biomaterials in vitro.

Biomaterial topography alters healing in vivo and monocyte/macrophage activation in vitro

The effect of biomaterial topography on healing in vivo and monocyte/macrophage stimulation in vitro was assessed. A series of expanded polytetrafluoroethylene (ePTFE) materials were characterized by increasing average intranodal distance of 1.2 μm (1.2-ePTFE), 3.0 μm (3.0-ePTFE), and 4.4 μm (4.4-ePTFE), but presented consistent surface chemistry with nonporous PTFE (np-PTFE). Subcutaneous implantation of 4.4-ePTFE into mice resulted in a statistically thinner capsule that appeared less organized and less dense than the np-PTFE response. In vitro, isolated monocytes/macrophages cultured on np-PTFE produced low levels of interleukin 1-beta (IL-1β), 1.2-ePTFE and 3.0-ePTFE stimulated intermediate levels, and 4.4-ePTFE stimulated a 15-fold increase over np-PTFE. Analysis of cDNA microarrays demonstrated that additional proinflammatory cytokines and chemokines, including IL-1β, interleukin 6, tumor necrosis factor alpha, monocyte chemotactic protein 1, and macrophage inflammatory protein 1-beta, were expressed at higher levels by monocytes/macrophages cultured on 4.4-ePTFE at 4 and 24 h, respectively. Expression ratios for several genes were quantified by RT-PCR and were consistent with those from the cDNA array results. These results demonstrate the effect of biomaterial topography on early proinflammatory cytokine production and gene transcription by monocytes/macrophages in vitro and decreased fibrous capsule thickness in vivo.

Extracellular proteomes of M-CSF (CSF-1) and GM-CSF-dependent macrophages

Macrophage colony-stimulating factor (M-CSF) (also known as CSF-1) and granulocyte-macrophage colony-stimulating factor (GM-CSF) have distinct effects on macrophage lineage populations, which are likely to be contributing to their functional heterogeneity. A comparative proteomic analysis of proteins released into culture media from such populations after M-CSF and GM-CSF exposure was carried out. Adherent macrophage populations, termed bone marrow-derived macrophage (BMM) and GM-BMM, were generated after treatment of murine bone marrow precursors with M-CSF and GM-CSF, respectively. Proteins in 16-h serum-free conditioned media (CM) were identified by two-dimensional gel electrophoresis and mass spectrometry. Respective protein profiles from BMM and GM-BMM CM were distinct and there was the suggestion of a switch from primarily signal peptide-driven secretion to non-classical secretion pathways from BMM to GM-BMM. Extracellular expression of cathepsins (lysosomal proteases) and their inhibitors seems to be a characteristic difference between these macrophage cell types with higher levels usually observed in BMM-CM. Furthermore, we have identified a number of proteins in BMM-CM and GM-BMM-CM that could be involved in various tissue regeneration and inflammatory (immune) processes, respectively. The uncharacterized protein C19orf10, a protein found at high levels in the synovial fluid of arthritis patients, was also differentially regulated; its extracellular levels were upregulated in the presence of GM-CSF.

Fluorescence two-dimensional difference gel electrophoresis for biomaterial applications

Fluorescence two-dimensional difference gel electrophoresis (DiGE) is rapidly becoming established as a powerful technique for the characterization of differences in protein expression levels between two or more conditions. In this review, we consider the application of DiGE-both minimal and saturation labelling-to biomaterials research, considering the challenges and rewards of this approach.

Identification of regulatory Hck and PAI-2 proteins in the monocyte response to PEG-containing matrices

Mass spectrometry is a powerful proteomic tool enabling researchers to survey the global proteome of a cell. This technique has only recently been employed to investigate cell-material interactions. We had previously identified material scarcity and limited adherent cells as challenges facing mass spectrometric analysis of cell-material interactions. U937 adherent to tissue culture poly(styrene) was used as a model system for identifying proteins expressed by adherent monocytes and analyzed by HPLC coupled offline to MALDI-ToF/ToF (LC-MALDI). We identified 645 proteins from two cation fractions of crude U937 monocyte cell lysate. Forty three proteins of interest from the 645 were chosen based on literature searches for relevance to monocyte-material inflammation and wound healing. Proteins such as 40S ribosomal protein S19 and tyrosyl tRNA synthetase highlight the ability of LC-MALDI to identify proteins relevant to monocyte-material interactions that are currently unexplored. We used PEG-based semi-interpenetrating polymer networks and PEG-only hydrogels to investigate surface dependent effects on the Src family kinase Hck and plasminogen activator inhibitor-2 (PAI-2) using the pyrazolo pyrimidine small molecule inhibitor PP2 and exogenous urokinase plasminogen activator addition, respectively. Hck is well researched in cell adhesion while PAI-2 is virtually unknown in cell-material interactions. U937 on TCPS and PEG-only hydrogels secreted similar levels of inflammatory cytokines and gelatinase MMP-9. MCP-1 secretion from monocytes on PEG-only hydrogels was Hck independent in contrast to Hck-dependent MCP-1 secretion in U937 on TCPS. Overall, U937 adherent to sIPNs secrete low levels of soluble gelatinase MMP-9, IL-1beta, TNF-alpha, IL-6, and MCP-1 independent of Hck and PAI-2. This work demonstrates significant changes in surface dependent expression of proteins from monocytes adherent to PEG-based materials compared to TCPS.

Cytokine profiling using monocytes/macrophages cultured on common biomaterials with a range of surface chemistries

Cytokines, chemokines, and growth factors were assayed from the supernatants of monocytes and macrophages cultured on common biomaterials with a range of surface chemistries. TNF-alpha, MCP-1, MIP-1alpha, IL-8, IL-6, IL-1beta, VEGF, IL-1ra, and IL-10 were measured from monocyte/macrophage cultures at different stages of activation and differentiation seeded onto polyethylene, polyurethane, expanded polytetrafluoroethylene, polymethyl methacrylate, and a hydrogel copolymer of 2-hydroxyethyl methacrylate, 1-vinyl-2-pyrrolidinone, and polyethylene glycol acrylate in tissue culture polystyrene (TCPS) plates. Empty TCPS wells and organo-tin polyvinyl chloride served as "blanks" and positive controls, respectively. Results showed an overall increase in cytokine, chemokine, and growth factor production as monocytes are activated or differentiated into macrophages and that proinflammatory and anti-wound healing cytokines and chemokines dominate this profile. However, cytokine production was only modestly affected by the surface chemistry of these four stable and noncytotoxic biomaterials.

Intracellular phospholipase A2 expression and location in human macrophages: influence of synthetic material surface chemistry

Phospholipase A(2) (PLA(2)) enzymes participate in a potent inflammatory pathway through the liberation of arachidonic acid upon hydrolysis of membrane glycerophospholipids. The presence of implanted polycarbonate-urethane (PCNU) materials, used in several medical applications, has the ability to influence inflammatory responses of human macrophages that are recruited to a tissue-material interface; however, the specific inflammatory pathways that are activated upon macrophage attachment to PCNU are largely unknown. Previous studies suggested the participation of PLA(2) pathways in material degradation with the use of chemical inhibitors, such as aristolochic acid (ARIST), however not accurately defining the specific PLA(2) enzymes involved. The current study aimed to establish specific groups of PLA(2) involved in the macrophage foreign body response to PCNU. ARIST was assessed for specific effects on secretory PLA(2) (sPLA(2)) protein expression and non-specific effects on key proteins, beta-actin and monocyte-specific esterase, implicated in the macrophage attack on PCNU materials. Macrophage attachment to PCNU materials induced increased intracellular expression of cytosolic PLA(2) (cPLA(2)), but not sPLA(2), relative to tissue culture polystyrene (TCPS) as detected by immunoblot analysis, demonstrating an early and delayed stimulation during the time course of increased cPLA(2) protein expression. Laser scanning confocal microscopy images indicated a change in location of cPLA(2) in macrophages adherent to PCNU surfaces compared to TCPS. This study has illustrated changes in macrophage cPLA(2) expression in response to cell-attachment to PCNU surfaces, demonstrating that the macrophage foreign body response to biomaterials induces a potent inflammatory pathway, which may lead to tissue damage near the site of material implantation.

Influence of biodegradable and non-biodegradable material surfaces on the differentiation of human monocyte-derived macrophages

Monocyte-derived macrophages (MDM) and multinucleated foreign body giant cells (FBGC) are the primary cell types that remain at the cell-material interface of polyurethane (PU)-based medical devices as a result of chronic inflammatory responses. In vitro studies have demonstrated that MDM possess degradative potential toward PU, which can result in device failure. Because most studies have followed the degradation potential, morphology, and function of these cells only once fully differentiated, the current study investigated the influence of a non-degradable control tissue culture-grade polystyrene (TCPS) surface relative to two degradable model polycarbonate-urethanes (PCNU), of different chemistry, on various parameters of MDM morphology and function during a 14-day differentiation time course. The differentiation of human monocytes isolated from whole blood on PCNU materials resulted in increased cell attachment, decreased multinucleation, and significant decreases in cell spreading when compared with cells differentiated on TCPS. Actin-stained podosome-like cell adhesion structures were increased in PCNU-adherent cells, accompanied by an alteration in beta-actin and vinculin protein expression. The expression of the CD68 macrophage marker was reduced when cells were adherent to the PCNU materials and compared with TCPS, suggesting altered cell activation by the degradable relative to non-degradable materials. The degradative potential of these cells was altered by the material surface they were exposed to as measured by esterase activity and protein expression of monocyte-specific esterase. This was also supported by physical material breakdown evident in scanning electron microscopy images that illustrated holes in the PCNU films generated by the presence of differentiating MDM. It was concluded from these studies that PCNU materials significantly alter the function and morphology of differentiating MDM. This must be taken into consideration when studying cell-material interactions because these cells will receive cues from their immediate environment (including the biomaterial) upon differentiation, thereby affecting their resulting phenotype.