Cyclic biaxial strain affects U937 macrophage-like morphology and enzymatic activities

Functional regeneration at the blood-biomaterial interface

The use of cardiovascular implants is commonplace in clinical practice. However, reproducing the key bioactive and adaptive properties of native cardiovascular tissues with an artificial replacement is highly challenging. Exciting new treatment strategies are under development to regenerate (parts of) cardiovascular tissues directly in situ using immunomodulatory biomaterials. Direct exposure to the bloodstream and hemodynamic loads is a particular challenge, given the risk of thrombosis and adverse remodeling that it brings. However, the blood is also a source of (immune) cells and proteins that dominantly contribute to functional tissue regeneration. This review explores the potential of the blood as a source for the complete or partial in situ regeneration of cardiovascular tissues, with a particular focus on the endothelium, being the natural blood-tissue barrier. We pinpoint the current scientific challenges to enable rational engineering and testing of blood-contacting implants to leverage the regenerative potential of the blood.

Macrophages in immunoregulation and therapeutics

Macrophages exist in various tissues, several body cavities, and around mucosal surfaces and are a vital part of the innate immune system for host defense against many pathogens and cancers. Macrophages possess binary M1/M2 macrophage polarization settings, which perform a central role in an array of immune tasks via intrinsic signal cascades and, therefore, must be precisely regulated. Many crucial questions about macrophage signaling and immune modulation are yet to be uncovered. In addition, the clinical importance of tumor-associated macrophages is becoming more widely recognized as significant progress has been made in understanding their biology. Moreover, they are an integral part of the tumor microenvironment, playing a part in the regulation of a wide variety of processes including angiogenesis, extracellular matrix transformation, cancer cell proliferation, metastasis, immunosuppression, and resistance to chemotherapeutic and checkpoint blockade immunotherapies. Herein, we discuss immune regulation in macrophage polarization and signaling, mechanical stresses and modulation, metabolic signaling pathways, mitochondrial and transcriptional, and epigenetic regulation. Furthermore, we have broadly extended the understanding of macrophages in extracellular traps and the essential roles of autophagy and aging in regulating macrophage functions. Moreover, we discussed recent advances in macrophages-mediated immune regulation of autoimmune diseases and tumorigenesis. Lastly, we discussed targeted macrophage therapy to portray prospective targets for therapeutic strategies in health and diseases.

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.

Ion channel mediated mechanotransduction in immune cells

The immune system performs critical functions to defend against invading pathogens and maintain tissue homeostasis. Immune cells reside within or are recruited to a host of mechanically active tissues throughout the body and, as a result, are exposed to varying types and degrees of mechanical stimuli. Despite their abundance in such tissues, the role of mechanical stimuli in influencing immune cell function and the molecular mechanisms responsible for mechanics-mediated changes are still poorly understood. The recent emergence of mechanically-gated ion channels, particularly Piezo1, has provided an exciting avenue of research within the fields of mechanobiology and immunology. Numerous studies have identified roles for mechanically-gated ion channels in mechanotransduction within various different cell types, with a few recent studies in immune cells. These initial studies provide strong evidence that mechanically-gated ion channels play pivotal roles in regulating the immune system. In this review, we discuss characteristics of ion channel mediated force transduction, review the current techniques used to quantify and visualize ion channel activity in response to mechanical stimuli, and finally we provide an overview of recent studies examining the role of mechanically-gated ion channels in modulating immune cell function.

Immuno-regenerative biomaterials for in situ cardiovascular tissue engineering - Do patient characteristics warrant precision engineering?

In situ tissue engineering using bioresorbable material implants - or scaffolds - that harness the patient's immune response while guiding neotissue formation at the site of implantation is emerging as a novel therapy to regenerate human tissues. For the cardiovascular system, the use of such implants, like blood vessels and heart valves, is gradually entering the stage of clinical translation. This opens up the question if and to what extent patient characteristics influence tissue outcomes, necessitating the precision engineering of scaffolds to guide patient-specific neo-tissue formation. Because of the current scarcity of human in vivo data, herein we review and evaluate in vitro and preclinical investigations to predict the potential role of patient-specific parameters like sex, age, ethnicity, hemodynamics, and a multifactorial disease profile, with special emphasis on their contribution to the inflammation-driven processes of in situ tissue engineering. We conclude that patient-specific conditions have a strong impact on key aspects of in situ cardiovascular tissue engineering, including inflammation, hemodynamic conditions, scaffold resorption, and tissue remodeling capacity, suggesting that a tailored approach may be required to engineer immuno-regenerative biomaterials for safe and predictive clinical applicability.

Polarized M2 macrophages induced by mechanical stretching modulate bone regeneration of the craniofacial suture for midfacial hypoplasia treatment

The underlying mechanism of the trans-sutural distraction osteogenesis (TSDO) technique as an effective treatment that improves the symptoms of midfacial hypoplasia syndromes is not clearly understood. Increasing findings in the orthopedics field indicate that macrophages are mechanically sensitive and their phenotypes can respond to mechanical cues. However, how macrophages respond to mechanical stretching and consequently influence osteoblast differentiation of suture-derived stem cells (SuSCs) remains unclear, particularly during the TSDO process. In the present study, we established a TSDO rat model to determine whether and how macrophages were polarized in response to stretching and consequently affected bone regeneration of the suture frontal edge. Notably, after performing immunofluorescence, RNA-sequencing, and micro-computed tomography, it was demonstrated that macrophages are first recruited by various chemokines factors and polarized to the M2 phenotype upon optimal stretching. The latter in turn regulates SuSC activity and facilitates bone regeneration in sutures. Moreover, when the activated M2 macrophages were suppressed by pharmacological manipulation, new bone microarchitecture could rarely be detected under mechanical stretching and the expansion of the sutures was clear. Additionally, macrophages achieved M2 polarization in response to the optimal mechanical stretching (10%, 0.5 Hz) and strongly facilitated SuSC osteogenic differentiation and human umbilical vein endothelial cell angiogenesis using an indirect co-culture system in vitro. Collectively, this study revealed the mechanical stimulation-immune response-bone regeneration axis and clarified at least in part how sutures achieve bone regeneration in response to mechanical force.

The mechano-response of murine annulus fibrosus cells to cyclic tensile strain is frequency dependent

The intervertebral disk (IVD) is a composite structure essential for spine stabilization, load bearing, and movement. Biomechanical factors are important contributors to the IVD microenvironment regulating joint homeostasis; however, the cell type-specific effectors of mechanotransduction in the IVD are not fully understood. The current study aimed to determine the effects of cyclic tensile strain (CTS) on annulus fibrosus (AF) cells and identify mechano-sensitive pathways. Using a cell-type specific reporter mouse to differentiation NP and AF cells from the murine IVD, we characterized AF cells in dynamic culture exposed to CTS (6% strain) at specific frequencies (0.1 Hz, 1.0 Hz, or 2.0 Hz). We demonstrate that our culture model maintains the phenotype of primary AF cells and that the bioreactor system delivers uniform biaxial strain across the cell culture surface. We show that exposure of AF cells to CTS induces cytoskeleton reorganization resulting in stress fiber formation, with acute exposure to CTS at 2.0 Hz inducing a significant yet transient increase ERK1/2 pathway activation. Using SYBPR-based qPCR to assess the expression of extracellular matrix (ECM) genes, ECM-remodeling genes, candidate mechano-sensitive genes, inflammatory cytokines and cell surface receptors, we demonstrated that exposure of AF cells to CTS at 0.1 Hz increased Acan, Prg4, Col1a1 and Mmp3 expression. AF cells exposed to CTS at 1.0 Hz showed a significant increase in the expression of Acan, Myc, and Tnfα. Exposure of AF cells to CTS at 2.0 Hz induced a significant increase in Acan, Prg4, Cox2, Myc, Fos, and Tnfα expression. Among the cell surface receptors assessed, AF cells exposed to CTS at 2.0 Hz showed a significant increase in Itgβ1, Itgα5, and Trpv4 expression. Our findings demonstrate that the response of AF cells to CTS is frequency dependent and suggest that mechanical loading may directly contribute to matrix remodeling and the onset of local tissue inflammation in the murine IVD.

Mechano-Immunomodulation: Mechanoresponsive Changes in Macrophage Activity and Polarization

In recent years, biomaterial- and scaffold-based immunomodulation strategies were implemented in tissue regeneration efforts for manipulating macrophage polarization (a.k.a. phenotype or lineage commitment, or differentiation). Yet, most of our understanding of macrophage phenotype commitment and phagocytic capacity is limited to how physical cues (extracellular matrix stiffness, roughness, and topography) and soluble chemical cues (cytokines and chemokines released from the scaffold) influence macrophage polarization. In the context of immune response-tissue interaction, the mechanical cues experienced by the residing cells within the tissue also play a critical role in macrophage polarization and inflammatory response. However, there is no compiled study discussing the effect of the dynamic mechanical environment around the tissues on macrophage polarization and the innate immune response. The aim of this comprehensive review paper is 2-fold; (a) to highlight the importance of mechanical cues on macrophage lineage commitment and function and (b) to summarize the important studies dedicated to understand how macrophage polarization changes with different mechanical loading modalities. For the first time, this review paper compiles and compartmentalizes the studies investigating the role of dynamic mechanical loading with various modalities, amplitude, and frequency on macrophage differentiation. A deeper understanding of macrophage phenotype in mechanically dominant tissues (i.e. musculoskeletal tissues, lung tissues, and cardiovascular tissues) provides mechanistic insights into the design of mechano-immunomodulatory tissue scaffold for tissue regeneration.

Biomaterial-driven in situ cardiovascular tissue engineering-a multi-disciplinary perspective

There is a persistent and growing clinical need for readily-available substitutes for heart valves and small-diameter blood vessels. In situ tissue engineering is emerging as a disruptive new technology, providing ready-to-use biodegradable, cell-free constructs which are designed to induce regeneration upon implantation, directly in the functional site. The induced regenerative process hinges around the host response to the implanted biomaterial and the interplay between immune cells, stem/progenitor cell and tissue cells in the microenvironment provided by the scaffold in the hemodynamic environment. Recapitulating the complex tissue microstructure and function of cardiovascular tissues is a highly challenging target. Therein the scaffold plays an instructive role, providing the microenvironment that attracts and harbors host cells, modulating the inflammatory response, and acting as a temporal roadmap for new tissue to be formed. Moreover, the biomechanical loads imposed by the hemodynamic environment play a pivotal role. Here, we provide a multidisciplinary view on in situ cardiovascular tissue engineering using synthetic scaffolds; starting from the state-of-the art, the principles of the biomaterial-driven host response and wound healing and the cellular players involved, toward the impact of the biomechanical, physical, and biochemical microenvironmental cues that are given by the scaffold design. To conclude, we pinpoint and further address the main current challenges for in situ cardiovascular regeneration, namely the achievement of tissue homeostasis, the development of predictive models for long-term performances of the implanted grafts, and the necessity for stratification for successful clinical translation.

Role for Mechanotransduction in Macrophage and Dendritic Cell Immunobiology

Tissue homeostasis is not only controlled by biochemical signals but also through mechanical forces that act on cells. Yet, while it has long been known that biochemical signals have profound effects on cell biology, the importance of mechanical forces has only been recognized much more recently. The types of mechanical stress that cells experience include stretch, compression, and shear stress, which are mainly induced by the extracellular matrix, cell-cell contacts, and fluid flow. Importantly, macroscale tissue deformation through stretch or compression also affects cellular function.Immune cells such as macrophages and dendritic cells are present in almost all peripheral tissues, and monocytes populate the vasculature throughout the body. These cells are unique in the sense that they are subject to a large variety of different mechanical environments, and it is therefore not surprising that key immune effector functions are altered by mechanical stimuli. In this chapter, we describe the different types of mechanical signals that cells encounter within the body and review the current knowledge on the role of mechanical signals in regulating macrophage, monocyte, and dendritic cell function.

Comprehensive genetic analysis of early host body reactions to the bioactive and bio-inert porous scaffolds

To design scaffolds for tissue regeneration, details of the host body reaction to the scaffolds must be studied. Host body reactions have been investigated mainly by immunohistological observations for a long time. Despite of recent dramatic development in genetic analysis technologies, genetically comprehensive changes in host body reactions are hardly studied. There is no information about host body reactions that can predict successful tissue regeneration in the future. In the present study, porous polyethylene scaffolds were coated with bioactive collagen or bio-inert poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) (PMB) and were implanted subcutaneously and compared the host body reaction to those substrates by normalizing the result using control non-coat polyethylene scaffold. The comprehensive analyses of early host body reactions to the scaffolds were carried out using a DNA microarray assay. Within numerous genes which were expressed differently among these scaffolds, particular genes related to inflammation, wound healing, and angiogenesis were focused upon. Interleukin (IL)-1β and IL-10 are important cytokines in tissue responses to biomaterials because IL-1β promotes both inflammation and wound healing and IL-10 suppresses both of them. IL-1β was up-regulated in the collagen-coated scaffold. Collagen-specifically up-regulated genes contained both M1- and M2-macrophage-related genes. Marked vessel formation in the collagen-coated scaffold was occurred in accordance with the up-regulation of many angiogenesis-inducible factors. The DNA microarray assay provided global information regarding the host body reaction. Interestingly, several up-regulated genes were detected even on the very bio-inert PMB-coated surfaces and those genes include inflammation-suppressive and wound healing-suppressive IL-10, suggesting that not only active tissue response but also the inert response may relates to these genetic regulations.

In vitro response of monocyte-derived macrophages to a decellularized pericardial biomaterial

Decellularized tissue-derived heart valves are an example of biomaterials derived from natural scaffolds. These types of implants are increasing in popularity although their in vivo performance is still only poorly understood and has, at times, been catastrophic. It is apparent that better understanding is required before these biomaterials can be used safely. In this study, the human monocyte-derived macrophage (MDM) response to decellularized bovine pericardium (DBP) was used as a model to predict the biological performance of these materials on implantation. Human monocytes differentiated on tissue culture polystyrene (TCPS) for 14 days were trypsinized and reseeded onto DBP, TCPS, and polydimethylsiloxane (PDMS) for 48 h. The MDMs on DBP contained less intracellular and extracellular esterase activity compared with MDMs on TCPS and PDMS, as well as less acid phosphatase activity than on TCPS. As well, morphologically, MDMs on DBP were less spread, less multinucleated and did not display many lamellipodia. Taken together, these data represent the first evidence of the MDM response to intact, native extracellular matrix, demonstrating that these cells reacted with an altered, possibly reduced foreign body response on this natural scaffold compared with the two control surfaces. This in vitro MDM cell model may provide a novel method for predicting and elucidating the biological performance of tissue-derived biomaterials, thereby directing a more rational design of biomaterials for tissue regeneration purposes.

Mechanical strain induces involution-associated events in mammary epithelial cells

Background

Shortly after weaning, a complex multi-step process that leads to massive epithelial apoptosis is triggered by tissue local factors in the mouse mammary gland. Several reports have demonstrated the relevance of mechanical stress to induce adaptive responses in different cell types. Interestingly, these signaling pathways also participate in mammary gland involution. Then, it has been suggested that cell stretching caused by milk accumulation after weaning might be the first stimulus that initiates the complete remodeling of the mammary gland. However, no previous report has demonstrated the impact of mechanical stress on mammary cell physiology. To address this issue, we have designed a new practical device that allowed us to evaluate the effects of radial stretching on mammary epithelial cells in culture.

Results

We have designed and built a new device to analyze the biological consequences of applying mechanical stress to cells cultured on flexible silicone membranes. Subsequently, a geometrical model that predicted the percentage of radial strain applied to the elastic substrate was developed. By microscopic image analysis, the adjustment of these calculations to the actual strain exerted on the attached cells was verified. The studies described herein were all performed in the HC11 non-tumorigenic mammary epithelial cell line, which was originated from a pregnant BALB/c mouse. In these cells, as previously observed in other tissue types, mechanical stress induced ERK1/2 phosphorylation and c-Fos mRNA and protein expression. In addition, we found that mammary cell stretching triggered involution associated cellular events as Leukemia Inhibitory Factor (LIF) expression induction, STAT3 activation and AKT phosphorylation inhibition.

Conclusion

Here, we show for the first time, that mechanical strain is able to induce weaning-associated events in cultured mammary epithelial cells. These results were obtained using a new practical and affordable device specifically designed for such a purpose. We believe that our results indicate the relevance of mechanical stress among the early post-lactation events that lead to mammary gland involution.

Effect of phorbol esters on the macrophage-mediated biodegradation of polyurethanes via protein kinase C activation and other pathways

It was previously found that re-seeding monocyte-derived macrophages (MDM) on polycarbonate-based polyurethanes (PCNUs) in the presence of the protein kinase C (PKC) activator phorbol myristate acetate (PMA) inhibited MDM-mediated degradation of PCNUs synthesized with 1,6-hexane diisocyanate (HDI), as well as esterase activity and monocyte-specific esterase (MSE) protein. However, no effect on the degradation of a 4,4'-methylene bisphenyl (MDI)-derived PCNU (MDI321) occurred. This finding suggested that oxidation, a process linked to the PKC pathway, was not activated in the same manner for all PCNUs. In the current study MDM were re-seeded onto the above PCNU surfaces with PMA, PKC-inactive 4alphaPMA and the PKC inhibitor bisindolylmaleimide I hydrochloride (BIM) for 48 h before assaying for PCNU degradation, esterase activity, MSE protein, DNA, cell viability and cell morphology. 4alphaPMA did not alter MDM-mediated HDI PCNU degradation but MDI321 degradation increased in this condition. BIM alone had no effect on any parameter; however, when BIM and PMA were added together, the PMA inhibition of biodegradation, esterase activity and MSE protein was partially reversed for MDM on HDI PCNUs only. Adding PMA to MDM on HDI PCNUs increased intercellular connections, whereas 4alphaPMA or BIM+PMA increased cell size. Although this study demonstrated a role for oxidation via a PKC-activated pathway in MDM-mediated PCNU degradation, phorbol esters appear to also activate non-PKC pathways that have roles in biodegradation. Moreover, the sensitivity to material surface chemistry in the MDM response to each PCNU dictates a multi-factorial degradative process involving alternate material specific oxidative and hydrolytic mechanisms.

Mechanotransduction gone awry

Cells sense their physical surroundings through mechanotransduction - that is, by translating mechanical forces and deformations into biochemical signals such as changes in intracellular calcium concentration or by activating diverse signalling pathways. In turn, these signals can adjust cellular and extracellular structure. This mechanosensitive feedback modulates cellular functions as diverse as migration, proliferation, differentiation and apoptosis, and is crucial for organ development and homeostasis. Consequently, defects in mechanotransduction - often caused by mutations or misregulation of proteins that disturb cellular or extracellular mechanics - are implicated in the development of various diseases, ranging from muscular dystrophies and cardiomyopathies to cancer progression and metastasis.

A numerical model to predict abdominal aortic aneurysm expansion based on local wall stress and stiffness

Aneurysms of the abdominal aorta enlarge until rupture occurs. We assume that this is the result of remodelling to restore wall stress. We developed a numerical model to predict aneurysm expansion based on this assumption. In addition, we obtained aneurysm geometry of 11 patients from computed tomography angiographic images to obtain patient specific calculations. The assumption of a wall stress related expansion indeed resulted in a series of local expansions, adjusting global geometry in an exponential fashion similar as in patients. Furthermore, it revealed that location of peak wall stress changed over time. The assumptions of this model are discussed in detail in this manuscript, and the implications are related to literature findings.

A simple device to apply equibiaxial strain to cells cultured on flexible membranes

The biomechanical environment to which cells are exposed is important to their normal growth, development, interaction, and function. Accordingly, there has been much interest in studying the role of biomechanical forces in cell biology and pathophysiology. This has led to the introduction and even commercialization of many experimental devices. Many of the early devices were limited by the heterogeneity of deformation of cells cultivated in different locations of the culture plate membranes and were also attached with complicated technical/electronic efforts resulting in a restriction of the reproducibility of these devices. The objective of this study was to design and build a simple device to allow the application of dose-dependent homogeneous equibiaxial static stretch to cells cultured on flexible silicone membranes to investigate biological and biomedical questions. In addition, cultured neonatal rat atrial cardiomyocytes were stretched with the proposed device with different strain gradients. For the first time with this study we could demonstrate that stretch up to 21% caused dose-dependent changes in biological markers such as the calcineurin activity, modulatory calcineurin-interacting protein-1, voltage-gated potassium channel isoform 4.2, and voltage-gated K(+) channel-interacting proteins-2 gene expression and transient outward potassium current densities but not the protein-to-DNA ratio and atrial natriuretic peptide mRNA. With both markers mentioned last, dose-dependent stretch alterations could only be achieved with stretch up to 13%. The simple and low-cost device presented here might be applied to a wide range of experimental settings in different fields of research.

Is cell culture stressful? Effects of degradable and nondegradable culture surfaces on U937 cell function

In vitro cell culture has become one of the most widely used techniques in biological and health sciences research, with the most common culture supports being either tissue culture grade polystyrene (TCPS) or polydimethylsiloxane (PDMS). It has previously been shown that monocyte-derived macrophages (MDMs) respond to material surface chemistry, synthesizing and releasing degradative activities that could produce products, which alter the cell's response. In this study, functional parameters of differentiated U937 macrophage-like cells were compared when cultured on nondegradable standard control surfaces versus models of biomaterials (polycarbonate-based polyurethanes) used in the manufacture of medical devices previously shown to degrade and/or elicit pathways of inflammation. Although the influence of PDMS and TCPS on cell function is often underappreciated by investigators, both surfaces elicited enzyme markers of inflammation. Cells on TCPS had the highest intracellular and released esterase activities and protein levels. Cells on PDMS had the most released acid phosphatase activity and protein (P<0.001), as well as de novo 57− and 59− kDa released proteins. The criteria for defining an activated cell phenotype become critically important when materials such as PDMS and TCPS are used as standard control surfaces whether in experiments for research in elucidating metabolic pathways or in screening drugs and materials for therapeutic uses.

Differential effects of uniaxial and biaxial strain on U937 macrophage-like cell morphology: Influence of extracellular matrix type proteins

Tissue engineering concepts have expanded in the last decade to consider the importance of biochemical signaling from extracellular matrix (ECM) proteins adhered to substrates such as polymeric and ceramic scaffolds. This study investigated combined ECM/mechanical factors on the key signaling cells (macrophages) for wound healing, since previously, mechanical strain and ECM proteins have only been considered separately for their effects on macrophage morphology. Human U937 macrophage-like cells were cultured on a model elastomeric membrane, coated with either collagen type I or poly-RGD peptide (ProNectin). The cells were subjected to cyclic uniform uniaxial or nonuniform biaxial strain with the Flexercell Tension Plus system to simulate strains that various soft tissue implants may undergo during the critical tissue-implant integration period. The surface coatings affected total cellular protein, which was significantly higher in cells on collagen than ProNectin coated surfaces after biaxial, but not uniaxial strain, whereas ProNectin coated surfaces caused a decrease in DNA following uniaxial, but not biaxial strain. Adding the protein coatings that relate to the wound healing process during tissue regeneration, elicited effects specific to the strain type imposed. The combination of these parameters caused changes in U937 macrophage-like cells that should be considered in the outcome of the desired performance in the tissue-material constructs.

The functional response of U937 macrophage-like cells is modulated by extracellular matrix proteins and mechanical strain

Extracellular matrix proteins (ECMs) play a significant role in the transfer of mechanical strain to monocyte-derived macrophages (MDMs) affecting morphological changes in a foreign body reaction. This study investigated how the functional responses of U937 macrophage-like cells differed when subjected to 2 dynamic strain types (nonuniform biaxial or uniform uniaxial strain) while cultured on siloxane membranes coated with either collagen type I or RGD peptide repeats (ProNectin®). Biaxial strain caused an increase in intracellular esterase and acid phosphatase (AP) activities, as well as monocyte-specific esterase (MSE) protein levels in cells that were seeded on either uncoated surfaces (shown previously) or collagen, but not ProNectin®. Released AP activity, but not released esterase activity, was increased on all surfaces. Biaxial strain increased IL-6, but not IL-8 on all surfaces. When cells were subjected to uniaxial strain, intracellular esterase increased on coated surfaces only, whereas intracellular AP activity was unaffected. Both esterase and AP released activities increased on all surfaces. Uniaxial strain increased the release of IL-6 on all surfaces, but IL-8 on coated surfaces only. This study demonstrated for the first time that ECM proteins could specifically modulate cellular responses to different types of strain. Using this approach with an in vitro cell system may help to unravel the complex function of MDMs in the foreign-body reaction.