Cytokine and growth factor production by monocytes/macrophages on protein preadsorbed polymers

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

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

The Role of In Vitro Immune Response Assessment for Biomaterials

Grafts are required to restore tissue integrity and function. However, current gold standard autografting techniques yield limited harvest, with high rates of complication. In the search for viable substitutes, the number of biomaterials being developed and studied has increased rapidly. To date, low clinical uptake has accompanied inherently high failure rates, with immune rejection a specific and common end result. The objective of this review article was to evaluate published immune assays evaluating biomaterials, and to stress the value that incorporating immune assessment into evaluations carries. Immunogenicity assays have had three areas of focus: cell viability, maturation and activation, with the latter being the focus in the majority of the literature due to its relevance to functional outcomes. With recent studies suggesting poor correlation between current in vitro and in vivo testing of biomaterials, in vitro immune response assays may be more relevant and enhance ability in predicting acceptance prior to in vivo application. Uptake of in vitro immune response assessment will allow for substantial reductions in experimental time and resources, including unnecessary and unethical animal use, with a simultaneous decrease in inappropriate biomaterials reaching clinic. This improvement in bench to bedside safety is paramount to reduce patient harm.

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

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

Dendritic cells in host response to biologic scaffolds

Tissue regeneration and repair require a highly complex and orchestrated series of events that require inflammation, but can be compromised when inflammation is excessive or becomes chronic. Macrophages are one of the first cells to contact and respond to implanted materials, and mediate the inflammatory response. The series of events following macrophage association with biomaterials has been well-studied. Dendritic cells (DCs) also directly interact with biomaterials, are critical for specific immune responses, and can be activated in response to interactions with biomaterials. Yet, much less is known about the responses by DCs. This review discusses what we know about DC response to biomaterials, the underlying mechanisms involved, and how DCs can be influenced by the macrophage response to biomaterials. Lastly, I will discuss how biomaterials can be manipulated to enhance or suppress DC function to promote a specific desirable immune response - a major goal for implantable biologically active therapeutics.

Self‑assembled monolayers of alkanethiolates on surface chemistry groups in osteosarcoma cells

Cell biomedical behavior is influenced by a number of factors, and the extracellular matrix (ECM) of the cellular microenvironment affects certain cancer cells. In the current study, U-2OS cells were cultured on gold surfaces modified with different terminal chemical groups [methyl (-CH₃), amino (-NH₂), hydroxyl (-OH) and carboxyl (-COOH)]. The results revealed that different chemical surfaces convey different behaviors. The density of the different functional surfaces was confirmed by atomic force microscopy. Cell morphology, proliferation rate and cell cycle were investigated using scanning electron microscopy, cell counting and flow cytometry. In conclusion, the type of chemical group on a biomaterial is an important property for the growth of osteosarcoma cells; -NH₂ and -COOH surfaces sustained visible cell adhesion and promoted cell growth.

Integrin-directed modulation of macrophage responses to biomaterials

Macrophages are the primary mediator of chronic inflammatory responses to implanted biomaterials, in cases when the material is either in particulate or bulk form. Chronic inflammation limits the performance and functional life of numerous implanted medical devices, and modulating macrophage interactions with biomaterials to mitigate this response would be beneficial. The integrin family of cell surface receptors mediates cell adhesion through binding to adhesive proteins nonspecifically adsorbed onto biomaterial surfaces. In this work, the roles of integrin Mac-1 (αMβ2) and RGD-binding integrins were investigated using model systems for both particulate and bulk biomaterials. Specifically, the macrophage functions of phagocytosis and inflammatory cytokine secretion in response to a model particulate material, polystyrene microparticles were investigated. Opsonizing proteins modulated microparticle uptake, and integrin Mac-1 and RGD-binding integrins were found to control microparticle uptake in an opsonin-dependent manner. The presence of adsorbed endotoxin did not affect microparticle uptake levels, but was required for the production of inflammatory cytokines in response to microparticles. Furthermore, it was demonstrated that integrin Mac-1 and RGD-binding integrins influence the in vivo foreign body response to a bulk biomaterial, subcutaneously implanted polyethylene terephthalate. A thinner foreign body capsule was formed when integrin Mac-1 was absent (~30% thinner) or when RGD-binding integrins were blocked by controlled release of a blocking peptide (~45% thinner). These findings indicate integrin Mac-1 and RGD-binding integrins are involved and may serve as therapeutic targets to mitigate macrophage inflammatory responses to both particulate and bulk biomaterials.

Short-term in vitro responses of human peripheral blood monocytes to ferritic stainless steel fiber networks

Beneficial effects on bone-implant bonding may accrue from ferromagnetic fiber networks on implants which can deform in vivo inducing controlled levels of mechanical strain directly in growing bone. This approach requires ferromagnetic fibers that can be implanted in vivo without stimulating undue inflammatory cell responses or cytotoxicity. This study examines the short-term in vitro responses, including attachment, viability, and inflammatory stimulation, of human peripheral blood monocytes to 444 ferritic stainless steel fiber networks. Two types of 444 networks, differing in fiber cross section and thus surface area, were considered alongside austenitic stainless steel fiber networks, made of 316L, a widely established implant material. Similar high percent seeding efficiencies were measured by CyQuant® on all fiber networks after 48 h of cell culture. Extensive cell attachment was confirmed by fluorescence and scanning electron microscopy, which showed round monocytes attached at various depths into the fiber networks. Medium concentrations of lactate dehydrogenase (LDH) and tumor necrosis factor alpha (TNF-α) were determined as indicators of viability and inflammatory responses, respectively. Percent LDH concentrations were similar for both 444 fiber networks at all time points, whereas significantly lower than those of 316L control networks at 24 h. All networks elicited low-level secretions of TNF-α, which were significantly lower than that of the positive control wells containing zymosan. Collectively, the results indicate that 444 networks produce comparable responses to medical implant grade 316L networks and are able to support human peripheral blood monocytes in short-term in vitro cultures without inducing significant inflammatory or cytotoxic effects.

Design, fabrication, and implementation of a wireless, passive implantable pressure sensor based on magnetic higher-order harmonic fields

A passive and wireless sensor was developed for monitoring pressure in vivo. Structurally, the pressure sensor, referred to as the magneto-harmonic pressure sensor, is an airtight chamber sealed with an elastic pressure membrane. A strip of magnetically-soft material is attached to the bottom of the chamber and a permanent magnet strip is embedded inside the membrane. Under the excitation of an externally applied AC magnetic field, the magnetically-soft strip produces a higher-order magnetic signature that can be remotely detected with an external receiving coil. As ambient pressure varies, the pressure membrane deflects, altering the separation distance between the magnetically-soft strip and the permanent magnet. This shifts the higher-order harmonic signal, allowing for detection of pressure change as a function of harmonic shifting. The wireless, passive nature of this sensor technology allows for continuous long-term pressure monitoring, particularly useful for biomedical applications such as monitoring pressure in aneurysm sac and sphincter of Oddi. In addition to demonstrating its pressure sensing capability, an animal model was used to investigate the efficacy and feasibility of the pressure sensor in a biological environment.

Impact of pressure and gas type on adhesion formation and biomaterial integration in laparoscopy

BACKGROUND

Laparoscopic mesh repair of inguinal and incisional hernias has been widely adopted. Nevertheless, knowledge about the impact of pneumoperitoneum on mesh integration is rare. The present study investigates pressure and gas-dependent effects of pneumoperitoneum on adhesion formation and biomaterial integration in a standardized animal model.

METHODS

Laparoscopic intraperitoneal onlay mesh implantation (IPOM) was performed in 32 female chinchilla rabbits using CO(2) or helium for pneumoperitoneum. Intra-abdominal pressures were 3 or 6 mmHg. Animals were killed after 21 days, and the abdominal wall was explanted for subsequent histopathological examinations. Adhesions were assessed qualitatively with a scoring system, and the adhesion surface was analyzed semiquantitatively by planimetry. Infiltration of macrophages (CD68), expression of matrix metalloproteinase 13 (MMP-13), and cell proliferation (Ki67) were analyzed at the mesh to host interface by immunohistochemistry. The collagen type I/III ratio was analyzed by cross-polarization microscopy to determine the quality of mesh integration.

RESULTS

After 21 days, perifilamental infiltration with macrophages (CD68) and percentage of proliferating cells (Ki67) were highest after 6 mmHg of CO(2) pneumoperitoneum. The extent of adhesions, as well as the expression of MMP-13 and the collagen type I/III ratio, were similar between groups.

CONCLUSIONS

Our experiments showed no pressure or gas-dependent alterations of adhesion formation and only minor effects on biomaterial integration. Altogether, there is no evidence for a clinically negative effect of CO(2) pneumoperitoneum.

Temporal progression of the host response to implanted poly(ethylene glycol)-based hydrogels

Poly(ethylene glycol) (PEG) hydrogels hold great promise as in vivo cell carriers for tissue engineering. To ensure appropriate performance of these materials when implanted, the host response must be well understood. The objectives for this study were to characterize the temporal evolution of the foreign body reaction (FBR) to acellular PEG-based hydrogels prepared from PEG diacrylate precursors when implanted subcutaneously in immunocompentent c57bl/6 mice by (immuno)histochemical analysis and gene expression. Compared with a normal FBR elicited by silicone (SIL), PEG hydrogels without or with a cell adhesion ligand RGD elicited a strong early inflammatory response evidenced by a thick band of macrophages as early as day 2, persisting through two weeks, and by increased interleukin-1β expression. PEG-only hydrogels showed a slower, but more sustained progression of inflammation over PEG-RGD. Temporal changes in gene expression were observed in response to PEG-based materials and in general exhibited, elevated expression of inflammatory and wound healing genes in the tissues surrounding the implants, while the expression patterns were more stable in response to SIL. While a stabilized FBR was achieved with SIL and to a lesser degree with PEG-RGD, the PEG-only hydrogels had not yet stabilized after 4 weeks. In summary, PEG-only hydrogels elicit a strong early inflammatory reaction, which persists throughout the course of the implantation even as a collagenous capsule begins to form. However, the incorporation of RGD tethers partially attenuates this response within 2 weeks leading to an improved FBR to PEG-based hydrogels.

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.

Phenotypic changes in bone marrow-derived murine macrophages cultured on PEG-based hydrogels activated or not by lipopolysaccharide

Macrophages are phenotypically diverse cells performing a number of functions involved in immunity, inflammation, wound healing, tissue homeostasis and the foreign body reaction. In the latter, the type of biomaterial and the surrounding environment likely have an impact on macrophage phenotype and, subsequently, the severity of the reaction. The objectives for this study were to characterize the phenotype of bone marrow-derived murine macrophages in response to poly(ethylene glycol) (PEG)-based hydrogels, a promising class of materials for cell delivery. Gene expression was used as a measure of phenotype and characterized by IL-1β, TNF-α, iNOS, IL-12β, arginase, VEGF-A, and IL-10. Macrophages were cultured on PEG hydrogels, PEG hydrogels with RGD tethers, and medical grade silicone rubber, a well-characterized biomaterial, up to 96 h in the absence and presence of lipopolysaccharide (LPS) to simulate an inflammatory environment. Macrophage interrogation led to immediate up-regulation (10×) of IL-1β and TNF-α within 4h, followed by an increase in IL-10/IL-12β and a subsequent concomitant decrease in the pro-inflammatory genes by 96 h, suggesting a shift from classically activated to a regulatory phenotype. LPS stimulation led to a stronger early up-regulation of pro-inflammatory genes (e.g. 20-30× for IL-1β and TNF-α), followed by upregulation (4-6×) of arginase, suggesting a shift from an elevated classically activated to a wound healing phenotype. Material type played a significant role in regulating pro-inflammatory genes, which was most pronounced with PEG alone. Overall, our findings indicate that macrophages undergo similar phenotypic changes for the materials tested, but the magnitudes of these responses are highly material dependent.

Nanoporosity of alumina surfaces induces different patterns of activation in adhering monocytes/macrophages

The present study shows that alumina nanotopography affects monocyte/macrophage behavior. Human mononuclear cells cultured on alumina membranes with pore diameters of 20 and 200 nm were evaluated in terms of cell adhesion, viability, morphology, and release of proinflammatory cytokines. After 24 hours, cell adhesion was assessed by means of light microscopy and cell viability by measuring LDH release. The inflammatory response was evaluated by quantifying interleukin-1β and tumour necrosis factor-α. Finally, scanning electron microscopy was used to study cell morphology. Results showed pronounced differences in cell number, morphology, and cytokine release depending on the nanoporosity. Few but highly activated cells were found on the 200 nm porous alumina, while relatively larger number of cells were found on the 20 nm porous surface. However, despite their larger number, the cells adhering on the 20 nm surface exhibited reduced pro-inflammatory activity. The data of this paper implies that nanotopography could be exploited for controlling the inflammatory response to implants.

The role of multiple toll-like receptor signalling cascades on interactions between biomedical polymers and dendritic cells

Biomaterials are used in several health-related applications ranging from tissue regeneration to antigen-delivery systems. Yet, biomaterials often cause inflammatory reactions suggesting that they profoundly alter the homeostasis of host immune cells such as dendritic cells (DCs). Thus, there is a major need to understand how biomaterials affect the function of these cells. In this study, we have analysed the influence of chemically and physically diverse biomaterials on DCs using several murine knockouts. DCs can sense biomedical polymers through a mechanism, which involves multiple TLR/MyD88-dependent signalling pathways, in particular TLR2, TLR4 and TLR6. TLR-biomaterial interactions induce the expression of activation markers and pro-inflammatory cytokines and are sufficient to confer on DCs the ability to activate antigen-specific T cells. This happens through a direct biomaterial-DC interaction although, for degradable biomaterials, soluble polymer molecules can also alter DC function. Finally, the engagement of TLRs by biomaterials profoundly alters DC adhesive properties. Our findings could be useful for designing structure-function studies aimed at developing more bioinert materials. Moreover, they could also be exploited to generate biomaterials for studying the molecular mechanisms of TLR signalling and DC activation aiming at fine-tuning desired and pre-determined immune responses.

Quantitative in vivo cytokine analysis at synthetic biomaterial implant sites

To further elucidate the foreign body reaction, investigation of cytokines at biomaterial implant sites was carried out using a multiplex immunoassay and ELISA. Macrophage activation cytokines (IL-1beta, IL-6, and TNFalpha), cytokines important for macrophage fusion (IL-4 and IL-13), antiinflammatory cytokines (IL-10 and TGFbeta), chemokines (GRO/KC, MCP-1), and the T-cell activation cytokine IL-2 were quantified at biomaterial implant sites. Empty cages (controls) or cages containing synthetic biomedical polymer (Elasthane 80A (PEU), silicone rubber (SR), or polyethylene terephthalate (PET)) were implanted subcutaneously in Sprague-Dawley rats for 4, 7, or 14 days, and cytokines in exudate supernatants and macrophage surface adhesion and fusion were quantified. The presence of a polymer implant did not affect the levels of IL-1beta, TGFbeta, and MCP-1 in comparison to the control group. IL-2 was not virtually detected in any of the samples. Although the levels of IL-4, IL-13, IL-10, and GRO/KC were affected by polymer implantation, but not dependent on a specific polymer, IL-6 and TNFalpha were significantly greater in those animals implanted with PEU and SR, materials that do not promote fusion. The results indicate that differential material-dependent cytokine profiles are produced by surface adherent macrophages and foreign body giant cells in vivo.

Carcinogenesis induced by foreign bodies

This review deals with the contemporary investigations of carcinogenesis induced by foreign bodies. The main attention is given to the interactions of macrophages with an implanted foreign body and their possible role in tumorigenesis.

Proteomic analysis and quantification of cytokines and chemokines from biomaterial surface-adherent macrophages and foreign body giant cells

Implantation of biomaterial devices results in the well-known foreign body reaction consisting of monocytes, macrophages, and foreign body giant cells (FBGCs) at the material/tissue interface. We continue to address the hypothesis that material surface chemistry modulates the phenotypic expression of these cells. Utilizing our human monocyte culture system, we have used surface-modified polymers displaying hydrophobic, hydrophilic, and/or ionic chemistries to determine the cytokines/chemokines released from biomaterial-adherent macrophages/FBGCs. This study broadens our approach by using proteomic analysis to identify important factors expressed by these cells and further quantifies these molecules with ELISAs. Proteomic profiles changed over time suggesting that the adherent macrophages underwent a phenotypic switch. Macrophage/FBGC-derived proinflammatory cytokines, IL-1beta and IL-6, decreased with time, while the anti-inflammatory cytokine, IL-10, gradually increased with time. Resolution of the inflammatory response was also demonstrated by a decrease in chemoattractant IL-8 and MIP-1beta production with time. Material-dependent macrophage/FBGC activation was analyzed using cytokine/chemokine production and cellular adhesion. Monocyte/macrophage adhesion was similar on all surfaces, except for the hydrophilic/neutral surfaces that showed a significant decrease in cellular density and minimal FBGC formation. Normalizing the ELISA data based on the adherent cell population provided cytokine/chemokine concentrations produced per cell. This analysis showed that although there were fewer cells on the hydrophilic/neutral surface, these adherent cells were further activated to produce significantly greater amounts of each cytokine/chemokine tested than the other surfaces. This study clearly presents evidence that material surface chemistry can differentially affect monocyte/macrophage/FBGC adhesion and cytokine/chemokine profiles derived from activated macrophages/FBGCs adherent to biomaterial surfaces.

Foreign body reaction to biomaterials

The foreign body reaction composed of macrophages and foreign body giant cells is the end-stage response of the inflammatory and wound healing responses following implantation of a medical device, prosthesis, or biomaterial. A brief, focused overview of events leading to the foreign body reaction is presented. The major focus of this review is on factors that modulate the interaction of macrophages and foreign body giant cells on synthetic surfaces where the chemical, physical, and morphological characteristics of the synthetic surface are considered to play a role in modulating cellular events. These events in the foreign body reaction include protein adsorption, monocyte/macrophage adhesion, macrophage fusion to form foreign body giant cells, consequences of the foreign body response on biomaterials, and cross-talk between macrophages/foreign body giant cells and inflammatory/wound healing cells. Biomaterial surface properties play an important role in modulating the foreign body reaction in the first two to four weeks following implantation of a medical device, even though the foreign body reaction at the tissue/material interface is present for the in vivo lifetime of the medical device. An understanding of the foreign body reaction is important as the foreign body reaction may impact the biocompatibility (safety) of the medical device, prosthesis, or implanted biomaterial and may significantly impact short- and long-term tissue responses with tissue-engineered constructs containing proteins, cells, and other biological components for use in tissue engineering and regenerative medicine. Our perspective has been on the inflammatory and wound healing response to implanted materials, devices, and tissue-engineered constructs. The incorporation of biological components of allogeneic or xenogeneic origin as well as stem cells into tissue-engineered or regenerative approaches opens up a myriad of other challenges. An in depth understanding of how the immune system interacts with these cells and how biomaterials or tissue-engineered constructs influence these interactions may prove pivotal to the safety, biocompatibility, and function of the device or system under consideration.

Prosthetic vascular grafts: Wrong models, wrong questions and no healing

In humans, prosthetic vascular grafts remain largely without an endothelium, even after decades of implantation. While this shortcoming does not affect the clinical performance of large bore prostheses in aortic or iliac position, it contributes significantly to the high failure rate of small- to medium-sized grafts (SMGs). For decades intensive but largely futile research efforts have been under way to address this issue. In spite of the abundance of previous studies, a broad analysis of biological events dominating the incorporation of vascular grafts was hitherto lacking. By focusing on the three main contemporary graft types, expanded polytetrafluoroethylene (ePTFE), Dacron and Polyurethane (PU), accumulated clinical and experimental experience of almost half a century was available. The main outcome of this broad analysis-supported by our own experience in a senescent non-human primate model-was twofold: Firstly, inappropriate animal models, which addressed scientific questions that missed the point of clinical relevance, were largely used. This led to a situation where the vast majority of investigators unintentionally studied transanastomotic rather than transmural or blood-borne endothelialization. Given the fact that in patients transanastomotic endothelialization (TAE) covers only the immediate perianastomotic region of sometimes very long prostheses, TAE is rather irrelevant in the clinical context. Secondly, transmural endothelialization seems to have a time window of opportunity before a build-up of an adverse microenvironment. In selecting animal models that prematurely terminate this build-up through the early presence of an endothelium, the most significant 'impairment factor' for physiological tissue regeneration in vascular grafts remained ignored. By providing insight into mechanisms and experimental designs which obscured the purpose and scope of several decades of vascular graft studies, future research may better address clinical relevance.

On the transplantation, regeneration and induction of bone: the path to bone morphogenetic proteins and other skeletal growth factors

The clinical and experimental transplantation of bone dates back to the seventeenth century and human allogeneic (homogeneic) bone has been successfully used as an alternative to autogenous bone since 1878, when Sir William Macewen reconstructed the right humerus of William Connell. This review describes how subsequent studies of bone transplantation led to the eventual discovery of a new family of secreted signalling molecules--the bone morphogenetic proteins (BMPs), and the realisation of the important role of polypeptide growth factors in mediating the growth, remodelling and regeneration of the skeleton. The development of suitable alternatives to both autogenous and allogeneic bone has been a goal of bone and biomaterials research for more than 30 years. The first requirement is a biocompatible, bioresorbable, osteoconductive framework supporting the ingrowth of host cells from the recipient bed. Many materials including collagen, calcium phosphate ceramics and synthetic polymers have been widely tested experimentally with varying success. The discovery of osteoinductive BMPs and their availability in recombinant human forms has given considerable impetus to the field. However, progress to date in engineering significant quantities of functional bone tissue in vivo has been disappointing; finding suitable carriers for BMPs has proven to be a greater challenge than expected. The dilemma for the clinician and the biotechnology industry, at present, is that, while recombinant human growth factors are readily available for clinical use, the lack of delivery systems that can adequately mimic both the physical properties and release kinetics of bone matrix remains a major handicap.

Digital image analysis for morphometric evaluation of tissue response after implanting alloplastic vascular prostheses

The aim of this study was to examine the suitability of digital image analysis, using the KS400 software system, for the morphometric evaluation of the tissue response after prosthesis implantation in an animal model. Twenty-four female pigs aged 10 weeks were implanted with infrarenal Dacron(R) prostheses for 14, 21, 28, and 116 days. Following the explantation and investigation of the neointima region, the expression of beta-1-integrin, the proliferation rate by means of Ki-67 positive cells, and the intima thickness were evaluated as exemplary parameters of the tissue response after implantation. Frozen tissue sections were immunohistochemically stained and subsequently examined using computer-aided image analysis. A maximum expression of 32.9% was observed for beta-1-integrin 14 days after implantation, gradually declining over time to 9.8% after 116 days. The proliferation rate was found to be 19% on day 14, increasing to 39% on day 21 with a subsequent gradual decline to 5% after 116 days. The intima thickness increased from 189.9 microm on day 14 to 1228.0 microm on day 116. In conclusion, digital image analysis was found to be an efficient and reproducible method for the morphometric evaluation of a peri-prosthetic tissue response.

The interrelated role of fibronectin and interleukin-1 in biomaterial-modulated macrophage function

Macrophages play a critical role in mediating the host response to biomaterials, perhaps most notably by guiding the host inflammatory response through the release of inflammatory molecules such as the cytokine interleukin-1 (IL-1). The extent of the macrophage response following interaction with the biomaterial surface contributes greatly to device efficacy, yet the molecular mechanisms of this interaction are still unclear. The extracellular matrix (ECM) protein fibronectin (FN) is recognized by macrophages and frequently used in biomaterial modification to elicit greater cellular adhesion and tissue integration. Macrophage interaction with FN and other ECM molecules on the biomaterial surface has been shown to induce a variety of inflammatory responses, thus both FN and IL-1 can be utilized as model molecules to better understand the mechanisms of material-mediated macrophage responses. This literature review presents a comprehensive survey of past and current research on the interrelated role of IL-1, FN, and FN-derivatives in determining biomaterial-modulated macrophage function.

Controlled release of plasmid DNA from hydrogels prepared from gelatin cationized by different amine compounds

This paper is an investigation to compare the in vivo controlled release of a plasmid DNA from biodegradable hydrogels prepared from gelatin cationized by different amine compounds, ethylenediamine, putrescine, spermidine, and spermine and the consequent profile of gene expression. Cationized gelatin prepared through the chemical introduction of each amine compound was crosslinked by various concentrations of glutaraldehyde to obtain cationized gelatin hydrogels for the carrier of plasmid DNA release. When the cationized gelatin hydrogels incorporating 125I-labeled plasmid DNA were implanted into the femoral muscle of mice, the radioactivity remaining decreased with time and the retention period of radioactivity prolonged with a decrease in the water content of hydrogels. When 125I-labeled cationized gelatin hydrogels with the higher water content was implanted, the radioactivity remaining was decreased faster with time. The remaining time profile of plasmid DNA radioactivity was in good accordance with that of hydrogel radioactivity, irrespective of the type of cationized gelatin. Following intramuscular implantation, any cationized gelatin hydrogel incorporating plasmid DNA enhanced the expression level of plasmid DNA to a significantly higher extent than the free plasmid DNA injection. In addition, prolonged time period of gene expression was observed although there was no significant difference in the expressed period between the cationized gelatin hydrogels. It was concluded that plasmid DNA of biological activity was released from every cationized gelatin hydrogel accompanied with the in vivo degradation, resulting in enhanced and prolonged gene expression.

Molecular determinants of biocompatibility

The biocompatibility of medical implants dictates the fate of almost all medical devices. It is well established that medical devices trigger a variety of adverse tissue responses, such as inflammation, fibrosis, infection and thrombosis. However, the mechanisms involved in biomaterial-mediated tissue responses remain largely unknown. The lack of such knowledge hinders the development of biomaterials with better biocompatibility and safety. The aim of this review is to summarize our current understanding of the processes governing foreign body reactions to tissue-contact devices. Obviously, this information is urgently needed for assisting the rational design of materials or medical devices to minimize undesirable tissue reactions upon implantation and, in addition, to promote the wound healing process.

Endotoxin: The uninvited guest

In the laboratory environment where biomaterials are synthesized and their biocompatibility assessed, we find that endotoxin contamination is hard to avoid and must not be ignored. In those relatively few cases where endotoxin was known to be present, it has been clearly shown that endotoxin can significantly affect the biological response observed and hence confound any effect of the material. This short review explains what endotoxin is, how to test for it and remove it and what its effect on the biological response to biomaterials is. We advocate routine testing of endotoxin on biomaterials and of reagents used in experimental evaluation of biomaterials and this should be the responsibility of every scientist to ensure the validity of any biomaterial study.

A Model System to Assess Key Vascular Responses to Biomaterials

PURPOSE

To establish a reproducible laboratory test to evaluate prospective vascular biomaterials with respect to their thromboinflammatory properties by examining fibrinogen, platelet, and monocyte binding. Endothelial migration onto these surfaces was used as an index of vascular healing.

METHODS

To evaluate biomaterials for potential thrombogenicity and inflammation, binding assays of radiolabeled human fibrinogen, platelets, and monocytes were performed on standard pieces of vascular biomaterials, including metals and polymeric and ceramic-coated materials. Using an established in vitro endothelial cell migration model, the relative migration rate of cultured human aortic endothelial cells onto these vascular biomaterials was measured and compared. The fibrinogen, platelet, and monocyte binding results were combined along with the migration results to create an overall score of biocompatibility.

RESULTS

A significant direct relation of platelet and monocyte binding to the amount of adsorbed fibrinogen was observed. In contrast, migration rates of cultured human aortic endothelial cells onto the same biomaterial surfaces were found to be inversely related the amount of bound fibrinogen. Among the materials tested, stainless steel received the highest score of biocompatibility, while turbostratic carbon scored the lowest.

CONCLUSIONS

Fibrinogen, platelet, and monocyte binding levels, as well as endothelial migration rates onto vascular material surfaces, provide a basis for evaluating thrombogenicity, inflammatory potential, and endothelialization in the laboratory prior to in vivo testing.

Cytokine secretion from mononuclear cells culturedin vitro with starch-based polymers and poly-L-lactide

The cytokine network is one of the major controlling systems of the inflammatory process, driving the magnitude and duration of the host response against invading microorganisms, foreign materials, or altered internal stimuli. Pro- and antiinflammatory cytokines were quantified after in vitro culture of a mixed population of monocytes/macrophages and lymphocytes with biodegradable polymers. Different blends of starch-based polymers and their composites filled with hydroxyapatite were studied and compared with poly-L-lactide. Interleukin (IL)-1beta, IL-6, and tumour necrosis factor-alpha were investigated as the markers of immunological reactivity because they are known to act at the early stages of injury/invasion. Interferon-gamma, recognized as a proinflammatory cytokine, although not present during early responses was also investigated. Contrarily, IL-4 derived from T lymphocytes, was investigated because it is an immunoregulator that counteracts some aspects of inflammation. T lymphocyte activation was also determined by quantifying IL-2. The results support the hypothesis that different biodegradable polymers can affect mononuclear cell activation and the production of several cytokines associated with the inflammatory process. No IL-2 or interferon-gamma was found in the culture supernatants after 3, 7, and 14 days in the presence of any of the materials. IL-6 was detected in the highest amounts, for all the conditions, followed by tumour necrosis factor-alpha. IL-1beta was produced in very low amounts, being undetectable with some of the starch-based materials. IL-4 was the only cytokine that did not demonstrate any significant difference within this group of materials. Starch-based polymers and composites induced lower production of proinflammatory cytokines in comparison to poly-L-lactide.

Surface chemistry modulates focal adhesion composition and signaling through changes in integrin binding

Biomaterial surface properties influence protein adsorption and elicit diverse cellular responses in biomedical and biotechnological applications. However, the molecular mechanisms directing cellular activities remain poorly understood. Using a model system with well-defined chemistries (CH3, OH, COOH, NH2) and a fixed density of the single adhesive ligand fibronectin, we investigated the effects of surface chemistry on focal adhesion assembly and signaling. Surface chemistry strongly modulated integrin binding and specificity--alpha5beta1 integrin binding affinity followed the pattern OH>NH2=COOH>CH3, while integrin alphaVbeta3 displayed the relationship COOH>NH2>>OH=CH3. Immunostaining and biochemical analyses revealed that surface chemistry modulates the structure and molecular composition of cell-matrix adhesions as well as focal adhesion kinase (FAK) signaling. The neutral hydrophilic OH functionality supported the highest levels of recruitment of talin, alpha-actinin, paxillin, and tyrosine-phosphorylated proteins to adhesive structures. The positively charged NH2 and negatively charged COOH surfaces exhibited intermediate levels of recruitment of focal adhesion components, while the hydrophobic CH3 substrate displayed the lowest levels. These patterns in focal adhesion assembly correlated well with integrin alpha5beta1 binding. Phosphorylation of specific tyrosine residues in FAK also showed differential sensitivity to surface chemistry. Finally, surface chemistry-dependent differences in adhesive interactions modulated osteoblastic differentiation. These differences in focal adhesion assembly and signaling provide a potential mechanism for the diverse cellular responses elicited by different material properties.

Effects of adsorbed proteins and surface chemistry on foreign body giant cell formation, tumor necrosis factor alpha release and procoagulant activity of monocytes

The adhesion and activation of monocytes and macrophages are thought to affect the foreign body response to implanted medical devices. However, these cells interact with devices indirectly, because of the prior adsorption of proteins. Therefore, we preadsorbed several "model" biomaterial surfaces with proteins and then measured foreign body giant cell (FBGC) formation, tumor necrosis factor alpha (TNFalpha) release, and procoagulant activity. The model surfaces were tissue culture polystyrene (TCPS), untreated polystyrene (PS), and Primaria, whereas the proteins used were albumin, fibronectin, fibrinogen, and immunoglobulin. FBGC formation, TNFalpha release, and procoagulant activity of monocytes were the highest for surfaces preadsorbed with IgG. FBGC formation was lower on surfaces with adsorbed fibrinogen and fibronectin than on uncoated surfaces. TNFalpha release and procoagulant activity of monocytes were similar on surface adsorbed with fibrinogen, fibronectin, or albumin. Monocyte activation was also affected by the surface chemistry of the substrates, because FBGC formation was the highest on PS and the lowest on TCPS. Monocyte procoagulant activity was the highest on Primaria. Adsorbed proteins and surface chemistry were found to have strong effects on FBGC formation, monocyte TNFalpha release, and procoagulant activity in vitro, providing support for the idea that these same variables could affect macrophage-mediated foreign body response to biomaterials in vivo.

Differences in adsorption of serum proteins and production of IL-1ra by human monocytes incubated in different tissue culture microtiter plates

In vitro cell culture models can be of great value in order to further analyze the regulatory mechanisms underlying the inappropriate function of the immune system in diseases such as autoimmunity and cancer. Cell culture conditions have to be well controlled in a way that they mirror the in vivo situation. The objective of this study was to compare tissue culture microtiter plates from different manufacturers with respect to their ability to support monokine production by human monocytes cultured in human serum. Tissue culture ware, made of polystyrene, undergoes treatment by the manufacturers to make the surface more suitable for culture of adherent cell populations. It is possible that quality differences in this treatment can lead to variations in protein binding properties and thereby influence the adherence and functional properties of monocytes. We measured spontaneous interleukin-1 receptor antagonist (IL-1ra) production by peripheral blood monocytes, cultured in human serum, in five different microtiter plates made for adherent cell culture. Culture in plates from two of the five manufacturers resulted in significantly lower amounts of secreted IL-1ra. IL-1ra release by human monocytes can be induced by adherent IgG cross-linking membrane receptors for the Fc part of IgG (FcgammaR). We found that reduced IL-1ra production coincided with a reduced capacity for binding of serum IgG in one case. Furthermore, this brand of microtiter plate also displayed the lowest level of adsorption of human albumin. We conclude that the protein adsorption properties of the plastic tissue culture ware have to be taken into consideration when assessing monokine production by human monocytes in vitro.

Suppression of the inflammatory response from adherent cells on phospholipid polymers

The expression of interleukin-1beta (IL-1beta) messenger RNA (mRNA) in macrophage-like cells cultured on phospholipid polymers was evaluated to determine the extent of the inflammatory response. As phospholipid polymers, poly(2-methacryloyloxyethyl phosphorylcholine(MPC)-co-n-butyl methacrylate(BMA)s (PMBs) were synthesized. Poly(ethylene terephthalate) (PET), poly(2-hydroxyethyl methacrylate) (PHEMA), and segmented poly(ether urethane) (Tecoflex 60) were used as reference biomedical polymers. The protein adsorption onto the polymer surfaces from a cell culture medium was determined. The amount of the total protein adsorbed onto the PMBs was lower than that adsorbed onto the reference polymers, and the amount of adsorbed protein decreased with an increase in the MPC units in the PMBs. Human premyelocytic leukemia cell line (HL-60) was used, and the expression of IL-1beta mRNA was investigated with the reverse transcription polymerase chain reaction (RT-PCR) method. When HL-60 cells were cultured on PMBs, the expression of IL-1beta mRNA in the cells was much less than that on the reference polymers. In particular, the expression of IL-1beta mRNA in HL-60 cells cultured on the PMBs containing more than 10 mol % MPC units was not detected. This corresponded to the reduced amount of adsorbed proteins on the PMB surfaces. These results suggest that the PMBs effectively suppressed the activation and inflammatory response of adherent macrophagelike cells.

Reduction of surface-induced inflammatory reaction on PLGA/MPC polymer blend

Poly(lactide-co-glycolide) (PLGA) has been believed to be a good biocompatible material for tissue engineering due to its biodegradability and non-toxicity of the monomer. However, the inflammatory reaction of adherent cells on the surface has not been discussed sufficiently. We hypothesized that the inflammatory reaction of adherent cells on PLGA might occur and could be reduced by blending a 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer (PMEH) with the PLGA. PLGA/PMEH blend membranes were prepared by a solvent evaporation technique. The thermal properties of the PLGA/PMEH membrane were determined using a differential scanning calorimeter. The glass transition temperature of the PLGA/PMEH membranes was slightly decreased compared to that of a PLGA membrane. X-ray photoelectron spectrum analysis revealed that the MPC unit was exposed on the PLGA/PMEH membrane and that the surface concentration of the MPC unit on the membrane was increased with an increase in the concentration of the PMEH in the blended membrane. NIH-3T3 mouse fibroblast cells were cultured on the PLGA/ PMEH membrane for 2 days. The number of adherent cells on the PLGA/PMEH membrane was decreased with an increase in the concentration of the PMEH. Using the RT-PCR method, the amount of an inflammatory cytokine, IL-1beta, mRNA expressed from adherent human premyelocytic leukemia cells on PLGA and PLGA/PMEH membranes were determined. On a PLGA/PMEH membrane containing 0.2 wt% of PMEH, the expression of IL-1beta mRNA was significantly lower than that on PLGA, but no difference in the number of adherent cells was found. Therefore, the MPC polymer was a useful additive for reducing the inflammatory reaction of adherent cells on PLGA.

Interaction of blood components with heparin-immobilized polyurethanes prepared by plasma glow discharge

The blood compatibility of poly(ethylene oxide) (PEO)-grafted and heparin (Hep) immobilized polyurethanes was investigated using in vitro plasma recalcification time (PRT), activated partial thromboplastin time (APTT), platelet adhesion and activation, and peripheral blood mononuclear cell (PBMC) adhesion and activation. In the experiment with plasma proteins, the PRT of the polyurethane (PU) surface was prolonged by PEO grafting and further prolonged by heparin immobilization. The APTT was prolonged on PU-Hep, suggesting the binding of immobilized heparin to antithrombin III. The percentage of platelet adhesion on PU was not much different from that on acrylic acid- and PEO-grafted PUs (PU-C, PU-6, PU-33), yet was substantially decreased by heparin immobilization (PU-6-Hep, PU-33-Hep). The release of serotonin from adhering platelets was slightly suppressed on PEO-grafted PUs yet significantly suppressed on heparin-immobilized PUs. In the PBMC experiments, the adhesion and activation of the cells were significantly suppressed on heparin-immobilized PUs, and the amount of interleukin-6 (IL-6) released from PBMCs stimulated with surface-modified PUs decreased with a decrease in PBMC adhesion.

Ex vivo PMA-induced respiratory burst and TNF-alpha secretion elicited from inflammatory cells on machined and porous blood plasma clot-coated titanium

The release of inflammatory mediators around implants and normal wounds may differ due to the presence of the solid surface. In this study, machined and sub-micron porous titanium implants with and without a 100 nm thick blood plasma clot were inserted subcutaneously in rat for 3 or 24 h. The cell recruitment to the interfaces, in vivo secretion of TNF-alpha and the ex vivo PMA-induced production of reactive oxygen species were subsequently investigated. The thin plasma clot coating gave rise to an increased ex vivo PMA-stimulated oxygen radical production by implant-associated cells at both implantation times, and an increased cell recruitment at 24 h. The total TNF-alpha secretion was highest at sham sites and plasma clot-coated porous titanium at 24 h. After 24 h, the cell-type pattern in the exudate around the porous plasma-coated implant was more similar to that found at sham sites than that adjacent to the non-coated implants. No differences were observed between the machined Ti and the machined sub-micron porous Ti.

Interaction of bioactive glasses with peritoneal macrophages and monocytes in vitro

Macrophage activation was analyzed following exposure to pure, crystalline alpha-quartz powders, two bioactive gel-glass powders of different compositions, and a melt-derived glass, 45S5 Bioglass. The release of reactive oxygen metabolites (chemiluminescence test), modifications of cell morphology, the amount of tumor necrosis factor alpha (TNFalpha) secreted, and the amount of TNFalpha mRNA expression were evaluated. The 45S5 Bioglass powders elicited the highest chemiluminescence response while the two solgel glasses had a lower response with less of an oxidative burst difference between them. Particulate bioactive glasses are actively ingested by mouse peritoneal macrophages, and only the 58S solgel glass had a moderate toxic effect on the macrophages. Macrophage cell morphology showed increased size and cell spreading, consistent with the high level of cytokine secretion induced by 45S5 Bioglass. The 45S5 Bioglass powders led to an increased release of TNFalpha and expression of TNFalpha mRNA relative to unstimulated and control treated monocytes. Bioactive glasses (and particularly 45S5 Bioglass) that in vivo induce rapid bone growth appear to activate an autocrine-like process in which the response evoked by the material (for example monocyte and macrophage activation with cytokine production) enhances subsequent interactions with cells in contact with the material.

Apoptosis and cytokine release in human monocytes cultured on polystyrene and fibrinogen-coated polystyrene surfaces

The effects of polystyrene (PS) material surface preadsorption with fibrinogen (3 mg/ml) and a low concentration of lipopolysaccharide (LPS; 10 ng/ml) and polystyrene particles (PS; 10(5)/ml) on human monocyte adhesion, viability and cytokine release were studied during 24h culture in vitro. LPS caused an upregulation of CD14 in adherent cells. In comparison with unstimulated cells on uncoated polystyrene surfaces, LPS did not alter the number of adherent cells but caused a markedly increased release of the proinflammatory cytokines (IL-1alpha and TNF-alpha) and the down-regulating IL-10. The expression of indicators of various stages of cell death, TdT, annexin-V, propidium iodide (PI) and lactate dehydrogenase (LDH), were unaltered, decreased, decreased and increased, respectively, after LPS stimulation. PS particles (3 microm psi) caused an increased DNA fragmentation but had a reduced proportion of annexin-V and PI positive cells in comparison with unstimulated cells on uncoated PS. In contrast, 1microm psi particles had a similar proportion of TdT, annexin-V and PI expressing cells as unstimulated controls. Cultures stimulated with particles (irrespective of size), had a similar concentration of proinflammatory cytokines as unstimulated controls, whereas a higher level of IL-10 was detected. Precoating of PS with fibrinogen revealed an enhanced cell adhesion and a concomitant reduction of CD14 expression. irrespective of stimulation with various agonists. The proportions of TdT, annexin-V and PI positive cells were unaltered or reduced on fibrinogen-coated PS in both unstimulated and agonist-challenged cultures. However, depending on the presence and type of agonist, fibrinogen mediated either a markedly increased (LPS) or equivalent (particles and unstimulated) IL-1alpha and TNFalpha release. Further, in comparison with uncoated substrates, fibrinogen was associated with a reduction of IL-10 release, irrespective of the type of stimuli. These observations, using low concentrations of bacterial and material products, indicate that fibrinogen modulates cell material interactions and up- and down-regulates specific events depending on the nature/ type of immediate stimuli.

Neointima formation after stent implantation in an experimental model of restenosis: polytetrafluoroethylene-covered versus uncovered stainless steel stents

The aim of the study was to assess whether stents covered with a membrane of polytetrafluoroethylene spanned over the mashes of a sandwich-configured double stent (n = 15) prevent migration of smooth muscle cells through stent spaces, leading to less neointima formation compared with uncovered stainless steel stents (n = 14) in iliac arteries of male Chinchilla Bastard rabbits (n = 18). Lumen stenosis was assessed by quantitative angiography immediately before the animals were killed 5 weeks after stent deployment. Neointima formation was quantified by histomorphometric analysis. There were large regional and individual differences in neointima formation, leading locally to a significantly higher degree of stenosis in covered stents (histologically, 76.0 +/- 13.7 vs. 62.9 +/- 12.9%; angiographically, 33.5 +/- 21.1 vs. 7.8 +/- 8.8%) compared with uncovered stents, though mean neointimal and lumen area values were not significantly different. In conclusion, polytetrafluoroethylene-covered stents do not prevent neointima formation compared with uncovered stents. Although the membrane reduces local smooth muscle cell migration, the neointima hyperplasia at the proximal and distal ends of a covered stent stimulates migration along its longitudinal axis. In this stent-restenosis model, regional and individual proliferation processes and not the membrane-covering strut-to-strut distances determine lumen restenosis.

The Inflammatory Response and its Consequence for the Clinical Outcome Following Aortic Aneurysm Repair

OBJECTIVE

to review published studies on the outcome of the inflammatory response after abdominal aortic aneurysm (AAA) repair.

METHODS

a literature search on PubMed was performed. All studies that determined the inflammatory response (cytokine release) after AAA repair were included. The results of the studies and differences between open and endoluminal repair were compared and evaluated.

RESULTS

seventeen studies were identified. In most studies the investigated cytokines were TNF-alpha and IL-6. Determination of IL-1 beta, IL-8, TNFsr1 and TNFsr2 were less often performed. TNF-alpha may reflect, but not strictly predict, the clinical outcome in patients with ruptured AAA. IL-6 levels correlate well with the surgical trauma per se. Variations in recorded cytokine release during endovascular AAA repair may depend on the times of blood sampling.

CONCLUSION

both open and endovascular AAA repair provoke a cytokine response. This response is greater during open repair than during endovascular aortic aneurysm exclusion.

Human monocyte adhesion and activation on crystalline polymers with different morphology and wettability in vitro

This study evaluated the effects of crystalline polyamide (Nylon-66), poly(ethylene-co-vinyl alcohol) (PEVA), and poly(vinylidene fluoride) (PVDF) polymers with nonporous and porous morphologies on the ability of monocytes to adhere and subsequently activate to produce IL-1beta, IL-6, and tumor necrosis factor alpha. The results indicated monocyte adhesion and activation on a material might differ to a great extent, depending on the surface morphology and wettability. As the polymer wettability increases, the ability of monocytes to adhere increases but the ability to produce cytokines decreases. Similarly, these polymers, when prepared with porous surfaces, enhance monocyte adhesion but suppress monocyte release of cytokines. Therefore, the hydrophobic PVDF with a nonporous surface stimulates the most activity in adherent monocytes but shows the greatest inhibition of monocyte adhesion when compared with all of the other membranes. In contrast, the hydrophilic Nylon-66, which has a porous surface, is a relatively better substrate for this work. Therefore, monocyte behavior on a biomaterial may be influenced by a specific surface property. Based on this result, we propose that monocyte adhesion is regulated by a different mechanism than monocyte activation. Consequently, the generation of cytokines by monocytes is not proportional to the number of cells adherent to the surface.

Subcutaneous abscess formation around catheters induced by viable and nonviable Staphylococcus epidermidis as well as by small amounts of bacterial cell wall components

The use of catheters is often complicated by infection, mainly due to Staphylococcus epidermidis. Recently, a novel poly(vinylpyrrolidone)-grafted silicone elastomer catheter (SEpvp) was introduced. Less bacteria adhered to SEpvp than to conventional SE catheters in vitro. The frequency of S. epidermidis infection associated with SEpvp and SE was assessed in a rabbit model. Unexpectedly, abscesses were induced by the injection of low numbers of S. epidermidis along subcutaneously inserted SEpvp. No abscesses were seen around SE, even when very high numbers of S. epidermidis were injected. This bioincompatibility reaction observed around the SEpvp was independent of the host, bacterial strain, and method of inoculation. Abscesses were also induced by nonviable S. epidermidis and by bacterial cell wall components. Because these incompatibility reactions were not observed in the absence of bacteria, biocompatibility testing should include experiments in which the inflammatory effects of the combination of catheter and (non)viable bacteria are tested.