Effect of the addition of a labile gelatin component on the degradation and solute release kinetics of a stable PEG hydrogel.

Characterization of the degradation mechanisms and resulting products of biodegradable materials is critical in understanding the behavior of the material including solute transport and biological response. Previous mathematical analyses of a semi-interpenetrating network (sIPN) containing both labile gelatin and a stable cross-linked poly(ethylene glycol) (PEG) network found that diffusion-based models alone were unable to explain the release kinetics of solutes from the system. In this study, degradation of the sIPN and its effect on solute release and swelling kinetics were investigated. The kinetics of the primary mode of degradation, gelatin dissolution, was dependent on temperature, preparation methods, PEGdA and gelatin concentration, and the weight ratio between the gelatin and PEG. The gelatin dissolution rate positively correlated with both matrix swelling and the release kinetics of high-molecular-weight model compound, FITC-dextran. Coupled with previous in vitro studies, the kinetics of sIPN degradation provided insights into the time-dependent changes in cellular response including adhesion and protein expression. These results provide a facile guide in material formulation to control the delivery of high-molecular-weight compounds with concomitant modulation of cellular behavior.

In vivo modulation of host response and macrophage behavior by polymer networks grafted with fibronectin-derived biomimetic oligopeptides: the role of RGD and PHSRN domains.

Polymorphonuclear leukocytes, monocytes/macrophages, foreign body giant cells (FBGC), and lymphocytes are central in directing the host foreign body and inflammatory/immune reactions that impact material biostability, biocompatibility, and device efficacy. We employed the functional architecture of fibronectin to probe the mechanisms of protein-cell interaction in modulating leukocyte behavior. We demonstrated previously that the RGD and PHSRN domain of fibronectin and the spatial orientation between the motifs were crucial in regulating macrophage function in vitro. The current study delineates the role of RGD and PHSRN in modulating the host inflammatory response and macrophage behavior in vivo. Oligopeptides containing RGD and/or PHSRN domains were grafted onto a polyethyleneglycol-based substrate and subcutaneously cage implanted into rats. Peptide identity played a minimal role in modulating the host inflammatory response and adherent macrophage density. The RGD motif, either alone or at the terminal position with the PHSRN-containing flanking sequence, elicited a rapid macrophage fusion to form FBGCs at the early stage of implantation. Both the RGD motif and the PHSRN motif were important in mediating FBGC formation at the later implantation time. However, the PHSRN motif, specifically in the configuration of G3 RGDG6 PHSRNG, evoked a larger extent of FBGC coverage. Our results indicate the importance of RGD and PHSRN in modulating macrophage function in a time and orientation dependent fashion in vivo.

Preparation of heterodifunctional polyethyleneglycols: network formation, characterization, and cell culture analysis.

Polyethyleneglycols (PEG) are employed extensively in the development of biomaterials; however, the hydroxyl groups in PEG-diols have very limited chemical activity. We developed a synthesis scheme for a library of heterodifunctional PEG (hPEG) with two distinct terminal moieties to improve the reactivity and physicochemical properties of PEG. hPEG were employed in the formulation of polymer networks with various surface physicochemical properties and utilized to study cell-material interaction. Extensive NMR and HPLC analyses confirmed the chemical structure of hPEG. The hydrophilicity of the polymer network was predominantly dependent on the hPEG concentration with the molecular weight and terminal functional group playing lesser roles. Adherent human fibroblast density on the network remained constant with increasing hPEG concentration in the network formulation but decreased rapidly on networks containing 0.8-1.25 g ml(-1) of hPEG. This trend was independent of the hPEG terminal moiety and molecular weight. No adherent cell was observed on all films containing 2.5 g ml(-1) or more of hPEG.

Utilizing biomimetic oligopeptides to probe fibronectin-integrin binding and signaling in regulating macrophage function in vitro and in vivo.

Biomimetic oligopeptides were employed to elucidate the molecular mechanisms of fibronectin-integrin interaction in regulating macrophage function. Oligopeptides were designed based on of the functional structure of fibronectin and grafted onto a polymer network containing polyethyleneglycols. Macrophage adhesion was independent of the peptide identity that contained sequence RGD, PHSRN, PRRARV, or combinations thereof in an integrin-dependent fashion in vitro. However, integrin-dependent foreign body giant cell (FBGC) formation in vitro was highly dependent on both RGD and PHSRN in a single peptide formulation and with a specific orientation. In vivo results showed that peptide identity played a minimal role in modulating the host inflammatory response and adherent macrophage density. RGD-containing peptides mediated a rapid FBGC formation by 4 days of implantation by significantly increasing both the number of macrophages that participate in the cell fusion process and the rate of cell fusion. Both RGD and PHSRN domains were important in mediating FBGC formation at later implantation periods. In vitro intracellular signaling studies revealed that the requirement of protein tyrosine kinase and serine/threonine kinase activation and cross-talk compensation for macrophage adhesion dynamically varied with surfaces and culture time. Protein kinase C-dependent adhesion was related to RGD and PHSRN sequences, and to the sequence orientation thereof in a form of GGGRGDGGGGGGPHSRNG. Furthermore, we observed a multiple effect of the mitogen-activated protein kinase/extracellular-signal-regulated kinase signaling factor in mediating macrophage adhesion, which depended on the method of ligand immobilization. These findings represent a mechanistic correlation between the role of substrates and protein functional architectures in ligand-receptor recognition and post-ligation signaling events that control cellular behavior in vitro and in vivo.

Fibronectin modulates macrophage adhesion and FBGC formation: the role of RGD, PHSRN, and PRRARV domains.

To probe the role of human plasma fibronectin in modulating human blood-derived macrophage adhesion and fusion to form multinucleated foreign-body giant cells (FBGC), a series of biomimetic oligopeptides based on the functional structure of fibronectin was designed and synthesized. Peptides incorporated the RGD and PHSRN integrin-binding sequences from FIII-10 and FIII-9 modules, respectively, and the PRRARV sequence from the C-terminal heparin-binding domain, either alone or in combination. Peptides were immobilized onto a polyethyleneglycol-based polymer substrate. The following conclusions were reached. Fibronectin modulated macrophage adhesion and the extent (i.e., size) of FBGC formation on control surfaces in the presence of serum proteins. Macrophages adhered to all substrates with relatively subtle differences between adhesion mediated by RGD, PHSRN, PRRARV, or combinations thereof. beta1-integrin subunit was essential in macrophage adhesion to peptide-grafted networks in a receptor-peptide specific manner, whereas beta3-integrin subunit was less important. Macrophage adhesion to PRRARV was mediated primarily by the direct interaction with integrins. RGD or PHSRN alone did not provide an adequate substrate for macrophage fusion to form FBGCs. However, the PHSRN synergistic site and the RGD site in a single oligopeptide provided a substrate for FBGC formation that was statistically comparable to that on the positive control material in the presence of serum proteins. This response was highly dependent upon the relative orientation between RGD and PHSRN. PRRARV did not support FBGC formation. These results demonstrate the importance of fibronectin and, specifically, the synergy between RGD and PHSRN domains, in supporting macrophage fusion to form FBGCs.

Evaluation of leukocyte adhesion on polyurethanes: the effects of shear stress and blood proteins.

Leukocytes are a central cell type in directing host inflammatory and immune processes; thus, its response to biomaterials is extremely important in understanding material-host interaction. Blood contacting biomaterials may activate the complement cascade, thus promote leukocyte adhesion and activation to the biomaterial surface. We hypothesize that the extent of complement-mediated leukocyte activation is modulated by the material chemical formulation and the presence of fluid shear stress. Medical-grade polyurethanes with or without 4,4'-butyldiene bis(6-tert-butyl-m-cresol) antioxidant additives and a rotating disk system were utilized to study cell adhesion under a well-characterized shear stress field. Radioimmunoassay and ELISA were employed to assess the extent of complement activity. The results showed that adherent leukocyte densities decreased with increasing shear stress and that leukocyte adhesion was decreased significantly further by the presence of the antioxidant in the polyurethanes. Cell adhesion under flow conditions was abolished when complement C3 protein was depleted from the test medium. An increase in complement Factor H adsorption was observed at high shear region; however, no change in the complete complement activation was observed in the presence of shear stress as indicated by the protein S-terminal complement complex level. Based on these results, oligopeptides designed from C3a, C5a, and fibronectin were grafted onto a cell-nonadhesive polymer surface to probe the molecular mechanisms of leukocyte adhesion as mediated by protein-receptor complexation. The results showed that C3a-derived peptides mediated higher adherent macrophage density when compared to that mediated by C5a- and fibronectin-derived peptides.

Evaluation of protein-modulated macrophage behavior on biomaterials: designing biomimetic materials for cellular engineering.

Macrophage is a central cell type in directing host inflammatory and immune processes; hence, its response to biomaterials (i.e. adhesion and giant cell formation) has a direct impact on material biostability and biocompatibility. In this paper, several in vitro and in vivo techniques from previously published results and current investigations are highlighted and presented to demonstrate means of delineating a part of the complex molecular mechanisms involved in the interaction between biomaterials and macrophages. Complement component C3 was found critical in mediating the initial adhesion of human macrophages on medical-grade polyetherurethaneureas. From radioimmunoassay studies, the presence of a diphenolic antioxidant additive in polyetherurethaneureas increased the propensity for complement upregulation but did not affect adherent macrophage density. The subcutaneous cage-implant system was utilized to confirm the role of interleukin-4 in the fusion of adherent macrophages to form foreign body giant cells on polyurethanes in vivo. To probe the function-structural relationship of macrophage-active proteins, fibronectin was employed as a model in the formulation of synthetic oligopeptide mimetics. Peptides were grafted onto previously developed, non-cell adhesive polyethyleneglycol-based networks. The results indicate that grafted tripeptide RGD sequence supported higher adherent macrophage density than surfaces grafted with other peptides such as PHSRN and PRRARV sequences. However, the formation of foreign body giant cells on peptide-grafted networks was highly dependent on the relative orientation between PHSRN and RGD sequences located in a single peptide.

Protein-mediated macrophage adhesion and activation on biomaterials: a model for modulating cell behavior.

The elucidation of proteins involved in biomaterial-modulated macrophage behavior is critical for the improvement of material performance and the initial exploration of material design capable of manipulating macrophage function for tissue engineering. In this paper, several in vitro and in vivo techniques are presented to demonstrate means of delineating a part of the complex molecular mechanisms involved in the interaction between biomaterial and macrophage adhesion and phenotypic development. The following conclusions were reached: (1) using radioimmunoassay, complement component C3 was found to be critical in mediating human macrophage adhesion on polyurethanes. (2) The presence of a diphenolic antioxidant additive in polyurethanes increased the propensity for complement upregulation but did not affect adherent macrophage density. (3) The subcutaneous cage-implant system was utilized to delineate interleukin-4 participation in the fusion of adherent macrophages to form foreign body giant cells in vivo in mice. The injection of purified interleukin-4 neutralizing antibody into the implanted cages significantly decreased the giant cell density; conversely, the giant cell density was significantly increased by the injection of recombinant interleukin-4 when compared with the controls. (4) The RGD and PHSRN amino acid sequences of the central cell binding domain and the PRRARV sequence of the C-terminal heparin binding domain of human plasma fibronectin were utilized to study the structure-functional relationship of protein in mediating macrophage behavior. Polyethyleneglycol-based networks grafted with the RGD-containing peptide supported higher adherent human macrophage density than surfaces grafted with other peptides. The formation of foreign body giant cell was highly dependent on the relative orientation between PHSRN and RGD domains located in a single peptide.

Blood and tissue compatibility of modified polyester: thrombosis, inflammation, and healing.

Poly(ethylene terephthalate) (PET) has been reported in literature to be moderately inflammatory and thrombogenic. To moderate the inflammatory response, PET fabric was surface modified by either Fluoropassiv fluoropolymer (FC), or an RGD-containing peptide (RGD). Samples were subsequently autoclave sterilized and implanted subcutaneously in Sprague Dawley rats for 2 to 4 weeks. Retrieved samples were evaluated histopathologically for indications of material toxicity and healing. Minimal acute or chronic inflammation was associated with the fabrics after 2 and 4 week implant duration. However, fibroblast proliferation into FC modified fabric (PET/FC) was less than that into unmodified (PET) and RGD modified fabric (PET/RGD) after 4 weeks, suggesting that FC modification of PET may inhibit excessive tissue growth. Additional samples of modified and unmodified fabrics were placed in stainless steel mesh cages, which were then implanted subcutaneously for 4 weeks. Cellular exudate was extracted weekly and cell concentrations within the exudate measured. Total leukocyte count (TLC) (reflective of local inflammation) at 1 week for PET/RGD was greater than that for PET/FC and PET. TLCs after 4 week implant decreased for all sample groups. In a separate experiment, PET vascular grafts surface modified by either FC or RGD were contacted 1 h with blood using the baboon arteriovenous (AV) shunt model of thrombosis in both the presence and absence of heparin. Accumulation of 111In labeled platelets (reflective of thrombus accumulation) upon grafts was less in the presence of heparin (effect significant at p = 1.2 x 10(-6), two-way ANOVA). Accumulation (in the presence of heparin) upon PET/RGD was less (p = 0.19), and upon PET/FC significantly less (p = 0.016) than that upon the unmodified PET control, suggesting that FC modification of PET may inhibit thrombus accumulation.

Murine macrophage behavior on peptide-grafted polyethyleneglycol-containing networks.

Polyethyleneglycol-based networks were employed as substrates to graft bioactive peptides to study macrophage interactions with materials. Our overall objective was to utilize biologically active factors to stimulate certain macrophage function on materials suitable for implantation in connective tissues. In this study, we sought to explore the bioactivity of several peptides derived from extracellular matrix adhesion proteins and macrophage-active proteins that are normally soluble. The candidate peptides examined corresponded to residues 63 to 77 of complement component C3a (C3a(63-77)), residues 178 to 207 of interleukin-1 beta (IL1beta(178-207)), residues 1615 to 1624 of fibronectin (FN(1615-1624)), endothelial-macrophage activating polypeptide II, complement component C5a inhibitory sequence, macrophage inhibitory peptide, and YRGDG; materials lacking peptides were used as negative controls. An established murine cell-line IC-21 was employed as a macrophage model, and human dermal fibroblasts were used for comparison. Our results showed that the substrates without grafted peptides were free from artifactual cell adhesion associated with the adsorption of serum or cellularly secreted proteins for long duration of culture. Of all grafted samples, IL1beta(178-207)- and C3a(63-77)-grafted surfaces supported higher adherent macrophage densities. C3a(63-77)- and FN(1615-1624)-grafted surfaces supported higher adherent fibroblast densities. From competitive inhibition studies, cell adhesion was determined to occur in a receptor-peptide specific manner. The presence of grafted YRGDG in addition to IL1beta(178-207), C3a(63-77), or FN(1615-1624) synergistically increased macrophage and fibroblast adhesion. Materials grafted with IL1beta(178-207) or C3a(63-77) co-grafted with or without YRGDG did not support the formation of multinucleated giant cells from the fusion of adherent macrophages in vitro.

In vivo biocompatibility and biostability of modified polyurethanes.

Modified segmented polyurethanes were examined for biostability and biocompatibility using an in vivo cage implant system for time intervals of 1, 2, 3, 5, and 10 weeks. Two types of materials were used: polyether polyurethanes and polycarbonate polyurethanes. Two unmodified polyether polyurethanes (PEUU A' and SPU-PRM), one PDMS endcapped polyether polyurethane (SPU-S), and two polycarbonate polyurethanes (SPU-PCU and SPU-C) were investigated in this study. Techniques used to characterize untreated materials were dynamic water contact angle, stress-strain analysis, and gel permeation chromatography. Cellular response was measured by exudate analysis and by macrophage and foreign body giant cell (FBGC) densities. Material characterization, postimplantation, was done by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) in order to quantify biodegradation and scanning electron microscopy (SEM) to qualitatively describe the cellular response and biodegradation. The exudate analysis showed that the acute and chronic inflammatory responses for all materials were similar. Lower FBGC densities and cell coverage on SPU-S were attributed to the hydrophobic surface provided by the PDMS endgroups. The polycarbonate polyurethanes did not show any significant differences in cell coverage or FBGC densities even though the macrophage densities were slightly lower compared to polyether polyurethanes. By 10 weeks, biodegradation in the case of PEUU A' and SPU-PRM was extensive as compared to SPU-S because the PDMS endcaps of SPU-S provided a shield against the oxygen radicals secreted by macrophages and FBGCs and lowered the rate of biodegradation. In the case of polycarbonate polyurethanes, the oxidative stability of the carbonate linkage lowered the rate of biodegradation tremendously as compared to the polyether polyurethanes (including SPU-S). The minor amount of biodegradation seen in polycarbonate polyurethanes at 10 weeks was attributed to hydrolysis of the carbonate linkage.

Leukocyte-biomaterial interactions in the presence of Staphylococcus epidermidis: flow cytometric evaluation of leukocyte activation.

The adhesion of bacteria on a biomaterial surface is believed to be the first step in the development of biomaterial-related infection. The goal of this study was to investigate the mechanisms that permit adherent bacteria to persist on the surface of an implanted cardiovascular biomaterial. We hypothesized that circulating leukocytes are unable to adhere to the biomaterial surface under physiologic shear stress conditions, and this prevents them from interacting with adherent bacteria. To address this hypothesis, we investigated the adhesion profiles of Staphylococcus epidermidis and polymorphonuclear leukocytes (PMN), incubated under controlled shear stress conditions with the test biomaterial. We found that bacteria could adhere on the biomaterial surface, even when their concentration in the test medium was as low as 10(3) cfu/mL. At this concentration, the bacteria did not induce significant complement activation. PMN adhesion on the biomaterial surface was sensitive to shear stress and minimal at shear stress > 10 dynes/cm2. Low concentrations of bacteria could induce a significant increase in the expression of PMN adhesion molecules CD11b and CD11c. We conclude that the presence of bacteria induces PMN activation but does not increase PMN adhesion on biomaterial surfaces under physiologic shear stress conditions. This could be a major mechanism that protects adherent bacteria from PMN antibacterial activity.

Complement-mediated leukocyte adhesion on poly(etherurethane ureas) under shear stress in vitro.

Blood-contacting biomaterials may activate the complement cascade, thus promoting leukocyte adhesion to the biomaterial surface. We hypothesize that the extent of complement activation is modulated by biomaterial formulation and the presence of fluid shear stress. To investigate this hypothesis, we tested base poly(etherurethane ureas) formulated with or without Santowhite antioxidant, a nucleophilic additive. We found that adherent leukocyte densities decreased with increasing shear stress. Moreover, leukocyte adhesion was decreased significantly further by Santowhite additive under shear stress but not under static conditions. Monocytes showed a higher propensity for adhesion than did neutrophils under shear and static conditions. Under static conditions, adherent cells on the Santowhite-containing polyurethane had a slightly more activated morphology than those on the base polyurethane. Cell adhesion under shear stress was significantly decreased when C3 or fibronectin was depleted from the suspension medium. Santowhite additive increased Factor B adsorption to the test surface while shear stress increased Factor H adsorption. The combination of Santowhite additive and shear stress increased the adsorption of both Factor B and Factor H and the serum protein S-terminal complement complex levels, but it did not further increase the state of activation of adherent cells. We conclude that leukocyte adhesion on poly(etherurethane urea) surfaces is sensitive to the levels of shear stress and that both C3 and fibronectin are required to maintain adhesion in the presence of shear stress. The low state of cellular activation and increased Factor H adsorption may explain the decreased adherent leukocyte density on the Santowhite-containing polyurethane.

In vivo biocompatibility study of ABA triblock copolymers consisting of poly(L-lactic-co-glycolic acid) A blocks attached to central poly(oxyethylene) B blocks.

Films of three ABA-block copolymers composed of lactic-co-glycolic acid A blocks and poly(oxyethylene) (PEO) B blocks and one random lactic-co-glycolic acid copolymer (PLG) were studied to investigate the influence of different polymer compositions and molecular weights on the tissue reaction, appearance of toxic degradation products, and swelling behavior in the cage implant system in rats. The inflammatory tissue reaction was followed over a 21-day implantation period by monitoring the leukocyte concentration, the extracellular acid, and alkaline phosphatase activities in a quantitative manner. Size and density of adherent macrophages and foreign body giant cells on the film surfaces were determined. The ABA and PLG implants caused only a minimal inflammatory reaction, as characterized by a low concentration of leukocytes during the implantation period when compared to empty cage controls. The content of PEO had an influence on the density of the adherent cells on the surface of the polymer film. An increase in PEO content and molecular weight decreased the cellular density during the implantation period. As demonstrated by scanning electron microscopy, no degradation was observed for all polymers during the implantation period. Our results demonstrate that the ABA block copolymers and PLG copolymer, are equally well tolerated in the cage implant test system.

Role for interleukin-4 in foreign-body giant cell formation on a poly(etherurethane urea) in vivo.

Interleukin-4 (IL-4) was previously shown to induce extensive macrophage fusion to form foreign-body giant cells (FBGCs) in vitro. In the present study, our goal was to extend these findings to an in vivo test environment on biomaterials. The subcutaneous cage-implant system was modified for mice to elucidate IL-4 participation in mediating FBGC formation in vivo. Exudate leukocyte concentrations from cages containing poly(etherurethane urea) (PEUU A') and empty cage controls indicated a similar inflammatory response that turned toward resolution by 14 days postimplantation, thus confirming the applicability of the cage-implant system in mice. FBGC kinetic analysis showed that the formation of mouse FBGCs occurs through the fusion of adherent macrophages at a constant rate up to 14 days of implantation. Purified goat anti-mouse IL-4 neutralizing antibody (IL4Ab) or normal goat nonspecific control IgG (gtIgG) at various concentrations, or recombinant murine IL-4 (muIL4) was injected into the implanted cages containing PEUU A' every 2 days for 7 days. The injection of IL4Ab significantly decreased the FBGC density on PEUU A' cage-implanted in mice, when compared with the nonspecific IgG or PBS injection controls. Conversely, the FBGC density was significantly increased by the injection of muIL4 when compared with nonspecific IgG and PBS injection controls. Adherent macrophage density, FBGC morphology, FBGC average size, and size distribution were not significantly different among IL4Ab, nonspecific control gtIgG, muIL4, and PBS control groups. Our data suggest that IL-4 participates in FBGC formation on biomaterials in vivo.

Electroanalytical and biocompatibility studies on carboxylated poly(vinyl chloride) membranes for microfabricated array sensors.

Potassium ion-selective and pH membrane electrodes based on neutral carrier ionophores for K+ (valinomycin) and H+ (TDDA and ETH 5294), respectively, immobilized in carboxylated PVC (PVC-COOH) with normal (classical) and reduced amounts of plasticizer, were investigated with respect to their general analytical performances (linear range, slope, detection limit, selectivity, internal membrane resistance), their biocompatibility and cellular responses. The analytical performance of potassium selective electrodes was not affected by reducing the plasticizer content from 66% (m/m) to about 33% (m/m) while that of pH electrodes was significantly changed at the lower plasticizer concentration level. The adhesive properties of PVC-COOH membranes to an inert substrate such as polyimide-coated Kapton are greatly improved by reducing the plasticizer content of the membrane. In addition, as was reported earlier by this group, improved biocompatibility was observed with these membranes relative to those with increased plasticizer content. A ratio of 1:1 m/m for PVC-COOH to plasticizer is recommended for the construction of planar ISEs without massive use of internal solution.

Theoretical analysis of in vivo macrophage adhesion and foreign body giant cell formation on strained poly(etherurethane urea) elastomers.

Quantitative description of foreign body giant cell (FBGC) formation on poly(etherurethane urea) (PEUU) surfaces as a function of time can conceivably predict the effects of polymer characteristics on cellular responses in vivo. In the present study, the formation of FBGCs on strained and unstrained PEUUs was quantified with two parameters: the density of adherent macrophages present initially that participate in FBGC formation (d(o)) and the rate constant for cell fusion (k); both kinetic parameters were used to calculate the time-dependent FBGC density (dfc). Relationships were sought between results of the cellular analysis and the extent of environmental stress cracking (ESC), as characterized by scanning electron microscopy. Surface degradation was semiquantified with percent light transmittance. The materials used were: base PEUU, base PEUU with 1% Santowhite antioxidant powder, base PEUU with 5% Methacrol 2138F antifume agent, and base PEUU with both 1% Santowhite and 5% Methacrol 2138F. A comparison of unstrained base PEUU with base PEUU strained to 400% elongation indicated that the rate of cell fusion, but not d(o) and dfc, increased in the presence of strain. In all strained samples, additives that strongly affected the ESC also influenced FBGC kinetic parameters. Strained PEUU containing Santowhite had the lowest d(o), the slowest rate of cell fusion, and lowest dfc, and the least incidence of ESC. The results suggest that the incidence of ESC in PEUU was decreased in the presence of Santowhite, which also lowered the number of adherent macrophages participating in FBGC formation, the rate of FBGC formation and the subsequent FBGC density. These studies also indicate that strain in PEUUs does not directly modulate the adherent macrophage and FBGC density. Further studies are necessary to delineate the relationship between PEUU strain and adherent macrophage and FBGC activation, which leads to the exocytosis of degrading agents and the observed incidence of biodegradation.

Ion-selective membranes with low plasticizer content: electroanalytical characterization and biocompatibility studies.

High molecular weight poly(vinyl chloride) and aliphatic polyurethane (Tecoflex)-based ion selective membranes, with normal and reduced amounts of plasticizer, as well as without plasticizer, were tested with respect to their analytical properties, their biocompatibility, and cellular responses. The analytical properties of the membranes did not change significantly within a wide range of polymer to plasticizer ratios. However, the membranes with reduced plasticizer content had better adhesive properties, less anion interference, extended life time, and better biocompatibility. Using the cage implant system, the results showed that an increase of plasticizer weight percent in Tecoflex membranes correlated positively with the increase in host inflammatory response up to 14 days of implantation. The results also demonstrated that both PVC and Tecoflex-based ion-selective membranes with the most common membrane composition (1:2 polymer to plasticizer ratio) exhibited a similar acute inflammatory response, but the PVC-based membrane elicited a reduced chronic inflammatory response when compared with the Tecoflex-based membrane.

In vivo induction of macrophage Ia antigen (MHC class II) expression by biomedical polymers in the cage implant system.

Examination of the cellular components in the inflammatory exudate, which infiltrates subcutaneous cages, can be used to monitor the progress of an inflammatory response to an implanted material. Of particular interest is the study of monocyte/macrophage infiltration into the implanted cages containing biomaterials, as macrophages may initiate a wide spectrum of responses upon interaction with a foreign material. In this study, the authors propose a technique using subcutaneous tissue cages in conjunction with cytofluorimetric analysis of exudate leukocytes to evaluate the monocyte/macrophage cell activation in response to different materials. The studies reported here used several materials (thermoplastic and elastomeric polymers) as the challenging agent, to demonstrate whether polymers, chemically different from each other, could differentially activate macrophages to carry out their proinflammatory role more effectively. The materials tested included: poly(etherurethane ureas) (PEUU A'), poly(etherurethane ureas) with a surface active additive, Methacrol, (PEUU C'), polymethylsiloxane (PDMS), polyetherimide, (PEI), and polyetheretherketone, (PEEK). For all tested materials, the maximum numbers of exudate cells and of Ia-positive macrophages were found on day 7, although the entity of the cell increase was associated with the material used for the implant. Similarly, the percentage of Ia-positive macrophages varied according to the specific polymer present in the cages after 7 days. By day 14, the percentage of Ia-positive macrophages decreased with individual exudates showing 19-32% Ia-positive cells depending on the different type of material. Only in the case of PDMS did the percentage of Ia-positive macrophages remain the same as compared with control empty cage macrophages.

Theoretical analysis of in vivo macrophage adhesion and foreign body giant cell formation on polydimethylsiloxane, low density polyethylene, and polyetherurethanes.

Quantitative description of foreign body giant cell (FBGC) formation on implanted polymer surfaces as a function of time can conceivably correlate cell adhesion with polymer properties and possibly predict the behavior of the polymer in vivo. In the present study, the formation of FBGCs on various biomedical polymers was quantified by two parameters: the density of adherent macrophages present initially that participate in FBGC formation (d0) and the rate constant for cell fusion (k); both kinetic parameters were used to calculate the time-dependent FBGC density (dfc). The materials used were: three Pellethane poly(etherurethanes) (PEUs) varying in weight percent of hard segment, one poly(etherurethane urea) (PEUU), and NHLBI-DTB primary reference materials: low density polyethylene (LDPE), silica-free polydimethylsiloxane (PDMS). The results indicated that up to 5 weeks of implantation, FBGCs were formed from the fusion of one population of adherent macrophages present by 3 days post-implantation. Furthermore, only a small fraction (< 8%) of this initial adherent macrophage population participated in FBGC formation. Based on the results of previous studies and the current study, it was concluded that increase in PEU hard segment weight percent, surface hardness and hydrophobicity increased total protein adsorption and effectively increased d0 and dfc. No further correlations between the material properties of all polymers and the cell kinetics can be made at this time. However, this study demonstrated that macrophage adhesion and FBGC formation can be quantified with the cell fusion model, and are modulated by various polymer properties.