In vivo degradation of processed dermal sheep collagen evaluated with transmission electron microscopy

Multinucleated Giant Cells: Current Insights in Phenotype, Biological Activities, and Mechanism of Formation

Monocytes and macrophages are innate immune cells with diverse functions ranging from phagocytosis of microorganisms to forming a bridge with the adaptive immune system. A lesser-known attribute of macrophages is their ability to fuse with each other to form multinucleated giant cells. Based on their morphology and functional characteristics, there are in general three types of multinucleated giant cells including osteoclasts, foreign body giant cells and Langhans giant cells. Osteoclasts are bone resorbing cells and under physiological conditions they participate in bone remodeling. However, under pathological conditions such as rheumatoid arthritis and osteoporosis, osteoclasts are responsible for bone destruction and bone loss. Foreign body giant cells and Langhans giant cells appear only under pathological conditions. While foreign body giant cells are found in immune reactions against foreign material, including implants, Langhans giant cells are associated with granulomas in infectious and non-infectious diseases. The functionality and fusion mechanism of osteoclasts are being elucidated, however, our knowledge on the functions of foreign body giant cells and Langhans giant cells is limited. In this review, we describe and compare the phenotypic aspects, biological and functional activities of the three types of multinucleated giant cells. Furthermore, we provide an overview of the multinucleation process and highlight key molecules in the different phases of macrophage fusion.

Tissue Regenerating Capacity of Carbodiimide-Crosslinked Dermal Sheep Collagen during Repair of the Abdominal Wall

In future, the function of collagen-based biomaterials as temporary scaffolds for the generation of new tissue may be emphasized. In this study the function of dermal sheep collagen (DSC) crosslinked with carbodiimide (ENDSC) as repair material for abdominal wall defects in rats was compared with that of commercial hexamethylenediisocyanate-crosslinked HDSC. The results indicate that early after implantation both ENDSC and HDSC functioned well as a matrix for cellular ingrowth. However during further implantation HDSC soon degraded resulting in herniations, while ENDSC showed a delay in the degradation time of at least 20 weeks. ENDSC thereby enabled collagen new-formation and functioned as a guidance for muscle overgrowth. These results are very promising concerning the problem of the ongoing foreign body reaction with continuing risk of implant rejection observed in clinical practice with non-degradable materials.

Acellular dermal matrix for esophageal stricture prevention after endoscopic submucosal dissection in a porcine model

BACKGROUND AND AIMS

Endoscopic submucosal dissection (ESD) is considered an effective treatment for early esophageal cancer and precancerous lesions. Esophageal stenosis is closely associated with quasi-circumferential ESD. We examined whether post-ESD esophageal stricture can be prevented by grafting an acellular dermal matrix (ADM) membrane.

METHODS

Fourteen Bama miniature pigs were randomly divided into an ADM group (n = 7) and a control group (n = 7). Semicircumferential ESD was performed at the distal esophagus in all animals, and in the ADM group an ADM patch graft was placed at the resection site and secured innovatively with metal clips. Animals in the control group underwent ESD only. Endoscopy was performed at 3 days, 1 week, 2 weeks, and 4 weeks post-ESD, and fluoroscopy was performed at 4 weeks for assessment of the degree of stenosis, after which the remodeled esophageal tissues were excised for histologic analysis.

RESULTS

No animals in the ADM group developed clinically significant esophageal stenosis, whereas 42.8% (3/7) in the control group did. The degree of stenosis was severe in the control group (39.8% vs 17.2%, respectively; P = .01). Animals in the ADM group had less feeding difficulty and lost less weight (-.9 kg vs -4.1 kg, respectively; P = .007). Histologically, complete mucosal epithelium, slight local inflammation, and organized collagenous fibers were observed in the ADM group.

CONCLUSIONS

ADM patch graft appears, after short-term observation, to be a potentially useful new treatment strategy for prevention of esophageal stricture after ESD. A metal clip fixation technique is effective for endoscopic graft attachment.

Enzyme-Pretreatment Removes In Vitro Cytoxic Effects of Dermal Sheep Collagen

We investigated the in vitro cytotoxicity of commercially available hexamethylenediisocyanate-crosslinked dermal sheep collagen (HDSC). HDSC was found to induce medium cytotoxic effects, as measured with methylcellulose cell culture. Apart from primary cytotoxicity, due to direct release of (extractable) cytotoxic products, HDSC was found to contain secondary cytotoxicity, possibly released by enzymatic interactions. In this study we found proof for this hypothesis, by exposing extracted HDSC to enzyme-containing medium. Furthermore we observed, that enzymatic pre-treatment can remove all secondary cytotoxic products, possibly due to detachment of pendants, which are still coupled to fragments of collagen molecules. The possibility of enzymatic pretreatment of HDSC, to obtain a non-cytotoxic/biocompatible material, may be important for in vivo applications.

Stem cell based tissue engineering for meniscus repair

Defects of the meniscus greatly alter knee function and predispose the joint to degenerative changes. The purpose of this study was to test a recently developed cell-scaffold combination for the repair of a critical-size defect of the rabbit medial meniscus. A bilateral, complete resection of the pars intermedia of the medial meniscus was performed in 18 New Zealand White rabbits. A hyaluronan/gelatin composite scaffold was implanted into the defect of one knee of 6 rabbits and the contralateral defect was left untreated. Scaffolds loaded with autologous marrow-derived mesenchymal stem cells and cultured in a chondrogenic medium for 14 days were implanted in a second series of 12 rabbits. Empty scaffolds were implanted in the contralateral knees. Meniscii were harvested at 12 weeks. Untreated defects had a muted fibrous healing response. Defects treated with cell-free implants showed also predominantly fibrous tissue whereas fibrocartilage was present in some scaffolds. The cross-sectional width of the repair tissue after treatment with cell-free scaffolds was significantly greater than controls (p < 0.05). Pre-cultured implants integrated with the host tissue and 8 of 11 contained meniscus-like fibrocartilage, compared with 2 of 11 controls (p < 0.03). The mean cross-sectional width of the pre-cultured implant repair tissue was greater than controls (p < 0.004). This study demonstrates the repair of a critical size meniscal defect with a stem cell and scaffold based tissue engineering approach.

Material dependent differences in inflammatory gene expression by giant cells during the foreign body reaction

Multinucleated giant cells (GCs) are often observed in the foreign body reaction against implanted materials. The in vivo function of GCs in this inflammatory process remains to be elucidated. GCs degrade collagen implants in rats and may also orchestrate the inflammatory process via the expression and secretion of modulators, such as cytokines and chemokines. In this study, we show that the gene expression of PMN chemoattractants, CXCL1/KC and CXCL2/MIP-2, is high in GCs micro-dissected from explanted Dacron, cross-linked collagen (HDSC), and bioactive ureido-pyrimidinone functionalized oligocaprolactone (bioactive PCLdiUPy). Conversely, the gene expression levels of TGFbeta and pro-angiogenic mediators VEGF and FGF were found to be low in these GCs as compared with the expression levels in total explants. GCs in bioactive PCLdiUPy displayed high cytokine and angiogenic mediator expression compared with GCs isolated from the two other studied materials, whereas chemokine gene expression in GCs isolated form HDSC was low. Thus, GCs adopt their expression profile in response to the material that is encountered.

The modulation of angiogenesis in the foreign body response by the poxviral protein M-T7

The foreign body response is characterized by enhanced recruitment of inflammatory cells. As the directional movement of cells is controlled by chemokines, disruption of the chemokine network would be an attractive approach to improve biocompatibility of an implanted material. The sequestration of chemokines by cell surface-expressed glycosaminoglycans (GAGs) is vital for in vivo chemokine activity. The myxoma virus encodes a soluble protein, M-T7, that interacts with conserved GAG-binding domains of chemokines to block chemokine-mediated leukocyte recruitment. We hypothesized that M-T7 might also affect the function of other inflammation-associated proteins in addition to chemokines that bind to GAG. In our studies, we focussed on the modulation of the GAG-binding molecules macrophage chemoattractant protein-1 (MCP-1) and vascular endothelial growth factor-164 (VEGF164) in the inflammatory reaction against subcutaneously implanted degradable cross-linked dermal sheep collagen discs in AO rats. Genetic delivery of M-T7 delays the influx of macrophages into the collagen discs. In addition, angiogenesis around the implanted material was reduced. The discs revealed reduced levels of rat MCP-1 and rat VEGF164. This was not due to down regulation of transcription of the genes that encode MCP-1 and VEGF164. Our in vivo observations suggest that, in addition to chemokines such as MCP-1, M-T7 neutralizes VEGF164.

In vivo biocompatibility of dextran-based hydrogels

Dextran-based hydrogels were obtained by polymerization of aqueous solutions of methacrylated dextran (dex-MA) or lactate-hydroxyethyl methacrylate-derivatized dextran (dex-lactate-HEMA). Both nondegradable dex-MA and degradable dex-lactate-HEMA disk-shaped hydrogels, varying in initial water content and degree of substitution (DS, the number of methacrylate groups per 100 glucose units), were implanted subcutaneously in rats. The tissue reaction was evaluated over a period of 6 weeks. The initial foreign-body reaction to the dex-MA hydrogels was characterized by infiltration of granulocytes and macrophages and the formation of fibrin, and exudate, as well as new blood vessels. This reaction depended on the initial water content as well as on the DS of the hydrogel and decreased within 10 days. The mildest tissue response was observed for the gel with the highest water content and intermediate DS. At day 21 all dex-MA hydrogels were surrounded by a fibrous capsule and no toxic effects on the surrounding tissue were found. No signs of degradation were observed. The initial foreign-body reaction to the degradable dex-lactate-HEMA hydrogels was less severe compared with the dex-MA gels. In general, the size of the dex-lactate-HEMA hydrogels increased progressively with time and finally the gels completely dissolved. Degradation of the dex-lactate-HEMA hydrogels was associated with infiltration of macrophages and the formation of giant cells, both of which phagocytosed pieces of the hydrogel. A good correlation between the in vitro and the in vivo degradation time was found. This suggests that extra-cellular degradation is not caused by enzymes but depends only on hydrolysis of the ester and/or carbonate bonds present in the crosslinks of the hydrogels. After 21 days, the degradable hydrogels, as such, could not be retrieved, but accumulation of macrophages and giant cells was observed, both of which contained particles of the gels intracellularly. As for the dex-MA hydrogels, no toxic effects on the surrounding tissue were found. The results presented in this study demonstrate that dextran-based hydrogels can be considered as biocompatible materials, making these hydrogels attractive systems for drug delivery purposes.

Collagen--biomaterial for drug delivery

The use of collagen as a biomaterial is currently undergoing a renaissance in the tissue engineering field. The biotechnological applications focus on the aspects of cellular growth or delivery of proteins capable of stimulating cellular response. However, basic knowledge about collagen biochemistry and the processing technology in combination with understanding of the physico-chemical properties is necessary for an adequate application of collagen for carrier systems. The purpose of this review article is to summarize information available on collagen dosage forms for drug delivery as well as to impart an overview of the chemical structures and the galenical properties including detailed description of the processing steps - extraction, purification, chemical crosslinking and sterilization. The most successful and stimulating applications are shields in ophthalmology, injectable dispersions for local tumor treatment, sponges carrying antibiotics and minipellets loaded with protein drugs. However, the scientific information about manipulating release properties or mechanistic studies is not as abundant as for some synthetic polymers.

Tissue reactions to bacteria-inoculated rat lead samples. II. Effect of local gentamicin release through surface-modified polyurethane tubing

A surface modification technique was developed to achieve controlled release of gentamicin from implanted polyurethane (PU) rat lead samples. PU tubing first was provided with an acrylic acid/acrylamide copolymer surface graft and then loaded with gentamicin. This surface modification technique resulted in release of gentamicin base (GB) and was applied either to the inner luminal surface only (PU-GB-1x) or to both the inner and outer surfaces (PU-GB-2x). First we investigated whether the early tissue response was harmfully compromised when surface-modified rat lead samples were implanted without any infectious challenge. Additionally, the efficacy of this type of local gentamicin therapy was investigated by establishing its effect on tissue response and its ability to prevent lead-related infections after inoculation with Staphylococcus aureus. It was demonstrated that the applied surface modification(s) did not induce adverse effects although an increase in the infiltration of granulocytes and macrophages and an increase in the formation of wound fluid and fibrin were observed. This effect was stronger with PU-GB-2x than with PU-GB-1x. With bacterial inoculation the applied surface modification successfully suppressed the infectious challenge, PU-GB-2x more effectively than PU-GB-1x. PU-GB-2x also was more effective when compared to the gentamicin-delivery methods discussed in the first part of this two-part study, i.e., release through a vicinal gentamicin-containing collagen sponge and preoperative gentamicin solution-dipping of rat lead samples.

In vivo testing of crosslinked polyethers. I. Tissue reactions and biodegradation

The in vivo biocompatibility and biodegradation of cross-linked (co)polyethers with and without tertiary hydrogen atoms in the main chain and differing in hydrophilicity were studied by means of subcutaneous implantation in rats. After 4 days, 1 month, and 3 months postimplantation, the tissue reactions and interactions were evaluated by light microscopy (LM) and transmission electron microscopy (TEM). Poly(tetrahydrofuran) (poly(THF)), poly(propylene oxide) (poly(POx)), and poly(tetrahydrofuran-co-oxetane) (poly-(THF-co-OX)) were tested as relatively hydrophobic polyethers, and poly(ethylene oxide) (PEO) and a poly(THF)/ PEO blend were used as more hydrophilic materials. In general, all polyethers showed good biocompatibility with respect to tissue reactions and interactions, with low neutrophil and macrophage infiltration, a quiet giant cell reaction, and formation of a thin fibrous capsule. For the relatively hydrophobic polyethers studied, the biostability increased in the order poly(POx) < poly(THF-co-OX) < poly(THF), probably indicating that the absence of tertiary hydrogen atoms has a positive effect on the biostability. Concerning the more hydrophilic materials, crosslinked PEO showed the highest rate of degradation, probably due to the mechanical weakness of the hydrogel in combination with the highest presence of giant cells as a result of the high porosity. A frayed surface morphology was observed after implantation of the crosslinked poly(THF)/PEO blend, which might be due to preferential degradation of PEO domains.

Quantitative assessment of the tissue response to films of hyaluronan derivatives

The aim of this study was to evaluate the in vivo response following implantation into a rat model of three innovative hyaluronan derivatives for clinical use: HYAFF 7, HYAFF 11 and HYAFF 11p75 (respectively, the 100% ethyl ester, 100% and 75% benzyl esters). The tissue reaction evoked by films of these new biomaterials implanted into the dorsolumbar musculature of rats was assessed quantitatively using a well established technique based upon an image analysis system. The number of inflammatory cells present and the patterns of cell distribution around the implant up to a distance of 642 microns were examined at different time periods after implantation. Since a well-delineated tissue-material interface was needed for this type of investigation, it was not possible to apply image analysis to sections once dissolution of the implanted materials had begun. Films of both the total esters, HYAFF 7 and HYAFF 11, were found to undergo a slow dissolution process and, after a month, films of these materials were still present at the site of implantation. Differences in response to the two materials were observed only during the first two weeks, particularly with respect to neutrophil distribution and total cellularity. HYAFF 7 was found to be more reactive, with higher numbers of neutrophils near the surface of the implant than HYAFF 11. Thereafter, the differences between the two materials were minimal and owing mainly to a faster dissolution of HYAFF 7 films. After 3 and 5 months, considerable degradation of films of both total esters had occurred. Significant quantities of material appeared inside numerous macrophages with an ED1-positive phenotype. Only a very thin layer of fibrous connective tissue, indicative of low reactivity, was found to surround the site of implantation, separating the dissolved material and the phagocytic cells from healthy muscular tissue. ED2-positive macrophages were primarily confined within the lining connective tissue. The partial benzyl ester, HYAFF 11p75, showed a different behaviour. In fact, evidence of film dissolution was already present a week after the implantation. After two weeks, the implanted films were completely dissolved and numerous ED1-positive macrophages phagocytosing the material were observed at the site of implantation. Therefore, in agreement with previous in vitro studies, which showed a greater susceptibility to degradation of hyaluronan derivatives with lower percentage of esterification, HYAFF 11p75 underwent resorption faster than the corresponding total ester.

Myoblast seeding in a collagen matrix evaluated in vitro

Collagens may be used as biomaterials for soft tissue reconstruction, e.g., the abdominal wall. We previously developed a biocompatible dermal sheep collagen (DSC), which in an abdominal wall reconstruction model showed controlled biodegradation and functioned as a matrix for in-growth of fibroblasts but not of muscle. It was hypothesized that regeneration of muscle via DSC may be possible by seeding of muscle cells. Using a syringe, mouse C2C12 myoblasts were seeded in DSC disks and incubated in methylcellulose-based growth medium, changed at 24 h into differentiation medium. An estimated 85% of the cells were well distributed, especially in the top half of the DSC disks. Some 15% of the cells ended up on top. At 4 h, all cells showed a spherical morphology, sometimes with clear adhesion plaques. At 24 h, cells on the top started to form a "capsule" with well-spread cells. Underneath the capsule, of the remaining 85% of the cells, approximately 30% showed adhesion and spreading on/in between collagen bundles. At day 3 after the addition of differentiation medium, the spread cells showed first indications of myotube formation. At day 7, myotube formation had proceeded, while extracellular matrix, i.e., collagen and elastin, had been deposited. This study shows that myoblast seeding into DSC is feasible, resulting in a reasonable cell distribution and survival of 45% of the cells. The surviving cells are able to differentiate into myotubes and form an extracellular matrix.

Extracellular matrix interactions during the in vivo degradation of collagen membranes in the rat skin: immunohistochemical distribution of collagen types IV, V, and VI

The role of collagen implant material (CIM) in periodontology is of considerable interest to the clinical dentist because of the capacity of connective tissue (CT) regeneration and partial prevention of epithelial cell migration onto the root surface. The aim of this study was to demonstrate alterations of the CT matrix after the use of CIM in subcutaneous pockets in the rat skin. We used 15 rats in this study. After sedation, two subcutaneous pockets (2 cm in length) were surgically made in the animals' backs. Collagen membranes were implanted in one of the two pockets (test site). The other pocket served as control. Then, 4, 7, 14, 21, and 28 days after implantation, the animals were sacrificed and biopsies preserved for histologic and immunohistochemical examination. Incubation with antibodies against CT matrix components (collagen type IV, V, and VI) were used for immunostaining. Histologically, the CIM was migrated by inflammatory cells in the first 7 days. Newly formed fibroblasts and blood vessels (BV) were present 14 days postimplantation. Collagen type IV was localized in the basement membranes of the epithelium, BV, and nerves. An increase in the BV amount was demonstrated around (and later in) the implant material. Collagen type V was found in a filament pattern of distribution and was inserted into the implant after 4 weeks of healing. Collagen type VI showed a microfibrillar pattern of distribution with a delayed formation in the graft mass. The data showed the alterations of the matrix after implantation of collagen type I membranes in the rat skin.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of surface morphology and wettability on the inflammatory response against poly(L-lactic acid): a semi-quantitative study with monoclonal antibodies

In this study, the influence of surface morphology and wettability of both degradable and nondegradable polymer films on the inflammatory response after subcutaneous implantation in the rat was investigated. Degradable non-porous, porous, and "combi" (porous with a nonporous layer on one side) poly(L-lactic acid) (PLLA) films and nondegradable polytetrafluoroethylene (PTFE) and (porous) expanded PTFE (e-PTFE) were used. Contact angles measurements indicate that PLLA is more hydrophillic than PTFE. Assessment of the inflammatory response was performed after various periods of implantation (up till 180 days), with both conventional light microscopy and immunohistochemistry using monoclonal antibodies (mAbs). The inflammatory response observed initially can largely be considered as part of the wound healing reaction, and up till day 40 the inflammatory response against PLLA was minimally more intense than against PTFE (porous as well as nonporous). From day 40 on, the PLLA films provoke a more intense inflammatory response as compared to the PTFE films. Both porous PLLA and the porous side of the "combi" PLLA film provoke a more intense inflammatory response than nonporous PLLA and the nonporous side of the "combi" PLLA film, respectively. In general, PTFE and e-PTFE films provoke an inflammatory response which is minimally more intense than the one provoked by the sham operation. Almost no ingrowth of tissue was observed in the porous e-PTFE films. In contrast, there was abundant tissue ingrowth in and an inflammatory response against porous PLLA. It can be concluded that biodegradable PLLA films provoke a more intense inflammatory response than nondegradable PTFE films. Also, porosity enhances the inflammatory response. However, porosity enhances the inflammatory response only when the wettability of a biomaterial permits cellular ingrowth.

Biocompatibility and tissue regenerating capacity of crosslinked dermal sheep collagen

The biocompatibility and tissue regenerating capacity of four crosslinked dermal sheep collagens (DSC) was studied. In vitro, the four DSC versions were found to be noncytotoxic or very low in cytotoxicity. After subcutaneous implantation in rats, hexamethylenediisocyanate-crosslinked DSC (HDSC) seldom induced an increased infiltration of neutrophils or macrophages, as compared with normal wound healing; whereas new formation of collagen was observed. DSC crosslinked with glutaraldehyde (GDSC) followed by reaction with NaBH4 shortly after implantation showed an increased infiltration of neutrophils with a deviant morphology. Furthermore, a high incidence of calcification was observed, which may explain the minor ingrowth of giant cells and fibroblasts, and the poor formation of new rat collagen. Acyl azide-crosslinked DSC (AaDSC) first induced an increased infiltration of macrophages, and then of giant cells, both with high lipid formation. AaDSC degraded at least twice as slowly as HDSC and GDSC, finally leaving a matrix of newly formed rat collagen. Samples crosslinked with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide (ENDSC) induced the same mild cellular reaction as HDSC; whereas, similar to AaDSC, the degradation rate was slow and an optimal rat collagen matrix was formed. Of the crosslinked DSC samples, ENDSC seems most promising for tissue regeneration.

The effect of phagocytosis of poly(L-lactic acid) fragments on cellular morphology and viability

The aim of this study was to investigate the effect of phagocytosed poly(L-lactic acid) particles on the morphology and viability of phagocytes, mainly macrophages. Therefore, predegraded poly(L-lactic acid) (P-PLLA) and nontreated PLLA (N-PLLA) particles, both having diameters not exceeding 38 microns, were injected intraperitoneally in mice. P-PLLA particles were obtained by 25 kGy gamma-irradiation of N-PLLA particles. N-PLLA and P-PLLA particles were injected using an 0.3% ethanol/0.9% saline solution intraperitoneally to the mice. We also studied the release of the absorbed ethanol as a possible model for the release of low molecular weight, potentially toxic products. As control, nondegradable polytetrafluoroethylene (PTFE) particles and the carrier solution were used. After 1, 2, 3, 4, 5, and 7 days, the cells of the abdominal cavity were harvested to study the effect of phagocytosis of polymer particles on phagocytic cell morphology and viability. Studies with transmission electron microscopy indicated that, upon injection of particles in the peritoneal cavity, macrophages demonstrated signs of cell damage, cell death, and cell lysis due to phagocytosis of a large amount of P-PLLA particles. The morphology of the cells that had phagocytosed the N-PLLA and PTFE particles did not differ substantially from those of control animals in which only the solution was injected. Also, in the controls, hardly any cell death and no debris was observed. When the PLLA particles were injected as a suspension in a 0.3% ethanol/0.9% saline solution, no difference was observed between N-PLLA and P-PLLA. After phagocytosis, both cause cell damage, sometimes leading to cell death.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative in vivo assessment of the tissue response to dermal sheep collagen in abdominal wall defects

We quantified the tissue response, tissue organization and patency of biodegradable patches for the repair of abdominal wall defects. We used dermal sheep collagen, cross-linked with hexamethylenediisocyanate in a model. The collagen patches were implanted either untreated or plasma polymerized with tetrafluoroethylene (TFE), to improve the properties of the patch for bowel adhesion and rate of degradation. The implants with surrounding tissue were retrieved after 3 d, 1, 2, 4, 6 and 8 wk, then sectioned and stained specifically for macrophages, neutrophils, T-lymphocytes and endothelium. Only macrophages and neutrophils were observed in the implant and surrounding tissue, with different antigen expression in the macrophages. This was found to be dependent on whether the macrophages were found within the implant or in the surrounding tissue. The neutrophils and macrophages were assessed using image analysis techniques to quantify the tissue responses to treated and untreated collagen, enabling comparison of the respective tissue responses. No significant differences were found between the two forms of this collagen. Infection played a key role in the severity of the tissue response around both types of implants, resulting in large variations in cell counts at each time period. Treating the collagen with TFE did not significantly improve its performance in this application.

Relations between in vitro cytotoxicity and crosslinked dermal sheep collagens

Collagen-based biomaterials have found various applications in the biomedical field. However, collagen-based biomaterials may induce cytotoxic effects. This study evaluated possible cytotoxic effects of (crosslinked) dermal sheep collagen (DSC) using a 7-d-methylcellulose cell culture with human skin fibroblasts. Non-crosslinked DSC (NDSC), hexamethylene-diisocyanate-crosslinked DSC (HDSC), and glutaraldehyde-crosslinked DSC (GDSC), their extracts (1 x 10 d to 4 x 10 d extracts), or the corresponding extracted DSC samples were tested. Cell growth was evaluated by cell counting, while cell morphology was assessed by light microscopy and transmission-electron microscopy. Both GDSC and, to a lesser extent, HDSC, induced cytotoxicity, observed as inhibited cell growth and deviant cell morphology. The deviant morphology consisted of extensive accumulations of lipid, reduction in the amount and dilatation of rough endoplasmatic reticulum, increased inclusions of cell remnants, and relatively rounded cell membranes. With HDSC, both primary cytotoxicity, due to extractable products from the material, and secondary cytotoxicity, possibly due to a release of cytotoxic products resulting from enzymatic cell-biomaterial interactions, could be discriminated. With GDSC, however, no clear distinction between primary and secondary cytotoxicity could be made. With NDSC, only primary cytotoxicity, measured as low inhibition of cell proliferation, but without deviant morphology, was observed. These remarkable differences in cytotoxicity are discussed in relation to residual agents and specific crosslinks present in DSCs as a consequence of processing and the crosslinking agents used. The residual agents and the specific crosslinks give rise to differences in direct release of products and in sensitivity to hydrolysis and enzymatic breakdown.

Secondary cytotoxicity of cross-linked dermal sheep collagens during repeated exposure to human fibroblasts

We investigated commercially available dermal sheep collagen either cross-linked with hexamethylenediisocyanate, or cross-linked with glutaraldehyde. In previous in vitro studies we could discriminate primary, i.e. extractable, and secondary cytotoxicity, due to cell-biomaterial interactions, i.e. enzymatic actions. To develop dermal sheep collagen for clinical applications, we focused in this study on the release, e.g. elimination, of secondary cytotoxicity over time. We used the universal 7 d methylcellulose cell culture with human skin fibroblasts as a test system. Hexamethylenediisocyanate-cross-linked dermal sheep collagen and glutaraldehyde-cross-linked dermal sheep collagen were tested, with intervals of 6 d, over a culture period of 42 d. With hexamethylenediisocyanate-cross-linked dermal sheep collagen, cytotoxicity, i.e. cell growth inhibition and deviant cell morphology, was eliminated after 18 d of exposure. When testing glutaraldehyde-cross-linked dermal sheep collagen, the bulk of cytotoxic products was released after 6 d, but a continuous low secondary cytotoxicity was measured up to 42 d. As a control, non-cross-linked dermal-sheep collagen was tested over a period of 36 d, but no secondary cytotoxic effects were observed. The differences in release of secondary cytotoxicity between hexamethylenediisocyanate-cross-linked dermal sheep collagen, glutaraldehyde-cross-linked dermal sheep collagen and non-cross-linked dermal sheep collagen are explained from differences in cross-linking agents and cross-links obtained. We hypothesize that secondary cytotoxicity results from enzymatic release of pendant molecules from hexamethylene-diisocyanate-cross-linked dermal sheep collagen, e.g. formed after reaction of hydrolysis products of hexamethylenediisocyanate with dermal sheep collagen.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytotoxicity testing of wound dressings using methylcellulose cell culture

Wound dressings may induce cytotoxic effects. In this study, we check several, mostly commercially available, wound dressings for cytotoxicity. We used our previously described, newly developed and highly sensitive 7 d methylcellulose cell culture with fibroblasts as the test system. Cytotoxicity is assessed by monitoring cell growth inhibition, supported by cell morphological evaluation using light and transmission electron microscopy. We tested conventional wound dressings, polyurethane-based films, composites, hydrocolloids and a collagen-based dressing. It was shown that only 5 out of 16 wound dressings did not induce cytotoxic effects. All 5 hydrocolloids were found to inhibit cell growth (greater than 70%), while cells had strongly deviant morphologies. The remaining wound dressings showed medium cytotoxic effects, with cell growth inhibition, which varied from low (+/- 15%), medium-low (+/- 25%) to medium-high (+/- 50%). Measurable cytotoxic effects of dressings detected in vitro are likely to interfere with wound healing when applied in vivo. The results are discussed in view of the clinical uses with contaminated wounds, impaired epithelialization or hypergranulation.