Characterization and biocompatibility of epoxy-crosslinked dermal sheep collagens

Dermal sheep collagen (DSC), which was crosslinked with 1, 4-butanediol diglycidyl ether (BD) by using four different conditions, was characterized and its biocompatibility was evaluated after subcutaneous implantation in rats. Crosslinking at pH 9.0 (BD90) or with successive epoxy and carbodiimide steps (BD45EN) resulted in a large increase in the shrinkage temperature (T(s)) in combination with a clear reduction in amines. Crosslinking at pH 4.5 (BD45) increased the T(s) of the material but hardly reduced the number of amines. Acylation (BD45HAc) showed the largest reduction in amines in combination with the lowest T(s). An evaluation of the implants showed that BD45, BD90, and BD45EN were biocompatible. A high influx of polymorphonuclear cells and macrophages was observed for BD45HAc, but this subsided at day 5. At week 6 the BD45 had completely degraded and BD45HAc was remarkably reduced in size, while BD45EN showed a clear size reduction of the outer DSC bundles; BD90 showed none of these features. This agreed with the observed degree of macrophage accumulation and giant cell formation. None of the materials calcified. For the purpose of soft tissue replacement, BD90 was defined as the material of choice because it combined biocompatibility, low cellular ingrowth, low biodegradation, and the absence of calcification with fibroblast ingrowth and new collagen formation.

Biocompatibility of a novel tissue connector for fixation of tracheostoma valves and shunt valves

Rehabilitation after laryngectomy often includes the use of a shunt valve and a tracheostoma valve to restore voice. To improve the fixation method of these valves, a new tissue connector has been developed, basically consisting of a ring that will be integrated into surrounding tracheal soft tissue. The valves can be placed in the ring. To test the principle of the tissue connector, a prototype consisting of a subcutaneous polypropylene mesh and a percutaneous titanium stylus was implanted into the backskin of 10 rats by a two-stage surgical procedure. We reasoned that if a firm connection can be realized with the skin, a firm connection with the trachea will also be possible. The subcutaneous part was implanted first, followed by the percutaneous part after 6 weeks. The complete tissue connector with surrounding tissue was removed 8 weeks later and examined histologically. The principle of the new tissue connector proved to be effective: hardly any epithelial downgrowth appeared, and adhesion of soft tissue was demonstrated. No infection or severe inflammation reaction was detected. The tissue connector seems appropriate for its intended use.

TGF-beta and bFGF affect the differentiation of proliferating porcine fibroblasts into myofibroblasts in vitro

Fibroblasts and myofibroblasts are involved in the foreign body reaction to biomaterials, especially in capsule formation. However, contraction or detachment of the capsule can lead to complications. Biocompatibility of biomaterials may be improved by the application of proteins regulating the differentiation or activation of (myo)fibroblasts. Myofibroblasts, differentiating from fibroblasts can be identified by the expression of alpha-smooth muscle actin (alpha-SM actin). We investigated the influence of proliferation and quiescence on the differentiation of porcine dermal cells and whether transforming growth factor-beta (TGF-beta) and basic fibroblast growth factor (bFGF) are involved in the differentiation of proliferating cells. Porcine cells were used because pigs increasingly function as in vivo models while little is known of the characteristics of their cells. Serum-free cultured, quiescent fibroblasts differentiated into myofibroblasts, while proliferating fibroblasts cultured in the presence of serum containing TGF-beta, formed alpha-SM actin-negative cell clusters. After reaching confluency, these clusters started to expressing alpha-SM actin. Moreover, these proliferating cells produced TGF-beta from day 4 onwards while bFGF did not. Differentiation into myofibroblasts was inhibited by bFGF and to an even greater extent by antibodies to TGF-beta. Further, two theories concerning the role of the myofibroblast in tissue contraction in view of two biomaterial application will be discussed.

Crosslinking and modification of dermal sheep collagen using 1, 4-butanediol diglycidyl ether

Crosslinking of dermal sheep collagen (DSC) was accomplished using 1, 4-butanediol diglycidyl ether (BDDGE). At pH values > 8.0, epoxide groups of BDDGE will react with amine groups of collagen. The effects of BDDGE concentration, pH, time, and temperature were studied. Utilization of a 4-wt % BDDGE instead of 1-wt % resulted in a faster reaction. Whereas similar values of shrinkage temperature were obtained, fewer primary amine groups had reacted at a lower BDDGE concentration, which implies that the crosslinking reaction had a higher efficacy. An increase in pH from 8.5 to 10.5 resulted in a faster reaction but reduced crosslink efficacy. Furthermore, an increase in reaction temperature accelerated the reaction without changing the crosslink efficacy. Crosslinking under acidic conditions (pH < 6.0) evoked a reaction between epoxide groups and carboxylic acid groups of collagen. Additional studies showed that no oligomeric crosslinks could be formed. However, hydrolysis of the epoxide groups played a role in the crosslink mechanism especially under acidic reaction conditions. The macroscopic properties of these materials were dependent on the crosslinking method. Whereas a flexible and soft tissue was found if crosslinking was performed at pH < 6.0, a stiff sponge was obtained under alkaline conditions. Reaction of DSC with a monofunctional compound (glycidyl isopropyl ether) led to comparable trends in reaction rate and in similar macroscopical differences in materials as observed with BDDGE.

Organization of the rabbit vitreous body: lamellae, Cloquet's channel and a novel structure, the 'alae canalis Cloqueti'

Even though the rabbit is a frequently used animal model for studies on vitreous function and pathobiology, data on the structural organization of the rabbit vitreous are scarce. The aim of the present study is to give a detailed description of rabbit vitreous structure in order to provide a basis for studies on changes in vitreous organization induced by pathophysiological processes. We studied the vitreous body of adult rabbit eyes by complementary anatomical evaluation methods, by light microscopy and by transmission electron microscopy. Regional and local variations in vitreous matrix organization were observed. Regionally, a cortex, an intermediate area, and a centre were distinguished. In addition, specific structures were locally observed. Lamellae run through the intermediate area in a funnel-like pattern, converging upon the asymmetrically positioned optic disc. A central channel (Cloquet's channel) was found in all eyes. We demonstrated a novel structure, attached to Cloquet's channel and to the medullary rays. Because of its wing-shaped sheet-like morphology, we named it the 'alae canalis Cloqueti'.

Successive epoxy and carbodiimide cross-linking of dermal sheep collagen

Cross-linking of dermal sheep collagen (N-DSC, T(S) = 46 degrees C, number of amine groups = 31 (n/1000)) with 1,4-butanediol diglycidyl ether (BDDGE) at pH 9.0 resulted in a material (BD90) with a high T(S)(69 degrees C), a decreased number of amine groups of 15 (n/1000) and a high resistance towards collagenase and pronase degradation. Reaction of DSC with BDDGE at pH 4.5 yielded a material (BD45) with a T(S) of 64 degrees C, hardly any reduction in amine groups and a lower stability towards enzymatic degradation as compared to BD90. The tensile strength of BD45 (9.2 MPa) was substantially improved as compared to N-DSC (2.4 MPa), whereas the elongation at break was reduced from 210 to 140%. BD90 had a tensile strength of 2.6 MPa and an elongation at break of only 93%. To improve the resistance to enzymes and to retain the favorable tensile properties, BD45 was post-treated with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) in the presence of N-hydroxysuccinimide (NHS) to give BD45EN. Additional cross-linking via the formation of amide bonds took place as indicated by the T(S) of 81 degrees C and the residual number of amine groups of 19 (n/1000). BD45EN was stable during exposure to both collagenase and pronase solutions. The tensile properties (tensile strength 7.2 MPa, elongation at break 100%) were comparable to those of BD45 and glutaraldehyde treated controls (G-DSC). Acylation of the residual amine groups of BD45 with acetic acid N-hydroxysuccinimide ester (HAc-NHS) yielded BD45HAc with a large reduction in amine groups to 10 (n/1000) and a small reduction in T(S) to 62 degrees C. The stability towards enzymatic degradation was reduced, but the tensile properties were comparable to BD45.

Absence of muscle regeneration after implantation of a collagen matrix seeded with myoblasts

Collagens are widely used as biomaterials for e.g. soft tissue reconstruction. The present study was aimed at reconstruction of abdominal wall muscle using processed dermal sheep collagen (DSC) and myoblast seeding. Myoblasts were harvested from foetal quadriceps muscle of an inbred rat strain, cultured, seeded as non-differentiated cells into DSC-discs and incubated in vitro for 2 h. The discs were implanted in the abdominal wall defects in adult rats. Non-seeded discs functioned as control. Implantation periods till week 6 were chosen. At day 1 and 2 after implantation infiltration of granulocytes and macrophages was clearly more intense in the seeded discs than in the controls. Relatively large numbers of mast cells infiltrated from the side of the adhering omentum. In central areas of the discs, seeded cells were easily recognized till day 5, since non-seeded control discs did not contain such cells. Ingrowth of host cells and tissue at the margins proceeded faster with the seeded discs. Lymphocyte accumulations were observed in the 3 week seeded specimen. At week 3 and week 6, in the seeded discs muscle tissue was not present, in contrast to very large giant-like cells. It is concluded that the chosen method of myoblast seeding did not result in the regeneration of muscle during this observation period. Unfavorable circumstances such as humoral factors, direct cellular interactions (phagocytosis), indirect cellular interactions (cytokines), or initial absence of vascularization, may play a role. Further studies are required.

Inhibition of the tissue reaction to a biodegradable biomaterial by monoclonal antibodies to IFN-gamma

Biomaterials are increasingly used for clinical applications. However, loss of function may occur owing to tissue reactions, which are mainly caused by a variety of inflammatory reactions. Recently, we demonstrated that macrophages (MO) and T cells play key roles in these reactions. Since immunological studies showed that the T cell-derived cytokine interferon-gamma (IFN-gamma) activates MO, the aim of this study was to investigate the possibility of modulating tissue reactions to biodegradable biomaterials by inactivating IFN-gamma. Dermal sheep collagen (DSC) was used as a test biomaterial. DSC impregnated with anti-IFN-gamma or phosphate-buffered saline (control) was implanted in rats. The results showed that cellular ingrowth and formation and function of giant cells were strongly delayed by anti-IFN-gamma. Also, MHC class II expression was strongly inhibited. In the treated DSC, some huge giant cells were formed at the interface but association with the DSC bundles did not occur. Finally, in both the control and treated DSC, T cells and NK cells were rarely detected. This study demonstrates that IFN-gamma plays an important role in the inflammatory reaction to biomaterials. This reaction can be modulated by anti-IFN-gamma, which warrants further studies of anti-IFN-gamma for clinical application to prevent unwanted tissue reactions to biomaterials.

Tissue reactions to bacteria-challenged implantable leads with enhanced infection resistance

Tissue reactions to implantable pacemaker leads were investigated in an early infection model in rabbits. Both standard leads and surface-modified leads were used. The surface modification technique was applied to achieve controlled release of the antibiotic gentamicin. The insulating polyurethane tubing material of the leads was provided with an acrylic acid/acrylamide copolymer surface graft and then loaded with gentamicin. Implantation periods varied from day 4, to week 3 1/2, to week 10. We investigated tissue reactions in the absence of an infectious challenge and also the efficacy of surface-modified leads in preventing infection after challenge with Staphylococcus aureus was evaluated. It was demonstrated that the applied surface modification did not induce adverse effects although during early postimplantation an increase in infiltration of granulocytes and macrophages and wound fluid and fibrin deposition were observed. After bacterial challenge, standard leads were heavily infected at each explantation period, denoted by abscesses, cellular debris, and bacterial colonies. In contrast, little or no infection was observed, either macroscopically or by bacterial cultures, with the surface-modified leads. Microscopy showed little evidence of the bacterial challenge, and that primarily at day 4. It was concluded that the applied surface modification demonstrated enhanced infection resistance and thus represents a sound approach to the battle against infectious complications with biomaterials.

Modulation of the tissue reaction to biomaterials. II. The function of T cells in the inflammatory reaction to crosslinked collagen implanted in T-cell-deficient rats

Unwanted tissue reactions are often observed resulting in events such as early resorption of the biomaterial, loosening of the implant, or a chronic (immunologic) response. From immunologic studies it is known that inflammatory reactions can be modulated by use of (anti)-growth factors or anti-inflammatory drugs. Before this can be employed with respect to biomaterials, the role of individual factors (humoral and cellular) has to be studied. In this part of the investigation, the role of T cells was studied by use of T-cell-deficient (nude) rats and control (AO) rats. Hexamethylenediisocyanate-crosslinked dermal sheep collagen (HDSC) was selected as the test material. The results showed that T cells or T cell-related factors played a prominent role in the attraction of macrophages and the formation of giant cells, their antigen presentation, and their phagocytotic capacity. As a consequence, degradation of HDSC was strongly delayed. This study also showed that infiltration of fibroblasts and creation of stromal areas in HDSC was restricted to areas subjected to degradation. However, in time, absence of T cells resulted in increased formation and maturation of autologous rat collagen. Results obtained suggest that the inflammatory reaction to biomaterials might be modulated by controlling T-cell activation.

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.

Tissue reactions to bacteria-inoculated rat lead samples. I. Effect of local gentamicin release through vicinal sponge or solution-dipping

The effect of local gentamicin release through a vicinal collagen sponge or through preoperative solution-dipping of rat lead samples was investigated in an early-infection model. The efficacy of these methods and their effect on tissue response were determined. It was demonstrated that both methods of local gentamicin release suppress lead-related infectious complications as compared to the control lead, which showed a high presence of inflamed/infected tissues and bacterial growth at each explantation time point. The first day the vicinal collagen sponge was more effective in suppressing the infection than was the solution-dipped lead, probably because there is a faster and higher dose release of gentamicin from the sponge. However, continued implantation time revealed that gentamicin release from the solution-dipped lead was more effective than the sponge. This supports our hypothesis that the presence of lumina are decisive for bacterial growth and persistence of implant-related infections.

Effects of keratin 14 ablation on the clinical and cellular phenotype in a kindred with recessive epidermolysis bullosa simplex

We studied a kindred with recessive epidermolysis bullosa simplex in which the affected members lacked expression of the basal cell keratin 14. The patients had severe generalized skin blistering that improved slightly with age. The basal cells of the patients did not express keratin 14 and contained no keratin intermediate filaments. The expression of keratin 5, the obligate copolymer of keratin 14, was slightly reduced. The expression of keratin 15, the alternative basal cell keratin, was increased, suggesting upregulation or stabilization to compensate for the lack of keratin 14. The expression of keratin 16, keratin 17, and keratin 19 in the patient's skin was not different from controls. Immunoelectron microscopy showed a loose network of keratin 5/keratin 15 protofilaments in the basal cells. Keratin 15 filaments did not aggregate into higher order bundles. Sequence analysis of genomic DNA revealed a homozygous mutation in the 3'-acceptor splice site of intron 1 (1840 A-->C) in the affected individuals. This mutation led to the skipping of exon 2 in 24% of the KRT14 transcripts and to the use of a cryptic splice site in 76% of the transcripts. Premature termination codons were generated in all transcripts (codons 175+1 or 175+29), leading to a truncated keratin 14 protein within the helical 1B rod domain. The disorder was associated with circumscribed hyperkeratotic lesions with the histology of epidermolytic hyperkeratosis. The prognosis of keratin 14 ablation is much better in the human than in the mouse.

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.

Cross-linking of dermal sheep collagen using a water-soluble carbodiimide

A cross-linking method for collagen-based biomaterials was developed using the water-soluble carbodiimide 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide hydrochloride (EDC). Cross-linking using EDC involves the activation of carboxylic acid groups to give O-acylisourea groups, which form cross-links after reaction with free amine groups. Treatment of dermal sheep collagen (DSC) with EDC (E-DSC) resulted in materials with an increased shrinkage temperature (Ts) and a decreased free amine group content, showing that cross-linking occurred. Addition of N-hydroxysuccinimide to the EDC-containing cross-linking solution (E/N-DSC) increased the rate of cross-linking. Cross-linking increased the Ts of non-cross-linked DSC samples from 56 to 73 degrees C for E-DSC and to 86 degrees C for E/N-DSC samples, respectively. For both cross-linking methods a linear relation between the decrease in free amine group content and the increase in Ts was observed. The tensile strength and the high strain modulus of E/N-DSC samples decreased upon cross-linking from 18 to 15 MPa and from 26 to 16 MPa, respectively. The elongation at break of E/N-DSC increased upon cross-linking from 142 to 180%.

In vitro degradation of dermal sheep collagen cross-linked using a water-soluble carbodiimide

Bacterial collagenase was used to study the susceptibility of dermal sheep collagen (DSC) cross-linked with a mixture of the water-soluble carbodiimide 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide hydrochloride and N-hydroxysuccinimide (E/N-DSC) towards enzymatic degradation. Contrary to non-cross-linked DSC (N-DSC), which had a rate of weight-loss of 18.1% per hour upon degradation, no weight loss was observed for E/N-DSC during a 24 h degradation period. The tensile strength of the E/N-DSC samples decreased during this time period, resulting in partially degraded samples having 80% of the initial tensile strength remaining. The susceptibility of E/N-DSC samples towards enzymatic degradation could be controlled by varying the degree of cross-linking of the samples. Ethylene oxide sterilization of E/N-DSC samples made the material more resistant against degradation compared with non-sterilized E/N-DSC samples. This may be explained by a decrease of the adsorption of bacterial collagenase onto the collagen owing to reaction of ethylene oxide with remaining free amine groups in the collagen matrix.

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.

Regeneration of full-thickness wounds using collagen split grafts

Collagen-based skin substitutes are among the most promising materials to improve regeneration of full-thickness wounds. However, additional meshed grafts or cultured epidermal grafts are still required to create epidermal regeneration. To avoid this, we substituted collagen-based split grafts, i.e., grafts with a separated top and bottom layer, in a rat full-thickness wound model and compared regeneration with nontreated, open control wounds. We hypothesized that epidermal regeneration would occur in the split in between the two layers, with the top layer functioning as a clot/scab and the bottom layer as a dermal substitute. Two types of dermal sheep collagen (DSC) split grafts were tested: one with a top layer of noncrosslinked DSC (NDSC) and bottom layer of hexamethylenediisocyanate crosslinked DSC (HDSC), further called N/HDSC; and the second with both a top and bottom layer of HDSC (H/HDSC). With the N/HDSC split graft NDSC did not function as a sponge for formed exudate and as a consequence the split was not longer available to facilitate epidermal regeneration. In contrast, with the H/HDSC graft the split facilitated proliferation and differentiation of the epidermal cells in the proper way. With this graft, clot formation was restricted to the top layer, which was rejected after 8 weeks, while the bottom layer functioned during gradual degradation as a temporary matrix for the formation of autologous dermal tissue. H/HDSC strongly inhibited infiltration of myofibroblasts, resulting in a 30% wound contraction, while a 100% contraction was found with the open control wound. The results show that H/HDSC split-grafts function conforms to the hypothesis in regeneration of large, full-thickness wounds without further addition of seeded cells or use of meshed autografts.

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.

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.

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.

Electronmicroscopic examination of white cell reduction by four white cell-reduction filters

The mechanisms of white cell (WBC) reduction in 16-hour-old CPDA-1 red cell (RBC) concentrates by filtration on a column filter and on three different flatbed filters were studied by electron microscopy, with special emphasis on cell-to-cell interaction, cell damage, and interaction of blood cells with the material. Generally, lymphocytes were removed by mechanical sieving and monocytes by adherence and mechanical sieving. Granulocyte depletion occurred by mechanical sieving, direct adhesion to the fibers, and indirect adhesion to activated and spread platelets. In the column filter, most granulocytes were captured by adhesion. In the coarse layers of two of the flatbed filters, indirect adhesion was most prominent, whereas direct adhesion was most prominent in the other flatbed filter. For the most part, granulocytes were captured by direct adhesion in the fine layers, but in one flatbed filter, capture apparently occurred by mechanical sieving. The results of this study suggest that the efficiency and the mechanism of WBC reduction depend on the physicochemical characteristics of the non-woven materials in the filters as well as the cellular composition of the RBC concentrates.

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.

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

The in vivo degradation of hexamethylenediisocyanate-tanned dermal sheep collagen was studied with transmission electron microscopy. Discs of hexamethylenediisocyanate-tanned dermal sheep collagen were subcutaneously implanted in rats. Both an intra- and an extracellular route of degradation could be distinguished. In addition to normal components of a typical foreign body reaction, remarkable phenomena, such as locally deviant neutrophil morphology, infiltration of basophil-like cells, indications of foreign body multinucleate giant cells formed from different cell types, aluminium silicate accumulations and calcium phosphate depositions, were observed. Foreign body multinucleate giant cells intracellularly degraded hexamethylenediisocyanate-tanned dermal sheep collagen after internalization. Both internalized and cellularly enveloped hexamethylenediisocyanate-tanned dermal sheep collagen degraded by the detachment of fibrils. Another extracellular route of degradation was characterized by calcium phosphate depositions in large bundles of hexamethylenediisocyanate-tanned dermal sheep collagen. From 6 wk, the hexamethylenediisocyanate-tanned dermal sheep collagen implant was replaced by rat connective tissue, which was subsequently also degraded. After 15 wk, the presence of basophil-like foreign body multinucleated giant cells containing aluminium/silicon-crystalline accumulations still persisted. These phenomena were related to the specific nature of the material used and suggest cytotoxicity. They emphasize the need for detailed evaluation at the ultrastructural level of newly developed biomaterials before they can be used for medical applications.