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  • 1
    Electronic Resource
    Electronic Resource
    Methylcellulose cell culture as a new cytotoxicity test system for biomaterials (1991)
    Springer
    Journal of materials science 2 (1991), S. 142-148 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The cytotoxicity of biomaterials can be testedin vitro using various culture systems. Liquid culture systems may detect cytotoxicity of a material either by culture of cells with extracts or with the material itself. In the latter instance, renewing the medium will remove possible released cytotoxic products. The agar-overlay test is a short term semi-solid culture system in which the possible cytotoxicity of biomaterials is identified only by the presence of cell free zones. The aim of this study was to develop a more sensitive cytotoxicity test system for biomaterials, using methylcellulose as a culture gel, mixed with human fibroblasts. The main advantage of the test system is the possibility of evaluating cytotoxicity for a period of up to seven days without renewal of the culture gel. Furthermore it is possible to both quantitatively evaluate by counting absolute cell numbers and to qualitatively evaluate by studying cell morphology with light- and/or electron microscopy. Processed dermal sheep collagen was selected as test material, since contradictory results concerning the cytotoxicity of its extracts have been reported by others [2, 15, 18, 19]. Using our test system, both primary and secondary cytotoxic effects were found. Primary cytotoxicity is due to direct leakage of products from the material, detected by testing, extracts of the collagen or the collagen itself. Secondary cytotoxicity is due to release of cytotoxic products resulting from cell-biomaterial interactions. We conclude that our test system is extremely useful to test materials which are suspected of primary and/or secondary cytotoxicity, either with slow release of cytotoxic products or release of products with late cytotoxic effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00692972
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  • 2
    Electronic Resource
    Electronic Resource
    Calcification of subcutaneously implanted collagens in relation to cytotoxicity, cellular interactions and crosslinking (1995)
    Springer
    Journal of materials science 6 (1995), S. 288-296 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: In general, calcification of biomaterials occurs through an interaction of host and implanted material factors, but up to now the real origin of pathologic calcification is unknown. In this study we aimed to investigate incidence of calcification of (crosslinked) dermal sheep collagens (DSCs) with respect to their specific properties, during subcutaneous implantation in rats. Three types of DSCs were commercially obtained: non-crosslinked DSC (NDSC), and DSC crosslinked with glutaraldehyde (GDSC) and hexamethylenediisocyanate (HDSC). NDSC, HDSC and GDSC were (enzymatically) tissue culture pretreated to eliminate their cytotoxic products. Beside this, crosslinking methods were modified to optimize mechanical properties and to decrease cytotoxicity, which resulted in HDSC* and GDSC*. Furthermore, DSC was crosslinked by activation of the carboxylic groups, i.e. by means of acyl azide and carbodiimide, resulting in AaDSC and CDSC, respectively. After implantation of HDSCs and GDSCs a relation between cytotoxicity and calcification of crosslinked DSC could be made. No relation was found between cellular infiltration of DSCs and calcification. However, from the use of different types and modification of crosslinking methods it might be concluded that calcification is mainly related to stable crosslinks, i.e. to the chemical properties of the obtained material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00120273
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  • 3
    Electronic Resource
    Electronic Resource
    Glutaraldehyde as a crosslinking agent for collagen-based biomaterials (1995)
    Springer
    Journal of materials science 6 (1995), S. 460-472 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: The formation of Schiff bases during crosslinking of dermal sheep collagen (DSC) with glutaraldehyde (GA), their stability and their reactivity towards GA was studied. All available free amine groups had reacted with GA to form a Schiff base within 5 min after the start of the reaction under the conditions studied (0.5% (w/w) GA). Before crosslinks are formed the hydrolysable Schiff bases initially present were stabilized by further reaction with GA molecules. An increase in shrinkage temperature (T s) from 56°C for non-crosslinked DSC (N-DSC) to 78°C for GA crosslinked DSC (G-DSC) was achieved after crosslinking for 1 h. From the relationship between the free amine group content and the T s during crosslinking it was concluded that higher GA concentrations and longer reaction times will result in the introduction of pendant-GA-related molecules rather than crosslinks. After 24 h crosslinking an average uptake of 3 GA molecules per reacted amine group was found. No increase in the tensile strength of the materials was observed after crosslinking, which may be a result of formation of crosslinks within the fibres rather than in between fibres. Aligning of the fibres by applying a pre-strain to the samples and subsequent crosslinking yielded materials with an increased tensile strength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00123371
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  • 4
    Electronic Resource
    Electronic Resource
    Incidence of infection in implanted polyurethane tubing segments serially injected with staphylococci (1994)
    Springer
    Journal of materials science 5 (1994), S. 628-634 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: One of the major clinical complications in the biomedical application of synthetic materials is the incidence of implant-associated infections. Such infections are very often induced by Staphylococcus aureus. To obtain information on tissue reactions and minimal bacterial challenge needed to create an infection related to untreated implant surfaces, we injected polyurethane tubing segments with a series of Staphylococcus aureus. The segments were subcutaneously implanted in rats. Implantation periods varied from 2, 5 and 10 days to 3 weeks. Specimen were evaluated using light and transmission electron microscopy. At least 0.25×104 of Staphylococci aureus were needed to clearly recognize that bacteria had been injected in the polyurethane tubing segments. The evidence was indirect, showing high infiltration and activation of neutrophils and macrophages, but not bacteria. Furthermore, 0.25×106 S. aureus were needed to induce a persistent specific inflammatory reaction with high concentrations of lymphocytes, i.e. mainly plasma-cells, at 3 weeks. The results indicate that this model functioned well to obtain the wanted information. Results are discussed with respect to (a-) specific inflammatory reactions occurring with (bacterial-challenged) biomaterials. Ultimately, our goal is to develop infection-resistant materials, for which the in vivo model developed may be used to qualify the processed materials
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00120344
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  • 5
    Electronic Resource
    Electronic Resource
    Crosslinking of dermal sheep collagen using hexamethylene diisocyanate (1995)
    Springer
    Journal of materials science 6 (1995), S. 429-434 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: The use of hexamethylene diisocyanate (HMDIC) as a crosslinking agent for dermal sheep collagen (DSC) was studied. Because HMDIC is only slightly water soluble, a surfactant was used to obtain a clear and micellar crosslinking solution and to promote the penetration of HMDIC in the DSC matrix. Using optimized conditions treatment of non-crosslinked DSC (N-DSC) with HMDIC (H-DSC) increased the shrinkage temperature (T s) of N-DSC from 56°C to 74°C for H-DSC. A linear relation between the decrease in free amine group content and the increase in T s was observed. Crosslinking with HMDIC did not influence the tensile strength of the N-DSC samples but increased the elongation at break from 141% to 163% and decreased the high-strain modulus from 26 MPa to 16 MPa for the H-DSC samples, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00120286
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  • 6
    Electronic Resource
    Electronic Resource
    Modulation of the tissue reaction to biomaterials (1994)
    Springer
    Journal of materials science 5 (1994), S. 671-678 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Although in the last few years in general the biocompatibility of biomaterials has significantly improved, unwanted tissue reactions are often observed resulting in early resorption of the biomaterial, loosening of the implant or in 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 the role of individual factors (humoral and cellular) involved in the inflammatory reaction against biomaterials has to be studied. In this part of the study the role of macrophages is studied with and without depletion by use of the liposomes-mediated macrophage suicide technique. Crosslinked dermal sheep collagens were used as biodegradable test materials. The results showed that macrophage depletion increases vascularization, and decreases the infiltration of granulocytes into the collagens. The foreign body reaction, i.e. the infiltration of macrophages and giant cells was significantly inhibited, resulting in a strongly delayed degradation time of the biomaterials. However, macrophage depletion did not inhibit attraction of fibroblasts and even resulted in increased formation of autologous rat-collagen, which improved the biocompatibility and the function of the biomaterials as a tempory scaffold.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00120354
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  • 7
    Electronic Resource
    Electronic Resource
    Tissue reactions to lead samples in a late infection rat model (1996)
    Springer
    Journal of materials science 7 (1996), S. 415-423 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Tissue reactions to rat lead samples, modelling for clinically used leads, were investigated in a late infection model, in which injection of bacteria was performed after a 3-week encapsulation process. At the site of injection, detachment of the original fibrous capsule, wound fluid infiltration, fibrin formation and granulocyte and macrophage infiltrations, occurred. Spreading of infection did not occur via the generally assumed direct bacterial adhesion to materials, but through blood vessels at the outside of capsules and through wound fluid passage at the interface and in the lumen of the lead sample. At day 5, infection had spread all over, but, apart from two small abscesses, seemed to be suppressed at day 10. However, probably due to luminal bacterial growth, at weeks 3 and 6 the reaction intensified showing larger abscesses with accumulations of lymphocytes. The results of this study represent a good basis for further studies aimed at developing infection-resistent lead material. Research efforts are first directed on modification of material surfaces to provide controlled release of antimicrobial agents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00122011
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  • 8
    Electronic Resource
    Electronic Resource
    Relations between in vitro cytotoxicity and crosslinked dermal sheep collagens (1992)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 26 (1992), S. 1091-1110 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: 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 × 10 d to 4 × 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 morphoIogy, was observed. These remarkable differences in cytotoxicity are discussed in relation to residual agents and specific crosslinks present i n DSCs as a consequence of processing and the crosslinking agents used. The residual agents and the specific crosslinks give rise to differ- ences in direct release of products and in sensitivity to hydrolysis and enzymatic breakdown.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820260810
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  • 9
    Electronic Resource
    Electronic Resource
    Influence of ethylene oxide gas treatment on the in vitro degradation behavior of dermal sheep collagen (1995)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 29 (1995), S. 149-155 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The influence of ethylene oxide gas treatment on the in vitro degradation behavior of noncrosslinked, glutaraldehyde crosslinked or hexamethylene diisocyanate crosslinked dermal sheep collagen (DSC) using bacterial collagenase is described. The results obtained were compared with the degradation behavior of either nonsterilized or γ-sterilized DSC. Upon ethylene oxide sterilization, reaction of ethylene oxide with the free amine groups of DSC occurred, which resulted in a decreased helix stability, as indicated by a lowering of the shrinkage temperature of all three types of DSC. Except for the low strain modulus the mechanical properties of the ethylene oxide sterilized materials were not significantly altered. γ-Sterilization induced chain scission in all three types of DSC, resulting in a decrease of both the tensile strength and the high strain modulus of noncrosslinked and crosslinked DSC. When exposed to a solution of bacterial collagenase, ethylene oxide sterilized materials had a lower rate of degradation compared with nonsterilized DSC. This has been explained by a reduced adsorption of the collagenase onto the collagen matrix as a result of the introduction of pendant N-2-hydroxy ethyl groups. © 1995 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820290203
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  • 10
    Electronic Resource
    Electronic Resource
    Regeneration of full-thickness wounds using collagen split grafts (1995)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 29 (1995), S. 1425-1436 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: 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 no 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. © 1995 John Wiley & Sons, Inc.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820291114
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