Collagen-based wound dressing: effects of hyaluronic acid and fibronectin on wound healing

Studies on the desamidation of bovine collagen

The most important reactive groups in collagen are amino, amido, guanidino, and carboxyl, all of which are present in comparatively large numbers. It is possible to modify amide groups present in the collagen of achilles tendons and hide trimmings by desamidation (DAM). DAM causes progressive hydrolysis of the amide groups of asparagine and glutamine side chains of collagen, thereby resulting in the reduction of the amide content of collagen. Loss of amide brings about an increase in the number of free carboxyl groups in the desamidated collagen, shown by reduction in its isoionic pH. The new modified collagen, like type I bovine collagen, has high viscosity and high hydroxyproline content. The fibril formation of the modified collagen showed slight variation, and polyacrylamide gel electrophoretic analysis indicated largely alpha components, indicating destruction of inter- and intramolecular crosslinks. The swelling behavior of the modified collagen is significantly higher compared to type I bovine collagen.

Application of benzyl hyaluronate membranes as potential wound dressings: evaluation of water vapour and gas permeabilities

Membranes of 75% and 100% benzyl hyaluronate esters (percentage of total carboxylate groups esterified) were prepared and their water vapour, oxygen and carbon dioxide transmission rates determined. The values of these properties were compared with the values obtained for several commercial wound dressings under the same conditions. The benzyl hyaluronate membranes showed water vapour transmission rates (2157-2327 gm-2 per day) comparable to those from commercial skin dressings (426-2047 gm-2 per day). In the dry state, the benzyl hyaluronate membranes showed lower oxygen and carbon dioxide transmission rates. Taking into account the biocompatibility of the hyaluronic acid esters, and the possibility that therapeutic agents could be incorporated into these membranes, the results indicate that the benzyl hyaluronate membranes have potential wound dressing applications.

Biomaterial supports for colonic wall defect healing. An experimental study in the rat

New artificial biomaterials were tested for support of gastro-intestinal tract wound healing in the rat. Double layered collagenic matrices were prepared with purified collagens extracted from human placental tissues. Two types of patches were tested, the first constituted from a collagen type I + III layer covered by collagen IV in a liquid phase (patch I + III/IV) and the second from a collagen IV layer covered by liquid collagen IV (patch IV/IV). The matrices were applied with fibrin sealant to the edges of a 1 cm diameter colonic wall defect in the rat. Healing evolution was determined by macroscopic, microscopic and immunostaining studies. The reconstitution of the three colonic wall layers was achieved within 45 days without retraction or inflammatory reaction, while the biomaterial was resorbed. Human collagen I and III antibodies failed to stain extracellular matrix. This failure may be a consequence of outdated antibodies or more likely epitope alteration during extraction and preparation of the collagens. A human collagen type IV antibody staining of the scar zone showed the basement membranes of newly developed vessels within 10 days, and newly formed colonic mucosa within 20 days. The collagen reconstituted matrix was able to assist healing of normal digestive tract defects as shown by the labelling of the new synthesized extracellular matrix by collagen type IV antibody. These findings support the use of collagen biomaterial in gastro-intestinal anastomosis. This new surgical approach allowing healing of colonic wall defects could reduce occurrence of anastomotic leakage in human.

Evaluation of an artificial dermis full-thickness skin defect model in the rat

An artificial dermis product was applied to full-thickness skin defects in rats and cell infiltration into the collagen matrix was investigated. Host fibroblasts and capillaries infiltrated as far as the upper end of the collagen matrix by day 14 after application. Determination of glycosaminoglycan levels in the matrix showed that hyaluronic acid was generated in a similar amount to that seen in the intact skin by day 14. An autologous thin split-thickness skin graft was placed onto the artificial dermis simultaneously or several days after its application to the defect. The take rate was 100% when a split-thickness skin graft was performed on day 14 after application of the artificial dermis. At 6 weeks after the skin defect was created, the wound area was 80% of the original area and the dermis at the grafted site was as thick as that of normal skin. These results suggested that the artificial dermis provides a good matrix for thin split-thickness skin graft and is useful for the reconstruction of full-thickness skin defects. This method is considered to be an alternative to the conventional procedure using thick skin grafts or skin flaps.

Histological evaluation of skin reconstruction using artificial dermis

An artificial dermis, composed of a collagen matrix, was applied to a full-thickness skin defect prepared on the back of rats. Two weeks later, a thin split-thickness skin autograft was overlaid on the matrix at each recipient site. The dermal layer at the recipient sites was 1.02 mm thick with prior application of artificial dermis, as compared with the 0.46 mm thickness observed without such pretreatment. Histologically, the split-thickness skin graft normally lies with no gap on the artificial dermis, which looks like natural dermis. Six days after grafting, the epithelial basal cells in the grafts showed an active uptake of bromodeoxyuridine (a thymidine analogue), indicating high activity of cell proliferation. About 50 and 20% respectively of the artificial dermis remained at each recipient site at 12 and 20 weeks after its application (after the skin defect). This finding indicates that bovine collagen, which is a constituent of the artificial dermis, is gradually replaced by the host tissue.

Confocal laser-scanning microscopy for determining the structure of and keratinocyte infiltration through collagen sponges

The development of artificial skin substitutes based on cultured cells and biomaterials such as collagen requires an understanding of cellular interactions with the substrate. In this study, human keratinocytes were cultured on the surface of collagen sponges, and confocal laser-scanning microscopy (CLSM) was used to assess both the microstructure of the sponge, and the cell morphology and distribution throughout the sponge. It was found that the pore size increased with increasing depth into the sponge. Both pore size and fiber thickness increased during incubation for up to 10 days at 37 degrees C in culture medium in the absence of cells. This latter effect was not observed when the sponges were incubated in distilled water. Keratinocytes penetrated into the sponge even after only 3 days in culture. By 10 days in culture, the cells had penetrated to the maximum depth that could be examined (120 microns from the sponge surface). In the presence of cells, the inner structure of the collagen sponge had altered after 10 days in culture, with the collagen fibers becoming thicker, and pore geometry less regular. The mechanism responsible for this is unknown at present. Although the presence of the keratinocytes increases distortion of the sponge structure, factors from the medium itself also contribute to this effect. CLSM is a powerful tool for assessing cellular interactions with bioimplants, providing both qualitative and quantitative information. It offers many advantages over scanning electron microscopy (SEM) and histological techniques. CLSM minimizes the time-consuming, extensive preparation of samples required with the latter two methods, and allows noninvasive serial optical sectioning of intact samples.

Acceleration of granulation tissue ingrowth by hyaluronic acid in artificial skin

Hyaluronic acid (HA), which is known to play an important role in wound healing, was incorporated in an artificial skin material and studied for its potential to create a wound bed which would support a skin graft. Collagen sponge based artificial skin was soaked in 0.3% HA in phosphate buffered saline and grafted onto skin defects in rats. Control grafts were soaked in normal saline solution. HA incorporated implants and control implants were simultaneously grafted onto wounds made on either side of the spine. To examine the effect of HA incorporation, the percentage area of cellular tuft infiltration and the number of capillaries present in the graft matrix were evaluated at 7 and 14 days after the operation. At postoperative day 7, there was a statistically significant difference in the number of capillaries in the matrix of the experimental versus the control implants. There was no difference in the percentage area of cellular tuft infiltration. At postoperative day 14, all implants exhibited better ingrowth of granulation tissue than at day 7. The differences between the experimental and control implants were statistically significant with respect to both the percentage area of cellular tuft infiltration and the number of capillaries. It is therefore concluded that in artificial skin HA incorporation accelerates the ingrowth of granulation tissue, making a more suitable graft bed.

Porosity and biological properties of polyethylene glycol-conjugated collagen materials

Collagen-based materials can be designed for use as scaffolds for connective tissue reconstruction. The goal of the present study was to evaluate the behavior of collagen materials as well as cell and tissue reactions after the conjugation of activated polyethylene glycols (PEGs) with collagen. It is known that proteins conjugated with PEGs exhibit a decrease in their biodegradation rate and their immunogenicity. Different concentrations and molecular weights of activated PEGs (PEG-750 and PEG-5000) were conjugated to collagen materials (films or sponges) which were then investigated by collagenase assay, fibroblast cell culture, and subcutaneous implantation. PEG-conjugated collagen sponge degradation by collagenase was delayed in comparison to untreated sponges. In culture, fibroblasts with a normal morphology reached confluency on PEG-conjugated collagen films. In vivo, the porous structure of non-modified sponges collapsed by day 15 with a few observable fibroblasts between the collagen fibers. In PEG-modified collagen sponges, the porous structure remained stable for 30 days. Cell infiltration was particularly enhanced in PEG-750-conjugated collagen sponges. In conclusion, PEGs conjugated onto collagen sponges stabilize the porous structure without deactivating the biological properties of collagen. These porous composite materials could function as a scaffold to organize tissue ingrowth.

Heparin-fibroblast growth factor-fibrin complex: in vitro and in vivo applications to collagen-based materials

Biological molecules such as fibrin and growth factors could have interesting features to design bioactive biomaterials and particularly collagen-based materials used as connective tissue replacement. Different combinations of fibroblast growth factor (FGF) and heparin complexed to fibrin were analysed. In vitro, FGF bound to matrix was rapidly, but partially released, specifically with heparin. Heparin concentrations were progressively equilibrated between matrix and medium. DNA replication of fibroblasts grown either on or within fibrin matrices was increased in the presence of both FGF and high doses of heparin incorporated in fibrin. Subcutaneous implantations of collagen sponges impregnated with composite fibrin matrices showed qualitative and quantitative tissue ingrowth within the sponges. The uncross-linked collagen of fibrin-impregnated sponges swelled after implantation. The resulting fibroblast-infiltrated tissue resembled a normal dense connective tissue that was observed particularly in the presence of high doses of heparin and FGF incorporated in fibrin.

Bioadhesive, collagen-modified liposomes: molecular and cellular level studies on the kinetics of drug release and on binding to cell monolayers

Liposomes, modified by covalently-anchoring collagen to their surface, were investigated for their abilities to be bioadhesive and to act as sustained-release drug carriers. These bioadhesive liposomes have the potential to induce significant improvements in topical and regional therapies. The major findings for uni-(ULV) and multilamellar (MLV) bioadhesive liposomes are: (a) Both ULV and MLV release small molecular weight drugs over prolonged periods. For example, rate constants of (6 +/- 0.5) x 10(-3) and (2.6 +2- 0.8) x 10(-3) h-1, were obtained for the release of vinblastine and fluconazole, respectively, from collagen-ULV. (b) For a given drug, that rate constant can be shifted (up or down) by the choice of liposome type and collagen-surface density and the latter, if high enough, lead to the formation of an additional liposome-associated drug reservoir. (c) Using monolayers of the A431 cell line to model the in vivo targets, the bioadhesive (but not the regular) liposomes were found to bind with high affinity to the monolayers. For example, equilibrium dissociation constants of 6.3(+/- 3) microM and 2.7(+/- 0.5) microM were determined for bioadhesive MLV and ULV, respectively, with corresponding saturation occupancies of 3.7(+/- 1) and 4.0(+/- 0.2) pmoles liposomal collagen/monolayer of 10(5) cells. (d) Following the retention of bioadhesive MLV at A431 monolayers for 24 h, it was found that: at 4 degrees C, 24 h did not suffice to reach equilibrium, but at 37 degrees C equilibrium binding was obtained within 3-5 h and there was quantitative liposome retention (per viable monolayer) thereafter. It is concluded that these liposomes are bioadhesive sustained-release carriers, as desired, meriting further cellular and in vivo studies.

Inverse relationship between hyaluronan and collagens in development and angiogenesis

The extracellular matrix plays a vital role in regulating normal tissue development and function--largely via the specific arrangement of macromolecules such as collagens, proteoglycans, glycosaminoglycans and glycoproteins. Previous reports have concentrated on associations between combinations of collagens/proteoglycans, collagens/glycoproteins and proteoglycans/glycosaminoglycans whilst little information is available on associations between collagens and free glycosaminoglycans. In this review, we discuss possible associations between collagens and the glycosaminoglycan hyaluronan; macromolecules which are known to exhibit changes in amount and composition during development and under pathological conditions. We demonstrate two types of collagen/hyaluronan association in vivo: the first, during the formation of extracellular matrix structures where neither collagens nor hyaluronan are degraded, resulting in the regulation of collagen fibrillogenesis, and the second, involving an inverse correlation between collagen synthesis and hyaluronan degradation and vice versa. We suggest that associations between collagens and hyaluronan play an important role in the initiation and maintenance of angiogenesis and put forward a model of cartilage vascularisation which relies on these associations.

A new type of biomaterial for artificial skin: dehydrothermally cross-linked composites of fibrillar and denatured collagens

A new type of biomaterial for artificial skin was developed as a form of sponge by combining fibrillar collagen (F-collagen) with gelatin. The sponge was physically and metabolically stabilized by introducing dehydrothermal cross links. To get the final product, various conditions in the preparation of sponges were evaluated by in vitro cellular responses and in vivo tissue reactions. Fibroblasts placed on a sponge of gelatin attached themselves to it, migrated well into the sponge, and remained inside it for at least 7 days. However, sponges of gelatin showed structural instability for hydrolytic degradation by the cells. Most fibroblasts appeared not to penetrate into the interior of a sponge of F-collagen but to remain on its surface when fibroblasts were placed on the sponge, suggesting poor attraction of F-collagen toward cells. Implantation experiments of sponges of F-collagen revealed an intense infiltration of neutrophils into the sponge, indicating F-collagen as an inducer of the inflammatory reaction. These aggravating characters of F-collagen sponges were greatly improved by blending gelatin with F-collagen. The new type of collagen-based biomaterials developed in the present study is expected to become a useful matrix substance for artificial skin.

Anterior cruciate ligament reconstruction using a composite collagenous prosthesis. A biomechanical and histologic study in rabbits

We evaluated a prototype composite collagenous anterior cruciate ligament replacement device designed to possess the advantages of biological grafts and synthetic materials. Collagenous anterior cruciate ligament prostheses were made by embedding 225 reconstituted type I collagen fibers in a type I collagen matrix, and placing polymethylmethacrylate bone fixation plugs on the ends. The collagenous prosthesis was used to replace the anterior cruciate ligament of 31 mature rabbits. At 4 and 20 weeks postimplantation, histologic and mechanical studies were performed on the developing neoligament tissue, and compared to values for the contralateral sham-operated control. At 4 weeks, neoligament tissue infiltrated the collagen fibers of the prostheses. The tibial bone tunnel attachment site contained new bone approaching the fibrous neoligament. The glutaraldehyde-treated prosthetic fibers appeared intact, while the carbodiimide-treated prosthetic fibers began to resorb. The ultimate load and ultimate tensile strength of femur-neoligament-tibia complexes had decreased. At 20 weeks, glutaraldehyde-treated fibers appeared partially intact; in contrast, the carbodiimide-treated prostheses appeared to be completely degraded, and were replaced by organized, crimped neoligament tissue. The ultimate tensile strength and ultimate load increased substantially due to deposition and remodeling of neoligament tissue. The neoligament ultimate load was 2 to 4 times the initial load value of the prosthesis. Implantation of a resorbable, composite collagenous anterior cruciate ligament prosthesis encourages the development of functional neoligament tissue. Studies are underway to optimize the mechanical and biological properties of the prostheses.

A new biodegradable elastin-fibrin material; its use in urological, digestive and cardiovascular surgery

A new original artificial connective matrix mainly made of elastin and fibrin-like product is used to reinforce damaged tissues and to close and restore a loss of substance in several domains of surgery: all sites in the digestive system and urinary tract; besides, it can substitute for the pericardium in iterative heart operations. In all cases, the original tissue is restored ad integrum while the biodegradable material disappears completely, without any complications.

Wettability of cross-linked collagenous biomaterials: in vitro study

Collagenous biomaterials can be treated by chemical and physical agents to decrease biodegradation rate. Treatments to collagen may modify surface properties and subsequently cell and platelet behaviour. Collagenous films were either uncross-linked and cross-linked by glutaraldehyde, formaldehyde or cyanamide and/or treated by a severe dehydration. Contact angles, platelet contacting assay and fibroblast morphology were investigated. After severe dehydration, wettability was diminished except for formaldehyde-cross-linked and severely dehydrated films. Glutaraldehyde-cross-linked collagen results in an increase in wettability. Platelets were similarly distributed, except on formaldehyde-cross-linked films that exhibited no platelet aggregation. Fibroblasts were in a spreading phase on most collagenous films. However, cytotoxicity was noticed on some aldehyde-cross-linked films. No direct relationship was found between contact angles and platelet-cell attachment.

In vitro contraction rate of collagen in sponge-shape matrices

Connective tissue substitute can be made of collagen sponge-shaped matrice which is reconstituted by freeze-drying a collagen dispersion. This procedure is then followed by a crosslinking treatment to decrease the in vivo biodegradation rate. In the present study, collagen dispersions made of collagen fibrils with a D-staggered pattern were submitted to the following treatments: (1) cyanamide or glutaraldehyde was introduced during the dispersion step followed by the manufacture of sponges; (2) uncrosslinked sponges were exposed to formaldehyde vapor; or (3) uncrosslinked and crosslinked sponges were severely dehydrated. To characterize the in vitro contraction rate, the surface areas of sponges were sequentially recorded in relation to soaking time. Contraction did not significantly occur when sponges were chemically treated. However, collagen in sponges treated by either severe dehydration or by both cyanamide treatment and severe dehydration contracted. On the other hand, the different treatments of the collagen modified the distribution of the D-staggered pattern within fibrils. After glutaraldehyde treatment, the periodicity of collagen fibrils disappeared and large fibres were observed. These experiments show that the different treatments of the collagen can be useful for designing a contractile as well as a non-contractile biomaterial.

Skin replacement using collagen extracted from bovine hide

This paper reviews the use of biological sponge-shape matrices as dermal replacements in order to orient newly formed wound tissue. Sponge-shape matrices consist of a scaffold made of cross-linked collagen extracted from bovine hide. Other molecules with specific activities on wound tissue ingrowth are bound to collagen. The lamination of sponge with a synthetic material allows this device to be implanted as a temporary skin substitute. For the epidermal cell layer replacement, a biological film-shape matrix can be used in order to cultivate autologous cells during the period that biological sponge-shape matrices are invaded by wound tissue.

Water-curable and biodegradable prepolymers

In an attempt to develop biodegradable polymers which can be shaped in situ and adhere to living tissues, we synthesized esterurethane prepolymers which can be cured upon contact with water in living tissues. First, D,L-lactide polymerization or D,L-lactide-epsilon-caprolactone (50:50) copolymerization was carried out using ethylene glycol or poly(ethylene glycol) as initiator to obtain hydroxyl-terminated biodegradable polyesters. They were then reacted with an excess of diisocyanate such as hexamethylene diisocyanate, toluylene diisocyanate, and diphenylmethane diisocyanate to introduce a reactive isocyanate group to both of the end groups of the polyesters. The isocyanate-terminated prepolymers could be cured in the presence of water and the cured polymers were degraded by hydrolysis both in vitro and in vivo. It was found that the presence of appropriate amounts of hydrophilic units in the main chain was essential for giving a high curing rate and a high degradation rate for the biodegradable urethane prepolymers. The tissue responses to the cured polymers were not severe.

In vitro studies on biocompatibility of hyaluronic acid esters

The biocompatibility of semisynthetic polymers formed from hyaluronic acid esters has been studied using fibroblast cultures. The polymers, added to the culture medium, used either in powdered form or as thin membranes, behave as inert materials. The cells used in the experiments grow normally in the culture dishes. With regard to adhesiveness the cells were not able to spread on the biomembranes and tended to form isolated clusters of round cells. Human fibronectin, placental collagen (type I-IV) and fibrin could be stratified on biomembranes. When these molecules reacted with the biomaterial the film became suitable for fibroblasts spreading and growth.

Inert wound dressing is not desirable

Four Yorkshire piglets were inflicted with a total of 92 split-thickness wounds 4.8 cm2 in area and 400 microns deep. The wounds were treated with eight dressing regimens under the same experimental design. The rate of reepithelialization of the wound was quantitated by a morphometric method. The magnitude of inflammatory reaction of the wound to the dressing was scored from histological slides. The results indicate a relationship between the rate of reepithelialization of split-thickness wounds and the inflammatory response of the wound to the dressing. Dressings, such as collagen sponge, polyethyleneglycol, Duoderm, and lanolin ointment, induce moderate to severe inflammatory changes when placed on the wounds. These wounds reepithelialize significantly faster than control, gauze-covered wounds. This contrasts with inert dressings, such as hydrated hydrogel membrane, Carbopol 934P, or Silvadene cream, which did not affect the rate of reepithelialization when compared with the healing of control wounds. Simultaneously, these dressings induced no or minimal inflammatory reaction in the wound tissue. Only when the inflammatory reaction to the wound dressing was excessive (methylcellulose) was the rate of reepithelialization of the wounds significantly inhibited in comparison with control wounds. We hypothesize that wound dressings, by inducing inflammatory reaction, enhance healing by activating cells, such as macrophages or fibroblasts, that produce growth factors and other mediators of the repair process.

Current status of fibronectin in transfusion medicine: focus on clinical studies

It has long been hypothesized that fibronectin (Fn) is essential to the function of the reticuloendothelial system (RES) and that the reversal of Fn deficiency in critically ill patients would result in a clinical benefit to these patients. Fn administration to deficient patients was postulated to improve the function of the RES, decrease the incidence of organ failure, sepsis and ultimately mortality. Over the past 15 years, several clinical studies have been performed to test these hypotheses. The initial anecdotal studies using cryoprecipitate (a plasma fraction enriched in Fn) revealed promising results but were neither controlled nor blinded. Further controlled studies were published utilizing both cryoprecipitate and purified Fn. Unfortunately, the great majority of authors found no beneficial effects of Fn administration in critically ill patients, in relation to incidence of organ failure, sepsis, or mortality. These results do not support the use of Fn in this setting. Fn utilization in wound healing has shown promising results in case reports. Although its role in wound healing is not yet fully delineated, initial reports with corneal wounds show a beneficial influence of Fn administration. Further studies are needed to determine the exact function(s) of Fn in a healing wound. Efficacy must still be shown in controlled clinical trials; dosing and administration regimens need to be elucidated.

Tissue reaction to subcutaneous implantation of a collagen sponge. A histological, ultrastructural, and immunological study

The biocompatibility of a subcutaneously implanted bovine collagen sponge (Haemostagen) was studied in rats by analyzing tissue reactions up to 3 months by histological and ultrastructural methods; in addition, the level of serum antibodies to bovine type I collagen (the major implant collagen) was measured by solid-phase radioimmunoassay. By 8 h after implantation, the implant was completely filled with polymorphonuclear cells (PMNs). After 8 days, fibroblasts had developed a granulation tissue within the sponge and the PMNs had almost disappeared. The small residue that remained after 1 month consisted of some densely packed collagen fibrils containing giant cells, which had disappeared by 3 months. No antibodies to bovine type I collagen were found in the sera of implanted rats.

The attachment and growth of an established cell line on collagen, chemically modified collagen, and collagen composite surfaces

The attachment and growth of an established cell line derived from mouse fibroblasts on collagen, chemically modified collagen, and collagen composite surfaces were compared. Tissue culture polystyrene dishes provided a suitable control. The substrates included native bovine dermal collagen, succinylated, acetylated and methylated collagen, and a series of composite materials formed from collagen and the glycosaminoglycans hyaluronic acid, chondroitin 4-sulphate and chondroitin 6-sulphate and the glycoprotein fibronectin. Attachment and growth of cells on each of these substrates were assessed by visual inspection under optical microscopy, by detachment of the cells using trypsinization and subsequent counting in a Coulter counter; and by 3H-thymidine incorporation studies. A very good correlation between the results was obtained by the three methods employed which showed that collagen, in comparison to polystyrene, is a relatively poor substrate for cellular attachment, growth and proliferation, but it may be improved by chemical modification and by incorporation of either fibronectin, chondroitin sulphate (5 and 10%), or low levels (less than 5%) of hyaluronic acid into the collagen matrix. Concentrations in excess of 5% hyaluronic acid into the collagen matrix, however, appeared to inhibit cellular attachment and growth and such materials provided a poorer substrate than native collagen.

Formation of continuous collagen fibres: evaluation of biocompatibility and mechanical properties

Reconstituted collagen fibres have potential applications in repair of soft and hard tissues. Preliminary studies conducted in our laboratory suggest that discontinuous reconstituted type I fibres have strengths similar to those of fibres teased from tendons. The purpose of this paper is to report a method for continuous collagen fibre production and the properties of fibres produced. Ultimate tensile mechanical properties and biocompatibility of continuous type I collagen fibres were studied and compared with the properties of fibres produced manually (discontinuous fibres). In general, continuously made cyanamide cross-linked fibres show slightly inferior mechanical properties and faster biodegradation rates compared with manually made fibres because of minor differences in the fibreformation protocol introduced by design constraints. However, continuous and discontinuous fibres crosslinked with glutaraldehyde had comparable properties. These results demonstrate that production of 50 microns diameter continuous collagen fibre is possible.

In vivo evaluation and comparison of collagen, acetylated collagen and collagen/glycosaminoglycan composite films and sponges as candidate biomaterials

Native collagen, acetylated collagen, collagen/10% chondroitin sulphate, collagen/2.5% hyaluronic acid and collagen/20% hyaluronic acid were implanted both as film and as sponge into rat lumbar muscle for 7 and 14 d. After 7 d implantation, all materials elicited an acute inflammatory cell response characterized by numerous polymorphs and histocytes. The cell population after 14 d was principally mononuclear, i.e. leucocytes, neutrophils, macrophages, lymphocytes and fibroblasts. Both films and sponges followed a similar pattern. Native collagen elicited a subacute inflammatory response after 7 d. However, 14 d after implantation, a marked infiltration by neutrophils was apparent with subsequent degradation of existing collagen material. Acetylated collagen film evoked a much greater inflammatory cell response than native collagen. Both collagen/hyaluronic acid composites elicited a similar response. The collagen/10% chondroitin sulphate composite elicited the least inflammatory cell response at 7 d, whereas infiltration by host fibroblasts after 14 d implantation was clearly seen.

Cellular invasion and breakdown of three different collagen films in the lumbar muscle of the rat

Collagen films were prepared by three different methods involving acid homogenization at pH 3.0 of a collagen suspension for 1.5 min (film A) and 15 min (film B) and alkaline homogenization at pH 10 for 15 min (film C), after which the resulting slurries were degassed and dried over sterile air. Subsequent examination by scanning electron microscope (SEM) revealed that all samples showed a distinctly layered structure which was much finer in the acid films. Implantation into the lumbar muscle of rats followed by histology and SEM studies revealed that film B was completely resorbed at 14 d whereas remnants of film A could still be seen at this period. The slowest rate of resorption was observed with film C, traces of which could still be found at 70 d. Invading inflammatory cells moved into the collagen films between the layers from the edges only causing the whole structure to 'ribbon out'. The surfaces of all three films appeared to be impenetrable to cells. Incubation of the three films with bacterial collagenase revealed similar relative rates of degradation to those observed in vivo.

Hyaluronate-binding proteins of murine brain

The distribution of hyaluronate-binding activity was determined in the soluble and membrane fractions derived from adult mouse brain by sonication in low-ionic-strength buffer. Approximately 60% of the total activity was recovered in the soluble fraction and 33% in membrane fractions. In both cases, the hyaluronate-binding activities were found to be of high affinity (KD = 10(-9) M), specific for hyaluronate, and glycoprotein in nature. Most of the hyaluronate-binding activity from the soluble fraction chromatographed in the void volume of Sepharose CL-4B and CL-6B. Approximately 50% of this activity was highly negatively charged, eluting from diethylaminoethyl (DEAE)-cellulose in 0.5 M NaCl, and contained chondroitin sulfate chains. This latter material also reacted with antibodies raised against cartilage link protein and the core protein of cartilage proteoglycan. Thus, the binding and physical characteristics of this hyaluronate-binding activity are consistent with those of a chondroitin sulfate proteoglycan aggregate similar to that found in cartilage. A 500-fold purification of this proteoglycan-like, hyaluronate-binding material was achieved by wheat germ agglutinin affinity chromatography, molecular sieve chromatography on Sepharose CL-6B, and ion exchange chromatography on DEAE-cellulose. Another class of hyaluronate-binding material (25-50% of that recovered) eluted from DEAE with 0.24 M NaCl; this material had the properties of a complex glycoprotein, did not contain chondroitin sulfate, and did not react with the antibodies against cartilage link protein and proteoglycan. Thus, adult mouse brain contains at least three different forms of hyaluronate-binding macromolecules. Two of these have properties similar to the link protein and proteoglycan of cartilage proteoglycan aggregates; the third is distinguishable from these entities.

Transected spinal cords grafted with in situ self-assembled collagen matrices

The purpose of this work was to evaluate if the implantation into the gap of a transected spinal cord of a biomaterial providing a scaffolding structure for tissue ingrowth would favor the permeation and the growth of regenerating axons across the spinal-bioimplant interface. The interstump gap of rat transected spinal cords was injected with an ice-cold neutral solution of collagen, either alone or mixed with glyoxal, a harmless tanning agent. Upon warming to the temperature of the tissue, the fluid implant self-assembled forming a loose fibrillar network which simultaneously re-established a physical continuity to the transected organ. At various post-implantation timepoints, the bioimplants were studied by light microscopy, with the picrosirius-polarization method and with scanning electron microscopy. We observed that the bioimplants evolved following three overlapping phases: first a massive inflammatory response characterized by the invasion of cells of heterogeneous nature, then, a phase where microcysts predominated and during which, there is a major remodeling of the biomatrix by the deposition of newly synthesized collagen and of a periodic acid Schiff-positive material. Finally, a regeneration phase occurred where astroglial processes followed by regenerating axons invaded the biomatrix. Three months after implantation, spinal axons had grown from the two spinal stumps and penetrated the bioimplant across at least one lesion interface. However, the glyoxal-tanned collagen matrices showed a better biostability and durability than collagen alone. We conclude that the histopathological reaction of the mammalian lesioned spinal cord, when adequately directed by a scaffolding structure can be beneficial for the expression of the intrinsic regenerative capacity of the spinal cord tissue.

In vitro mineralization of a three-dimensional collagen matrix by human dental pulp cells in the presence of chondroitin sulphate

These matrices were used as cell culture substrates to investigate the influence of extracellular molecules on mineralization. Pulp cells seeded in type I collagen or type I collagen-chondroitin-4-sulphate sponges were able to grow and were morphologically similar to cells responsible for reparative dentine formation in vivo. In sponges consisting of collagen only, the cells elaborated an abundant new matrix which became organized with time and consisted of collagen fibres surrounded by fibrillar material, but no mineralization was observed. In collagen-chondroitin sulphate sponges, cells deposited less and poorly organized matrix; in these, calcification occurred, increasing with time, and at the ultrastructural level, small needle-like crystals containing calcium and phosphorus were scattered throughout the sponge fibres. These observations suggest that chondroitin sulphate might influence in vitro calcification induced by pulp cells.

The effect of hyaluronate and its oligosaccharides on endothelial cell proliferation and monolayer integrity

Hyaluronidase treatment of hyaluronic acid produced a series of oligosaccharides. Those between 3 and 16 disaccharides in length stimulated angiogenesis in vivo and the proliferation of tissue cultured endothelial cells in vitro. This effect appears to be cell type specific, as no stimulation of fibroblasts or smooth muscle cells was observed. Endothelial cells were found to endocytose both high- and low-molecular-mass hyaluronate, which might be receptor mediated. Fibroblasts and smooth muscle cells, cultured under the same conditions, showed negligible uptake of hyaluronate. Thus, the cell-specific effects may be due to the differences in internalization of hyaluronate. High-molecular-weight hyaluronate both inhibited endothelial cell proliferation and disrupted newly formed monolayers. These data are consistent with the ability of hyaluronate to inhibit new blood vessel formation in vivo and also suggest that hyaluronate metabolism plays a pivotal role in the regulation of angiogenesis.

Mechanical properties of collagen fibres: a comparison of reconstituted and rat tail tendon fibres

This study involves comparison of the mechanical properties of reconstituted collagen fibres with those of collagen fibres obtained from rat tail tendons. Reconstituted collagen fibres were cross-linked in the presence of glutaraldehyde vapour for 2 and 4 d or using a combination of severe dehydration and carbodiimide treatment. Ultimate tensile strengths for reconstituted fibres cross-linked with glutaraldehyde ranged from 50 to 66 MPa while those cross-linked by severe dehydration and carbodiimide treatment had ultimate tensile strengths between 24 and 31 MPa. Rat tail tendon fibres had tensile strengths that ranged from 33 to 39 MPa. These results indicate that high-strength collagen fibres can be reconstituted in vitro and that these fibres may be useful in repair of dermal, dental, cardiovascular and orthopaedic defects.

Material properties of living soft tissue composites

Collagen sponges seeded with fibroblasts have been used as a soft tissue substitute in wound healing applications. This biomaterial is a good in vitro analog of a connective tissue. Therefore, analysis of the properties of this material may be useful for theoretically modeling soft tissues. Stress-strain curves for such cell-seeded collagen sponges were measured to determine composite stiffness and ultimate tensile strength. Theoretical modeling was done by defining a particle-reinforced matrix using the composite sphere model. A system of uniaxially oriented fibers was then introduced to this equivalent homogeneous media and material properties were determined using the composite cylinder model. Geometric averaging was performed to yield the stiffness and Poissons' ratio for a composite with randomly oriented fibers. Inputs to the model were constituent material properties, cell volume fraction, and fiber volume fraction. From theoretical results, material properties of soft tissues and their substitutes depend on fiber mechanical properties and volume fraction and not cellular mechanical properties and volume fraction. Therefore, the increase in experimentally observed composite stiffness with increased cell number was due to deposition of newly synthesized stiffer collagen fibers, and not due to the physical presence of cells themselves.

Wound healing using a collagen matrix: effect of DC electrical stimulation

Rapid fibroblast ingrowth and collagen deposition occurs in a reconstituted type I collagen matrix that is implanted on full-thickness excised animal dermal wounds. The purpose of this study is to evaluate the effects of direct current stimulation on dermal fibroblast ingrowth using carbon fiber electrodes incorporated into a collagen sponge matrix. Preliminary results suggest that fibroblast ingrowth and collagen fiber alignment are increased in collagen sponges stimulated with direct currents between 20 and 100 microA. Maximum fibroblast ingrowth into the collagen sponge is observed near the cathode at a current of 100 microA. These results suggest that electrical stimulation combined with a collagen matrix may be a method to enhance the healing of chronic dermal wounds.

Porous collagen sponge wound dressings: in vivo and in vitro studies

Collagen-based materials can be formed into a three-dimensional sponge for use as a wound dressing and as a support for cell cultured skin components. Factors such as biocompatibility, morphological structure and addition of non-collagenous molecules to collagen are analyzed and discussed. Large pores or channels, interchannel communications and combinations of macromolecules of the connective tissue enhance wound tissue infiltration in vivo as well as cell growth in vitro into collagen sponges. The presence of such factors can be useful in patients with excised burn wounds and pressure skin ulcers.

Growth of stratified squamous epithelium on reconstituted extracellular matrices: long-term culture

Oral keratinocytes grown at an air-liquid interface on stabilized matrices of collagen or a basement membrane exhibit a pattern of tissue organization more similar to the parent tissue than the same cells cultured conventionally. An orderly sequence of cell migration and differentiation is maintained, and the full complement of terminally differentiated cells is retained on the surface of the culture for up to 65 days following subculture. The pattern of histodifferentiation of cultured stratified squamous epithelium differs according to the matrix upon which it is grown. Pliant, fine meshed gels of type III collagen are corrugated by the cultured keratinocytes with adjustments occurring in the various suprabasal cell strata that result in the retention of a flat stratum corneum. Such pliant gels can be stabilized by pouring a supporting underlayer of coarse type I guinea pig collagen. Keratinocytes grown directly on the irregular surface of guinea pig type I collagen migrate into spaces between collagen fibrillar bundles and aberrantly keratinize 20-30 days following subculture. Keratinocytes grown on a basement membrane do not aberrantly keratinize, suggesting that contact with a basement membrane may suppress signals for keratinocyte differentiation. Keratinocytes also form hemidesmosomes opposite a basement membrane but not opposite collagen fibrils. The keratin pattern of oral keratinocytes cultured in different configurations does not change; a finding that indicates that a greater degree of tissue organization does not automatically result in the synthesis of keratins more characteristic of upper cell strata or cornified cells in the native tissue.

Behaviour of fibroblasts and epidermal cells cultivated on analogues of extracellular matrix

A porous collagen sponge can be used for supporting epidermal cells and fibroblasts in order to manufacture an artificial skin. Fibroblasts were grown on analogues of extracellular matrix containing collagen and glycosaminoglycans and/or glycoproteins. Cell replication, and also infiltration of fibroblasts, were enhanced by the presence of hyaluronic acid and/or fibronectin. Epidermal cells grown on a collagen sponge have been characterized by microscopic observations. Epidermal cells on the surface of the sponge showed an incomplete differentiation in comparison to normal skin; clumps of epidermal cells were found in the interior of the sponge. Epidermal cell replication was enhanced in the presence of collagen sponge seeded with fibroblasts.