Cytotoxicity testing of wound dressings using normal human keratinocytes in culture

In vitro effects of wound-dressings on key wound healing properties of dermal fibroblasts

Healing of complex wounds requires dressings that must, at least, not hinder and should ideally promote the activity of key healing cells, in particular fibroblasts. This in vitro study assessed the effects of three wound-dressings (a pure Ca2+ alginate: Algostéril®, a Ca2+ alginate + carboxymethylcellulose: Biatain alginate® and a polyacrylate impregnated with lipido-colloid matrix: UrgoClean®) on dermal fibroblast activity. The results showed the pure calcium alginate to be non-cytotoxic, whereas the other wound-dressings showed moderate to strong cytotoxicity. The two alginates stimulated fibroblast migration and proliferation, whereas the polyacrylate altered migration and had no effect on proliferation. The pure Ca2+ alginate significantly increased the TGF-β-induced fibroblast activation, which is essential to healing. This activation was confirmed by a significant increase in Vascular endothelial growth factor (VEGF) secretion and a higher collagen production. The other dressings reduced these fibroblast activities. The pure Ca2+ alginate was also able to counteract the inhibitory effect of NK cell supernatants on fibroblast migration. These in vitro results demonstrate that tested wound-dressings are not equivalent for fibroblast activation. Only Algostéril was found to promote all the fibroblast activities tested, which could contribute to its healing efficacy demonstrated in the clinic.

Process and applications of alginate oligosaccharides with emphasis on health beneficial perspectives

Alginates are linear polymers comprising 40% of the dry weight of algae possess various applications in food and biomedical industries. Alginate oligosaccharides (AOS), a degradation product of alginate, is now gaining much attention for their beneficial role in food, pharmaceutical and agricultural industries. Hence this review was aimed to compile the information on alginate and AOS (prepared from seaweeds) during 1994-2020. As per our knowledge, this is the first review on the potential use of alginate oligosaccharides in different fields. The alginate derivatives are grouped according to their applications. They are involved in the isolation process and show antimicrobial, antioxidant, anti-inflammatory, antihypertension, anticancer, and immunostimulatory properties. AOS also have significant applications in prebiotics, nutritional supplements, plant growth development and others products.

Effect of non-adhering dressings on promotion of fibroblast proliferation and wound healing in vitro

Non-adhering dressings are commonly used during granulation, tissue formation, and re-epithelialization. Elucidating cytotoxic effects and influence on proliferation/migration capacity of cells like fibroblasts is of interest. Dressings’ effects were investigated by comprehensive in vitro approach: (1) MTT assay measuring cell viability after direct contact, (2) ATP assay determining effects on cell proliferation, and (3) scratch wound assay featuring an in vitro wound healing model. One cotton-based dressing with vaseline (vas) was included in the study and four polyester dressings containing vas and technology-lipido-colloid matrix (TLC), carboxymethylcellulose (CMC), hydrocolloid (HC), or glycerin (gly) as additives. A polyamide dressing with vas + CMC and three silicone-based dressings (AT, CC, M) were tested. Polyester + vas + CMC did not negatively affect cell viability or proliferation but it was found that fibroblast layers appeared more irregular with decreased F-actin network structure and tubulin density possibly leading to hampered scratch closure. Silicone AT, polyester + gly and polyamide + vas + CMC caused distinct cell damage. The latter two further reduced cell viability, proliferation and scratch healing. From the overall results, it can be concluded that cotton + vas, polyester + TLC, polyester + vas + HC and the silicone dressings CC and M have the potential to prevent damage of newly formed tissue during dressing changes and positively influence wound healing.

Effects of wound dressings on cultured primary keratinocytes

Autologous cell-spray grafting of non-cultured epidermal cells is an innovative approach for the treatment of severe second-degree burns. After treatment, wounds are covered with dressings that are widely used in wound care management; however, little is known about the effects of wound dressings on individually isolated cells. The sprayed cells have to actively attach, spread, proliferate, and migrate in the wound for successful re-epithelialization, during the healing process. It is expected that exposure to wound dressing material might interfere with cell survival, attachment, and expansion. Two experiments were performed to determine whether some dressing materials have a negative impact during the early phases of wound healing. In one experiment, freshly isolated cells were seeded and cultured for one week in combination with eight different wound dressings used during burn care. Cells, which were seeded and cultured with samples of Adaptic(®), Xeroform(®), EZ Derm(®), and Mepilex(®) did not attach, nor did they survive during the first week. Mepitel(®), N-Terface(®), Polyskin(®), and Biobrane(®) dressing samples had no negative effect on cell attachment and cell growth when compared to the controls. In a second experiment, the same dressings were exposed to pre-cultured cells in order to exclude the effects of attachment and spreading. The results confirm the above findings. This study could be of interest for establishing skin cell grafting therapies in burn medicine and also for wound care in general.

An in vitro evaluation of the cell toxicity of honey and silver dressings

OBJECTIVE

To establish whether honey and silver-impregnated dressings used by wound-healing practitioners are cytotoxic in vitro to human skin keratinocytes and dermal fibroblasts.

METHOD

Human keratinocyte and fibroblast tissue cultures were established in vitro. Untreated cultures served as controls (group I). Small dressing implants of monofloral, medicinal honey (L-Mesitran) (group 2) and nanocrystalline silver (Acticoat) (group 3) were placed in test wells and co-cultured with each of the two cell lines. Morphological changes, including cell toxicity, were assessed using inverted microscopy, trypan blue staining and the Rosdy and Clauss cell toxicity scoring system.

RESULTS

Untreated cultures consisting of both keratinocytes and fibroblasts (group 1) were established in 90% of all cases. In group 2, cultures with honey-impregnated implants, cell proliferation remained present at two and four months. Cell viability remained intact and cell toxicity was not evident at four months after continuous tissue culture. In group 3, marked toxicity was observed with high non-viability staining and cell-scoring counts compared with groups 1 and 2 (p<0.05). This demonstrates that the silver interfered with epidermal cell proliferation and migration, implying that it contains cytotoxic material.

CONCLUSION

The honey-based product showed excellent cytocompatibility with tissue cell cultures compared with the silver dressing, which demonstrated consistent culture and cell toxicity. Further studies are needed to assess if these comparative in-vitro findings should influence a clinician's choice of wound dressing.

Development of two alginate-based wound dressings

Two types of new alginate-based wound dressings, Type-AP and Type-AE, were fabricated by the EDC-activated crosslinking of alginate with Polyethyleneimine and Ethylenediamine, respectively. As compared with the commercial non-woven wound dressing, Kaltostat, both Type-AP and Type-AE dressings had higher degradation temperature, lower calcium content, and a sponge-like macroporous structure. In addition, these two alginate-based dressings had higher mechanical stress (12.37 +/- 1.72 and 6.87 +/- 0.5 MPa for Type-AP and -AE, respectively) and higher water vapor transmission rates (both about 3,500 g/m2/day) than Kaltostat (0.87 +/- 0.12 MPa and 2,538 g/m2/day). Fibroblasts proliferated faster on these two newly developed wound dressings at a higher rate as compared with that on Kalostat dressing. The results of animal study showed that the wounds treated with either Type-AP or Type-AE dressings healed faster than Kaltostat with less encapsulation of residuals by fibrous tissue and more neo-capillary formation. These two newly developed Type-AP and Type-AE porous wound dressings thus have great potential for clinical applications.

Treating the chronic wound: A practical approach to the care of nonhealing wounds and wound care dressings

Chronic wounds are a major healthcare problem costing the United States billions of dollars a year. The American Academy of Dermatology has underscored the significance of wound care in dermatological practice. It is critical for all dermatologists to understand the elements of diagnosis and therapy. We emphasize major aspects of diagnosis and present a simple classification of wound dressings with guidelines for usage and relative cost data.

LEARNING OBJECTIVE

After completing this learning activity, participants should be able to diagnose common types of chronic wounds, formulate a therapeutic plan, and describe the major classes of topical therapies and dressings for the chronic wound.

Preparation of carbon nanotube-alginate nanocomposite gel for tissue engineering

A novel scaffold material based on an alginate hydrogel which contained carbon nanotubes (CNTs) was prepared, and its mechanical property and biocompatibility evaluated. Soluble CNTs were prepared with acid treatment and dispersed in sodium alginate solution as a cross-linker. After which, the mechanical property (elastic deformation), saline sorption, histological reaction, and cell viability of the resultant nanocomposite gel (CNT-Alg gel) were evaluated. The CNT-Alg gel showed faster gelling and higher mechanical strength than the conventional alginate gel. Saline sorption amount of freeze-dried CNT-Alg gel was equal to that of the alginate gel. In terms of histological evaluation and cell viability assay, CNT-Alg gel exhibited a mild inflammatory response and non-cytotoxicity. These results thus suggested that CNT-Alg gel could be useful as a scaffold material in tissue engineering with the sidewalls of CNTs acting as active sites for chemical functionalization.

Effect of Different Wound Dressings on Cell Viability and Proliferation

BACKGROUND

Many new dressings have been developed since the early 1980s. Wound healing comprises cleansing, granulation/vascularization, and epithelialization phases. An optimum microenvironment and the absence of cytotoxic factors are essential for epithelialization. This study examines the effect of extracts of different wound dressings on keratinocyte survival and proliferation.

METHODS

Keratinocyte cultures were exposed for 40 hours to at least three extracts of each of the following wound dressings, which were tested in octuplicate: Acticoat, Aquacel-Ag, Aquacel, Algisite M, Avance, Comfeel Plus transparent, Contreet-H, Hydrasorb, and SeaSorb. Silicone extract provided the reference material. Controls were included of cells cultured in medium that had been incubated under conditions identical to those used with the extracts. Cell survival (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide reduction) and proliferation (5-bromo-2':-deoxyuridine incorporation) were measured.

RESULTS

Extracts of silver-containing dressings (Acticoat, Aquacel-Ag, Contreet-H, and Avance) were most cytotoxic. Extracts of Hydrasorb were less cytotoxic but markedly affected keratinocyte proliferation and morphology. Extracts of alginate-containing dressings (Algisite M, SeaSorb, and Contreet-H) demonstrated high calcium concentrations, markedly reduced keratinocyte proliferation, and affected keratinocyte morphology. Extracts of Aquacel and Comfeel Plus transparent induced small but significant inhibition of keratinocyte proliferation.

CONCLUSIONS

The principle of minimizing harm should be applied to the choice of wound dressing. Silver-based dressings are cytotoxic and should not be used in the absence of infection. Alginate dressings with high calcium content affect keratinocyte proliferation probably by triggering terminal differentiation of keratinocytes. Such dressings should be used with caution in cases in which keratinocyte proliferation is essential. All dressings should be tested in vitro before clinical application.

Effect of Viscous Injectable Pure Alginate Sol on Cultured Fibroblasts

BACKGROUND

Alginates have a wide variety of potential clinical applications, including use in cell encapsulation, drug delivery, and tissue engineering. Although the compounds are typically used in the form of a calcium hydrogel, alginates in this form possess several disadvantages, including low biodegradability, induction of foreign body reactions, and cytotoxicity secondary to Ca2+ efflux and contamination with bioincompatible substances. Thus, the goal of the present study was to develop a new method of obtaining sterilized, pure, highly viscous alginate sol from seaweed alginates and to determine its utility as an injectable antiadhesion drug.

METHODS

Viscous injectable pure alginate sol was produced from a commercially available sodium alginate, and its molecular and physical characteristics were analyzed. The biological properties of the viscous injectable pure alginate sol were analyzed using cultured fibroblasts prepared from the dorsal skin of neonatal rats to determine its biocompatibility and its effects on cell proliferation, cell migration, and collagen lattice contraction.

RESULTS

The mannuronic acid-to-glucuronic acid ratio of viscous injectable pure alginate sol, as determined by nuclear magnetic resonance studies, was 1.2, and its viscosity at 5 percent was 17,800 mPa. Purification used to produce viscous injectable pure alginate sol decreased contamination by insoluble particles by 20 percent and decreased polyphenol concentration by 17 percent. In vitro analyses with cultured fibroblasts demonstrated that viscous injectable pure alginate sol had excellent biodegradability and biocompatibility and that viscous injectable pure alginate sol inhibited fibroblast proliferation and migration. Furthermore, assessment of collagen contraction with floating fibroblast-loaded collagen lattices indicated that viscous injectable pure alginate sol enhanced wound healing in surrounding connective tissues.

CONCLUSIONS

The authors conclude that viscous injectable pure alginate sol can inhibit scar formation by presenting a physical barrier to invading fibroblasts and by enhancing wound healing of surrounding tissues.

Prolonged ectopic calcification induced by BMP-2-derived synthetic peptide

Bone morphogenetic protein-2 (BMP-2) promotes the formation and regeneration of bone and cartilage, and therefore constitutes the most promising candidate for a bone repair material. However, it also has a wide range of functions, such as in organogenesis and apoptosis. Therefore, we investigated a novel synthetic peptide corresponding to residues 73-92 of BMP-2. This peptide bound to a BMP-2-specific receptor and elevated both alkaline phosphatase activity and osteocalcin mRNA in the murine cell line, C3H10T1/2. The 73-92 peptide also induced ectopic calcification when conjugated to a covalently crosslinked alginate gel. Here we report that the 73-92 peptide-conjugated alginate gel showed prolonged ectopic calcification for up to 7 weeks in rat calf muscle. In contrast, rhBMP-2-impregnated collagen gel showed maximum ectopic calcification at 3 weeks, and the calcified products that had formed disappeared after 5 weeks. Histological examination showed that the 73-92 peptide-conjugated alginate gel induced many osteoblast-like cells and few osteoclasts. In contrast, rhBMP-2-impregnated collagen gel induced many osteoclasts. These results suggest that the 73-92 peptide on alginate gel remains active at the implanted site, continuously induces differentiation of osteoblast precursor cells into osteoblasts, and activates osteoblasts to promote ectopic calcification.

Comparison of different wound dressings on cultured human fibroblasts and collagen lattices

OBJECTIVE

We compared the effects on cultured human fibroblasts of a new non-adhesive wound dressing, Urgotul, with five other wound dressings. Urgotul is a hydrocolloid dressing; the comparator dressings included impregnated gauze and modern wound dressings.

METHOD

Cultures in monolayer were used to study the morphology and growth of fibroblasts. The Bell model of cultured dermis equivalents was used to investigate myofibroblast differentiation. These cultures were labelled a-SM actin and F-actin.

RESULTS

Two of the tested dressings induced cytotoxic effects. They were found to inhibit cell growth (greater than 60%) and to disturb cell shape and cytoskeletal differentiation. Urgotul and the remaining three dressings showed no effect on proliferation. However, some of them modified fibroblast morphology and affected F-actin distribution.

CONCLUSION

Depending on their nature and components, wound dressings may respect or affect fibroblast behaviour in vitro (proliferation, morphology and a-SM actin and F-actin distribution). The significance of these in vitro observed findings require further investigations.

Cytotoxicity evaluation of gelatin sponges prepared with different cross-linking agents

Gelatin is a natural polymer used in pharmaceutical and medical applications, especially in the production of biocompatible and biodegradable wound dressings and drug delivery systems. Gelatin granules hydrate, swell and solubilize in water, and rapidly degrade in vivo. The durability of these materials could, however, be prolonged by cross-linking by aldehydes, carbodiimides, and aldose sugars, but the biocompatibility of collagenous biomaterials is profoundly influenced by the nature and extent of cross-linking. In this study, gelatin sponges were prepared by using various cross-linkers such as glutaraldehyde (GA), 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDAC), and D-fructose. The effects of the type and the amount of cross-linker on thermal and mechanical properties, stability, and cytotoxicity were investigated. The mechanical analysis data showed that an increase in the amount of GA in the sponge structures caused a slight increase in the modulus of elasticity but had almost no effect on the tensile strength. Increase in the EDAC concentration produced a maximum in the modulus of elasticity and tensile strength values. The stability of the sponges and the time required for complete degradation in aqueous media increased in parallel with the cross-linker content. In vitro studies carried out with fibroblast cells demonstrated a higher cell viability for the samples cross-linked with low concentrations of GA than for those cross-linked with EDAC.

Reconstruction of rat peripheral nerve gap without sutures using freeze-dried alginate gel

Many materials have been used for artificial tubular prostheses to assist peripheral nerve gap reconstruction. However, the clinical use of these devices has been restricted because a microsurgical procedure requires specialized techniques and expensive equipment, such as operating microscope systems. Therefore the authors developed a new gluing method, without sutures, that uses freeze-dried alginate gel. A 7-mm gap in the sciatic nerve of rats was bridged with freeze-dried alginate gel. Regeneration was evaluated by electrophysiologic testing and histologic study. Eighteen weeks after surgery, functional reinnervation of motor and sensory nerves had occurred, as demonstrated by recovery of compound muscle action potentials (CMAP), compound nerve action potentials (CNAP), and somatosensory-evoked potentials (SEP). Histologically, many regenerated nerve fasciculi, including myelinated and unmyelinated fibers, were observed and the implanted alginate gel had disappeared. In conclusion, a gluing technique using alginate gel is a potential alternative to the conventional nerve autograft technique. Advantages include simple application and rapid repair. Freeze-dried alginate gel is a promising material for artificial nerve guides for peripheral nerves and also could be used for repair of disrupted pathways in central nervous tissue that is amorphous and cannot be sutured.

In vivo evaluation of a novel alginate dressing

Alginate dressings are currently used in the management of epidermal and dermal wounds, and provide a moist environment that leads to rapid granulation and reepithelialization. However, a cytotoxic effect on proliferation of fibroblasts and residual material with inflammation in healing wounds have been reported recently. We have developed a new alginate dressing (AGA-100), which does not have an inhibitory effect on proliferation of fibroblasts. The purpose of this study was to evaluate the new alginate dressing with respect to wound healing in full- and partial-thickness pig wounds and with respect to biodegradation following implantation into rabbit muscle. Kaltostat and Sorbsan, both well-established commercial dressings, were used as control. The closure rate of full-thickness wounds treated with AGA-100 was significantly higher on day 15 compared with that with Kaltostat and Sorbsan. Reepithelialization rate of partial-thickness wounds treated with Sorbsan was statistically significantly lower on day 3 than those with the other two dressings. As to dressing debris remained in the healing wound, a large amount of foreign debris was noted in all the full-thickness wounds treated with Kaltostat or Sorbsan, while only about one-third of wounds treated with AGA-100 showed a little dressing debris. AGA-100 implanted into the muscle of rabbits was bioresorbed completely within 3 months. Therefore, dressing residue in AGA-100-treated full-thickness wounds might be fully absorbed in a few months. In conclusion, it is shown that our newly developed AGA-100 possesses superior properties compared with typical alginate dressings.

Evaluation of a novel alginate gel dressing: cytotoxicity to fibroblasts in vitro and foreign-body reaction in pig skin in vivo

Calcium alginate dressings have beneficial effects on wound healing by providing a moist wound environment. However, cytotoxicity and the nonbiodegradable nature of calcium alginate dressings induce unresolved chronic foreign-body reaction. In this study, a novel freeze-dried alginate gel dressing (AGA-100) low in calcium ions was evaluated for cytotoxicity to L929 cells in vitro and in full-thickness pig wounds in vivo. Cytotoxicity testing on L929 cells showed the cytocompatibility of AGA-100 extracts, while extracts from Kaltostat, a well-established alginate dressing, induced cytopathic effects. In an in vivo study using pigskin, AGA-100, Kaltostat, and gauze were applied on 1-in-diameter circular full-thickness wounds on the back of pigs and the time course of wound closure was evaluated. Kaltostat and gauze dressings were used as controls. For histologic evaluation, wound tissue was harvested on day 18. AGA-100-treated wounds showed rapid wound closure compared to control wounds on day 15. Foreign-body reaction was marked in Kaltostat- and gauze-treated wounds, and differed significantly from AGA-100-treated wounds. Based on these data, AGA-100 could reduce the cytotoxicity to fibroblasts and foreign-body reaction that have been observed with currently available calcium alginate dressings; it was also found to be useful as an alginate dressing.

Effects of calcium alginate on cellular wound healing processes modeled in vitro

Although the clinical experience with calcium alginate has been generally good, well-controlled studies examining the effect of such dressings on the processes of wound healing have not been conducted. The healing of cutaneous ulcers requires the development of a vascularized granular tissue bed, filling of large tissue defects by dermal regeneration, and the restoration of a continuous epidermal keratinocyte layer. These processes were modeled in vitro in the present study, utilizing human dermal fibroblast, microvascular endothelial cell (HMEC), and keratinocyte cultures to examine the effect of calcium alginate on the proliferation and motility of these cultures, and the formation of capillarylike structures by HMEC. This study demonstrates that the calcium alginate tested increased the proliferation of fibroblasts but decreased the proliferation of HMEC and keratinocytes. In contrast, the calcium alginate decreased fibroblast motility but had no effect on keratinocyte motility. There was no significant effect of calcium alginate on the formation of capillarylike structures by HMEC. The effects of calcium alginate on cell proliferation and migration may have been mediated by released calcium ions. These results suggest that the calcium alginate tested may improve some cellular aspects of normal wound healing, but not others.

Bacterial recolonization of the skin under a polyurethane drape in hip surgery

This study investigated the proliferation of skin flora under polyurethane (PU) wound dressings following surgical interventions. In vitro the film proved to be impermeable to staphylococci. However, bacteria migrated under the film, showing a preference for the adhesive rather than the adhesive-free areas. The skin of 43 patients with incisions of the proximal thigh was covered postoperatively with a transparent PU-dressing. This was examined bacteriologically preoperatively and at the third and seventh postoperative days. The use of an antiseptic (povidone iodine) reduced the number of colony forming units in the postoperative skin but at the same time there was a significant reduction of bacteria under the film in comparison with the uncovered skin. The numbers and species of bacteria in different areas under the film did not suggest a spread of organisms from the uncovered skin to the skin under the film, but rather that there was a multifocal microbial regeneration.

Cytotoxicity of wound dressing materials assessed using cultured skin equivalents

An in vitro system, based on the Bell model of cultured composite skin equivalents, was used to assess the effect of a number of wound dressing materials on DNA synthesis. DNA synthesis was quantified using immunocytohistochemical identification of incorporated bromodeoxy-uridine and the percentage of labelled cells measured, following 7 days' exposure to the dressing material. Differences in labelling index were observed from replica gels covered by different dressing materials and between dressings of the same type of material, but made by different manufacturers.

Toxicity testing of wound dressing materials in vitro

There is a bewildering array of dressing materials available for wound coverage. The choice of dressing is often by local custom or practical experience. We wished to investigate if different dressings varied in their ability to either stimulate or inhibit proliferative activity and differentiation in an in vitro test system. We have used a number of test systems for this study. Human dermal fibroblast and keratinocyte cultures were used to screen for proliferative and cytotoxic effects. A more complex "organotypic" method involving fibroblast-impregnated collagen gels overlaid with epidermal keratinocytes was used to investigate effects on differentiation. Dressings were selected from each of the major types available, from simple gauze to hydrocolloids. Of the dressings tested, some reduced cell growth rates but the majority showed no major effect on proliferation or differentiation. Of those displaying an effect, only one could be attributed to cytotoxicity.

In vitro biocompatibility of a polyurethane catheter after deposition of fluorinated film

The in vitro biocompatibility of an experimental surface-treated polyurethane was compared with an untreated polyurethane already used for intravascular catheters. The experimental surface was coated with a fluorinated film using a glow discharge treatment. Neither of the catheters was cytotoxic for L929 murine fibroblasts, caused platelet adhesion or release reaction, or changed the mean platelet volume. The surface-treated polyurethane, however, caused a higher adhesion of Staphylococcus aureus than did the untreated one. Therefore, using in vitro testing, it has been ascertained that the examined material, though not being cytotoxic and not modifying platelet behaviour, could favour bacterial adherence.

Subperiosteal behaviour of alginate and cellulose wound dressing materials

A histological comparison was undertaken of the tissue response to a new sodium calcium alginate material (Kaltostat) and an oxidized regenerated cellulose wound dressing (Surgicel) when implanted between bone and periosteum in the jaws at intervals of up to 24 wk. Both biomaterials caused a foreign body reaction, persisting up to 12 wk after surgery. New bone formation occurred along the surface of the mandible in some specimens, but was not apparently related to the implants. It was concluded that the implantation of Kaltostat or Surgicel between bone and periosteum in the jaws caused a delay in wound healing, and had no effect on bone induction.

Alginate fiber dressing for oral mucosal wounds

The aim of this study was to evaluate the effect on hemostasis and wound healing of a proprietary alginate fiber dressing when applied to a wound of the buccal mucosa of approximately 2 mm depth. The study showed a significant reduction in the number of residual bleeding points in shallow wounds when the alginate fiber dressing was applied for 5 minutes as compared with the use of non-alginate-impregnated surgical gauze. There was no significant difference in the rate of epithelial repair of the test and control sites nor in the area of the resulting mucosal scar. In addition, there was no significant difference in the numbers of tissue components in the submucosa. It is concluded that the alginate fiber dressing material evaluated in this study may be effective as a hemostatic mucosal dressing in shallow wounds, but it does not accelerate mucosal wound healing.

Toxicity of cyanoacrylates in vitro using extract dilution assay on cell cultures

Comparative cytotoxicity testing of four cyanoacrylate adhesives suggested for orthopaedic applications was performed. These substances were placed in complete culture medium with serum and the resulting extraction fluids were tested on L 929 cells and human lymphocytes. Testing procedures include cell morphology assessment using light microscopy and vital dyes, cell counting using a computer-assisted image analysis system, cell growth measurement using total protein content assay and cell viability assessment using the MTT method. Quantitation of the toxicity of the degradation products released by cyanoacrylates in the extracts was achieved and differences in the cytopathic effect related to the chemical composition of the cyanoacrylates were found. A toxicity rating of the assayed cyanoacrylate adhesives was obtained as follows (in order of increasing toxicity): BCA < xCA < ECAg < ECAl.

Cell culture methods for testing biocompatibility

Cell culture systems may be of value in testing the biocompatibility of prosthetic materials before they are introduced into clinical use. In recent years, in vitro methods for assaying biomaterials have gained in importance owing to the growing concern over the use of animals for biomaterials testing. Significant effort is therefore being focused toward developing predictive and quantitative, but also simple and reliable, methods of testing using cultured cells. At present, a number of methods for measuring both the cytotoxicity and the specific cytocompatibility of different materials are available. The usefulness of these systems is no longer confined to screening new materials; they can be used to study the mechanisms of action of various materials during tissue/material interaction. This paper reviews the published literature on the use of cell culture models in evaluating biocompatibility and reports on the personal experience of the authors, who have been using cell culture systems for many years and for different purposes.

Tissue response to a haemostatic alginate wound dressing in tooth extraction sockets

Kaltostat is a new haemostatic wound dressing composed of non-woven sodium calcium alginate fibres, and was originally developed to cover exposed wounds of the skin. A histopathological study was undertaken to determine the tissue response to Kaltostat in healing tooth sockets, to obtain a comparison with oxidised regenerated cellulose (Surgicel). Tooth sockets filled with blood clot acted as controls. The results showed that both biomaterials delayed wound healing in the early phase (1-4 weeks), giving rise to foreign body reactions. At 12 weeks there was little difference between the control sockets and the sockets containing the test materials, although remnants of retained dressing materials were identified. Healing of the tooth sockets was complete at 24 weeks.

Toxicity of L-ascorbic acid to L929 fibroblast cultures: relevance to biocompatibility testing of materials for use in wound management

Fibroblast cultures are often used to evaluate materials intended for medical use, cytotoxicity being taken as an indicator of bioincompatibility. Such an approach has previously been taken with ascorbic acid in determining its value in wound healing. We have now reexamined the toxicity of L-ascorbic acid to L929 fibroblast cells in culture. Concentrations of ascorbic acid between 0.5 mM and 11 mM were tested. At concentrations above 2 mM, ascorbic acid was found to inhibit cell proliferation, with cell viability decreasing as the concentration was increased. This effect could be prevented by the addition of either superoxide dismutase or catalase to the culture medium. Assays of glutathione and glutathione disulfide were carried out on 8 day old cultures exposed for 24 h to the same concentrations of ascorbic acid. A dose-related depletion of glutathione occurred whilst glutathione disulfide levels remained essentially constant. Lactate dehydrogenase and glucose-6-phosphate dehydrogenase activities were induced by ascorbic acid at all concentrations tested but the ratio of NADP to NADPH nevertheless increased as the concentration of ascorbic acid increased. Finally, ATP in cells from 8-day-old cultures became depleted in the presence of ascorbic acid at concentrations in excess of about 5 mM when assayed after 24 h incubation. These biochemical changes and the concomitant cytostatic/cytotoxic effects may be ascribed to the reactive oxygen species produced by the autoxidation of ascorbic acid in the culture medium. Ascorbic acid breakdown products appeared not to be directly involved. In addition, our results suggested that superoxide acted cooperatively with hydroxyl to elicit these effects on the fibroblasts. It is evident from this study that the microenvironment surrounding fibroblasts in culture may differ fundamentally from that surrounding fibroblasts in a healing wound, making it impossible to extrapolate directly to an in vivo situation and hence to make any recommendations from these results concerning the use of ascorbic acid in wound healing.

Skin organ culture model to test the toxicity of polyoxyethylene networks

Films of polyoxyethylene network were prepared from two types of triethoxysilane-terminated prepolymers. In this way, films of polyoxyethylene network with possible applications in the biomedical field could be made easier. To test their biocompatibility, these networks were added to organ cultures of adult human skin and embryonic chicken skin. A rapid toxic effect was observed, especially with the urethane-linked network. Enzymatical degradation of the network by enzymes in the culture medium might be responsible for the formation of toxic metabolites. Testing of related chemical compounds in our in vitro assay suggested that the formation of a silane group with an amino terminal is most likely to be responsible for the toxic effects observed.

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.

Terminal epidermal differentiation of human keratinocytes grown in chemically defined medium on inert filter substrates at the air-liquid interface

A fully differentiated epithelium having the features of epidermis was obtained in vitro by culturing second-passage normal human keratinocytes (NHK) in the chemically defined medium MCDB 153 on inert filter substrates at the air-liquid interface for 14 d. Vertical sections stained for histology and indirect immunofluorescence studies show a correct stratification and expression of differentiation markers. The presence of desmosomes, keratohyalin granules, and lamellar granules, and the formation of a more than ten-layers stratum corneum was evidenced by electron microscopy. Moreover, lipids typical for differentiated epidermis were present in these cultures, including ceramides, which are thought to be responsible for the relative impermeability of the stratum corneum. Under our culture conditions, i.e., in defined medium and at the air-liquid interface, the use of de-epidermized dermis as a substrate did not stimulate keratinocyte differentiation more than acetate cellulose or polycarbonate filter membrane substrates. The obtaining of a well-differentiated epidermis grown in vitro on inert filters in a chemically defined medium should be useful as a standard system for studying epidermal differentiation, re-epidermization, cytotoxicity, epidermal permeation, and transepidermal drug delivery.