Cytotoxicity testing of wound dressings using methylcellulose cell culture

Green, pH-Sensitive, Highly Stretchable, and Hydrogen Bond-Dominated Ionogel for Wound Healing Activity

Traditional hydrogel dressings generally have poor mechanical properties and stability when subjected to external stress due to the undesirable chain entanglement structure of their single valence bond compositions. Therefore, it is particularly important to develop a type of gel dressing with good mechanical strength, stability, and environment-friendly monitoring. In this work, a transparent, pH-sensitive, highly stretchable, and biocompatible anthocyanidin ionogel dressing was prepared, realizing green and accurate detection. Attributed to the antibacterial activity of the ionic liquid, the biocompatibility of the pectin, and the ability to scavenge free radicals of the anthocyanidin, the ionogel dressing exhibited excellent re-epithelialization in the 14 day wound healing process. Besides, changes in pH values monitoring of the ionogel over 3 days coincided with normal wound exudate. The obtained ionogel also showed good water retention, swelling properties, mechanical stretchability, and 5 week stability, illustrating great potential in wound dressings.

The assessment and management of hypergranulation

Wound healing follows a process of four distinct phases: haemostasis, inflammation, proliferation and maturation. Problems can arise in any of these phases, delaying the wound process. Hypergranulation (also known as overgranulation) during the proliferation phase occurs when granulation tissue over grows beyond the wound surface. Such wounds have a discoloured, raised or swollen appearance and bleed easily. The cause may be infection, the effects of friction on the wound area, nutritional deficit or stress. Treatments will depend on the cause. There is a lack of studies on treatments for hypergranulaton and more research is required.

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

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

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.

Biocompatibility and stability of disulfide-crosslinked hyaluronan films

Hyaluronan (HA) can be chemically modified to engineer robust materials with pre-selected mechanical properties and resorption rates that can be dictated by the intended clinical use. Disulfide-crosslinked HA films were prepared by air oxidation of thiol-modified HA, followed by treatment with 0.3% hydrogen peroxide. The degradation of the disulfide-crosslinked films in vitro was very slow (<10% in 7 days) in buffer alone and shorter (t1/2=3-5 days) in the presence of hyaluronidase (HAse). The cytocompatibility of the disulfide-crosslinked HA films was determined using two separate conditions: (i) in vitro culture of mouse fibroblasts in indirect contract with the films, and (ii) in vitro culture of fibroblasts directly on films coated with poly d-lysine. Excellent cytocompatibility was observed in murine fibroblasts that were cultured in indirect contact with thiolated HA films. Although cells were unable to attach and spread on thiolated HA films, pre-coating the thiolated HA films with poly D-lysine resulted in attachment and spreading equivalent to that observed on polystyrene. Rates of resorption in vivo were obtained by subcutaneous implantation of disulfide-crosslinked HA films into the backs of Wistar rats. Biocompatibility in vivo was determined in both subcutaneous flank and peritoneal cavity implantation of the films in Wistar rats. The disulfide-crosslinked HA films were less than 30% resorbed after 42 days in vivo, and histochemical and cytochemical analysis indicated that the films were well-tolerated with mild inflammatory response at both sites of implantation.

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.

A hyaluronan-based nerve guide: in vitro cytotoxicity, subcutaneous tissue reactions, and degradation in the rat

We investigated possible cytotoxic effects, biocompatibility, and degradation of a hyaluronan-based conduit for peripheral nerve repair. We subjected the conduits to an in vitro fibroblast cytotoxicity test and concluded that the conduits were not cytotoxic. Subsequently, we implanted the conduits subcutaneously in rats, in order to investigate tissue reactions and biodegradation. Initially, a fibrin matrix was formed around the material, while the surroundings were relatively quiet. Macrophages (MØ) migrated to the conduits and formed giant cells next to the material after 5 days. The maximum presence of MØ was found after 3-6 weeks. The appearance of MHC class II cells showed a similar pattern. Highest numbers of giants reached a maximum after 6-12 weeks. Angiogenesis was started in the surroundings of the hyaluronan-based conduit within a few days. Massive ingrowth of blood vessels into the biomaterial was found after 6 weeks as well as cellular ingrowth into the lumen of the tube. At that time the tubular structure of the conduit was lost and loose biomaterial fibers were observed. The results show that a hyaluronan-based conduit is not cytotoxic and shows good biocompatibility. Such a conduit may be suitable as a guide in peripheral nerve repair.

Flexible chitin films as potential wound-dressing materials: wound model studies

Chitin films possessing increased flexibility, softness, transparency, and conformability have been prepared. These attributes enable the potential application of chitin films as occlusive, semipermeable film wound dressings similar to commercial products such as Opsite trade mark. The chitin films are generally nonabsorbent, exhibiting a total weight gain of only up to 120-160% in physiological fluid. Dry chitin films transpire water vapor at a rate of about 600 g/m(2)/24 h, similar to commercial polyurethane-based film dressings, but rises to 2400 g/m(2)/24 h, when wet, which is higher than the water vapor transmission rate of intact skin. The chitin films are nontoxic to human skin fibroblasts, maintaining 70-80% cell viability. Wound studies using a rat model showed no signs of allergenicity or the high inflammatory response associated with biodegradable biomaterials. The chitin films displayed accelerated wound-healing properties. Based on histological examination, wound sites dressed with the chitin films stabilized and healed faster, and appeared stronger than those dressed with Opsite trade mark and gauze dressings after 7 days of healing.

In vitro biocompatibility of biodegradable dextran-based hydrogels tested with human fibroblasts

The cytotoxicity of dextran T40, methacrylated dextran (dex-MA) and hydroxyethyl-methacrylated dextran (dex-HEMA), dextran-based hydrogel discs and microspheres, and their degradation products, was studied by measuring the cell proliferation inhibition index (CPII) on human fibroblasts in vitro. In addition, during the 72 h incubation period light-microscopic observations were performed daily. After 24 h of incubation with dextran and dex-HEMA polymers, the cells showed elongated or spider-like forms, some lipid droplets and intracellular granula, indicative of pinocytosis and internalization of the polymers. During the next two days, the fibroblasts' appearance did not change. Methacrylic acid (MAA), formed by hydrolysis of dex-HEMA, did not influence the cell morphology. Dex-HEMA polymer solutions with a low and high degree of substitution (DS) at 100 mg/ml caused a CPII of 30-40% after 72 h. This is less than 10% growth inhibition per cell cycle and statistically not different from the CPII induced by 100 mg/ml dextran T40. Growth inhibition induced by MAA was also low. The various dex-MA hydrogel discs caused similar low growth inhibition. Interestingly, hydrogel microspheres of dex-MA and dex-(lactate-)HEMA caused a CPII of only 0-20% after 72 h. The results presented in this study demonstrate that methacrylate-derivatized dextran hydrogels show good biocompatibility in vitro making these degradable biomaterials promising systems for drug delivery purposes.

Characterization and biocompatibility of epoxy-crosslinked dermal sheep collagens

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

The cytocompatibility of hydrocolloid dressings

The purpose of this study was to evaluate the effect on fibroblast proliferation of hydrophilic particles isolated from six commercial hydrocolloid dressings. The hydrophobic adhesive matrix of six hydrocolloid dressings was removed using a reflux extraction method with an organic solvent (xylene). The remaining hydrophilic particles were dissolved in complete cell growth medium containing 10% (v/v) foetal calf serum and added to confluent human dermal fibroblasts grown in monolayer in final concentrations of 0.1 and 0.01% (w/v). Control cells received growth medium alone. The fibroblasts were incubated with the hydrophilic particles and the thymidine analogue 5-bromo-2'-deoxyuridine (BrdU) for 24 hours. The incorporation of BrdU into DNA was used as a measure of cell proliferation and determined using an ELISA kit. The results were expressed in percentage of control-treated wells and analysed using analysis of variance. Apart from Comfeel Plus, the hydrophilic particles of hydrocolloid dressings significantly inhibited fibroblast proliferation at 0.1% compared to control-treated fibroblasts (p < 0.05).

In vitro effects of bone cements on the cell cycle of osteoblast-like cells

The effects of orthopaedic cements on the proliferation and cell cycle of in vitro cultured MG63 osteoblast-like cells were examined. Five different cements were mixed and extracted at different time intervals (15 and 60 min, 6, 24 and 48 h). Cell proliferation inhibition (CPI) was evaluated after 72 h culture as the toxicity parameter. As for the toxicity degree, the extracts were considered to have 'high toxicity' (CPI > or = 50%), 'medium toxicity' (50% > CPI > 25%), 'low toxicity' (CPI < or = 25%) and 'no toxicity' (CPI = 0). Cell cycle phases of MG63 cells were evaluated at 24, 48 and 72 h by flow cytometry; the DNA content was assessed using the propidium iodide uptake and the percentage of cells in the S phase was determined using 5'-bromodeoxyuridine uptake. According to our results, the toxicity is inversely correlated with the time interval between polymerization and extract preparation, and is different according to the cement type. For some cements the effects are still observed 48 h after polymerization. The damaging effect is not linked to a specific phase of the cell cycle, nor does it hamper the restarting of cell proliferation at 72 h.

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.

Common problems in wound care: overgranulation

Overgranulation in wounds causes a delay in wound healing and often produces an increase in wound exudate and is therefore difficult to dress. This article suggests non-traumatic methods of removal in order to preserve the granulation of tissue required for healing.

Melanized poly(HEMA) hydrogels: basic research and potential use

Synthetic melanogenesis, using epinephrine and other melanin precursors, within the matrix of hydrophilic polymers and copolymers of 2-hydroxyethyl methacrylate resulted in hydrogels able to absorb ultraviolet and visible radiation. This significantly enhances their value as materials for extraocular (contact lenses) or intraocular (artificial crystalline lenses) devices that should protect the retina of aphakic patients from potential damage induced by light. The two-phase morphology of melanized hydrogels, as investigated by TEM, revealed a fine structure that is possibly indicative of a true sequential interpenetrating polymer network. Their biocompatibility was evaluated by a set of different assays involving human choroidal fibroblasts. No cytotoxicity was found in the aqueous extracts of materials. By using an assay with cells and polymers embedded in a collagen gel, a short-range toxic effect was detected, presumably caused by melanin itself. However, in vivo experiments in animal eyes with melanized hydrogel intraocular lenses did not reveal any toxic reaction.

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

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