A prospective analysis of the role of silicon in wound care.

Silicon is an important micronutrient associated with the development of bone and connective tissue. This article discusses the properties of silicon, its absorption in the human body and its current and potential use in wound management.

Critical observations on the neurotoxicity of silver.

Silver is a xenobiotic element with no recognized trace metal value in the human body. It is absorbed into the body through the lungs, gastrointestinal tract, mucus membranes of the urinogenital tract, and through the skin, mainly in the form of silver protein complexes. Although silver is metabolized throughout the soft tissues, available evidence from experimental animal studies and human clinical reports has failed to unequivocally establish that it enters tissues of the central nervous system or is a cause of neurotoxic damage. Argyria characterized by deposition of particles of silver sulfide or silver selenide is the principle contraindication for using silver in medical devices or occupationally. This presents discoloration of the skin but is not regarded as a health risk or manifestation of toxicity. No evidence is available to demonstrate the toxic risk of silver to the peripheral nervous system, although silver sulfide deposits have been identified in the region of cutaneous nerves. Transitory silver sulfide deposits seen in the tissues of the blood-brain and blood-CSF barriers are mostly lysosomally bound or deposited on basement membranes or collagen without toxic effect. Silver is mostly excreted from the body in the urine and feces. Further research is indicated to evaluate the role of metal binding proteins including metallothioneins as cytoprotectants for neurological tissue.

Silver absorption and antibacterial efficacy of silver dressings.

OBJECTIVE: To evaluate the patterns of silver release from selected sustained silver-release dressings and the protective role of proteins in wound exudate and wound scale. The bactericidal action of silver in chronic wound therapy is also examined. METHOD: Sequential microbiological examination of wound swabs from seven patients with chronic wounds and sampling of wound exudate and wound scale. Silver content was measured using atomic absorption spectrometry. The ability of Contreet Foam to absorb exudate and release silver was studied in punch biopsy wounds in a rodent model. RESULTS: Silver accumulation in wound exudate correlated well with its viscosity and protein content. Silver bound to wound scale and debris was approximately proportional to the silver ion release from dressings. Bacterial burden was controlled, but not eliminated, following chronic silver therapy. CONCLUSION: Silver dressings (Acticoat-7, Actisorb Silver, Contreet Foam, Aquacel Ag and Flamazine) were found to be safe for use in chronic wound therapy. Excess silver ion is bound by wound exudate and wound scale as a protective mechanism. Silver-release dressings are not likely to result in germ-free wounds. Further studies are needed to examine potential silver resistance.

How safe is silver in wound care?

Use of silver in burns, chronic ulcers and diabetic ulcers can lead to circulatory absorption and deposits in wound sites, liver, kidney and other organs. Despite this, the risks of lasting tissue damage or functional disorders are low.

Contreet Foam and Contreet Hydrocolloid: an insight into two new silver-containing dressings.

In vitro laboratory tests and preliminary clinical trials have found that two silver-containing dressings, Contreet Foam and Contreet Hydrocolloid, promote healing in infected and chronic venous leg ulcers and diabetic foot ulcers.

A reappraisal of the role of cerium in burn wound management.

A rare earth element, cerium, was introduced as an antibacterial agent in 1976 but has rarely been used due to the emphasis on wound excision. Used in combination with silver sulphadiazine, it may improve patient survival when excision is not possible.

Silver. 2: Toxicity in mammals and how its products aid wound repair.

The second article examining the role of this metallic element in a wound environment discusses toxicity in individual cells, animals and humans and considers how different silver-based dressings assist in wound healing.

Silver. I: Its antibacterial properties and mechanism of action.

Silver products have two key advantages: they are broad-spectrum antibiotics and are not yet associated with drug resistance. This article, the first in a two-part series, describes the main mechanism of action of this metallic element.

Experimental observations in the rat on the influence of cadmium on skin wound repair.

Wound healing in the skin depends upon the availability of appropriate trace metals as enzyme cofactors and structural components in tissue repair. The present study forms part of a series of experimental investigations to examine the influence of xenobiotic elements with no known nutritional function and which are known to compete with essential trace metals. It was designed to investigate further the importance of trace metals in wound healing as an aid to wound management and to identify mechanisms of nonhealing which constitute a major problem in human medicine. Surgically induced skin wounds in young adult male Wistar rats were exposed topically to 0.2 ml of 0.01, 0.10 or 1.0% cadmium chloride (aq.) daily for up to 10 days. Control wounds received de-ionized water only. Wounds exposed to cadmium chloride at 0.01 or 0.10% healed in a similar fashion to controls and exhibited a comparable histological profile with metallothionein distribution. Wounds receiving 1.0% cadmium chloride failed to heal or fully re-epithelialize within 7 days and animals were humanely killed. They showed a persistent mass of inflammatory cell infiltration, oedema, wound debris and aberrant epidermal cell growth. Metallothionein concentrations in the epidermis and fibroblasts of the papillary dermis increased greatly by 5 days postwounding and remained high through the observation period. Cadmium was identified in the liver, kidney and wound sites. In the wound, 1.0% cadmium chloride induced statistically significant (P > 0.001) changes in local concentrations of zinc and calcium at key stages in the healing process, and as a consequence disturbed the trace metal balance necessary for normal wound repair. Zinc levels were increased twofold after 7 days, but calcium was markedly reduced. Local changes in the distribution of metallothionein indicate interaction of cadmium and trace metal carrier proteins as a probable mechanism for impaired wound healing. The cytotoxicity of cadmium is considered to be largely responsible.

Iron: a cosmetic constituent but an essential nutrient for healthy skin.

Iron compounds have an established role as colorants in many cosmetic products applied to the skin, hair and nails. Evidence is reviewed showing that in addition to its importance as an essential nutrient necessary for oxygen metabolism and mitrochondrial function, iron exhibits a fundamental importance as a trace metal in the normal growth and functional maturation of the skin and in the health of hair and nails. The implications of iron from cosmetic sources in the nutrition of human skin is discussed.

Sequential changes in trace metal, metallothionein and calmodulin concentrations in healing skin wounds.

Metalloenzymes have an important role in repair and regenerative processes in skin wounds. Demands for different enzymes vary according to the phase in the healing cascade and constituent events. Sequential changes in the concentrations of calcium, copper, magnesium and zinc were studied in the incisional wound model in the rat over a 10 d period. Copper levels remained low (< 10 microg/g dry weight) throughout, but calcium, magnesium and zinc increased from wounding and peaked at about 5 d at a time of high inflammation, granulation tissue formation and epidermal cell proliferation. Metal concentrations declined to normal by 7 d when inflammation had regressed, re-epithelialisation of the wound site was complete and the 'normalisation' phase had commenced. Although the wound was overtly healed by 10 d, the epidermis was still moderately hyperplastic. In view of competitive binding of trace metals at membrane receptors and carrier proteins, the ratios or balance between these trace metals was examined and the significance is discussed. Using immunocytochemistry, we demonstrated increases in metallothionein immunoreactivity as an indication of zinc and copper activity in the papillary dermis and in basal epidermal cells near the wound margin 1-5 d after wounding. This is consistent with metalloenzyme requirements in inflammation and fibrogenesis. Calmodulin, a major cytosolic calcium binding protein was highest in maturing keratinocytes and in sebaceous gland cells of normal skin; it was notably more abundant in the epidermis near the wound margin and in re-epithelialising areas at a time when local calcium levels were highest.

Zinc and titanium oxides: promising UV-absorbers but what influence do they have on the intact skin?

Suspensions (20%) of microfine and ACS grade zinc oxide, or 20% titanium oxide in water, castor oil or polyethylene glycol were applied topically to rabbit skin over 4 h (1 day) or 2 h daily (3 days). Skin sites were analysed for metal uptake. Percutaneous absorption of the oxides was probably low, most remaining on the skin surface. Uptake patterns were influenced by the vehicles used. Appreciably more microfine zinc oxide was taken up by the skin in subacute studies. Local changes in trace metal concentration were construed as evidence of percutaneous absorption of zinc and titanium oxides. Further studies are indicated to validate the significance of these preliminary observations.

Silver aids healing in the sterile skin wound: experimental studies in the laboratory rat.

Incisional wounds 15 mm long were induced surgically in the back skin of young adult Wistar rats. They were sutured and used as an experimental model in the therapeutic evaluation of daily applications of 0.5 mL of silver nitrate (SN) at 0.01, 0.1 or 1.0% w/v aqueous solution, or 0.5 g silver sulphadiazine (SSD) over a 10-day period. Control wounds received deionized water only. The silver preparations were not toxic but SN did stain the hair and superficial layers of the stratum corneum. The wounds remained microbiologically clean. Wounds exposed to SN (0.1 or 1.0%) or SSD healed more rapidly than controls. From about the fourth day of treatment, we noted a more rapid exteriorization of sutures, improved wound closure and an earlier loss of scabs and wound debris. Silver treatment appeared to reduce the inflammatory and granulation tissue phases of healing and enhance epidermal repair. Silver from SN was deposited as silver sulphide in extrafollicular hair shafts and superficial aspects of the skin and wound debris but not at deeper levels. Silver uptake was four-fold higher in damaged skin than in intact tissue. SSD was absorbed by intact and wounded skin but the silver did not precipitate as silver sulphide and its localization in the tissue is not known. Uptake of silver from SN or SSD was associated with changes in the concentrations of zinc and calcium in the skin. Zinc levels were depressed during the inflammatory and proliferative phases of healing and then increased. Zinc concentrations had normalized by 10 days when wound healing was achieved. Calcium levels remained higher than normal throughout the observation period. The mechanism of action of silver in advancing wound healing in the rat is unclear. Its ability to reduce the inflammatory and granulation phases of healing, and to invoke metallothionein production and influence metal ion binding are possibly important.

Trace metals in keratinising epithelia in beagle dogs.

The concentrations of the trace elements zinc, copper and iron and the minerals calcium and magnesium were measured in keratinising epithelia from 12 beagle dogs. The richly vascular tissues of the snout and tongue that showed parakeratotic changes, contained the highest concentrations of iron, zinc and copper. Zinc, calcium and magnesium concentrations were high in the pressure keratinisation tissue of the footpad. There was a high concentration of calcium in the nose tip. The thin skin of the back contained the lowest concentration of all five elements.

Dermal toxicity and percutaneous absorption of cadmium in rats and mice.

Cadmium is a common contaminant in sawdust and other materials used in laboratory animal bedding. This study was conducted to assess the irritancy of a soluble cadmium compound to the skin and percutaneous absorption of the cadmium ion. Cadmium chloride solution was administered to the shaved skin of the dorsum of rats and mice daily for 10 days at concentrations of 1.0, 0.1, and 0.01% (wt/vol). Cadmium accumulated in the skin in association with approximately 6,000 ng/g in animals exposed to the high dose. Skin damage of hyperkeratosis and acanthosis with some ulcerative change was dose-related. The mitotic index in mouse skin was increased up to twofold. In rat blood, concentrations of cadmium, after 10 days of administration of a 1% concentration, were 11.65 micrograms/L, indicating percutaneous absorption. Clear evidence was seen of an accumulation of cadmium in the liver (526 ng/g) and kidney (216 ng/g), but histopathologic evidence of damage was absent, after this period at least. Concentrations of zinc were increased in the skin, probably as a consequence of local increases in metallothionein, a zinc-binding protein.