Accelerated epithelization under a highly vapor-permeable wound dressing is associated with increased precipitation of fibrin(ogen) and fibronectin

Iodine-responsive poly (HEMA-PVP) hydrogel for self-regulating burst-free extended release

Swollen hydrogels with extended iodine release kinetics is highly desirable for burn and scald treatment. In this paper semi-interpenetrating poly (HEMA-PVP) hydrogels were prepared by radical polymerization followed by thermo-treatment to crosslink its PVP component. Incorporation of PVP component endows the hydrogels responsive to loaded iodine undergoing a reversible shrunken/swollen volume transition. This resulted in a self-regulating iodine release model, in which shrunken hydrogel at high iodine loading decreased drug diffusion thereby reducing burst release, and then gradually swollen hydrogel as drug release ensures rapid release of dissociated drug from strong affinity sites on hydrogel backbone, achieving a burst-free extended release. The hydrogels demonstrated 11.5-fold higher iodine loading than pure pHEMA hydrogel and showed a highest 40% volume shrink. Initial burst release of iodine was efficiently decreased from 12,894 μg/day of pure pHEMA hydrogel to 2570 μg/day of pHEMA/PVP hydrogel with 37% PVP content. Iodine-loaded hydrogels showed zero-order release at three time periods of 0-15 h, 15 h-3.5 days and 3.5-23.5 days corresponding to release rate of 2570, 776 and 493 μg/day. The work gained a new insight into swollen hydrogel drug delivery system with burst-free extended drug release kinetics.

The external microenvironment of healing skin wounds

The skin wound microenvironment can be divided into two main components that influence healing: the external wound microenvironment, which is outside the wound surface; and the internal wound microenvironment, underneath the surface, to which the cells within the wound are exposed. Treatment methods that directly alter the features of the external wound microenvironment indirectly affect the internal wound microenvironment due to the exchange between the two compartments. In this review, we focus on the effects of temperature, pressure (positive and negative), hydration, gases (oxygen and carbon dioxide), pH, and anti-microbial treatment on the wound. These factors are well described in the literature and can be modified with treatment methods available in the clinic. Understanding the roles of these factors in wound pathophysiology is of central importance in wound treatment.

Hydrocellular foam dressing promotes wound healing along with increases in hyaluronan synthase 3 and PPARα gene expression in epidermis

BACKGROUND

Hydrocellular foam dressing, modern wound dressing, induces moist wound environment and promotes wound healing: however, the regulatory mechanisms responsible for these effects are poorly understood. This study was aimed to reveal the effect of hydrocellular foam dressing on hyaluronan, which has been shown to have positive effects on wound healing, and examined its regulatory mechanisms in rat skin.

METHODOLOGY/PRINCIPAL FINDINGS

We created two full-thickness wounds on the dorsolateral skin of rats. Each wound was covered with either a hydrocellular foam dressing or a film dressing and hyaluronan levels in the periwound skin was measured. We also investigated the mechanism by which the hydrocellular foam dressing regulates hyaluronan production by measuring the gene expression of hyaluronan synthase 3 (Has3), peroxisome proliferator-activated receptor α (PPARα), and CD44. Hydrocellular foam dressing promoted wound healing and upregulated hyaluronan synthesis, along with an increase in the mRNA levels of Has3, which plays a primary role in hyaluronan synthesis in epidermis. In addition, hydrocellular foam dressing enhanced the mRNA levels of PPARα, which upregulates Has3 gene expression, and the major hyaluronan receptor CD44.

CONCLUSIONS/SIGNIFICANCE

These findings suggests that hydrocellular foam dressing may be beneficial for wound healing along with increases in hyaluronan synthase 3 and PPARα gene expression in epidermis. We believe that the present study would contribute to the elucidation of the mechanisms underlying the effects of hydrocellular foam dressing-induced moist environment on wound healing and practice evidence-based wound care.

Meshed skin grafts placed upside down can take if desiccation is prevented

BACKGROUND

The role of the wet environment in wound healing has been investigated in various studies. The current study explores the role of the wet wound environment in promoting healing of skin grafts. The authors hypothesized that the survival of skin grafts is dependent not only on the orientation of transplantation but also on the environment into which the skin is transplanted.

METHODS

This study included 72 full-thickness (2.5 x 2.5-cm) wounds in six Yorkshire pigs. The wounds were grafted with autologous split-thickness skin grafts (meshed or sheet), placed either regularly (dermal side down) or inverted (dermal side up), and treated in a wet or a dry environment. Behavior of the skin grafts and healing were analyzed in histologic specimens collected on days 4, 6, 9, and 12 after wounding. Wound contraction was quantified by photoplanimetry.

RESULTS

In the wet environment, not only did inverted meshed skin grafts survive, but also they proliferated to accelerate reepithelialization. In this environment, wounds transplanted with inverted and regular meshed grafts showed no significant difference in reepithelialization rate and contraction. In contrast, in the dry environment, wounds transplanted with inverted meshed grafts showed a significantly lower reepithelialization rate and a higher contraction rate than wounds transplanted with regular grafts. Inverted meshed grafts in a dry environment and inverted sheet grafts did not survive.

CONCLUSION

The wound environment has an important role in the survival and proliferation of skin grafts, as demonstrated by survival of inverted meshed grafts in the wet environment and their contribution to accelerated reepithelialization, equal to the regularly placed grafts.

A Review of Moisture-Control Dressings in Wound Care

Wound healing progresses most rapidly in an environment that is clean, moist (but not wet), insulated, and protected from trauma and bacterial invasion. Selection of a dressing is based on specific wound characteristics: (1) the presence or absence of necrotic tissue, (2) bacterial load, (3) exudate volume, and (4) need for a bacterial barrier. Therefore, the optimal dressing should be able to control exudate without desiccating the wound surface; act as a bacterial barrier; allow atraumatic removal with no dressing left in the wound; and provide moisture vapor permeability sufficient to prevent overhydration of the wound and surrounding skin. There are a multitude of dressings on the market, and clinicians are frequently confused as to which type of dressing is the best for a particular wound. Effective dressing selection requires both accurate wound assessment and current knowledge of available dressings. The articles in the current supplement to the Journal of Wound, Ostomy and Continence Nursing review research about wound exudate management and the use of foam dressings.

PVP-iodine in hydrosomes and hydrogel--a novel concept in wound therapy leads to enhanced epithelialization and reduced loss of skin grafts

BACKGROUND

Moist wound treatment improves healing at a possibly increased risk of bacterial infection and many local antiseptics impair healing. A moist treatment modality with efficient antimicrobial activity would be desirable.

METHODS

In this monocentric, randomized, observer blinded, phase III study, a new hydrosome polyvinyl-pyrrolidone (PVP)-iodine preparation in hydrogel containing iodine in a 3% concentration (Repithel) was investigated for its effect on epithelialization in patients receiving meshed skin grafts. Grafts of 167 patients (donor site defects, burn wounds, or chronic defects) were dressed either with Repithel (n=83) covered with a gauze (Jelonet), or Jelonet-gauze only (n=84) until healing.

RESULTS

Grafts receiving Repithel healed significantly earlier (9.4 days versus 12.4 days; p<0.0001) and faster than controls as measured by neo-epithelialization of mesh holes between days 7 and 11 (91.2+/-22.8% versus 82.3%+/-28.6, p<0.0001). A subgroup analysis showed that the effects on grafted burn wounds (p=0.0042) and chronic defects (p<0.0001) was more significant than on donor sites. Also a higher take rate of grafts (p=0.0053) and a reduced loss of grafts was observed with Repithel treatment (8 grafts versus 20 grafts) (p=0.0063, respectively). Smokers had improved graft take (p=0.0069) and higher rate of epithelialization (p=0.0040) compared to smokers of the control group.

CONCLUSIONS

The results demonstrate significant clinical advantages of Repithel. This new local wound healing drug combines antisepsis and wound moisture efficiently resulting in significantly enhanced epithelialization, decreased transplant losses, and significantly improved healing especially in smokers.

Scar quality and physiologic barrier function restoration after moist and moist-exposed dressings of partial-thickness wounds

BACKGROUND

There is growing evidence of improved healing of full- and partial-thickness cutaneous wounds in wet and moist environments. Retention of biologic fluids over the wound prevents desiccation of denuded dermis or deeper tissues and allows faster and unimpeded migration of keratinocytes over the wound surface. It allows also the naturally occurring cytokines and growth factors to exert their beneficial effect on wound contracture and re-epithelialization. Despite all of these documented benefits, applying the moist healing principles to large surface areas, in particular to large burns, is hindered by the major technical handicap of creating and maintaining a sealed moist environment over these areas.

METHODS

From January to September 2001, healing of partial-thickness skin graft donor sites was studied in a prospective comparative study of two types of moist dressings, Tegaderm (3M Health Care, St. Paul, MN), a semipermeable membrane occlusive dressing, and moist exposed burn ointment (MEBO) (Julphar; Gulf Pharmaceutical Industries, United Arab of Emirates), an ointment that can provide a moist environment without the need of an overlying occlusive dressing. Healing was assessed both clinically and with serial measurements of transepidermal water loss (TEWL) and moisture. Following healing, scar quality was evaluated by two members of the team separately using a visual analog scale. Results were statistically analyzed.

RESULTS

Faster healing was observed clinically with MEBO application. Physiologic healing as determined by TEWL measurements occurred at an extremely significant earlier stage for MEBO, and this was associated with better scar quality, demonstrating a positive relationship between function and cosmetic appearance. Moreover, the ointment is definitely easier to apply than the occlusive self-adhesive membrane, which requires some degree of dexterity and expertise.

CONCLUSION

MEBO application is an effective and valid alternative to conventional occlusive dressings. Moreover, the observed improved anatomic and physiologic healing indicates that MEBO may have a positive effect on healing more that the mere fact of passive moisture retention.

Moist wound healing: does the theory apply to chronic wounds?

Winter's research on moist wound healing continues to exert a strong influence on tissue viability practice. But does this theory, which is based on porcine acute wounds, apply to human chronic wounds. This review explores the evidence.

A study to evaluate primary dressings for the application of cultured keratinocytes

Despite the recent improvements in cell culture and dermal regeneration methods, tissue engineering of skin has yet to receive widespread acceptance in the management of burn injuries. The reasons for this are complex and include not only the inherent costs of (particularly) setting up and running such a system but also the continuing difficulties in achieving successful engraftment of the neoepidermis. The latter has previously been addressed in a number of ways, including improving the recipient bed and using pre-confluent delivery systems to allow earlier application of cells to that wound bed. One area that has received little attention is that of the optimal wound dressing to use with this technology; the cells are very poorly attached at early time points, and, in this context, the traditional dressing of paraffin gauze has never been formally assessed in comparison with newer materials. Using a porcine acute wound chamber model, we performed a prospective randomised trial to assess four different wound dressings with reference to the amount of epidermal cover gained and the histological quality of the regenerated skin after 3 weeks. Out of the four materials tested, polyurethane foam (Allevyn) was superior histologically (although equal in take rate with paraffin gauze), whilst polythene sheet (Opsite) and silicone sheet were substantially inferior. We conclude that the traditional dressing used with this technology should be compared with polyurethane foam in a clinical trial. In the future, novel dressings should be formally tested against traditional methods before being adopted.

Polyvinyl pyrrolidone-iodine liposome hydrogel improves epithelialization by combining moisture and antisepis. A new concept in wound therapy

Moist treatment of wounds has been shown to improve epithelialization, however at an increased risk of bacterial infection. In this monocentric, randomized, open, phase II pilot study of polyvinyl pyrrolidone-iodine, a well-established topical antiseptic was tested in a new liposomal complexed form in patients receiving meshed skin grafts after burns or reconstructive procedures. Mesh skin graft sites of 36 patients were dressed either with the new polyvinyl-pyrrolidone-iodine liposome hydrogel formulation (Betasom hydrogel) (n = 21), or chlorhexidine-gauze (n = 15). After the first dressing change, wounds were assessed daily and documented every other day until they were healed. Methods of analysis included clinical assessment, photoplanimetry (rate of epithelialization), impedance measurement (moisture of surface and wound healing quality), patient's assessment of pain and other sensations, and thyroid hormones (T3, T4, and TSH). The rate of epithelialization was improved with Betasom hydrogel compared to chlorhexidine-gauze on day 11 (96.3% vs. 75.9% p = 0.056) and significantly on day 13 (100% vs. 82.3% p = 0.005), respectively. Impedance measurements showed an earlier return to normal values (day 9) in Betasom-hydrogel-treated wounds as opposed to chlorhexidine treatment (day 11). Clinical assessment indicated significantly better antiseptic efficacy (p = 0.002) and wound healing quality (p = 0.004) of Betasom hydrogel. Graft loss occurred at a significantly lower rate in Betasom treatment (n = 1; 5%), than in chlorhexidine treatment (n = 5; 35.7%) (p = 0.001). No relevant adverse events or clinically relevant changes of thyroid hormones were observed with Betasom hydrogel. The rationale of this new polyvinyl pyrrolidone-iodine liposomal formulation was based on the properties of liposomes that provide higher moisture to the wound surface, release PVP-iodine at a low rate, and target the substance more exactly by interaction with the cell surface. These initial clinical results show earlier epithelialization and better healing in wounds treated with polyvinyl pyrrolidone-iodine liposome hydrogel, which combines moisture and antisepsis, compared to wounds treated with a conventional antiseptic chlorhexidine-gauze.

Basement membrane formation during wound healing is dependent on epidermal transplants

The purpose of the study was to compare directly the effect of healing and the formation of the basement membrane during wound healing from two autologous primary keratinocyte cultures in the liquid environment in full-thickness wounds in pigs. Wounds were either transplanted with cultured epidermal autografts (n = 26) or autologous keratinocyte suspensions (n = 24) or treated with saline alone (n = 40) and covered with a chamber. All wounds transplanted with cultured epidermal autografts and keratinocyte cell suspensions had positive "take" after transplantation. Healing times were significantly shorter for wounds treated with either cultured epidermal autografts or keratinocyte suspensions (p = 0.0001) compared with saline-treated wounds but were not different from each other (p = 0.1835). There were no differences in cytokeratin and laminin expression; however, staining with monoclonal antibody against collagen type VII showed a lower signal for cultured epidermal autografts only on days 8 and 16 compared with keratinocyte suspensions. Electron microscope evaluation showed a higher incidence of anchoring fibrils and a more mature dermal-epidermal junction in wounds treated with keratinocyte cell suspensions at day 8. These findings may be due to the single, noncontact-inhibited cells and the early formation of an in vivo neodermis to the wet wound environment. These data suggest that wounds transplanted with autologous keratinocyte suspensions in a wet environment may be an alternative method in the treatment of wounds.

Randomized clinical trial of the effect of semi-occlusive dressings on the microflora and clinical outcome of acute facial wounds

This study investigated whether treatment with occlusive, hydroactive polyurethane dressings affects the microflora and clinical outcome of acute wounds. A randomized, controlled trial was performed on 60 patients with acute facial lacerations. Following primary closure, patients were provided with either a dry-gauze dressing or a hydroactive polyurethane dressing (Cutinova Thin). The wounds were assessed clinically and microbiologically prior to closure, then after 5, 28 and 56 days. The dressing, which was removed at day 5, was also sent for microbiological culture. Wounds treated with the polyurethane dressing showed improved comfort and contour (p < 0.04), less erythema (p < 0.03) and less potential for scarring (p < 0.01) at day 5. At day 28 and day 56, there were no significant differences in the clinical assessment between the test and control groups (p > 0.05). A total of 518 isolates were recovered from the patients during the study. Mean number of isolates and bacterial growth density were calculated in both groups. A similar range of microorganisms were obtained from both treatment groups with no clear difference in organism colonization. This study shows the potential usefulness of facial wounds as a human model for studying acute wound healing responses and anti-scarring therapy. While short-term, clinical benefits of occlusive dressings were evident in the management of acute wounds, these data clearly show that all studies of scarring following acute wounding should extend over at least 3 months post-injury to allow for spontaneous improvement to occur.

Healing of full-thickness wounds in pigs: effects of occlusive and non-occlusive dressings associated with a gel vehicle

This study, based upon a pig model, was conducted to investigate the effects of moist and dry healing conditions on wound closure (epithelialization, granulation tissue, contraction) of full-thickness wounds. Thirty-two full-thickness square wounds (3 cm x 3 cm) covered with either an occlusive polyurethane dressing (Tegaderm) or a non-occlusive dressing (Melolin) were evaluated. The effect of the presence or the absence of a gel (3% Idroramnosan) was also investigated with both dressings. The dressings were renewed twice a week. The time required for wound closure was 19.2 +/- 1.6 days for Tegaderm and 26.6 +/- 3.0 days (means +/- SD) for Melolin, respectively. The healing time of the full-thickness porcine wounds was significantly (P < 0.001) reduced by the occlusive dressing. Equivalent results were found with the 3% gel, indicating that the gel can be used as a neutral vehicle. The healing rate, calculated according to Gilman's method, was also significantly (P < 0.001) enhanced by the occlusive dressing. This progression was 0.073 +/- 0.004 cm/day and 0.050 +/- 0.009 cm/day (means +/- SD) for Tegaderm and Melolin, respectively. The contribution of contraction to wound closure was similar in all wounds, indicating that the occlusive dressing did not have an effect on wound contraction. Histological evaluation was performed on full-thickness skin biopsies of whole wound harvested from the time of wound closure to 3 months after. At any time point, no significant histological variations were observed between the different treated wounds. This study demonstrates in a porcine model that for full-thickness wounds, as for split-thickness wounds, occlusive dressing enhances healing rate and shortens the time for wound repair. The shortened healing time is a function primarily of the effect of occlusive dressing on epithelialization, especially the third phase of wound resurfacing.

A reevaluation of the effect of occlusion on the trichloroacetic acid peel

BACKGROUND

Prior studies have demonstrated reduced wounding with trichloracetic acid (TCA) peels after tape occlusion. It is therefore reasonable to question whether or not other types of occlusion may have similar effects, particularly those used in routine postoperative care.

OBJECTIVE

To reevaluate the effect of occlusion after TCA peels in multiple human models using various forms of dressings, at various times postoperatively, and to make recommendations regarding wound care that will not adversely affect the efficacy of the peel.

METHODS

Equal-sized sections of anterior alopecic scalps of four patients were peeled with 50% TCA, occluded with bacitracin, Vigilon, or Tegaderm at various times postoperatively, and biopsied 1 day later. Depths of necrosis were measured and compared with nonoccluded controls.

RESULTS

Bacitracin ointment and Vigilon did not lessen TCA wounding, and sometimes actually enhanced it. Conversely, Tegaderm lessened the degree of the TCA wound. Timing of application played a role in the case of occlusion with Vigilon.

CONCLUSION

Occlusives used in conjunction with TCA peels do not have a uniform effect on depth of necrosis. Ointments and Vigilon can be used without reducing the efficacy of the TCA peel. Multiple subjects and rigid control of variables are necessary in studies of TCA-induced necrosis.

Occlusive dressings

BACKGROUND

Although occlusive dressings speed epithelialization, reduce inflammation and tenderness, reduce the chance of infection, stimulate healing of chronic wounds, and produce less scarring, they are still underutilized by physicians and nurses. The principal reasons for their underutilization are fear of infection, the time needed for instructing patients in their use, a lack of knowledge about occlusive dressings, and the general unavailability and high cost of the dressings.

METHODS

This chapter describes the principles which help in selection of the proper dressing, discusses the mechanisms of action of occlusive dressings, lists some novel new occlusive dressings, and emphasizes some of the drawbacks of occlusive dressings for chronic wounds.

CONCLUSION

While occlusive dressings have become an important treatment protocol, their role in opening the minds of clinicians to the possibility of controlling the repair process may be their greatest contribution to medical science.