How Wound Care Fell in Love With Amorphous Hydrogels

Back when many competitors were developing advanced wound care dressings capable of handling greater amounts of exudate while maintaining a moist wound surface, some companies were looking at the conformability for deep cavities and sinuses.

One of them was Sheering, which introduced its Sherisorb Gel (amorphous) in foil sachets and promoted the product as having “100’s of uses.” Indeed, Sherisorb Gel could be applied to almost any type of wound, but it also had little capacity to manage exudate and was difficult to hold in place. With those drawbacks and no clear indications, Shearing had little success with the product.

MediPlus Advanced Wound Care hydrogel dressing

After being acquired by Smith & Nephew, Sherisorb Gel became INTRASITE Gel. Initial marketing efforts promoted the “100’s of uses” message until the Canadian marketing team took a closer look at the properties of the gel and the needs of the clinicians/patients. IntraSite gel was composed of two-percent graft-T starch that generated the gelling properties and held onto moisture. Propylene glycol acted as humectant and preservative while the rest of the gel was in fact water. The product offered no advantage in exuding wounds other than its use for packing dead space. However, it had excellent properties when applied to dry wounds as a source of moisture to rehydrate tissue.

A series of trials established that when INTRASITE Gel was applied to necrotic wounds (slough or black necrotic tissue), it had the unique ability to donate moisture to necrotic tissue. That differentiated it from other advanced wound care products at the time, which could only hydrate tissue by preventing evaporation and holding back exudate produced by the wound. INTRASITE Gel both blocked the escape of wound fluid and actively donated moisture to tissue and debris in the wound. When applied to necrotic wounds (at which time included black or yellow classifications), INTRASITE rapidly moisturized and softened the dead tissue. Once moisture penetrated the necrotic mass, normal cells and enzymes could digest and loosen the necrotic tissue, and rapid autolytic debridement would take place.

Product representatives were instructed to ask for a trial on two patients with necrotic wounds and to return in two days for removal of the dressing. In most every case, stalled necrotic wounds presented significant improvement, with obvious breakdown of necrotic tissue. Debridement was far more rapid and complete than what was experienced with transparent, hydrocolloid or foam products.

Amorphous hydrogels that could donate moisture also provided a new and powerful alternative to surgical debridement—which could be attempted before calling a surgeon. That significantly increased the utility of ETs that worked on wounds, as it gave them another tool to successfully manage a wider range of wounds. Additionally autolytic debridement is less costly, less painful, and probably as complete on a cellular level compared to surgical detriment. Further, it offers multiple advantages over chemical and mechanical debridement methods.

In the United States, similar results were being seen with Carrington® Gel, which was based on research on aloe vera and a naturally occurring component, acemannan. With a clear indication and very visible dramatic results, the use of these two gels grew rapidly in virtually every facility or office where there were necrotic wounds. Soon thereafter, numerous other amorphous gel products soon found their way into the market.

Most introductions of new amorphous gel products were intended to mimic the properties of INTRASITE or Carrington gels, but a few diverged from that pattern. For instance, Mölnlycke Hypergel® incorporated a 20-percent saline content that created a hypertonic solution that actively drew moisture from the wound bed to hydrate necrotic tissue and purported to speed autolytic debridement.

Later amorphous hydrogels were based on carboxymethylcellulose (CMC), alginate, pectin, xanthan gum, and more recently, collagen, keratin and GAGs. (Honey—currently classified by PDAC as a hydrocolloid—would probably be better classified as a hydrogel based on complex carbohydrates more akin to aloe vera acemannan or beta glucan than cellulose particles.)

Hydrogels represent a potential carrier of active substances to the wound surface, and various additives have been used, including analgesics and digestive enzymes. Clinical comparisons to demonstrate superiority of one over another have not shown differences significant enough to override commercial or individual preference.

As more and more hydrogels were used with increasing success, the practical aspects of actually delivering the product to the wound became differentiating factors. For instance, INTRASITE Gel’s delivery evolved from a unit-dose foil sachet to a plastic “mushroom cap” delivery device that maintained its unit-dose character, but proved to be much easier to direct into the wound

Preserved amorphous hydrogels that could be delivered in single-patient reusable tubes helped to bring down the cost of treatment. Observation of those products in use revealed that nurses and ETs often applied the hydrogel to simple gauze that was used to deliver the gels to the wound surface. The gauze provided a controlled manner to get gel where it was needed and helped stabilize it in-place as it absorbed water and became more fluid. In short, the homemade impregnated gauze dressings got the gel to the wound—and kept it there—while avoiding leaking and maceration of periwound skin. Gel producers soon began to supply pre-impregnated hydrogel gauze pads that proved to be widely popular and which overcame the PDAC limitation of a three-ounces per-month reimbursement for amorphous gels.

Various claims are attached to the alternate hydrogel formulations and the featured components of each. Two things are common across the hydrogel spectrum, and these are in intimate contact with the wound surface—and a varying degree in their ability to absorb or donate moisture to the wound. DuoDERM®, NuGEL™, Purilon® and INTRASITE (in that order) were shown to donate the most moisture in in-vitro testing, which suggested they would be most effective in hydrating necrotic tissue for autolytic debridement. That compared to Carrasyn®, Normlgel® and Hypergel, which absorbed the most fluid and could be expected to stay in place longer when used in lightly exuding wounds.

Although nearly all hydrogels at some point claimed reduction of pain due to their “cooling effect”—which took it out of the physiological zone where healing occurs and slows wound healing—it’s argued that its better to apply dressings at skin temperature to avoid healing downtime.

Another relatively recent development in hydrogels was the addition of antimicrobials to reduce bioburden and to potentially speed the progression of healing from the inflammatory to granulation phase. Some of the antimicrobials that were used ranged from hypochlorous acids (Anasept®), plant extracts like oakin (Amerigel®) or multiple extracts (WinVivo) and of course, silver (SilverMed™, SilvaSorb®, SilvaKollagen®).

Hydrogels containing vitamins (Dermacyn™), zinc (Dermagran®), and dexpanthenol (PanoPlex™) were promoted as having (not fully demonstrated) advantages, and at least one—Regencare®—used lidocaine to address wound pain and the interruptions to healing that pain in its various forms has on wound healing.

Adding enzymes to amorphous hydrogels would be expected to increase their debriding effects, however, this has not yet been demonstrated with double-blind clinical trials. However, the addition of collagen may help reduce the damage to healing wound from MMPs by providing a sacrificial substrate to spare collagen being laid down during repair of the wound bed. And although the addition of other structural substances—such as keratin or GAGs—may differentiate hydrogels in the future, at this time, moisture handling characteristics and practical delivery issues best differentiate the amorphous hydrogel options.

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