Collagen dressings Made Easy
Complex wounds, Products, Surgical wounds | Westgate S, Cutting KF, DeLuca G, Asaad K
Collagen is a key component of the extracellular matrix (ECM) and plays a critical role in all phases of wound healing. There are a number of advanced wound care dressings available that incorporate collagen to enhance wound bed preparation. Some comprise type I collagen and may be combined with other ingredients such as alginates or oxidised regenerated cellulose (ORC). This article focuses on the use of fish-derived type I collagen dressings in the treatment of stalled traumatic and surgical wounds or hard-to-heal chronic ulcers.
Advances in wound dressings
Over the last 30 years there has been a shift from traditional wound dressings towards those advanced therapies that aim to optimise the wound healing environment (Enoch and Harding, 2003). In more recent years, wound care products have been developed that aim to replicate or add to the ECM. The ECM is the major component of the dermis and provides a structural support for cells, growth factors and receptors that are essential to wound healing (International Consensus, 2011).
With a wide range of dressings to choose from, dressing selection is a significant challenge for wound care clinicians. Increased costs and the need for evidence-based treatment approaches are creating a demand for well-designed randomised controlled trials to support purchase and use (Rudnick et al, 2006). The ideal dressing should achieve rapid healing at reasonable cost with minimal inconvenience to the patient (Boateng et al, 2007).
What is collagen?
Collagen is the most abundant protein in the human body and is a major component of the ECM. It comprises three polypeptide chains that are rich in hydroxyproline amino acids (Mian et al, 1992) and are twisted together into a triple-helical structure.
Over 20 different types of collagen have been identified in humans; the main types are type I, II and III and together they make up 80% of the body's collagen. Type I and III are important for wound healing (Li et al, 2007).
Role of collagen in wound healing.
In a healing wound a cascade of events occurs that includes platelet accumulation, inflammation, fibroblast proliferation, cell contraction, angiogenesis and re-epithelialisation (Moore, 2010), ultimately leading to scar formation (Rudnick, 2006) and wound remodelling (Brett, 2008).
Collagen plays an important role in each of these phases of wound healing due to its chemotactic role. It attracts cells such as fibroblasts and keratinocytes to the wound. This encourages debridement, angiogenesis and re-epithelialisation (Weber et al, 1984; Zbigniew, 2003).
A chronic wound is stalled at one of these healing stages (Vowden, 2011). This usually occurs during the inflammatory phase and is linked to elevated levels of matrix metalloproteinases (MMPs) in the wound (Singh et al, 2011; Gibson et al, 2009). In normal wound healing, proteases such as MMPs are attracted to the wound during the inflammatory phase and have an important role in breaking down unhealthy ECM so that new tissue forms (Parks, 1995; Jeffrey, 1995). However, when MMPs are present in a wound at elevated levels for a prolonged period of time, this results in the destruction of healthy ECM, which is associated with delayed wound healing and an increase in wound size (Vowden, 2011).
When the excess of MMPs is not balanced by normal physiological processes, alternative methods are required to reduce protease levels in the wound. This suggests a role for dressings containing collagen in the management of wounds where healing is stalled (Rangaraj et al, 2011).
What are collagen dressings?
Native intact collagen provides a natural scaffold or substrate for new tissue growth (Ruszczak, 2003). Dressings containing collagen are thought to provide the wound with an alternative collagen source that can be degraded by the high levels of MMPs as a sacrificial substrate, leaving the endogenous native collagen to continue normal wound healing (Brett, 2008).
There are a number of different collagen dressings available that use a variety of carriers and combining agents such as gels, pastes, polymers and oxidised regenerated cellulose (Brett, 2008). The collagen contained in these products also varies in type and source. Certain dressings contain native (type I) collagen in which the triple helix formation is intact; others contain denatured or reconstituted collagen, which is referred to as gelatin.
Most collagen dressings contain collagen derived from bovine and porcine sources (Vivas et al, 2011). Although these collagens are purified, there remains a theoretical concern regarding the potential for prion diseases such as bovine spongiform encephalopathy (BSE) (Liu et al, 2006; Jabar, 2011). There have also been concerns regarding the integration of porcine collagens into scar tissue (Burns et al, 2010), while cultural/religious issues may prevent their use on some patients (Jabar, 2011). Human-derived collagens are linked with fewer immunological concerns, however they tend to be more expensive than animal-derived collagens (Vivas et al, 2011). More recently collagen derived from fish has been proposed as a cost-effective source of collagen for use in dressings.