Innovations In Waterproof Wound Coverings

Wounds, a break in or damage to skin tissue, are broadly classified into acute or chronic types. Acute wounds generally heal in their entirety without issue, and skin integrity is restored. Chronic wounds, in comparison, are of a more severe nature and are defined by a failure to heal completely after one month. Chronic wounds also have a higher risk of developing further complications such as infection and tissue necrosis.¹

To facilitate wound healing, the dressings used must possess particular qualities, the principal of which is to act as a protective barrier from ‘the elements’. As such, waterproofing plays an integral part in the design and development of materials intended to serve as wound coverings. Waterproofing, however, does not imply the creation of a vacuum or airtight seal over a wound. The ideal wound covering has to allow a sufficient measure of moisture as parameters like air permeability, vapour transmission, and particle filtration are also considered critical for encouraging wound healing.² Other sizable characteristics that are required of an ideal dressing are mechanical strength, biocompatibility, and the ability to impart a degree of comfort to the patient. With so many parameters to consider and to what extent, getting the balance right in a singular material can be quite a challenge.

Given that there is a lot to contemplate when creating a wound dressing, it is safe to say that not all of these characteristics can be successfully incorporated into a singular material, and most available wound coverings will give weight or value to one or more of these characteristics at the expense of another. It is, therefore, noteworthy to mention that adopting effective wound management practices is just as important as the choice of wound covering used over an injury. In concert, both the materials and techniques used to manage a wound (sterility, cleaning or debridement) help to encourage healing, lower infection risks, and prevent the loss of tissue function or pliability (fibrosis and scarring).

While the development of the perfect wound dressing is still a work in progress, some incredible advances have been made since the humble bandage, and this article is a whistlestop tour of a few of those achievements made along the way to perfection.

Advances in waterproof coverings

Wound healing as a process is dynamic, and the needs of the organism or tissue change while progressing stages of the healing process. These stages are nominally categorised into four phases – haemostasis, inflammation, proliferation, and maturation/remodeling³ Recognizing these stages in healing means wound management practices can change accordingly, as well as making adjustments to the type of wound covering used to suit the patient’s needs. Conventional materials such as cotton wool, lint, and gauze used in clinical practice, whilst providing a physical barrier, suffer a number of impractical drawbacks, like sticking to the wound and not maintaining a suitably moist environment. Recently, newer wound coverings for clinical applications not only meet the benchmark of traditional wound dressings/coverings, but the design and application of especially waterproof coverings have improved beyond the mere protective barrier. New designs additionally allow the formation of a ‘microniche’ between the wound surface and the covering. A localised controlled space where the healing process can be better expedited in a number of highly creative ways.

Materials: the building blocks for wound coverings

Unsurprisingly, the sought-after qualities in an ideal wound dressing align with the high functionality of the skin itself: A rudimentary protective barrier with a measure of permeability for oxygen and vapour exchange. As well as having good elasticity and mechanical strength and allows for innate structural remodelling as the skin rebuilds itself. To what extent a wound dressing meets these criteria often depends on numerous factors, including the type of wound and the underlying health of the patient. Nonetheless, to meet this challenge, a dizzying array of materials has become available from both the natural and man-made (synthetic) worlds. Small molecules are used as building blocks to create a tertiary material structure. Examples of naturally occurring materials used as wound coverings are alginate (derived from seaweed) hydrogels, collagen meshes and hydrocolloids (pectin or gelatine colloids coated with a waterproof polyurethane layer). Synthetic materials comprise carbon or silicon-based polymers such as polyethene glycol and polyacrylate, which can also be assembled as hydrogels, fibre meshes and colloids.³

Composite materials, comprising both natural and synthetic moieties, can also be designed and developed to create materials that give mutual benefit, such as improving the structural longevity of some naturally occurring materials by introducing a compatible synthetic polymer. A feature that can be particularly important for controlling the sustained release of a drug imbued within a material, for example.

Designs

Bioactive design for drug delivery and cell therapy  

The ability to control polymerisation or cross-linking of the molecular building blocks during material formation means the mechanical properties of the biomaterial can be tailored to control characteristics like flexibility and degradation rate. This level of control allows the advantage of fewer changes to the wound dressing, significantly reducing the risk of infections.

Both hydrogels and nanofibrous biomaterials allow for the sequestering of small molecules within their design. Therefore, these biomaterials not only act as a sustaining wound covering but also as a delivery vehicle for compounds like growth factors or drugs that can enhance the healing process. In a similar fashion, cell therapies can be administered in this manner to significantly reduce healing times. For example, the delivery of stem cells can be made directly to an injury site to help promote vascularisation, collagen deposition and remodelling, which would be otherwise difficult for the body to do naturally.⁴

The chemical inertness and specific surface patterning (nano topography) of some biomaterials possess bactericidal properties as they play an intricate role in discouraging the attachment and growth of bacteria or their ability to create biofilms. The anti-bacterial properties of surface patterns, in particular, take their cue from nature, as this is very much the case for cicada and dragonfly wings.⁵ Mimicry of this pattern in synthetic materials has also shown the same anti-bacterial and anti-fouling effects.⁶

Smart coverings

Waterproofing wound coverings allows for the integration of wireless systems that are capable of monitoring the healing process of a wound. By assimilating these systems into the material design, continuous monitoring becomes a remote, non-invasive process that subsequently reduces disturbance of the wound site, as related management procedures like visual inspection, washing, and changes can be reduced.

Physiological changes during wound healing serve as good indicators of how the healing process progresses. Uric acid from wound secretions and pH are two of the most reliable biomarkers for monitoring the healing process. As bacteria typically use up available uric acid for metabolism, a significant decrease in uric acid concentrations typically points to an infection. Wound secretions also have a typical pH signature (5.5 – 6.5), which is raised when bacteria is present in the wound.⁷

Sensors designed with pH-sensitive metal oxides such as SnO2 and RuO2 are able to quickly detect changes in wound pH with good sensitivity. However, the more recent development of pH-sensitive polymers, like polypyrrole and polyaniline, now offer a cost-friendly alternative⁷. Omniphobic (hydrophobic and oleophobic) paper coupled to electrochemical sensors have also been developed to monitor both uric acid and pH in real time for chronic wounds.⁷

Biodegradable coverings

Although hydrogel and nanofiber dressings can be imbued with small molecules and different cell types to encourage rapid healing, an added advantage is also the fact that most of these materials, such as alginate, fibrin or collagen, are biodegraded by the cells during matrix remodelling. While the aforementioned natural polymers are easily biodegradable, it is often challenging to exert precise control over their kinetics. On the other hand, biocompatible synthetic polymers such as polyethylene glycol, can be used to design wound coverings with highly precise degradation properties. This afforded precision and control is of particular importance when treating patients who suffer from impaired healing. Individuals with diabetes, obesity, cardiovascular and renal disease, for example.⁸

Cell therapies delivered via a wound covering must balance the rate at which a biomaterial is degraded with its ability to house the desired therapeutic. As maintaining cells ex vivo will inevitably have an effect on the innate functionality and the therapeutic capabilities of the cells⁴.

Summary

Waterproofing material used to aid wound healing can not be underestimated, especially as it protects against the patient incurring further compilations. For patients with impaired healing capabilities, sealing and waterproofing an injury site is of particular importance as it not only helps to create a conducive ‘microniche’, but lowers the risk of developing further complications by helping to reduce the time it takes to heal.  A study comparing the waterproof nature of different types of post-operative casts reported that patients were more likely to suffer from skin breakdown, pressure sores, dermatitis or repeated infection when the casts suffered water damage.⁹

The global chronic wound care market is currently estimated to cost an average of 12.3 billion USD and is projected to rise to 19 billion USD by 2029.¹⁰ As there is no standardised risk stratification method for assessing wound healing, healing rates are often overestimated,11 and therefore, the actual associated care cost is likely to be much higher. The newly designed coverings mentioned in this article not only help to alleviate a burgeoning economic cost but go a long way to improving patient comfort during convalescence, reducing the burden of disease, and improving quality of life.