Science Society: Professor Toby Jenkins discusses nanotechnology in wound dressings

Professor Toby Jenkins of Bath University Chemistry Department has been researching nanotechnology for wound dressings for seven years now and this is his second visit to Bryanston.  His study is based on the need to diagnose wound infections.  This is a difficult thing and there is no definitive way to do it.  There are various types of wounds such as chronic, burns, trauma, surgical sites and all are susceptible to infection and there are hundreds of millions that need treatment every year globally.  What are the principle risk factors for Infection?  There are three:  

• How many bacteria are present.
• How aggressive the bacteria are (strain and type).
• The individual's immune response.

Signs of wound infection are erythema (redness), localised pain or heat, cellulitis and oedema (swelling and water retention).  There are many more, including discolouration and smell, something that experienced nurses and doctors can detect and diagnose from personal experience.  Confirming infection diagnosis currently involves swabbing and microbiology, but it is frequently neither helpful nor cost effective.  Testing blood samples and biopsies can be used, but the latter can be traumatic and is not used in the UK.  We need better diagnostic tools.

Bio markers of infection will be bacterial secretions of toxins and enzymes and bacterial DNA.  The first two can be detected directly in the wound.  All wounds start as contaminated, but problems arise if the wound is colonised and bacteria develop to critical levels which quickly leads to infection. We want to diagnose the infection before the penultimate stage.

Bacteria are living things that reproduce rapidly, communicate using secretions, live in communities, consume resources and modify their environment.  They like to form colonies and their density can become very high.  They secrete toxins and enzymes and some of these secretions are only emitted when the colony is developing and so is a sign of imminent infection.

So, to detect the risk of infection we can detect the secretions directly, or detect the immune response, or local temperature and pH changes.  Detecting the toxins is Toby's theme this evening.

The solution is a wound-dressing which has a dramatic colour change when the secretions are detected.  The toxins break down the walls of tiny spheres that are engineered to have walls similar to cell walls.  When the wall is broken, a dye inside is released.  Fluorescein is used, which fluoresces as its concentration decreases as the dye spreads out.  Designing and making the sphere walls has been a major challenge.  They are now stable for some 18 months but will break down if exposed to the bacterial toxins showing a colour change within 10 minutes of exposure.

The current clinical study is called EVIDEnT and is being developed in four burns units in Bristol, London and East Grinstead.  The aim is to estimate the sensitivity and predictive value of the dressing, taking used dressings from real patients from a suspected infection group and a control group who it is believed have no infection.  Material is taken from the dressings and any bacteria are allowed to grow in model wounds in the laboratory, with the new diagnostic dressings attached.  The findings so far are very promising with a 90% success rate in diagnosing infections.  By 2020 he hopes that the clinical testing can be advanced enough to use directly on patients.