A Healthy Coating

12 November 2009 (Last Updated November 12th, 2009 18:30)

Protective coatings are coming to the forefront of every industry, including healthcare. Dr Gareth Evans examines the history of antimicrobial technologies and where their future is set to lead in the fight against infection.

A Healthy Coating

The healthcare industry has a long history of driving the development of new technologies and effectively adopting or diversifying existing ones to meet changing therapeutic needs. Today, the pressures to continue to do both are in many ways greater than they have ever been.

On the one hand, increasingly innovative procedures and treatments continue to emerge while on the other, the spectre of the 'hospital superbug' looms large over the whole sector.

Drug resistance is widely considered to be one of the world's most serious and urgent public health issues, with over 70% of hospital-acquired bacterial infections commonly found to be resistant to at least one drug. Against this, any approach which offers a route to achieving microbial control without compromising the opportunity to deploy the fullest appropriate array of patient care is going to be in the ascendancy – and coating technology seems to be leading the charge.

From pharmaceutical excipients and antimicrobial agents for surgical implants, through to meeting the demands of rigorously disinfected surfaces, specialist medical biosystems companies are finding a growing call for the full range of their surface coating technologies. Consultant biochemist Clare Miles says that the technologies have moved into centre stage. "Coatings are pretty hot across the board, right now," she says. It is not hard to see why.

"In the US alone as many as 80,000 bloodstream infections occur every year as a result of catheter use."

Implant growth

The science of medical implants and devices has changed beyond recognition since 1958, when the team at Sweden's Karolinska Institute fitted Arne Larsson with the world's first fully implantable pacemaker.

For all the advances in scope and reliability over the intervening half-century, however, there is no escaping the fact that there is always a certain amount of risk bound up with inserting any kind of foreign device entering a human body.

It has been estimated that in the US alone as many as 80,000 bloodstream infections occur every year as a result of catheter use, while around 0.5% of pacemaker recipients will develop serious infections.

Countering statistics such as these is an obvious priority for device manufacturers and developments in antimicrobial coatings are increasingly being seen as the way ahead, along with allied innovations in antithrombogenic, hydrophilic and lubricant coatings.

It is clearly a major growth area. According to a recent report by BCC Research analyst Jim Wilson, the global market for medical device coatings will increase by $500m to $4.7bn in 2009, and reach $7.5bn by 2014, of which the North American Free Trade Agreement (NAFTA) region and the EU together account for about 80%.

Future trends

Traditionally, device coatings have largely fallen into clearly defined, single-function categories but there is now an increasing move within the industry to combine coating properties in pursuit of a synergistic result.

"The global market for medical device coatings will increase by $500m to $4.7bn in 2009."

Companies such as AST Products and Biocoat have demonstrated success in uniting their proprietary antimicrobial and antithrombogenic technologies with single coatings, leading to improved patient care and greater patient safety.

Miles says, however, that the future of hydrophilic coatings – long established in improving the "wettability" of a range of medical devices such as vascular access guide wires, introducers and catheters – may hold even more promise.

"Hydrophilic coatings are already playing a part in helping fight infections but before too long we could see them being tailored to function more precisely, especially when it comes to how tissues and devices interact," Miles says.

She adds that the trend of developing hydrophilic coatings that have biofilm-inhibiting surfaces to reduce bacterial colonisation will continue in tandem with the increased use of synergistic antimicrobials.

In effect, this would remove any propensity for recently implanted devices to become relatively easy sites for attachment, therefore denying invasive microbes much of the protection from conventional antimicrobial coatings that having a well-formed biofilm layer provides.

"Coatings for devices with short-term residence might be designed to release appropriate pharmaceuticals to aid healing."

Taking this a step further, next-generation multifunctional hydrophilic materials could become highly application specific. The coatings for devices with short-term residence might be designed to release appropriate pharmaceuticals to aid healing while at the same time preventing clotting and infection.

Permanent or semi-permanent implants, by contrast, could be coated with agents engineered to promote or prohibit tissue integration as required. If so, the next 50 years of medical devices look to be shaping up to be every bit as revolutionary as the last.

Surface coating innovations

The need to control microbial infection and especially high-risk examples such as MRSA, Clostridium difficile and Pseudomonas aeruginosa is not, however, confined to the internal environment. To meet the growing demand for safe and effective bactericidal surface coatings for "exterior" items, a number of the most promising recent research efforts have turned to some cutting-edge technologies.

Novel antimicrobial polymers got a boost in March 2009 when it was announced that scientists from the University of Bath are to receive funding under a pioneering €3m pan-European research collaboration to take their new materials to the next stage.

Less than a fortnight later, researchers at the UCL Eastman Dental Institute presented their work on a new, light-activated hard coating – based on titanium dioxide and able to kill 99.9% of E. coli – to the Society for General Microbiology's spring conference.

The antimicrobial effect of titanium dioxide photocatalysis is well known but what makes this development different is the light being used. Normally the technique requires exposure to UV but the addition of nitrogen enables activation by the photons in the visible spectrum, which proves an obvious practical advantage.

"The Auburn University team came up with a nanocomposite solution, combining the antimicrobial properties of lysozyme with the strength of single-walled carbon nano-tubes."

Perhaps one of the most innovative recent developments in the field has seen the application of nanotechnology to overcome the limitations of the naturally occurring antimicrobial agent, lysozyme.

Found in tears and saliva – and elsewhere, including egg white – this enzyme damages bacterial cells principally by catalysing the hydrolysis of peptidoglycan (that forms on the outside of bacteria). However, while it is highly efficient, it is not mechanically robust, making it unsuitable for general surface use.

To overcome this, the Auburn University research team came up with a nanocomposite solution, combining the antimicrobial properties of lysozyme with the strength of single-walled carbon nano-tubes (SWCNTs). Perfect cylinders of carbon, just 1nm in diameter,100 times stronger than steel and equal to only a sixth of its weight, can keep the lysozyme intact and functional within the composite coating matrix.

In laboratory tests it has already proven effective in preventing Staphylococcus aureus from growing on coated surfaces. Auburn University research team leader, assistant professor Virginia Davis says that the advantages are clearly apparent.

"Disinfection generally requires rigorous cleaning with solvent that must remain wet for a given period of time to ensure that surface germs are killed," she explains. "In contrast, we have created a surface that is inherently antimicrobial, so how long it is wet is not an issue."

Although she is the first to admit that the work is still in its preliminary stages, if the planned long-term investigations do show that the coating can hold up to extended use and regular cleaning, it could have considerable potential across the healthcare industry and beyond.

Today, the demand for effective antimicrobial coatings extends far beyond hospitals and other medical facilities, into areas such as consumer products, transport hubs and public spaces. It seems within the hospital setting and across the board, coatings really are pretty hot right now.