Around 10m medical devices are implanted each year into patients, while one-third of patients suffer some complication as a result. Now, researchers in Switzerland have developed a way to protect implants by dressing them in a surgical membrane of cellulose hydrogel to make them more biocompatible with patients’ own tissues and body fluids.
‘It is more than 60 years since the first medical implant was implanted in humans and no matter how hard we have tried to imitate nature, the body recognises the implant as foreign and tends to initiate a foreign body reaction, which tries to isolate and kill the implant,’ says Simone Bottan at, who leads ETH Zurich spin-off company Hylomorph.
Up to one-fifth of all implanted patients require corrective intervention or implant replacement due to an immune response that wraps the implant in connective tissue (fibrosis), which is also linked with infections and can cause patients pain. Revision surgeries are costly and require lengthy recovery times.
The new membrane is made by growing bacteria in a bioreactor on micro-engineered silicone surfaces, pitted with a hexagonal arrangement of microwells. When imprinted onto the membrane, the microwells impede the formation of layers of fibroblasts and other cells involved in fibrosis.
The researchers ‘tuned’ the bacteria, Acetobacter xylinum, to produce ca 800 micron-thick membranes of cellulose nanofibrils that surgeons can wrap snuggly around implants. The cellulose membranes led to an 80% reduction of fibrotic tissue thickness in a pig model after six weeks, according to a study currently in press. Results after three and 12 months should be released in January 2018.
It is hoped the technology will receive its first product market authorisation by 2020. First-in-man trials will focus on pacemakers and defibrillators and will be followed by breast reconstruction implants. The strategy will be to coat the implant with a soft cellulose hydrogel, consisting of 98% water and 2% cellulose fibres.
‘Fibrosis of implantables is a major medical problem,’ notes biomolecular engineer Joshua Doloff at Massachusetts Institute of Technology, adding that many coating technologies are under development.
‘[The claim] that no revision surgery due to fibrosis will be needed is quite a strong claim to make,’ says Doloff, who would also like to see data on the coating’s robustness and longevity.
The silicone topography is designed using standard microfabrication techniques used in the electronics industry, assisted by IBM Research Labs.