If you google the word medical device, you will get pictures of sophisticated hospital equipment and diagnostic devices. In practice, a term medical device is wider than just that and covers a range of different kinds of articles, starting from plasters and bandages to endosseous implants and implantable pacemakers, intended to be used for therapeutic purposes of humans or animals. We have previously written about the role of MFC in wound care products and today we are going to take a step deeper to the current status of nanocellulose in medical devices, especially topical and implantable ones.
Several materials from our everyday life are used in medical devices both in permanent and temporary purpose. Some examples of commonly used materials for permanent implants are titanium, silicone, apatite, Teflon and polypropylene. Instead, resorbable polymers such as polylactic acid (PLA), polycaprolactone (PCL) and polyglycolic acid (PGA) are used in the cases where temporary structures are needed. The major challenge with the current compounds is the foreign body response which can lead into serious physiological problems. There is a clear need for polymers which mimic human tissues in a way that they are not recognized as foreign matter.
Cotton and cellulose based non-woven products have been used for decades for wound care due to the excellent biocompatibility. Thus it is no surprise that nanocellulose as well has gained a lot of attention as a biomedical material for different types of medical devices. Nanocelluloses' high biocompatibility and mechanical strength, combined with suitable physical properties has made them a true candidate for several medical applications. The mechanical and physical properties of nanocellulose in dry state are comparable to human bone whereas the properties of a wet nanocellulose film resembles more of the extracellular matrix (ECM).
In addition to the mechanical properties, the high compatibility of nanocellulose with other polymer allows the development of products with higher performance and better biocompatibility. Although cellulose doesn't readily degrade in the human body due to the lack of cellulolytic enzymes, it hasn't been seen as a problem even for the commercial development, due to the lack of foreign body reaction. For further information on physical properties, toxicology and biocompatibility, take a closer look of the review by Ning Lin, about the use of nanocellulose in biomedicine.
Bacterial cellulose, a subclass of nanocellulose, has been used in food as well as biomedicine for a long time. Nata de coco, a traditional Philippines food product, made of coconut water by fermentation, is a popular desert in several Asian countries and at the same time a classical example of bacterial cellulose. On the other hand, several wound care products based on bacterial cellulose are used continuously worldwide.
These products, mainly intended for short term use, are either sold in a form of hydrogel sheet containing 96% water(Suprasorb® X) or as dry thin films (~50 µm) such as NanodermTM , Cuticell® Epigraft and Nexfill. Usually they are also available as antimicrobial versions, containing either silver particles or antimicrobial agents. There is also a product targeted for long-term use in a body by DePuy Synthes. They introduced their bacterial cellulose sheet in 2015 indented for repair of dura mater (outer layer of brain) which is called SYNTHECEL® Dura Repair. This is a first concrete product targeted for long-term body part repair, made of cellulose fibrils and at the same time an excellent example of the biocompatibility of nanocellulose.
There are challenges related to the use of bacterial cellulose and the biggest of them is the way it is produced. It practically requires growing the cellulose to the desired final form, typically in sheets. Also, the addition/immersion of particles (active compounds) is difficult into the bacterial cellulose membranes. Today, the only practical way is to introduce them by precipitation. Using cellulose fibrils could help with both problems. Firstly, the liquid form of the product allows the mixing of active ingredients, either powder or liquids, and secondly, cellulose fibrils can be shaped or molded into different shapes fairly easily.
Bacterial cellulose has already paved the road in food, topical as well as in implantable use, which could mean that the effort needed for cellulose fibrils, from the regulatory point of view, is lower. Especially, for the commercially available, high purity cellulose based products such as cellulose fibrils. The possibilities are high as cellulose fibrils can be easily formed to different structures, for example, by 3D printing or they can be used to coat medical devices in order to increase the biocompatibility. It will be interesting to see which type of products will enter the market first and how soon.