Metal Modified Nanocellulose as a Synthetic Biofilm Substitute for Mechanical Removal Testing

Introduction: Nanocellulose, a plant cellulose derivative, is a functional and modifiable material its applications go beyond those of raw cellulose. One underexplored application is mimicking bacterial biofilms, which have a wide range of uses in biomaterials, tissue engineering, bioleaching, and many other applications. Bacterial biofilms pose threats to human health, food systems, and water systems. Biofilms consist of communities of bacteria that adhere to surfaces and resist mechanical, chemical, and biological removal. Understanding the behavior of biofilms is essential for maintaining the well-being of critical societal systems. While decellularized eukaryotic systems serve as a valuable platform for understanding mechanical and chemical tissue behavior, biofilms cannot be decellularized. Unlike eukaryotic systems, where the extracellular matrix is more resilient than individual cells, biofilms exhibit the opposite behavior, with individual cells being more robust than the extracellular matrix they produce. The absence of a living, adaptable, material platform increases the challenge in establishing biofilm transport, chemical, and mechanical behavior.<br/><br/>Objective: A nanocellulose synthetic analogue offers the advantage of being a non-living material platform, making production, testing, and replication easier. In-depth understanding of nanocellulose through rheology and research aimed at exploring novel applications, such as biofilm mimicry, would expand its potential applications and contribute to the development of more robust and more environmentally benign responses to biofilm challenges.<br/><br/>Methods: This research generated nanocellulose hydrogels using an ionic liquid solution of 7:12:81 sodium hydroxide:urea:water, and used nanocellulose hydrogels in several experiments including rheology testing where the storage and loss modulus was measured. Hydrogels were modified with metal ions (Cu2+, Zn2+, Sr2+, Co2+, Ca2+, Ni2+) and rheology testing was conducted. Two metal ion modified hydrogels (Ni2+, Ca2+) with rheological properties closer to biofilms were further tested for dental removal.<br/><br/>Results: The metal chelated hydrogels showed similar mechanical behavior to biofilms much more than currently used synthetic biofilm analogues like alginate. The storage and loss modulus that demonstrated biofilm-like behavior were hydrogels chelated with calcium chloride, nickel sulfate, and strontium chloride each exhibiting a storage modulus between 1200-1300, 920-850 and 1050-1020 Pa respectively. In dental removal experiments tested with calcium chloride and nickel sulfate after 60 seconds of irrigation at 30 and 130 psi, it was shown that nanocellulose was 99% removed from ceramic coupons. This research shows that for force removal nanocellulose hydrogels chelated with these ions serve as a good model for bacterial biofilms.