# Biofabricating Three-Dimensional Bacterial Cellulose Composites Using Waste-Derived Scaffolds
## 1 Introduction  
Today, the world faces significant challenges that demand quick and sustainable solutions. Key challenges include resource shortages due to overexploitation [1] and waste of valuable resources that end up in landfills [2]. There is an urgent need to develop innovative materials that are sustainable and use some of the valuable materials that end up in landfills. It has been shown that the metabolism of microorganisms and fungi can be harnessed to convert various carbon sources including waste into innovative materials; one such material is Bacterial Cellulose (BC) [3, 4, 5, 6]. BC, a material stronger than steel at the nanoscale [7], stands out as, compared to plant cellulose, BC is purer, mechanically stronger due to its highly polymerised and crystalline structure, and requires less processing, making it more cost-effective and versatile for a wide range of applications [8]. It has been reportedthat nanocellulose also has resistance to environmental moisture and can enhance water resistance of films, making it a suitable candidate for usage in food packaging [9; 10]. A promising approach to producing BC involves is using Symbiotic Cultures of Bacteria and Yeast (SCOBYs), constituting a diverse consortium of microorganisms, particularly acetic acid bacteria and osmophilic yeast. Traditionally, SCOBYs are associated with kombucha production, a fermented tea beverage originating from China [11]. During fermentation, yeast metabolises sucrose into glucose, fructose, and ethanol, while acetic acid bacteria convert glucose into organic acids, leading to the formation of a nanostructured cellulose biofilm [12; 13; 14]. Bacterial cellulose synthesis involves the polymerisation of D-glucopyranose units via \(\beta\)-1,\(A\)-glycosidic bonds, resulting in macromolecules with degrees of polymerisation ranging from 4000 to 10,000. These polymer chains self-assemble into fibrils via hydrogen bonds, which further organise into ribbons with a length of about 80 nm and a diameter of 4 nm [15]. Due to hydrogen bonding, these ribbons form densely packed fibres, which reach crystallinities between 84-90%. These fibres have lengths in the micrometre range and diameters in the nanometre range, with a length/diameter ratio of about 500. Interfibrillar entanglement and \(\beta\)-1,\(A\)-glycosidic bonds form a highly porous and cross-linked network, resulting in a hydrogel with a minimum water content of 98% [7; 15; 16]. Research into SCOBYs has exponentially increased over the last 20 years, as indicated by the Scopus analysis of publications containing the keywords \"SCOBY\" or \"kombucha\". This rising research interest in SCOBYs mirrors the popularity of healthy, unprocessed, probiotic foods [12; 17]. The main research application fields include the optimisation of beverage production, enhancing health benefits, developing new food recipes and supplements, food packaging, composites with nanocellulose, medical composites incorporating metal ions, biomedical materials, 3D tissue engineering, textiles, sustainable leather alternatives, filtration systems, cosmetics, smart materials, sensors, and electrically active materials or conductors as reviewed in detail by [PERSON] et al. [18] and [PERSON] et al. [11]. Additionally, new applications are being investigated, such as self-cooling materials [19], joule heating elements [20], random lasers with ZnO bionanocomposite foam [21], and aerogels [22]. As is often the case in materials science, research outpaces actual commercial implementation. Despite the growing interest and research in BC, available products made from BC, and more precisely SCOBYs, consist of design prototypes and do-it-yourself projects (see Figure 1). The focus appears to be creating/using these materials as leather or textile alternatives. However, while research into leather alternatives developed from BC is widespread, much less investigation is being performed on grown composite materials.