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Bacterial nanocellulose (BNC), as a natural polymer, produced in vivo by bacteria and in vitro by the cell-free enzymes system, is comprised of nano-sized fibers. The pristine BNC possesses unique structural, physiological, and biological properties. Its fibrous and porous morphology allows the incorporation of natural and synthetic polymers, nanomaterials, clays, etc., while the presence of free hydroxyl (OH) groups allows its chemical modification with a variety of functional groups to form nanohybrids. These hybrids not only have superior properties to those of pristine BNC but possess additional functionalities imparted by the reinforcement materials. The properties of BNC-based nanohybrids can be tuned at macro, micro, and nano-scales as well as controlled at molecular levels. This review consolidates the current knowledge on the synthesis of β-(1,4)-glucan chains, their excretion and organization into high-ordered nano-sized fibers, as well as functionalization, both at physiological and molecular levels. It comparatively discusses the microbial and cell-free synthesis of cellulose and discusses the potential merits and limitations of each method. It further explores the methods used for developing BNC-based hybrids and discusses the synthesis-structure-properties relationship of BNC-based hybrids to justify their use for targeted biotechnological applications. A large portion of this review is devoted to discussing the recent trends in the preparation of BNC-based nanohybrids for their biotechnological applications, including biomedical (i.e., wound healing, cardiovascular devices, neural tissues, bone and cartilage tissues, dental implants, and drug delivery) and non-biomedical (biosensing, cosmetics, food, bio- and optoelectronics, environment, energy, and additive manufacturing). Finally, it provides an outlook on the future BNC research for human welfare.

Chitosan is obtained from chitin, which is abundantly found in crustaceans and obtained through various methods. The demineralization, deproteinization, discoloration, and deacetylation of chitin produce chitosan consisting of d-glucosamine and N-acetyl d-glucosamine units that are linked through β-(1,4)-glycosidic linkages. Chitosan has gained significant attention in the biomedical field due to its unique properties such as abundance, renewability, non-toxic nature, antimicrobial activity, biodegradability, and polyfunctionality. One of its key properties is its antimicrobial activity, which is why it has been heavily utilized in the biomedical field. To provide a comprehensive overview of chitosan, this review discusses its extraction from chitin and its properties based on its source and extraction methods. It also delves into various chemical modifications and nanocomposite development using natural and synthetic materials. The review emphasizes the multitude of properties that make chitosan an excellent choice for a wide range of biomedical applications. It discusses various mechanisms of antibacterial activity and the factors affecting this activity. Additionally, the review highlights biodegradability, hemocompatibility, antioxidant activity, anti-inflammation, and other properties of chitosan that contribute to its suitability for different biomedical applications, including wound dressing materials, drug delivery carriers, biosensing and diagnostic devices, bone substitutes, and bioimaging. While discussing some limitations of chitosan, the review concludes with an overview of the future perspective for developing multifunctional chitosan-based nanomaterials that could potentially move from laboratory to clinical trials for treating various diseases.