# A Review of Properties of Nanocellulose, Its Synthesis, and Potential in Biomedical Applications
## 1 Introduction  
Congenital abnormalities, trauma, malfunctioning, aging, disease, and functional loss of organs or tissues are the most common public health challenges [1, 2]. Biopolymers are obtained from natural sources and are biocompatible with the human body. Chitosan, alginate, starch collagen, cellulose, and other biopolymers have been found in many natural species [3, 4].  
Cellulose is an abundant, sustainable, naturally occurring biopolymer that has aroused attention in the biomaterial community to produce eco-friendly and biocompatible goods [5, 6]. These naturally occurring polymers have attracted significant interest in biomedical applications such as the administration of drugs, wound healing, and scaffold tissue engineering [7]. Cellulose is a naturally occurring linear molecule made up of D-anhydroglucopyranoside subunits linked via \(\beta\)-glycosic bonds, in which cellobiose is the repetitive unit [8, 9]. The term nanocellulose (NC) refers to cellulose with a dimension in the nanoscale [10]. Obtained from native cellulose, nanocellulose occurs mainly in plants, animals, and bacteria in three primary forms: (1) cellulose nanocrystals (CNC), (2) cellulose nanofibers (CNF) which are sometimes also known as nanofibrilated cellulose (NFC), and micro-fibrilated cellulose (MFC), and (3) microbial or bacterial nanocellulose (BNC) [11, 12]. The molecular backbone of cellulose is similar to all three types of nanocellulose; however, chemical and physical characteristics may differ based on the origin and purification procedures [13].  
The sources of bacterial cellulose (BC) or bacterial nanocellulose (BNC) include mainly the Gram-negative bacteria _Acetobacter xylinum_ (_Glucanacetobacter xylinum_). _Archromobacter_, _Acetobacter_, _Ataligenes_, _Sarcina_, _Pseudomonas_, and _Rhizobium_ are the microbial sources capable of producing nanocellulose [14; 15; 16; 17; 18; 19]. Maize cob, cotton, wheat bran, banana leaves, sugar beet, wood, potato tuber, and mulberry husks are potential plant sources for nanocellulose extraction [20; 21]. CNC is primarily obtained by the acid hydrolysis of natural cellulose [22; 23; 24]. The CNC is 100-500 nm long and 4-20 nm wide, with crystalline syringe-like structures. CNF is frequently produced from biomass degradation and chemical reactions. CNF is a 1 \(\upmu\)m long combination of amorphous and crystalline, having a diameter of 20-100 nm, and is the purest type of nanocellulose without any contaminating components [19; 25; 26; 27].  
Nanocellulose offers tunable surface functionalization, excellent mechanical strength, high hydrophilicity, and biocompatibility. It can also easily create hydrogen bond networks [13; 28; 29; 30; 31; 32; 33; 34]. Therefore, nanocellulose is receiving a deep interest in biological applications, where it can be used as a carrier for the successful delivery of drugs to damaged tissues and other biomedical applications [35; 36; 37]. In the current study, we aim to provide a detailed study on the characteristics of nanocellulose, their production, and fabrication methods of nanocellulose-based composites by using additive manufacturing techniques. Moreover, the biomedical applications of nanocellulose-based composites have been discussed. In the end, future trends, challenges, and possible opportunities for nanocellulose in the biomedical field have also been highlighted. Figure 1 represents a schematic visual of the current review paper.