Biomacromolecules are particularly promising for the fabrication of novel, more effective antimicrobial wound dressings. Contrary to the petroleum-derived synthetic polymers, traditionally utilised, biomacromolecules are more biocompatible and conductive towards re-epithelialization, and can be easily and sustainably processed into films and hydrogels [40]. When these properties are combined with the antibacterial and wound-healing action of nZnO, new biocomposite materials emerge. Biocomposites provide better conditions for injured tissues to re-grow while preventing infections, decreasing healing times, and improving patients’ health. Many biomacromolecules, alone or in a blend, have been used for nZnO-BNC film and dressings obtaining different properties and peculiarities. An overview has been reported in Table 1.

Among these, some have attracted more attention in the scientific communities, which can be classified into two major categories: polysaccharides and proteins.

Chitin is a natural polycationic polymer of N-acetylglucosamine. It is typically obtained from the cuticles of crustaceans, insects, and cell walls of fungi [88,89]. Chitin deacetylation produces chitosan, a renowned antimicrobial material [90] that is also active against some resistant strains, such as the methicillin-resistant Staphylococcus aureus (MRSA) [91]. Chitosan is biocompatible, non-toxic, haemostatic, and, thus, frequently used in biomedicine, also for wound healing [92,93,94,95] and the delivery of drugs and biomolecules [96]. Owing to these properties and due to its good processability, it is often mixed with other polymers, such as poly(ε-caprolactone) [97,98], polyurethane [99], or poly(vinyl)alcohol [100] to produce advanced wound dressing films, hydrogels, and membranes. It also lends itself very well for use in new techniques, such as electrospinning [101,102].

Cellulose is a polymer of β-bonded D-glucose units that can be obtained from plants or synthesised by bacteria [103,104]. It is non-toxic, biocompatible, and biodegradable. It is water-insoluble and possesses good thermal stability. It is gaining increasing attention, particularly in its nanostructured forms [105,106,107,108], and extensive research exists exploring drug loading and combination with nanomaterials [109,110,111]. Gopi and Zhong offered a wide review of its uses and applications in the medical field, including wound dressing and drug delivery [104,112]. Here, bacterial cellulose emerged as particularly promising for the fabrication of films and fibrous mats for wound therapy [113,114]. Several cellulose derivatives can also be obtained by modifying cellulose molecules with different functional moieties, such as carboxyl [115] and allyl [116] groups. This allows the manipulation of key properties, such as hydrophilicity, or enabling its conjugation with drugs or other medical compounds.

Hyaluronic acid, a glycosaminoglycan, is a component of the extracellular matrix. It is typically extracted from animal tissues or produced by the fermentation of some Streptococcus strains [117,118].

Its biocompatibility and hydrophilicity are valuable for the development of biomedical materials, especially hydrogels [119]. Recently, Graça and coworkers [120] offered a review of its applications in wound dressings, underlying its highly beneficial role in wound repair and cell signalling [121,122]. Another review by Ucm focused on the synthesis of hyaluronic acid by bacteria and its applications—including wound healing [123].

Alginate is a linear co-polymer constituting two monomeric units of D-mannuronic acid and L-guluronic acid. It shares similar properties [124] with hyaluronic acid, namely its high biocompatibility and hydrophilicity. Commercial alginate is isolated from brown seaweeds, and its bacterial production has recently gained interest [125]. Its high water-absorption capacity has been known for a long time; thus, this biomacromolecule has been extensively used in the production of wound dressings for high-exudate wounds. Alginate stimulates macrophages’ activation, supporting the healing process [19]. The abundance of hydroxyl and carboxyl groups in its molecule provides this polymer with high reactivity, which is also useful in the design of encapsulation and drug-delivery systems [124]. Its biocompatibility and printability meet the need for biomaterials for tissue engineering and modern wound dressings [126,127,128].

Starch is an abundant, plant-derived polysaccharide composed of α-bonded glucose units. It is endowed with biodegradability, non-toxicity, and film-forming ability. It can be processed with simple extrusion or solvent casting methods to obtain films [129], as well as with electrospinning [130].

β-glucans are typically found in the cell walls of fungi, yeasts, algae, and plants. They are a heterogeneous group of glucose polymers with a common structure comprising a main chain of β-(1,3) and/or β-(1,4)-glucopyranosyl units, along with side chains with various branches and lengths.

They are known for their immunostimulatory properties [131] and they have been shown to stimulate collagen deposition, fibroblasts and keratinocytes migration, and overall reepithelialisation [132,133,134]. Therefore, these polysaccharides have been recently researched to produce advanced dressings, such as wet gels and nanofibers for hard-to-treat and chronic diabetic wounds, as well as for antimicrobial films [74,135,136].

Protein-based biopolymers, such as collagen and gelatin [83,137], are also very popular. Collagen is the main constituent protein of the extracellular matrix and is extracted from animal skin and hides. It is a source of many bioactive peptides. It favours tissue regeneration, has good moisture-retention properties, and has been used for the controlled release of bioactive molecules [40]. Several collagen films have been described in the literature for wound healing and tissue engineering [138,139,140]. Gelatin is a heterogeneous mixture of peptides derived from collagen. It has good film-forming ability, transparency, and ease of combination with functional and reinforcing additives or other biopolymers [141,142]. It has also been used to fabricate scaffolds [143,144], aerogels [145], and antimicrobial nanofibrous composites [146].

Keratin is a fibrous protein that is usually extracted from feathers, nails, horns, or wool [147]. This has raised concerns around the extraction methods and the environmental issues related to the accumulation of waste keratin-containing biomasses [148,149]. It has been extensively researched for the fabrication of films, hydrogels, and fibres, with uses in wound healing, drug delivery, and tissue engineering owing to its biocompatibility, biodegradability, and self-assembly properties [150,151].

Whey proteins are biocompatible and biodegradable byproducts of the dairy industry and are mostly used as food additives and supplements. Their excellent film-forming ability and gelation properties have been extensively investigated and used for the formulation of edible films and particles for the delivery of nutraceuticals. The combination of whey protein isolate (WPI) with nZnO has been described in a previous study [152].