Although several therapeutic approaches are available for wound and burn treatment and much progress has been made in this area, room for improvement still exists, driven by the urgent need of better strategies to accelerate wound healing and recovery, mostly for cases of severe burned patients. Bacterial cellulose (BC) is a biopolymer produced by bacteria with several advantages over vegetal cellulose, such as purity, high porosity, permeability to liquid and gases, elevated water uptake capacity and mechanical robustness. Besides its biocompatibility, BC can be modified in order to acquire antibacterial response and possible local drug delivery features. Due to its intrinsic versatility, BC is the perfect example of a biotechnological response to a clinical problem. In this review, we assess the BC main features and emphasis is given to a specific biomedical application: wound dressings. The production process and the physical-chemical properties that entitle this material to be used as wound dressing namely for burn healing are highlighted. An overview of the most common BC composites and their enhanced properties, in particular physical and biological, is provided, including the different production processes. A particular focus is given to the biochemistry and genetic manipulation of BC. A summary of the current marketed BC-based wound dressing products is presented, and finally, future perspectives for the usage of BC as wound dressing are foreseen.

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Bacterial cellulose: a versatile biopolymer for wound dressing applications

Electroconductive natural polymer-based hydrogels.

Cellulose is mainly produced by plants, although many bacteria, especially those belonging to the genus Gluconacetobacter, produce a very peculiar form of cellulose with mechanical and structural properties that can be exploited in numerous applications. However, the production cost of bacterial cellulose (BC) is very high to the use of expensive culture media, poor yields, downstream processing, and operating costs. Thus, the purpose of this work was to evaluate the use of industrial residues as nutrients for the production of BC by Gluconacetobacter hansenii UCP1619. BC pellicles were synthesized using the Hestrin–Schramm (HS) medium and alternative media formulated with different carbon (sugarcane molasses and acetylated glucose) and nitrogen sources [yeast extract, peptone, and corn steep liquor (CSL)]. A jeans laundry was also tested. None of the tested sources (beside CSL) worked as carbon and nutrient substitute. The alternative medium formulated with 1.5% glucose and 2.5% CSL led to the highest yield in terms of dry and hydrated mass. The BC mass produced in the alternative culture medium corresponded to 73% of that achieved with the HS culture medium. The BC pellicles demonstrated a high concentration of microfibrils and nanofibrils forming a homogenous, compact, and three-dimensional structure. The biopolymer produced in the alternative medium had greater thermal stability, as degradation began at 240°C, while degradation of the biopolymer produced in the HS medium began at 195°C. Both biopolymers exhibited high crystallinity. The mechanical tensile test revealed the maximum breaking strength and the elongation of the break of hydrated and dry pellicles. The dry BC film supported up to 48 MPa of the breaking strength and exhibited greater than 96.98% stiffness in comparison with the hydrated film. The dry film supported up to 48 MPa of the breaking strength and exhibited greater than 96.98% stiffness in comparison with the hydrated film. The values obtained for the Young’s modulus in the mechanical tests in the hydrated samples indicated low values for the variable rigidity. The presence of water in the interior and between the nanofibers of the hydrated BC only favored the results for the elasticity, which was 56.37% higher when compared to the dry biomaterial.

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Production of Bacterial Cellulose by Gluconacetobacter hansenii Using Corn Steep Liquor As Nutrient Sources.

With the development of cellulose chemistry and processing technology, the applications of cellulose materials were not limited to traditional fields as engineering materials in forest originated products, paper, and textile industries, but also used for advanced functional applications in the field of biomedical and smart health care, printed electronics, and responsive wearable textiles. With the advantage of sophisticated geometry fabrication and low cost production, 3D printing technologies have been employed with many materials for a variety of applications. This critical review focuses specifically on the development and assessment of cellulose materials for 3D printing. A special focus was paid on extrusion based 3D printing. Detailed examinations of cellulose hydrogel rheology, fiber entanglement, fiber alignment, gelation, printability, shape fidelity, cell viability and processing parameters in extrusion based 3D printing are explored. Other 3D printing techniques such as inkjet 3D printing, 3D spinning, stereolithography, laminated object manufacturing and selective laser sintering are also introduced. The functionality of 3D printed constructs was designed either by cellulose surface modification or by incorporation of functional components. The properties and performances of 3D printed cellulose constructs as well as their potential applications in the fields of medical, electronics, and smart textile are discussed. Finally, perspective and current important limitations of 3D printing with cellulose materials for advanced application are provided.

3D printing with cellulose materials

Strategies for cost-effective and enhanced production of bacterial cellulose

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Time-dependent rheological behaviour of bacterial cellulose hydrogel

Biological hydrogels, e.g. bacterial cellulose (BC) hydrogel, attracted increasing interest in recent decades since they show a good potential for biomedical engineering as replacements of real tissues thanks mainly to their good biocompatibility and fibrous structure. To select potential candidates for such applications, a comprehensive understanding of their performance under application-relevant conditions is needed. Most hydrogels demonstrate time-dependent behaviour due to the contribution of their liquid phase and reorientation of fibres in a process of their deformation. To quantify such time-dependent behaviour is crucial due to their exposure to complicated loading conditions in body environment. Some hydrogel-based biomaterials with a multi-layered fibrous structure demonstrate a promise as artificial skin and blood vessels. To characterise and model time-dependent behaviour of these multi-layered hydrogels along their through-thickness direction is thereby of vital importance. Hence, a holistic study combining mechanical testing and micro-morphological observations of BC hydrogel with analytical modelling of its relaxation behaviour based on fraction-exponential operators was performed. The results show a good potential to use a fraction-exponential model to describe such behaviour of multi-layered hydrogels, especially at stages of stress decay at low forces and of stress equilibrium at high forces.

Piotr Kuśmierczyk

Papers

Time-dependent rheological behaviour of bacterial cellulose hydrogel

Through-thickness stress relaxation in bacterial cellulose hydrogel