Introduction:
In the field of regenerative medicine, bacterial cellulose, due to its biocompatibility, biodegradability, and non-toxicity, is of great interest as a material for implants, dressings for wounds and burns, since its structure is close to that of soft tissues. The high biocompatibility and functionality of Komagataeibacter xylinus B-12068 bacterial cellulose has been confirmed. To control the processes of cell adhesion and increase the mechanical strength, the surface of the material was modified with calcium phosphates, which also affect the ordering of the fibers in the structure. There are various approaches to modifying bacterial cellulose with hydroxyapatite (HA), such as hydrothermal and sol-gel syntheses. The most promising method is the chemical deposition of HA particles on the surface of bacterial cellulose by immersing lyophilized biopolymer films in a buffer solution of calcium chloride (pH = 7.2); however, this method makes it possible to form a uniform coating of calcium phosphate conglomerates on the surface of the cellulose matrix, while in some cases, a different rate of cell proliferation is required for better tissue repair. In this regard, the aim of this work is to develop gradient materials based on a periodically ordered pattern of HA and bacterial cellulose. In this work, the formation of periodic HA structures was obtained by analogy with their formation in an agar matrix. The xerogel and hydrogel of bacterial cellulose were preliminarily kept in a phosphate buffer solution (pH = 7.4) to saturate the biopolymer matrix with phosphate ions, then, a solution of calcium chloride was applied to the surface of the cellulose matrix, which, upon its diffusion into the 3D structure of the cellulose material, formed periodically ordered precipitates in the form of Liesegang rings. Periodically ordered precipitates were stained with alizarin red to visualize the diffusion of calcium ions into the hydrogel. The calcium phosphates were detected by X-ray phase analysis. The biocompatibility of the obtained structures was studied using C2C12 and HeLa cell lines. It was found that higher rates of cell proliferation were observed on cellulose with 3D HA patterns compared to control samples. Thus, a new method for modifying bacterial cellulose with ordered patterns of HA has been developed, which makes it possible to form areas with increased cell density.

Conflicts of Interest:
The authors declare that they have no conflict of interest in the publication of this article. The authors have no conflicts of interest to report in this work. Abstract was not submitted elsewhere and published here firstly.

Funding:
The study was funded by Russian Science Foundation grant (No. 19-79-10244).