Zn-Modified Composite Materials Based on Hydroxyapatite and Cucurbit[n]urils

Zinc is an essential trace element that plays a key role in bone metabolism and possesses osteogenic and antimicrobial properties, making it a promising component for biocompatible bone implant materials. Zinc-modified hydroxyapatite (ZnₓHA) demonstrates enhanced osteoconductivity and the ability to suppress bacterial growth. To further expand the functionality of such materials towards controlled drug delivery, their modification with macrocyclic compounds is of significant interest. This work investigates novel composite materials based on zinc-substituted hydroxyapatite (Zn₀.₅HA) functionalized with cucurbit[n]urils (CB[n], where n = 6, 7, 8).The synthesis of CB[6], CB[7], and CB[8] was carried out using a standard procedure, and their structures were confirmed by XRPD and IR spectroscopy. Modification of the pre-synthesized porous Zn₀.₅HA scaffolds was performed via the solution immersion method using solutions/dispersions of the respective cucurbit[n]urils. IR spectroscopy confirmed the formation of the composites and revealed that the interaction between Zn₀.₅HA and CB[n] occurs primarily through the carbonyl groups of the macrocycle portals. Scanning electron microscopy (SEM) showed that the morphology of the deposited layer significantly depends on the type of macrocycle: for CB[6], the formation of needle-like nanocrystals is observed; for CB[7], rare agglomerates due to its high solubility; and for CB[8], macroscopic conglomerates with a complex hierarchical structure.Biological testing revealed that all obtained materials (Zn₀.₅HA + CB[6], Zn₀.₅HA + CB[7], Zn₀.₅HA + CB[8]) exhibited no hemolytic activity (< 5%), meeting the requirements for medical materials. However, functionalization with CB[n] led to a statistically significant reduction in the antibacterial activity of the composites against Escherichia coli compared to unmodified Zn₀.₅HA. This reduction correlates with the macrocycle cavity size and is presumably due to their high complexing ability towards zinc ions, which slows the release of active Zn²⁺ ions.It is demonstrated that the developed composite materials based on Zn₀.₅HA and CB[n] combine osteoconductive properties, biocompatibility, and potential for use as controlled drug delivery systems, opening prospects for their application in regenerative medicine as components of bone implants. Further research aimed at controlling the release of zinc ions in the presence of macrocyclic carriers is necessary to optimize their functional characteristics.