Functional Chitosan–Collagen Microaerogels Incorporating Bursera microphylla Fruit Extract with Antibacterial Properties

Bursera microphylla A. Gray is a native medicinal plant from northwestern Mexico whose fruit extract has demonstrated relevant bioactivity. Chitosan (Cs) and collagen (Co) are naturally derived polymers widely recognized for their biodegradability, biocompatibility, and suitability for environmentally friendly biomedical applications. In this study, Cs/Co microaerogels loaded with B. microphylla fruit extract were synthesized, physicochemically characterized, and evaluated for in vitro degradation, cytotoxicity, and antibacterial activity. Three-dimensional Cs/Co hydrogels were prepared by physical crosslinking using ammonium hydroxide, followed by lyophilization and mechanical grinding to obtain microaerogels. Morphological and structural characterization was conducted using scanning electron microscopy (SEM), optical microscopy (OM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and moisture absorption assays. Cytotoxicity was assessed in RAW 264.7 macrophages by MTT assay, while antibacterial activity was evaluated against Staphylococcus aureus . In vitro degradation was analyzed under physiological conditions in the presence of lysozyme (Lz). The resulting microaerogels exhibited irregular morphologies with rounded protrusions and particle sizes mainly ranging from 45 to 90 µm. FTIR spectra confirmed the preservation of native functional groups without new chemical bond formation, while TGA indicated adequate thermal stability of the encapsulated extract. The microaerogels showed hydrophilic properties and a reduced lysozyme-mediated degradation rate due to the presence of collagen and the encapsulated extract. Compared to the free extract, Cs/Co microaerogels displayed lower cytotoxicity, reducing macrophage viability by only 32% at 200 µg/mL. Additionally, extract-loaded microaerogels significantly decreased S. aureus viability by 37% and 57% for the 0.5% and 1% extract formulations, respectively (p < 0.05). These results highlight the role of collagen in modulating structural stability and support the potential of Cs/Co microaerogels loaded with B. microphylla fruit extract as sustainable biopolymeric delivery systems for antibacterial applications.