Physical–Chemical Assessment and Antimicrobial Activity of Chlortetracycline-Loaded Collagen Sponges

Collagen-based biomaterials are increasingly explored in dentistry for their ability to deliver drugs locally and support healing. In this study, we developed chlortetracycline-loaded collagen sponges aimed at preventing postoperative infections. Five formulations were prepared by lyophilization, each with the same collagen-to-drug ratio but different glutaraldehyde (GA) concentrations: 0%, 0.25%, 0.5%, 0.75%, and 1% (<i>w</i>/<i>w</i>) relative to dry collagen. The sponges were characterized using FT-IR and UV-VIS-NIR spectroscopy, and their swelling capacity, enzymatic stability, and drug release kinetics were evaluated. Antibacterial activity was tested against <i>Escherichia coli</i>, <i>Staphylococcus aureus</i>, and <i>Enterococcus faecalis</i>. Statistical differences between formulations were assessed using one-way ANOVA followed by Tukey's post hoc test (<i>p</i> < 0.05). All sponges released the antibiotic rapidly within the first 60 min, followed by a sustained release for up to 10 h. The non-crosslinked sponge showed the highest antimicrobial effect, while the 0.25% GA formulation offered a good balance between stability and bioactivity. While higher cross-linking enhanced structural stability, it progressively reduced antimicrobial efficacy, highlighting a crucial design trade-off. These findings underline the need to fine-tune cross-linking conditions to achieve both durability and strong antimicrobial action in collagen-based drug delivery systems for dental applications.