## Materials and Methods
### Antimicrobial Properties  
#### 2.3.1 Antimicrobial Activity of Gels Loaded with D-CTL  
We evaluated the minimal inhibitory concentration (MIC) of D-CTL against _P. gingulis_ (ATCC\({}^{\otimes}\) 32277\({}^{\text{TM}}\)) (anaerobic Gram-negative bacteria) in Brain Heart Infusion (BHI) (Sigma Aldrich, St. Louis, MO, USA) supplemented with hemim (5 \(\upmu\)g\(\cdot\)mL\({}^{-1}\), Sigma Aldrich, St. Louis, MO, USA) and menadione (1 \(\upmu\)g\(\cdot\)mL\({}^{-1}\), Sigma Aldrich, St. Louis, MO, USA). All experiments were conducted under anaerobic conditions in a hermetic box with a sachet generating anaerobic gas (AnnaeroGen 2.5 L, Thermo Scientific, Waltham, MA, USA). Before all experiments the gels were rinsed twice with distilled water to induce the desorption of sodium hydroxyde from the gel; this compound was required to speed up the gelation process but by itself is cytotoxic. We did the antimicrobial tests with a volume ratio of 90% bacteria (OD\({}_{620}\) 0.001)/10% (\(m/v\)) CTL at different concentrations inside the gel (from 470 \(\upmu\)g\(\cdot\)mL\({}^{-1}\) to 50 \(\upmu\)g\(\cdot\)mL\({}^{-1}\)). Bacterial test ranges were performed in triplicate in an incubator at 37 \({}^{\circ}\)C. At t + 24 h, the optical density (OD\({}_{620}\)) was compared with the control media and 5 \(\upmu\)L were dropped in triplicate on a Petri dish that was put in the incubator at 37 \({}^{\circ}\)C. After 24 h, we did a visual control of contaminated dishes: abacteriostatic effect of the gel allows a new bacterial growth in contrast with a bactericide activity, which completely kills microorganisms. In each experiment, Alg-Cat in PBS buffer was mixed with a specific concentration of D-CTL that was freshly diluted in ultra-pure Milli-Q\({}^{\circled{\text{\textregistered}}}\) water. According to previous data relating to a release rate of approximately 10% of AMP outside the Alg-Cat gel [31], we evaluated the optimal concentration of D-CTL to introduce inside the Alg-Cat gel in order to produce the antibacterial hydrogel. 3.2 Analysis with HPLC and Mass Spectrometry of Remaining CTL Inside the Gel and Its Released Derived Fragments  
A measurement of 20 \(\mu\)L from an initial stock solution of L-CTL or D-CTL at 1 mg\(\cdot\)mL\({}^{-1}\) concentration was added to 80 \(\mu\)L of the Alg-Cat initial mixture with 28 \(\mu\)L of gelling solution. A measurement of 180 \(\mu\)L of Milli-Q\({}^{\circled{\text{\textregistered}}}\) water was added to the gel for 24 h at 18 \({}^{\circ}\)C. We performed the release experiments in the presence of distilled water and not a physiological buffer in order to simplify the chromatographic analysis, but we are aware that this could slightly modify the gel swelling and hence the peptide release. For the evaluation of the peptide released, 20 \(\mu\)L of the supernatant was directly collected. For the estimation of the remaining CTL inside the gel after 24 h or 7 days, the gel was extracted and crushed with a razor blade in order to increase the surface to volume ratio to ensure quantitative release of the still-incorporated peptide. A measurement of 180 \(\mu\)L of Milli-Q\({}^{\circled{\text{\textregistered}}}\) water was added to the solution of released fragments and after centrifugation for 15 min (13,000 rpm), 20 \(\mu\)L were collected. In all cases, the liquid sample aspired was mixed with 980 \(\mu\)L of a H\({}_{2}\)0-trifluoroacetic acid (TFA) mixture at 0.1% (vol/vol). The sample was chromatographed with high-performance liquid chromatography (HPLC) and compared with a pure sample of L-CTL/D-CTL from the stock solution. The purity of these peptides was tested by reverse phase (RP) HPLC with a Dionex HPLC system (Ultimate 3000; 13 Sunnyvale, USA) on a Vydac 208 TP C8 column (2.1 \(\times\) 150 mm\({}^{2}\)) equipped with a pre-column Vydac 208 TP 14 (7.5 \(\times\) 2.1 mm\({}^{2}\)) (Vydac, AIT France, Houilles, France).