## 1 Introduction  
Nowadays, dental implants are a widely-used option to replace a missing tooth. Basically, assemblies are made of a titanium implant and a crown screwed onto the implant. Due to their biocompatibility, as well as corrosion and mechanical resistence properties, titanium and its derived alloys are considered most suitable for use in implant dentistry [1]. The implant is placed inside the bone and the crown emerges through the gingiva in the oral cavity. Up to several years after placement of the implant, a marginal bone destruction may occur (periimplantitis) because of bacterial contamination from the teeth to the implant [2]. Indeed, bacterial colonization is considered the main cause of inflammatory events [3,4]. In fact, in some pathological situations, bacteria incriminated in dental plaque may cause an initial inflammatory reaction of the gingiva [5]. When hygiene cannot be well controlled at this step this process can become worse and resorb the periodontal bone surrounding the implant, leading to periimplantitis [6]. Among other etiologies, the hollow spaces inside the implant and the crown can also get contaminated during this process, creating a reservoir of bacteria that can disseminate to living tissues and worsen the periimplantitis [7, 8, 9, 10]. To overcome such inflammation processes, gels with intrinsic antimicrobial properties [11,12] have been proposed in medicine and research [13]. These gels could be good candidates to fill the implant/crown connection without obstructing the insertion of components. However, the first oral gels to be proposed incorporated chlorhexidine that only provides a short-term antimicrobial action [14]. Antibiotics have also been used but they may promote resistance or allergic reactions [15,16]. In all cases, the main issues are gel degradation in the oral conditions (due to hydrolysis, pH or temperature variations) and quantitative release of antimicrobial molecules from the gel over time. Among others, gel formulations based on polymers associated to cathecol groups appeared good candidates to use for such an objective. Different kinds of polymers that are able to undergo gelation were modified with catechol groups for biomedical applications: chitosan [17,18], hyaluronic acid [19], gelatin [20,21], polyethylene glycol [22,23], polyamines [24] and alginate [25]. Their 3D framework is a scaffold that is organized for specific applications such as drug delivery or healing material [25,26]. Gels based on Alginate-Catechol (Alg-Cat) are a promising candidate for this medical use [27]. This combination is bioinspired from holdfast mussel in a wet environment [28] and associates a backbone of alginate grafted with dopamine [29,30]. Synthesis and use of Alg-Cat to build up films was conducted using the layer-by-layer deposition method [30]. In a previous work, we improved the mechanical properties of these gels by adding thiol-modified Pluronic to Alg-Cat in order to induce disulfide-based crosslinks [31]. Here, we chose to evaluate Alg-Cat 1% alone (m/vol) that forms a thinner sticky layer in order to seal the implant/crown connection. In addition, endogenous antimicrobial peptides (AMPs) are an alternative to antibiotics or antibiotics [32,33]. They are naturally produced by organisms as a first line of defense and belong to the innate immune response [34]. Their amino acid (aa) sequence is generally short with an amphipathic structure, and they are often positively charged, interacting with negatively charged surfaces of bacteria, leading to a penetration of the membrane and the destruction of the microorganisms [35]. Catestatin (CTS) is a 20-aa natural cationic peptide derived from the natural processing of bovine Chromogranin A (CgA\({}_{344-364}\)) [36] and displays antimicrobial activities against bacteria, yeasts, fungus and parasites [32,37,38,39]. CTS also contributes to the regulation of the immune system and can modulate a severe inflammatory response [40,41,42,43,44,45,46].