## 1 Introduction  
Biomaterials (BMs) are natural or synthetic substances that interact with the human body, enhancing the repair or replacement of tissues because of their biocompatibility [1]. BMs can be divided into different classes: metallic, ceramic, glassy, polymeric, composite, and biodegradable polymers [2, 3]. Among these classes, bioceramics and bioglasses have attracted great interest from researchers because of their ability to promote osteointegration [4, 5, 6, 7]. The introduction of new implants to a living body may cause inflammation phenomena with consequent infection processes. These phenomena could be avoided by producing hybrid composite BMs with anti-inflammatory and antimicrobial agents, improving the therapeutic effect, and enhancing controlled drug delivery [8]. Traditional bioceramic and bioglass materials used for the implant are made by high-temperature processes that may be up to 1000 \({}^{\circ}\)C, and they do not allow the entrapping of thermolabite compounds, such as drugs. To avoid this drawback, the use of sol-gel synthesis allows the incorporation of a bioactive agent (anti-inflammatory or antimicrobial drug) [9, 10, 11]. The sol-gel process is a colloidal route used to synthesize any material with an intermediate stage, including a sol and/or a gel state, starting from a molecular precursor (e.g., metal salts, alkoxides, organic monomers, oligomers) or colloidal particles (e.g., graphene oxide sheet, carbon nanotubes) [12]. In the case of the sol-gel synthesis for organic/inorganic hybrid glassy biomaterial, it occurs with hydrolysis and polycondensation of a molecular precursor, generally, a metal alkoxide M(OR)\({}_{\chi}\) where M is a metal (such as Al, B, Si, Ti, Zr, etc.) and R is an alkyl group, by heating and stirring processes [13]. These reaction steps led to the formation of a gel structure, which turns into glass material after the drying process [14; 15]. Despite some disadvantages (costs of the precursor, long gelation time, and strong reduction in the gel volume after the drying procedure [12; 14]), the sol-gel allows the control of reaction parameters, such as the concentration of reactants, temperature, and catalysts; therefore, the control of materials synthesized, such as the morphology and mechanical properties. Current state-of-the-art research reflects how sol-gel chemistry shows several advantages since it allows the possibility to synthesize functional materials, which are usable in various fields [16; 17; 18; 19]. Recent studies have been conducted on the feasibility of synthesizing via the sol-gel route hybrid systems (formed by silica, polyethylene glycol, and quercetin) having antibacterial properties [20; 21]. Like quercetin, caffeic acid (A), is one of the major nutritional antioxidants and belongs to the family of flavonoids. It is ubiquitous in vegetables, fruits, tea, wine, and food supplements in the form of extracts and/or pure forms [22]. Caffeic acid, also known as 3_A_-dihydroxycinnamic acid, is a phenolic acid derived from hydroxcinnamic acid. This organic acid has many effects on various diseases, such as osteoporosis, certain cancers, lung diseases, cardiovascular diseases, and ageing [23; 24]. Moreover, it also has interesting biological properties, such as antimicrobial, fungicides, and antioxidants [25; 26]. It has been reported that caffeic acid shows antimicrobial potential against _Staphylococcus aureus_, _Staphylococcus epidermidis_, _Klebsiella pneumoniae_, _Serratia marcescens_, _Proteus mirabilis_, _Escherichia coli_, _Pseudomonas aeruginosa_, _Bacillus cereus_, _Microoccus luteus_, _Listeria monocytogenes_, and _Candida albicans_ strains [26; 27; 28; 29]. The antimicrobial activities of caffeic acid are partly due to its lipophilic nature that allows the interaction with the cytoplasmic membrane of the microbial cells, especially with the hydrophobic portion [27].