# Investigation of Gentamicin Release from
## 1 Introduction  
Nano-based drug delivery systems have received remarkable attention in the past few decades in various biomedical disciplines, including medical biology, diagnosis, prevention and remediation of diseases [1, 2]. A considerable number of nanoparticles have been investigated so far, for the delivery of drugs and other biomolecules in a controlled manner to their specific targeted sites [3, 4]. Some of these drug-loaded NPs are in clinical use for the treatment of various life-threatening disorders, particularly cancers [5, 6]. However, there is still a continuous demand for exploring such NPs to improve the quality of life. Since 2007, PDA NPs have gained extensive attention from researchers all over the world in several fields of life [7, 8]. The main reasons for the interest in PDA NPs are attributed to their highly reactive nature, as well as their availability in various forms and shapes, including nanocapsules, nanoparticles, nanocoatings and core-shell nanocomposites [9, 10]. The concept of PDA was conceived by researchers from the amine-assisted catechol moieties, lysine and3,4-dihydroxyphenylalanine (DOPA), found in marine mussels and mainly responsible for their super adherence on diverse surfaces [11]. From this discovery, [PERSON] et al. investigated the DOPA derivative, dopamine hydrochloride, which carries both of the amine and catechol functional moieties, thereby, responsible for coating diverse substrates in mild alkaline conditions [11; 12]. The dopamine undergoes self-polymerization, hence giving rise to various forms of PDA, depending on specific method conditions. Of all of these methods, the solution oxidation method was found to be versatile, convenient, reproductive and cost-effective [13; 14]. However, minor modifications, in terms of polymerization time and type of reactants, could be tailored depending on the required morphology and/or form of PDA. Researchers are still investigating new methods of PDA synthesis with certain modifications [10; 15]. Recently, [PERSON] and [PERSON] published their review illustrating various methods reported so far, for PDA synthesis and its structural derivatives [16]. Moreover, structural analogues of PDA and its properties are still not clear, hence are under investigation by several researchers, since its discovery in 2005 [17; 18; 19]. Recently, [PERSON] et al. also reported various synthetic methods and formation mechanisms of PDA [20]. Based on its highly reactive nature, PDA exhibits an outstanding and wide variety of properties, such as intensive light absorption in the UV-visible range, photothermal conversion efficiency, metal chelating ability, as a reducing agent, super-magnetism, optoelectronic properties, as a photoacoustic agent, biosensor, photocatalyst, chemotherapeutic and other physicochemical characteristics. Consequently, PDA has emerged significantly in every field of research [20; 21; 22; 23; 24]. Moreover, based on its biocompatible, biodegradable and non-toxic nature, we have aimed in our work to determine the loading and release kinetics of an aminoglycosotide, i.e., gentamicin as a model drug. Gentamicin is used to treat various types of bacterial infections. However, some clinicians have limited its use because of its limited bioavailability, toxicity, shorter half-life and low intestinal absorption. Therefore, the nano-formulation approach may be helpful to overcome such challenges [25; 26]. In a recent work, we reported on the synthesis of PDA NPs and gentamicin loading using an in situ polymerization method [14; 27]. We particularly investigated an in situ method for drug loading to overcome the problems encountered with other loading methods, including the use of toxic substances during synthesis; increased labor and time; and premature and uncontrolled drug release. These drawbacks ultimately lead to drug instability and efficacy, hence compromising the actual purpose of loading drugs into NPs [28; 29; 30].