# Therapeutic Potential of Polymer-Coated Mesoporous Silica Nanoparticles
## 1 Introduction
The selection of the right approach for drug loading depends largely on the physicochemical properties of the drug molecule, as well as the polymer characteristics and coating procedure. \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**S. No** & **Title** & **Submission Date** & **Identifier** & **Recruitment Status** \\ \hline \multirow{4}{*}{1} & \multicolumn{2}{l}{Plasmonic Photothermal Therapy of} & \multirow{4}{*}{30 December 2010} & \multirow{4}{*}{NCT01270139} & \multirow{4}{*}{Completed} \\  & Flow-Limiting Atherostic Lesions with Silica-Gold Nanoparticles: & & & \\  & a First-in-Man Study & & & \\ \hline \multirow{4}{*}{2} & Targeted Silica Nanoparticles for Real-Time & \multirow{4}{*}{3 April 2014} & \multirow{4}{*}{NCT02106598} & \multirow{4}{*}{Recruiting} \\  & Image-Guided Intraoperative Mapping of & & & \\  & Nodal Metastases & & & \\ \hline \multirow{4}{*}{3} & Molecular Phenotyping and Image-Guided & \multirow{4}{*}{18 November 2019} & \multirow{4}{*}{NCT04167969} & \multirow{4}{*}{Recruiting} \\  & Surgical Treatment of Prostate Cancer Using & & & \\ \cline{1-1}  & Ultra small Silica Nanoparticles & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Clinical trials on silica nanoparticles. Natural polymers such as chitosan and poly(dopamine), as well as chemically synthesised artificial polymers such as poly(ethyleneimine) (PEI) and poly(ethyleneglycol) (PEG), have been widely utilized for coating purposes (Figure 2). The selection of a polymer for coating is mostly based on the predefined properties required for the desired outcome, such as sustained release, biocompatibility, targeting, or stimuli responsive release of cargo from MSNs [16]. The stimuli-responsive drug release characteristic in MSNs could be of great benefit, which allows the release of the loaded drug only at the target site and thus enhances the therapeutic response and minimizes the side effects. The stimuli-responsive trigger can be either exogenous (external stimuli such as magnet, light, temperature) or endogenous (internal stimuli such as pH, redox, enzyme). However, a combination of more than one stimuli-responsive character to generate multiresponsive systems are reported to be superior to single systems. Specifically, the endogenous stimuli responses are highly variable in different patients due to changes in the pathophysiology of disease in each individual. Thus, a dual or triple responsive carrier system with a combination of endogenous and/or exogenous characteristics is capable of releasing the drug more precisely at target sites [17,18]. Figure 1: Graphical representation of the approaches used to prepare drug loaded MSNs coated with polymer. Figure 2: Polymers of natural and synthetic origin that have been used as coating agent for MSN for providing control over drug release. The pathophysiological condition of the targeted disease forms the basis of properties required to design a polymer coated MSN, and effective treatments of numerous diseases through polymer coated MSNs have already been explored (Figure 3). Therefore, in this review, the polymer coated MSNs have been categorized based on the disease conditions, and the associated advantages are discussed in detail.