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Nanotechnologies have enabled novel solutions for the treatment of various diseases. Nano‐drug delivery systems present some advantages over conventional (non‐targeted) drug delivery systems such as high cellular uptake and reduced side effects (Singh et al. 2019). Figure 1.6 represents the comparison between untargeted and targeted drug delivery systems. The development of drug delivery systems by using nanotechnology for various diseases, particularly for cancer treatment, is making revolutionary changes in treatment methods and handling side effects of chemotherapy (Zhao et al. 2018). Furthermore, nanotechnology allows for selective targeting of disease‐ and infection‐containing cells and malfunctioning cells. Nanotechnology has also opened a new era in implantable delivery systems such as those used in bone cement, nano‐needle patches, etc., which are preferable than using other modes of direction like injections and oral delivery. Therefore, nano‐based drug delivery systems have attracted a great of attention due to novel and promising properties like enhanced bioavailability and stability of the drug.

Figure 1.6 Schematic representation of comparison between untargeted and targeted drug delivery systems.

Moreover, antimicrobials are one of the most important therapeutic discoveries in the history of medicine. Some projections suggest that by 2050 the annual deaths caused by multidrug‐resistant bacterial infections will reach up to 10 million per year (de Kraker et al. 2016). Nanotechnology provides an innovative platform to address this challenge, because of their small size and various other physical, chemical, and optical properties. As mentioned above, numerous nanomaterials are reported to have significant antimicrobial efficacies and hence such nanomaterials can be used as next‐generation antimicrobials against various multidrug‐resistant organisms and also in the treatment of different infectious diseases (Rai et al. 2012; Beyth et al. 2015; Rai et al. 2016).

The bioavailability of a drug within the body depends on some factors like the size of the drug molecules and solubility factors (Kesharwani et al. 2018). The conventional dosage system consequently faces some challenges in reaching the target site at an appropriate dose. For example, highly water‐soluble drugs cause fluctuations in drug concentration in the body due to high disintegration properties, and also result in quicker clearance of the drug from the bloodstream. However, some medicines are fat‐soluble and when such drugs are taken in the form of conventional dosage, they face bioavailability difficulties. Similarly, patients suffering from chronic diseases like diabetes need to take painful insulin injections regularly. Likewise, cancer patients regularly have to undergo powerful chemotherapy, which involves quite severe side effects as the anticancer drugs target cancer cells and normal cells equally. Therefore, proper platforms to deliver the drugs at targeted sites without losing their efficacies, and while limiting the associated side effects, are highly required (Mura et al. 2013).

Many novel technologies for developing effective drug delivery systems came into existence in this context, among which nanotechnology platforms for achieving targeted drug delivery are gaining prominence. Research in this field includes the development of drug nanoparticles, polymeric and inorganic biodegradable nanocarriers for drug delivery, and surface engineering of carrier molecules (Senapati et al. 2018). These nanocarriers help in solubilizing the lipophilic drugs, protecting fragile drugs from enzymatic degradation, pH conditions, etc., and targeting specific sites with triggered release of drug contents.

To date, a wide range of nanomaterials enlisted above has been developed and used for applications in nano‐drug delivery. There are many reports on the usage of metallic nanoparticles in drug delivery and diagnostic applications. It mainly includes the applications of silver, gold, and iron‐based superparamagnetic nanoparticles as nanocarriers for controlled and targeted delivery of potential drugs and genes for enhanced clinical efficacy. In addition, nanosuspensions or nanodispersions, which are theoretically considered the simplest form of nanomedicine, contain two specific components, the active pharmaceutical ingredients nanoparticle and the adsorbed surface stabilizer(s), which have been also effectively used in the treatment of various diseases (Adeyemi and Sulaiman 2015).

Similarly, polymeric nanoparticles or nanopolymer manufactured through the chemical conjugation of active pharmaceutical ingredients and a water‐soluble polymer have been used to develop a polymer‐drug or polymer‐protein conjugate or pro‐drug compounds which are further used in the treatment of a wide range of diseases. The chemical degradation releases the active pharmaceutical ingredients into the bloodstream or the site of disease (Tong et al. 2009). Likewise, various other nanocarrier systems like liposome, SLN, dendrimers, quantum dots, etc., are promisingly used in the development of efficient drug delivery systems for potential management of diseases (Liang et al. 2014; Núñez et al. 2018; Mitragotri and Stayton 2019). The role of such nano‐based drug delivery systems in the treatment of various diseases has been briefly discussed here.