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topical therapy of psoriasis. The assessment of the in vitro skin permeation of MTX in their study showed its capability to go through the skin barrier when loaded within NLCs formulation which confirms the high potential of NLC as carriers for MTX and feasibility for topical delivery.

      1.3.2.4 HIV

To deal with HIV progression and prevent development of resistance, a combination of multiple drugs is given which is known as highly active antiretroviral therapy (HAART). Antiretroviral drugs should be able to cross the mucosal epithelial barrier when used orally. It has been reported that nanoparticles conjugated with antiretroviral drugs have the potential to target monocytes and macrophages in vitro. Poly(lactic‐co‐glycolic acid) (PLGA) nanoparticles were entrapped with three antiretroviral drugs, ritonavir, lopinavir, and efavirenz, and analyzed. It was observed that PLGA nanoparticles depicted sustained drug release for over 4 weeks (28 days), whereas the free drugs within 48 hours (2 days) (Rizvi and Saleh 2018). Thus, nanoparticles could be utilized for drug delivery of anti‐HIV drugs.

      1.3.2.5 Neurodegenerative Diseases

      Nerve growth factor (NGF) is very crucial for the survival of neurons and can be used a potential therapeutic agent for neurodegenerative disorders. NGF could not cross the blood‐brain barrier (BBB) but can be preferably used as a drug delivery vehicle to transport drugs across BBB. Various studies have reported NGF encapsulated in transferring and cereport‐functionalized liposomes improve the permeability across the BBB. Also, resveratrol in combination with lipid core nanocapsules were found to be highly efficient against Aβ‐induced neurotoxicity. The drug delivery system was observed to improve short‐term and long‐term memory (Singh et al. 2019).

      1.3.2.6 Blood Pressure (BP) and Hypertension

      Polymer nanoparticles like PLGA, poly(lactic acid) (PLA), and chitosan have been used in conjugation with antihypertensive drugs for targeted and controlled drug delivery. A significant and sustained reduction in blood pressure (BP) has been recorded employing nifedipine conjugated with PLGA, PCl nanoparticles. The most important benefit of sustained release of hypertensive drugs is that it regulates BP fluctuations; also, lower doses are required compared to conventional drugs (Singh et al. 2019). Liposomal drug formulations have also been investigated using animal models for hypertension. It was observed that a single intravenous dose of liposomal formulation encapsulated with vasoactive intestinal peptide normalized BP for longer duration compared to non‐encapsulated peptide. Thus, successful conjugation of anti‐hypertensive drugs with nanoparticles increases drug circulation and also prolongs systemic availability of drugs at required concentrations (Singh et al. 2019).

      1.3.2.7 Pulmonary Tuberculosis

      Mycobacterium tuberculosis (MTB) is the causative agent for pulmonary tuberculosis causing worldwide deaths. It affects all the parts of the body, but lungs are mostly infected due to inhalation of MTB. Drug dosage for the treatment is generally given orally and repeated doses in high concentration are required for the treatment process. However, drug administration through inhalation is more advantageous and requires lower doses. Encapsulated nanoparticles for drug delivery efficiently penetrate the biological membrane and reach the target site. MSNPs were reported to act as a platform for the delivery of anti‐TB drugs. Functionalized MSNPs could be internalized competently and used as controlled drug delivery vehicles (Singh et al. 2019).

1.4 Advantages and Challenges Associated with Nanomaterials Used in Drug Delivery, Diagnosis, and Treatment of Diseases

Nanotechnology is a double‐edged sword. On one edge, it has revolutionized medicine as well as the healthcare system by introducing innovative ways of developing new drug delivery systems or reformulation of existing drugs, as well as new devices for diagnosis, monitoring, and treatment of diseases owing to their enhanced permeability, retention, and therapeutic effects; the other edge showed potential health risks (Patel et al. 2015). As discussed earlier, nanomaterials which are considered as building blocks of nanotechnology possess novel and unique properties such as small size, high surface to volume ratio, high performance, etc. All these properties make them suitable candidates for the various biomedical applications discussed previously. On the other hand, sometimes the same properties become responsible for causing harmful effects in human beings. However, while focusing on the significant advantages of nanomaterials, their toxicological aspects are overlooked.

      1.4.1 Advantages of Nanomaterials

      There are many studies have been performed and some of them are already discussed above which proposed the potential role of various nanomaterials such as liposomes, SLN, polymeric nanoparticles, etc. in specialized drug delivery, in the development of biocompatible nanomaterial prosthetic implants, the metal‐containing engineered nanoparticles, etc. for both the imaging and treatment of various diseases including cancers (Wright et al. 2016). Moreover, such nano‐scale size materials usually encapsulate therapeutic and/or imaging compounds, popularly known as nanomedicine, in nano‐size systems typically with sizes smaller than eukaryotic or prokaryotic cells. They offer immense opportunity in patient‐specific, targeted, and regenerative medicine technology with applications such as: regeneration of tissue cell therapy; regeneration of tissue with help of nano‐scale biomaterials; active or passive drug release; diagnostic tests; in vitro tests with sensors for determination of molecules that react with particular disease (biomarkers); in vivo measurements of biomarkers by imaging techniques using nanoparticles as contrast media; and more (Sharma et al. 2018).

      Also, nanomaterials on chips, nanorobotics, and magnetic nanoparticles attached to specific antibodies, nano‐size empty virus capsids, and magnetic immunoassay are new dimensions of their use in drug delivery. The benefit of nano‐scale drug delivery systems, like nanotubes, nanocrystals, fullerenes, nanosphere, nanoparticles, nanoliposomes, dendrimers, nanopores, nanoshells, quantum dots, nanocapsule, nano vaccines, etc., is that they increase the efficacy and efficiency of the loaded drug by delivering a notable array of medications to almost any organ or specific site in the body (Mukherjee et al. 2014). As well, they minimize accumulation in healthy body sites to reduce toxic effects of the drug, as they can reach the specific site through active or passive means providing targeted, controlled, and sustained therapeutic effects. These unique characteristics lead them to generally inaccessible areas such as cancer cells, inflamed tissues, etc., and also provide an opportunity for the peroral route of administration of genes and proteins on account of weakening lymphatic drainage.

      Formulation scientists can modify the structure of materials to extremely small scales leading to an increase in surface area relative to volume, and large surface area allows for increased functionalities of these multifunctional nanosized molecules, which consecutively promote selective targeting to the desired sub‐cellular targets, avoid destruction by macrophages, effect permeation through barriers, and deliver its components in a controlled way once it gets to the target cells and tissues. They also facilitate passive targeting of actives to the macrophages of the liver and spleen through direct delivery to reticuloendothelial cells and thus permitting a natural system for treating intracellular infections. Their suitability for enhancing the efficacy of drugs with short half‐lives is attributable to the long‐time spent in circulation and can be used to examine drugs as sustained‐release formulations as well as for delivering DNA (Mukherjee et al. 2014; Sharma et al. 2018).

There is no denying the fact that articulating drugs at the nano‐scale provides potential advantages with the possibility to modify properties like solubility, drug release profiles, diffusivity, bioavailability, and immunogenicity. The dissolution rate of the drug can be enhanced with an increase in the onset of therapeutic action as well as the reduction in dose and dose‐dependent side effects (Patra et al. 2018). Furthermore, an amalgamation of drug therapy and diagnosis, termed “theranostics,” at the nano‐scale has exceptional applications and can help diagnose the disease, affirm the location, identify the stage of the disease, and provide information about the treatment response.

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