**2. Significance of nanomaterials in drug delivery**

There are many reasons for which nanoscale size drug delivery systems are attractive to formulation scientists. The most important reason is that number of surface atoms or molecules to the total number of atoms or molecules increases in drug delivery systems. Thus the surface area increases. This helps to bind, adsorb and carry with other com‐ pounds such as drug, probes and proteins. The drug particles itself can be engineered to form nanoscale size materials too [4]. The nanosize device systems, sizes smaller than eukaryotic or prokaryotic cells, can eventually much more in amount reach in generally inaccessible areas such as cancer cells, inflamed tissues etc. due to their enhanced permea‐ bility and retention effect (EPR) and can impair lymphatic drainage thus that can be used for administration of genes, proteins through the peroral route of administration [5]. They can be used to target the reticuloendothelial cells, thereby facilitating passive targeting of drug to the macrophages of liver and spleen and thus enabling a natural system for treating intracellular infections [6]. The nanomaterials used for the purpose should be soluble, safe and biocompatible as well as bioavailable. They should not occlude blood vessel and less invasive and the toxicity associated with the nanomaterials for drug delivery should be

very low so that they can be used to target the specific diseased tissue in a safe concentra‐ tion [7]. They need protecting drug from enzymatic and hydrolytic degradation in the gastrointestinal tract and help in bypassing the "first-pass" metabolism in the liver. They generally remain in the circulation for longer time especially those coated with hydrophil‐ ic polymers and hence suitable for enhancing the efficacy of drugs with short half-lives and can be used to monitor drug as sustained release formulation as well as for delivering DNA [8]. The dissolution rate of drug is enhanced, onset of therapeutic action is increased, and the dose is reduced. The premature loss of drug through rapid clearance and metabolism can also be prevented [6]. They also increase retention due to bio-adhesion.

Nanoscale drug delivery systems such as nanoparticles, nanoliposomes, dendrimers, fullerence, nanopores, nanotubes, nanoshells, quantum dots, nanocapsule, nanosphere, nanovaccines, nanocrystals etc. are believed to have potentials to revolutionize drug delivery systems. Further nanomaterials on chips, nano robotics, and magnetic nanoparti‐ cles attached to specific antibody, nanosize empty virus capsids and magnetic immunoas‐ say are new dimensions of their use in drug delivery. Thus nanomaterials can be used for strategic development of new drug delivery systems and reformulating existing drugs to enhance the effectiveness, patent protection, patient-compliance, safety of drugs and decreasing the cost of health care [9].
