Nanoparticles for Targeted Drug Delivery

Nanotechnology

Nanotechnology is one of the fastest growing technologies with wide research going in almost every stream of science and nanomedicine is one among the lot. The use of nanotechnology in the field of medicine is referred as nanomedicine. In this article, how precisely the properties of nanoparticles and with the help of nanobots the drugs can be released on the targeted site is explained. Besides the synthesis techniques, characterization and release mechanism are explained.

Nanotechnology in general deals with particles or structures atleast one dimension in the order of one by billionth of a meter. The size reduction of the particles into nanoscale introduces a drastic change in their properties when compared to their bulk counterpart. This size reduction of the particles has made it a better candidate for intravenous delivery (IV). The smallest capillaries in our body are in the range of few micrometers, so the particles to be distributed in the bloodstream should be less than that and moreover it should not aggregate which can lead to the formation of embolism.

There are various protocols for synthesizing the nanoparticles but they are selected depending upon the drug used and the delivery route. Polymer nanoparticles especially synthetic ones like PCL, PGA etc are used which are known for their biocompatibility and resorbability.

Different Nanoparticles Injected With Drugs

Targeted Drug Delivery

Emulsification-solvent evaporation technique is commonly used for encapsulation for hydrophobic drugs. In an organic solvent the polymer and compound is dissolved followed by adding water and surfactant for emulsion. Nano-sized particles are induced by sonication or homogenization and finally the organic solvent is evaporated and the particles are collected by centrifugation and lyophilisation. An improvised version of this protocol for hydrophilic drug is to first dissolve the drug and stabilizer followed by emulsion preparations and finally encapsulating the drugs. The polymer membrane should form properly to have efficient drug loading.

Process of targeting drug to a nanoparticle

These hydrophilic drugs have a problem that they leak out from the polymer phase during solvent diffusion step and to overcome this they changed the medium from aqueous to oily.

There are several processing parameters for synthezing polymer nanoparticles. Surfactant/stabilizer, type of polymer, polymer choice, polymer molecular weight and collection method are the processing parameters and by slight variations of these the total drug loading, nanoparticle stability and release characteristics vary.

For drug delivery, the particle size and encapsulation efficiency are two important characteristics and they are determined by the goal of nanoparticle delivery system. For rapid dissolution the size should be less than 100 nm and for prolonged dissolution the particle size should be around 800 nm.

The nanoparticles thus synthesized can be used for targeted delivery like oral delivery, brain delivery, arterial delivery, pulmonary delivery. The nanobots or nanorobots can be employed for diagnostics and therapy. They act as vehicle for delivery of therapeutic agents, detectors or guardians against early disease and perhaps repair of metabolic or genetic defects. They are programmed to perform specific functions which can be accessed remotely and can travel and perform functions inside the human body.

Infected Human consuming Drug Loaded Nanoparticles

The nanobots will seek the target and release some drugs which minimize the potential side effects of generalized drug or may bind with the target inhibiting further growth. They will have a carrier to carry payload and there are three groups which has fascinated the researchers are carbon nanotubes or buckyballs, dendrimers and nanoparticles and nanocrystals. Targeting mechanism to guide the nanobots to the specific location through antigen or antibody reaction or binding of target molecules to membrane –bound receptors. They will navigate through the body dropping anchor when the nanobots reach the target. Single molecular electronics will perform the function of switch. Retrieving these nanobots is quite challenging some may eliminate through natural mechanism of metabolism and excretion or they degrade themselves if biodegradable. A new approach is under study called homing in which they are collected and removed after performing the targeted action.

Like everything has its pros and cons these system too have like pollution and clog of systems in human body or becoming uncontrollable when some functions are lost or nanobots malfunction. The drugs once reach the target has to be released and it can be done in two ways erosion and diffusion. Erosion can be defined as the physical dissolution of polymer as a result of its degradation. Most biodegradable polymers are degraded by hydrolysis. Hydrolysis is the reaction between the water molecules and polymer backbone which repeatedly cuts the polymer chain until it become monomer.

The two possible mechanisms of erosion are bulk erosion and surface erosion. When water is confined to the surface of the polymer matrix, for hydrophobic polymer, chain scission occur only on the surface and drug will be released as the surface of the polymer matrix erodes – this erosion is called surface erosion. If the water penetrates the polymer matrix faster than it hydrolyzes the bonds on the surface, then erosion will occur throughout the entire material- this is also called bulk erosion.

For diffusion –controlled release, the drug’s concentration gradient in the polymer matrix is the driving force for the molecules to diffuse into the surrounding medium. It depends upon the solubility of the drug in the polymer matrix and the surrounding medium, the diffusion coefficient of the drug molecule, the molecular weight of the drug, its concentration throughout the polymer matrix, and the distance necessary for diffusion.

Check this video of nanobots travelling in a fluid.