## 2 Nanotechnology and Nanomedicine
### Nanoparticles  
Nanoparticles have unique physicochemical characteristics at the nanoscale compared to their former properties at micron or higher scales due to certain modified phenomenon like increased reactivity or stability in a chemical process, enhanced mechanical strength, enhanced solubility and relatively large surface area to volume ratio, which make them applicable in various fields of research studies [1]. Nanoparticles differ in physicochemical properties such as their surface morphology (uniform or irregular surface variations), some are amorphous or crystalline with loose or agglomerated features which are either single or multi crystal solids [37]. Nanoparticles have the ability to cross the brain barriers especially the blood brain barrier thereby shielding the encapsulated therapeutic agent and efficiently delivering them to the targeted areas, thus, it is considered suitable for drug delivery systems for the treatment of neurodegenerative diseases [38]. Nanomaterials are indeed very effective and have potential abilities to alter and modify a drug's mechanisms of action, bone reinforcement, DNA structure probes, tissue engineering, drug and gene delivery, protein detection and tumor destruction, molecular imaging, diagnostics, regenerative medicine, pharmaceutical sciences, engineering and industrial chemistry [39]. Abundant biocompatible nanoparticles differ in chemical constituents, nature and physical properties. These nanoparticles are efficient enough to maintain a slow sustained release of loaded drugs at the targeted area which is vital for therapeutic purposes [9]. They are generally applicable in the biomedical field for drug delivery systems, thus, their drug carrying capacity, stability and delivery, encapsulation or adsorption determines their level of effectiveness [40]. Thus, different types of nanoparticles are highlighted below:  
1. Dendrimers
2. Dendrimers are branched nanosized polymers that have simple modifiable surfaces with numerous chain ends which can be adjusted to perform special chemical functions [41]. These macromolecules have monodispersed homogenous shapes, sizes and surfaces with three basic components: repetitive branching units, a terminal group and a central core promoting modified surface functionalities [42]. They are hydrophilic, non-immunogenic and biocompatible in nature which are used for drug and gene delivery [41]. Convergent growth and divergent methods are the well explored methods for synthesizing dendrimers [41; 42]. The three major types of dendrimers are: poly-L-lysine (PLL), poly(propylene imine) (PPI) and polyamidoamine (PAMAM) [42]. The presence of functional groups at the extremist surface of dendrimers, promotes its conjugation with other moieties to aid delivery and detection of other diseases thus, drugs can bind to these functional groups or get completely entrapped at the intramolecular cavity of the dendrimers [41; 43]. The biomolecule-like physicochemical properties, alongside their nanosize, globular shape, multivalence as well as their tubular inner cores, advances their importance thereby attracting interest of scientific researchers [44]. Toxicity and hemolytic properties of dendrimers set their major drawbacks leading to a concern regarding their safety [44]. The toxicity can be due to the characteristic nature of the dendrimers which is related to its core chemistry [41; 44]. 3. Micelles
4. Micelles are self-assemblies of co-polymers which are supramolecular aggregates of surfactant molecules dispersed in a solution colloid with a diameter ranging between 10-100 nm [45; 46]. The small molecule that forms conventional micelles consists of a hydrophilic (polar or charge) \"head\" and hydrophobic \"tail\", which is composed of hydrocarbons of long fatty acid [47]. It comprises of a \"core\" and \"shell\" which forms the inner and outer domains respectively.