Alec Bangham in 1961, at the Babraham Institute, in Cambridge (Bangham and Horne 1964). Liposomes are among the group of organic nanomaterials which are comparatively small, spherical vesicles that are amphipathic (contains both hydrophilic and hydrophobic structures). Liposomes are generally composed of phospholipids and spontaneously formed when certain lipids are hydrated in an aqueous media (Singh et al. 2019). The unique structure of liposome (i.e. lipid bilayer[s] structure) facilitates the incorporation of both hydrophilic and hydrophobic drugs, which helps to prevent the rapid decomposition of the incorporated drug and also to release the drug molecules at a specific targeted site (Lujan et al. 2019). Liposomes reported having several promising properties such as small size, lipid bilayer structure, surface charge, biocompatibility, biodegradability, low toxicity, site‐specific delivery, etc. Due to all these properties, liposomes have attracted a great deal of attention from researchers all over the world for their use as potential drug delivery systems in various diseases including cancer (El‐Hammadi and Arias 2019). Moreover, liposomes have been modified to develop some other phospholipid vesicles which selectively have their applications in the delivery of specific drugs or biomolecules (mostly for transdermal delivery). These vesicles mainly include transferosomes, niosomes, and ethosomes.
1.2.2.4 Transferosomes
Transferosomes are the modified form of liposomes which are considered to be highly elastic and deformable. These modified forms of liposome were developed by Gregor Ceve for the first time in 1990 (Blume and Ceve 1990). Transferosomes are almost similar to liposomes in their basic structural arrangement; the only difference is that the outer layer of transferosomes is more complex in nature compared to liposomes. These nanomaterials reported having enhanced flexibility due to edge activator presence in lipid bilayer (Abdallah 2013). Usually, transferosomes are formed by self‐controlled assembly and they are efficient to cross the various transport barriers, and hence are selectively used as carriers for the delivery of drugs and other macromolecules instead of liposomes (Sharma 2019).
1.2.2.5 Niosomes
Niosomes are another kind of liposomes that are supposed to be osmotically active, highly flexible, and comparatively more stable than liposomes (Bartelds et al. 2018; Sharma 2019). These nanomaterials are mainly composed of nonionic surfactants like alkyl ethers, alkyl glyceryl ethers, sorbitan fatty acid esters, and polyoxyethylene fatty acid esters stabilized by cholesterol (CH) (Muzzalupo and Mazzotta 2019). Like liposomes, they also form a lamellar structure in which the hydrophilic heads have oriented outward and the hydrophobic tails point inward or facing the opposite direction to form a bilayer (Sharma 2019). Niosomes are economically viable nanomaterials compared to liposomes and other related nanomaterials; moreover, they possess various novel properties such as their biodegradable, biocompatible, and non‐immunogenic nature (Singh et al. 2019).
1.2.2.6 Ethosomes
Ethosomes are also a type of phospholipid vesicles, considered a modified form of liposome mainly composed of ethanol, phospholipids, and water. In addition, some other components can also be included in ethosomes for specific characteristics e.g. polyglycol as a permeation enhancer, cholesterol to increase the stability, and dyes useful for characterization studies (Sharma 2019). These vesicles for the first time were developed by Prof. Elka Touitou around 1997. The simple synthesis process, high efficacy, and nontoxic nature of ethosomes allowed their use in widespread applications related to transdermal delivery. Ethosomes are soft, malleable vesicles tailored for enhanced delivery of active agents (Verma and Pathak 2010). Ethosomes are noninvasive delivery nanocarriers that facilitate penetration of drugs deep in the skin layers and the systemic circulation, and are reported to have higher transdermal flux than liposomes (Godin and Touitou 2003). The presence of ethanol in higher concentrations makes the ethosomes novel and unique, as ethanol is known for its disturbance of skin lipid bilayer organization.
1.2.2.7 Solid Lipid Nanoparticles (SLN)
SLNs (Figure 1.2e) are among the class of lipid nanoparticles having a size in the range of 1–1000 nm, usually have a crystalline lipid core which is stabilized by interfacial surfactants (Sun et al. 2019). These nanomaterials were introduced in 1991 for the first time. SLN are reported as having various novel properties such as easy synthesis, low cost, ability to store various molecules/drugs with high loading capacity, controlled drug release, improved stability, improved biopharmaceutical performance, etc. Therefore, SLN have been preferably used over the other various drug delivery systems like emulsions, liposomes, and polymeric nanoparticles (Pink et al. 2019).
1.2.2.8 Dendrimers
Dendrimers (Figure 1.2f) are highly branched three‐dimensional nanomaterials consisting of polymeric branching units attached to a central core through covalent bonding, which are organized in concentric layers and that terminate with several external surface functional groups (Lombardo et al. 2019). Dendrimers are synthetic nanomaterials fabricated by a specific synthesis approach involving a series of different reactions that allow precise control on various parameters like size, shape, and surface chemistry which result in highly monodisperse nanostructures. Like various other nanomaterials described above, it is possible to conjugate suitable drugs or macromolecules like proteins or nucleic acid into the surface of dendrimers in order to use them as potential nanocarrier (Virlan et al. 2016). Dendrimers reportedly enhance the solubility and bioavailability of hydrophobic drugs that are entrapped in their intramolecular cavity or conjugated on their surface. However, various factors such as surface modification, ionic strength, pH, temperature, etc., influence the structural properties of dendrimers (Choudhary et al. 2017). Figure 1.2 represents the schematic illustration of various organic nanomaterials.
1.3 Role of Nanomaterials in Diagnosis, Drug Delivery, and Treatment
All the above‐mentioned inorganic and organic nanomaterials are reported as having direct applications as antimicrobial agents, or indirect applications as a nanocarrier for the conjugation of a variety of drugs and other biomolecules in order to develop efficient drug delivery systems for various life‐threatening diseases, including cancers.
1.3.1 In Diagnosis
Nanotechnology has provided many useful tools that can be applied to the detection of biomolecules and analyte relevant for diagnostic purposes (Baptista 2014). This new branch of laboratory medicine, termed nanodiagnostics, includes early disease detection even before symptoms' presentation, improved imaging of internal body structure, and ease of diagnostic procedures; determines disease state and any predisposition to such pathology; and identifies the causative organisms by using recently developed methods and techniques of nanotechnology such as microchips, biosensors, nanorobots, nano identification of single‐celled structures, and microelectromechanical systems (Figure 1.3) (Jain 2003; Baptista 2014; Jackson et al. 2017). As an evolving field of molecular diagnostics, nanodiagnostics have been positively changing laboratory procedures by providing new ways for patient's sample assessment and early detection of disease biomarkers with increased sensitivity and specificity while nanomaterials used for detection of pathogens or disease biomarkers have been developed and optimized in such way that becomes less nuisance for patients (Jackson et al. 2017; Bejarano et al. 2018). Although nanotechnologies have been applied to diagnostics of several diseases with promising results, the medical imaging and oncology are still the most active areas of development (Bejarano et al. 2018). In recent years, many studies have been directed to the design of new contrast agents allowing easy, reliable, and noninvasive identification of various diseases (Ahmed and Douek 2013).