**3.2 Modified two-step method**

*Role of Novel Drug Delivery Vehicles in Nanobiomedicine*

(**Figure 1**) [18].

**3. Method of preparation**

individual components.

**3.1 Two-step conventional method**

explored indicate that the arrangement and fusion process are based on the method of preparation (that were discussed in the next section). In the two-step conventional method, the layer might be due to formation of lipid by layer that get adhere to the core particle that followed by the integration due to hydrophilic and hydrophobic interaction among the lipid and polymer component. However, in the single-step method, the most investigated and revealed mechanism is the precipitation of the lipid component on the polymeric core material. Some newer techniques might also involve the self-assembling of these structural components

Various formulation methods have been designed and employed for the preparation of LPHNPs based on the chemical and physical nature of the structural components and the desired therapeutic purpose or outcome. These hybrid DDS include the lipid-polymer, lipid metal, polymer-inorganic hybrid, metal (Gold, Silver or Iron) along with polymer hybrid NPs have investigated and employed for the clinical use. Conventionally, two different approaches have been investigated including the two-step and single-step processes. First approach employed the mixing of the inner core and the outer layers to prepare the LPHNPs. While the single-step approach the lipid and polymer that are assembled using the different mechanisms to form the LPHNPs that overcome the drawback of

Two-step method was the most primitive and frequent method applied for the preparation of different hybrid nanoparticles and other DDS. In the method, the different layers comprise of structurally, different components were separately fabricated and then co incubated to make a complete particle by using the various approaches including the adsorption, self-assembling and encapsulation. The core and shell morphology might be obtained and the various hybrid nanoparticles were obtained by using the sonication [19], solvent emulsification, solvent evaporation [13], nanoprecipitation [20], extrusion, high speed homogenizers and other techniques. However, the selection of the method is based on the physicochemical properties of the loaded drug, size of the core particle and the desired properties that you want to introduce in the NP formulation [18]. For example, the single-step method has been chosen when the encapsulating materials are miscible with the coating substance and soluble in the organic

This method involves multiple preparatory steps to prepare the polymeric core materials and then the lipid vesicles by the different techniques. The polymeric core material might be prepared by dissolving the polymer in a suitable solvent and then precipitated into some nonsolvent phase. Finally, the both components are co-incubated and mixed under gentle stirring for certain time period to allow them to get assembled into lipid-polymer hybrid particles [22, 23]. The mixing may be carried out by vortexing, thin film hydration, probe sonication or extrusion processes so that the final LPHNPs were obtained. These processes actually provide the energy for the mixing, layering or adsorption of the outer coating material on the polymeric core material that might be strengthen by the electrostatic forces among

**62**

solvent [21].

these structural components.

Different modifications have been suggested in the conventional two-step process for the fabrication of the LPHNPs. These modifications might include the use spray drying and lithographic molding along with the freeze drying [24]. The inner central core of the NPs have been prepared with the process that further suspended or dispersed in any suitable organic solvent containing the different structural components of the LPHNPs [2]. Different studies indicate the formulation of LPHNPs loaded with various antibiotics agents including levofloxacin, ciprofloxacin and isoniazid in the form of freeze dried powders for the inhalation therapy that were entrapped in the mono or multiple layers of the lipid shell. The coating of the lipid might provide the core shell morphology to the NPs. This modification in the preparation of the NPs added advantage in term of better inhalation efficiency and greater control on the overall average particle size of the LPHNPs relative to the conventional method [25]. The nanoparticles and hybrid microfiber fabrication are the some other examples that utilized the polyglutamic acid, poly lysine and various grade of PLG and PLA using the freeze-drying method [26, 27].
