## 4 Lipsosomal Microencapsulation Using Conventional and Innovative Methods
### Innovative Methods  
#### 4.2.1 Microfluidic Microencapsulation  
The utilisation of microfluidics affords the opportunity for more precise control over fluid streams, circumventing the disordered flows that are characteristic of conventional methodologies. This is achieved through the use of microscale processes that are governed by distinct principles [66]. One notable microfluidics technique is the microfluidic  
Figure 6: Liposome preparation via sonication; (a) bath-type, (b) probe-type. hydrodynamic focusing (MHF) method, which was developed by [PERSON] et al. [67] for the production of liposomes. In this approach, a lipid solution in alcohol is directed through the central channel of the microfluidic device, while aqueous solutions are directed through the adjacent channels. The lateral aqueous streams act to focus the lipid stream into a narrow junction within the device. The formation of liposomes occurs as a result of the diffusion of different molecular species at the interface between the alcohol and aqueous phases. Initially, micelles form, followed by the formation of liposomes (Figure 7). By precisely adjusting the flow rate ratio (FRR) between the lipid and aqueous streams and the total flow rate (TFR), it is possible to achieve monodisperse liposomes with diameters typically ranging from 50 to 200 \(\upmu\)m. This precise size control is critical for ensuring uniformity in liposomal applications. The mean diameter of the liposomes was shown to be directly related to lipid concentration and inversely related to FRR. Additionally, device geometry was identified as a factor influencing liposome characteristics [50; 68]. In summary, microfluidic techniques offer superior control over the physical properties of nanoparticles. The MHF method produces uniform vesicles in terms of size and lamellarity in a single step, in contrast to the TFH method, which necessitates additional steps, such as extrusion or sonication to achieve uniformity. Furthermore, this technique exhibits enhanced encapsulation efficiency (up to 80%) and reproducibility, even at large scales, rendering it well-suited for the production of personalised products [50]. The interaction between the encapsulated compound and the lipids can influence the overall stability of the liposome. Hydrophilic drugs that interact strongly with the lipid headgroups may be more stably encapsulated, while hydrophobic drugs that partition the lipid bilayer can have their release rates modulated by altering the lipid acyl chain length and saturation. An example of the application of microfluidic encapsulation is the fabrication of isohexol-containing liposomes for medical imaging purposes. [PERSON] et al. [69] utilized the microfluidic technique, which involves precise mixing of lipid and aqueous solutions under controlled flow conditions, to create stable liposomes encapsulating iohexol, a contrast agent used in imaging. The study investigated various phosphocholine lipids, including DMPC, DOPC, DPPC, and DSPC, combined with cholesterol at a fixed 2:1 molar ratio. The microfluidic method achieved a high encapsulation efficiency of over 70% across all formulations. In terms of release profiles, the study found that the majority of formulations exhibited an iohexol release of approximately 0.12 mg/mL after two hours, which was non-toxic to kidney cells, highlighting its potential safety for biomedical applications. Notably, the release profile was influenced by the specific lipid composition, with DOPC emerging as the optimal formulation. Stability studies showed that the DOPC-based liposomes maintained their stability for four weeks, as indicated by consistent particle size, polydispersity index (PDI), and zeta potential, at both 5 \({}^{\circ}\)C and 37 \({}^{\circ}\)C. This long-term stability, coupled with the high encapsulation efficiency and controlled release, underscores the effectiveness of the microfluidic technique in producing liposomes suitable for medical imaging, particularly in CT imaging where iohexol serves as a key contrast agent [69].