Liposomes are well-known as excellent drug delivery vehicles, with a variety of drugs authorised, including carry generics. Modern liposome production procedures are often sophisticated multi-batch techniques. Moreover, liposome manufacturing procedures used in the laboratory may not lend themselves easily to large-scale manufacturing, thereby delaying the development and acceptance of new liposomal systems. This study covers the variety of liposome production techniques known, from small size and scale up to big production, and analyzes their benefits and limits in order to stimulate development and invention in liposome production processes.
Liposomes are spherical lipid-based vesicular structures with a lipophilic bilayer wedged by two hydrophilic surfaces. Liposomes' flexibility and benefits as a therapeutic delivery mechanism for small compounds, peptides, genes, and monoclonal antibodies have been thoroughly explored and accepted in the community of scientific literature. Liposomes are nanomedicines that play an important role in several different areas of healthcare, including the treatment of individuals ailing from heart disease, neurological disease, obesity, malignancy, and inflammation. The worldwide nanomedicine industry was worth USD 135 billion in 2015, and it is expected to grow to USD 350.8 billion by 2025. However, the scalable synthesis of nanomedicines using standard production processes poses a considerable hurdle to its clinical development, and the expense of commercial fabrication is a known obstacle to its transfer from bench to bedside. Despite significant study, it is widely acknowledged that the present procedures for producing liposomes suffer from a number of serious issues, including: I multi-step batch processes; ii) the necessity for particle size reduction (sometimes requiring specialised techniques and apparatus such as extruder and high-pressure homogenization); and iii) restricted batch sizes. This raises the cost of production and impedes the growth of liposomes. This was highlighted by the worldwide scarcity of Doxil®, which was caused by the shutdown of a sterilized injectables production site owing to manufacturing issues. This anti-cancer medicine was in low supply throughout the world for more than two years. As a result, it is critical to develop strategies to make the liposomal manufacturing process leaner, as well as ways to make this drug delivery alternative more appealing from an industrial standpoint.
Phospholipids are dissolved in an organic solvent (usually an equimolar combination of chloroform and methanol, but others such as ether, ethanol, or dichloromethane) in the solvent evaporation procedure, also known as lipid film hydration. If the medicine is lipophilic, it is additionally combined with the organic solvent to create a one-phase solution. The organic solvent is then gently evaporated undervacuum to generate thin sheets of lipid films with homogenous drug dispersion. Tiny lipid sheets are wetted with an aqueous buffer layer well above lipid's glass transition phase. The medicine should be dissolved in the aqueous buffer solution if it is hydrophilic. MLVs with particle sizes in the micrometre range are produced as a result of the dispersion.
The phospholipids are dissolved in an organic solvent that is commonly mixable with water in the solvent dispersion process, with ethanol being the recommended solvent. A lipophilic medication would be dissolved in the ethanolic solution alongside the phospholipids (several other water miscible solvents could be used if the lipophilic drug is not soluble in ethanol). The ethanolic phospholipid/drug solution is mixed with an aqueous buffer solution, resulting in ethanol dilution and the spontaneous production of MLVs. MLVs have particle sizes in the micrometre range. This method is best suited for lipophilic medicines with high entrapment efficiency.Reverse phase evaporation is one of the most used methods for encapsulating a hydrophilic medication in liposomes. The interior watery core is the sole location where hydrophilic medicines may be loaded. As a result, a strategy that can entrap a big quantity of aqueous core during liposome production will result in a high entrapment efficiency and therefore a high drug load. A w/o emulsion is created using the reverse phase evaporation method through dissolving the hydrophilic medication in water and the phospholipid in a water-immiscible solvent (usually chloroform). The organic solvent is then gently evaporated under vacuum, resulting in the formation of a gel phase. Subsequent drying of the organic solvent results in lipid-based dispersion with strong trapping of the aqueous core in the liposomes' internal core.
Though liposomes have been proved to be safe carriers, several liposome preparationprocedures attempt to examine the idea but are challenging to apply on a wide scale. Many researchers, for example, adopt the thin film hydration technique, which uses round-bottomed flasks (50-1000ml) and a few millilitres of organic solvents (e.g., chloroform or methanol). The usage of considerably bigger flasks and, more importantly, massive quantities of organic solvents to scaled up the process may be impractical and harmful to the environment, as vast amounts of organic solvents will need to be vaporized.Regardless of the fact that various methods exist for generating liposomes at the laboratory scale, only a few technologies are employed for commercial manufacture and can supply liposomes with the needed key quality qualities. The most frequent way of producing large-scale parenteral liposomes is ethanol injection followed by extrusion, which has been detailed earlier. The rationale for this is the repeatability of liposome particle size and polydispersity index compared to other small-scale manufacturing procedures, as well as the preference for employing ethanol (Solvent diffusion) over chloroform (Solvent evaporation). The size of the particle and accompanying polydispersity index determine the biodistribution and pharmacokinetics of liposomes, and hence the effectiveness of liposomes. Liposome manufacture on a big scale is a time-consuming and labor-intensive procedure with several unit operations and accompanying testing. Buffer production, filtering, phospholipid solution preparation, filtering, lipid hydration, extrusion, diafiltration, dilution, sterile filtration, and lastly filling are common steps. The related in-process controls for each stage add to the entire process's complexity. pH control at important processes, filter integrity testing, particle size and zeta potential measurements, phospholipid content, bioburden testing bulk drug product assay/pH/related chemicals, and visual inspection at critical steps are all examples of quality control. This is a simple large-scale liposome production procedure that takes no additional complexity into account, such as active loading as in the case of doxorubicin liposomes or freeze drying at the conclusion of the manufacturing process. Every such step will complicate an already complicated production process. A typical large-scale production procedure for liposomes employing the ethanol injection method followed by extrusion comprises roughly 9 unit operations for a model lipophilic or hydrophilic medication. Furthermore, the complexity grows as each unit operation necessitates in-process quality control.
Regardless of the fact that various methods exist for generating liposomes at the laboratory scale, only a few technologies are employed for commercial manufacture and can supply liposomes with the needed key quality qualities. The most frequent way of producing large-scale parenteral liposomes is ethanol injection followed by extrusion, which has been detailed earlier. The rationale for this is the repeatability of liposome particle size and polydispersity index in comparison to other small-scale production procedures, as well as the choice for ethanol over chloroform. The particle size and accompanying polydispersity index have an effect on the biodistribution and pharmacokinetics of liposomes, and hence on their effectiveness. As a result, rigorous control over particle size is required, making the extrusion process important.Currently, the emphasis is mostly on large-scale production. To achieve a predictable therapeutic effect, the product must be subjected to strict regulation, and acceptability standards for both the quality and the procedure must be established. Furthermore, undesired by-products, such as organic solvent residues and/or degradation products, are just as crucial as pyrogen-free and sterile settings. The latter, in particular, remains a significant challenge for industrial operations. So yet, no universally acceptable procedure has been effectively created. Sterile filtration and autoclaving are two common methods for achieving sterility in pharmaceutical items. Both approaches have no or very limited applicability to liposomal medicinal preparations. disruption and/or inappropriate product loss, in conjunction with medication release and instability, are common outcomes in many circumstances. Many firms are currently attempting to overcome this critical problem by using alternate tactics such as lyophilization and production procedures in closed containments equipped with sterile filter barriers.
Liposomes seem to be reliable transporters of a wide range of chemical and biomolecules substances. Liposomes have undergone substantial change in terms of constitution, production, and applications since their discovery, offering up several opportunities in both fundamental and applied life sciences. The broad information offered herein aims to fill some of the gaps in liposome technology and create new avenues for future study. A significant future advance might be the identification of low-cost materials for the formulation of liposome vesicles with amazing adaptability, such as being suited as vehicles for diverse compounds while retaining a clear molecular architecture to operate as cell models for in vitro bioassays. Furthermore, innovative production methods that allow for the simple encapsulation of both lipophilic and hydrophilic molecules without the need of organic solvents, specialised equipment, or complicated infrastructure are greatly sought. Furthermore, the essential issue of disruptions for liposomes filled with hydrophilic materials necessitates the development of novel ways for achieving acceptable loading while aiming for cargo delivery at the location of interest. Finally, because liposomes have shown some clinical effectiveness as drug carriers, future efforts should be directed at guaranteeing the widespread development and application of therapeutic liposomes. This would increase the market usability and viability of liposome products worldwide, particularly in developing and underdeveloped nations.
Assistant Professor, Department of Basic Science and Humanities, IEM, India
