Stem cell therapies
bilayer (Nagalingam, 2017). Furthermore, the phospholipid bilayer is both biocompatible and biodegradable. This implies that the nanoparticle is safe for oral or intravenous delivery and will breakdown in the blood to release its contents. Therefore, the liposomal membrane allows liposomes to travel in the blood, passing through the plasma membrane and acting as a container for therapeutic macromolecules. These biochemical properties entail that liposomes are well-designed for drug delivery, thus being used in many clinical trials and they are available on the market for usage. However, though synthesized using naturally occurring biological polymers and materials, the liposome is not produced by the human body. Instead, the drug vehicles are commercially manufactured (Rooijen, 1998) . As a result, liposomes are identified by the body as ‘non - self’ or foreign cells that do not share the same antigenic materials as the host. Firstly, this results in a significant level of immunogenicity (Schwendener, 2014). Upon entering the blood plasma, the liposome could be detected as foreign, causing an immune response to be initiated that will destroy the drug vehicle and dispersing all of its contents. This trait of low-level toxicity reduces efficacy. Also, the liposome is not stable. Not naturally produced by the body, liposomes are not suited to interact with other molecules within the bloodstream. The phospholipid bilayer of the liposome can react with substances in the bloodstream, either hydrolysing or oxidizing and becoming ruptured (Crommelin, 1986). In the gastrointestinal tract, bile can solvate, irreversibly react with, the liposomes, causing tears that will release the encapsulated therapeutic agents (Deb, 2019). Thus, the biochemical instability reduces the effectiveness of this drug delivery method. An alternative to liposomes is the exosome. Exosomes are vesicles that transport proteins, RNA, and other molecules for intercellular communications. These fluid-filled sacs are naturally occurring, produced in all eukaryotic cells by the endosomal compartment, the region responsible for sorting molecules (Dammai, 2017). Their natural function is to carry cargos of macromolecules, such as proteins and nucleic acids, between cells. On arriving at their destination, exosomes can deposit their cargos (Figure 3.1). This is achieved by fusing with the cell membrane of the targeted cell before hydrolysing, dispersing their contents into the cell (Bhagyashree, 2020).
Figure 3.1 – Exosomes detect proteins on the cell surface and are then taken up by endocytosis.
As with liposomes, the outer layer of exosomes is made of a phospholipid bilayer. This entails exosomes are soluble, so they will pass through the plasma membranes easily. The phospholipid bilayer also ensures that the exosome will be biodegradable and biocompatible. So, its degradation can be
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