Abstract
Liposomes are used as a delivery vehicle for drug molecules and imaging agents. The major impetus in their biomedical applications comes from the ability to prolong their circulation half-life after administration. Conventional liposomes are easily recognized by the mononuclear phagocyte system and are rapidly cleared from the blood stream. Modification of the liposomal surface with hydrophilic polymers delays the elimination process by endowing them with stealth properties. In recent times, the development of various materials for surface engineering of liposomes and other nanomaterials has made remarkable progress. Poly(ethylene glycol)-linked phospholipids (PEG-PLs) are the best representatives of such materials. Although PEG-PLs have served the formulation scientists amazingly well, closer scrutiny has uncovered a few shortcomings, especially pertaining to immunogenicity and pharmaceutical characteristics (drug loading, targeting, etc.) of PEG. On the other hand, researchers have also begun questioning the biological behavior of the phospholipid portion in PEG-PLs. Consequently, stealth lipopolymers consisting of non-phospholipids and PEG-alternatives are being developed. These novel lipopolymers offer the potential advantages of structural versatility, reduced complement activation, greater stability, flexible handling and storage procedures and low cost. In this article, we review the materials available as alternatives to PEG and PEG-lipopolymers for effective surface modification of liposomes.
Highlights
Over the past few decades, liposomes have acquired wide acceptance as the nanocarriers of choice for pharmaceutical applications [1,2]
The accelerated blood clearance‖ (ABC) phenomenon affects bioavailability, and passive targeting and its resultant efficacy of the liposome-encapsulated drug [98]. This specific IgM antibody response has been found to recognize the interface between hydrophilic poly(ethylene glycol) (PEG) and hydrophobic lipid [99], which again points to the importance of choosing the right linker between the two moieties
We found that the surface superhydrophilicity imparted by HDAS-SHP
Summary
Over the past few decades, liposomes have acquired wide acceptance as the nanocarriers of choice for pharmaceutical applications [1,2]. Liposomes have a hydrophobic bulk membrane and a hydrophilic inner space This enables them to entrap water-soluble, as well as lipophilic substances, while remaining dispersed in the aqueous environment. These attributes make liposomes a unique nano-vehicle for the delivery of biomedical agents. Liposomes having long-circulating properties have especially drawn considerable attention for prolonged drug persistence in the body, blood pool imaging and targeted delivery of drugs. These applications primarily required liposomes to remain invisible to the normal clearance mechanisms, by the organs of the mononuclear phagocyte system (MPS). With a renewed interest in drug delivery using nano-technologies, this review will encompass the materials and technologies developed to accomplish effective surface modification of the liposomes
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