According to the polymer materials used for the preparation of microspheres, they can be divided into synthetic polymers and natural polymers.
Commonly used synthetic materials include polylactic acid (PLA), polyglycolic acid (PGA), poly lactic-co-glycolic acid (PLGA) and polycaprolactone (PCL). ), etc.
PLA is a straight-chain aliphatic polyester obtained by fermenting lactic acid from fast-growing corn as the main raw material and then condensing it with lactic acid. The most commonly used method to prepare microspheres with PLA as the carrier material is the complex emulsion (W/O/W) method. PLA porous microspheres are very suitable for drug delivery of protein peptides because of their interconnected internal pore channels and high specific surface area, and the drug can be integrated onto the porous microspheres by solution impregnation, thus avoiding the deactivation of the drug due to the drastic preparation conditions.
(2) Poly(lactic acid)-hydroxyacetic acid copolymer
PLGA is a polymer material made by polymerizing a certain ratio of lactic acid and hydroxyacetic acid, which has good biocompatibility and biodegradability, and its material degradation products are the same as the metabolism products of the body, so it will not produce adverse reactions to the body, so it is widely used in the field of medical engineering materials and drug delivery. In general, the higher the ratio of ethylene glycol ester, the easier it is to degrade.
Natural polymer materials are large organic compounds that are not synthesized and exist naturally in animals, plants and microorganisms. Natural polymer materials have the following excellent characteristics: wide variety of sources; renewable, in line with the needs of sustainable development; excellent biocompatibility; biodegradable, can be gradually degraded from large molecules to small molecules in the body's physiological environment through hydrolysis, enzymatic digestion and other means, and finally completely absorbed or excreted through metabolism; easy to modify and widely used. It is easy to be modified and versatile. The following are the common natural polymer materials.
(1) Chitosan and its derivatives
Chitosan is a natural cationic polysaccharide obtained by deacetylation of chitin, which is widely used in biomedical and drug delivery fields because of its high safety, good biocompatibility, broad-spectrum antibacterial, tissue repair, hemostasis and immunity enhancement.
(2) Sodium alginate
Sodium alginate is a natural anionic polysaccharide extracted from brown algae and is composed of β-D-mannuronic acid (M segment) and α-L-gulonic acid (G segment) linked by 1,4-glycosidic bonds. Sodium alginate is non-toxic, biocompatible, and its molecular chain contains free hydroxyl and carboxyl groups, which can cross-link with most divalent or multivalent cations to produce a water-insoluble, three-dimensional reticulated hydrogel structure, of which calcium ion is the most commonly used cross-linking agent due to its good safety.
Gelatin is the product of partial denaturation or degradation of collagen in connective or epidermal tissues of animals. It is a straight-chain polymer formed by cross-linking 18 amino acids with polypeptides, and structurally the gelatin molecule is mainly composed of glycine-proline-hydroxyproline repeat sequence, which forms the basic module of the gel structure.
Starch microspheres are generally formed by cross-linking reaction of starch or its modified products. As an excellent carrier material for microspheres, starch has the advantages of non-toxicity, degradability, non-immunogenicity, good biocompatibility, as well as high drug-carrying capacity and low cost, and has been widely used in the fields of nasal drug delivery, arterial embolization, targeted drug delivery, and immunoassay.