Polymer coacervation

One of the first methods for making capsules involved polymer coacervation. In this method, macromolecules are dissolved in either the dispersed or continuous phase of an emulsion and are induced to precipitate as a shell around the dispersed phase. Coacervation can be brought about in several ways, such as changes in temperature or pH, addition of salts or a second macromolecular substance, or solvent evaporation (Bungenberg de Jong 1949). 

The earliest commercial application of coacervation was for the development of carbonless carbon copy paper by the National Cash Register Company in the late 1950s. More recently, the field of polymer coacervation has developed steadily so that a more refined and complete classification of coacervation systems can be proposed here (Table 1). Other classification schemes and related principles of coacervation for microencapsulation are available in the literature with illustrated examples. " ... 

According to the classification proposed in this paper (Table 1), polymer coacervation is generally observed in binary or ternary systems, in either aqueous or organic liquids. Three main mechanisms govern the process of coacervation in these systems ... 

Table 1 Classification of common aqueous and organic systems for polymer coacervation Binary systems Coacervation by partial polymer desolvation ...

Generally, all the mechanisms of polymer coacervation involve some sort of phase separation, thereby producing more or less dense coacervate microdroplets. These microdroplets can either engulf an additional component, such as a dissolved drug, or deposit on solid surfaces, which is typically used for coating solid particles added to the system, e.g., drug particles or living cells. 

POLYMER COACERVATION INDUCED BY PARTIAL POLYMER DESOLVATION (SIMPLE COACERVATION)... 

Simple polymer coacervation is based on partial polymer desolvation in binary or ternary systems. This... 

POLYMER COACERVATION INDUCED BY POLYMER 2-POLYMER 3 REPULSION IN TERNARY SYSTEMS... 

Macromolecular Characteristics for Effective Polymer-Polymer Coacervates... 

For alginates, the copolymer composition (ratio of mannuronic to guluronic acid units) can influence the ultimate complex properties. These include elasticity as well as permeability and mechanical resistance of coacer-vates cast into 2D or spherical membrane structures. The type of polymer-polymer coacervate (precipitate, sol, network) will also often be highly molar mass dependent, with useful membranes formd within a narrow window. This often does not correspond to the molar mass range required for bioapplications, which is dictated by factors such as cell toxicity and biocompatability. 

Polymer-polymer coacervates, in microcapsule form, can be characterized by a number of methods, though the most accurate involves a compression-based micromanipulated probe connected to a sensitive transducer.f The precision of such techniques can be as high as 10%. Generally, a 1 1 stoichiometry provides the most stable microcapsules. Other properties, including the sphericity, transparency, or membrane homogeneity are also often characterized. Novel methods based on analytical ultracentrifugation are particularly useful for 2D membranes. ... 

The encapsulation of hepatocytes for a bioartificial liver, and cell therapy for the treatment of other hormone deficiencies or neurodegenerative diseases, such as Alzheimer s and Parkinson s, are also under investigation. Additional examples of cell encapsulation in polymer-polymer coacervates include non-autologous gene therapy,blood substitutes as well as the treatment of prostate cancer. Pharmaceutical applications of microcapsules encompass, in addition, trans-dermal drug delivery and protein delivery such as is required in anti-inflammatory therapy for arthritis. 

Hydrotropes are small, highly water soluble additives that increase markedly the solubility of other components, including surfactants, in water. They are employed very widely in industry. In fact, they only work when the insoluble phase is a mesophase with high molecular mobility (e.g. polymer coacervate or surfactant mesophase). They include weakly self-associating elec-... 

Polymer coacervation is one of the earliest microencapsulation techniques. The first commercial application of encapsulation with coacervation was to the development of carbonless copy paper by the National Cash Register Company, which resulted from patents by Barrett K. Green and Lowell Schleicher in the late 1950s. Since then, coacervation has been used for various applications. 

Polymer coacervation can occur in either aqueous or organic liquids. Coacervation in aqueous liquids and the related processes are mainly used to encapsulate water-immiscible liquids or water-insoluble solid particles. On the other hand, coacervation in organic liquids, or sometimes called phase separation in organic liquids, is used to encapsulate core materials that are not miscible or soluble in the organic liquids. It may be induced by the addition of a nonsolvent to the polymer solution or by the addition of an incompatible polymer based on polymer-polymer incompatibility. This chapter will only discuss the coacervation in aqueous liquids. 

Into linked polymers (coacervation), into liposomes... 

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