Capsules, binary polymer

Table 14. List of binary polymer blends which formed stable capsules...

The majority of the scientific literature describes capsules produced through binary polymer interactions. The most typical capsule is based on alginate-polyly-... 

In a previous publication [8] we described a systematic screening of the binary interactions between 36 polyanions and 40 polycations. As a result of this study it became clear that capsules prepared from simple binary polymer complexes would not be mechanically adequate and multicomponent polymer systems would offer advantages. The rationale for capsule improvement, and for the use of a multicomponent system, has been presented in the Introduction. We have elected to investigate the methods outlined in Sects. 1.2.7 and 1.2.8 (polymer... 

Table 13 lists the properties of individual polymers for each binary pair which yielded a stable capsule. This, along with Table 4, represent the principal contributions of this paper and their results will be utilized throughout the following discussion. 

The majority of the aforementioned capsules were either not sufficiently mechanically stable or suffered from other surface or matrix related deficiencies. These deficiencies include poor morphology, such as capsule sphericity and surface smoothness, which result from an osmolar imbalance. Membranes are also often leaky (an internal polymer slowly diffuses out through the capsule wall) or shrink in either PBS or in culture media over a period of a few hours. Exceptionally, some capsules are observed to swell excessively and burst. Furthermore, some complex membranes, although stable in water, dissolve over several days upon a contact with culture media. This is true for pectin based capsules (pectin/calcium salt) and for alginate-chitosan membranes and maybe a consequence of the polycation substitution by electrolytes present in the media [10]. In order to improve the existing binary capsules several approaches, both traditional and novel, have been considered and tested herein. These are discussed in the following sections. 

Typically, a binary system was selected as the base component of the recipe and the addition of polyelectrolytes to either side (core or receiving bath) was tested to evaluate the change in the capsule properties. The 33 successful multicomponent membrane systems are presented in Table 1. The components of the core material side (21 different chemical compositions) are listed in the first column, while the receiving bath components (20 different chemical compositions) are listed in the second column. With the exception of xanthan and CMC, the first polymer listed on the core side are gelling polymers which form beads with the appropriate ionotropic cation (salt). CMC can also be gelled by ions (alum), although they are considered to be non-compatible for cellular applications. The cations were tested both sequentially, usually with ionotropic cation first, and simultaneously. Walled capsules with adequate mechanical properties were often obtained through the simultaneous application of two polycations. Such a... 

Tiarks et al. have described in detail the theory of droplets composed of binary mixtures in relation to the preparation of polymeric nanocapsules containing HD by miniemulsion polymerization using poly(methyl methacrylate) (PMMA) or PS polymer [37]. First, a miniemulsion of oil phase (monomer -r HD -t initiator) dispersed in aqueous phase and containing an appropriate surfactant is prepared by ultrasonication. The polymerization is initiated by heating the emulsion to 68 °C. When the polymer is formed it separates from the HD phase and, depending on the interfadal tension and spreading coeffidents of monomer/polymer, HD (hydrophobe) and water, capsules with different morphologies are obtained. 

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