Biopolymer entrapment

Setton and Chilkoti applied ELPs as a three-dimensional matrix to entrap chondrocytes. In their study, ELP[VsG3A2-90] with a transition temperature of 35°C at 50 mg/mL in PBS was used. This biopolymer can be used to generate a suspension with cells, which upon injection into a defect site will form a scaffold. They showed that in vitro the resulting ELP gel supported the viability of chondrocytes and the synthesis and accumulation of cartilage-specific extracellular matrix material. This suggested that ELPs indeed could be used for in situ formation... 

Entrapment of enzymes within reversed micelles can be achieved simply by dissolving the biopolymer, pure or solubilized in an appropriate solvent, in a solution of reversed micelles or by extraction from an immiscible liquid phase [13,165,166]. 

Entrapment of Biopolymers into Sol-Gel-derived Silica Nanocomposites... 

TEOS is of considerable current use on an industrial scale owing to some advantages over sodium metasilicate. Limitations on the sol-gel processing with TEOS arise in the entrapment of biopolymers in silica. They are caused primarily by the alcohol that is separated in the course of precursor hydrolysis Equation (7). Most... 

The next publication appeared in 1984. Venton et al. [67] entrapped antiprogesterone antiserum into a sol-gel derived silica. It retained about 56 % of progesterone binding capacity. The authors mentioned the considerable promise of the sol-gel technique for biopolymer immobilization, but their study was not further continued. 

Interest in sol-gel processing was awakened by the work of Avnir et al. in 1990 who performed successful experiments with such enzymes as [1-glucosidasc, alkaline phosphatase, chitinase and aspartase [68]. This gave impetus to their own systematic study of the entrapment of biopolymers in a silica matrix as well as those of other teams [69-79]. The results have been summarized and discussed in numerous review articles (see, e.g., Refs. [41—43,45—49,51,80—85]). 

Fig. 3.3 The common two-stage sol-gel process used to entrap biopolymers in a silica matrix (see Scheme 3.1). The first stage serves to hydrolyze alkoxide Equation (2) in the acidic or alkaline media. This is also attended with condensation reactions Equations (3) and (4) resulting in the formation of oligomeric silica that self-organizes in the form of sol nanoparticles. Biopolymers are entrapped in the...

These examples demonstrate that additives can have a beneficial effect on the entrapped biopolymers. Unfortunately, they are generally not universal. The additives need to be found for individual immobilized biopolymers and that is not so easy to do. For instance, lactate oxidase retained its activity in a silica matrix if the enzyme was taken as a complex with poly(N-vinylimidazole) prior to the immobilization, but the polymer did not stabilize glycolate oxidase [87,114], Its stabilization was observed after an exchange of poly(N-vinylimidazole) for poly(ethyleneimine). This is a decisive disadvantage of the approaches because they do not offer a general solution that might be extended to any immobilized biopolymer. 

It did not give rise to phase separation or precipitation. Similar behavior was observed when other types of polysaccharides were examined [53,54]. By now all the commercially important polysaccharides have been applied to the fabrication of hybrid silica nanocomposites in accordance with Scheme 3.2. What is more, various proteins have been entrapped in silica by the same means. In all instances the THEOS demonstrated good biocompatibility with biopolymers, even though its amount in formulations was sometimes up to 60 wt%. Biopolymer solutions after the precursor admixing remained homogeneous to the point of transition into a gel state. 

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