Entrapment, biomaterials

In this chapter, I would like to review polymer materials and bioencapsulation techniques focusing on the analysis of their merits and disadvantages, and to discuss some biomedical applications of nano- and microcarriers (both particles and capsules) with entrapped biomaterial, which have been recently reported in the literature. 

An original universal technique based on layer-by-layer (LbL) adsorption of oppositely charged macromolecules onto a surface of inorganic colloid particles has been recently elaborated [30,31]. Hollow nano- or microcapsules with entrapped biomaterial can be easily prepared by decomposing an inorganic core, although the microcapsule wall can provide desired release properties. The use of various polymer materials allows a proper shell design, in order to adjust required stability, biocompatibility, and affinity properties of the microcapsules. 

The main advantage is that the entrapment conditions are dictated by the entrapped enzymes, but not the process. This includes such important denaturing factors as the solution pH, the temperature and the organic solvent released in the course of precursor hydrolysis. The immobilization by THEOS is performed at a pH and temperature that are optimal for encapsulated biomaterial [55,56]. The jellification processes are accomplished by the separation of ethylene glycol that possesses improved biocompatibility in comparison with alcohols. 

The decreased denaturating action of the precursor and procedure enables one to immobilize reduced amounts of biomaterial. It was demonstrated in Ref. [55] that biocatalysts prepared by entrapping endo-l,3-P-D-glucanase and a-D-galactosidasc in amounts comparable to that in living cells had a reasonable level of activity. When the TEOS is applied, the enzyme content in silica matrix can be up to 20-30 wt.% to counterbalance losses due to denaturation [50]. 

Ben-Knaz R, Avnir D. (2009) Bioactive enzyme-metal composites The entrapment of acid phosphatase within gold and silver. Biomaterials 30 1263-1267. 

Plant cell cultures represent a potentially rich source of secondary metabolites of commercial importance and have been shown to produce them in higher concentrations than the related intact plants. However, plant cell cultures often produce metabolites in lower concentrations than desired and commonly store them intracellularly. These limitations can be overcome by product yield enhancement procedures, including immobilization of cultured cells, and permeabilization, or ideally using a combined immobilization/ permeabilization process with retained plant cell viability. Complex coacervate capsules consisting of chitosan and alginate or carrageenan proved to be effective biomaterials for entrapment, controlled permeabilization of cells and to allow control of capsule membrane diffusivity. 

Retama JR, Lopez-Ruiz B, Lopez-Cabarcos E (2003) Microstructural modifications induced by the entrapped glucose oxidase in cross-linked polyacrylamide microgels used as glucose sensors. Biomaterials 24 2965-2973... 

The overwhelming interest on the developments of CD inclusion polymers arose since the discovery of a-CD inclusion complexes with PEO of different molecular weights [16] and the subsequent synthesis of the polyrotaxanes composed of multiple a-CD rings threaded and entrapped on a polymer chain (Fig. 2) [17,18], So far, a large number of reports have been published on the CD-based polypseudorotaxanes and polyrotaxanes [12,18 19] and their applications in biomaterials [50-58],... 

The first event that generally occurs after blood contacts a polymer surface is the formation of a protein layer at the blood-polymer interface (1). The formation of this protein layer is followed by the adherence of platelets, fibrin, and possibly leukocytes (2). Further deposition with entrapment of erythrocytes and other formed elements in a fibrin network constitutes thrombus formation. The growth of the thrombus eventually results in partial or total blockage of the lumen unless the thrombus is sheared off or otherwise released from the surface as an embolus (3). Emboli can travel downstream, lodge in vital organs, and cause infarction of tissues. The degree to which the polymer surface promotes thrombus formation and embolization, hemolysis, and protein denaturation determines its usefulness as a biomaterial (4). 

S. Wen, et al.. Multifunctional dendrimer-entrapped gold nanoparticles for dual mode CT/MR imaging appUcations, Biomaterials 34 (5) (2013) 1570-1580. 

Tissue engineering scaffold for DNA delivery by cationic polymers. Biomimetic scaffolds can be encapsulated with growth factors and MSCs are seeded onto their surface [top]. Polymeric release bottom left) consists in the entrapment of the complexes between cationic polymers and DNA within the biomaterial for release into the environment. Conversely, substrate-mediated delivery bottom right), also termed reverse transfection delivery, employs the immobilization of complexes to the biomaterial. MSCs can internalize the complexes either directiy or by degrading the linkage between the biomaterial and DNA complexes. 

The bacteriostatic and antibacterial properties are in addition to pH-conditions and the nanostructural entrapping mechanism also related to the surface structure developed of the hydrated biomaterial. The nano-particle/crystal size of hydrates are in the interval 15-40 nm with a nanoporosity size of 1-3 nm. The number of pores per square micrometer is at least 500, preferably > 1000 [9]. The number of nanopores will thus be extremely high, which will affect the possibility of catching and fastening bacteria to the hydrate surface - an analogue to how certain peptides may function as antibacterial material due to a structure with nano-size holes within the structure. This may also provide a long-term antibacterial activity after the initial hydration. 

Ragheb, A. M. Hileman, O. E. Brook, M. A., The Use of Poly(ethylene oxide) for the Efficient Stabilization of Entrapped a-Chymotripsin in Silicone Elastomers A Chemometric Study. Biomaterials 2005,26,1653-1664. 

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