Biomedical applications Subject

Drug Release from PHEMA-l-PIB Networks. Amphiphilic networks due to their distinct microphase separated hydrophobic-hydrophilic domain structure posses potential for biomedical applications. Similar microphase separated materials such as poly(HEMA- -styrene-6-HEMA), poly(HEMA-6-dimethylsiloxane- -HEMA), and poly(HEMA-6-butadiene- -HEMA) triblock copolymers have demonstrated better antithromogenic properties to any of the respective homopolymers (5-S). Amphiphilic networks are speculated to demonstrate better biocompatibility than either PIB or PHEMA because of their hydrophilic-hydrophobic microdomain structure. These unique structures may also be useful as swellable drug delivery matrices for both hydrophilic and lipophilic drugs due to their amphiphilic nature. Preliminary experiments with theophylline as a model for a water soluble drug were conducted to determine the release characteristics of the system. Experiments with lipophilic drugs are the subject of ongoing research. 

Nucleic acids, DNA and RNA, are attractive biopolymers that can be used for biomedical applications [175,176], nanostructure fabrication [177,178], computing [179,180], and materials for electron-conduction [181,182]. Immobilization of DNA and RNA in well-defined nanostructures would be one of the most unique subjects in current nanotechnology. Unfortunately, a silica surface cannot usually adsorb duplex DNA in aqueous solution due to the electrostatic repulsion between the silica surface and polyanionic DNA. However, Fujiwara et al. recently found that duplex DNA in protonated phosphoric acid form can adsorb on mesoporous silicates, even in low-salt aqueous solution [183]. The DNA adsorption behavior depended much on the pore size of the mesoporous silica. Plausible models of DNA accommodation in mesopore silica channels are depicted in Figure 4.20. Inclusion of duplex DNA in mesoporous silicates with larger pores, around 3.8 nm diameter, would be accompanied by the formation of four water monolayers on the silica surface of the mesoporous inner channel (Figure 4.20A), where sufficient quantities of Si—OH groups remained after solvent extraction of the template (not by calcination). 

Applications of metal-peptide conjugates in general were published in several areas, also extending the range of subjects covered herein. We are restricting the discussion below (1) to metal-peptide conjugates with organometallic compounds and (2) to biomedical applications only. 

The subject of polymer solubility in CO2 has stimulated research with biomedical applications. These are discussed in a later section. 

The synthesis, functionalization and biomedical applications of ONPs is a broad field. In this section we give one approach to the subject, illustrated with some examples. 

The CRP on The Stability and Stabilization of Polymers under Irradiation was organized from 1994 to 1997 (IAEA-TECDOC-1062). The participants began research into the production of polymers under preparation of blends, which should withstand irradiation through the course of their useful lifetimes. They concluded that much remains to be learned in terms of understanding degradation mechanisms and phenomena. The application of radiation for the preparation of polymers for biomedical applications was the subject of the CRP on Radiation Synthesis and Modification of Polymers for Biomedical Applications implemented from 1996 to 2000 (IAEA-TECDOC-1324). 

An important chemical aspect of apatites for biomedical use is the Ca/P molar ratio. Synthesized apatites may be calcium deficient or rich and yet display an X-ray diffraction pattern typical of apatite. Those apatites that are subjected to low temperature processing such as cements and biomimetically processed coatings require a wet chemical analysis for determination of the Ca/P molar ratio. With the new interest in chemically modified apatites, the Ca/P molar ratio, the impurity elements according to present standards (ASTM 1998) and the major substituent elements will need to be reported to provide a better understanding of the apatites being investigated for biomedical applications. 

Un-cross-linked semicrystalline poly vinyl alcohol) hydrogels were prepared by solvolysis of the corresponding vinyl trifluoroacetate polymers and copolymers. The relationships between polymer crystallinity, hydrogel structure, and mechanical properties in the subject hydrogels were examined. Evidence was presented that comonomers acted to disrupt crystal structure and increase water content. The effects of copolymer structure on surface characteristics important to biomedical applications were examined, and the importance of hydrogel nonionic character was demonstrated through protein binding studies. 

When a stability constant is derived from measurements in an ionic medium, the value will vary when the medium is changed. This is a subject of considerable importance, because often the medium of interest is different from the medium of measurement for example, in biomedical applications, the medium of interest is a biological medium such as blood, but that medium is unsuitable for stability constant measurements. CoiTections for variation of ionic strength can be made by using the Davies equation (Eq. 8) to estimate activity coefficients ... 

Of late, significant interest has been paid to hollow polymeric nanostructures (HPNSs) because of the new functionalities and unique physiochemical properties anticipated from polymeric materials at the nanoscale. The development of HPNSs is reflected by the rapid increase in the number of scientific publications and patents on this subject in recent years. HPNSs in the size range of 1-1,000 nm with spherical or cylindrical geometries are of special interest. Spherical HPNSs generally include hollow polymeric nanospheres (HPNSPs), vesicles, or nanopoly-mersomes. Cylindrical HPNSs are basically polymeric nanotubes (PNTs). In view of possible biomedical applications, HPNSPs are potentially useful as encapsulates... 

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