Hydrophobic microdomain structures

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. 

The formation of a microphase structure can be sensitively detected by using hydrophobic fluorescent probes. Hydrophobic microdomains tend to solubilize hydrophobic small molecules present together in aqueous solution. For example, diphenylhexatriene (DHT) is hydrophobically bound to the St aggregates in ASt-x in aqueous solution and, as a result, the fluorescence intensity is greatly enhanced. Figure 9 shows the fluorescence intensity of DHT in the presence of ASt-x relative to the intensity in its absence (I/I0) as a function of the ASt-x concentration [29],... 

Y. Morishima, M. Tsuji, M. Kamachi, and K. Hatada, Photochromic isomerization of azobenzene moieties compartmentalized in hydrophobic microdomains in a microphase structure of amphiphilic polyelectrolytes, Macromolecules 25, 4406-4410 (1992). 

The hydrophobic microdomains in the macromolecules discusssed here occur also in soaps and proteins. Indeed, one may consider our hydrophobic polyacids as a link between these two substances. Because these synthetic macromolecules allow the investigator great latitude in the design of their chemical structure, they promise to continue to enhance our insight into hydrophobic phenomena, as well as to permit their exploitation for a variety of attractive applications. 

When polymerised systems adopt a polysoap structure, the hydrophobic microdomains joined together by covalent bonds can provide compartments for encapsulating substances. 

Ito E, et al. Active platelet movements on hydrophobic/hydrophilic microdomain-structured surfaces. J Biomed Mater Res 1998 42(1) 148—55. 

The extent of the restriction on the mobility of an azobenzene moiety covalently incorporated into higher-order unimer micelles, monitored by photoisomerization and thermal back isomerization rates, is much more pronounced in cyclododecyl domains than in dodecyl domains, which can be related to a difference in the mobility of these aliphatic hydrophobes in the microdomains (52). Cyclododecane is a rigid molecule with much less conformational freedom than dodecane because of its cyclic structure. The latter is a flexible chain that can adopt a variety of conformations. Therefore, cyclododecyl groups may be more tightly associated than dodecyl groups and form a more rigid hydrophobic microdomain. 

The main feature making pyrene a useful probe for the study of hydrophobic microdomains is the sensitivity of the vibrational band structure of its fluorescence emission spectrum to the polarity of its environment [18]. The relative intensity of the peaks of the emission spectrum undergoes significant perturbation when the solvent polarity increases. In particular, the intensity of the first peak (7i) increases in polar solvents while that of the third peak (73) is essentially unaffected. So the ratio is sensitive to the solvent polarity and more... 

PAS-8 were greater than those on SILASTIC 500-1, PAS-41, and 71. Although the surfaces of PASs and SILASTIC 500-1 were hydrophobic, the contact angle for PAS-8 was slightly lower than those for SILASTIC 500-1, PAS-41, and 71 (see Table 9). It was thought that the PAS-8 surface might have an influence on the aramid block. The phenomenon of the cell adhesion onto PAS-41 and 71 could not be explained by hydrophobicity alone. In former sections, the results of the gas-permeability measurement and the dynamic thermomechanical analysis of PAS implied the presence of a microphase-separated structure between PDMS and aramid phases in the PASs containing over 26 wt% of PDMS [14]. Moreover, a TEM study indicated that PAS films possessed microdomain structures in their bulk phases. That is, not only the hydrophobicity of the surfaces, but also the presence of a microphase-separated structure in the PASs may influence cell adhesion. 

The difference in the extent of the restriction on the mobility of the azobenzene species in the La and Cd domains is related to the difference in the mobilities of the aliphatic hydrophobic groups in the microdomains. Because the self-association of the La and Cd groups of the terpolymers in water is completely due to hydrophobic interactions, the bulky alkyl groups would self-associate to form microdomains to release the largest possible number of structured water molecules into free water and gain a maximum positive entropy [57-59]. If hydrophobic molecules can sterically fit with each other to attain a large contact area, a hydrophobic microdomain so... 

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