Poly SIBS

The TAXUS DES utilizes the Translute polymer—a matrix-controlled system made of a soft elastomeric triblock co-polymer, poly(styrene-b-isobutylene-b-styrene) (SIBS) (37). The chemical structure of SIBS is shown in Figure 6. 

See color plate/ Vascular compatibility of poly(styrene-fxisobutylene-fxstyrene) (SIBS) as examined in the porcine coronaiy model. (A) Histology in the porcine coronary artery for the control bare metal versus SIBS-coated stents at 180 days. (B) Comparative vessel lumen area for the control bare metal versus SIBS-coated stents at 28 and 90 days. Abbreviation SIBS, poly(styrene-Msobutylene- >styrene). Source From Ref. 55. 

See color plate) Atomic force microscopy images and drug release kinetics of the paclitaxel-poly(styrene-i>isobutylene-i>styrene) polymer combination. Abbreviations PTx, paclitaxel SIBS, poly(styrene-b-isobutylene-b-slyrene). 

Biostable polymers have been chosen for use in the majority of DES that are marketed or in clinical development. The main attractiveness of biostable polymers is their physical stability, inertness toward the drug, and predictable drug kinetics. In Cypher, a blend of poly(ethylene-co-butyl methacrylate) (PEVAc/PBMA) is used as the drug carrier. This hydrophobic polymer, along with additional polymer process steps, effectively controls the release of sirolimus, eluting 80% of the drug over 30 days after implantation. In the case of Taxus, atri-block copolymer of styrene-isobutylene-styrene (SIBS) is used as the hydrophobic polymer matrix that releases 10% of incorporated paclitaxel in the first 30 days (20). 

Abbreviations PBMA, poly (ethylene-co-butyl methacrylate) PC, phosphoryl choline PEVAc, poly (ethylene-co-vinyl autate) PLGA, poly (lactide-co-glycolide) SIBS, styrene-isobutylene-styrene SS,. ... 

SIBS Poly(s(yrcnc-f -isobu(ylcnc-/ -styrenc) triblockcopolymcr... 

As outlined in the previous section, the good charge storage of the binary PPE/PS blends was in part attributed to the proposed presence of heterogeneities in the polymer bulk. In this section, heterogeneities are further introduced by adding a third component, namely the triblockcopolymer poly(styrene-Msobutylene-fe-styrene) (SIBS) to form ternary polymer blends with PPE and PS [65], The chemical struc-... 

Scheme 3 Chemical structure of the poly(styrene-Msobutylene-fc-styrene) triblockcopolymer (SIBS) used in this study. The SIBS (grade 103T Kaneka Co.) had a Mw of 78kg/mol (PDI = 1.74) at a PS content of 34.2 wt%...

Ranade et al. [33] describe the paclitaxel-eluting coronary stent, including the methodology to characterise drug delivery from this stent. The polymer chosen for this stent was poly (styrene-P-isobutylene- P-styrene) (SIBS shown in Figure 13) and showed good mechanical properties and stent performance. 

Figure 13. Chemical structure of poly(styrene-P-isobutylene- P-styrene) - SIBS...

Further research has continued into the development of drug eluting coronary stents for the treatment of cardiovascular restenosis. Because the miscibility of paclitaxel with SIBS as demonstrated by the previous authors [33] is low as measured by DSC, Sipos et al. [34] have reported on the synthesis of poly (p-tertbutyldimethylsiloxy)styrene (TBDMS)-P-isobutylene (IB)-PTBDMS), which can be hydrolysed to poly(PHOS-P-PIB-P-PHOS) in order to modulate the solubility of PTx in the polymer, which, in turn, affects its release from the polymer. Further chemical modification of the polymer can be undertaken to effect changes in the polarity of the polymer, including acetylation, which gives rise to PAcOS-P-PIB-p-PAcOS. 

FIGURE 13.16 AFM phase images of poly(styrene-b-isobutylene-b-styrene) (SIBS) triblock copolymers. The images are for (a) polyisobutylene homopolymer (b) branched SIBS with 16% styrene content and (c) linear SIBS with 30% styrene. The darker regions have greater hardness and thus represent the polystyrene domains. (From Puskas et al. (2000) reprinted with permission from John Wiley Sons, Ltd., copyright 2003.)... 

The basic concept to use block co-polymer for the application to the DMFC is that ordered hydrophilic/hydrophobic phase separations offer a route for the selective transport of proton ions with reduced methanol crossover in the hydrophilic domains, because block co-polymers can be selectively sulfonated using post-sulfonation methods, and the block co-polymers can be verified over a wide range of structures during anionic polymerization. For example, methanol transport behaviors of a triblock co-polymer ionomer, sulfonated poly(styrene-isobutylene-styrene) (S-SIBS), were compared with Nafion to determine whether the sulfonated block co-polymer could serve as a viable alternative membrane for application to the DMFC [62]. The S-SIBS membranes showed approximately 5-10 times more methanol selectivity than that of Nafionll , although the S-SIBS membranes exhibited low conductivity compared with Nafion 117. 

PEVA poly(ethylene-co-vinyl acetate), PBMA poly(n-butyl methacrylate), SIBS poly(styrene-b-isobutylene-b-styrene) block copolymer, PC phosphorylcholine pol5rmer, PVDF-HFP poly(vinyUdene fluoride)-hexafluoropropylene, BioLinx hydrophobic Cio-polymer/hydrophilic Ci9-polymer/poly(vinylpyrrolidone) (PVP), PLA polylactide... 

Poly(styrene-b-isobutylene-b-styrene) (SIBS) Permanent matrix for diffusion-controlled DD... 

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