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Thermoresponsive characteristics of oligo(ethylene glycol)derivativesof lithocholic acid (LCA) depend on the hydrophilic/hydrophobic balanceof the compounds. Below a threshold temperature (∼30 °C),one of the derivatives, LCA(EG4)2, self-assemblesin water into hollow nanotubes that form thixotropic gels at highconcentrations. Two concentration regimes were observed in the plateaumoduli (G0∼ G′). At high concentrations, the mobility of the nanotubesis restricted at the ordered microdomains acting as cross-links. Insemidilute aqueous solutions, the linkers between the aggregated domainsin the fragile gel rupture easily, and this effect depends stronglyon dilution. Organic hydrophobic additives perturb the self-assemblingprocess, leading to changes in the two transition temperatures andpoorer mechanical properties of the gel. [ABSTRACT FROM AUTHOR]

Poly(vinyl alcohol) (PVA) is a cytocompatible synthetic polymer and has been commonly used to prepare hydrogels. Bile acids and β-cyclodextrin are both natural compounds and they form stable host-guest inclusion complexes. They are attached covalently onto a low molecular weight PVA separately. Self-healing hydrogels can be easily formed by mixing the aqueous solutions of these PVA based polymers. The mechanical properties of the hydrogels can be tuned by varying the molar fractions of bile acid units on PVA. The dynamic inclusion complexation of the host-guest pair of the hydrogel allows the self-healing rapidly under ambient atmosphere and their mechanical properties could recover their original values in 1 min after incision. These PVA based polymers exhibited the good cytocompatibility and high hemocompatibility as shown by their biological evaluations. The use of natural compounds for host-guest interaction make such gels especially convenient to use as biomaterials, an advantage over conventional hydrogels prepared through freeze-thaw method. [ABSTRACT FROM AUTHOR]

Acrylamide derivatives of bile acids are chosen as a hydrophobic comonomer to copolymerize with acrylamide via reversible addition and fragmentation chain transfer (RAFT) polymerization to afford a series of copolymers of P(AAm-co-CAA). These copolymers exhibit a sharp and reversible insoluble-soluble transition in water upon heating to a mixing temperature (T mix) related to the upper critical solution temperature (UCST). T mix of these copolymers can be conveniently tuned to a practical temperature range, around 37 °C for biomedical applications. T mix rises with increasing molar fraction of the bile acid-based acrylamide and increasing concentration of the aqueous solution of the copolymers. The addition of a natural host molecule β-cyclodextrin lowered the T mix. The insoluble-soluble transition of the copolymers was also evidenced by dynamic light scattering and transmission electron microscopy. The biocompatible nature of the bile acids and β-cyclodextrins may make these copolymers potentially useful for biomedical applications. [ABSTRACT FROM AUTHOR]

A mixture of a cholic acid dimer with a secondary amine group and formic acid at a molar ratio of 1/1 is regarded as an organic salt, and it self-assembles in aqueous solutions to form monodisperse nanofibers. The nanofibers are separated at low concentrations of the mixture but entangle with each other at high concentrations to form well-dispersed and randomly arranged 3D fibrous networks. Above the minimum gelation concentration of the dimer, the fibrous network is strong enough to gelate the aqueous solutions to form a hydrogel. Hydrogels obtained from the dimer salt at a lower concentration are isotropic and show extinction between crossed polarizers in the polarizing microscope, whereas they become anisotropic (i.e., nematic hydrogels) upon increasing the dimer salt concentration or under physical stirring. The parallel arrangement of nanofibers from randomly directed fibrous networks may be responsible for the formation of such nematic hydrogels. [ABSTRACT FROM AUTHOR]

Bile acids are amphiphilic endogenous steroids that actas anionicsurfactants in the digestive tract and aggregate in aqueous solutions.Nonionic surfactants were synthesized by grafting poly(ethylene glycol)chains of various lengths (pegylation) to three bile acids (lithocholic,deoxycholic, and cholic acid) using anionic polymerization. The aggregationproperties of the derivatives were studied with viscosity measurementsand light scattering as well as with steady-state and time-resolvedfluorescence techniques, and the aggregates were visualized by transmissionelectron microscopy to elucidate the effect of pegylation on the aggregationprocess. The fluorescence results showed a good correlation with thecapacity of the bile acid derivatives to solubilize a hydrophobicdrug molecule. The solubilization of ibuprofen depends on the lengthand the number of grafted PEG chains, and the solubilization efficiencyincreases with fewer PEG chains on the bile acid. The results indicatetheir potential for use in the design of new bile acid-based drug-deliverysystems. [ABSTRACT FROM AUTHOR]