As part of our continuing research work, studies toward the self-aggregation behaviour of amphiphilic triblock copolymers containing b-CD-Pluronic F127 polyrotaxane as a central block and hydrophilic brush-like PPEGMA as flanking blocks in aqueous solution were conducted by using dynamic and static light scattering (DLS and SLS) analyses and transmission electron microscopy (TEM). These self-aggregates are characterized by a unique random coil structure. Their hydrodynamic radius (R h ) and radius of gyration (R g ) decrease as the number of the entrapped b-CD molecules increases, while the core of the random coils becomes looser due to the increase of the rigidity and steric hindrance of the brush-like polymer chains. Interestingly, it was observed that the morphology of the aggregates changes greatly after loading amphotericin B (AmB). According to the DLS/SLS and TEM results, it was speculated that a solid sphere is formed, and that the density of spheres increases as the number of entrapped b-CDs increases. For these self-aggregates, as the number of entrapped b-CDs increases, their drug-loading content (DLC) and drug-loading efficiency (DLE) for AmB increases, while their hemolytic activity against rabbit erythrocytes decreases. It appears that the multiple hydrogen-bonding interactions between AmB and the entrapped b-CDs make a significant contribution to the morphology change of the self-aggregates and their high loading capability for AmB.
A series of biodegradable polyurethanes (PUs) were synthesized using poly(ε-caprolactone) diol (PCL) to react with L-lysine ethyl ester diisocyanate (LDI) chain extend with L-lysine ethyl ester (LEE) in solution of DMF. The structure was characterized by gel permeation chromatography, ¹H-NMR, Fourier transform infrared, and DSC analyses. Mechanical property testing showed that their tensile strength rose with increasing the hard segment content with a maximum tensile strength of 34.43 ± 1.73 MPa. The average mass loss for the hydrolytic degradation was only about 13 % in 56 days while this value for the enzymatic degradation was around 95 % in 30 days. The morphological and biomechanical characters of the tubular scaffolds electrospun from the as-prepared PUs were also examined. As the solution concentration was varied from 10 to 18% (w/v), the fiber diameter was progressively increased, and the scaffold tensile strength was enhanced from 2.82 ± 0.16 MPa to 7.07 ± 0.44 MPa, the suture retention strength from 2.48 ± 0.33 to 8.38 ± 0.35 N, and the burst pressure strength from 72 ± 2 to 172 ± 2 kPa, all higher than those of native blood vessels. At the same time, the L-929 mouse fibroblasts (L-929) and human umbilical vein endothelial cells were used in cytotoxicity and cell-adhesion evaluations toward the electrospun scaffolds. The level of toxicity is less than level 1, and cells were found to attach well to and remain viable on the scaffolds.
A biocompatible diisocyanate, lysine ethyl ester diisocyanate, was prepared. Afterwards, biodegradable polyurethane (PU) was synthesized by the stepgrowth polymerization of this diisocyanate with hydroxyl terminated poly(ε-caprolactone) in the presence of 1,4-butanediol as a chain-extender. The resulting PU was characterized by GPC, IR and DSC measurements. Its mechanical strength was found to increase with increasing the hard segment content. The PU microfiber meshes with high porosity were obtained by solution electrospinning technique. Their degradation behavior in the PBS and enzymatic solution was also investigated.
Shape memory polyurethanes (SMPUs) are usually produced with aromatic hard segments in order to ensure high shape recoverability. Here a series of non-aromatic shape memory polyurethane-ureas (SMPUUs) synthesized with isophorone diisocynate (IPDI) and aliphatic or cycloaliphtic diamines as hard segments are reported. The SMPUUs were proved to be not phase separated while the intermolecular hydrogen bonds gave rise to the physical cross-links. The influences of soft-segment length, hard-segment content (HSC) and type of chain extenders on the structure and properties of the SMPUUs were investigated. As the molecular weight of soft segments (polycaprolactone diols) increased from 4000 to 10 000 g mol−1, shape fixing and shape recoveries of the SMPUUs were raised prominently because the longer polyols favor the crystallization of soft segments in the deformation state and the longer hard segments increase the density of intermolecular hydrogen bonds. The HSC exhibited two opposite effects on shape recovery. Increasing HSC on one hand increased shape recovery due to the increasing stability of physical cross-links and on the other hand reduced shape recovery due to the increasing deformation of hard segments. The polyurethane-urea having isophorone diamines (IPDA) as chain extenders showed over 95% of shape recovery and as high as 4.2 MPa recovery stress. The shape memory properties of the IPDI-based SMPUUs are even comparable with those of aromatic SMPUs.
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