Amino‐alkoxy‐bis(phenolate) yttrium complexes act in the presence of an excess of alcohol (up to 50 equiv. vs. Y) as highly active and stereoselective catalysts for rac‐lactide and rac‐β‐butyrolactone polymerizations. These versatile systems enable the production of large quantities of polymer with small amounts of catalyst, optimizing productivity, and also allow the preparation of polymers with functional end groups, which may be employed as intermediates for macromolecular engineering applications.
Compositions based on chitosan/β-glycerophosphate hydrogels with highly porous polylactide granules can be used to obtain moldable bone graft materials that have osteoinductive and osteoconductive properties. To eliminate the influence of such characteristics as chain length, degree of purification, and molecular weight on a designed material, the one-stock chitosan sample was reacetylated to degrees of deacetylation (DD%) of 19.5, 39, 49, 55, and 56. A study of the chitosan/β-glycerophosphate hydrogel with chitosan of a reduced DD% showed that a low degree of deacetylation increased the MSCs (multipotent stromal cells) viability rate in vitro and reduced the leukocyte infiltration in subcutaneous implantation to Wistar rats in vivo. The addition of 12 wt% polylactide granules resulted in optimal composite mechanical and moldable properties, and increased the modulus of elasticity of the hydrogel-based material by approximately 100 times. Excessive filling of the material with PLA (polylactide) granules (more than 20%) led to material destruction at a ~10% strain. Osteoinductive and osteoconductive properties of the chitosan hydrogel-based material with reacetylated chitosan (39 DD%) and highly porous polylactide granules impregnated with BMP-2 (bone morphogenetic protein-2) have been demonstrated in models of orthotopic and ectopic bone formation. When implanted into a critical-size calvarial defect in rats, the optimal concentration of BMP-2 was 10 μg/mL: bone tissue areas filled the entire material’s thickness. Implantation of the material with 50 μg/mL BMP-2 was accompanied with excessive growth of bone tissue and material displacement beyond the defect. Significant osteoinductive and osteoconductive properties of the material with 10 μg/mL of BMP-2 were also shown in subcutaneous implantation. 相似文献
Electrospun nonwovens of poly(L-lactide) (PLLA) modified with multiwall carbon nanotubes (MWCNT) and linear ladder-like poly(silsesquioxane) with methoxycarbonyl side groups (LPSQ-COOMe) were obtained. MWCNT and LPSQ-COOMe were added to the polymer solution before the electrospinning. In addition, nonwovens of PLLA grafted to modified MWCNT were electrospun. All modified nonwovens exhibited higher tensile strength than the neat PLA nonwoven. The addition of 10 wt.% of LPSQ-COOMe and 0.1 wt.% of MWCNT to PLLA increased the tensile strength of the nonwovens 2.4 times, improving also the elongation at the maximum stress. 相似文献
Innovations in food and drink packaging result mainly from the needs and requirements of consumers, which are influenced by changing global trends. Antimicrobial and active packaging are at the forefront of current research and development for food packaging. One of the few natural polymers on the market with antimicrobial properties is biodegradable and biocompatible chitosan. It is formed as a result of chitin deacetylation. Due to these properties, the production of chitosan alone or a composite film based on chitosan is of great interest to scientists and industrialists from various fields. Chitosan films have the potential to be used as a packaging material to maintain the quality and microbiological safety of food. In addition, chitosan is widely used in antimicrobial films against a wide range of pathogenic and food spoilage microbes. Polylactic acid (PLA) is considered one of the most promising and environmentally friendly polymers due to its physical and chemical properties, including renewable, biodegradability, biocompatibility, and is considered safe (GRAS). There is great interest among scientists in the study of PLA as an alternative food packaging film with improved properties to increase its usability for food packaging applications. The aim of this review article is to draw attention to the existing possibilities of using various components in combination with chitosan, PLA, or bacteriocins to improve the properties of packaging in new food packaging technologies. Consequently, they can be a promising solution to improve the quality, delay the spoilage of packaged food, as well as increase the safety and shelf life of food. 相似文献
Insulin entrapped nanocapsules to use polylactide (PLA) as the encapsulating material were prepared through a modified water-in-oil-in-water (W/O/W) emulsification and solvent evaporation method, The average particle size of PLA nanocapsules obtained was decreased to (181.5 ± 8.4) nm, and capably adjusted from 180 to 370 nm by using different types and content of nonionic emulsifiers. The influence of emulsifiers on property of nanocapsules was discussed in detail. The effects of spans and tweens to modify the size of the nanocapsules were different, which can be due to the distribution of the surfactants on the inner interface between the inner water and oil of the double emulsion. The encapsulation efficiency and drug release of nanocapsules were affected obviously by the content and type of emulsifiers. 相似文献
A series of L‐lactide (LLA), 1,3‐trimethylene carbonate (TMC) and glycolide (GA) terpolymers (LTG) of different monomer molar ratios were synthesized by using ring‐opening copolymerization. An effective and low‐toxic zirconium (IV) acetylacetonate Zr(Acac)4 was used as catalyst. The viscosity‐average molecular weights (Mη) of obtained polymers were all above 2.2×104 g/mol. The chemical structure and viscosity of terpolymers were confirmed by Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance (1HNMR), 13C nuclear magnetic resonance (13CNMR) and an Ubbelohde viscometer. The thermal and mechanical properties were investigated by means of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X‐ray diffraction (XRD) and stress‐strain measurements. Results suggested that all terpolymers were amorphous and showed good thermal stability. Also it was found that elongation increased with the decreasing of LLA unit. More importantly, terpolymers displayed shape memory property when deformation temperatures were 14‐15 °C above Tg. 相似文献