Reversible Supramolecular Polylactides Gels Obtained via Stereocomplexation

In this paper, stereocomplexation is used as a driving force for the formation of 3D polymer networks by hydrogen bonding cross‐linking between complementary enantiomeric polylactides (PLAs). Thus, the formation of the gels after the mixing of equimolar solutions of l ‐ and d ‐star‐shaped PLAs in the biocompatible N‐methyl‐2‐pyrrolidone (NMP) is observed. The utility of star‐shaped polymers facilitates the cross‐linking of macromolecules by increasing the number of functional end groups. Moreover, the well‐established reaction with succinic anhydride is used to functionalize the star‐shaped PLAs with carboxylic functions. These end groups have a significant impact on the viscosity and stability of the resulting PLA gels. Importantly, the formation of the supramolecular gel is reversible, and it can return to sol upon heating. These results demonstrate that the gel formation is a result of a synergic interaction of the PLA functional end groups and stereocomplexation. These novel stereocomplex gels have potential for biomedical applications due to the biocompatibility of both components: PLA and NMP.     

Fabrication of Polyurethane/Polylactide (PU/PLDL) Nanofibers Using Electrospinning Method

Polylactide and aliphatic polyurethane are biodegradable synthetic polymers which are broadly used as biomaterials in regenerative medicine for implants and scaffolds for tissue engineering. In this paper, the detailed studies of the fabrication of the electrospun fibers of polyurethane/polylactide mixtures were described. The influence of the used solvent (dimethylformamide (DMF)) and diluents (acetone and dichloromethane (DCM)) on the rheological parameters and electrospinning of the described mixtures was examined. Rheological studies showed that polyure-thane/polylactide mixtures have mostly non-Newtonian character, strongly influenced by the diluent. Solutions containing 50 wt.% or more of polyurethane became less viscous after the addition of DCM or acetone, whereas those with bigger amount of polylactide showed higher viscosity after the addition of DCM and lower viscosity after the addition of acetone. Optimized electrospinning process has been elaborated. Fibers with diameters from 250 nm up to 1 µm have been produced and compared. Pure acetone worsened the electrospinning process, but the more DCM was in the mixture, the thinner and more aligned fibers were produced.     

Star-Shaped and Linear POSS-Polylactide Hybrid Copolymers

Novel octakis-2[(6-hydroxyhexyl)thio]ethyl-octasilsesquioxane (POSS-S-OH) as well as heptaisobutyl-2[(6-hydroxyhexyl)thio]ethyl-octasilsesquioxane (iBu-POSS-S-OH) were synthesized. POSS structures, bearing both types of groups i.e., 2[(6-hydroxyhexyl)thio]ethyl and the vinyl ones, pendant from the octahedral cage are also described. The synthetic pathway involved thiol-ene click reaction of 6-mercapto-1-hexanol (MCH) to octavinyloctasilsesquioxane (POSS-Vi), and heptaisobutylvinyloctasilsesquioxane (iBu-POSS-Vi), in the presence of 2,2′-azobisisobutyronitrile. The functionalized silsesquioxane cages of regular octahedral structure were used further as initiators for ring opening polymerization of l,l-dilactide, catalyzed by tin (II) 2-ethylhexanoate. The polymerization afforded biodegradable hybrid star shape and linear systems with an octasilsesquioxane cage as a core, bearing polylactide arm(s).     

Hetero‐Stereocomplex Crystallization between Star‐Shaped 4‐Arm Poly(l‐2‐hydroxybutanoic acid) and Poly(d‐lactic acid) from the Melt

Four‐arm poly(l ‐2‐hydroxybutanoic acid) [P(L‐2HB)]/poly(d ‐lactic acid) (PDLA) blends are phase‐separated to form P(L‐2HB)‐rich and PDLA‐rich domains. Hetero‐stereocomplex (HTSC) crystallization should occur at the interface of two types of domains. The crystallization temperature ranges, wherein HTSC crystallites, P(L‐2HB), and PDLA homocrystallites are crystallizable in the star‐shaped 4‐arm P(L‐2HB)/PDLA blends, are much narrower than those reported for linear 1‐arm P(L‐2HB)/PDLA blends, indicating that the star‐shaped architecture disturbs the isothermal crystallization of the blends. Exclusive HTSC crystallization is not observed for the star‐shaped 4‐arm blends during isothermal crystallization in marked contrast with the result reported for the linear 1‐arm blends.

     

An Amylose‐Poly(l‐lactide) Inclusion Supramolecular Polymer: Enzymatic Synthesis by Means of Vine‐Twining Polymerization Using a Primer–Guest Conjugate

An inclusion supramolecular polymer composed of amylose and poly(l ‐lactide) (PLLA) is successfully synthesized by phosphorylase‐catalyzed enzymatic polymerization using a malto­heptaose‐functionalized poly(l ‐lactide) (G₇‐PLLA) as a primer–guest conjugate substrate according to vine‐twining polymerization. The product forms a polymeric continuum of an inclusion complex in which PLLA is included by an amylose chain enzymatically elongated from the other G₇‐PLLA. The product is characterized by powder X‐ray diffraction, ¹H NMR spectroscopy, and gel‐permeation chromatography measurements. The analytical results indicate that such an inclusion supramolecular polymer is efficiently produced, even under the low concentration of the guest polymer, PLLA, owing to the high local concentration of PLLA segments in the present system because G₇‐PLLA forms aggregates 50–110 nm in diameter in aqueous media.

     

聚乳酸人工神经支架的构建

目的用聚乳酸构建一种具有纵行排列管径的三维立体神经组织工程支架,并观察体外培养的雪旺细胞在支架上的生长情况.方法用组织块培养法获得新生SD大鼠坐骨神经的雪旺细胞,利用反复贴壁法纯化雪旺细胞.将消旋聚乳酸R206采用热致相分离法制备成三维立体支架,并涂俯50μg/ml浓度的纤维粘连蛋白,把雪旺细胞种植到该支架材料上培养2周,扫描电镜观察.结果构建的支架材料为白色、泡沫状,具有管状定向排列的立体结构,直径60～100μm,孔积率为91%,重均分子量330×103.体外培养的雪旺细胞成功种植在该支架上,在材料的深处有细胞生长.结论用热致相分离法制备的聚乳酸三维立体支架有良好的立体构型,类似天然周围神经结构.该支架有较好的生物相容性,雪旺细胞可以在支架上生长.     

Application of peripheral nerve conduits in clinical practice: A literature review

Understanding the pathomechanisms behind peripheral nerve damage and learning the course of regeneration seem to be crucial for selecting the appropriate methods of treatment. Autografts are currently the gold standard procedure in nerve reconstruction. However, due to the frequency of complications resulting from autografting and a desire to create a better environment for the regeneration of the damaged nerve, artificial conduits have become an approved alternative treatment method. The aim of this mini-review is to present the nerve scaffolds that have been applied in clinical practice to date, and the potential directions of developments in nerve conduit bioengineering.Articles regarding construction and characterization of nerve conduits were used as the theoretical background. All papers, available in PubMed database since 2000, presenting results of application of artificial nerve conduits in clinical trials were included into this mini-review.Fourteen studies including ≤10 patients and 10 trials conducted on >10 patients were analyzed as well as 24 papers focused on artificial nerve conduits per se. Taking into consideration the experiences of the authors investigating nerve conduits in clinical trials, it is essential to point out the emergence of bioresorbable scaffolds, which in the future may significantly change the treatment of peripheral nerve injuries. Also worth mentioning among the advanced conduits are hybrid conduits, which combine several modifications of a synthetic material to provide the optimal regeneration of a damaged nerve.     

Effect of Arrangement of L‐Lactide and D‐Lactide in Poly[(L‐lactide)‐co‐(D‐lactide)] on its Resistance to Hydrolysis Studied by Molecular Modeling

Molecular modeling is used to explain how the resistance of poly[(L ‐lactide)‐co‐(D ‐lactide)] to hydrolysis is affected by the percentages of L ‐ and D ‐lactide and their arrangements in blocks or random arrangements in the polymer. Previous studies on improving the hydrolysis resistance of PLA have involved forming either poly(L ‐lactide)/poly(D ‐lactide) (PLLA/PDLA) polyblends or copolymers of L ‐ and D ‐lactide. In this study, molecular modeling was used to study the hydrolysis resistance of PLA containing various arrangements of L ‐ and D ‐lactide in the polymers. PLA copolymers are found to have less resistance to hydrolysis than a PLLA/PDLA polyblend having the same percentages of L ‐ and D ‐lactide because a polyblend can form more stereocomplexes, which is the most stable structure PLA can form.

     

聚乳酸-聚乙二醇-聚乳酸三嵌段共聚物的降解性能

以辛酸亚锡为引发剂,聚乙二醇大分子为共引发剂进行现交酯开环聚合,制备了系列聚乳酸（PLA）－聚乙二醇（PEG）－聚乳酸（PLA）三嵌段共聚物。从共聚物在生理盐水 中降解时特性粘度[η],质量和热行为的变化,考察了PEG分子量和丙交酯／PEG（摩尔比）对共聚物降解行为的影响,结果表明,PEG嵌段对共聚物的降解速率有重要影响,丙交酯／PEG一定时,PEG分子量越大,共聚物越容易降解,PEG嵌段长度一定时,丙交酯／PEG越大,共聚物降解速率越小。     

骨炎1号聚乳酸微球中补骨脂素和异补骨脂素的HPLC测定

建立了HPLC法测定骨炎1号聚乳酸微球中补骨脂素和异补骨脂素的含量.采用DiamonsidTM C18柱,甲醇-1%乙酸(60:40)为流动相,流速0.8ml/min,检测波长245nm.补骨脂素和异补骨脂素分别在7.4～55.8μg/mi和6.5～48.9μg/ml范围内线性关系良好(r均为0.9997),平均回收率分别为102.3%(RSD=1.45%)和102.7%(RSD=0.64%).