Discharge Plasma Treatment as an Efficient Tool for Improved Poly(lactide) Adhesive–Wood Interactions

Poly(lactide) (PLA) films obtained by thermoforming or solution-casting were modified by diffuse coplanar surface barrier discharge plasma (300 W and 60 s). PLA films were used as hot-melt adhesive in joints in oak wood. It was demonstrated that lap shear strength increased from 3.4 to 8.2 MPa, respectively, for the untreated and plasma-treated series. Pull-off tests performed on particleboard for the untreated and treated PLA films showed 100% cohesive failure. Pull-off strength tests on solid oak demonstrated adhesion enhancement from 3.3 MPa with the adhesion failure mode to 6.6 MPa with the cohesion failure mode for untreated and treated PLA. XPS revealed that carbonyl oxygen content increased by two-to-three-fold, which was confirmed in the Fourier-transform infrared spectroscopy experiments of the treated PLA. The water contact angle decreased from 66.4° for the pristine PLA to 49.8° after treatment. Subsequently, the surface free energy increased from 47.9 to 61.05 mJ/m². Thus, it was clearly proven that discharge air plasma can be an efficient tool to change surface properties and to strengthen adhesive interactions between PLA and woody substrates.     

Fixation of horizontal maxillary osteotomies with biodegradable self-reinforced absorbable polylactide plates: preliminary results

Totally biodegradable, self-reinforced polylactide plates and titanium miniscrews were used for the fixation of horizontal maxillary osteotomies in 32 patients. In two cases the fixation was unstable because of technical problems. In the others the analysis of cephalometric radiographs between immediate and late postoperative showed very similar figures, indicating postoperative stability. There were no complications in the healing due to this biodegradable osteofixation in these patients.     

Antibacterial Films Based on Polylactide with the Addition of Quercetin and Poly(Ethylene Glycol)

A series of new films with antibacterial properties has been obtained by means of solvent casting method. Biodegradable materials including polylactide (PLA), quercetin (Q) acting as an antibacterial compound and polyethylene glycol (PEG) acting as a plasticizer have been used in the process. The effect of quercetin as well as the amount of PEG on the structural, thermal, mechanical and antibacterial properties of the obtained materials has been determined. It was found that an addition of quercetin significantly influences thermal stability. It should be stressed that samples containing the studied flavonoid are characterized by a higher Young modulus and elongation at break than materials consisting only of PLA and PEG. Moreover, the introduction of 1% of quercetin grants antibacterial properties to the new materials. Recorded results showed that the amount of plasticizer did not influence the antibacterial properties; it does, however, cause changes in physicochemical properties of the obtained materials. These results prove that quercetin could be used as an antibacterial compound and simultaneously improve mechanical and thermal properties of polylactide-based films.     

High AC and DC Electroconductivity of Scalable and Economic Graphite–Diamond Polylactide Nanocomposites

Two types of graphite/diamond (GD) particles with different ash content was applied to prepare new electroconductive polylactide (PLA)-based nanocomposites. Four samples of nanocomposites for each type of GD particles with mass fraction 0.01, 0.05, 0.10, and 0.15 were prepared via an easily scalable method—melt blending. The samples were subjected to the studies of electrical properties via broadband dielectric spectroscopy. The results indicated up to eight orders of magnitude improvement in the electrical conductivity and electrical permittivity of the most loaded nanocomposites, in reference to the neat PLA. Additionally, the influence of ash content on the electrical conductivity of the nanocomposites revealed that technologically less-demanding fillers, i.e., of higher ash content, were the most beneficial in the light of nanofiller dispersibility and the final properties.     

Hybrid Polypeptide/Polylactide Copolymers with Short Phenylalanine Blocks

Hybrid copolymers constituted by short l ‐phenylalanine (Phe) blocks (i.e., Phe_n with n ranging from 2 to 25) and l ‐lactide blocks of different length are synthesized and characterized. The diblock structure is obtained by ring opening polymerization of lactide using a Phe‐oligopeptide as macroinitiator. The length of the poly(l ‐lactide) (PLLA) block is controlled through the [lactide]/[macroinitiator] ratio. Morphologic studies of such hybrid copolymers indicate that the assembly of PLLA can be controlled by introducing short Phe blocks. Spherulites with both positive and negative birefringence are achieved in melt crystallization as a consequence of different lamellar distributions. Instead, a high variety of structures are detected in solution‐crystallized samples. Specifically, lozenge single crystals, flower‐like crystals, fibrillar structures, compact spheres, ringed sperulites, dendritic structures, microfibers, and braid‐like microstructures are observed. Some of the detected morphologies are characteristic of self‐assembled Phe‐oligopeptides, suggesting that Phe‐blocks play a crucial role in the self‐assembly properties.     

Aluminum Initiators Supported by Asymmetric [ONNO′]‐Type Salan Ligands for the Ring‐Opening Polymerization of rac‐Lactide

A novel series of aluminum complexes supported by asymmetric [ONNO′]‐type Salan ligands ( 1–4 ) is successfully synthesized. Polylactides (PLAs) with molecular weights close to the theoretical values and narrow polydispersity indices (PDIs) can be obtained. Kinetic studies reveal first‐order polymerization kinetics and a linear relationship between the molecular weight and the percentage conversion. Complexes 1–4 display heteroselective polymerization to give heterotactic‐enriched PLAs with P_r values ranging from 0.64 to 0.74. The character of the ligand substituents from the two different phenolic rings and the complex fluxionality arising from the ligand interconversion are suggested to be responsible for the different levels of stereoselectivity and activity.

     

A Novel Bioabsorbable Gel Formed from a Mixed Micelle Solution of Poly(oxyethylene)‐block‐poly(L‐lactide) and Poly(oxyethylene)‐block‐poly(D‐lactide) by Concomitant Stereocomplexation and Chain Extension

Furan‐terminated poly(oxyethylene)‐block‐poly(L‐lactide) (MePEG‐PLLA‐F) and poly(oxyethylene)‐block‐poly(D‐lactide) (MePEG‐PDLA‐F) are synthesized by ring‐opening polymerization of L‐ and D‐lactides, respectively, in the presence of poly(ethylene glycol) monomethyl ether (MePEG) and the following terminal reaction with furfuryl isocyanate. Their mixed micelle solution turns to gel quickly with stereocomplexation of the enantiomeric PLLA and PDLA. When 1,8‐bis(maleimido)diethylene glycol (BMG) is added to the mixed micelle solution, the gelation is promoted by the terminal coupling of the copolymers driven by the Diels–Alder reaction of the furanyl groups and BMG giving a gel having higher strength.

     

Enhancement of Tg of Poly(l‐lactide) by Incorporation of Biobased Mandelic‐Acid‐Derived Phenyl Groups by Polymerization and Polymer Blending

A high‐molecular‐weight polyester of poly(mandelate‐co‐lactate) (PML) is prepared by ring‐opening polymerization of stereo‐configuration controlled cyclic diester monomers of methyl‐6‐phenyl‐1,4‐dioxane‐2,5‐dione (MPDD) and lactide. The attained PML shows excellent glassy properties, although the original stereo‐configuration of MPDD is not preserved. The intrinsic high glass transition temperature (T_g) of PML is promising, and it is able to be further enhanced by thermal treatment to as high as 90 °C. Interestingly, the enhanced high T_g is attained by only 15 mol% of mandelate content in the polymer chain which is far lower than the ones suggested by theoretical calculation. The enhancement in T_g is also attained by polymer blending of PML and poly(l ‐lactide) (PLLA). The T_g of the polymer blend also reaches 90 °C which is almost 20 °C higher than the ones suggested by theoretical calculations. These results indicate that the rigid mandelate unit consisting of phenyl groups in PML chain effectively interact with PLLA chains in amorphous domain to restrict their chain mobility. The thermal and glassy properties are sufficient to explore new applications in engineering fields.     

Synthesis and characterization of polycaprolactone / poly(ethylene oxide) / polylactide tri-component copolymers

Polycaprolactonel/poly(ethylene oxide)/polylactide tri-component copolymers (PCEL) with different compositions were synthesized by copolymerization of ε-caprolactone and L-lactide in the presence of poly(ethylene glycol) using stannous octoate as a catalyst. The copolymers were purified and characterized by various analytical techniques such as GPC, FT-IR, H NMR, ¹³C NMR, DSC, and X-ray diffractometry. It was evidenced that these copolymers were pure tri-component compounds which exhibited partially random chain structures, and possessed good mechanical properties and variable biodegradability.     

PDLLA-T3对体外培养雪旺细胞影响的实验研究

目的观察甲状腺激素人工神经(PDLLA-T3)对体外培养雪旺细胞的影响.方法体外纯化、培养雪旺细胞后,在雪旺细胞培养板中加入PDLLA-T3(C组),混合培养6d,实验采用MTT法每天观察细胞活性的高低,用血球计数板对雪旺细胞进行计数,并用ELISA方法测定每天培养液中NGF含量的变化.另有不合T3的支架材料PDLLA(B组)、空白组(A组)作为实验对照组.结果培养的雪旺细胞纯度达到94.63%.PDLLA-T3比PDLLA和空白组明显增加雪旺细胞的数量,提高细胞活性,刺激雪旺细胞产生更多的NGF.结论 PDLLA-T3和雪旺细胞有较好的组织相容性,对培养的雪旺细胞有较好的正性促进作用,是一种良好的组织工程支架.