Biomineralized Composite Liquid Crystal Fiber Scaffold Promotes Bone Regeneration by Enhancement of Osteogenesis and Angiogenesis

Liquid crystals (LCs) are appealing biomaterials for applications in bone regenerative medicine due to their tunable physical properties and anisotropic viscoelastic behavior. This study reports a novel composite poly (L-lactide) (PLLA) scaffold that is manufactured by a simple electrospinning and biomineralization technique that precisely controls the fibrous structure in liquid LC phase. The enriched-LC composites have superior mineralization ability than neat PLLA; furthermore BMSC cells were inoculated onto the HAP-PLLA/LC with hydroxyapatite (HAP) composite scaffold to test the capability for osteogenesis in vitro. The results show that the PLLA/LC with HAP produced by mineralization leads to better cell compatibility, which is beneficial to cell proliferation, osteogenic differentiation, and expression of the angiogenic CD31 gene. Moreover, in vivo studies showed that the HAP-PLLA/LC scaffold with a bone-like environment significantly accelerates new and mature lamellar bone formation by development of a microenvironment for vascularized bone regeneration. Thus, this bionic composite scaffold in an LC state combining osteogenesis with vascularized activities is a promising biomaterial for bone regeneration in defective areas.

Interaction of Poly L-Lactide and Tungsten Disulfide Nanotubes Studied by in Situ X-ray Scattering during Expansion of PLLA/WS2NT Nanocomposite Tubes

In situ synchrotron X-ray scattering was used to reveal the transient microstructure of poly(L-lactide) (PLLA)/tungsten disulfide inorganic nanotubes (WS2NTs) nanocomposites. This microstructure is formed during the blow molding process (“tube expansion”) of an extruded polymer tube, an important step in the manufacturing of PLLA-based bioresorbable vascular scaffolds (BVS). A fundamental understanding of how such a microstructure develops during processing is relevant to two unmet needs in PLLA-based BVS: increasing strength to enable thinner devices and improving radiopacity to enable imaging during implantation. Here, we focus on how the flow generated during tube expansion affects the orientation of the WS2NTs and the formation of polymer crystals by comparing neat PLLA and nanocomposite tubes under different expansion conditions. Surprisingly, the WS2NTs remain oriented along the extrusion direction despite significant strain in the transverse direction while the PLLA crystals (c-axis) form along the circumferential direction of the tube. Although WS2NTs promote the nucleation of PLLA crystals in nanocomposite tubes, crystallization proceeds with largely the same orientation as in neat PLLA tubes. We suggest that the reason for the unusual independence of the orientations of the nanotubes and polymer crystals stems from the favorable interaction between PLLA and WS2NTs. This favorable interaction leads WS2NTs to disperse well in PLLA and strongly orient along the axis of the PLLA tube during extrusion. As a consequence, the nanotubes are aligned orthogonally to the circumferential stretching direction, which appears to decouple the orientations of PLLA crystals and WS2NTs.

Crystallization and Alkaline Degradation Behaviors of Poly(l-Lactide)/4-Armed Poly(ε-Caprolactone)-Block-Poly(d-Lactide) Blends with Different Poly(d-Lactide) Block Lengths

Four-armed poly(ε-caprolactone)-block-poly(d-lactide) (4-C-D) copolymers with different poly(d-lactide) (PDLA) block lengths (Mn,PDLAs) were synthesized by sequential ring-opening polymerization (ROP). The formation of stereocomplex (SC) crystallites in the 80/20 poly(l-lactide) (PLLA)/4-C-D blends were investigated with the change of Mn,PDLA from 0.5 to 1.5 kg/mol. It was found that the crystallization and alkaline degradation of the blends were profoundly affected by the formed SC crystallites. The PLLA/4-C-D0.5 blend had the lowest crystallization rate of the three blends, and it was difficult to see spherulites in this blend by polarized optical microscopy (POM) observation after isothermal crystallization at 140 °C for 4 h. Meanwhile, when Mn,PDLA was 1 kg/mol or 1.5 kg/mol, SC crystallites could be formed in the PLLA/4-C-D blend and acted as nucleators for the crystallization of PLLA homo-crystals. However, the overall crystallization rates of the two blends were still lower than that of the neat PLLA. In the PLLA/4-C-D1.5 blend, the Raman results showed that small isolated SC spherulites were trapped inside the big PLLA homo-spherulites during isothermal crystallization. The degradation rate of the PLLA/4-C-D blend decreased when Mn,PDLA increased from 0.5 to 1.5 kg/mol, and the degradation morphologies had a close relationship with the crystallization state of the blends. This work revealed the gradual formation of SC crystallites with the increase in Mn,PDLA in the PLLA/4-C-D blends and its significant effect on the crystallization and degradation behaviors of the blend films.

Synthesis, Geometry Structure and Properties of N, N’-Carbonic Bis(Piperonylic Acid) Dihydrazide

In this study, N, N’-carbonic bis(piperonylic acid) dihydrazide (BPACH) was synthesized to broaden the category of piperonylic acid derivative and evaluate its influences on the thermal properties of poly(L-lactic acid) (PLLA). The geometry optimization of BPACH showed that the highest occupied molecular orbital mainly focused on the formed amide group and carbonic dihydrazide, whereas the lowest unoccupied molecular orbital mainly focused on the piperonylic acid, and the orbital energy gap was 0.10418 eV. The differences in melt-crystallization processes of the neat PLLA and PLLA/BPACH samples indicated that the BPACH could provide the effective nucleation site to accelerate the crystallization of PLLA, but the crystallization accelerating effect was still further improved compared to some reported nucleating agents. The melting behaviors of PLLA/BPACH samples after crystallization depended on the crystallization temperatures and heating rates; additionally, the melting processes could also effectively reflect the previous crystallization behaviors.

Stereocomplex formation in injection-molded poly(L-lactic acid)/poly(D-lactic acid) blends

Poly(L-lactic acid)/poly(D-lactic acid) (PLLA/PDLA) blends were prepared by hand mixing, followed by injection molding at 210°C to produce tensile specimens. Thermal properties, crystalline structure, and mechanical properties were measured by differential scanning calorimetry (DSC), thermogravimetric analysis, wide-angle X-ray diffraction (XRD), and tensile testing. From the DSC tests of blends ranging from 10% to 30% PDLA in PLLA, the PDLA melting peak was absent and was replaced by a stereocomplex melting peak at 210°C, which was ~50°C higher than that for neat PLLA or PDLA. The reverse blending of PLLA into PDLA showed a similar behavior. Surprisingly, three melting peaks (for PLLA, PDLA, and the complex crystal) appeared in the 1:1 PLLA:PDLA pellet blends. However, the PLLA and PDLA powders (ground to less than 200 μm) and hand mixed, prior to injection molding, showed only small amounts of homocrystals and much higher fractions of stereocomplex crystals (18–44%). Compared to the hand mixed un-ground pellets, molded specimens from the PLLA and PDLA powders also exhibited higher tensile strengths (33–48 MPa) and moduli (1100–1250 MPa). Moreover, the stereocomplex formation was found to enhance the thermal stability compared with those of the pure PLLA and PDLA.

In Vivo Investigation into Effectiveness of Fe3O4/PLLA Nanofibers for Bone Tissue Engineering Applications

Fe3O4 nanoparticles were loaded into poly-l-lactide (PLLA) with concentrations of 2% and 5%, respectively, using an electrospinning method. In vivo animal experiments were then performed to evaluate the potential of the Fe3O4/PLLA nanofibrous material for bone tissue engineering applications. Bony defects with a diameter of 4 mm were prepared in rabbit tibias. Fe3O4/PLLA nanofibers were grafted into the drilled defects and histological examination and computed tomography (CT) image detection were performed after an eight-week healing period. The histological results showed that the artificial bony defects grafted with Fe3O4/PLLA nanofibers exhibited a visibly higher bone healing activity than those grafted with neat PLLA. In addition, the quantitative results from CT images revealed that the bony defects grafted with 2% and 5% Fe3O4/PLLA nanofibers, respectively, showed 1.9- and 2.3-fold increases in bone volume compared to the control blank sample. Overall, the results suggest that the Fe3O4/PLLA nanofibers fabricated in this study may serve as a useful biomaterial for future bone tissue engineering applications.

Plasticizer effect on melt blending of polylactide stereocomplex

Poly(l-lactide) (PLLA)/poly(d-lactide) (50/50) with plasticizer contents ranging from 2% to 16% w/w were prepared by melt blending using an internal mixer. Wide-angle X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry results confirmed that complete stereocomplex polylactide crystallites without any homocrystallites were produced. Compared to neat PLLA, the melting temperature of the stereocomplex polylactide and its plasticized samples was approximately 55°C higher. Higher plasticizer contents decreased glass transition temperature of the stereocomplex, which implied higher flexibility and enhanced the crystallization rate. However, the plasticizer in the stereocomplex reduced the thermal stability.

Preparation and Physical Performance of Green Poly(L-lactic acid) Composition by Blending with Starch

Objective: To develop more green polymer composites and further know the performance of green composites, the composites based on green poly(L-lactic acid) (PLLA) and starch were fabricated by a counter-rotating mixer. And effect of starch on the fluidity and nucleating performance of PLLA was investigated using melt index instrument, optical depolarizer and wide angle X-ray diffraction instrument, respectively. Method and Conclusion: The fluidity of PLLA/starch composites showed that, compared to the neat PLLA, the addition of starch made the fluidity of PLLA increase significantly and the melt mass flow rate of PLLA/5%starch sample had the maximum value 13.36 g/10min. In addition, the introduction of starch could also increase the crystallization rate of PLLA through isothermal crystallization measurement and x-ray diffraction analysis, the maximum value of crystallization rate of PLLA/starch composites appeared in low crystallization temperature zone, and 10 wt% starch could make the t1/2 of PLLA decrease from 3999.4s to 421.4s.

Study on Thermal Performance of Composites Prepared Using Poly(L-Lactic Acid) and Melamine

The goal of this work was to study the non isothermal and isothermal crystallization behavior of Poly(L-lactic acid) (PLLA) with melamine (TP) through differential scanning calorimeter and optical depolarizer. The study of the crystallization behavior of PLLA/TP composites indicated that TP could promote the crystallization of PLLA. The half time of overall crystallization of PLLA with 1.5 wt% TP, compared with the neat PLLA, gave rise to a decrease from 3999.44 s to the minimum value 228 s at 100 °C. In addition, the cooling rate also affected significantly the crystallization behavior of PLLA. The melting behavior of PLLA/TP composites exhibited a complicated and different melting process after cooling crystallization, and the increasing of TP content made melt mass flow rate of PLLA firstly decrease, then increases.

Composites Based Green Poly(L-Lactic Acid) and Dioctyl Phthalate: Preparation and Performance

The effects of dioctyl phthalate (DOP) on performances of poly(L-lactic acid) (PLLA) were investigated in detail using optical depolarizer, X-ray diffraction, melt index instrument, and electronic tensile tester. Crystallization performance showed that the half time of overall PLLA crystallizationt1/2decreased with increasing of crystallization temperature (80°C to 105°C), but thet1/2of PLLA/DOP composites firstly decreased and then increased, andt1/2of PLLA/DOP exhibited minimum value at 85°C. Compared to neat PLLA, 20%DOP made thet1/2decrease from 7258.3 s to 265.4 s. X-ray diffraction experiment further confirmed that DOP could accelerate the crystallization of PLLA. The fluidity of PLLA/DOP composites indicated that the melt mass flow rate firstly decreased and then greatly increased with increasing of DOP content. The mechanical performance showed that DOP could improve the general mechanical performance, and the elongation at break of PLLA/25%DOP was about 30 times longer than that of neat PLLA.