Synergism of Zinc Oxide/Organoclay-Loaded Poly(lactic acid) Hybrid Nanocomposite Plasticized by Triacetin for Sustainable Active Food Packaging

The synergistic effect of organoclay(OC)and zinc oxide(ZnO)nanoparticles on the crucial properties of poly(lactic acid)(PLA)nanocompositefilms was systematically investigated herein.After their incorporation into PLA via the solvent casting technique,the water vapor barrier property of the PLA/OC/ZnOfilm improved by a maximum of 86%compared to the neat PLAfilm without the deterioration of Young’s modulus or the tensile strength.Moreover,thefilm’s self-antibacterial activity against foodborne pathogens,including gram-negative(Escherichia coli,E.coli)and gram-positive(Staphylococcus aureus,S.aureus)bacteria,was enhanced by a max-imum of approximately 98–99%compared to the neat PLAfilm.Furthermore,SEM images revealed the homo-geneous dispersion of both nano-fillers in the PLA matrix.However,the thermal stability of thefilm decreased slightly after the addition of the OC and ZnO.Thefilm exhibited notable light barrier properties in the UV-Vis range.Moreover,the incorporation of a suitable biodegradable plasticizer significantly decreased the Tg and notably enhanced theflexibility of the nanocompositefilm by increasing the elongation at break approxi-mately 1.5-fold compared to that of the neat PLAfilm.This contributes to its feasibility as an active food packa-ging material.

Poly(lactic acid)-aspirin microspheres prepared via the traditional and improved solvent evaporation methods and its application performances

Drug-loaded microspheres are significant for the development of modern pharmaceutical products. It is well known that the taken of aspirin for long-term increases the risk of serious gastrointestinal complications, therefore a controllable delivery of aspirin is of importance to lighten those side effects. In this work, poly(lactic acid)(PLA) was chosen as the carrier to prepare PLA-aspirin microspheres by using the traditional and the improved solvent evaporation methods. It was found that no matter which experimental condition was, the encapsulation efficiency of aspirin was higher by using the improved method than that of the traditional method. Specifically, when the concentration of polyvinyl alcohol = 1%(mass),the polymer concentration = 1:20, the oil/water rate = 1:2.5, PLA-aspirin microspheres were obtained via the improved method with a high yield of 82.83%(mass) and an encapsulation efficiency of 44.09%. PLAaspirin microspheres were then prepared continuously using the improved method, which further enhanced the encapsulation efficiency to 54.56%. Approximate 85% aspirin released from microspheres within 7 days. Obvious degradation which was represented by reduction on hardness was observed by soaking microspheres in PBS for 60 days. This work is of interest because it provides a continuous route to prepare PLA-aspirin microspheres continuously with a high drug encapsulation efficiency.

Preparation and properties of short natural fiber reinforced poly(lactic acid) composites

The natural fiber/poly(lactic acid) (PLA) composites were prepared with ramie and jute short fiber as reinforcement and PLA as matrix. The mechanical and thermal properties of the composites were investigated. The results show that the properties of the composites are better than those of plain PLA. When the content of the fiber is 30%, the composites can get the best mechanical properties. The dynamic mechanical analysis results show that the storage moduli of the PLA/ramie and PLA/jute composites increase with respect to the plain PLA. The Vicat softening temperature of the composites is greatly higher than that of PLA. The results of thermogravimetric analysis show that adding fiber to the PLA matrix can improve the degradation temperature of PLA.

Synergistic effect of MXene on the flame retardancy and thermal degradation of intumescent flame retardant biodegradable poly(lactic acid)composites

The effect of Ti3C2 MXene nanosheets on the intumescent flame retardant(IFR)poly(lactic acid)(PLA)composites was investigated among a series of PLA/IFR/MXene,which were prepared by melt blending 0-2.0 wt%MXene,10.0 wt%-12.0 wt%IFR and PLA together.The results of limiting oxygen index(LOI)and vertical burning(UL-94)discover that the combination of 0.5 wt%MXene and 11.5 wt%IFR synergistically improves the fire safety of PLA to reach UL-94 V-0 rating with LOI value of 33.0%.The PLA/IFR/MXene composites perform an obvious reduction in peak of heat release rate(HRR)in cone calorimeter tests(CCTs).Furthermore,the carbon residues after CCTs were characterized by scanning electron microscope(SEM),laser Raman spectroscopy(LRS),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).It is demonstrated that both the titanium composition of the MXene structure and the characteristics of the two-dimensional material enhance the PLA/IFR/MXene composite materials’ability to produce a dense barrier layer to resist burnout during thermal degradation.

Morphological, Mechanical and Thermal Properties of Poly(lactic acid)(PLA)/Cellulose Nanofibrils(CNF) Composites Nanofiber for Tissue Engineering

Composite nanofiber membranes based on biodegradable poly(lactic acid)(PLA) and cellulose nanofibrils(CNF) were produced via electrospinning. The influence of CNF content on the morphology, thermal properties, and mechanical properties of PLA/CNF composite nanofiber membranes were characterized by field scanning electron microscopy(FE-SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA), and dynamic mechanical analysis(DMA), respectively. The results show that the PLA/CNF composite nanofibers with smooth, free-bead surface can be successfully fabricated with various CNF contents. The introduction of CNF is an effective approach to improve the crystalline ability, thermal stability and mechanical properties for PLA/CNF composite fibers. The Young's moduli and tensile strength of the PLA/CNF composite nanofiber reach 106.6 MPa and 2.7 MPa when the CNF content is 3%, respectively, which are one times higher and 1.5 times than those of pure PLA nanofiber. Additionally, the water contact angle of PLA/CNF composite nanofiber membranes decreases with the increase of the CNF loading, resulting in the enhancement of their hydrophilicity.

Study of Thermal,Phase Morphological and Mechanical Properties of Poly(L-lactide)-b-Poly(ethylene glycol)-b-Poly(L-lactide)/Poly(ethylene glycol)Blend Bioplastics

A poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide)(PLLA-PEG-PLLA)block copolymer has great potential for use as a flexible bioplastic.Highly flexible bioplastics are required for flexible packaging applications.In this work,a PEG was incorporated into block copolymer as a plasticizer by solvent casting.PLLA-PEG-PLLA/PEG blends with different blend ratios were prepared,and the plasticizing effect and miscibility of PEG in block copolymer were intensively investigated compared to PLLA/PEG blends.The results indicated that the PEG was an effective plasticizer for the block copolymer.The blending of PEG decreased glass-transition temperature and accelerated the crystallization of both the PLLA and PLLA-PEG-PLLA matrices.The PEG was completely miscible when blended with block copolymer and it improved thermal stability of the block copolymer matrix but not of the PLLA matrix.Film extensibility of PLLA-PEG-PLLA/PEG blends steadily increased as the PEG ratio increased.These non-toxic and highly flexible PLLA-PEG-PLLA/PEG bioplastics are promising candidates for several applications such as biomedical devices,tissue scaffolds and packaging materials.

Comparison of morphological and functional outcomes of mouse sciatic nerve repair with three biodegradable polymer conduits containing poly (lactic acid)

Poly（lactic acid）（PLA）-containing nerve guidance conduits（NGCs） are currently being investigated for nerve repair as an alternative to autograft, which leads to permanent functional impairment in the territory innervated by the removed nerve. Combination of polymers modifies the physical properties of the conduits, altering their nerve-guidance properties. Conduits made from PLA-only or combined with other polymers have been used successfully for nerve repair, but their efficiency has not been compared. We compared the morphological and functional outcomes of peripheral nerve repair by using NGCs made of poly（lactic acid） and combined or not with polycaprolactone（PLA/PCL） or polyvinylpyrrolidone（PLA/PVP）. To assess the functional recovery, we employed a mechanical hyperalgesia analysis, sciatic functional index（SFI）, and electroneuromyography. The mechanical hyperalgesia analysis showed that the PLA group improved more rapidly than the PLA/PVP and PLA/PCL groups; similarly, in the electroneuromyography assay, the PLA group exhibited higher amplitude than the PLA/PCL and PLA/PVP groups. However, the SFI improvement rates did not differ among the groups. Morphologically, the PLA group showed more vascularization, while the nerve fiber regeneration did not differ among the groups. In conclusion, the PLA-only conduits were superior to the other NGCs tested for nerve repair.

Melt Synthesis and Characterization of Poly(L-lactic Acid) Chain Linked by Multifunctional Epoxy Compound

High molecular weight（Mw） poly（L-lactic acid）s（PLLAs） were synthesized using multifunctional epoxy compound（Joncryl-ADR4370） as chain extender. The products were characterized by gel permeation chromatography（GPC） and spectroscopy（1HNMR and FTIR）. The results indicated that the Mw of PLLA increased with the increasing of the ratio of epoxy compound and the extending of reaction time. The highest Mw of PLLA reached 360 000 g/mol when the ratio of epoxy compound was 1.5 wt%. However, the reactants turned to cross-linking when the ratio of epoxy compound was over 1.5 wt%. Differential scanning calorimetry（DSC） measurements demonstrated that the glass transition（Tg） and melting temperatures（Tm） of products increased slightly as the increase of the molecular weight. Analysis of the hydrolytic degradation in vitro showed that the branched PLLA possessed the quicker degradability than that of the linear PLLA.

Synthesis and Hydrophilic Performance of Poly(Lactic Acid)-Poly(Ethylene Glycol) Block Copolymers

Lactide was synthesized using lactic acid and stannous octoate as raw material and catalyst, respectively. Poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) was prepared by lactide and poly (ethylene glycol) (PEG) via ring-opening polymerization. The most appropriate technological conditions of synthesis of lactide were researched in the paper. The copolymers were measured by Infrared spectroscopy (IR) and 1H nuclear magnetic resonance (1H NMR). The results proved that the lactide and PLA-PEG were synthesized successfully. Hydrophilic performance of the copolymer was measured by a water contact angle tester after prepared into a flat membrane. The water contact angle changed from 81.5? to 71.6?, which proved that the hydrophily of PLA-PEG was better than PLA.

Poly(lactic acid)-starch/Expandable Graphite (PLA-starch/EG) Flame Retardant Composites

This work reports on the effect of commercial expandable graphite(EG)on the flammability and thermal decomposition properties of PLA-starch blend.The PLA-starch/EG composites were prepared by melt-mixing and their thermal stability,volatile pyrolysis products and flammability characteristics were investigated.The char residues of the composites,after combustion in a cone calorimeter,were analyzed with environmental scanning electron microscopy(ESEM).The thermal decomposition stability of the composites improved in the presence of EG.However,the char content was less than expected as per the combination of the wt%EG added into PLA-starch and the%residue of PLA-starch.The flammability performance of the PLA-starch/EG composites improved,especially at 15 wt%EG content,due to a thick and strong worm-like char structure.The peak heat release rate(PHRR)improved by 74%,the total smoke production(TSP)by 40%and the specific extinction area(SEA)by 55%.The improvements are attributed to the ability of EG to exfoliate at increased temperatures during which time three effects occurred:(i)cooling due to an endothermic exfoliation process,(ii)dilution due to release of H2O,SO2 and CO2 gases,and (iii)formation of a protective intumescent char layer.However,the CO and CO2 yields were found to be unfavorably high due to the presence of EG.

The Green Composites: Millet Husk Fiber (MHF) Filled Poly Lactic Acid (PLA) and Degradability Effects on Environment

This study provides an overview on green composites degradability. Practically, the main drawbacks of using natural fibers are their poor dimensional stability, degradability and high degree of moisture absorption. While, end use of product from natural fiber filled or reinforced composites has become subject of concern to material engineers and scientist. The major properties of natural fiber reinforced polymer composites are greatly dependent on the hydrophilic tendency and dimensional stability of the fibers used, morphology aspect ratio for long fiber, while voids for powder fibers. The effects of chemical treatments on cellulosic fibers that are used as reinforcements for thermoplastics were studied. The chemical source for the treatments is alkalization. The significance of chemically-treated natural fibers is seen through the improvement of mechanical properties. The untreated fiber composites degrade faster in municipal soil compared to treated fiber composites.

Synthesis and Characterization of Chitosan-g-poly- (D, L-lactic acid) Copolymer

Biodegradable chitosan-g-poly (D, L-lactic acid) copolymers were prepared via two methods. (1) The lactide was grafted onto hydroxyl groups of chitosan by using macromolecular initiator sodium of trimethylsilyl-chitosan, (2) poly (D,L-lactic acid)(PLA) with low molecular weight can be linked to the amino group by coupling activated PLA to trimethylsilyl-chitosan. Two graft copolymers had hydrophilic-hydrophobic character and can be applied as carriers for drug delivery.

Degradation mechanisms of poly (lactic-co-glycolic acid) films in vitro under static and dynamic environment

To understand their degradation mechanisms, PLGA (50:50) polymer films were prepared and eroded in the static and dynamic medium system. The degradation behavior was characterized through weight-average molecular weight change, mass loss, water uptake, etc. The results show that in dynamic system, significant mass loss begins until 10 d while mass loss does not begin until 30 d later, while weight-average molecular weight decreases observably at the beginning, and the appeasable mass loss happens in 20 d in static system, which suggests that the dynamic degradation rate is slower even than degradation in static medium. A mechanism was proposed that specimens in static medium take up water homogeneously and cause the polymer chains to degrade all over the specimen cross sections, which creates free carboxylic acid groups which lead to a decrease of pH value inside the swollen polymer and accelerate degradation of the polymer. While pH value inside polymer keeps constant in dynamic medium because of flowing of simulated medium, which make the hydrolytic cleavage of ester bonds inside specimen delayed.

Improving the Compatibility of Biodegradable Poly (Lactic Acid) Toughening with Thermoplastic Polyurethane (TPU) and Compatibilized Meltblown Nonwoven

Poly (Lactic Acid) (PLA) is a biodegradable polymer which originates from natural resources such as corn and starch, offering excellent strength, biodegradability, nevertheless its inherent brittleness and low impact resistance properties have limited its application. On the other hand, Thermoplastic Polyurethane (TPU) has high toughness, durability and flexibility, which is one of the most potential alternatives for enhancing the flexibility and mechanical strength of Poly (Lactic Acid) (PLA) by blending it with a compatibilizer. With the aim to improve the mechanical and thermal properties of Poly (Lactic Acid) (PLA) meltblown nonwovens, The Thermoplastic Polyurethane (TPU) was melt blended with Poly (Lactic Acid) (PLA) at the different corresponding proportions for toughening the Poly (Lactic Acid) and the corresponding PLA/TPU MBs (meltblown nonwovens) were also manufactured. Joncryl ADR 4400 is mixed into the PLA matrix during processing. It was found that Joncryl had a much higher chain extension that substantially increased the molecular weight of the PLA matrix. SEM study revealed that Joncryl ADR 4400 is a good compatibilizer. Moreover, in this study, the crystallization, thermal and rheological behaviors of the corresponding PLA and TPU blends were also investigated. PLA/TPU MBs were also characterized by morphology and mechanical properties. The rheological property of the PLA/TPU meltblown nonwoven revealed that the viscosity is increasing as the amount of TPU is increasing in the blend, PLA/TPU meltblown nonwovens exhibited excellent mechanical properties;they are soft, elastic, and have certain tensile strength. New materials have potential applications in the medical and agricultural fields. Joncryl ADR 4400 compatibilized blends showed higher strength than simple PLA/TPU blends at the same PLA/TPU ratio.

Dorsal root ganglion-derived Schwann cells combined with poly(lactic-co-glycolic acid)/chitosan conduits for the repair of sciatic nerve defects in rats

Schwann cells, nerve regeneration promoters in peripheral nerve tissue engineering, can be used to repair both the peripheral and central nervous systems. However, isolation and puriifcation of Schwann cells are complicated by contamination with ifbroblasts. Current reported measures are mainly limited by either high cost or complicated procedures with low cell yields or purity. In this study, we collected dorsal root ganglia from neonatal rats from which we obtained highly puriifed Schwann cells using serum-free melanocyte culture medium. The purity of Schwann cells （〉95%） using our method was higher than that using standard medium containing fetal bovine serum. The obtained Schwann cells were implanted into poly（lactic-co-glycolic acid）/chi-tosan conduits to repair 10-mm sciatic nerve defects in rats. Results showed that axonal diameter and area were signiifcantly increased and motor functions were obviously improved in the rat sciatic nerve tissue. Experimental ifndings suggest that serum-free melanocyte culture medium is conducive to purify Schwann cells and poly（lactic-co-glycolic acid）/chitosan nerve conduits combined with Schwann cells contribute to restore sciatic nerve defects.

A novel artificial nerve graft for repairing longdistance sciatic nerve defects:a self-assembling peptide nanofiber scaffold-containing poly (lactic-co-glycolic acid) conduit

In this study, we developed a novel artificial nerve graft termed self-assembling peptide nanofiber scaffold （SAPNS）-containing poly（lactic-co-glycolic acid） （PLGA） conduit （SPC） and used it to bridge a 10-mm-long sciatic nerve defect in the rat. Retrograde tracing, behavioral testing and histomorphometric analyses showed that compared with the empty PLGA conduit implantation group, the SPC implantation group had a larger number of growing and extending axons, a markedly increased diameter of regenerated axons and a greater thickness of the myelin sheath in the conduit. Furthermore, there was an increase in the size of the neuromuscular junction and myofiber diameter in the target muscle. These findings suggest that the novel artificial SPC nerve graft can promote axonal regeneration and remyelination in the transected peripheral nerve and can be used for repairing peripheral nerve injury.

Electrospun and woven silk fibroin/poly(lactic-coglycolic acid) nerve guidance conduits for repairing peripheral nerve injury

We have designed a novel nerve guidance conduit（NGC） made from silk fibroin and poly（lactic-co-glycolic acid） through electrospinning and weaving（ESP-NGCs）. Several physical and biological properties of the ESP-NGCs were assessed in order to evaluate their biocompatibility. The physical properties, including thickness, tensile stiffness, infrared spectroscopy, porosity, and water absorption were determined in vitro. To assess the biological properties, Schwann cells were cultured in ESP-NGC extracts and were assessed by morphological observation, the MTT assay, and immunohistochemistry. In addition, ESP-NGCs were subcutaneously implanted in the backs of rabbits to evaluate their biocompatibility in vivo. The results showed that ESP-NGCs have high porosity, strong hydrophilicity, and strong tensile stiffness. Schwann cells cultured in the ESP-NGC extract fluids showed no significant differences compared to control cells in their morphology or viability. Histological evaluation of the ESP-NGCs implanted in vivo indicated a mild inflammatory reaction and high biocompatibility. Together, these data suggest that these novel ESP-NGCs are biocompatible, and may thus provide a reliable scaffold for peripheral nerve repair in clinical application.

Controlled release of cisplatin and cancer cell apoptosis with cisplatin encapsulated poly(lactic-co-glycolic acid) nanoparticles

The goal of the present study is to utilize cis-diamminedichloroplatinum (cisplatin) loaded polymer nanoparticles (NPs) to give a controlled, extended, and local drug therapy for the treatment of cancer. We have used biodegradable and biocompatible poly(lactic-co-glycolic acid) (PLGA) to prepare the NPs by adjusting the double emulsion technique using poly(vinylalcohol) as a surface active agent. The PLGA NPs were characterized for particle size and shape, controlled release of cisplatin, and degradation. Cisplatin solubility in deionized water was increased up to 4 mg/mL by simply changing the solution parameters. Cisplatin encapsulated NPs were incubated in phosphate buffered saline (PBS) at 37?C to study the release kinetics of cisplatin. Cisplatin was released in a sustained manner with less than 20% release during a 3-day period followed by 50% release during a 21-day period. A degradation study of PLGA NPs demonstrated the loss of spherical shape during a 21-day period. We also examined the cisplatin sensitive A2780 cell apoptosis when cells were incubated with cisplatin encapsulated PLGA NPs. A large number of cell apoptosis occurred as a result of cisplatin release from the PLGA NPs. These results suggest that cisplatin encapsulated PLGA NPs can be used to treat the cancer cells by injecting them into a localized site minimizing the side effects.

Poly(lactic-co-glycolic acid) conduit for repair of injured sciatic nerve A mechanical analysis

Tensile stress and tensile strain directly affect the quality of nerve regeneration after bridging nerve defects by poly（lactic-co-glycolic acid） conduit transplantation and autogenous nerve grafting for sciatic nerve injury. This study collected the sciatic nerve from the gluteus maximus muscle from fresh human cadaver, and established 10-mm-long sciatic nerve injury models by removing the ischium, following which poly（lactic-co-glycolic acid） conduits or autogenous nerve grafts were transplanted. Scanning electron microscopy revealed that the axon and myelin sheath were torn, and the vessels of basilar membrane were obstructed in the poly（lactic-co-glycolic acid） conduit-repaired sciatic nerve following tensile testing. There were no significant differences in tensile tests with autogenous nerve graft-repaired sciatic nerve. Following poly（lactic-co-glycolic acid） conduit transplantation for sciatic nerve repair, tensile test results suggest that maximum tensile load, maximum stress, elastic limit load and elastic limit stress increased compared with autogenous nerve grafts, but elastic limit strain and maximum strain decreased. Moreover, the tendencies of stress-strain curves of sciatic nerves were similar after transplantation of poly（lactic-co-glycolic acid） conduits or autogenous nerve grafts. Results showed that after transplantation in vitro for sciatic nerve injury, poly（lactic-co-glycolic acid） conduits exhibited good intensity, elasticity and plasticity, indicating that poly（lactic-co-glycolic acid） conduits are suitable for sciatic nerve injury repair.