Low Molecular Weight Polylactic Acid Research Articles

Radial basis function neural network and overlay sampling uniform design toward polylactic acid molecular weight prediction

Polylactic acid (PLA) is a potential polymer material as a substitute for traditional plastics, and the accurate molecular weight distribution range of PLA is strictly required in practical applications. Therefore, exploring the relationship between synthetic conditions and PLA molecular weight is crucially important. In this work, direct polycondensation combined with overlay sampling uniform design (OSUD) was applied to synthesize the low molecular weight PLA. Then a multiple regression model and two artificial neural network models on PLA molecular weight versus reaction temperature, reaction time, and catalyst dosage were developed for PLA molecular weight prediction. The characterization results indicated that the low molecular weight PLA was efficiently synthesized under this method. Meanwhile, the experimental dataset acquired from OSUD successfully established three predictive models for PLA molecular weight. Among them, both artificial neural network models had significantly better predictive performance than the regression model. Notably, the radial basis function neural network model had the best predictive accuracy with only 11.9% of mean relative error on the validation dataset, which improved by 67.7% compared with the traditional multiple regression model. This work successfully predicted PLA molecular weight in a direct polycondensation process using artificial neural network models combined with OSUD, which provided guidance for the future implementation of molecular weight-controlled polymer’ synthesis.

Biocoating-A Critical Step Governing the Oral Delivery of Polymeric Nanoparticles.

Decades of research into the topic of oral nanoparticle (NP) delivery has still not provided a clear consensus regarding which properties produce an effective oral drug delivery system. The surface properties-charge and bioadhesiveness-as well as in vitro and in vivo correlation seem to generate the greatest number of disagreements within the field. Herein, a mechanism underlying the in vivo behavior of NPs is proposed, which bridges the gaps between these disagreements. The mechanism relies on the idea of biocoating-the coating of NPs with mucus-which alters their surface properties, and ultimately their systemic uptake. Utilizing this mechanism, several coated NPs are tested in vitro, ex vivo, and in vivo, and biocoating is found to affect NPs size, zeta-potential, mucosal diffusion coefficient, the extent of aggregation, and in vivo/in vitro/ex vivo correlation. Based on these results, low molecular weight polylactic acid exhibits a 21-fold increase in mucosal diffusion coefficient after precoating as compared to uncoated particles, as well as 20% less aggregation, and about 30% uptake to the blood in vivo. These discoveries suggest that biocoating reduces negative NP charge which results in an enhanced mucosal diffusion rate, increased gastrointestinal retention time, and high systemic uptake.

Alternative modification by grafting in bamboo cellulose nanofibrils: A potential option to improve compatibility and tunable surface energy in bionanocomposites

Chemical modification in surface of cellulose nanofibrils CNFs (20 nm) from an endemic and non-significant value-added, Argentine bamboo, was developed. The modification in the CNFs was carried out with three simple routes using a low molecular weight polylactic acid synthesized in our laboratory (PLA1). The first step comprises of protection of the hydroxyl groups of PLA1 through a benzoylation (PLA1Bz). The next step consisted of the activation of carboxyl groups using thionyl chloride and the last reaction was the grafting of the modified PLA onto the CNFs (PLA1Bz-g-CNF). The covalently functionalization is confirmed by spectroscopically techniques as well as PLA1Bz-g-CNFs were characterized by thermal analyses. The PLA1Bz-g-CNFs were taken up such as nanocharges to improve properties of compatibilization and changing surface properties in films based on PLA. The comparison between the films with PLA1Bz-g-CNFs with respect to the physic mixture of the components (PLA1Bz/CNF), shows an improvement in the thermal, mechanical, and surface properties of the material, particularly when 5% of PLA1Bz-g-CNFs was added. The dispersive (γS D) component of film is increased in 36.1 mN/m respect to 29.3 mN/m from the films obtained with the physic mixture nanofibrils without modification and a plasticizing effect was noticed in the final material.

Arapey sweet potato peel waste as renewable source of antioxidant: extraction, nanoencapsulation and nanoadditive potential in films

In this work, the peel of Arapey Sweet Potato (Ipomoea batatas), a vegetable waste, was used as a source of phenolic compounds which are widely recognized as beneficial antioxidants for human health. The extract obtained from Ipomoea batatas exhibited an antioxidant activity significantly higher than many antioxidant agents reported in literature (476.96 mg of TROLOX mL-1), as well as good thermal stability. Nanocapsules of the extract coated with low molecular weight polylactic acid were prepared by the emulsification-solvent evaporation method and the nanoparticles obtained were characterized physical; thermal; and morphologically. An analysis of the variables that were investigated to increase the encapsulation efficiency is presented here. Besides, PLA films prepared via the solution-casting method exhibited good compatibility with the nanoparticles loaded with the antioxidant extract, as was evidenced by the uniform and stable dispersion of these particles in the films. Furthermore, an improvement of the mechanical properties of the PLA films due to the presence of the nanoparticles were clearly observed. Results reported here are encourage enough to propose the nanocapsules described in this work as additives or to be used immersed in films for controlled release of antioxidants, putting in value a vegetable waste.

Nanoarchitectonics Composites of Thermoplastic Starch and Montmorillonite Modified with Low Molecular Weight Polylactic Acid.

Nano montmorillonite (MMT) was modified by low molecular weight polylactic acid (PLA), then, the PLA modified MMT and raw MMT were added into thermoplastic starch (TPS) to prepare biodegradable nanocomposite films, respectively. For both nanocomposite films with raw MMT and modified MMT, the Tmax of degradation was enhanced and the mechanical properties were improved. The composite films containing 4 wt.% MMT displayed tensile strength of 5.06 MPa, approximately 1.4 times of that for the pure TPS films. The tensile strength of composite films containing 4 wt.% modified MMT is 6.74 MPa approximately 2 times of those for pure starch films. On the other hand, the composite film containing 4 wt.% modified MMT displayed elongation at break as high as 34.25%, which is 1.3 times of that of the pure starch film, while the composite films containing raw MMT had reduced elongation at break. This study showed that the MMT modified with PLA could significantly enhance the mechanical properties of TPS, and provides a new method to prepare fully biodegradable starch-based nanocomposites.

Development of eco-environmental nano-emulsified active coated packaging material

Coated packaging film with nano-emulsified polylactic acid (PLA) was prepared as an extended shelf life package for chicken fillet. PLA was prepared by direct polycondensation to be prepared after that nanoparticles by solvent displacement as potential coating for packaging systems. The characterizations of PLAwere done by thermo-gravimetric measurement size exclusion chromatography and differential scanning calorimetry. Additionally, the particle size distribution was measured by dynamic light scattering which exhibited narrow particle size distribution with mean particle size ≈70 nm. The effect of PLA nanoparticles coating was evaluated as an active packaging for a chicken fillet stored at 4 °C. An aerobic plate, coliforms counts (APC) and sensory score were also studied. The Low molecular weight PLA (LM-PLA) reduces APC by 1.5 log cfu/g and coliforms count by 75 MPN/g than the control and extended the storage time more than 2 days. Meanwhile, a high molecular weight PLA (HM-PLA) significantly reduces APC by 2.1 log cfu/g and coliforms count by 107 MPN/g lower than the control beside extended the storage time by more than 3 days. Although dipping in lactic acid 1% for 5 min and 2% for 10 min was increased the storage time to 11th and 15th days respectively. Moreover, the sensory score of chicken fillet packaged in PLA were significantly high.

Study of engineered low-modulus Mg/PLLA composites as potential orthopaedic implants: An in vitro and in vivo study.

Low molecular weight poly-lactic acid (PLLA) is a polymer matrix of orthopaedic implants. The PLLA matrix incorporating bioactive magnesium ion (Mg2+) enhances bone regeneration. But the optimal ratio of Mg2+ to PLLA matrix has not been well reported and is worthy of study. We synthesized silane-coated Mg/PLLA composites containing 1%, 2%, 3%, 4% and 5% Mg micro-particles. The mechanical properties, in vitro cytocompatibility, cell viability and osteogenesis differentiation and in vivo performance of silane-coated Mg/PLLA composites were evaluated. These results showed that the bending and tensile strength of PLLA matrix was reduced by incorporation of Mg micro-particles. Mg/PLLA composites with higher Mg micro-particles ratio showed higher Mg2+ leaching rate and pH value in immersion solutions. MC3T3-E1 pre-osteoblasts incubated with Mg/PLLA composites containing higher ratio of Mg micro-particles showed higher cytocompatibility, cell viability, osteogenesis differentiation and migration. In vitro cellular responses showed that MC3T3-E1 pre-osteoblasts had the highest cell viability at 50 ppm Mg2+. In vivo animal studies showed there was no change in serum Mg2+ concentration after implanting Mg/PLLA composites comparing with control and the implants of silane-coated Mg/PLLA composites accelerated bone formation. In summary, our study revealed the feasibility of silane-coated Mg/PLLA composites as orthopaedic implants. Silane-coated Mg/PLLA composites with Mg micro-particles ratio of 3% ∼ 5% were optimal substitutes for bone regeneration.

Synthesis and structures of aluminum ion-pair complexes that act as L- and racemic-lactide ring opening polymerization initiators

Seven aluminum ion-pair complexes (1–7) were synthesized by reaction of NNO Schiff base ketoimines with differing substituents with tris(2,6-dimethylphenoxy) aluminum dimer in an inert atmosphere glovebox at room temperature. The complexes were characterized with 1H, 13C, and 19F nuclear magnetic resonance spectroscopy, absorbance spectroscopy, and elemental analysis. Furthermore, the dinuclear nature of the complexes was elucidated with single crystal X-ray crystallography and 27Al NMR. The ion-pair complexes consisted of a bis-ligating homoleptic ketoiminate with octahedral coordination as an aluminum cation complex and a tetrahedral aluminum anion complex of 2,6-dimethylphenoxide. Each ion-pair was used to initiate the ring opening polymerization (ROP) of L- and rac-lactide to poly-lactic acid (PLA) in toluene at 100 °C at a 100:1 [LA]:[ion-pair] ratio. Proton NMR spectra showed percentage conversions of monomer to polymer of 96–99% in 18 h. The isolated polymeric materials were determined to have moderate molecular weights with low to moderate polydispersity index values using gel permeation chromatography. The bis-ligated aluminum cation and tetraphenoxide aluminate anions of 1 were isolated into separate compounds (8 and 9) with unreactive counter ions, and each yielded low molecular weight PLA under the polymerization conditions. Thus, lactide polymerization appeared to require both ion-pair components to yield the moderately high molecular weight PLA, and this was investigated spectroscopically.

Facile fabrication of polylactic acid stereocomplex microspheres

An efficient and scalable method to prepare polylactic acid stereocomplex microspheres (sc-PLA-MPs) is achieved. Low molecular weight polylactic acid containing triethoxysilane end-groups (Si-PLA) were firstly synthesized via coupling reaction of 3-(triethoxysilyl)propyl isocyanate with low molecular weight poly (l-lactic acid) (PLLA) and poly (D-lactic acid) (PDLA). Then, the triethoxysilane terminated poly (l-lactic acid) and poly (d-lactic acid) were dissolved in 1,4-dioxane where the triethoxysilane end-groups could hydrolytic condense in-situ, leading to the formation of the architecture having both PLLA and PDLA arms in one molecule, and consequently the stereocomplex microparticles spontaneously precipitated in the form of spherical microspheres with size of approximately ∼5μm.

Sustained release of aspirin and vitamin C from titanium nanotubes: An experimental and stimulation study

Anodization is a promising method to change the topography and wettability of titanium (Ti) implant. The formed TiO2 nanotubes (TiNTs) arrays could enhance the biological properties of Ti implants. In this study, to investigate the possibility of TiNTs arrays on a Ti implant surface as nano-reservoirs for small molecular drugs when using in orthopedic and dental prosthesis, TiNTs on a Ti implant surface were prepared. Then, aspirin and/or vitamin C were loaded into TiNTs as model drugs. Meanwhile, low molecular weight polylactic acid (PLA, Mw=3000) was synthesized and loaded alternately along with aspirin or vitamin C. The release rates of aspirin and vitamin C with/or without PLA loading were investigated by using a UV–Vis spectrometer. The results showed that when loading without PLA, drugs released quickly with presence of burst release. However, when loading with PLA, the cumulative release duration of aspirin and vitamin C was prolonged to over 240h. Molecular dynamics (MD) simulation and dissipative particle dynamics (DPD) simulation results proved that when loading with PLA, PLA molecules aggregated gradually and formed clusters or micelles in these nanotubes. Meanwhile, drug molecules were captured and distributed inside the PLA matrix, which retarding the release of drugs. Only when PLA micelles degrade gradually in body fluid, drugs could be released slowly from nanotubes. These knowledge laid ground basis for the following biological experiments.

Chitosan grafted low molecular weight polylactic acid for protein encapsulation and burst effect reduction

Chitosan and chitosan-grafted polylactic acid as a matrix for BSA encapsulation in a nanoparticle structure were prepared through a polyelectrolyte complexation method with dextran sulfate. Polylactic acid was synthetized via a polycondensation reaction using the non-metal-based initiator methanesulfonic acid and grafted to the chitosan backbone by a coupling reaction, with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide as the condensing agent. The effect of concentration of the polymer matrix utilized herein on particle diameter, ζ-potential, encapsulation efficiency, and the release kinetic of the model protein bovine serum albumin at differing pH levels was investigated. The influence of pH and ionic strength on the behavior of the nanoparticles prepared was also researched. Results showed that grafting polylactic acid to chitosan chains reduced the initial burst effect in the kinetics of BSA release from the structure of the nanoparticles. Furthermore, a rise in encapsulation efficiency of the bovine serum albumin and diminishment in nanoparticle diameter were observed due to chitosan modification. The results suggest that both polymers actually show appreciable encapsulation efficiency; and release rate of BSA. CS-g-PLA is more suitable than unmodified CS as a carrier for controlled protein delivery.

Improving the properties of polylactic acid by blending with low molecular weight polylactic acid‐g‐natural rubber

The low molecular weight (Mw) polylactic acid‐g‐natural rubber (PLA‐g‐NR) was synthesized by grafting the maleated natural rubber (MNR) with low molecular weight PLA at a weight ratio of 1:1 in toluene at 80°C. Two types of MNR (MNR10 and MNR20) having anhydride moieties of 10 and 20 wt%, respectively, were prepared. The reaction was followed by IR analysis. Next, the obtained PLA‐g‐NR was blended with pristine PLA using a twin‐screw extruder at PLA to PLA‐g‐NR weight ratios of 90:10, 80:20, 70:30, and 60:40 followed by compression to obtain specimens for testing. In case of 10 wt% PLA‐g‐NR having MNR10, it was found that blending of PLA with PLA‐g‐NR resulted in a 200% improvement in impact strength and twofold percent elongation at break (flexibility). Further SEM analysis confirmed that PLA‐g‐NR was compatible with PLA matrix. In contrast, NR was present as disperse particles which exhibited poor adhesion to PLA. From these findings, it was also found that PLA‐g‐NR was capable of improving the properties of PLA more than NR due to the fact that it exhibited higher compatibility. POLYM. ENG. SCI., 54:2770–2776, 2014. © 2013 Society of Plastics Engineers

Degradation Behaviors of Different Blends of Polylactic Acid Buried in Soil

Polylactic acid (PLA), as the biodegradable polymer becomes more attention as a green material for industrial applications. Lipase-catalysed polymerization with Lecitase Ultra and Lipozyme TL IM were applied to synthesize PLA to decrease the chemical-catalysts utilization which having toxicity interferes in products. PLA products were characterized by end group/HPLC analyses for Mn/Mw determination. The results indicated that low molecular weight PLA could be successfully produced from commercial lactic acid by using the commercial lipases. With using Lipozyme TL IM as biocatalyst, obtainable Mn and Mw of PLA were 7,933Da and 194Da, respectively. For Lecitase Ultra used as biocatalyst obtainable Mn and Mw of PLA were 8,330Da and 216Da, respectively. Subsequently, the resulting PLA products from this method were prepared as PLA films blended with commercial PLA beads varying the blending ratios by casting on glass plate. Their degradable behaviors were studied under controlled soil burial laboratory conditions. The characteristics of PLA blend films were analyzed using visual observations, measuring weight loss, DSC and FTIR analysis. The results observed that the different blends ratios of PLA films showed more flexible than pure PLA film. Besides, the different blends of PLA films were disintegrated in soil within the short burial time.

Morphology and thermal properties of foams prepared via thermally induced phase separation based on polylactic acid blends

Blends of poly-l-lactic acid with two different types of polylactic acid with different average molecular weights (50,000 and 175,000 g/mol, respectively) in different proportions (90/10, 80/20 and 70/30) were utilized in order to produce biodegradable and biocompatible scaffolds for soft tissue engineering applications. The scaffolds were produced via thermally induced phase separation starting from ternary systems where dioxane was the solvent and water the non-solvent. Morphology (average pore size and interconnection) was evaluated by scanning electron microscopy. Foams apparent density was also evaluated (porosity ranges from 87% to 92%). Moreover, a differential scanning calorimetry analysis was carried out on the as-obtained scaffold, so as to obtain information about their thermal properties (enthalpy of melting and crystallization). The results showed that is possible to prepare scaffolds of poly-l-lactic acid/polylactic acid via thermally induced phase separation with both polylactic acids and to tune their average pore size (from 40 to 70 µm) by changing some experimental parameters (e.g. demixing temperature). Moreover, the average molecular weight of the polylactic acid in the blend seems to influence the thermally induced phase separation process in terms of demixing temperatures, which resulted higher than pure poly-l-lactic acid for the blends containing the high molecular weight polylactic acid, and lower for the blends containing the low molecular weight polylactic acid. Finally, a decrease in the crystallinity of the foams when increasing polylactic acid content in poly-l-lactic acid/polylactic acid blends was observed, as witnessed by a drop in the enthalpy of melting and crystallization. The results confirm that the morphology and the mechanical properties of the scaffold can be tuned up, starting from poly-l-lactic acid and blending it in different proportions with polylactic acid with different molecular weights.

Lipase-Catalysed Polymerization of Lactic Acid and the Properties of the Polymer

Lipase-catalysed polymerization is an emerging green alternative method for the synthesis of polylactic acid (PLA) from lactic acid (LA) monomer. Use of the lipase catalyst avoids the need for potentially toxic chemical catalysts. The concentration of the lipase enzyme is one of several factors which influence the polymerization process. This paper reports on the effects of the lipase concentration on the characteristics of the low molecular weight polylactic acid (PLA) formed via lipase-catalyzed polymerization of lactic acid. The polylactic acid products made by this method are characterized by Fourier Transform Infrared Spectroscopy (FTIR). Low molecular weight polylactic acid could be successfully produced from commercial lactic acid by using the commercial lipase Lipozyme TL IM at 50 °C in a 5-hour reaction.

In vitro effect on cancer cells: Synthesis and preparation of polyurethane membranes for controlled delivery of curcumin

Urethane polymers (PU) have been prepared from low-molecular weight polylactic acid (PLA) and hexamethylene diisocyanate (HMDI) using polydimethylsiloxane (PDMS) as a chain extender. These formed the supporting polymeric matrix of curcumin-containing PU membranes which were prepared using a solvent evaporation technique. FTIR and XRD data indicated the molecular-level dispersion and random distribution of curcumin in the polymer matrix, and data were consistent with observations from tensile-strength measurements and from AFM imaging. Determination of water vapor permeability and moisture uptake measurements have indicated that the PU membrane were appropriate for use on human skin. Skin permeation studies of curcumin were consistent with zero order (R² = 0.9874) and with Korsmeyer-Peppas (R² = 0.9978) kinetics-analytical data pointed to permeation by a combination of diffusion and erosion processes, with the latter dominating. The biocompatibility of these PU membranes was indicated by in vitro cytotoxicity studies using 3T3-L1-murine fibroblast cell. The in vitro therapeutic potential of the patches was demonstrated against A549 human lung cancer cells.

Interfacial properties of phosphate glass fibres/PLA composites: Effect of the end functionalities of oligomeric PLA coupling agents

Polylactic acid (PLA) oligomers as coupling agents have shown higher interfacial shear strength in phosphate based glass fibres/PLA composites. To influence bonding on the glass fibre surface, short chain PLA oligomers with different end groups were used as coupling agents. The low molecular weight PLA with a sodium salt terminal group, a carboxylic acid end group and also with one, two and five hydroxyl groups were produced and applied on the fibre surface through a condensation reaction. Mechanical properties of the sized fibres/PLA composites were found to be increased. XPS and TG analyses showed the presence of the coupling agents on the fibres surface. SEM analysis further confirms the presence of the agents.

Low Molecular Weight Polylactic Acid as a Matrix for the Delayed Release of Pesticides

Low molecular weight polylactic acid (LMW PLA) was used as a matrix to formulate biodegradable matrix granules and films with bromacil using a melt process. The compatibility of the PLA with bromacil was evaluated. The release characteristics of the formulations were investigated in vitro. The degradation and erosion of the formulations were monitored by pH and gravimetric analysis during the course of release. Various granules and films had similar biphasic release patterns, a delayed release followed by an explosive release. The release rates were independent of bromacil content in the matrix, but varied with the geometry of matrices. The mechanisms of diffusion and erosion were involved in the release. The delayed release of the formulations was dominantly governed by the degradation and erosion of PLA. LMW PLA underwent bulk erosion. LMW PLA-based matrix formulations could thus be useful for the application of pesticides to sensitive targets such as seed treatment.

Survival of Escherichia Coli 0157:H7 on Vacuum‐Packaged Raw Beef Treated with Polylactic Acid, Lactic Acid, and Nisin

ABSTRACT: The antimicrobial effect of 2% low molecular weight polylactic acid (LMW‐PLA), 2% lactic acid (LA), 200 IU nisin (Nisaplin™)/mL, and combinations of nisin and each acid on Escherichia coli O157:H7 on raw beef was investigated. Fresh beef, inoculated with E. coli O157:H7 and treated with each solution, was vacuum packaged and stored at 4 °C for 28 d. At day 28, counts of samples treated with LMW‐PLA, NPLA, LA, and NLA were significantly reduced to 3.13,2.91, 2.99, and 2.83 log10 CFU/cm2, respectively. However, the antimicrobial effect of LMW‐PLA and LA was not significantly different from each other and Nisaplin did not enhance the effects of either acid against this organism.

Synthesis and Characterization of Low Molecular Weight Polylactic Acid

The polymerization of (D, L)-lactic acid in the absence of catalysts was studied. Azeotropic distillation using xylene, gave poly(lactic acid) with very low molecular weight, which however, was further increased by post-curing in an air oven. Moreover degradation phenomena and residual xylene were observed, with this procedure. Polycondensation of lactic acid at temperatures up to 180 C under vacuum, resulted in fast reaction with poor control and the products are still characterized by low molecular weight. When the reaction was run at 220 C in inert atmosphere, amorphous poly(lactic acid) was obtained with molecular weight exceeding 3000. The product was found pure, since it is free from solvents, catalysts and monomer. Also, no evidence of thermal degradation was observed. The above characteristics are well acceptable design aspects for biomedical uses.