Lactic Acid Oligomers Research Articles

Influence of Oligomeric Lactic Acid and Structural Design on Biodegradation and Absorption of PLA-PHB Blends for Tissue Engineering

The advancing development in biomaterials and biology has enabled the extension of 3D printing technology to the bioadditive manufacturing of degradable hard tissue substitutes. One of the key advantages of bioadditive manufacturing is that it has much smaller design limitations than conventional manufacturing and is therefore capable of producing implants with complex geometries. In this study, three distinct blends of polylactic acid (PLA) and polyhydroxybutyrate (PHB) were produced using Fused Deposition Modeling (FDM) technology. Two of these blends were plasticized with oligomeric lactic acid (OLA) at concentrations of 5 wt% and 10 wt%, while the third blend remained unplasticized. Each blend was fabricated in two structural modifications: solid and porous. The biodegradation behavior of the produced specimens was examined through an in vitro experiment using three different immersion solutions: saline solution, Hank’s balanced salt solution (HBSS), and phosphate-buffered saline (PBS). All examined samples were also subjected to chemical analysis: atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS). The results of the degradation experiments indicated a predominantly better absorption capacity of the samples with a porous structure compared to the full structure. At the same time, the blend containing a higher concentration of OLA exhibited enhanced pH stability over the evaluation period, maintaining relatively constant pH values before experiencing a minor decline at the end of the study. This observation indicates that the increased presence of the plasticizer may provide a buffering effect, effectively mitigating the acidification associated with material degradation.

Optimizing the injection molding process for thermally and electrically conductive, carbon fiber and carbon nanotube‐reinforced poly(lactic acid) hybrid composites with enhanced mechanical properties

AbstractWe produced poly(lactic acid) (PLA) matrix carbon fiber and carbon nanotube‐reinforced hybrid composites with enhanced thermal conductivity (0.48–0.59 W/mK) and electrical conductivity (0.35–0.97 S/cm). The conductive fillers greatly decreased the toughness, which was compensated with oligomeric lactic acid (OLA). Since fillers and plasticizers greatly alter the flow and thermal properties of the material as well, it was necessary to optimize several parameters of the injection molding process that were predetermined based on theoretical considerations. Based on oscillatory shear rheometry, we explored the rheological behavior of the materials in a wide temperature and shear rate range for the optimum injection molding temperatures, injection volume rates. We showed that by adding 15 wt% OLA as a plasticizer to the composites, the optimal processing temperature decreased by 45–135°C. This remarkable change illustrates the need for rheological studies of PLA compounds. The injection molded hybrid composites containing 5% oligomeric lactic had a tensile strength, modulus of elasticity, and work of fracture higher by 41%, 10%, and 150%, respectively, compared to samples without OLA.

Thermally-Activated Shape Memory Behavior of Biodegradable Blends Based on Plasticized PLA and Thermoplastic Starch.

Biodegradable blends based on plasticized poly(lactic acid) PLA and thermoplastic starch (TPS) have been obtained. The influence of the PLA plasticizer as a compatibility agent has been studied by using two different plasticizers such as neat oligomeric lactic acid (OLA) and functionalized with maleic acid (mOLA). In particular, the morphological, thermal, and mechanical properties have been studied as well as the shape memory ability of the melt-processed materials. Therefore, the influence of the interaction between different plasticizers and the PLA matrix as well as the compatibility between the two polymeric phases on the thermally-activated shape memory properties have been studied. It is very interesting to use the same additive able to act as both plasticizer and compatibilizer, decreasing the glass transition temperature of PLA to a temperature close to the physiological one, obtaining a material suitable for potential biomedical applications. In particular, we obtain that OLA-plasticized blend (oPLA/TPS) show very good thermally-activated capability at 45 °C and 50% deformation, while the blend obtained by using maleic OLA (moPLA/TPS) did not show shape memory behavior at 45 °C and 50% deformation. This fact is due to their morphological changes and the loss of two well-distinguished phases, one acting as fixed phase and the other one acting as switching phase to typically obtain shape memory response. Therefore, the thermally-activated shape memory results show that it is very important to make a balance between plasticizer and compatibilizer, considering the need of two well-established phases to obtain shape memory response.

Synthesis of L-Lactide from Lactic Acid and Production of PLA Pellets: Full-Cycle Laboratory-Scale Technology.

Lactide is one of the most popular and promising monomers for the synthesis of biocompatible and biodegradable polylactide and its copolymers. The goal of this work was to carry out a full cycle of polylactide production from lactic acid. Process conditions and ratios of reagents were optimized, and the key properties of the synthesized polymers were investigated. The influence of synthesis conditions and the molecular weight of lactic acid oligomers on the yield of lactide was studied. Lactide polymerization was first carried out in a 500 mL flask and then scaled up and carried out in a 2000 mL laboratory reactor setup with a combined extruder. Initially, the lactic acid solution was concentrated to remove free water; then, the oligomerization and synthesis of lactide were carried out in one flask in the presence of various concentrations of tin octoate catalyst at temperatures from 150 to 210 °C. The yield of lactide was 67-69%. The resulting raw lactide was purified by recrystallization in solvents. The yield of lactide after recrystallization in butyl acetate (selected as the optimal solvent for laboratory purification) was 41.4%. Further, the polymerization of lactide was carried out in a reactor unit at a tin octoate catalyst concentration of 500 ppm. Conversion was 95%; Mw = 228 kDa; and PDI = 1.94. The resulting products were studied by differential scanning calorimetry, NMR spectroscopy and gel permeation chromatography. The resulting polylactide in the form of pellets was obtained using an extruder and a pelletizer.

Effect of oligomeric lactic acid plasticizer on the mechanical recycling of poly(3-hydroxybutyrate-co-3-hydroxyvalerate).

Bioplastics such as polyhydroxyalkanoates (PHA) emerge as an interesting alternative to conventional fossil fuel-based plastics and as part of the solution their associated environmental issues. Nevertheless, end-of-life scenarios are still a major concern, especially within a circular economy framework. When feasible, mechanical recycling appears as the best alternative, since it saves raw materials and energy. However, the viability of mechanical recycling can be compromised by the degradation of the plastic during its use and during the recycling process and by the presence of certain additives. Consequently, the main objective of this work is to study the effect of accelerated ageing and mechanical recycling on the structure and properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)-based formulations. The obtained results suggest that accelerated ageing and mechanical recycling led only to a slight degradation of the pure PHBV material, along with small variations in the thermal and mechanical properties. However, the plasticized PHBV formulations showed a more severe degradation and increased thermal stability and stiffness, which could be result of the elimination of the plasticizer during the recycling. Overall, mechanical recycling seems to be an interesting valorization strategy for PHBV wastes, although especial attention should be paid to the additives present in the materials.

Designing of Drug Delivery Systems to Improve the Antimicrobial Efficacy in the Periodontal Pocket Based on Biodegradable Polyesters.

Delivery systems for biologically active substances such as proanthocyanidins (PCANs), produced in the form of electrospun nonwoven through the electrospinning method, were designed using a polymeric blend of poly(L-lactide-co-glycolide) (PLGA)and poly[(R,S)-3-hydroxybutyrate] ((R,S)-PHB). The studies involved the structural and thermal characteristics of the developed electrospun three-dimensional fibre matrices unloaded and loaded with PCANs. In the next step, the hydrolytic degradation tests of these systems were performed. The release profile of PCANs from the electrospun nonwoven was determined with the aid of UV-VIS spectroscopy. Approximately 30% of the PCANs were released from the tested electrospun nonwoven during the initial 15-20 days of incubation. The chemical structure of water-soluble oligomers that were formed after the hydrolytic degradation of the developed delivery system was identified through electrospray ionization mass spectrometry. Oligomers of lactic acid and OLAGA oligocopolyester, as well as oligo-3-hydroxybutyrate terminated with hydroxyl and carboxyl end groups, were recognized as degradation products released into the water during the incubation time. It was also demonstrated that variations in the degradation rate of individual mat components influenced the degradation pattern and the number of formed oligomers. The obtained results suggest that the incorporation of proanthocyanidins into the system slowed down the hydrolytic degradation process of the poly(L-lactide-co-glycolide)/poly[(R,S)-3-hydroxybutyrate] three-dimensional fibre matrix. In addition, in vitro cytotoxicity and antimicrobial studies advocate the use of PCANs for biomedical applications with promising antimicrobial activity.

PLA reinforced with modified chokeberry pomace and beetroot pulp fillers. Effect of oligomeric chain extender on the properties of biocomposites

Agri-food waste is an exciting way to use as a polymer filler. It is an ecological option for cutting down the material cost, especially relatively expensive biodegradable plastics. In this paper, lignocellulosic residues of chokeberry pomace (CP) and beetroot pulp (BP) are grafted with lactic acid oligomers (OLAs) in direct condensation of lactic acid (LAc) into the lignocellulosic backbone. Biocomposites with modified and unmodified fillers were prepared using poly (lactic acid) (PLA) matrix. Additionally, the influence of an epoxy-based chain extender (Joncryl® ADR 4468 (ADR)) on the properties of the biocomposites mentioned above was checked. SEM was used for the characterisation of modified and unmodified fillers. The success of the grafting reaction was confirmed by FTIR and 1HNMR analyses. DSC, DMA and TGA was applied for the characterisation of thermal properties of produced biocomposites. The influence of chemical modification and introduction of ADR to the biocomposite on water absorption, rheological and mechanical properties were tested. Moreover, the reaction between ADR and the lignocellulosic backbone of the CP filler was studied by FTIR analysis. Results showed, that modification of the filler using OLAs has a significant influence on reducing water absorption by 48.3 and 56.5 % for CP and BP biocomposites, respectively. The tensile strength increased after the modification and introduction of ADR. The chemical treatment of the filler causes an increase in the tensile strength by about 29 and 8 % compared to unmodified CP and BP fillers, respectively. 0.75 % of ADR in CP/PLA biocomposite allowed for an increase in tensile strength by 51 %. Rheological study showed that presence of ADR compensates the consequences of hydrolysis and segment exchange of the PLA chains caused by water and OLAs, respectively. Results are promising for the production of ecological biocomposites with satisfying mechanical, thermal and rheological properties compared to biocomposites with unmodified lignocellulosic filler.

Molecular Weight Distribution of Lactic Acid Oligomer from the Polycondensation Without Catalyst and Its Application for the Starch Modification

Molecular Weight Distribution of Lactic Acid Oligomer from the Polycondensation Without Catalyst and Its Application for the Starch Modification

A critical review of computational efforts towards identifying secondary structure elements in polylactic acid (PLA)

Polylactic acid (PLA) may be regarded as an analogue of a poly-alanine oligo/polypeptide, where the amino group has been replaced by a hydroxyl. As a consequence, a series of studies have explored the possibility that PLA can adopt peptide-type secondary structures – i.e., repetitive structural patterns characterized by intramolecular hydrogen bonds between neighboring functional groups. To this end, computational techniques (molecular mechanics, semiempirical, Hartree-Fock, density functional theory DFT) geometry optimizations of isolated oligomers of lactic acid (generally ten-unit oligomers), or oligomers attached to solid surfaces, or dimers have been reported, as well as spectral simulations thereof - looking at relative stabilities of helices (α, π, 310), and β sheets. A significant variation in the predicted structures and spectra was noted, depending on the computational method employed. With the most accurate method available (a DFT functional parametrized especially for describing non-covalent interactions), in isolated PLA models the π helix was found to be the most likely structure, closely followed by the 310 helix, and β sheets being the least stable. We review here these data and add two important elements: (1) first, a comparison with an experimentally-derived model of PLA, proposed by De Santis, and (2) second, a Ramachandran analysis of the Φ and Ψ angles in the optimized geometries. It is shown that (1) the De Santis structure is in fact slightly more stable than the helices, and (2) the optimized geometries in fact stray far from the initial Φ, Ψ values – to the extent that all of the peptide-like secondary structures in fact end up as turns (mostly type III β turns), while the DFT-optimized De Santis structure has no classical correspondent in the Ramachandran series of secondary structures.

Evaluation of Biocompatibility of PLA/PHB/TPS Polymer Scaffolds with Different Additives of ATBC and OLA Plasticizers.

One of the blends that is usable for 3D printing while not being toxic to cell cultures is the lactic acid (PLA)/polyhydroxybutyrate (PHB)/thermoplastic starch (TPS) blend. The addition of plasticizers can change the rate of biodegradation and the biological behavior of the material. In order to evaluate the potential of the PLA/PHB/TPS material in combination with additives (plasticizers: acetyl tributyl citrate (ATBC) and oligomeric lactic acid (OLA)), for use in the field of biomedical tissue engineering, we performed a comprehensive in vitro characterization of selected mixture materials. Three types of materials were tested: I: PLA/PHB/TPS + 25% OLA, II: PLA/PHB/TPS + 30% ATBC, and III: PLA/PHB/TPS + 30% OLA. The assessment of the biocompatibility of the materials included cytotoxicity tests, such as monitoring the viability, proliferation and morphology of cells and their deposition on the surface of the materials. The cell line 7F2 osteoblasts (Mus musculus) was used in the experiments. Based on the test results, the significant influence of plasticizers on the material was confirmed, with their specific proportions in the mixtures. PLA/PHB/TPS + 25% OLA was evaluated as the optimal material for biocompatibility with 7F2 osteoblasts. The tested biomaterials have the potential for further investigation with a possible change in the proportion of plasticizers, which can have a fundamental impact on their biological properties.

Transcriptomic analysis of PLA-degrading bacteria Brevibacillus brevis grown on polylactic acid

Polylactic acid (PLA) is a promising biodegradable material used in various fields, such as mulching films and disposable packaging materials. Biological approaches for completely degrading biodegradable polymers can provide environmentally friendly solutions. However, to our knowledge, no studies have performed transcriptome profiling to analyze PLA-degrading genes of PLA-degrading bacteria. Therefore, this study reports for the first time an RNA sequence approach for tracing genes involved in PLA biodegradation in the PLA-degrading bacterium Brevibacillus brevis. As a result, the hydrolase genes (mhqD, nap, and besA) were mainly up-regulated, indicating that the hydrolase plays a key role in the biodegradation of PLA by B. brevis. In addition, genes involved in biofilm formation and transporter genes were also up-regulated. Taken together, genes related to biofilm formation were up-regulated for access to PLA and biodegradation, and hydrolase genes were up-regulated to degrade PLA into lactic acid oligomers and monomers. Finally, transport-related genes were up-regulated for cellular assimilation of the degraded oligomers. Our results provide transcriptome-based insights into the biodegradation mechanism of PLA, which pitches a better understanding of microbial biodegradation of plastics.

Biodegradation and thermal-oxidative degradation of propanediol based poly (lactic acid) oligomers

Biodegradation and thermal-oxidative degradation of propanediol based poly (lactic acid) oligomers

2nd generation PLA; Lactide formation directly from aqueous lactic acid

In order to develop a 2nd generation polylactic acid (PLA) process, lactide (LD) was synthesized directly from a commercially available 90% aqueous lactic acid (LA) solution. Experiments were conducted in an ordinary continuous flow fixed bed reactor. The reaction was carried out over various zeolites and γ-Al2O3 catalysts. Furthermore, the influence of pressure, temperature and water content in the inlet was studied. The highest LD selectivity of 98.9% was obtained using 90% LA and γ-Al2O3 as catalyst. In addition, it is concluded that LD yield increases when using highly concentrated LA oligomer with a minor amount of water. The catalysts were characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray powder diffraction (XRD), nitrogen adsorption isotherms (BET), temperature programmed desorption of ammonia (NH3-TPD) and pyridine Fourier transformed infrared spectroscopy (Py-FTIR).

Antibacterial and Antimycotic Properties of Modified Carbon Sorbents

The aim of the work was to study the biological activity of modifiers and carbon sorbent samples modified by them in relation to some types of microorganisms.Material and methods. The carbon sorbent under study and the modified samples were obtained at the Center of New Chemical Technologies BIC. Glycolic acid, lactic acid, glycine, and glutamic acid were used as modifiers. Strains of Staphylococcus aureus ATCC 25923, Pseudomonas aeruginosa ATCC 27853, Klebsiella pneumoniae 418, Esherichia coli ATCC 25922, Candida albicans (clinical strain) were used as test cultures. The test sample was placed in the wells of a sterile plate, then a working suspension of the test culture was added in the amount of 2.0 ml until completely wet 1:1. The survival of microorganisms was determined by quantitative inoculation from each well of the «sample — microorganism» mixture on Petri dishes with simple nutrient agar using the sector crop method (Gold). The culture species were confirmed by studying their cultural, morphological, and biochemical properties.Results. The conducted studies have demonstrated high antibacterial and antimycotic activity of carbon sorbent samples modified with hydroxyl acids in relation to the most common opportunistic pathogens of pyoinflammatory diseases of bacterial and fungal nature in comparison with the initial sorbent sample. The carbon sorbent modified with lactic acid oligomer showed the highest antibacterial and antimycotic activity.Conclusion. High antibacterial and antimycotic activity of carbon sorbent samples modified with hydroxy acids and amino acids in relation to the most common opportunistic pathogens of pyoinflammatory diseases of bacterial and fungal nature was established in comparison with the initial sample of the sorbent. The carbon sorbent sample modified with amino acids has a pronounced antibacterial effect against all studied bacterial test strains, but exhibits weak antimycotic properties. The use of modified carbon sorbents is a promising direction for the application therapy of pyoinflammatory infections.

Biodegradation of polylactic acid by a mesophilic bacteria Bacillus safensis

A mesophilic bacterial strain, Bacillus safensis PLA1006, was isolated from landfill soil and was tested for growth on polylactic acid (PLA) emulsion medium. The strain formed clear zones on the medium and produced protease and lipase. The macroscopic morphology of the PLA films was not changed significantly after treatment with Bacillus safensis PLA1006 but the films were whitened. Weight loss of PLA films was about 8% after 30 days of incubation with Bacillus safensis PLA1006 in mineral salt medium. Scanning electron microscopy revealed etching on the surface of PLA film treated by Bacillus safensis PLA1006. This also caused an increase in hydrophilicity of the PLA films surface. Attenuated total reflectance - Fourier transform infrared spectroscopy analysis of PLA films after treated by Bacillus safensis PLA1006 showed no new absorption peaks but a decrease in the intensity of all absorption peaks. The hydrolysis products of PLA by the strain contained monomers and oligomers of lactic acid. Zymogram detection showed that proteases may play a role in the degradation of PLA.

Biodegradable boron-containing poly(lactic acid) for fertilizers with prolonged action

A new strategy for obtaining long-acting fertilizers in the process of joint polycondensation of lactic and boric acids is presented. The article shows the effect of boric acid or boric anhydride additives in an amount of 0.1-1%wt. on the synthesis and final properties of poly(lactic acid). With increase in the amount of boric acid or boric anhydride in poly(lactic acid), polymers show higher T g and T m at approximately equal molecular weights compared to poly(lactic acid) without additives. Comprehensive studies of the structure of the obtained compositions were carried out: theoretical calculations using method DFT (Becke-Lee-Yang-Parr) and experimental - proton NMR, IR spectroscopy and melt rheometry. It has been suggested that the addition of boric acid when heated promotes the formation of B-O-C bonds and the branching of lactic acid oligomer chains. The compositions and the dynamic of boric acid release by granules obtained from boron-containing poly(lactic acid) melts were studied using elemental analysis for aqueous systems. During 7 days of testing in aqueous medium, the granules lose from 16 to 72% of boric acid. This study can serve as further development of the use of low-molecular-weight poly(lactic acid) with different molecular weights in the design of long-acting fertilizers. • Boric acid and boric anhydride were added to a lactic acid during synthesis of poly(lactic acid); • The effect of additives on the thermophysical, molecular-mass and rheological properties of poly(lactic acid) is estimated; • B-O-C bonds are not preserved in polycondensation products; • The results of hydrolysis indicate a prospect of using boric acid-containing poly(lactic acid) as a slow-release fertilizer.

Antimicrobial and Gas Barrier Crustaceans and Fungal Chitin-Based Coatings on Biodegradable Bioplastic Films

Chitin nanofibrils (CN) can be obtained from crustaceans and fungal sources and can be used for preparing coatings for bioplastic films, that are fundamental for developing a safe and sustainable biodegradable food packaging. Coatings with different concentrations of CN from shrimps were applied on different bioplastic substrates, like Poly (butylene succinate-co-adipate)/Poly(3-hydroxybutyrate-co-3-hydroxyvalerate (PBSA/PHBV) blend, Polybutylene succinate (PBS), and Polybutylene adipate terephthalate/Poly(lactic acid) (PBAT/PLA) blend, but the adhesion to the substrates was scarce. On the contrary, the fungal-based CN showed a better adhesion. Additionally, it was found that the use of an additive based on oligomeric lactic acid was useful to prepare a coating with an improved adhesion to bioplastics. The gas barrier properties to oxygen and water vapour of coated and un-coated films were measured, revealing an improvement of these properties thanks to applied coatings, especially towards the oxygen. Antimicrobial properties and biodegradation capacity were also evaluated revealing an antibacterial effect of the coatings that did not significantly interfere with their biodegradability. The results are discussed and interpreted considering the correlation between composition and macromolecular structures with the observed functional properties.

In-situ oligomerization of lactic acid within broiler skin extracted elastin/collagen matrix for the efficacy of ointment base

Elastin and collagen were isolated from waste broil skin and modified with l-lactic acid oligomer for the efficacy of substituting petroleum based ointment base matrix. Paraffin wax, which is one of the most extensively used petroleum ointment derivative is well known for its incompatibility with the skin. Chronically it clogs the skin pores, which subsequently affects the release of moisture. To mitigate this problem, a novel approach has been followed to synthesize a fully green and biocompatible ointment base matrix. The extracted Elastin and Collagen (which exists naturally in our skin) and lactic acid monomer (commonly known as a part of a body fluid) mixed at different proportion and used to synthesize a lactic acid modified elastin/collagen (OLLA-m-ELN/COL) bioconjugate matrix with lubricating characteristics via in-situ polycondensation reaction. The macromolecular interaction between Amide I group of elastin/collagen and C=O of a lactic acid oligomer was confirmed by FTIR analysis. Organoleptic analysis, spreadability, pH, and viscosity were analyzed. The six-mass loss stages which was observed in the ELN/COL matrix was changed into a single mass loss for the synthesized bioconjugate with improved thermal stability. The thermal stability improvement can be correlated with the formation of secondary macromolecular interaction.

Development of electrically conductive hybrid composites with a poly(lactic acid) matrix, with enhanced toughness for injection molding, and material extrusion-based additive manufacturing

In this study, we developed electrically conductive nano- and hybrid composites with a poly(lactic acid) (PLA) matrix for different melt processing technologies. We used short carbon fiber and multi-walled carbon nanotube reinforcements to enhance electric conductivity. We prepared the composite compounds with twin-screw extrusion; then the compounds were processed via injection molding and fused filament fabrication. We showed that electric conductivity only slightly increased by when only carbon nanotubes were added to the PLA matrix. However, when carbon fibers were added to the nanocomposites, the higher shear during melt mixing helped the uniform dispersion of the carbon nanotubes, resulting in a highly conductive reinforcement network in the composite. On the other hand, the hybrid reinforcement resulted in higher viscosity, making melt processing difficult and the material also became more brittle. Therefore, we added an oligomeric lactic acid plasticizer to the hybrid composites, and produced specimens by injection molding and 3D printing. The tensile strength increased by 140% and the elongation at break increased by 56%, and at the same time, the electrical conductivity of the material remained at a high level.

Wheat bran addition as potential alternative to control the plasticizer migration into PLA/PBSA blends

Wheat bran (WB) was investigated as potential filler for controlling the plasticizer migration in poly(lactic acid) (PLA)/poly(butylene succinate adipate) (PBSA) binary blends (with 60 wt.% of PLA and 40 wt.% of PBSA). The migration process of three different biobased and biodegradable plasticizers [Triacetin (TA), acetyl tri-n-butyl citrate (ATBC) and oligomeric lactic acid (OLA)] was investigated adding them at a fixed amount of 10 wt.%. TA revealed the greater mass loss over the time as confirmed from the calculation of the diffusion coefficients. The addition of WB in different amount (from 10 to 30 wt.%) revealed its tendency to influence the diffusion process in a manner strictly dependent on its content. The great dimensions of the WB, however, weaken the material suggesting to adopt a preliminary dimensional reduction of the filler to mitigate the negative effect observed on the mechanical properties. From this study emerged the WB potential to be used as filler for controlling the plasticizer migration, thus suggesting a possible valorization of this waste byproduct in biobased and biodegradable materials.