Polylactide Stereocomplexation Leads to Higher Hydrolytic Stability but More Acidic Hydrolysis Product Pattern

Simultaneous and in situ syntheses of an enantiomeric pair of homochiral polymers as their perfect stereocomplex in a crystal

Circumventing the issues of conventional stereocomplexation of preformed polymers, herein, we synthesize two enantiopure polymers of opposite chirality simultaneously and in situ as their 1:1 stereocomplex via topochemical polymerization. We design and synthesize an inositol-based achiral monomer for topochemical ene-azide cycloaddition (TEAC) polymerization. In the crystal, the monomer exhibits conformational enantiomerism, and its conformational enantiomers are self-sorted in an arrangement for TEAC polymerization to yield two enantiopure polymers of opposite chirality. Upon heating the monomer crystals, each self-sorted set of conformational enantiomers undergoes regio- and stereospecific polymerization in a single-crystal-to-single-crystal fashion, generating two 1, 4-triazolinyl-linked polymers of opposite chirality simultaneously. The new chiral carbons in all the triazoline rings of a particular polymer chain have the same absolute configuration. These homochiral polymer strands align parallelly, forming a layer, and such enantiopure layers of opposite chirality stack alternately, forming a perfect 1:1 stereocomplex, which we confirmed using single-crystal XRD analysis.

Designed to Degrade: Tailoring Polyesters for Circularity

A powerful toolbox is needed to turn the linear plastic economy into circular. Development of materials designed for mechanical recycling, chemical recycling, and/or biodegradation in targeted end-of-life environment are all necessary puzzle pieces in this process. Polyesters, with reversible ester bonds, are already forerunners in plastic circularity: poly(ethylene terephthalate) (PET) is the most recycled plastic material suitable for mechanical and chemical recycling, while common aliphatic polyesters are biodegradable under favorable conditions, such as industrial compost. However, this circular design needs to be further tailored for different end-of-life options to enable chemical recycling under greener conditions and/or rapid enough biodegradation even under less favorable environmental conditions. Here, we discuss molecular design of the polyester chain targeting enhancement of circularity by incorporation of more easily hydrolyzable ester bonds, additional dynamic bonds, or degradation catalyzing functional groups as part of the polyester chain. The utilization of polyester circularity to design replacement materials for current volume plastics is also reviewed as well as embedment of green catalysts, such as enzymes in biodegradable polyester matrices to facilitate the degradation process.

Stereo-complex polylactide composite aerogel for crude oil adsorption

Adsorption materials are a cost-effective and simple method for oil spill remediation, but their efficiency is limited by high crude oil viscosity. Additionally, non-degradable materials pose another risk of secondary pollution, such as microplastic debris. Here, an environmentally-friendly stereo-complex polylactide composite (SCC) aerogel were developed via water-assisted thermally induced phase separation. The SCC with 3 wt% carbon nanotubes had a hierarchical structure of micro/nanoscale pores and high content of stereo-complex crystallites (35.7 %). Along with the excellent water repellency (water contact angle: 157°), SCC aerogel was 2.7 times as resistant to hydrolysis than poly(l-lactide) aerogel (Ph = 13, 37 °C). Additionally, a maximum absorption capacity of 41.2 g g-1 and over 97 % oil/water separation efficiency after 10 cycles were obtained in low viscosity conditions; while in high viscosity conditions, it displayed excellent photothermal performance, reaching a surface temperature of 85 °C under 1 sunlight, reducing crude oil absorption time from 42 min to 60 s (97.6 %-time savings). Moreover, it facilitated continuous crude oil spill recovery under sunlight with an adsorption rate of 3.3 × 104 kg m-3 h-1. The SCC aerogel presents a potential route for utilizing solar energy in crude oil adsorption applications without additional environmental burden.

Influence of polylactide coating stereochemistry on mechanical and in vitro degradation properties of porous bioactive glass scaffolds for bone regeneration

The mechanical properties of polylactide stereocomplexes (PLA SC) have been primarily studied through tensile testing, with inconsistent results, and the compressive properties of PLA SC compared to homocrystalline or amorphous PLA remain poorly understood. In this study, we coated porous bioactive glass 13-93 scaffolds with amorphous, homocrystalline, or stereocomplex PLA to investigate their mechanical and degradation properties before and after immersion in simulated body fluid. The glass scaffolds had interconnected pores and an average porosity of 76%. The PLA coatings, which were 10-100 μm thick and approximately 3% of the glass scaffold mass, covered the glass to a large extent. The compressive strength and toughness of all PLA-coated scaffolds were significantly higher than those of uncoated scaffolds, with approximately a fourfold increase before immersion and a twofold increase after immersion. The compressive strength and toughness of PLA SC-coated scaffolds were similar to those of scaffolds with homocrystalline PLA coating, and significantly higher than for scaffolds with amorphous PLA coating. All PLA coatings moderated the initial pH increase caused by the glass, which could benefit surrounding cells and bone tissue in vivo after implantation.

In Vitro and In Vivo Hydrolytic Degradation Behaviors of a Drug-Delivery System Based on the Blend of PEG and PLA Copolymers

This paper presents the in vitro and in vivo degradation of BEPO, a marketed in situ forming depot technology used for the formulation of long-acting injectables. BEPO is composed of a solution of a blend of poly(ethylene glycol)-block-poly(lactic acid) (PEG-PLA) triblock and diblock in an organic solvent, where a therapeutic agent may be dissolved or suspended. Upon contact with an aqueous environment, the solvent diffuses and the polymers precipitate, entrapping the drug and forming a reservoir. Two representative BEPO compositions were subjected to a 3-month degradation study in vitro by immersion in phosphate-buffered saline at 37 °C and in vivo after subcutaneous injection in minipig. The material erosion rate, as a surrogate of the bioresorption, determined via the depot weight loss, changed substantially, depending on the composition and content of polymers within the test item. The swelling properties and internal morphology of depots were shown to be highly dependent on the solvent exchange rate during the precipitation step. Thermal analyses displayed an increase of the depot glass transition temperature over the degradation process, with no crystallinity observed at any stage. The chemical composition of degraded depots was determined by 1H NMR and gel permeation chromatography and demonstrated an enrichment in homopolymers, i.e., free PLA and (m)PEG, to the detriment of (m)PEG-PLA copolymers in both formulations. It was observed that the relative ratio of the degradants within the depot is driven by the initial polymer composition. Interestingly, in vitro and in vivo results showed very good qualitative consistency. Taken together, the outcomes from this study demonstrate that the different hydrolytic degradation behaviors of the BEPO compositions can be tuned by adjusting the polymer composition of the formulation.

Polylactide Degradation Activates Immune Cells by Metabolic Reprogramming

Polylactide (PLA) is the most widely utilized biopolymer in medicine. However, chronic inflammation and excessive fibrosis resulting from its degradation remain significant obstacles to extended clinical use. Immune cell activation has been correlated to the acidity of breakdown products, yet methods to neutralize the pH have not significantly reduced adverse responses. Using a bioenergetic model, delayed cellular changes were observed that are not apparent in the short-term. Amorphous and semi-crystalline PLA degradation products, including monomeric l-lactic acid, mechanistically remodel metabolism in cells leading to a reactive immune microenvironment characterized by elevated proinflammatory cytokines. Selective inhibition of metabolic reprogramming and altered bioenergetics both reduce these undesirable high cytokine levels and stimulate anti-inflammatory signals. The results present a new biocompatibility paradigm by identifying metabolism as a target for immunomodulation to increase tolerance to biomaterials, ensuring safe clinical application of PLA-based implants for soft- and hard-tissue regeneration, and advancing nanomedicine and drug delivery.

Biomimetic Polylactic Acid Electrospun Fibers Grafted with Polyethyleneimine for Highly Efficient Methyl Orange and Cr(VI) Removal

The rapid growth of industrialization has resulted in the release of large quantities of pollutants into the environment, especially dyes and heavy metals, which are environmentally hazardous for humans and animals. It is considered as the most promising and environmentally friendly route to develop green materials by using the green modification method, which has no negative impact on the environment. In this work, the green material of polylactic acid (PLA) was used as the substrate material, and a novel modification method of polydopamine (PDA)-assisted polyethyleneimine (PEI) grafting was developed. The electrospun PLA fibers are mainly composed of stereocomplex crystallites, which were achieved via the electrospinning of poly(l-lactic acid) and poly(d-lactic acid). The water-soluble PEI was grafted onto the PDA-modified PLA fibers through the glutaraldehyde-assisted cross-linking reaction. The prepared composite fibers can be degraded, which is environmentally friendly and meets the requirements of sustainable development. The potential application of such PLA composite fibers in wastewater treatment was intensively evaluated. The results show that at appropriate fabrication conditions (PDA concentration of 3 g·L^-1 and a PEI molecular weight of 70,000 g·mol^-1), the composite fibers exhibit the maximum adsorption capacities of 612 and 398.41 mg·g^-1 for methyl orange (MO) and hexavalent chromium [Cr(VI)], respectively. Simultaneously, about 64.79% of Cr(VI) adsorbed on the composite fibers was reduced to Cr(III). The above results show that the PLA composite fibers have a good development prospect in the field of wastewater treatment.

Stereochemistry Determines Immune Cellular Responses to Polylactide Implants

Repeating l- and d-chiral configurations determine polylactide (PLA) stereochemistry, which affects its thermal and physicochemical properties, including degradation profiles. Clinically, degradation of implanted PLA biomaterials promotes prolonged inflammation and excessive fibrosis, but the role of PLA stereochemistry is unclear. Additionally, although PLA of varied stereochemistries causes differential immune responses in vivo, this observation has yet to be effectively modeled in vitro. A bioenergetic model was applied to study immune cellular responses to PLA containing >99% l-lactide (PLLA), >99% d-lactide (PDLA), and a 50/50 melt-blend of PLLA and PDLA (stereocomplex PLA). Stereocomplex PLA breakdown products increased IL-1β, TNF-α, and IL-6 protein levels but not MCP-1. Expression of these proinflammatory cytokines is mechanistically driven by increases in glycolysis in primary macrophages. In contrast, PLLA and PDLA degradation products selectively increase MCP-1 protein expression. Although both oxidative phosphorylation and glycolysis are increased with PDLA, only oxidative phosphorylation is increased with PLLA. For each biomaterial, glycolytic inhibition reduces proinflammatory cytokines and markedly increases anti-inflammatory (IL-10) protein levels; differential metabolic changes in fibroblasts were observed. These findings provide mechanistic explanations for the diverse immune responses to PLA of different stereochemistries and underscore the pivotal role of immunometabolism in the biocompatibility of biomaterials applied in medicine.

Hierarchically Designed Biodegradable Polylactide Particles with Unprecedented Piezocatalytic Activity and Biosafety for Tooth Whitening

At-home tooth whitening solutions with good efficacy and biosafety are highly desirable to meet the ever-growing demand for aesthetic dentistry. As a promising alternative to the classic peroxide bleaching that may damage tooth enamel and gums, piezocatalysis has been recently proposed to realize non-destructive whitening by toothbrushing with piezoelectrical particles. However, traditional particles either pose potential threats to human health or exhibit low piezoresponse to weak mechanical stimuli in the toothbrushing. Here, biocompatible and biodegradable polylactide particles constructed from interlocking crystalline lamellae have been hierarchically designed as next-generation whitening materials with ultra-high piezocatalytic activity and biosafety. By simultaneously controlling the chain conformation within lamellae and the porosity of such unique lamellae network at the nano- and microscales, the particles possessing unprecedented piezoelectricity have been successfully prepared due to the markedly increased dipole alignment, mechanical deformability, and specific surface area. The piezoelectric output can reach as high as 18.8 V, nearly 50 times higher than that of common solid polylactide particles. Consequently, their piezocatalytic effect can be readily activated by a toothbrush to rapidly clean the teeth stained with black tea and coffee, without causing detectable enamel damage. Furthermore, these particles have no cytotoxicity. This work presents a paradigm for achieving high piezoelectric activity in polylactide, which enables its practical application in tooth whitening.

Scalable Preparation of Complete Stereo-Complexation Polylactic Acid Fiber and Its Hydrolysis Resistance

Due to their high sensitivity to temperature and humidity, the applications of polylactic acid (PLA) products are limited. The stereo-complexation (SC) formed by poly(L-lactic acid) (PLLA) and its enantiomer poly(D-lactic acid) (PDLA) can effectively improve the heat resistance and hydrolysis resistance of PLA products. In this work, the blended melt-spinning process of PLLA/PDLA was carried out using a polyester fiber production line to obtain PLA fiber with a complete SC structure. The effects of high-temperature tension heat-setting on the crystalline structure, thermal properties, mechanical properties, and hydrolysis resistance were discussed. The results indicated that when the tension heat-setting temperature reached 190 °C, the fiber achieved an almost complete SC structure, and its melting point was 222.5 °C. An accelerated hydrolysis experiment in a 95 °C water bath proved that the SC crystallites had better hydrolysis resistance than homocrystallization (HC). The monofilament strength retention rate of SC−190 fiber reached as high as 78.5% after hydrolysis for 24 h, which was significantly improved compared with PLLA/PDLA drawn fiber.

Reactive Desorption Electrospray Ionization Mass Spectrometry To Determine Intrinsic Degradability of Poly(lactic-co-glycolic acid) Chains

Because of its speed, sensitivity, and ability to scrutinize individual species, mass spectrometry (MS) has become an essential tool in analytical strategies aimed at studying the degradation behavior of polyesters. MS analyses can be performed prior to the degradation event for structural characterization of initial substrates or after it has occurred to measure the decreasing size of products as a function of time. Here, we show that MS can also be usefully employed during the degradation process by online monitoring the chain solvolysis induced by reactive desorption electrospray ionization (DESI). Cleavage of ester bonds in random copolymers of lactic acid (LA) and glycolic acid (GA) was achieved by electrospraying methanol-containing NaOH onto the substrates. Experimental conditions were optimized to generate methanolysis products of high abundance so that mass spectra can be conveniently processed using Kendrick-based approaches. The same reactive-DESI performance was demonstrated for two sample preparations, solvent casting for soluble samples or pressed pellets for highly crystalline substrates, permitting to compare polymers with LA/GA ratios ranging from 100/0 to 5/95. Analysis of sample fractions collected by size exclusion chromatography showed that methanolysis occurs independently of the original chain size, so data recorded for poly(LA-co-GA) (PLAGA) copolymers with the average molecular weight ranging from 10 to 180 kDa could be safely compared. The average mass of methanolysis products was observed to decrease linearly (R² = 0.9900) as the GA content increases in PLAGA substrates, consistent with the susceptibility of ester bonds toward solvolysis being higher in GA than in LA. Because DESI only explores the surface of solids, these data do not reflect bulk degradability of the copolymers but, instead, their relative degradability at the molecular level. Based on a "reactive-DESI degradability scale" such as that established here for PLAGA, the proposed method offers interesting perspectives to qualify intrinsic degradability of different polyesters and evaluate their erosion susceptibility or to determine the degradability of those polymers known to degrade via erosion only.

Properties Enhancement of High Molecular Weight Polylactide Using Stereocomplex Polylactide as a Nucleating Agent

As one of the most attractive biopolymers nowadays in terms of their sustainability, degradability, and material tune-ability, the improvement of polylactide (PLA) homopolymer properties by studying the utilization of stereocomplex polylactide (s-PLA) effectively and efficiently is needed. In this sense, we have studied the utilization of s-PLA compared to poly D-lactide (PDLA) homopolymers as a nucleating agent for PLA homopolymers. The mechanical and thermal properties and crystallization behavior of PLA homopolymers in the presence of nucleating agents have been evaluated using a universal testing machine, differential scanning calorimeter, and X-ray diffractometer instruments, respectively. PDLA and s-PLA materials can be used to increase the thermal and mechanical properties of poly L-lactide (PLLA) homopolymers. The s-PLA materials increased the mechanical properties by increasing crystallinity of the PLLA homopolymers. PLLA/s-PLA enhanced mechanical properties to a certain level (5% s-PLA content), then decreased them due to higher s-PLA materials affecting the brittleness of the blends. PDLA homopolymers increased mechanical properties by forming stereocomplex PLA with PLLA homopolymers. Non-isothermal and isothermal evaluation showed that s-PLA materials were more effective at enhancing PLLA homopolymer properties through nucleating agent mechanism.

Electrospun stereocomplex polylactide porous fibers toward highly efficient oil/water separation

The urgent needs for water protection are not only developing the highly efficient wastewater treatment technologies but also designing the eco-friendly materials. In this work, the eco-friendly composite fibers composed of poly(L-lactide) (PLLA), poly(D-lactide) (PDLA) and maghemite nanoparticles γ-Fe₂O₃ nanoparticles were fabricated through electrospinning technology. Through regulating the processing parameters and introducing additional annealing treatment, nanoscale porous structure and the stereocomplex crystallites (SCs) are simultaneously constructed in the composite electrospun fibers. Physicochemical performances measurements exhibited that the fiber membranes had excellent lipophilicity, good mechanical performances, and high hydrolysis resistance, and all of which endowed the fiber membranes with high oil adsorption capacities, and the maximum oil adsorption capacities achieved 148.9 g/g at 23 °C and 114.8 g/g at 60 °C. Further results showed that the fiber membranes had good oil/water separation ability. The gravity-driven oil flux was 6824.4 L/m²h², and the water rejection ratio was nearly 100% during separating oil/water mixture. Specifically, the fiber membranes showed good stability during the cycling measurements. It is evidently confirmed that the composite PLLA-based fiber membranes with porous structure and SCs can be used in wastewater treatment, especially in some rigorous circumstances.

The role of bioresorbable intraluminal airway stents in pediatric tracheobronchial obstruction: A systematic review

INTRODUCTION

Tracheal stenosis and tracheobronchomalacia are complicated, patient-specific diseases that can be treated with intraluminal stenting. Most commonly, silicone and metal stents are utilized, however, they pose significant early and late morbidity and are further complicated by growth of the airway in the pediatric population. Given recent improvements in materials science, there is a growing body of evidence suggesting a strong role for bioresorbable intraluminal stents in treating pediatric tracheobronchial obstruction.

METHODS

A PubMed.gov literature search was performed on December 3, 2019 and May 15, 2020, and a 2-researcher systematic review was performed following the PRISMA criteria. The following search query was utilized: (((((((bioresorbable) OR bioabsorbable) OR resorbable) OR absorbable) OR biodegradable AND airway) OR trachea) AND stent. A pooled statistical analysis was performed on all reported pediatric patients using SPSS software.

RESULTS

1369 publications were screened and 26 articles with original data were identified. Materials used included polydioxanone (PDO), poly-l-lactic acid (PLLA), polyglycolic acid/poly-l-lactide co-polymer with Proglactin 910 (Vicryl®-PDS®), polycaprolactone (PCL), magnesium alloys, and co-polymers in varying proportions. Twelve articles presented data on human subjects, 8 of which were case series and case reports on pediatric populations using polydioxanone (PDO) stents. Pooled statistical analysis demonstrated an average age of 19 months (range 0.25-144), 56.5% associated with a cardiovascular anomaly, and overall complication rate of 21.7%, with a stent fragment foreign body being the most common (8.7%), followed by significant granulation tissue (4.3%), stent migration (4.3%), and local stenosis (4.3%). Comparative analysis demonstrated short-term improvement (up to 1 month) has a statistically significant association with tracheobronchomalacia versus tracheal stenosis on chi-squared test (p = 0.001). The remaining analyses did not yield statistical significance.

CONCLUSION

The reported application of bioresorbable materials as intraluminal airway stents is positive. All comparative animal studies report biocompatibility and fewer morbidities compared to metal and silicone stents, however, in human studies there are concerns over the short interval of degradation and the potential for obstructive foreign bodies in poorly seated stents. Overall, there are clear, reproducible advantages to bioresorbable intraluminal stents in pediatric airway obstruction, as well as common pitfalls, that warrant further research.

Ruthenium-Catalyzed Hydrogenative Degradation of End-of-Life Poly(lactide) to Produce 1,2-Propanediol as Platform Chemical

The chemical recycling of end-of-life polymers can add some value to a future circular economy. In this regard, the hydrogenative degradation of end-of-life PLA was investigated to produce 1,2-propanediol as product, which is a useful building block in polymer chemistry. In more detail, the commercially available Ru-MACHO-BH complex was applied as catalyst to degrade end-of-life PLA efficiently to 1,2-propanediol under mild conditions. After investigations of the reaction conditions a set of end-of-life PLA goods were subjected to degradation.

Biodegradable, Flexible, and Transparent Conducting Silver Nanowires/Polylactide Film with High Performance for Optoelectronic Devices

As a synthetic renewable and biodegradable material, the application of polylactide (PLA) in the green flexible electronics has attracted intensive attention due to the increasingly serious issue of electronic waste. Unfortunately, the development of PLA-based optoelectronic devices is greatly hindered by the poor heat resistance and mechanical property of PLA. To overcome these limitations, herein, we report a facile and promising route to fabricate silver nanowires/PLA (AgNW/PLA) film with largely improved properties by utilizing the stereocomplex (SC) crystallization between poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA). Through embedding the AgNW networks into the PLLA:PDLA blend matrix via a transfer method, the AgNW/PLLA:PDLA film with both high transparency and excellent conductivity was obtained. Compared with the AgNW/PLLA film, the formation of SC crystallites in the composites matrix could significantly enhance not only heat resistance but also mechanical strength of the AgNW/PLLA:PDLA film. Exceptionally, the AgNW/PLLA:PDLA film exhibited superior flexibility and could maintain excellent electrical conductivity stability even under the condition of 10,000 repeated bending cycles and 100 tape test cycles. In addition, the organic light-emitting diodes (OLEDs) with the AgNW/PLLA:PDLA films as electrodes were successfully fabricated in this work for the first time and they exhibited highly flexible, luminous, as well as hydrolytic degradation properties. This work could provide a low-cost and environment-friendly avenue towards fabricating high-performanced PLA-based biodegradable electronics.

Blends of poly(butylene adipate-co-terephthalate) (PBAT) and stereocomplex polylactide with improved rheological and mechanical properties

Schematic representation of formed solid sc-PLA in the PBAT melting during melt processing.

Migration of oligomers from a food contact biopolymer based on polylactic acid (PLA) and polyester

Polylactic acid (PLA) is a biopolymer commonly used in food packaging due to its good characteristics, similar to PET. To evaluate the safety of this material, the analysis of the non-intentionally added substances (NIAS) is required. Oligomers are NIAS and their behavior needs a deep study, especially if they migrate to the food. In this work, the analysis of the polymer and the migration to food simulants was carried out. A total dissolution/precipitation procedure was applied to PLA pellets and films, using dichloromethane and ethanol as solvent and antisolvent system respectively. The migration tests were carried out in three liquid simulants to mimic any kind of food. Since oligomers are not present in the positive list of the Directive 10/2011/EC, their concentration must be below the 0.01 mg/kg of food. UPLC-QTOF-MS, with and without ion mobility (IM), was used for the analysis. Thirty-nine different PLA oligomers made of repeated monomer units of [LA] (C₃H₄O₂) and with different structures were identified. They corresponded to cyclic oligomers with [LA]_n structure and two groups of linear oligomers, one with an hydroxyl group, OH-[LA]_n-H, and the other one with an ethoxy group, CH₃-CH₂-O-[LA]_n-H. Cyclic oligomers only appeared in the material and were not present in migration solutions. Linear oligomers HO-[LA]_n-H were already present in the pellets/film and they migrated in a higher extension to aqueous food simulants (EtOH 10% and AcH 3%). However, linear oligomers CH₃-CH₂-O-[LA]_n-H were not present initially in the pellets/film, but were detected in migration to simulants with ethanol content, EtOH 95% and EtOH 10%. Furthermore, 5 cyclic polyester oligomers were identified in migration. Ethanol 95% and ethanol 10% migration solutions were also analyzed by scanning electron microscopy (SEM), and the presence of microstructures that could be attributed to the oligomers migration was found. They could be seen as microplastics.

Innovative biodegradable poly(L-lactide)/collagen/hydroxyapatite composite fibrous scaffolds promote osteoblastic proliferation and differentiation

The development of an artificial bone graft which can promote the regeneration of fractures or diseased bones is currently the most challenging aspect in bone tissue engineering. To achieve the purpose of promoting bone proliferation and differentiation, the artificial graft needs have a similar structure and composition of extracellular matrix. One-step electrospinning method of biocomposite nanofibers containing hydroxyapatite (HA) nanoparticles and collagen (Coll) were developed for potential application in bone tissue engineering. Nanocomposite scaffolds of poly(L-lactide) (PLLA), PLLA/HA, PLLA/Coll, and PLLA/Coll/HA were fabricated by electrospinning. The morphology, diameter, elements, hydrophilicity, and biodegradability of the composite scaffolds have been investigated. The biocompatibility of different nanocomposite scaffolds was assessed using mouse osteoblasts MC3T3-E1 in vitro, and the proliferation, differentiation, and mineralization of cells on different nanofibrous scaffolds were investigated. The results showed that PLLA/Coll/HA nanofiber scaffolds enhanced cell adhesion, spreading, proliferation, differentiation, mineralization, and gene expression of osteogenic markers compared to other scaffolds. In addition, the nanofibrous scaffolds maintained a stable composition at the beginning of the degradation period and morphology wastage and weight loss were observed when incubated for up to 80 days in physiological simulated conditions. The PLLA/Coll/HA composite nanofibrous scaffolds could be a potential material for guided bone regeneration.

Near-Infrared Spectroscopic Evaluation of the Water Content of Molded Polylactide under the Effect of Crystallization

During melt processing, the moisture inside polylactide (PLA) easily induces hydrolysis, which deteriorates the mechanical and thermal properties of the product. The state of dryness of resin pellets must be monitored to prevent PLA hydrolysis. In this study, near-infrared (NIR) spectroscopy was applied to measure water content in PLA. In addition, the shape of the NIR spectrum is also affected by crystallization, which could lead to a reduction in the accuracy of evaluating the water content. The objective of this research is to construct a robust model for estimating the water content with varying dispersive extents of crystallization. Two methods for estimating water content measured during a drying process were conducted: the integration of absorbance and partial least squares (PLS) regression were conducted to estimate the water contents in PLA considering the effect of crystallization. The slope of the calibration line of the water content obtained from integrating absorbance varied between PLA with different crystallinities. This is due to the overlap between the NIR band of water and that of PLA crystal in the range of 5100-5400 cm^-1. We found that the shape of the NIR spectrum was changed by crystallization, and the crystallinity, compared to the thickness of lamellae, was the dominant factor determining such a change of NIR spectra. The PLS model of water content constructed from only amorphous PLA showed large error of estimation in crystallized PLA. In contrast, the PLS model constructed from both amorphous and crystallized PLA estimated the water contents with lower errors. This was because latent variables obtained from both amorphous and crystallized PLA cancelled the effect of crystallization on NIR spectra.

Evaluating polymeric biomaterial-environment interfaces by Langmuir monolayer techniques

Polymeric biomaterials are of specific relevance in medical and pharmaceutical applications due to their wide range of tailorable properties and functionalities. The knowledge about interactions of biomaterials with their biological environment is of crucial importance for developing highly sophisticated medical devices. To achieve optimal in vivo performance, a description at the molecular level is required to gain better understanding about the surface of synthetic materials for tailoring their properties. This is still challenging and requires the comprehensive characterization of morphological structures, polymer chain arrangements and degradation behaviour. The review discusses selected aspects for evaluating polymeric biomaterial-environment interfaces by Langmuir monolayer methods as powerful techniques for studying interfacial properties, such as morphological and degradation processes. The combination of spectroscopic, microscopic and scattering methods with the Langmuir techniques adapted to polymers can substantially improve the understanding of their in vivo behaviour.

Recent advances in degradable lactide-based shape-memory polymers

Biodegradable polymers are versatile polymeric materials that have a high potential in biomedical applications avoiding subsequent surgeries to remove, for example, an implanted device. In the past decade, significant advances have been achieved with poly(lactide acid) (PLA)-based materials, as they can be equipped with an additional functionality, that is, a shape-memory effect (SME). Shape-memory polymers (SMPs) can switch their shape in a predefined manner upon application of a specific external stimulus. Accordingly, SMPs have a high potential for applications ranging from electronic engineering, textiles, aerospace, and energy to biomedical and drug delivery fields based on the perspectives of new capabilities arising with such materials in biomedicine. This study summarizes the progress in SMPs with a particular focus on PLA, illustrates the design of suitable homo- and copolymer structures as well as the link between the (co)polymer structure and switching functionality, and describes recent advantages in the implementation of novel switching phenomena into SMP technology.

Poly(lactic acid) stereocomplexes: A decade of progress

Upon blending enantiomeric poly(l-lactide) [i.e., poly(l-lactic acid) (PLLA)] and poly(d-lactide) (PDLA) [i.e., poly(d-lactic acid) (PDLA)] or synthesis of stereo block poly(lactide) [i.e., poly(lactic acid) (PLA)], a stereocomplex (SC) is formed. PLA SC has a higher melting temperature (or heat resistance), mechanical performance, and hydrolysis-resistance compared to those of neat PLLA and PDLA. Because of such effects, PLA SC has been extensively studied in terms of biomedical and pharmaceutical applications as well as commodity, industrial, and environmental applications. Stereocomplexation stabilizes and strengthens PLA-based hydrogel or nanoparticles for biomedical applications. Stereocomplexation increases the barrier property of PLA-based materials and thereby prolongs drug release from PLA based materials. In addition, PLA SC is attracting significant attention because it can act as a nucleating agent for the widely used biobased polymer PLLA and thereby the heat resistance of PLLA-based materials can be enhanced. Interestingly, a wide variety of SCs other than PLA SC are found to have been formed in the enantiomeric substituted PLA blends and stereo block substituted PLA polymers. In the present review article, a decade of progress in investigation of PLA SCs is summarized.