Newly Developed Techniques on Polycondensation, Ring-Opening Polymerization and Polymer Modification: Focus on Poly(Lactic Acid)

Ti and Zr complexes bearing guanidine-phenolate ligands: coordination chemistry and polymerization studies

A series of group 4 bis(isopropoxide) complexes M[N^O]2(OiPr)2, stabilized by guanidine-phenolate N^O ligands, have been prepared and used as catalysts for the polymerization of unpurified rac-lactide under solvent-free conditions at 130 °C. The resulting polylactic acid (PLA) presented heterotactic bias (P r = 0.56-0.62) with molecular weights similar to those obtained in control experiments with Zr(OiPr)4·iPrOH, Ti(OiPr)4, and Sn(Oct)2. The molecular weights were lower than expected for living polymerization due to chain transfer and/or transesterification. Zr complexes were more active than the Ti homologues, with rate constants ranging from 1.17-3.21 × 10-4 s-1, comparable to that observed with the free guanidine-phenol ligands. The corresponding bis(guanidine-phenolate) titanium dichloride complexes Ti[N^O]2Cl2 were also prepared and tested in ethylene polymerization. The low activity (up to 1.1 kgPE mol-1 h-1) was associated to the strong electron-donating ability of the guanidine moiety and to the trans-N,N-cis-O,O-cis-Cl,Cl coordination mode of the guanidine-phenolate ligand.

Advanced biopolymeric materials and nanosystems for RNA/DNA vaccines: a review

The post COVID-19 pandemic era has emerged with more efficient vaccines, all based on genetic materials. However, to expand the use of nucleic components as vaccines, a new generation of nanosystems particularly constructed to increase RNA/DNA stability, half-life and facilitate administration are still required. This review highlights novel developments in mRNA and pDNA vaccines formulated into nanostructures exclusively composed by biopolymeric materials. Recent advances suggest that a new generation of vaccines may arise by adapting the structural features of biopolymers with the effectiveness of nucleic acids. The advantages offered by biopolymers, such as increased stability and targeting ability may cause a revolution in the immunization field for offering promptly adaptable and effective formulations for worldwide distribution.

Crafting sustainable solutions: architecting biodegradable copolymers through controlled ring-opening copolymerization

Polylactic acid (PLA) is a biodegradable and biocompatible polymer with versatile applications in packaging and medicine. It is derived from lactic acid and thus represents an eco-friendly option sourced from renewable raw materials. Despite its advantages, PLA exhibits few drawbacks, such as brittleness and relatively high melting and glass transition temperatures. However, these limitations can be addressed through copolymerization with other monomers like ε-caprolactone (ε-CL), resulting in a composite material with improved physical properties. This paper comprehensively reviews achievements in PLA-PCL copolymerization using organometallic catalysts, discussing scientific findings and various copolymer architectures obtained, including random or block configurations. It also demonstrates various sustainable catalysts for achieving the required microstructure under mild reaction conditions without the aid of any external initiator.

Enzymatic degradation of polylactic acid (PLA)

Environmental concerns arising from the increasing use of polluting plastics highlight polylactic acid (PLA) as a promising eco-friendly alternative. PLA is a biodegradable polyester that can be produced through the fermentation of renewable resources. Together with its excellent properties, suitable for a wide range of applications, the use of PLA has increased significantly over the years and is expected to further grow. However, insufficient degradability under natural conditions emphasizes the need for the exploration of biodegradation mechanisms, intending to develop more efficient techniques for waste disposal and recycling or upcycling. Biodegradation occurs through the secretion of depolymerizing enzymes, mainly proteases, lipases, cutinases, and esterases, by various microorganisms. This review focuses on the enzymatic degradation of PLA and presents different enzymes that were isolated and purified from natural PLA-degrading microorganisms, or recombinantly expressed. The review depicts the main characteristics of the enzymes, including recent advances and analytical methods used to evaluate enantiopurity and depolymerizing activity. While complete degradation of solid PLA particles is still difficult to achieve, future research and improvement of enzyme properties may provide an avenue for the development of advanced procedures for PLA degradation and upcycling, utilizing its building blocks for further applications as envisaged by circular economy principles. KEY POINTS: • Enzymes can be promisingly utilized for PLA upcycling. • Natural and recombinant PLA depolymerases and methods for activity evaluation are summarized. • Approaches to improve enzymatic degradation of PLA are discussed.

Biodegradable biopolymers: Real impact to environment pollution

Biobased biodegradable polymers (BBP) derived from different renewable resources are commonly considered as attractive alternative to petroleum-based polymers, such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), etc. It is because they can address the issues of serious environmental problems resulted from accumulation of plastic wastes. In the review current methods of obtaining of most abundant BBP, polylactic acid (PLA) and polyhydroxybutyrate (PHB), have been studied with an emphasis on the toxicity of compounds used for their production and additives improving consumer characteristics of PLA and PHB based market products. Substantial part of additives was the same used for traditional polymers. Analysis of the data on the response of different organisms and plants on exposure to these materials and their degradation products confirmed the doubts about real safety of BBP. Studies of safer additives are scarce and are of vital importance. Meanwhile, technologies of recycling of traditional petroleum-based polymers were shown to be well-developed, which cannot be said about PLA or PHB based polymers, and their blends with petroleum-based polymers. Therefore, development of more environmentally friendly components and sustainable technologies of production are necessary before following market expansion of biobased biodegradable products.

The Effects of Nucleating Agents and Processing on the Crystallization and Mechanical Properties of Polylactic Acid: A Review

Polylactic acid (PLA) is a biobased, biodegradable, non-toxic polymer widely considered for replacing traditional petroleum-based polymer materials. Being a semi-crystalline material, PLA has great potential in many fields, such as medical implants, drug delivery systems, etc. However, the slow crystallization rate of PLA limited the application and efficient fabrication of highly crystallized PLA products. This review paper investigated and summarized the influence of formulation, compounding, and processing on PLA's crystallization behaviors and mechanical performances. The paper reviewed the literature from different studies regarding the impact of these factors on critical crystallization parameters, such as the degree of crystallinity, crystallization rate, crystalline morphology, and mechanical properties, such as tensile strength, modulus, elongation, and impact resistance. Understanding the impact of the factors on crystallization and mechanical properties is critical for PLA processing technology innovations to meet the requirements of various applications of PLA.

Recent Advances in the Degradability and Applications of Tissue Adhesives Based on Biodegradable Polymers

In clinical practice, tissue adhesives have emerged as an alternative tool for wound treatments due to their advantages in ease of use, rapid application, less pain, and minimal tissue damage. Since most tissue adhesives are designed for internal use or wound treatments, the biodegradation of adhesives is important. To endow tissue adhesives with biodegradability, in the past few decades, various biodegradable polymers, either natural polymers (such as chitosan, hyaluronic acid, gelatin, chondroitin sulfate, starch, sodium alginate, glucans, pectin, functional proteins, and peptides) or synthetic polymers (such as poly(lactic acid), polyurethanes, polycaprolactone, and poly(lactic-co-glycolic acid)), have been utilized to develop novel biodegradable tissue adhesives. Incorporated biodegradable polymers are degraded in vivo with time under specific conditions, leading to the destruction of the structure and the further degradation of tissue adhesives. In this review, we first summarize the strategies of utilizing biodegradable polymers to develop tissue adhesives. Furthermore, we provide a symmetric overview of the biodegradable polymers used for tissue adhesives, with a specific focus on the degradability and applications of these tissue adhesives. Additionally, the challenges and perspectives of biodegradable polymer-based tissue adhesives are discussed. We expect that this review can provide new inspirations for the design of novel biodegradable tissue adhesives for biomedical applications.

Recyclable and (Bio)degradable Polyesters in a Circular Plastics Economy

Polyesters carrying polar main-chain ester linkages exhibit distinct material properties for diverse applications and thus play an important role in today's plastics economy. It is anticipated that they will play an even greater role in tomorrow's circular plastics economy that focuses on sustainability, thanks to the abundant availability of their biosourced building blocks and the presence of the main-chain ester bonds that can be chemically or biologically cleaved on demand by multiple methods and thus bring about more desired end-of-life plastic waste management options. Because of this potential and promise, there have been intense research activities directed at addressing recycling, upcycling or biodegradation of existing legacy polyesters, designing their biorenewable alternatives, and redesigning future polyesters with intrinsic chemical recyclability and tailored performance that can rival today's commodity plastics that are either petroleum based and/or hard to recycle. This review captures these exciting recent developments and outlines future challenges and opportunities. Case studies on the legacy polyesters, poly(lactic acid), poly(3-hydroxyalkanoate)s, poly(ethylene terephthalate), poly(butylene succinate), and poly(butylene-adipate terephthalate), are presented, and emerging chemically recyclable polyesters are comprehensively reviewed.

Synthesis and characterization of lactide from Bacillus amyloliquefaciens brewed lactic acid utilizing cheap agricultural sources

Lactic acid (LA) is a nifty molecule with an eclectic range of applications in innumerable industries and is produced through biological and chemical processes. Factually, LA is converted into lactide (LAC), which is the precursor for polylactic acid (PLA). PLA is considered one of the first-rate replacements for petroleum-based products and is believed to be environmentally sustainable. Nevertheless, it has always been challenging due to increased PLA productivity costs. Reduction in the LA and LAC production price directly echoes the production price of PLA. Therefore, low-cost LA and LAC production methods have to be found to produce PLA effectively. Hence, this study uses cheap agricultural sources derived microbial LA to make LAC through dimerization. Produced LAC was analyzed through FT-IR, NMR, TGA and XRD. FT-IR results revealed that the successful dimerization of LA to LAC, NMR analysis revealed that the aligning of methine and methyl groups in produced LAC, TGA analysis exposed that the microbial LAC has more thermal stability than the commercial LAC, XRD results showed that the produced LACs are crystalline with 32% and 42% crystallinity. To the best of our acquaintance, this manuscript is pioneering one to describe LA production through microbial fermentation and uses this monomer to produce LAC through dimerization.

Recent progress on biodegradable polylactic acid based blends and their biocomposites: A comprehensive review

Being less dependent on non-renewable resources as well as protecting the environment from waste streams have become two critical primers for a global movement toward replacing conventional plastics with renewable and biodegradable polymers. Despite all these efforts, only a few biodegradable polymers have paved their way successfully into the market. Polylactic acid is one of these biodegradable polymers that has been investigated thoroughly by researchers as well as manufactured on a large industrial scale. It is synthesized from lactic acid obtained mainly from the biological fermentation of carbohydrates, which makes this material a renewable polymer. Besides its renewability, it benefits from some attractive mechanical performances including high strength and stiffness, though brittleness is a major drawback of this biopolymer. Accordingly, the development of blends and biocomposites based on polylactic acid with highly flexible biodegradable polymers, specifically poly(butylene adipate co terephthalate) has been the objective of many investigations recently. This paper focuses on the blends and biocomposites based on these two biopolymers, specifically their mechanical, rheological, and biodegradation, the main characteristics that are crucial for being considered as a biodegradable substitution for conventional non-biodegradable polymers.

Recent trends in lactic acid-producing microorganisms through microbial fermentation for the synthesis of polylactic acid

Polylactic acid (PLA) is a range of unique bioplastics that are bio-based and biodegradable. PLA is currently driving market expansion for lactic acid (LA) due to its high demand as a building block in production. One of the most practical and environmentally benign techniques for synthesising PLA is through enzymatic polymerisation of microbial LA monomers. However, microbial LA fermentation does have some limitations. Firstly, it requires the use of a nutritionally rich medium. Secondly, LA production can be disrupted by bacteriophage infection or other microorganisms. Lastly, the yield can be low due to the formation of by-products through heterofermentative pathway. Considering the potential use of PLA as a replacement for conventional petrochemical-based polymers in industrial applications, researchers are focused on exploring the diversity of LA-producing microorganisms from various niches. Their goal is to study the functional properties of these microorganisms and their ability to produce industrially valuable metabolites. This review highlights the advantages and disadvantages of lactic acid-producing microorganisms used in microbial fermentation for PLA synthesis.

Development of PLA/Lignin Bio-Composites Compatibilized by Ethylene Glycol Diglycidyl Ether and Poly (ethylene glycol) Diglycidyl Ether

Poly (lactic acid) (PLA) is a promising green substitute for conventional petroleum-based plastics in a variety of applications. However, the wide application of PLA is still limited by its disadvantages, such as slow crystallization rate, inadequate gas barrier, thermal degradation, etc. In this study, lignin (1, 3, 5 PHR) was incorporated into PLA to improve the thermal, mechanical, and barrier properties of PLA. Two low-viscosity epoxy resins, ethylene glycol diglycidyl ether (EGDE) and poly (ethylene glycol) diglycidyl ether (PEGDE), were used as compatibilizers to enhance the performance of the composites. The addition of lignin improved the onset degradation temperature of PLA by up to 15 °C, increased PLA crystallinity, improved PLA tensile strength by approximately 15%, and improved PLA oxygen barrier by up to 58.3%. The addition of EGDE and PEGDE both decreased the glass transition, crystallization, and melting temperatures of the PLA/lignin composites, suggesting their compatabilizing and plasticizing effects, which contributed to improved oxygen barrier properties of the PLA/lignin composites. The developed PLA/lignin composites with improved thermal, mechanical, and gas barrier properties can potentially be used for green packaging applications.

Poly lactic acid production using the ring opening polymerization (ROP) method using Lewis acid surfactant combined iron (Fe) catalyst (Fe(DS)3)

LASC catalyst synthesis process was carried out using iron metal (Fe) and its characterization properties were tested. There are five stages carried out, namely, the manufacture of the LASC Fe(DS)3 catalyst, lactic acid dehydration, polycondensation of lactic acid into l-lactic acid oligomers (OLLA), depolymerization of oligomers into l-lactide, and the ROP process to convert l-lactide into Polymers. l-lactic acid (PLLA). The analysis used is as follows, Karl-Fisher; Spectroscopy Fourier Transform Infrared (FTIR); and Nuclear Magnetic Resonance (HNMR); Gel Permeation Chromatography (GPC); Thermogravimetry Gravity Analysis (TGA) and X-Ray Diffraction (XRD). Based on the experimental results, the catalyst Fe(DS)₃ has a crystallinity value of 24% which indicates an amorphous nature and is easy to react. The value of the thermal stability of the catalyst is at 180 °C where the catalyst is able to process up to a temperature of 180 ^°C. Each step of the ROP is validated by FTIR analysis which shows that the components of the group are in accordance with the expected product. The comparison of the crystallinity values of PLA produced with FeCl₃ and Fe(DS)₃ were 37.5 and 49%, respectively. Melting temperature (Tm) values are 111 and 107 ^°C, respectively, Td values are 327 and 352 °C, and the resulting molecular weights are 23,720 and 20,232 g/mol. Based on the results obtained, it can be seen that the use of a LASC catalyst in the form of Fe(DS)₃ is more effective than without using a LASC catalyst.

Printability of Poly(lactic acid) Ink by Embedded 3D Printing via Immersion Precipitation

Immersion precipitation three-dimensional printing (ip3DP) and freeform polymer precipitation (FPP) are unique and versatile methods of 3D printing to fabricate 3D structures based on nonsolvent-induced phase separation via direct ink writing (DIW). Immersion precipitation involves complex dynamics among solvents, nonsolvents, and dissolved polymers, and the printability of 3D models in these methods requires further understanding. To this end, we characterized these two methods of 3D printing using polylactide (PLA) dissolved in dichloromethane (7.5-30% w/w) as model inks. We analyzed the rheological properties of the solutions and the effect of printing parameters on solvent-nonsolvent diffusion to achieve printability. The PLA inks exhibited shear-thinning properties, and their viscosities varied over three orders of magnitude (10^-1∼10² Pa·s). A processing map was presented to understand the ideal ranges of the concentration of PLA in inks and the nozzle diameter to ensure printability, and the fabrication of complex 3D structures was fabricated with adequate applied pressure and nozzle speed. The processing map also highlighted the advantages of embedded 3D printing over solvent-cast 3D printing based on solvent evaporation. Lastly, we demonstrated that the porosity of the interface and inner structure of the printed objects was readily tailored by the concentration of the PLA and the porogen added to the ink. The methods presented here offer new perspectives to fabricate micro-to-centimeter objects of thermoplastics with nanometer-scale inner pores and provide guidelines for successful embedded 3D printing based on immersion precipitation.

Calixarene-Metal Complexes in Lactide Polymerization: The Story so Far

Polylactide synthetic procedures have lately gained attention, possibly due to their biocompatibility and the environmental problems associated with fossil-fuel-based polymers. Polylactides can be obtained from natural sources such as cassava, corn, and sugar beet, and polylactides can be manufactured in a laboratory using a variety of processes that begin with lactic acid or lactide. One of the most effective synthetic pathways is through a Lewis acid catalyzed ring-opening polymerization of lactides to obtain a well-defined polymer. In this regard, calixarenes, because of their easy functionalization and tunable properties, have been widely considered to be a suitable 3D molecular scaffold for new metal complexes that can be used for lactide polymerization. This review summarizes the progress made in applying some metal-calixarene complexes in the ring-opening polymerization of lactide.

A review on biodegradable polylactic acid (PLA) production from fermentative food waste - Its applications and degradation

Due to its low carbon footprint and environmental friendliness, polylactic acid (PLA) is one of the most widely produced bioplastics in the world. Manufacturing attempts to partially replace petrochemical plastics with PLA are growing year over year. Although this polymer is typically used in high-end applications, its use will increase only if it can be produced at the lowest cost. As a result, food wastes rich in carbohydrates can be used as the primary raw material for the production of PLA. Lactic acid (LA) is typically produced through biological fermentation, but a suitable downstream separation process with low production costs and high product purity is also essential. The global PLA market has been steadily expanding with the increased demand, and PLA has now become the most widely used biopolymer across a range of industries, including packaging, agriculture, and transportation. Therefore, the necessity for an efficient manufacturing method with reduced production costs and a vital separation method is paramount. The primary goal of this study is to examine the various methods of lactic acid synthesis, together with their characteristics and the metabolic processes involved in producing lactic acid from food waste. In addition, the synthesis of PLA, possible difficulties in its biodegradation, and its application in diverse industries have also been discussed.

Toward MOF@Polymer Core-Shell Particles: Design Principles and Potential Applications

ConspectusCompositing MOFs with polymers brings out the best properties of both worlds. The solubility and excellent mechanical properties of polymers endow the brittle, powdery MOFs with enhanced processability, thereby enriching their functions as solid sorbents, filters, membranes, catalysts, drug delivery vehicles, and so forth. While most MOF-polymer composites are random mixtures of two materials with little control over their fine structures, MOF@polymer core-shell particles have recently emerged as a new platform for precise composite design. The well-defined polymer coating can keep the rich pore characteristics of the MOF intact while furnishing the MOF with new properties such as improved dispersibility in various media, tunable surface energy, enhanced chemical stability, and regulated guest diffusion. Nevertheless, the structural and chemical complexity of MOFs poses a grand challenge to the development of a generalizable and feasible strategy for constructing MOF@polymer. Examples in the literature that showcase the presence of a well-defined polymer shell on the MOF with fully reserved porosity are rare. Moreover, methods for coating MOFs with condensation polymers (e.g., polyimide, polysulfone) are severely underexplored, despite their clear potential as membrane materials. In this Account, we present our group's effort over the past 4 years on the synthesis and applications of MOF@polymer composites. We first described a highly generalizable surface polymerization method that utilizes the rapid physisorption of a random copolymer (RCP) to carry initiating groups to the MOF surfaces. Subsequent controlled radical polymerization led to the formation of a uniform methacrylate or styrenic polymer on the MOF with tunable thickness and composition. To utilize the properties of condensation polymers, we pioneered the covalent grafting of polyimide (PI) brushes to UiO-66-NH₂ surfaces. In addition, to circumvent the need for a covalent anchoring group, we further developed an MOF surface grafting method based on mechanical linkage. Instead of connecting to the ligand, polyimide (PI) oligomer was linked to a functionalized linear polymer physically entangled within an MOF, thus realizing surface grafting with PI. Alternatively, PIs, polysulfone (PSF), and polycarbonate (PC) can also be grafted to various MOF surfaces through a metal-organic nanocapsule (MONC)-mediated method using a combination of electrostatic interaction and coordination bonds. To find a rapid and low-cost surface coating method suitable for commercialization, a new approach called non-solvent-induced surface-aimed deposition (NISAP) was developed. The action of the solvent phase separation drives dianhydrides and polyamines to the MOF surface, thus realizing accelerated polymerization and the rapid formation of a polymer coating on the MOF. Finally, we provided an overview of the unique properties and potential applications of MOF@polymer composites, including improved stability, MMMs, porous liquids (PLs), and immobilizing homogeneous catalysts. We hope that this Account can inspire more researchers to further develop and optimize the synthetic strategies for MOF@polymer and uncover its full application potential.

Promising Role of Polylactic Acid as an Ingenious Biomaterial in Scaffolds, Drug Delivery, Tissue Engineering, and Medical Implants: Research Developments, and Prospective Applications

In the present scenario, the research is now being focused on the naturally occurring polymers that can gradually replace the existing synthetic polymers for the development of bio composites having applications in medical surgeries and human implants. With promising mechanical properties and bio compatibility with human tissues, poly lactic acid (PLA) is now being viewed as a future bio material. In order to examine the applicability of PLA in human implants, the current article sheds light on the synthesis of PLA and its various copolymers used to alter its physical and mechanical properties. In the latter half, various processes used for the fabrication of biomaterials are discussed in detail. Finally, biomaterials that are currently in use in the field of biomedical (Scaffolding, drug delivery, tissue engineering, medical implants, derma, cosmetics, medical surgeries, and human implants) are represented with respective advantages in the sphere of biomaterials.

A comprehensive review on fused deposition modelling of polylactic acid

Fused Deposition Modelling (FDM) is one of the additive manufacturing (AM) techniques that have emerged as the most feasible and prevalent approach for generating functional parts due to its ability to produce neat and intricate parts. FDM mainly utilises one of the widely used polymers, polylactic acid, also known as polylactide (PLA). It is an aliphatic polyester material and biocompatible thermoplastic, with the best design prospects due to its eco-friendly properties; when PLA degrades, it breaks down into water and carbon dioxide, neither of which are hazardous to the environment. However, PLA has its limitations of poor mechanical properties. Therefore, a filler reinforcement may enhance the characteristics of PLA and produce higher-quality FDM-printed parts. The processing parameters also play a significant role in the final result of the printed parts. This review aims to study and discover the properties of PLA and the optimum processing parameters. This review covers PLA in FDM, encompassing its mechanical properties, processing parameters, characterisation, and applications. A comprehensive description of FDM processing parameters is outlined as it plays a vital role in determining the quality of a printed product. In addition, PLA polymer is highly desirable for various field industrial applications such as in a medical, automobile, and electronic, given its excellent thermoplastic and biodegradability properties.

Development of Biodegradable Polyesters: Study of Variations in Their Morphological and Thermal Properties through Changes in Composition of Alkyl-Substituted (ε-DL) and Non-Substituted (ε-CL, EB, L-LA) Monomers

Three series of polyesters based on monomer combinations of ε-caprolactone (ε-CL), ethylene brassylate (EB), and l-Lactide (LLA) with the alkyl substituted lactone ε-decalactone (ε-DL) were synthesized at different molar ratios. Copolymers were obtained via ring opening polymerization (ROP) employing TBD (1,5,7-triazabicyclo-[4.4.0]-dec-5-ene), an organic catalyst which can be handled under normal conditions, avoiding the use of glove box equipment. The molar monomer composition of resulting copolymers differed from theoretical values due to lower ε-DL reactivity; their M_n and M_w values were up to 14 kDa and 22.8 kDa, respectively, and distributions were (Ɖ) ≤ 2.57. The thermal stability of these materials suffered due to variations in their ε-DL molar content. Thermal transitions such as melting (T_m) and crystallization (T_c) showed a decreasing tendency as ε-DL molar content increased, while glass transition (T_g) exhibited minor changes. It is worth mentioning that changes in monomer composition in these polyesters have a strong impact on their thermal performance, as well as in their crystallization degree. Consequently, variations in their chemical structure may have an effect on hydrolyic degradation rates. It should be noted that, in future research, some of these copolymers will be exposed to hydrolytic degradation experiments, including characterizations of their mechanical properties, to determine their adequacy in potential use in the development of soft medical devices.

Polyethylene glycol (PEG): The nature, immunogenicity, and role in the hypersensitivity of PEGylated products

Polyethylene glycol (PEG) is a versatile polymer that is widely used as an additive in foods and cosmetics, and as a carrier in PEGylated therapeutics. Even though PEG is thought to be less immunogenic, or perhaps even non-immunogenic, with a variety of physicochemical properties, there is mounting evidence that PEG causes immunogenic responses when conjugated with other materials such as proteins and nanocarriers. Under these conditions, PEG with other materials can result in the production of anti-PEG antibodies after administration. The antibodies that are induced seem to have a deleterious impact on the therapeutic efficacy of subsequently administered PEGylated formulations. In addition, hypersensitivity to PEGylated formulations could be a significant barrier to the utility of PEGylated products. Several reports have linked the presence of anti-PEG antibodies to incidences of complement activation-related pseudoallergy (CARPA) following the administration of PEGylated formulations. The use of COVID-19 mRNA vaccines, which are composed mainly of PEGylated lipid nanoparticles (LNPs), has recently gained wide acceptance, although many cases of post-vaccination hypersensitivity have been documented. Therefore, our review focuses not only on the importance of PEGs and its great role in improving the therapeutic efficacy of various medications, but also on the hypersensitivity reactions attributed to the use of PEGylated products that include PEG-based mRNA COVID-19 vaccines.

An In Situ Depolymerization and Liquid Chromatography-Tandem Mass Spectrometry Method for Quantifying Polylactic Acid Microplastics in Environmental Samples

Polylactic acid (PLA) is the most commonly used biodegradable plastic with rapid growth in recent years. This leads to predictable increased pollution of PLA microplastics (MPs) in the environment. However, quantification methods for the PLA MPs are still lacking. In this study, a method based on alkali-assisted thermal depolymerization and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was developed to quantify PLA MPs. After the background monomer compound was removed, PLA MPs were efficiently depolymerized to lactic acid and detected by LC-MS/MS with a limit of quantification of 18.7 ng/g. The ideal recovery of spiked PLA MPs of 93% was obtained, and the PLA MPs did not need to be separated or extracted in advance from the environmental samples. Using this method, PLA MPs were detected in all the sediment samples of a reservoir at a range of 53.5-491 ng/g dw, and the concentrations decreased with the sediment depth. In addition, after soaking in water at 95 °C for 30 min, approximately 12 μg of PLA MPs was released from a single teabag.

Functional bioplastics from food residual: Potentiality and safety issues

Plastic pollution and food waste are two global issues with much in common. Plastic containers were introduced as a practical and easy remedy to improve food preservation and reduce the risk of creating waste, but ironically, to address one problem, another has been made worse. The spread of single-use containers has dramatically increased the amount of plastic that has to be discarded, and the most urgent task is now to find a solution to what has become part of the problem. An innovative way around it consists of promoting the valorization of food residues by turning them into novel materials for packaging. Although the results are promising, the aim of completely replacing plastics with biodegradable materials still seems far from being achieved. This review illustrates the main strategies adopted thus far to produce new bioplastic materials and composites from waste resources and focuses on the pros and cons of the food recovery process to look for the aspects that represent an obstacle to the development of the circular food economy on an industrial scale.

Polymers Based on PLA from Synthesis Using D,L-Lactic Acid (or Racemic Lactide) and Some Biomedical Applications: A Short Review

Poly(lactic acid) (PLA) is an important polymer that is based on renewable biomass resources. Because of environmental issues, more renewable sources for polymers synthesis have been sought for industrial purposes. In this sense, cheaper monomers should be used to facilitate better utilization of less valuable chemicals and therefore granting more sustainable processes. Some points are raised about the need to study the total degradability of any PLA, which may require specific composting conditions (e.g., temperature, type of microorganism, adequate humidity and aerobic environment). Polymerization processes to produce PLA are presented with an emphasis on D,L-lactic acid (or rac-lactide) as the reactant monomer. The syntheses involving homogeneous and heterogeneous catalytic processes to produce poly(D,L-Lactic acid) (PDLLA) are also addressed. Additionally, the production of blends, copolymers, and composites with PDLLA are also presented exemplifying different preparation methods. Some general applications of these materials mostly dedicated to the biomedical area over the last 10–15 years will be pointed out.

Microalgae-based bioplastics: Future solution towards mitigation of plastic wastes

Global demand for plastic materials has severely harm the environment and marine sea life. Therefore, bioplastics have emerged as an environmentally friendly alternative due to sustainability, minimal carbon footprint, less toxicity and high degradability. This review highlights the sustainable and environmentally friendly approach towards bioplastic production by utilizing microalgae as a feed source in several ways. First, the microalgae biomass obtained through the biorefinery approach can be processed into PHA under certain nutrient limitations. Additionally, microalgae biomass can act as potential filler and reinforcement towards the enhancement of bioplastic either blending with conventional bioplastic or synthetic polymer. The downstream processing of microalgae via suitable extraction and pre-treatment of bioactive compounds such as lipids and cellulose are found to be promising for the production of bioplastics. Moving on, the intermediate processing of bioplastic via lactic acid synthesized from microalgae has favoured the microwave-assisted synthesis of polylactic acid due to cost efficiency, minimum solvent usage, low energy consumption, and fast rate of reaction. Moreover, the reliability and effectiveness of microalgae-based bioplastics are further evaluated in terms of techno-economic analysis and degradation mechanism. Future improvement and recommendations are listed towards proper genetic modification of algae strains, large-scale biofilm technology, low-cost cultivation medium, and novel avocado seed-microalgae bioplastic blend.

One-pot two-step process directly converting biomass-derived carbohydrate to lactide

This study proposed a strategy for the production of lactide from biomass-derived carbohydrate with excellent yield, involving sugar to racemic lactic acid conversion over Sn-containing Beta zeolite and racemic lactic acid to lactide conversion over H-Beta zeolite. Structural characteristics of the resulting lactide and extensive applicability for various substrates are also presented.

3D Printing of Polymeric Bioresorbable Stents: A Strategy to Improve Both Cellular Compatibility and Mechanical Properties

One of the leading causes of death is cardiovascular disease, and the most common cardiovascular disease is coronary artery disease. Percutaneous coronary intervention and vascular stents have emerged as a solution to treat coronary artery disease. Nowadays, several types of vascular stents share the same purpose: to reduce the percentage of restenosis, thrombosis, and neointimal hyperplasia and supply mechanical support to the blood vessels. Despite the numerous efforts to create an ideal stent, there is no coronary stent that simultaneously presents the appropriate cellular compatibility and mechanical properties to avoid stent collapse and failure. One of the emerging approaches to solve these problems is improving the mechanical performance of polymeric bioresorbable stents produced through additive manufacturing. Although there have been numerous studies in this field, normalized control parameters for 3D-printed polymeric vascular stents fabrication are absent. The present paper aims to present an overview of the current types of stents and the main polymeric materials used to fabricate the bioresorbable vascular stents. Furthermore, a detailed description of the printing parameters' influence on the mechanical performance and degradation profile of polymeric bioresorbable stents is presented.

Synthesis, Properties, and Enzymatic Hydrolysis of Poly(lactic acid)-co-Poly(propylene adipate) Block Copolymers Prepared by Reactive Extrusion

Poly(lactic acid) (PLA) is a biobased polyester with ever-growing applications in the fields of packaging and medicine. Despite its popularity, it suffers from inherent brittleness, a very slow degradation rate and a high production cost. To tune the properties of PLA, block copolymers with poly(propylene adipate) (PPAd) prepolymer were prepared by polymerizing L-lactide and PPAd oligomers via reactive extrusion (REX) in a torque rheometer. The effect of reaction temperature and composition on the molecular weight, chemical structure, and physicochemical properties of the copolymers was studied. The introduction of PPAd successfully increased the elongation and the biodegradation rate of PLA. REX is an efficient and economical alternative method for the fast and continuous synthesis of PLA-based copolymers with tunable properties.

Zinc Polyaleuritate Ionomer Coatings as a Sustainable, Alternative Technology for Bisphenol A-Free Metal Packaging

Sustainable coatings for metal food packaging were prepared from ZnO nanoparticles (obtained by the thermal decomposition of zinc acetate) and a naturally occurring polyhydroxylated fatty acid named aleuritic (or 9,10,16-trihydroxyhexadecanoic) acid. Both components reacted, originating under specific conditions zinc polyaleuritate ionomers. The polymerization of aleuritic acid into polyaleuritate by a solvent-free, melt polycondensation reaction was investigated at different times (15, 30, 45, and 60 min), temperatures (140, 160, 180, and 200 °C), and proportions of zinc oxide and aleuritic acid (0:100, 5:95, 10:90, and 50:50, w/w). Kinetic rate constants calculated by infrared spectroscopy decreased with the amount of Zn due to the consumption of reactive carboxyl groups, while the activation energy of the polymerization decreased as a consequence of the catalyst effect of the metal. The adhesion and hardness of coatings were determined from scratch tests, obtaining values similar to robust polymers with high adherence. Water contact angles were typical of hydrophobic materials with values ≥94°. Both mechanical properties and wettability were better than those of bisphenol A (BPA)-based resins and most likely are related to the low migration values determined using a hydrophilic food simulant. The presence of zinc provided a certain degree of antibacterial properties. The performance of the coatings against corrosion was studied by electrochemical impedance spectroscopy at different immersion times in an aqueous solution of NaCl. Considering the features of these biobased lacquers, they can be potential materials for bisphenol A-free metal packaging.

Revisiting the production of L( +)-lactic acid from vine shoots: bioconversion improvements by employing thermotolerant bacteria

Vine shoots (Vitis vinifera L.) constitute an abundant lignocellulosic source which is frequently underutilised. Alkaline and acidic pretreatments (with and without washing steps) were compared and optimised to release fermentable sugars from vine shoots. An acidic pretreatment using 1.72% H₂SO₄ at 134 °C for 17 min (with 10% w/w solid biomass), followed by an enzymatic hydrolysis, offered the most cost-effective results, releasing 40.21 g/L sugars. Three thermotolerant strains, namely, Bacillus coagulans DSM 2314, Geobacillus stearothermophilus DSM 2313, and G. stearothermophilus DSM 494, were assessed to produce lactic acid from vine-shoot hydrolysates under aerobic and non-sterile conditions, without the need of detoxification steps. In addition, wine lees were satisfactorily employed as nitrogen sources for the fermentation, providing similar results to yeast extract and being the only nutrient added to vine-shoot hydrolysates. Under optimal conditions, B. coagulans DSM 2314 produced 29.21 ± 0.23 g/L lactic acid in 24 h, with a sugar consumption of 98.74 ± 0.07% and a yield of 96.38 ± 0.76%, when supplemented with red wine lees. The purity of the isomer L( +) reached 97.59 ± 1.35% of the total lactic acid produced. Although G. stearothermophilus was able to transform the hexoses from vine-shoot hydrolysates into lactic acid, it proved to be inefficient for metabolising pentoses, thus obtaining lower lactic acid values (16-18 g/L).

Synthesis of block copolymers used in polymersome fabrication: Application in drug delivery

Amphiphilic block copolymers are common materials used for the fabrication of various nanostructures with biomedical applications including nanocapsules, nanospheres, micelles and polymeric vesicles. According to the literature, polymersomes have several advantages compared to other nanostructures used as drug delivery systems comprising better stability, facile synthesis, prolonged circulation time, and passive/active targeting capability. Various types of nanoparticles are formed by varying the ratio of the hydrophobic/hydrophilic blocks. Changing hydrophobic/hydrophilic ratio of amphiphilic block copolymers has an impact on the structural characteristics of polymers such as changing molecular weight and surface functionalization of the block copolymer. Thus, polymerization strategies are an important factor that influences polymersomes quality. In this review, different polymerization strategies for the synthesis of block copolymers applied in polymersomes formation, are described.

Polylactic acid production from biotechnological routes: A review

Polylactic acid (PLA) has been highlighted as an important polymer due to its high potential for applicability in various areas, such as in the chemical, medical, pharmaceutical or biotechnology field. Very recently, studies have reported its use as a basic component for the production of personal protective equipment (PPE) required for the prevention of Sars-Cov-2 contamination, responsible for the cause of coronavirus disease, which is currently a major worldwide sanitary and social problem. PLA is considered a non-toxic, biodegradable and compostable plastic with interesting characteristics from the industrial point of view, and it emerges as a promising product under the concept of "green plastic", since most of the polymers produced currently are petroleum-based, a non-renewable raw material. Biotechnology routes have been mentioned as potential methodologies for the production of this polymer, especially by enzymatic routes, in particular by use of lipases enzymes. The availability of pure lactic acid isomers is a fundamental aspect of the manufacture of PLA with more interesting mechanical and thermal properties. Due to the technological importance that PLA-based polymers are acquiring, as well as their characteristics and applicability in several fields, especially medical, pharmaceutical and biotechnology, this review article sought to gather very recent information regarding the development of research in this area. The main highlight of this study is that it was carried out from a biotechnological point of view, aiming at a totally green bioplastic production, since the obtaining of lactic acid, which will be used as raw material for the PLA synthesis, until the degradation of the polymer obtained by biological routes.

Development of Biodegradable Polymer Blends Based on Chitosan and Polylactide and Study of Their Properties

Composite materials of various compositions based on chitosan and polylactide were obtained in the form of films or porous bulk samples. Preliminarily, poly-d,l-lactide was synthesized by ring-opening polymerization of lactide in the presence of Ti(OⁱPr)₄. Polylactide obtained at components molar ratio [lactide]:[Ti(OⁱPr)₄] = 3:1 had the best molecular weight characteristics at a high product yield. Film composition with the weight ratio chitosan-polylactide 50:50 wt. % was characterized by high mechanical properties. The value of the tensile strength of the film was 72 MPa with a deformation of 10% and an elastic modulus of 40 GPa, which is higher than the tensile strength of native chitosan by ~three times. The observed effect is a consequence of the fact that the chitosan-polylactide composite has an amorphous structure in contrast to the native chitosan, which is proved by X-ray phase analysis. An increase in the elastic modulus of the composite in the range of 20–60 °C in contrast to polylactide was found by dynamic mechanical analysis. The observed effect is apparently caused by the formation of hydrogen bonds between functional groups of chitosan and polylactide which is possible through an increase in polylactide segments mobility when its glass transition temperature is reached. The composite material is biocompatible and characterized by high cellular adhesion of fibroblasts (line hTERT BJ-5ta). Their growth on the composite surface was 2.4 times more active than on native chitosan. Bulk porous samples of the composition with the weight ratio chitosan-polylactide 50:50 wt. % were synthesized by original method in ammonium bicarbonate presence. Samples were characterized by a porosity of 82.4% and an average pore size of 100 microns. The biodegradability of such material and absence of inflammatory processes were proven in vivo by the blood parameters of experimental animals. Thus, materials with the weight ratio chitosan-polylactide 50:50 wt. % are promising for potential use in regenerative medicine.

Effect of an Antioxidant Based on Red Beetroot Extract on the Abiotic Stability of Polylactide and Polycaprolactone

This study investigated the effect of natural antioxidants inherent to beetroot (Beta vulgaris var. Vulgaris) on the ageing of environmentally friendly plastics. Certain properties were examined in this context, comprising thermal, mechanical, and morphological properties. A visual evaluation of relevant changes in the given polymers (polylactide and polycaprolactone) was conducted during an ageing test in a UV chamber (45 °C, 70% humidity) for 720 h. The films were prepared by a casting process, in which samples with the extract of beetroot were additionally incorporated in a common filler (bentonite), this serving as a carrier for the extract. The results showed the effect of the incorporated antioxidant, which was added to stabilize the biodegradable films. Its efficiency during the ageing test in the polymers tended to exceed or be comparable to that of the reference sample.

Poly(lactic Acid): A Versatile Biobased Polymer for the Future with Multifunctional Properties-From Monomer Synthesis, Polymerization Techniques and Molecular Weight Increase to PLA Applications

Environmental problems, such as global warming and plastic pollution have forced researchers to investigate alternatives for conventional plastics. Poly(lactic acid) (PLA), one of the well-known eco-friendly biodegradables and biobased polyesters, has been studied extensively and is considered to be a promising substitute to petroleum-based polymers. This review gives an inclusive overview of the current research of lactic acid and lactide dimer techniques along with the production of PLA from its monomers. Melt polycondensation as well as ring opening polymerization techniques are discussed, and the effect of various catalysts and polymerization conditions is thoroughly presented. Reaction mechanisms are also reviewed. However, due to the competitive decomposition reactions, in the most cases low or medium molecular weight (MW) of PLA, not exceeding 20,000-50,000 g/mol, are prepared. For this reason, additional procedures such as solid state polycondensation (SSP) and chain extension (CE) reaching MW ranging from 80,000 up to 250,000 g/mol are extensively investigated here. Lastly, numerous practical applications of PLA in various fields of industry, technical challenges and limitations of PLA use as well as its future perspectives are also reported in this review.

A new and efficient lactic acid polymerization by multimetallic cerium complexes: a poly(lactic acid) suitable for biomedical applications

Among many, poly(lactic acid) (PLA) has received significant consideration. The striking price and accessibility of l-lactic acid, as a naturally occurring organic acid, are important reasons for poly-(l)-lactic acid (PLLA) improvement. PLLA is a compostable and biocompatible/bioresorbable polymer used for disposable products, for biomedical applications, for packaging film, in the automotive industry, for electronic device components, and for many other applications. Formerly, titanium and other metals have been used in different orthopaedic screws and plates, but they are not degradable and therefore remain in the body. So, the development of innovative and eco compatible catalysts for polyester synthesis is of great interest. In this study, an innovative and eco sustainable catalyst was employed for PLLA synthesis. The combined CeCl3·7H2O-NaI system has been demonstrated to be a very valuable and nontoxic catalyst toward PLLA synthesis, and it represents a further example of how to exploit the antibacterial properties of cerium ions in biomaterials engineering. A novel synthesis of poly-(l)-lactic acid was developed in high yields up to 95% conversion and with a truly valuable molecular weight ranging from 9000 to 145 000 g mol-1, testing different synthetic routes.

Processability and Mechanical Properties of Thermoplastic Polylactide/Polyhydroxybutyrate (PLA/PHB) Bioblends

This work considers the application of eco-friendly, biodegradable materials based on polylactide (PLA) and polyhydroxybutyrate (PHB), instead of conventional polymeric materials, in order to prevent further environmental endangerment by accumulation of synthetic petro-materials. This new approach to the topic is focused on analyzing the processing properties of blends without incorporating any additives that could have a harmful impact on human organisms, including the endocrine system. The main aim of the research was to find the best PLA/PHB ratio to obtain materials with desirable mechanical, processing and application properties. Therefore, two-component polymer blends were prepared by mixing different mass ratios of PLA and PHB (100/0, 50/10, 50/20, 40/30, 50/50, 30/40, 20/50, 10/50 and 0/100 mass ratio) using an extrusion process. The prepared blends were analyzed in terms of thermal and mechanical properties as well as miscibility and surface characteristics. Taking into account the test results, the PLA/PHB blend with a 50/10 ratio turned out to be most suitable in terms of mechanical and processing properties. This blend has the potential to become a bio-based and simultaneously biodegradable material safe for human health dedicated for the packaging industry.

Microbial Production of Biodegradable Lactate-Based Polymers and Oligomeric Building Blocks From Renewable and Waste Resources

Polyhydroxyalkanoates (PHAs) are naturally occurring biopolymers produced by microorganisms. PHAs have become attractive research biomaterials in the past few decades owing to their extensive potential industrial applications, especially as sustainable alternatives to the fossil fuel feedstock-derived products such as plastics. Among the biopolymers are the bioplastics and oligomers produced from the fermentation of renewable plant biomass. Bioplastics are intracellularly accumulated by microorganisms as carbon and energy reserves. The bioplastics, however, can also be produced through a biochemistry process that combines fermentative secretory production of monomers and/or oligomers and chemical synthesis to generate a repertoire of biopolymers. PHAs are particularly biodegradable and biocompatible, making them a part of today's commercial polymer industry. Their physicochemical properties that are similar to those of petrochemical-based plastics render them potential renewable plastic replacements. The design of efficient tractable processes using renewable biomass holds key to enhance their usage and adoption. In 2008, a lactate-polymerizing enzyme was developed to create new category of polyester, lactic acid (LA)-based polymer and related polymers. This review aims to introduce different strategies including metabolic and enzyme engineering to produce LA-based biopolymers and related oligomers that can act as precursors for catalytic synthesis of polylactic acid. As the cost of PHA production is prohibitive, the review emphasizes attempts to use the inexpensive plant biomass as substrates for LA-based polymer and oligomer production. Future prospects and challenges in LA-based polymer and oligomer production are also highlighted.

Three-Step Synthesis of a Redox-Responsive Blend of PEG-block-PLA and PLA and Application to the Nanoencapsulation of Retinol

Smart polymeric nanocarriers have been developed to deliver therapeutic agents directly to the intended site of action, with superior efficacy. Herein, a mixture of poly(lactide) (PLA) and redox-responsive poly(ethylene glycol)-block-poly(lactide) (PEG-block-PLA) containing a disulfide bond was synthesized in three steps. The nanoprecipitation method was used to prepare an aqueous suspension of polymeric nanocarriers with a hydrodynamic diameter close to 100 nm. Retinol, an anti-aging agent very common in cosmetics, was loaded into these smart nanocarriers as a model to measure their capacity to encapsulate and to protect a lipophilic active molecule. Retinol was encapsulated with a high efficiency with final loading close to 10% w/w. The stimuli-responsive behavior of these nanocarriers was demonstrated in vitro, in the presence of l-Glutathione, susceptible to break of disulfide bond. The toxicity was low on human keratinocytes in vitro and was mainly related to the active molecule. Those results show that it is not necessary to use 100% of smart copolymer in a nanosystem to obtain a triggered release of their content.