Biodegradable Aliphatic Polyesters Research Articles

Performance comparison of PLA- and PLGA-coated porous bioceramic scaffolds: Mechanical, biodegradability, bioactivity, delivery and biocompatibility assessments.

Bioceramics, particularly calcium phosphates, bioactive glasses, and crystalline silicates, are a principal group of biomaterials employed for the regeneration of damaged tissues and therapeutic delivery. The development of ceramic tissue engineering scaffolds with an appropriate combination of mechanical and biological properties is still one of the key challenges in this field. In this regard, the deposition of polymeric coatings on the scaffolds is a simple and effective approach to reinforce their functions. Among different polymers, the influences of biodegradable aliphatic polyester coatings, especially polylactic acid (PLA) and poly(lactic-co-glycolic acid) (PLGA), over the performance of the scaffolds have been investigated in numerous research. This review paper provides a comprehensive comparison of PLA- and PLGA-coated bioceramic scaffolds which are mainly employed in bone tissue engineering. It is concluded that both the polymers enhance the mechanical behaviors of the scaffolds, but control their biodegradability, bioactivity, and delivery kinetics, where PLA acts almost more influentially than PLGA in comparison. However, the response of biocompatibility to this surface treatment is condition-dependent and requires case-by-case experiments to be determined accurately.

Crystalline aliphatic polyesters from eight‐membered cyclic (di)esters

AbstractRing‐opening polymerization (ROP) of lactones or cyclic (di)esters is a powerful method to produce well‐defined, high‐molecular‐weight (bio)degradable aliphatic polyesters. While the ROP of lactones of various ring sizes has been extensively studied, the ROP of the simplest eight‐membered lactone, 7‐heptanolactone (7‐HL), has not been reported using metal‐based catalysts. Accordingly, this contribution reports the ROP of 7‐HL via metal‐catalyzed coordinative‐insertion polymerization to the corresponding high‐molecular‐weight polyester, poly(7‐hydroxyheptanoate) (P7HHp). The resulting P7HHp is a semi‐crystalline material, with a Tm of 68 °C, which is ~10 °C higher than poly(ε‐caprolactone) derived from the seven‐membered lactone. Mechanical testing showed that P7HHp is a hard and tough plastic, with elongation at break >670%. P7HHp‐based polyesters with higher Tm values have been achieved through stereoselective copolymerization of 7‐HL with an eight‐membered cyclic diester, racemic dimethyl diolide (rac‐8DLMe), known to lead to high Tm poly(3‐hydroxyburtyrate) (P3HB). Notably, catalyst's strong kinetic preference for polymerizing rac‐8DLMe over 7‐HL in the 1/1 comonomer mixture rendered the formation of di‐block copolymer P3HB‐b‐P7HHp, showing two crystalline domains with Tm1 ~ 65 °C and Tm2 ~ 160 °C. Semi‐crystalline random copolymers with Tm up to 164 °C have also been obtained by adjusting copolymerization conditions. Mechanical testing showed that P3HB‐b‐P7HHp can synergistically combine the high modulus of isotactic P3HB with the high ductility of P7HHp.

Ecofriendly poly(3-hydroxybutyrate-co-4-hydroxybutyrate) microbeads for sanitary products

In the past, plastic microbeads (MBs) were added to personal healthcare products to improve the cleaning and exfoliating effects, but these have been withdrawn owing to their non-degradable nature and contribution to the pollution of marine environment, especially that caused by the adsorption of persistent organic pollutants (POPs) on MBs. Therefore, natural biodegradable alternatives are being developed, but these often do not exhibit sufficient performance to replace non-degradable MBs. In this study, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB-4HB), a biodegradable aliphatic polyester, was used to prepare MBs via melt-electrospraying. We carried out the rheological characterization of P3HB-4HB with respect to melting temperature, and the melt-electrospray process was optimized to prepare MBs having sizes similar to those of commercially available MBs. Furthermore, the adsorption properties of the P3HB-4HB MBs for POPs were investigated. Unlike commercial MBs, the P3HB-4HB MBs adsorbed significantly fewer contaminants owing to their smooth and regular surfaces. Finally, a cleansing product containing P3HB-4HB MBs was prepared to evaluate their cleaning ability, and we found that the MB-based product could remove dirt and contaminants that were not easily removed by water alone. Thus, the biodegradable P3HB-4HB MBs have great potential for use as sustainable additives for cosmetic products for skin exfoliation.

Electrospun Membranes of Poly(butylene succinate) and Poly(butylene/2‐butyl,2‐ethyl‐propylene succinate)

AbstractPoly(butylene succinate) (PBS) and poly(butylene/2‐butyl,2‐ethyl‐propylene succinate) (PBSBEPS) membranes are prepared by electrospinning technique. In recent years, interest in biodegradable aliphatic polyesters, including PBS and its copolymers, is increasing as they have potential applications in various sectors such as mulching films, food packaging, tissue engineering, and drug delivery. In this work, the synthesized polymers are dissolved in different solvents, namely acetone, chloroform (CHCl3), methanol, dichloromethane (DCM), and dimethylformamide in order to obtain the best solvent system. These solutions are then electrospun at room temperature to produce micron‐sized fibers. The variables examined in determining the optimal solution and electrospinning conditions are the solvent system used, the concentration of PBS and PBS‐based random copolymer, applied voltage, flow rate, humidity, and the distance between the needle tip and the collector, all of which have a meaningful effect on the fiber morphology. Among the various solvents used, the DCM and the less toxic CHCl3 result in fewer bead defects among fibers. Besides, an increase in PBS and PBS‐based random copolymer concentration determines the reduction of bead defects, which from 12 to 14 wt% results in bead‐free uniform fibers, when suitable processing parameters are set. Promising results, which can pave the way for the production of membranes loaded with appropriate anticancer molecules for targeted biomedical applications, are obtained.

Manganese oxidation and prokaryotic community analysis in a polycaprolactone-packed aerated biofilm reactor operated under seawater conditions.

Biogenic manganese oxides (BioMnOx) have been receiving increasing attention for the removal of environmental contaminants and recovery of minor metals from water environments. However, the enrichment of heterotrophic Mn(II)-oxidizing microorganisms for BioMnOx production in the presence of fast-growing coexisting heterotrophs is challenging. In our previous work, we revealed that polycaprolactone (PCL), a biodegradable aliphatic polyester, can serve as an effective solid organic substrate to enrich Mn-oxidizing microbial communities under seawater conditions. However, marine BioMnOx-producing bioreactor systems utilizing PCL have not yet been established. Therefore, a laboratory-scale continuous-flow PCL-packed aerated biofilm (PAB) reactor was operated for 238days to evaluate its feasibility for BioMnOx production under seawater conditions. After the start-up of the reactor, the average dissolved Mn removal rates of 0.4-2.3mg/L/day, likely caused by Mn(II) oxidation, were confirmed under different influent dissolved Mn concentrations (2.5-14.0mg/L on average) and theoretical hydraulic retention time (0.19-0.77day) conditions. The 16S rRNA gene amplicon sequencing analysis suggested the presence of putative Mn(II)-oxidizing and PCL-degrading bacterial lineages in the reactor. Two highly dominant operational units (OTUs) in the packed PCL-associated biofilm were assigned to the genera Marinobacter and Pseudohoeflea, whereas the genus Lewinella and unclassified Alphaproteobacteria OTUs were highly dominant in the MnOx-containing black/dark brown precipitate-associated biofilm formed in the reactor. Excitation-emission matrix fluorescence spectroscopy analysis revealed the production of tyrosine- and tryptophane-like components, which may serve as soluble heterotrophic organic substrates in the reactor. Our findings indicate that PAB reactors are potentially applicable to BioMnOx production under seawater conditions.

Biodegradable polymer-based microfluidic membranes for sustainable point-of-care devices

Microfluidic paper-based analytical devices (µPADs) have gained substantial attention as portable analytical devices in various (bio)technological fields, for being affordable, user-friendly, portable, energy efficient and for allowing multiplexed analysis. Although significant progress has been achieved, there is still need for improvement in terms of performance and sustainability. In this work, a biodegradable aliphatic polyester poly(D,L-lactide-co-glycolide acid) lactide:glycolide 50:50 (PDLG), is used to produce pore- and fibre-based membranes, as alternative to conventional paper substrates. Two fabrication methods are used, with potential for industrial scale-up. The processed hydrophobic membranes are post-treated with oxygen plasma to turn them hydrophilic, allowing capillary flows. The physicochemical characterization demonstrates the suitability of the plasma-treated PDLG membranes as microfluidic substrates based on their tailorable morphologies and capillary flow rate from 36.2 ± 4.2 to 84.1 ± 5.2 mm·min−1, excellent mechanical properties and biocompatibility. Further, the membranes maintain their properties for at least 6 months when kept in vacuum and degrade quickly after their use (reaching values higher than 90% after 6 weeks when wet). Finally, portable analytical platforms suitable for the colorimetric quantification of glucose are demonstrated. These results are of great importance for the design and manufacture of a new generation of sustainable portable analytical devices, compatible with circular economy paradigms, and a step forward to cross the challenging academia to industry barrier for their commercialization and widespread adoption.

Nucleation roles of cellulose nanocrystals and chitin nanocrystals in poly(ε-caprolactone) nanocomposites.

Using polysaccharide nanocrystals such as chitin nanocrystals (ChNCs) or cellulose nanocrystals (CNCs) as fillers of biodegradable aliphatic polyesters is an attractive approach of fabricating completely biodegradable nanocomposites. Most aliphatic polyesters are semi-crystalline and hence to reveal the effect of nanocrystals on their crystallization behaviors is key to regulate final properties of the nanocomposites. In this work, poly(ε-caprolactone) (PCL) nanocomposites filled with ChNCs and CNCs were prepared as templates for the study. It is intriguing that these two nanocrystals play completely different roles towards crystallization of PCL. CNCs are nucleating agent, promoting nucleation of PCL and accelerating subsequent crystal growth; while ChNCs are anti-nucleation agent, retarding nucleation of PCL and depressing whole process of PCL crystallization. This difference arises from different particle-polymer affinities in the nanocomposites, which is confirmed by the thermodynamic and rheological tests. This work provides valuable information around tuning the thermal properties of polysaccharide nanocrystals filled polymeric nanocomposites.

Miscibility effect of biodegradable aliphatic poly(butylene succinate)/aromatic polycarbonate blends

Biodegradable polymers are gaining attention for applications in drug delivery, tissue engineering, and wound management. Methods for enhancing their potential in these applications include blending biodegradable aliphatic polyester with other biodegradable aliphatic polyester and/or blending aliphatic polyesters with aromatic polyesters to form blends with unique properties. Herein, we report on the effect of a non-biodegradable aromatic polycarbonate (PC) on the physical, mechanical, and thermal properties of biodegradable aliphatic polybutylene succinate (PBS). The PBS/PC blends contained 3, 13, and 27 wt% PC and were prepared by melt extrusion. The FTIR results revealed apparent compatibility between the two polymers. Even though the blends are compatible, the extent of miscibility depends on thermodynamics terms such as enthalpy, entropy, and Gibbs free energy. According to the SEM micrographs, adding 3 wt% PC resulted in a miscible polymer blend. Above this content, phase dispersion was observed. XRD results revealed peak shifts to higher angles and new peaks forming between 25 and 30°. This is related to the interaction between the components in the blends. The crystallinity was also improved at 3 wt% PC and this is consistent with the DSC results. TGA analysis indicated no improvement in the thermal stability of the blends. DMA revealed that at low PC content (3 wt%), there is a marked improvement in the elastic modulus. This study will benefit the field of Polymer Science because if one wants to prepare PBS/PC they will know that they perform optimally at low PC content.

Significantly Enhanced Crystallization of Poly(ethylene succinate-co-1,2-propylene succinate) by Cellulose Nanocrystals as an Efficient Nucleating Agent.

Poly(ethylene succinate-co-1,2-propylene succinate) (PEPS) is a novel aliphatic biodegradable polyester with good mechanical properties. Due to the presence of methyl as a side group, the crystallization rate of PEPS is remarkably slower than that of the poly(ethylene succinate) homopolymer. To promote the potential application of PEPS, the effect of cellulose nanocrystals (CNC) on the crystallization behavior, crystalline morphology, and crystal structure of PEPS was investigated in this research with the aim of increasing the crystallization rate. CNC enhanced both the melt crystallization behavior of PEPS during the cooling process and the overall crystallization rate during the isothermal crystallization process. The crystallization rate of PEPS became faster with an increase in CNC content. The crystalline morphology study directly confirmed the heterogeneous nucleating agent role of CNC. The crystal structure of PEPS remained unchanged in the composites. On the basis of the interfacial energy, the nucleation mechanism of PEPS in the composites was further discussed by taking into consideration the induction of CNC.

Synthesis and evaluation of electrospun PCL-plasmid DNA nanofibers for post cancer treatments

Poly-ε-caprolactone (PCL) incorporated with plasmid DNA was electrospun, and the resultant nanofibers were used to observe DNA release from the nanofibers. The plasmid DNA enhanced green fluorescent protein (EGFP) with cytomegalovirus (CMV) promoter (PCMVb-GFP) was amplified with E. coli. PCL was chosen because it is biodegradable aliphatic polyester, which plays a critical role in tissue engineering, such as scaffolding, drug, DNA, gene and protein delivery vehicles. Some of the physical and biological properties of the nanofibers were determined using different methods. Scanning electron microscopy (SEM) micrographs showed that nanofibers have an average diameter of about 100 nm. Cytotoxicity tests showed that cell viability for 1 day, 4 days, and 7 days of the tests were above 80 %. These data demonstrated that PCL-plasmid DNA nanofibers have no cytotoxicity and showed benign biocompatibility for biomedical applications. PCMVb-GFP plasmid-linked electrospun nanofibers continuously released double-stranded DNA for at least seven days. For the first 15 min, there was a burst release of about 1.8 ng/ml. For the following hours and days, the release was about to be the same (release of 0.575 ng/ml). Therefore, PCL nanofibers may be an ideal candidate for various biomedical applications such as cancer treatment, scaffolding, tissue engineering, and protein delivery vehicles.

Cytocompatible, soft and thick brush-modified scaffolds with prolonged antibacterial effect to mitigate wound infections.

Biomedical device or implant-associated infections caused by pathogenic bacteria are a major clinical issue, and their prevention and/or treatment remains a challenging task. Infection-resistant antimicrobial coatings with impressive cytocompatibility offer a step towards addressing this problem. Herein, we report a new strategy for constructing highly antibacterial as well as cytocompatible mixed polymer brushes onto the surface of 3D printed scaffold made of biodegradable tartaric acid-based aliphatic polyester blends. The mixed brushes were nothing but a combination of poly(3-dimethyl-(methacryloyloxyethyl) ammonium propane sulfonate) (polyDMAPS) and poly((oligo ethylene glycol) methyl ether methacrylate) (polyPEGMA) with varying chain length (n) of the ethylene glycol unit (n = 1, 6, 11, and 21). Both homo and copolymeric brushes of polyDMAPS with polyPEGMA exhibited antibacterial efficacy against both Gram positive and Gram negative pathogens such as E. coli (Escherichia coli) and S. aureus (Staphylococcus aureus) because of the combined action of bacteriostatic effects originating from strongly hydrated layers present in zwitterionic (polyDMAPS) and hydrophilic (polyPEGMA) copolymer brushes. Interestingly, a mixed polymer brush comprising polyDMAPS and polyPEGMA (ethylene glycol chain unit of 21) at 50/50 ratio provided zero bacterial growth and almost 100% cytocompatibility (tested using L929 mouse fibroblast cells), making the brush-modified biodegradable substrate an excellent choice for an infection-resistant and cytocompatible surface. An attempt was made to understand their extraordinary performance with the help of contact angle, surface charge analysis and nanoindentation study, which revealed the formation of a hydrophilic, almost neutral, very soft surface (99.99% reduction in hardness and modulus) after modification with the mixed brushes. This may completely suppress bacterial adhesion. Animal studies demonstrated that these brush-modified scaffolds are biocompatible and can mitigate wound infections. Overall, this study shows that the fascinating combination of an infection-resistant and cytocompatible surface can be generated on biodegradable polymeric surfaces by modulating the surface hardness, flexibility and hydrophilicity by selecting appropriate functionality of the copolymeric brushes grafted onto them, making them ideal non-leaching, anti-infective, hemocompatible and cytocompatible coatings for biodegradable implants.

A local green composite study: the effect of edible oil on the morphological and mechanical properties of PBS/bentonite composite

Abstract Composites of a biodegradable thermoplastic aliphatic polyester, polybutylene succinate (PBS), with bentonite were investigated for morphological and mechanical properties. The bentonite was modified with soybean oil (SBO) and lard oil (LO) (2:98 clay:oil % by weight) by mechanical stirring and ultrasonication. The PBS/modified bentonite composite was prepared by using an internal mixer and processed by compression molding. Under bentonite modification conditions, XRD and SEM showed that the bentonite layers were broken into small layers, and the d-spacing between the layers was increased by edible oil molecules. A small plate like structure of modified bentonite composite was observed by SEM micrograph, which revealed short and long layer silicate structure non-directionally throughout the matrix phase. The mechanical properties of PBS were reinforced by this structure. The tensile modulus and elongation at break seem to depend on its directional bentonite. Interestingly, considerable improvement in impact strength was observed at over 2 wt% of clay. The impact strengths of PBS, PBS/modified BTN with SBO composite, and PBS/modified BTN with LO composite were increased from 1 to 1.5 and 2 kJ/m2, respectively. Comparatively, using LO modified bentonite had a better performance for increased interlayer and resulted in higher impact strength of the composite than that of SBO composite. The results demonstrated that PBS/modified bentonite using edible oil could be a potential alternative low cost, eco-friendly material with superior impact properties useful for further applications.

Poly(lactic acid)-PLA: An Analysis Based on Literature Text Mining

The most researched and used biodegradable aliphatic polyester worldwide is poly (lactic acid) - PLA. Due to its inherent properties, PLA is a leading biomaterial for several and numerous applications and the most promising biopolymer capable of replacing conventional petroleum-derived polymers. Besides, PLA is also one of the most promising candidates for new developments in the traditional sectors such as packaging and the automotive industry, in the electronics industry, and the biomedical area. To verify the importance of drug release in the various applications of PLA, a text mining of the last ten years was carried out. The text-mining tool was used to identify this polymer's main applications in the last ten years, allowing us to draw a map year by year based on correlation analysis. Firstly, an analysis was made of the main applications of PLA in scientific research, by searching for "PLA", in the ScienceDirect scientific base (https://www.sciencedirect.com/) and using the online tool Voyant Tools. Some words related to drug release were selected, checking how many times they were mentioned over the years. In this way, it was possible to see which years were the most and least used PLA in drug release. It was not possible to observe a gradual increase or decrease in this polymer's use, for this purpose, over time. The text mining presented here proved to be an efficient and fast way to observe the desired theme.

Biodegradable and pH-responsive piperazine-based aliphatic polyesters with tunable hydrophilicity

In this article, we report on a new class of biodegradable piperazine-based aliphatic pH-responsive polyesters with tunable hydrophilicity. The aliphatic polyesters PC1-PC4 with high thermal stability up to 340 °C were synthesized by polycondensation of dimethyl 2,2′-(piperazin-1,4-diyl)diacetate with a series of alkane diols (C4 to C10). The resulting polyesters are found to be highly crystalline with ∼47–55% crystallinity as estimated from XRD and moderately hydrophilic as the water contact angle was found to be in the range of 63°–72°. An N-alkylation or protonation approach was used to tune their crystallinity and hydrophilicity so as to enhance biodegradability. Upon quaternization with methyl iodide, a significant effect on functional and structural properties was observed with reduced crystallinity and enhanced hydrophilicity, as the contact angle decreased down to 24° upon methylation. The pH-responsive nature of the material was evaluated with zeta potential measurements, and the surface charge increased up to +41.4 mV with a more positive charge on the polymer backbone at pH 2 for polyester PC2. Further, microbial and hydrolytic degradation studies showed that the quaternized polyesters PC6 and PC9 exhibit faster degradation when compared to their parent polymer PC2, demonstrating their significance as a new class of biodegradable polyesters.

Potential of Serratia plymuthica IV-11-34 strain for biodegradation of polylactide and poly(ethylene terephthalate)

Serratia plymuthica strain IV-11-34 belongs to the plant growth promoting bacteria (PGPR). In the sequenced genome of S. plymuthica IV-11-34, we have identified the genes involved in biodegradation and metabolisms of xenobiotics. The potential of S. plymuthica IV-11-34 for the degradation of biodegradable aliphatic polyester polylactide (PLA) and resistant to biodegradation – poly(ethylene terephthalate) (PET) was assessed by biochemical oxygen consumption (BOD) and carbon dioxide methods. After seven days of growth, the bacteria strain showed more than 80% and 60% increase in respiratory activity in the presence of PLA and PET, respectively. We assume that during biodegradation, S. plymuthica IV-11-34 colonise the surface of PLA and PET, since the formation of a biofilm on the surface of polymers was shown by the LIVE/DEAD method. We have demonstrated for the relA gene, which is an alarmone synthetase, a 1.2-fold increase in expression in the presence of PLA, and a 4-fold decrease in expression in the presence of PET for the spoT gene, which is a hydrolase of alarmones. Research has shown that the bacterium has the ability to biodegrade PLA and PET, and the first stage of this process involves bacterial stringent response genes responsible for survival under extreme conditions.

Biodegradable Aliphatic Polyesters for Application in Tissue Engineering

Biodegradable Aliphatic Polyesters for Application in Tissue Engineering

Nonwoven Releasing Propolis as a Potential New Wound Healing Method—A Review

Wound healing poses a serious therapeutic problem. Methods which accelerate tissue regeneration and minimize or eliminate complications are constantly being sought. This paper is aimed at evaluation of the potential use of biodegradable polymer nonwovens releasing propolis as wound healing dressings, based on the literature data. Propolis is honeybee product with antioxidant, antibacterial, antifungal, anticancer, anti-inflammatory, analgesic, and regenerative properties. Controlled release of this substance throughout the healing should promote healing process, reduce the risk of wound infection, and improve aesthetic effect. The use of biodegradable aliphatic polyesters and polyester carbonates as a propolis carrier eliminates the problem of local drug administration and dressing changes. Well-known degradation processes and kinetics of the active substance release allows the selection of the material composition appropriate to the therapy. The electrospinning method allows the production of nonwovens that protect the wound against mechanical damage. Moreover, this processing technique enables adjusting product properties by modifying the production parameters. It can be concluded that biodegradable polymer dressings, releasing a propolis, may find potential application in the treatment of complicated wounds, as they may increase the effectiveness of treatment, as well as improve the patient’s life quality.

Monitoring pilot-scale polyhydroxyalkanoate production from fruit pulp waste using near-infrared spectroscopy

Given the current plastic disposal global crisis, biodegradable polymers may have an important role in leading the way towards a more sustainable plastic industry. Polyhydroxyalkanoates (PHA) are biobased and biodegradable aliphatic polyesters synthesized by bacteria and stored as intracellular granules. In this study, PHA was produced at pilot scale by a mixed microbial culture (MMC) fed with fermented fruit pulp waste. The PHA accumulation reactor was monitored at line by near-infrared (NIR) spectroscopy to develop and optimize partial least squares (PLS) calibration models for predicting bulk PHA concentration and intracellular PHA content. The PLS models were subjected to internal cross-validation (62 spectra) and the ones with best performance were validated with an external test set (12 spectra). For bulk PHA concentration, a root mean squared error of prediction (RMSEP) of 0.69 g/L and a coefficient of determination (R2) of 0.89 were attained, while intracellular PHA content was predicted with a RMSEP of 14.6% and a R2 of 0.86. These NIR-based calibration models demonstrated a great potential for the real-time monitoring of the MMC pilot-scale PHA production from a complex fruit pulp waste substrate. This approach can be used for in situ control of the pulse-wise feeding strategy of the PHA accumulation stage, minimizing PHA consumption triggered by carbon source depletion and contributing for an improved global process efficiency and productivity.

Development of self-degradable aliphatic polyesters by embedding lipases via melt extrusion

Several lipases were embedded into the aliphatic biodegradable polyesters poly(butylene succinate), poly(butylene succinate-co-adipate) and polycaprolactone, all of which normally exhibit limited environmental degradation. Observed composite films were all enzymatic self-degraded in buffered solutions. Four different lipases (Lipase AK Amano, Lipase G Amano 50 and Lipase PS Amano SD and Lipozyme CALB L) that have sufficient thermal stability and high degradation activity for each polyester, were selected out and embedded in films of these polymers produced using melt extrusion. Even low concentrations of these lipases embedded in the polyester films resulted in significant degradation after a short time period, suggesting that the lipases retained their activities after melt extrusion. The mechanical properties of the films containing these lipases were essentially unchanged except for decreased elongation at break values. This study demonstrates the viability of using embedded enzymes to obtain self-degradable polymers as an approach that can provide the existing polymers a degradation initiation function to solving environmental issues related to plastic waste.

Coordination Insertion Mechanism of Ring‐Opening Polymerization of Lactide Catalyzed by Stannous Octoate†

Main observation and conclusionRing‐opening polymerization (ROP) of cyclic esters in the presence of stannous octoate (Sn(Oct)2) is the main way to obtain biodegradable aliphatic polyesters, an important family of biodegradable polymers which have been widely used and still rapidly developed in the fields of biomedical polymers and environment‐friendly materials. The underlying mechanism is thought via a coordination‐insertion way, but the pathway is still open owing to the absence of direct experimental evidence. Herein, we inquire this issue through density functional theory (DFT) calculations. According to our DFT calculations and the following Curtin‐Hammett evaluation, the carbonyl oxygen has a significant advantage over the ester oxygen, and thus the ring is opened mainly through pathway A instead of pathway B. The stannous octoate is identified as a catalyst rather than an initiator. We eventually summarize the main stages during the whole polymerization of lactide.