Variation in structure and properties of poly(glycerol adipate) via control of chain branching during enzymatic synthesis

Controlled Enzymatic Synthesis of Polyesters Based on a Cellulose-Derived Triol Monomer: A Design of Experiment Approach

Regioselective enzymatic polycondensation of the bio-based cellulose derived polyol, Triol-citro, and dimethyl adipate using Candida antarctica Lipase B (CaLB) was investigated. A Design of Experiment approach with MODDE® Pro 13 was used to determine important factors in the branching behavior of this polymer, and reactant ratio, temperature, reaction time and enzyme wt % were the studied factors. Multifunctional polyesters with pendant hydroxy groups were synthesized and fully characterized using 2D NMR techniques to determine degree of branching. Branching was minimal, with a maximum of 16 % observed, and monomer ratio, temperature and reaction time were all determined to be significant factors. In this work, Mn of up to 13 kDa were achieved, while maintaining degree of branching below 15 %, resulting in a linear polyester with the potential to be further functionalized.

Polyglycerol Sebacate Elastomer: A Critical Overview of Synthetic Methods and Characterisation Techniques

Poly (glycerol sebacate) is a widely studied elastomeric copolymer obtained from the polycondensation of two bioresorbable monomers, glycerol and sebacic acid. Due to its biocompatibility and the possibility to tailor its biodegradability rate and mechanical properties, PGS has gained lots of interest in the last two decades, especially in the soft tissue engineering field. Different synthetic approaches have been proposed, ranging from classic thermal polyesterification and curing to microwave-assisted organic synthesis, UV crosslinking and enzymatic catalysis. Each technique, characterized by its advantages and disadvantages, can be tailored by controlling the crosslinking density, which depends on specific synthetic parameters. In this work, classic and alternative synthetic methods, as well as characterisation and tailoring techniques, are critically reviewed with the aim to provide a valuable tool for the reproducible and customized production of PGS for tissue engineering applications.

Enzymatic Synthesis of Copolyesters with the Heteroaromatic Diol 3,4-Bis(hydroxymethyl)furan and Isomeric Dimethyl Furandicarboxylate Substitutions

Polyesters from furandicarboxylic acid derivatives, i.e., dimethyl 2,5-furandicarboxylate (2,5-DMFDCA) and 2,4-DMFDCA, show interesting properties among bio-based polymers. Another potential heteroaromatic monomer, 3,4-bis(hydroxymethyl)furan (3,4-BHMF), is often overlooked but holds promise for biopolymer synthesis. Cleaning and greening synthetic procedures, i.e., enzymatic polymerization, offer sustainable pathways. This study explores the Candida antarctica lipase B (CALB)-catalyzed copolymerization of 3,4-BHMF with furan dicarboxylate isomers and aliphatic diols. The furanic copolyesters (co-FPEs) with higher polymerization degrees are obtained using 2,4-isomer, indicating CALB's preference. Material analysis revealed semicrystalline properties in all synthesized 2,5-FDCA-based co-FPEs, with multiple melting temperatures (Tm) from 53 to 124 °C and a glass-transition temperature (Tg) of 9-10 °C. 2,4-FDCA-based co-FPEs showed multiple Tm from 43 to 61 °C and Tg of -14 to 12 °C; one of them was amorphous. In addition, all co-FPEs showed a two-step decomposition profile, indicating aliphatic and semiaromatic segments in the polymer chains.

Tunable structure and linear viscoelastic properties of poly(glycerol adipate urethane)-based elastomeric composites for tissue regeneration

Elastomeric biocomposites based on poly(glycerol adipate urethane) and hydroxyapatite were fabricated for tissue regeneration. The poly(glycerol adipate urethane) (PGAU) elastomeric composite matrices were obtained by chemical crosslinking of the poly(glycerol adipate) prepolymer (pPGA) with diisocyanate derivative of L-lysine. Two series of composites varying in the amount of L-lysine diisocyanate ethyl ester (LDI) used as a crosslinking agent were manufactured. As a ceramic filler both unmodified and L-lysine surface-modified hydroxyapatite (HAP) particles were used. The novelty of our research consists in the manufactured elastomeric materials and characterization of their linear viscoelastic (LVE) properties. The LVE properties of the composites were investigated by means of dynamic thermomechanical analysis. Frequency sweep and amplitude sweep measurements were performed in shear mode. The influence of the crosslinking agent (LDI) amount, HAP content and surface modification of HAP on the LVE properties of the composites was determined based on the analysis of the master curves of storage (G') and loss (G″) moduli and of tanδ of the composites. Depending on the amount of LDI, HAP and surface modification, the materials differ in the values of rubber elasticity plateau modulus (G0) and G' and G″ determined at selected shear frequencies and at the glassy state. G0 ranges from 278 kPa to 3.98 MPa, G' in the glassy state is within the range of 219 MPa-459 MPa. The G0 values of the PGAU-based composites are within the stiffness range of soft tissue. In view of the choice of HAP as the ceramic component and the G0 values, elastomeric composites have the potential to be used as filling materials in small bone defects (due to their mechanical similarity to osteoid) as well as materials for cartilage tissue regeneration.

Glycerol- and diglycerol-based polyesters: Evaluation of backbone alterations upon nano-formulation performance

Despite the success of polyethylene glycol-based (PEGylated) polyesters in the drug delivery and biomedical fields, concerns have arisen regarding PEG's immunogenicity and limited biodegradability. In addition, inherent limitations, including limited chemical handles as well as highly hydrophobic nature, can restrict their effectiveness in physiological conditions of the polyester counterpart. To address these matters, an increasing amount of research has been focused towards identifying alternatives to PEG. One promising strategy involves the use of bio-derived polyols, such as glycerol. In particular, glycerol is a hydrophilic, non-toxic, untapped waste resource and as other polyols, can be incorporated into polyesters via enzymatic catalysis routes. In the present study, a systematic screening is conducted focusing on the incorporation of 1,6-hexanediol (Hex) (hydrophobic diol) into both poly(glycerol adipate) (PGA) and poly(diglycerol adipate) (PDGA) at different (di)glycerol:hex ratios (30:70; 50:50 and 70:30 mol/mol) and its effect on purification upon NPs formation. By varying the amphiphilicity of the backbone, we demonstrated that minor adjustments influence the NPs formation, NPs stability, drug encapsulation, and degradation of these polymers, despite the high chemical similarity. Moreover, the best performing materials have shown good biocompatibility in both in vitro and in vivo (whole organism) tests. As preliminary result, the sample containing diglycerol and Hex in a 70:30 ratio, named as PDGA-Hex 30%, has shown to be the most promising candidate in this small library analysed. It demonstrated comparable stability to the glycerol-based samples in various media but exhibited superior encapsulation efficiency of a model hydrophobic dye. This in-depth investigation provides new insights into the design and modification of biodegradable (di)glycerol-based polyesters, potentially paving the way for more effective and sustainable PEG-free drug delivery nano-systems in the pharmaceutical and biomedical fields.

Novel green-based polyglycerol polymeric nanoparticles loaded with ferulic acid: A promising approach for hepatoprotection

In the pursuit of eco-friendly and sustainable materials, polyglycerol diacid polymers hold immense promise for drug delivery compared to those derived from fossil fuels. Harnessing this potential, we aimed to prepare nanoparticles (NPs) derived from sustainable polymers, loaded with ferulic acid (FA), a natural polyphenolic compound known for its shielding effect against liver-damaging agents, including carbon tetrachloride (CCl4). Glycerol was esterified with renewable monomers, such as succinic acid, adipic acid, and/or FA, resulting in the creation of a novel class of polyglycerol diacid polymers. Characterization via Fourier-transform infrared spectroscopy and nuclear magnetic resonance confirmed the successful synthesis of these polymers with <7 % residual monomers. FA-loaded NPs were fabricated using the newly synthesized polymers. To further augment their potential, the NPs were coated with chitosan. The chitosan-coated NPs boasted an optimal PS of 290 ± 5.03 nm, showing superior physical stability, and a commendable EE% of 58.79 ± 0.43%w/v. The cytotoxicity was examined on fibroblast cells using the SRB assay. In-vivo experiments employing a CCl4-induced liver injury model yielded compelling evidence of the heightened hepatoprotective effects conferred by chitosan-coated particles. This demonstrates the benefits of incorporating sustainable polymers into innovative composites for efficient drug delivery, indicating their potential for creating versatile platforms for various therapeutic applications.

Chemo-Enzymatic Derivatization of Glycerol-Based Oligomers: Structural Elucidation and Potential Applications

Switching from oil-based to bio-based feedstocks to ensure the green transition to a sustainable and circular future is one of the most pressing challenges faced by many industries worldwide. For the cosmetics and personal and house care industries there is a strong drive to accelerate this transition from the customers that starts favoring the purchase of naturally derived and bio-degradable products over the traditionally available products. In this work we developed a series of fully biobased macromolecules constituted of a glycerol-based oligoester backbone. Based on the subsequent derivatization with fatty acids or peptides, the resulting products may find application as emulsifiers, wetting agents, and potential vectors for the delivery of bioactive peptides. All steps of the resulting macromolecules were conducted following the green chemistry principles with no toxic or environmentally damaging compounds that were used in the overall production process.

Multifunctionality of Iodinated Halogen-Bonded Polymer: Biodegradability, Radiopacity, Elasticity, Ductility, and Self-Healing Ability

A polymer with high contents of ester bonds and iodine atoms was synthesized, exhibiting sufficient biodegradability and radioactivity for biomedical applications. The iodine moieties of the synthesized polyester can generate halogen bonding between molecules, which may develop additional functional properties through the bonding. In this study, poly(glycerol adipate) (PGA) was selected and synthesized as a polyester, which was then adequately conjugated with three different types of iodine compounds via the hydroxy groups of PGA. It was found that the iodine compounds could effectively work as donors of halogen bonding. The thermal analysis by differential scanning calorimetry (DSC) revealed that the glass transition temperature increased with the increase in the strength of interactions caused by π-π stacking and halogen bonding, eventually reaching 49.6 °C for PGA with triiodobenzoic groups. An elastomeric PGA with monoiodobenzoic groups was also obtained, exhibiting a high self-healing ability at room temperature because of the reconstruction of halogen bonding. Such multifaceted performance of the synthesized polyester with controllable thermal/mechanical properties was realized by halogen bonding, leading to a promising biomaterial with multifunctionality.

Phosphorylated Polyesters Inspired by Phospholipids: Synthesis, Characterization, and Potential Applications

We report the synthesis of phosphorylated polyesters by the phosphorylation of hydroxylated polyesters synthesized by the lipase-catalyzed polycondensation of glycerol and aliphatic dicarboxylic acids and their characterization. The use of phosphoryl chloride as a phosphorylating agent and triethylamine as a catalyst in mild reaction conditions resulted in polyesters with repetitive units structurally similar to phospholipids, molar mass of around 14-38 kDa, and a degree of phosphorylation of 36 ± 11 mol %. These polyesters are composed mainly of 10 different repetitive units as determined by 1D and 2D NMR. Their properties change from more hydrophilic and amorphous for phosphorylated poly(glycerol adipate) to more hydrophobic and semicrystalline for phosphorylated poly(glycerol dodecanedioate). Preliminary investigations have shown the potential of these polyesters to self-assemble in aqueous media forming nanoparticles, which can be loaded with hydrophobic molecules and released into an organic phase, acting as a phase transfer agent, and used as a pH-responsive emulsifier.

Harnessing the power of polyol-based polyesters for biomedical innovations: synthesis, properties, and biodegradation

Polyesters based on polyols have emerged as promising biomaterials for various biomedical applications, such as tissue engineering, drug delivery systems, and regenerative medicine, due to their biocompatibility, biodegradability, and versatile physicochemical properties. This review article provides an overview of the synthesis methods, performance, and biodegradation mechanisms of polyol-based polyesters, highlighting their potential for use in a wide range of biomedical applications. The synthesis techniques, such as simple polycondensation and enzymatic polymerization, allow for the fine-tuning of polyester structure and molecular weight, thereby enabling the tailoring of material properties to specific application requirements. The physicochemical properties of polyol-based polyesters, such as hydrophilicity, crystallinity, and mechanical properties, can be altered by incorporating different polyols. The article highlights the influence of various factors, such as molecular weight, crosslinking density, and degradation medium, on the biodegradation behavior of these materials, and the importance of understanding these factors for controlling degradation rates. Future research directions include the development of novel polyesters with improved properties, optimization of degradation rates, and exploration of advanced processing techniques for fabricating scaffolds and drug delivery systems. Overall, polyol-based polyesters hold significant potential in the field of biomedical applications, paving the way for groundbreaking advancements and innovative solutions that could revolutionize patient care and treatment outcomes.

Modification of Poly(Glycerol Adipate) with Tocopherol and Cholesterol Modulating Nanoparticle Self-Assemblies and Cellular Responses of Triple-Negative Breast Cancer Cells to SN-38 Delivery

This study aimed to fabricate new variations of glycerol-based polyesters by grafting poly(glycerol adipate) (PGA) with hydrophobic bioactive moieties, tocopherol (TOC), and cholesterol (CHO). Their effects on nanoparticle (NP) formation, drug release, and cellular responses in cancer and normal cells were evaluated. CHO and TOC were successfully grafted onto PGA backbones with 30% and 50% mole grafting. Increasing the percentage of mole grafting in both molecules increased the glass transition temperature and water contact angle of the final polymers but decreased the critical micelle concentration of the formulated particles. PGA-TOC NPs reduced the proliferation of MDA-MB-231 cancer cells. However, they enhanced the proliferation of primary dermal fibroblasts within a specific concentration range. PGA-CHO NPs minimally affected the growth of cancer and normal cells. Both types of NPs did not affect apoptosis or the cell cycle of cancer cells. PGA-CHO and PGA-TOC NPs were able to entrap SN-38, a hydrophobic anticancer drug, with a particle size <200 nm. PGA-CHO NPs had a higher drug loading capacity and a greater drug release than PGA-TOC NPs. However, SN-38-loaded PGA-TOC NPs showed higher toxicity than SN-38 and SN-38-loaded PGA-CHO NPs due to the combined effects of antiproliferation and higher cellular uptake. Compared with SN-38, the drug-loaded NPs more profoundly induced sub-G1 in the cell cycle analysis and apoptosis of cancer cells in a similar pattern. Therefore, PGA-CHO and PGA-TOC polymers have potential applications as delivery systems for anticancer drugs.

Poly (diglycerol adipate) variants as enhanced nanocarrier replacements in drug delivery applications

Sustainably derived poly(glycerol adipate) (PGA) has been deemed to deliver all the desirable features expected in a polymeric scaffold for drug-delivery, including biodegradability, biocompatibility, self-assembly into nanoparticles (NPs) and a functionalisable pendant group. Despite showing these advantages over commercial alkyl polyesters, PGA suffers from a series of key drawbacks caused by poor amphiphilic balance. This leads to weak drug-polymer interactions and subsequent low drug-loading in NPs, as well as low NPs stability. To overcome this, in the present work, we applied a more significant variation of the polyester backbone while maintaining mild and sustainable polymerisation conditions. We have investigated the effect of the variation of both hydrophilic and hydrophobic segments upon physical properties and drug interactions as well as self-assembly and NPs stability. For the first time we have replaced glycerol with the more hydrophilic diglycerol, as well as adjusting the final amphiphilic balance of the polyester repetitive units by incorporating the more hydrophobic 1,6-n-hexanediol (Hex). The properties of the novel poly(diglycerol adipate) (PDGA) variants have been compared against known polyglycerol-based polyesters. Interestingly, while the bare PDGA showed improved water solubility and diminished self-assembling ability, the Hex variation demonstrated enhanced features as a nanocarrier. In this regard, PDGAHex NPs were tested for their stability in different environments and for their ability to encode enhanced drug loading. Moreover, the novel materials have shown good biocompatibility in both in vitro and in vivo (whole organism) experiments.

CD44-Targeted Lipid Polymer Hybrid Nanoparticles Enhance Anti-Breast Cancer Effect of Cordyceps militaris Extracts

This study aimed to improve the anticancer effect of Cordyceps militaris herbal extract (CME) on breast cancer cells with hyaluronic acid (HYA) surface-decorated lipid polymer hybrid nanoparticles (LPNPs) and evaluate the applicability of a synthesized poly(glycerol adipate) (PGA) polymer for LPNP preparation. Firstly, cholesterol- and vitamin E-grafted PGA polymers (PGA-CH and PGA-VE, respectively) were fabricated, with and without maleimide-ended polyethylene glycol. Subsequently, CME, which contained an active cordycepin equaling 9.89% of its weight, was encapsulated in the LPNPs. The results revealed that the synthesized polymers could be used to prepare CME-loaded LPNPs. The LPNP formulations containing Mal-PEG were decorated with cysteine-grafted HYA via thiol-maleimide reactions. The HYA-decorated PGA-based LPNPs substantially enhanced the anticancer effect of CME against MDA-MB-231 and MCF-7 breast cancer cells by enhancing cellular uptake through CD44 receptor-mediated endocytosis. This study demonstrated the successful targeted delivery of CME to the CD44 receptors of tumor cells by HYA-conjugated PGA-based LPNPs and the new application of synthesized PGA-CH- and PGA-VE-based polymers in LPNP preparation. The developed LPNPs showed promising potential for the targeted delivery of herbal extracts for cancer treatment and clear potential for translation in in vivo experiments.

A road map on synthetic strategies and applications of biodegradable polymers

Biodegradable polymers have emerged as fascinating materials due to their non-toxicity, environmentally benign nature and good mechanical strength. The toxic effects of non-biodegradable plastics paved way for the development of sustainable and biodegradable polymers. The engineering of biodegradable polymers employing various strategies like radical ring opening polymerization, enzymatic ring opening polymerization, anionic ring opening polymerization, photo-initiated radical polymerization, chemoenzymatic method, enzymatic polymerization, ring opening polymerization and coordinative ring opening polymerization have been discussed in this review. The application of biodegradable polymeric nanoparticles in the biomedical field and cosmetic industry is considered to be an emerging field of interest. However, this review mainly highlights the applications of selected biodegradable polymers like polylactic acid, poly(ε-caprolactone), polyethylene glycol, polyhydroxyalkanoates, poly(lactide-co-glycolide) and polytrimethyl carbonate in various fields like agriculture, biomedical, biosensing, food packaging, automobiles, wastewater treatment, textile and hygiene, cosmetics and electronic devices.

Recent Advances in the Enzymatic Synthesis of Polyester

Polyester is a kind of polymer composed of ester bond-linked polybasic acids and polyol. This type of polymer has a wide range of applications in various industries, such as automotive, furniture, coatings, packaging, and biomedical. The traditional process of synthesizing polyester mainly uses metal catalyst polymerization under high-temperature. This condition may have problems with metal residue and undesired side reactions. As an alternative, enzyme-catalyzed polymerization is evolving rapidly due to the metal-free residue, satisfactory biocompatibility, and mild reaction conditions. This article presented the reaction modes of enzyme-catalyzed ring-opening polymerization and enzyme-catalyzed polycondensation and their combinations, respectively. In addition, the article also summarized how lipase-catalyzed the polymerization of polyester, which includes (i) the distinctive features of lipase, (ii) the lipase-catalyzed polymerization and its mechanism, and (iii) the lipase stability under organic solvent and high-temperature conditions. In addition, this article also focused on the advantages and disadvantages of enzyme-catalyzed polyester synthesis under different solvent systems, including organic solvent systems, solvent-free systems, and green solvent systems. The challenges of enzyme optimization and process equipment innovation for further industrialization of enzyme-catalyzed polyester synthesis were also discussed in this article.

Poly(Glycerol Succinate) as Coating Material for 1393 Bioactive Glass Porous Scaffolds for Tissue Engineering Applications

BACKGROUND

Aliphatic polyesters are widely used for biomedical, pharmaceutical and environmental applications due to their high biodegradability and cost-effective production. Recently, star and hyperbranched polyesters based on glycerol and ω-carboxy fatty diacids have gained considerable interest. Succinic acid and bio-based diacids similar to glycerol are regarded as safe materials according to the US Food and Drug Administration (FDA). Bioactive glass scaffolds utilized in bone tissue engineering are relatively brittle materials. However, their mechanical properties can be improved by using polymer coatings that can further control their degradation rate, tailor their biocompatibility and enhance their performance. The purpose of this study is to explore a new biopolyester poly(glycerol succinate) (PGSuc) reinforced with mesoporous bioactive nanoparticles (MSNs) as a novel coating material to produce hybrid scaffolds for bone tissue engineering.

METHODS

Bioactive glass scaffolds were coated with neat PGSuc, PGSuc loaded with dexamethasone sodium phosphate (DexSP) and PGSuc loaded with DexSP-laden MSNs. The physicochemical, mechanical and biological properties of the scaffolds were also evaluated.

RESULTS

Preliminary data are provided showing that polymer coatings with and without MSNs improved the physicochemical properties of the 1393 bioactive glass scaffolds and increased the ALP activity and alizarin red staining, suggesting osteogenic differentiation potential when cultured with adipose-derived mesenchymal stem cells.

CONCLUSIONS

PGSuc with incorporated MSNs coated onto 1393 bioactive glass scaffolds could be promising candidates in bone tissue engineering applications.

Polyglycerol Adipate-Grafted Polycaprolactone Nanoparticles as Carriers for the Antimicrobial Compound Usnic Acid

Nanoparticle (NP) drug delivery systems are known to potentially enhance the efficacy of therapeutic agents. As for antimicrobial drugs, therapeutic solutions against drug-resistant microbes are urgently needed due to the worldwide antimicrobial resistance issue. Usnic acid is a widely investigated antimicrobial agent suffering from poor water solubility. In this study, polymer nanoparticles based on polyglycerol adipate (PGA) grafted with polycaprolactone (PCL) were developed as carriers for usnic acid. We demonstrated the potential of the developed systems in ensuring prolonged bactericidal activity against a model bacterial species, Staphylococcus epidermidis. The macromolecular architecture changes produced by PCL grafted from PGA significantly influenced the drug release profile and mechanism. Specifically, by varying the length of PCL arms linked to the PGA backbone, it was possible to tune the drug release from a burst anomalous drug release (high PCL chain length) to a slow diffusion-controlled release (low PCL chain length). The developed nanosystems showed a prolonged antimicrobial activity (up to at least 7 days) which could be used in preventing/treating infections occurring at different body sites, including medical device-related infection and mucosal/skin surface, where Gram-positive bacteria are commonly involved.

Synthesis of Poly(glycerol butenedioate)-PGB-Unsaturated Polyester toward Biomedical Applications

A new polyester poly(glycerol butenedioate) (PGB) was obtained in the bulk polycondensation of glycerin and maleic anhydride. Glycerol polyesters are new biomaterials commonly used in tissue engineering. PGB, containing the α,β-unsaturated moiety, could be very interesting due to potential modifications such as additions or oxidation. Such modifications are not possible on the heretofore known glycerol polyesters due to their structure without α,β-unsaturated moieties. In this work, the developed process was optimized by applying the design of experiments. The optimization criterium was the minimization of the E/Z isomer ratio. Applying the two-stage process, the E/Z isomer ratio was reduced from 5.5 to 0.5 compared to the one-stage process. The degree of branching was also reduced from 17 to 9%, as well as the degree of esterification from 0.89 to 0.72. The obtained structure can be used in modifying or cross-linking via Michael additions.

Mechanism and Kinetics of Lipase-Catalyzed Polycondensation of Glycerol and Sebacic Acid: Influence of Solvent and Temperature

The mechanism for theCandida antacticalipase B (CALB)-catalyzed polycondensation of glycerol and sebacic acid in polar solvents was proposed based on the profile of formation and consumption of the glyceridic species in the reaction media and on the occurrence of the acyl migration reaction. The acyl migration is mainly responsible for the esterification of the secondary hydroxyl of glycerol and in an opposite way to the regioselective CALB-catalyzed esterification of primary hydroxyls. The enzymatic esterification of glycerol primary hydroxyls occurs preferentially up to carboxylic acid conversions of approximately 0.60-0.75 with rate constants in the range of 0.07-1.44 L mol^-1 h^-1, depending on the solvent. Above carboxylic acid conversions of 0.60-0.75, acyl migration occurs in parallel to enzymatic esterification with rate constants of approximately 0.04-0.12 h^-1 and is the rate-limiting step of the polymerization. The hydrogen bonding accepting ability of the solvents is the main parameter that dictates the enzymatic catalysis rate. However, the magnitude of the polymer-solvent interaction governs the polymer chain growth. Acetonitrile has a lower hydrogen bonding accepting ability and a less favorable polymer-solvent interaction compared with the other polymer-solvent pairs, and polycondensation achieves the highest enzymatic rate constant of approximately 0.84-1.44 L mol^-1 h^-1; however, low molar mass polymers with M_n = 1.4 kDa were formed. On the other hand, acetone has intermediate hydrogen bonding accepting ability and optimal intermediate polymer-solvent interactions and, therefore, an intermediate enzymatic rate constant of approximately 0.41-0.52 L mol^-1 h^-1, and the highest molar mass polymers with M_n = 4.9-9.4 kDa were obtained.

Lipase-Catalyzed Poly(glycerol-1,8-octanediol-sebacate): Biomaterial Engineering by Combining Compositional and Crosslinking Variables

This study examined poly(glycerol-1,8-octanediol-sebacate) (PGOS) copolymers with low-level substitution of O (1,8-octanediol) for G (glycerol) units (G/O ratios 0.5:0.5, 0.66:0.33, 0.75:0.25, 0.8:0.2, and 0.91:0.09) prepared in bulk by immobilized Candida antarctica Lipase B (N435) catalysis. The central question explored was the extent that exchanging less than half of poly(glycerol sebacate) (PGS) glycerol units with 1,8-octanediol can be used as a strategy to fine-tune biomaterial properties. Synthesized copolymers having G/O ratios of 0.66:0.33, 0.75:0.25, 0.8:0.2, and 0.91:0.09 have similar molecular weights, where M_w varied from 52,800 to 63,800 g/mol, M_n varied from 5100 to 6450 g/mol, and Đ_M (molecular mass dispersity, M_w/M_n) values were also similar (8.4-11.4). All of the copolymers were branched, and dendritic glycerol units reached 11% for PGOS-0.91:0.09:1.0. Analysis of DSC second heating scans revealed that copolymers with higher 1,8-octanediol contents have relatively higher T_m and ΔH_f values. Over the copolymer compositional range studied herein, T_m and ΔH_f values varied from 5.3 to 21.1 °C and 8.0 to 23.1 J/g, respectively. Stress-strain curves of PGOS copolymers cured at 140 °C for 48 h exhibited either a unimodal, bimodal, or trimodal response to tensile loading. Varying G/O from 10:1 to 2:1 resulted in significant increases in the peak stress (0.26-4.01 MPa), preyield modulus (0.65-62.59 MPa), failure to strain (64-110%), and failure toughness (0.1-0.56 MPa). This demonstrates that altering the G/O ratio over a narrow compositional range provides biomaterials with widely different yet tunable mechanical properties. Further investigation of PGOS-0.75:0.25:1.0 films revealed that varying the cure conditions from 120 to 160 °C for periods of 24-72 h provides access to biomaterials with a failure strain range from 15 to 224% and Young's modulus from 1.17 to 10.85 MPa. Hence, using the dual variables of compositional variation and changes in cure conditions provides an exciting platform for PGS analogues to optimize material-tissue interactions. Increased contents of 1,8-octanediol slowed in vitro degradation. Slowed degradation of PGOS relative to PGS will be valuable for use in slower healing wounds.

Delivery of acetogenin-enriched Annona muricata Linn leaf extract by folic acid-conjugated and triphenylphosphonium-conjugated poly(glycerol adipate) nanoparticles to enhance toxicity against ovarian cancer cells

The study demonstrated the fabrication of new poly(glycerol adipate) (PGA) nanoparticles decorated with folic acid (FOL-PGA) and triphenylphosphonium (TPP-PGA) and the potential on the delivery of acetogenin-enriched Annona muricata Linn leaf extract to ovarian cancer cells. FOL-PGA and TPP-PGA were successfully synthesized and used to fabricate FOL-decorated nanoparticles (FOL-NPs) and FOL-/TPP- decorated nanoparticles (FOL/TPP-NPs) by blending two polymers at a mass ratio of 1:1. All nanoparticles had small size of around 100 nm, narrow size distribution and high negative surface charge about -30 mV. The stable FOL/TPP-NPs showed highest drug loading of 14.9 ± 1.9% at 1:5 ratio of extract to polymer and reached to 35.8 ± 2.1% at higher ratio. Both nanoparticles released the extract in a biphasic sustained release manner over 5 days. The toxicity of the extract to SKOV3 cells was potentiated by FOL-NPs and FOL/TPP-NPs by 2.0 - 2.6 fold through induction of cell apoptosis. FOL/TPP-NPs showed lower IC₅₀ and higher cellular uptake as compared to FOL-NPs. FOL-NPs exhibited folate receptor-mediated endocytosis. FOL/TPP-NPs provided more advantages than FOL-NPs in terms of stability in physiological fluid, uptake efficiency and targeting ability to mitochondria and showed a promising potential PGA platform for targeted delivery of herbal cytotoxic extracts.

Microbial Transglutaminase-Mediated Formation of Erythropoietin-Polyester Conjugates

Erythropoietin (EPO) is a glycoprotein hormone that has been used to treat anemia in patients with chronic kidney disease and in cancer patients who are receiving chemotherapy. Here, we investigated the accessibility of the glutamine (Gln, Q) residues of recombinant human erythropoietin (rHuEPO) towards a thermoresistant variant microbial transglutaminase (mTGase), TG¹⁶ with the aim of developing novel rHuEPO conjugates that may potentially enhance its biological efficacy. As a model bioconjugation, we studied the reactivity of rHuEPO towards TG¹⁶ with a low molar mass amine group containing substrate, monodansyl cadaverine (MDC). The reactions were carried out at a T_m of 54.3 °C, the transition temperature of rHuEPO. Characterization by SDS-PAGE and mass spectrometry confirmed the conjugates formation. Then, we examined the conjugation of rHuEPO with a biodegradable and biocompatible polyester, poly(D-sorbitol adipate) (PDSA). To achieve this, PDSA was enzymatically synthesized using lipase B from Candida antartica (CAL-B), chemically modified with side chains having free primary amine (NH₂) groups that can be acyl acceptor substrate of TG¹⁶, thoroughly characterized by ¹H NMR spectroscopy, and then applied for the TG¹⁶-mediated conjugation reaction with rHuEPO. rHuEPO conjugates generated by this approach were identified by SDS-PAGE proving that the amine-grafted PDSA is accepted as a substrate for TG¹⁶. The successful conjugation was further verified by the detection of high molar mass fluorescent bands after labelling of amine-grafted PDSA with rhodamine B-isothiocyanate. Overall, this enzymatic procedure is considered as an effective approach to prepare biodegradable rHuEPO-polymer conjugates even in the presence of N- and O-glycans.

Lipase-Catalyzed Synthesis and Characterization of Poly(glycerol sebacate)

This study demonstrated that immobilized Candida antarctica lipase B (N435) catalysis in bulk leads to higher molecular weight poly(glycerol sebacate), PGS, than self-catalyzed condensation polymerization. Since the glass-transition temperature, fragility, modulus, and strength for rubbery networks are inversely dependent on the concentration of chain ends, higher molecular weight PGS prepolymers will enable the preparation of cross-linked PGS matrices with unique mechanical properties. The evolution of molecular species during the prepolymerization step conducted at 120 °C for 24 h, prior to enzyme addition, revealed regular decreases in sebacic acid and glycerol-sebacate dimer with corresponding increases in oligomers with chain lengths from 3 to 7 units such that a homogeneous liquid substrate has resulted. At 67 h, for N435-catalyzed PGS synthesis, the carboxylic acid conversion reached 82% without formation of a gel fraction, and number-average molecular weight (M_n) and weight-average molecular weight (M_w) values reached 6000 and 59 400 g/mol, respectively. In contrast, self-catalyzed PGS condensation polymerizations required termination at 55 h to avoid gelation, reached 72% conversion, and M_n and M_w values of 2600 and 13 800 g/mol, respectively. We also report the extent that solvent fractionation can enrich PGS in higher molecular weight chains. The use of methanol as a nonsolvent increased M_n and M_w by 131.7 and 18.3%, respectively, and narrower dispersity (Đ) decreased by 47.7% relative to the nonfractionated product.

Enzymatic Synthesis of Polyesters and Their Bioapplications: Recent Advances and Perspectives

This article reviews the most important advances in the enzymatic synthesis of polyesters. In first place, the different processes of polyester enzymatic synthesis, i.e., polycondensation, ring opening, and chemoenzymatic polymerizations, and the key parameters affecting these reactions, such as enzyme, concentration, solvent, or temperature, are analyzed. Then, the latest articles on the preparation of polyesters either by direct synthesis or via modification are commented. Finally, the main bioapplications of enzymatically obtained polyesters, i.e., antimicrobial, drug delivery, or tissue engineering, are described. It is intended to point out the great advantages that enzymatic polymerization present to obtain polymers and the disadvantages found to develop applied materials.

Achievements and Trends in Biocatalytic Synthesis of Specialty Polymers from Biomass-Derived Monomers Using Lipases

New technologies for the conversion of biomass into high-value chemicals, including polymers and plastics, is a must and a challenge. The development of green processes in the last decade involved a continuous increase of the interest towards the synthesis of polymers using in vitro biocatalysis. Among the remarkable diversity of new bio-based polymeric products meeting the criteria of sustainability, biocompatibility, and eco-friendliness, a wide range of polyesters with shorter chain length were obtained and characterized, targeting biomedical and cosmetic applications. In this review, selected examples of such specialty polymers are presented, highlighting the recent developments concerning the use of lipases, mostly in immobilized form, for the green synthesis of ε-caprolactone co-polymers, polyesters with itaconate or furan units, estolides, and polyesteramides. The significant process parameters influencing the average molecular weights and other characteristics are discussed, revealing the advantages and limitations of biocatalytic processes for the synthesis of these bio-based polymers.

Review on the Impact of Polyols on the Properties of Bio-Based Polyesters

Bio-based polyol polyesters are biodegradable elastomers having potential utility in soft tissue engineering. This class of polymers can serve a wide range of biomedical applications. Materials based on these polymers are inherently susceptible to degradation during the period of implantation. Factors that influence the physicochemical properties of polyol polyesters might be useful in achieving a balance between durability and biodegradability. The characterization of these polyol polyesters, together with recent comparative studies involving creative synthesis, mechanical testing, and degradation, have revealed many of their molecular-level differences. The impact of the polyol component on the properties of these bio-based polyesters and the optimal reaction conditions for their synthesis are only now beginning to be resolved. This review describes our current understanding of polyol polyester structural properties as well as a discussion of the more commonly used polyol monomers.

Mass spectrometry in bioresorbable polymer development, degradation and drug-release tracking

A detailed characterization of polymeric matrices and appropriate degradation monitoring techniques are required to sustain the development of new materials as well as to enlarge the applications of the old ones. In fact, polymer analysis is essential for the clarification of the intrinsic relationship between structure and properties that ascertains the industrial applications in diverse fields. In bioresorbable and biodegradable polymers, the role of analytical methods is dual since it is pointed both at the polymeric matrices and at degradation tracking. The structural architectures, the mechanical and morphological properties, and the degradation rate, are of outstanding importance for a specific application. In some cases, the complexity of the polymer structure, the processes of decomposition or the low concentration of the degradation products need the concurrent use of different complementary analytical techniques to give detailed information of the reactions taking place. Several analytical methods are used in bioresorbable polymer development and degradation tracking. Among them, mass spectrometry (MS) plays an essential role and it is used to refine polymer syntheses, for its high sensitivity, to highlight degradation mechanism by detecting compounds present in trace amounts, or to track the degradation product profile and to study drug release. In fact, elucidation of reaction mechanisms and polymer structure, attesting to the purity and detecting defects as well as residual catalysts, in biodegradable and bioresorbable polymers, requires sensitive analytical characterization methods that are essential in providing an assurance of safety, efficacy and quality. This review aims to provide an overview of the MS strategies used to support research and development of resorbable polymers as well as to investigate their degradation mechanisms. It is focused on the most significant studies concerning synthetic bioresorbable matrices (polylactide, polyglycolide and their copolymers, polyhydroxybutyrate, etc.), published in the last ten years.

Screening and Matching Polymers with Drugs to Improve Drug Incorporation and Retention in Nanoparticles

Key challenges hindering the clinical translation of the use of nanoparticles (NP) for delivery of drugs to tumors are inadequate drug loading and premature drug release. This study focused on understanding the conditions required to produce nanoparticles that can reach their target site with sufficient drug loading and drug retention for effective pharmacological action. Etoposide, etoposide phosphate, and teniposide were screened against modified poly(glycerol) adipate (PGA) based polymers by monitoring drug release from 40% drug in polymer films and using Fourier transform infrared spectroscopy (FTIR) and contact angle measurements to help understand the release results. Polymers were matched with the specific drugs based on the interactions observed. NP were then prepared by an interfacial deposition method. NPs were characterized and resulted in drug loadings ranging from 3.5% and 5%, respectively, for etoposide phosphate and etoposide with PGA modified with stearate (PGA85%C18) up to 13.4% for teniposide with PGA modified with tryptophan (PGA50%Try) and drug release of just 22-35% over 24 h. Assessment of cytotoxicity showed that etoposide nanoparticles with PGA85%C18 were more potent than an equivalent amount of free drug. This screening method to match polymers to drugs to monitor based drug and polymer interactions thus resulted in the formulation of nanoparticles with higher drug loading and slower release and potential for further development for clinical applications.

Starch/Poly(glycerol-adipate) Nanocomposites: A Novel Oral Drug Delivery Device

Biocompatible and bio-based materials are an appealing resource for the pharmaceutical industry. Poly(glycerol-adipate) (PGA) is a biocompatible and biodegradable polymer that can be used to produce self-assembled nanoparticles (NPs) able to encapsulate active ingredients, with encouraging perspectives for drug delivery purposes. Starch is a versatile, inexpensive, and abundant polysaccharide that can be effectively applied as a bio-scaffold for other molecules in order to enrich it with new appealing properties. In this work, the combination of PGA NPs and starch films proved to be a suitable biopolymeric matrix carrier for the controlled release preparation of hydrophobic drugs. Dynamic Light Scattering (DLS) was used to determine the size of drug-loaded PGA NPs, while the improvement of the apparent drug water solubility was assessed by UV-vis spectroscopy. In vitro biological assays were performed against cancer cell lines and bacteria strains to confirm that drug-loaded PGA NPs maintained the effective activity of the therapeutic agents. Dye-conjugated PGA was then exploited to track the NP release profile during the starch/PGA nanocomposite film digestion, which was assessed using digestion models mimicking physiological conditions. The collected data provide a clear indication of the suitability of our biodegradable carrier system for oral drug delivery.

Syntheses of high molecular weight hydroxy functional copolymers by green and selective polycondensation methods

Synthesizing hydroxy-functional linear copolymers with high molecular weights (M_n) and low branching degree (Den%) remains challenging, although there has been much headway in the area of functional copolymers. Here, we studied the effect of polymerization methods (one-step or two-step) and solvents (organic solvent: diphenyl ether or ionic liquids: [C_nmim]TF₂N/BF₄/PF₆, n = 2, 4, 6, 8, or 10) on M_n and Den% of copolymers P(OA–GA) (1,8-octanediol adipate (O-A)/glycerol adipate (G-A)). The M_n of P(OA–GA) reached up to 53 937 g mol⁻¹ in two-step in diphenyl ether, and the Den% of glycerol can be controlled within 30%. The physical properties of these copolymers were investigated by contact angles, differential scanning calorimetry (DSC), and in vitro biodegradation. With increasing glycerol content in the polyesters, both hydrophilic properties and degradation properties increased. This system not only facilitates the synthesis of functional polyesters with high molecular weight and low branching, but also expands the possibility of using bio-based monomers to synthesize functional polymers.

High molecular weight hydroxy functional copolymers have been synthesized by two-step polycondensation.

Polyglycerol Hyperbranched Polyesters: Synthesis, Properties and Pharmaceutical and Biomedical Applications

In a century when environmental pollution is a major issue, polymers issued from bio-based monomers have gained important interest, as they are expected to be environment-friendly, and biocompatible, with non-toxic degradation products. In parallel, hyperbranched polymers have emerged as an easily accessible alternative to dendrimers with numerous potential applications. Glycerol (Gly) is a natural, low-cost, trifunctional monomer, with a production expected to grow significantly, and thus an excellent candidate for the synthesis of hyperbranched polyesters for pharmaceutical and biomedical applications. In the present article, we review the synthesis, properties, and applications of glycerol polyesters of aliphatic dicarboxylic acids (from succinic to sebacic acids) as well as the copolymers of glycerol or hyperbranched polyglycerol with poly(lactic acid) and poly(ε-caprolactone). Emphasis was given to summarize the synthetic procedures (monomer molar ratio, used catalysts, temperatures, etc.,) and their effect on the molecular weight, solubility, and thermal and mechanical properties of the prepared hyperbranched polymers. Their applications in pharmaceutical technology as drug carries and in biomedical applications focusing on regenerative medicine are highlighted.

Poly (glycerol adipate) (PGA), an Enzymatically Synthesized Functionalizable Polyester and Versatile Drug Delivery Carrier: A Literature Update

The enzymatically synthesized poly (glycerol adipate) (PGA) has demonstrated all the desirable key properties required from a performing biomaterial to be considered a versatile “polymeric-tool” in the broad field of drug delivery. The step-growth polymerization pathway catalyzed by lipase generates a highly functionalizable platform while avoiding tedious steps of protection and deprotection. Synthesis requires only minor purification steps and uses cheap and readily available reagents. The final polymeric material is biodegradable, biocompatible and intrinsically amphiphilic, with a good propensity to self-assemble into nanoparticles (NPs). The free hydroxyl group lends itself to a variety of chemical derivatizations via simple reaction pathways which alter its physico-chemical properties with a possibility to generate an endless number of possible active macromolecules. The present work aims to summarize the available literature about PGA synthesis, architecture alterations, chemical modifications and its application in drug and gene delivery as a versatile carrier. Following on from this, the evolution of the concept of enzymatically-degradable PGA-drug conjugation has been explored, reporting recent examples in the literature.

Starch/Poly (Glycerol-Adipate) Nanocomposite Film as Novel Biocompatible Materials

Starch is one of the most abundant polysaccharides on the earth and it is the most important source of energy intake for humans. Thermoplastic starch (TPS) is also widely used for new bio-based materials. The blending of starch with other molecules may lead to new interesting biodegradable scaffolds to be exploited in food, medical, and pharmaceutical fields. In this work, we used native starch films as biopolymeric matrix carriers of chemo enzymatically-synthesized poly (glycerol-adipate) (PGA) nanoparticles (NPs) to produce a novel and biocompatible material. The prototype films had a crystallinity ranging from 4% to 7%. The intrinsic and thermo-mechanical properties of the composite showed that the incorporation of NPs in the starch films decreases the glass transition temperature. The utilization of these film prototypes as the basis for new biocompatible material showed promise, particularly because they have a very low or even zero cytotoxicity. Coumarin was used to monitor the distribution of the PGA NPs in the films and demonstrated a possible interaction between the two polymers. These novel hybrid nanocomposite films show great promise and could be used in the future as biodegradable and biocompatible platforms for the controlled release of amphiphilic and hydrophobic active ingredients.

Exploring the enzymatic degradation of poly(glycerol adipate)

Poly(glycerol adipate) (PGA) is a biodegradable, biocompatible, polymer with a great deal of potential in the field of drug delivery. Active drug molecules can be conjugated to the polymer backbone or encapsulated in self-assembled nanoparticles for targeted and systemic delivery. Here, a range of techniques have been used to characterise the enzymatic degradation of PGA extensively for the first time and to provide an indication of the way the polymer will behave and release drug payloads in vivo. Dynamic Light Scattering was used to monitor change in nanoparticle size, indicative of degradation. The release of a fluorescent dye, coupled to PGA, upon incubation with enzymes was measured over a 96 h period as a model of drug release from polymer drug conjugates. The changes to the chemical structure and molecular weight of PGA following enzyme exposure were characterised using FTIR, NMR and GPC. These techniques provided evidence of the biodegradability of PGA, its susceptibility to degradation by a range of enzymes commonly found in the human body and the polymer's potential as a drug delivery platform.

Multiple grafting to enzymatically synthesized polyesters

Enzymatic polymerization is an environmentally benign process for the synthesis of biodegradable and biocompatible polymers. The regioselectivity of lipase B from Candida Antarctica (CAL-B) produces linear functional polyesters without protection-deprotection steps. In this work, two different methods for the enzymatic synthesis of functional polyesters based on renewable resources, as, e.g., glycerol, using CAL-B are outlined. Poly(glycerol adipate) was synthesized by enzymatic transesterification between glycerol and divinyl adipate or dimethyl adipate. Methods are also reported to graft poly(glycerol adipate) with different amounts of hydrophobic side chains (lauric, stearic, behenic, and oleic acids) and hydrophilic poly(ethylene glycol) side chains, respectively. The hydrophilicity or lipophilicity of grafted polyesters is well controlled by changing the degree of grafting of hydrophilic and hydrophobic side chains. The multiple grafted polyesters are characterized by NMR spectroscopy, differential scanning calorimetry, gel permeation chromatography, and X-ray diffraction. Furthermore, the self-assembly of the graft copolymers in water and their use as steric stabilizers for cubosomes are discussed. For this purpose mainly dynamic light scattering and small angle X-ray scattering have been employed.

Enzymatic Synthesis of a Diene Ester Monomer Derived from Renewable Resource

The total or partial substitution of fossil raw materials by biobased materials from renewable resources is one of the great challenges of our society. In this context, the reaction under mild condition as enzyme-catalyzed esterification was applied to investigate the esterification of the biobased 10-undecenoic acid with 2-hydroxyethyl methacrylate (HEMA) to obtain a new diene ester monomer. The environmentally friendly enzymatic reaction presented up to 100% of conversion; moreover, the production of possible by-products was minimized controlling reaction time and amount of enzyme. Furthermore, the presence of chloroform was evaluated during the enzymatic reactions and despite high conversions with higher enzyme concentration, the solvent-free system showed fast kinetics even with 1.13 U/g substrates. In addition, the commercial immobilized lipases Novozym 435 and NS 88011 could be applied for up to 10 cycles keeping conversions about 90%. The scale-up of the reaction was possible and a purification procedure was applied in order to isolate the diene ester monomer 2-(10-undecenoyloxy)ethyl methacrylate, preserving its double bonds, which could allow a potential use of this product in the synthesis of new renewable polymers through techniques as metathesis, thiol-ene, or free-radical polymerization.