L-lysine Diisocyanate Research Articles

Breaking the boundaries of wound closure: A novel polyurethane tissue adhesive with enhanced healing properties.

Over the past few decades, there have been advancements in the development of high-performance tissue adhesives as alternatives to traditional sutures and staples for rapid and effective wound closure post-surgery. While tissue adhesives offer advantages such as ease of use, short application time, and minimal tissue damage, they also face challenges related to biocompatibility, biodegradability, and adhesive strength. In this study, L-lysine diisocyanate (LDI) and trimethylolpropane (TMP) were utilized as the primary raw materials to produce a prepolymer terminated with NCO, resulting in the development of a new biocompatible polyurethane tissue adhesive (TMP-LDI). Additionally, SiO2 nanoparticles were incorporated into the prepolymer, significantly enhancing the adhesive strength of the TMP-LDI tissue adhesive through the "nanobridging effect," achieving a strength of 170.4 kPa. Furthermore, the SiO2/TMP-LDI tissue adhesive exhibited satisfactory temperature change during curing and degradation performance. In vitro and in vivo studies demonstrated that SiO2/TMP-LDI exhibited good biocompatibility, efficient hemostasis, antimicrobial properties, and the ability to promote wound healing. This research presents a novel approach for the development of tissue adhesives with superior adhesive performance.

Investigating the structure and properties of polyurethane hydrogels with varying soft and hard segments

AbstractIn this study, polyurethane (PU) hydrogels were synthesized via mercapto curing reaction to elucidate the effect of molecular interactions between isocyanate and soft segments on the properties of hydrogels. Further, the mesh size, mechanical properties, hydrophilicity, and biological properties of the PU hydrogels were determined. In the isocyanate series, the structural regularity and rigidity of 4,4′‐dicyclohexylmethane diisocyanate (HMDI) favored the formation of hydrogel materials with small mesh size, high modulus, and low water absorption. In contrast, l‐lysine diisocyanate (LDI) favored the materials with large mesh size, low modulus, and good hydrophilicity. In the soft‐segment series, the strong hydrogen bonds of polycarbonate diol (PCDL) favored the formation of materials with small mesh size, dense cross‐link points, and high modulus, whereas weak hydrogen bonds of polytetrahydrofuran ether glycol (PTMG) favored the hydrogel materials with small mesh size, few crosslink points, and low modulus. PU hydrogels exhibit excellent cytocompatibility, anti‐cell adhesion, and anti‐inflammatory properties. Therefore, this study offers valuable insights into understanding the chain structure and macroscopic properties, thus contributing to preparing PU hydrogels with varying performances, as desired.

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.

Collagen/polyester-polyurethane porous scaffolds for use in meniscal repair.

Focusing on the regeneration of damaged knee meniscus, we propose a hybrid scaffold made of poly(ester-urethane) (PEU) and collagen that combines suitable mechanical properties with enhanced biological integration. To ensure biocompatibility and degradability, the degradable PEU was prepared from a poly(ε-caprolactone), L-lysine diisocyanate prepolymer (PCL di-NCO) and poly(lactic-co-glycolic acid) diol (PLGA). The resulting PEU (Mn = 52 000 g mol-1) was used to prepare porous scaffolds using the solvent casting (SC)/particle leaching (PL) method at an optimized salt/PEU weight ratio of 5 : 1. The morphology, pore size and porosity of the scaffolds were evaluated by SEM showing interconnected pores with a uniform size of around 170 μm. Mechanical properties were found to be close to those of the human meniscus (Ey ∼ 0.6 MPa at 37 °C). To enhance the biological properties, incorporation of collagen type 1 (Col) was then performed via soaking, injection or forced infiltration. The latter yielded the best results as shown by SEM-EDX and X-ray tomography analyses that confirmed the morphology and highlighted the efficient pore Col-coating with an average of 0.3 wt% Col in the scaffolds. Finally, in vitro L929 cell assays confirmed higher cell proliferation and an improved cellular affinity towards the proposed scaffolds compared to culture plates and a gold standard commercial meniscal implant.

Kinetic Analysis of the Reaction between Tannic Acid (TA) and L-Lysine Diisocyanate (LDI) Systems

The kinetics of the synthesis of green polyurethane from the reaction between tannic acid (TA) and L-lysine diisocyanate (LDI) were investigated using the differential scanning calorimeter (DSC) technique and dynamic rheological tests. The evaluation of the reaction behavior of the prepared samples was carried out using nonisothermal conditions at dynamic heating rates of 5, 10, 15, and 20°C/min. The evolution of the activation energy with conversion was computed through the five isoconversional methods of Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose (KAS), the Ozawa-Flynn-Wall method (OFW), Friedman (FR), Starink, and Vyazovkin. The average activation energy calculated from these methods was estimated at 46.5, 46.8, 47.2, 47.3, and 51.4 KJ/mol, respectively. The preexponential factor was evaluated at 5.04 × 10 5 1/s. The overall reaction order ( n + m ) was also found to be around 1.8912. The results of the combination of the model-free method and model-fitting approach exhibited that the reaction mechanism was an autocatalytic type, implying the autocatalytic effect of the urethane groups formed during the reaction. The obtained kinetic for TA/LDI was verified through its good agreement with the experimental data. Moreover, the results found from the isothermal rheological test show that with increasing temperature, the gelation time decreases.

Vanillin-Based Degradable Polyurethane Thermosets Demonstrating High Bio-Content and Mechanical Properties

Polyurethanes are widely used polymeric materials, but they are rarely biorenewable and degradable. Although some previously reported bio-based polyurethanes exhibit good thermal and mechanical properties, their bio-content is usually low, resulting from the only replacement of the diol monomer instead of the whole diol/diisocyanate pairs. In addition, traditional polyurethanes are often difficult to degrade, leading to environmental issues. To address these issues, we propose a solution by sourcing both the diols and isocyanates from biorenewable resources and introducing degradability into diols via the Tishchenko reaction, which is the disproportionation of two aldehydes to afford an ester bond with an atom economy of 100%. Commercially available bio-based vanillin was selected as the precursor for a vanillin-based diol (VBD) containing ester bonds. By reacting VBD with l-lysine diisocyanate (LDI) and trimethylolpropane (TMP) as a crosslinker, a series of bio-based thermosetting polyurethanes, VBD-TMPx, with high bio-based carbon content (>70.0%) were synthesized. The chemical structures and properties of monomers as well as polymers were characterized using nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and tensile tests. The obtained VBD-TMPx polyurethanes exhibit comparable mechanical properties (σ = 32.0 MPa; E′ = 2.7 GPa) to commercial thermosetting polyurethanes and demonstrate higher toughness (34 MJ/m3) than previously reported bio-based analogues. Additionally, the inherent ester bond in the VBD monomer enables the complete degradation of VBD-TMPx in a 0.1 M NaOH solution (THF/H2O = 1:1, v/v) within 3.5 h. This greatly broadens the available end-of-life choices, including the recovery of the monomers. This study presents a facile approach for creating degradable polyurethane materials with high bio-content and mechanical properties.

Nonwoven Mats Based on Segmented Biopolyurethanes Filled with MWCNT Prepared by Solution Blow Spinning.

To prepare nonwoven mats constituted by submicrometric fibers of thermally responsive biopolyurethanes (TPU) modified with multiwalled carbon nanotubes (MWCNT), solution blow spinning (SBS) was used. The TPU was the product of synthesis using poly(butylene sebacate)diol, PBSD, ethyl ester L-lysine diisocyanate (LDI), and 1,3-propanediol (PD) (PBSe:LDI:PD) as reactants. TPU was modified by adding different amounts of MWCNT (0, 0.5, 1, 2, and 3 wt.%). The effect of the presence and amount of MWCNT on the morphology and structure of the materials was studied using field-emission scanning electron microscopy (FESEM) and Fourier-transform infrared spectroscopy (FTIR), respectively, while their influence on the thermal and electric behaviors was studied using differential scanning calorimetry (DSC) and capacitance measurements, respectively. The addition of MWCNT by SBS induced morphological changes in the fibrous materials, affecting the relative amount and size of submicrometric fibers and, therefore, the porosity. As the MWCNT content increased, the diameter of the fibers increased and their relative amount with respect to all morphological microfeatures increased, leading to a more compact microstructure with lower porosity. The highly porous fibrous morphology of TPU-based materials achieved by SBS allowed turning a hydrophilic material to a highly hydrophobic one. Percolation of MWCNT was attained between 2 and 3 wt.%, affecting not only the electric properties of the materials but also their thermal behavior.

Diisocyanate-Induced Dynamic Vulcanization of Difunctional Fatty Acids toward Mechanically Robust PLA Blends with Enhanced Luminescence Emission

The toughening of poly(lactic acid) (PLA) often involves the use of nonbiodegradable or petrochemical elastomers owing to the lack of effective renewable alternatives and facile routes to tailor desirable morphologies. In this work, we developed a facile and universal dynamic vulcanization strategy of dual monomers to fabricate mechanically robust PLA blends. By increasing NCO/COOH equivalent ratios between l-lysine diisocyanate (LDI) and hydrogenated dimer acid (HDA) (i.e., nNCO,LDI/nCOOH,HDA) above 1.0:1, the phase structure of the resulting PLA blends transformed from the common “sea-island” morphology to partially or fully co-continuous ones. The extraordinary impact toughness (the maximum impact strength up to 109.8 kJ m–2) in combination with the balanced strength and stiffness was attributed to a continuous biopolyamide elastomer (HDAPA) with the simultaneous improvement in both the cross-linking level and interfacial compatibilization. Atomic force microscopy (AFM)-based nanomechanical mapping results suggested that the cross-linking of HDAPA domains gradually prevailed from the boundaries into the whole domains with the elevated nNCO,LDI/nCOOH,HDA ratios. The mechanisms regarding multiple reactions and co-continuity development at an ultralow concentration of the minor HDAPA phase were elucidated. Intriguingly, the enhanced clustering-triggered emission was observed for the PLA/HDAPA blends with a fully co-continuous structure.

Synthesis Characterization of Platinum (IV) Complex Curcumin Backboned Polyprodrugs: In Vitro Drug Release Anticancer Activity.

The conventional mono-chemotherapy still suffers from unsatisfied potency for cancer therapy due to tumor heterogeneity and the occurrence of drug resistance. Combination chemotherapy based on the nanosized drug delivery systems (nDDSs) has been developed as a promising platform to circumvent the limitations of mono-chemotherapy. In this work, starting from cisplatin and curcumin (Cur), we prepared a dual drug backboned shattering polymeric nDDS for synergistic chemotherapy. By in situ polymerization of the Cur, platinum (IV) complex-based prodrug monomer (DHP), L-lysine diisocyanate (LDI), and then conjugation with a hydrophilic poly (ethylene glycol) monomethyl ether (mPEG) derivative, a backbone-type platinum (IV) and Cur linkage containing mPEG-poly(platinum-co-Cur)-mPEG (PCPt) copolymer was synthesized. Notably, the platinum (IV) (Pt (IV)) and Cur were incorporated into the hydrophobic segment of PCPt with the fixed drugs loading ratio and high drugs loading content. The batch-to-batch variability could be decreased. The resulting prodrug copolymer then self-assembled into nanoparticles (PCPt NPs) with an average diameter around 100 nm, to formulate a synergetic nDDS. Importantly, PCPt NPs could greatly improve the solubility and stability of Cur. In vitro drug release profiles have demonstrated that PCPt NPs were stable in PBS 7.4, rapid burst release was greatly decreased, and the Pt and Cur release could be largely enhanced under reductive conditions due to the complete dissociation of the hydrophobic main chain of PCPt. In vitro cell viability test indicated that PCPt NPs were efficient synergistic chemotherapy units. Moreover, PCPt NPs were synergistic for cisplatin-resistant cell lines A549/DDP cells, and they exhibited excellent reversal ability of tumor resistance to cisplatin. This work provides a promising strategy for the design and synthesis of nDDS for combination chemotherapy.

Polyester urethane functionalizable through maleimide side-chains and cross-linkable by polylactide stereocomplexes

Sustainable multifunctional alternatives to fossil-derived materials, which can be functionalized and are degradable, can be envisioned by combining naturally derived starting materials with an established polymer design concept. Modularity and chemical flexibility of polyester urethanes (PEU) enable the combination of segments bearing functionalizable moieties and the tailoring of the mechanical and thermal properties. In this work, a PEU multiblock structure was synthesized from naturally derived L-lysine diisocyanate ethyl ester (LDI), poly(L-lactide) diol (PLLA) and N-(2,3-dihydroxypropyl)-maleimide (MID) in a one-step reaction. A maleimide side-chain (MID) provided a reactive site for the catalyst-free coupling of thiols shown for L-cysteine with a yield of 94%. Physical cross-links were generated by blending the PEU with poly(D-lactide) (PDLA), upon which the PLLA segments of the PEU and the PDLA formed stereocomplexes. Stereocomplexation occurred spontaneously during solution casting and was investigated with WAXS and DSC. Stereocomplex crystallites were observed in the blends, while isotactic PLA crystallization was not observed. The presented material platform with tailorable mechanical properties by blending is of specific interest for engineering biointerfaces of implants or carrier systems for bioactive molecules.

Development of Nontoxic Biodegradable Polyurethanes Based on Polyhydroxyalkanoate and L-lysine Diisocyanate with Improved Mechanical Properties as New Elastomers Scaffolds.

A nontoxic and biodegradable polyurethane was prepared, characterized, and evaluated for biomedical applications. Stretchable, biodegradable, and biocompatible polyurethanes (LPH) based on L-lysine diisocyanate (LDI) with poly(ethylene glycol) (PEG) and polyhydroxyalkanoates(PHA) of different molar ratios were synthesized. The chemical and physical characteristics of the LPH films are tunable, enabling the design of mechanically performance, hydrophilic, and biodegradable behavior. The LPH films have a Young’s modulus, tensile strength, and elongation at break in the range of 3.07–25.61 MPa, 1.01–9.49 MPa, and 102–998%, respectively. The LPH films demonstrate different responses to a change of temperature from 4 to 37 °C, with the swelling ratio for the same sample at equilibrium varying from 184% to 151%. In vitro degradation tests show the same LPH film has completely different degradation morphologies in pH of 3, 7.4, and 11 phosphate buffered solution (PBS). In vitro cell tests show feasibility that some of the LPH films are suitable for culturing rat bone marrow stem cells (rBMSCs), for future soft-tissue regeneration. The results demonstrate the feasibility of the LPH scaffolds for many biomedical applications.

Green Polyurethanes from Renewable Isocyanates and Biobased White Dextrins.

Polyurethanes (PUs) are an important class of polymers due to their low density and thermal conductivity combined with their interesting mechanical properties—they are extensively used as thermal and sound insulators, as well as structural and comfort materials. Despite the broad range of applications, the production of PUs is still highly petroleum-dependent. The use of carbohydrates in PU synthesis has not yet been studied extensively, even though, as multihydroxyl compounds, they can easily serve as crosslinkers in PU synthesis. Partially or potentially biobased di-, tri- or poly-isocyanates can further be used to increase the renewable content of PUs. In our research, PU films could be easily produced using two bio-based isocyanates—ethyl ester L-lysine diisocyanate (LLDI] and ethyl ester l-lysine triisocyanate (LLTI)—, one commercial isocyanate—isophorone diisocyanate (IPDI), and a bio-based white dextrin (AVEDEX W80) as a crosslinker. The thermal and mechanical properties are evaluated and compared as well as the stability against solvents.

Compatibility of banana starch nanocrystals/poly(butylene succinate) bio‐nanocomposite packaging films

ABSTRACTThis work focused on the effects of compatibility techniques [i.e., modification of filler and addition of an l‐lysine diisocyanate (LDI) coupling agent] and filler content on the properties of bio‐nanocomposite films prepared using poly(butylene succinate) (PBS) as a matrix and starch nanocrystals (SNC) as filler by chill‐roll cast film extrusion. The films reinforced with modified SNC had superior tensile and barrier properties than those reinforced with unmodified SNC or an added LDI. Elongation at break of 1%wt modified SNC/PBS film was increased up to 51.1% compared with neat PBS film. Water vapor transmission rate and oxygen transmission rate values of 9%wt modified SNC/PBS film (54.1 g m−2 day and 216.3 cc m−2 day) were lower than those of neat PBS film (114.5 g m−2 day and 560.3 cc m−2 day) due to the higher hydrophobicity and better dispersion of modified SNC in PBS leading to the superior properties of PBS films. The PBS bio‐nanocomposite films can be completely degraded within ~3 months under wastewater treatment condition. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46836.

High-Strain Shape-Memory Properties of Poly(Carbonate-Urea-Urethane)s Based on Aliphatic Oligocarbonates and L-Lysine Diisocyanate

ABSTRACTThe simultaneous capability of high-strain deformation and high shape recovery ratio constitutes a great challenge in design of the shape-memory polymers. Here we report on poly(carbonate-urea-urethane)s (PCUUs) synthesized by a precursor route, based on oligo(alkylene carbonate) diols, L-lysine diisocyanate (LDI), and water vapor. When programed with a strain of εprog = 800%, the PCUU networks exhibited a one-way shape-memory effect (1W-SME) with excellent shape fixity (> 97%) and shape recovery (> 99%) ratios. The switching temperatures (Tsw) varied between 50 and 56 °C and correlated to the melting transitions of the switching domains. The obtained PCUUs capable of high-strain are interesting candidate materials for degradable biomaterials as required in smart medical devices.

Hydrocortisone release from tablets based on bioresorbable poly(ether-ester-urethane)s

Bioresorbable linear poly(ether-ester-urethane)s with different hydrophilic characteristics were synthesized from triblock copolymers of poly(e-caprolactone)-poly(ethylene oxide)-poly(e-caprolactone) (PCL-PEO) as macrodiols, and L-lysine diisocyanate (LDI) or hexamethylenediisocyanate (HDI) were used as the required diisocyanates. Macrodiols were obtained by ring-opening polymerization (ROP) of e-caprolactone (CL). Polyurethanes were synthesized by the reaction of the triblock copolymers with LDI or HDI in solution using stannous 2-ethylhexanoate as catalyst. Polyurethane tablets were fabricated and investigated as prospective drug delivery systems. The effect of the PEO content on the polymers' performance as drug carriers was evaluated. It was found that water provoked more swelling and erosion of polymers with higher contents of PEO. The hydrocortisone release profiles were analyzed using the Ritger-Peppas approximation. An anomalous release behaviour (values of n higher than 0.5) was found for most of the analyzed samples.

Thermoplastic elastomers based on poly(l‐Lysine)‐Poly(ε‐Caprolactone) multi‐block copolymers

ABSTRACTNovel thermoplastic elastomers based on multi‐block copolymers of poly(l‐lysine) (PLL), poly(N‐ε‐carbobenzyloxyl‐l‐lysine) (PZLL), poly(ε‐caprolactone) (PCL), and poly(ethylene glycol) (PEG) were synthesized by combination of ring‐opening polymerization (ROP) and chain extension via l‐lysine diisocyanate (LDI). SEC and 1H NMR were used to characterize the multi‐block copolymers, with number‐average molecular weights between 38,900 and 73,400 g/mol. Multi‐block copolymers were proved to be good thermoplastic elastomers with Young's modulus between 5 and 60 MPa and tensile strain up to 1300%. The PLL‐containing multi‐block copolymers were electrospun into non‐woven mats that exhibited high surface hydrophilicity and wettability. The polypeptide–polyester materials were biocompatible, bio‐based and environment‐friendly for promising wide applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3012–3018

Mechanical Properties of Architectured Gelatin-Based Hydrogels on Different Hierarchical Levels

ABSTRACTPreparation of three-dimensionally architectured porous biomaterials can be achieved in a one-step process by stabilizing gelatin with L-lysine diisocyanate ethyl ester (LDI) in water. The reaction of gelatin with LDI in presence of water leads to the formation of oligourea bridges between gelatin molecules and oligourea chains grafted on gelatin. The number and the length of the bridges, as well as of the grafted chains strongly depend on the concentration of the LDI used for the stabilization, and this has huge influence on the mechanical properties of the material on different hierarchical levels. Higher LDI concentrations yield materials with increased deformation resistance in tensile tests due to the higher number of covalent and physical netpoints in the material. However, mechanical properties determined on the micro-level by AFM indentation showed the opposite trend, i.e. a decrease of Young’s modulus with increasing LDI content. This was interpreted by a decreasing number of shorter oligourea bridges between gelatin chains with decreasing LDI content.

Bio-based poly(urethane urea) dispersions with low internal stabilizing agent contents and tunable thermal properties

Poly(urethane urea)s dispersed in water were prepared from biobased monomers, including a fatty acid-derived diisocyanate (DDI), the lysine-derived ethyl ester l-lysine diisocyanate (EELDI) and 1,4:3,6-dianhydro-d-glucitol (isosorbide, IS). Ionic stabilization of the polymer particles in water was achieved by incorporating dimethylolpropionic acid (DMPA) in the polyurethane backbone. The synthesis of isocyanate-functional prepolymers with number-average molecular weights (Mn) of approximately 6000 g/mol was followed by their dispersion in water and chain extension using ethylene diamine. The chain extension procedure was optimized, resulting in final Mn values of approximately 17,000 g/mol. The replacement of DDI by EELDI and the incorporation of IS into the polymer composition effectively reduced the required amount of DMPA from 6.0 to 2.0 wt% to render stable dispersions and significantly enhanced the Tg values of dispersion-cast films to 60 °C (1st Tg) and to above 70 °C (2nd Tg), however, at the expense of slightly reduced thermal stability. The asymmetric structure of EELDI and its pendant ester group potentially facilitated the dispersion stability, the latter through possible (partial) hydrolysis. Accordingly, aqueous PU dispersions with a renewable content up to 97 wt% and sufficiently high, tunable film Tg values have been obtained.

Effect of diisocyanate linkers on the degradation characteristics of copolyester urethanes as potential drug carrier matrices

In this study, the effect of three aliphatic diisocyanate linkers, L-lysine diisocyanate ethyl ester (LDI), hexamethylene diisocyanate (HDI), and racemic 2,2,4-/2,4,4-trimethyl hexamethylene diisocyanate (TMDI), on the degradation of oligo[(rac-lactide)-co-glycolide] (64:36mol%) based polyester urethanes (PEU) was examined. Samples were characterized for their molecular weight, mass loss, water uptake, sequence structure, and thermal and mechanical properties. Compared to non-segmented PLGA, the PEU showed higher water uptake and generally degraded faster. Interestingly, the rate of degradation was not directly correlating with the hydrophilicity of the diisocyanate moieties; instead, competing intra-/intermolecular hydrogen bonds in between urethane moieties appear to substantially decrease the rate of degradation for LDI-derived PEU. By comparing microparticles (μm) and films (mm) as matrices of different dimensions, it was shown that autocatalysis remains a contributor to degradation of the larger-sized PEU matrices as it is typical for non-segmented lactide/glycolide copolymers. The shown capacity of lactide/glycolide-based multiblock copolymers to degrade faster than PLGA and exhibit improved elastic properties could be of interest for medical implants and drug release systems.

Enzymatic synthesis and preliminary evaluation as coating of sorbitol-based, hydroxy-functional polyesters with controlled molecular weights

By using a combination of bio-based monomers (sorbitol, 1,10-decanediol and a range of dicarboxylic acids), a series of novel sorbitol-based polyesters was prepared by solvent-free enzymatic polycondensation using an immobilized form of Candida antarctica lipase B (Novozyme 435). The aim was to prepare linear polyesters with pendant, curable hydroxyl groups along the polymer backbone. To achieve this, the polyester molecular weight was controlled by tuning the reaction time, enzyme loading and reaction stoichiometry. Extensive molecular and thermal characterization was performed, showing that the obtained polyesters were semi-crystalline materials with a low Tg. The presence of sorbitol in the polyesters was confirmed through a qualitative investigation using MALDI-ToF-MS. The quantification of the sorbitol content in the polymers was achieved by inverse-gated decoupling 13C NMR spectroscopy, while 31P NMR provided information regarding the selectivity of CALB for the primary vs. the secondary hydroxyl groups. Moreover, 31P NMR and potentiometric titration were utilized for the quantitative determination of the amount of carboxylic groups and hydroxyl functional groups present in the polyesters. The obtained hydroxyl-functional polyesters had suitable properties to be applied as solvent-borne coatings in terms of their molecular weight, functionality and thermal characteristics. Cross-linked coatings were prepared using different conventional curing agents, including two renewable diisocyanates (ethyl ester l-lysine diisocyanate and dimer fatty acid-based diisocyanate). The resulting poly(ester urethane) coatings were tested in terms of solvent resistance, hardness and resistance against rapid deformation, showing the beneficial effect of the implemented sorbitol on network formation.