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.

Poly(sebacic acid) microparticles loaded with azithromycin as potential pulmonary drug delivery system: Physicochemical properties, antibacterial behavior, and cytocompatibility studies

Recurrent bacterial infections are a common cause of death for patients with cystic fibrosis and chronic obstructive pulmonary disease. Herein, we present the development of the degradable poly(sebacic acid) (PSA) microparticles loaded with different concentrations of azithromycin (AZ) as a potential powder formulation to deliver AZ locally to the lungs. We characterized microparticle size, morphology, zeta potential, encapsulation efficiency, interaction PSA with AZ and degradation profile in phosphate buffered saline (PBS). The antibacterial properties were evaluated using the Kirby-Bauer method against Staphylococcus aureus. Potential cytotoxicity was evaluated in BEAS-2B and A549 lung epithelial cells by the resazurin reduction assay and live/dead staining. The results show that microparticles are spherical and their size, being in the range of 1-5 μm, should be optimal for pulmonary delivery. The AZ encapsulation efficiency is nearly 100 % for all types of microparticles. The microparticles degradation rate is relatively fast - after 24 h their mass decreased by around 50 %. The antibacterial test showed that released AZ was able to successfully inhibit bacteria growth. The cytotoxicity test showed that the safe concentration of both unloaded and AZ-loaded microparticles was equal to 50 μg/ml. Thus, appropriate physicochemical properties, controlled degradation and drug release, cytocompatibility, and antibacterial behavior showed that our microparticles may be promising for the local treatment of lung infections.

Different methods of synthesizing poly(glycerol sebacate) (PGS): A review

Poly(glycerol sebacate) (PGS) is a biodegradable elastomer that has attracted increasing attention as a potential material for applications in biological tissue engineering. The conventional method of synthesis, first described in 2002, is based on the polycondensation of glycerol and sebacic acid, but it is a time-consuming and energy-intensive process. In recent years, new approaches for producing PGS, PGS blends, and PGS copolymers have been reported to not only reduce the time and energy required to obtain the final material but also to adjust the properties and processability of the PGS-based materials based on the desired applications. This review compiles more than 20 years of PGS synthesis reports, reported inconsistencies, and proposed alternatives to more rapidly produce PGS polymer structures or PGS derivatives with tailor-made properties. Synthesis conditions such as temperature, reaction time, reagent ratio, atmosphere, catalysts, microwave-assisted synthesis, and PGS modifications (urethane and acrylate groups, blends, and copolymers) were revisited to present and discuss the diverse alternatives to produce and adapt PGS.

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.

Modulating nonlinear elastic behavior of biodegradable shape memory elastomer and small intestinal submucosa(SIS) composites for soft tissue repair

Structural repair of soft tissue for regenerative therapies can be advanced by developing biocompatible and bioresorbable materials with mechanical properties similar to the tissue targeted for therapy. Developing new materials modeling soft tissue mechanics can mitigate many limitations of material based therapies, specifically concerning the mechanical stress and deformation the material imposes on surrounding tissue structures. However, many elastomeric materials used in soft tissue repair lack the ability to be delivered through minimally invasive surgical (MIS) or transcatheter routes and require open surgical approaches for placement and application. We have developed a biocompatible and fully biodegradable shape memory elastomer, poly-(glycerol dodecanedioate) (PGD), which fulfills the requirements for hyperelasticity and exhibits shape memory behavior to serve as a novel substrate material for regenerative therapy in minimally invasive clinical procedures. Our previous work demonstrated control over the tangent modulus at 12.5% compressive strain between 1 and 3 MPa by increasing the crosslinking density in the polymer. In order to improve control over a broader range of mechanical properties, nonlinear behavior, and toughness, we 1) varied PGD physical crosslink density, 2) incorporated sheets of porcine small intestinal submucosa (SIS, Cook Biotech, Inc.) with varying thickness, and 3) mixed lyophilized SIS particulates into PGD at different weight percentages. Tensile testing (ASTM D412a) revealed PGD containing SIS sheets of were stiffer than controls (p < 0.01). Incorporating lyophilized SIS particulates into PGD increased the strain to failure (p < 0.001) compared to PGD controls. Test specimens with 1 ply sheets had greater tear strength (ASTM D624c) compared to PGD tear specimens prepared control specimens (p < 0.001). However, incorporating SIS particulates decreased tear strength of PGD-SIS 0.5 wt% particulate composites (p < 0.01) compared to PGD controls. Incorporating 2 ply and 4 ply sheets and 0.5 wt% particulates into PGD decreased the fixity and recovery of composite materials compared to controls (p < 0.01). Nonlinear modeling of stress strain curves under uniaxial tension demonstrated tunability of PGD-SIS composite materials to model various nonlinear soft tissues. These findings support the use of shape memory PGD-SIS composite materials towards the design of implantable devices for a variety of soft tissue regeneration applications by minimally invasive surgery.

Bio-Based Coatings for Food Metal Packaging Inspired in Biopolyester Plant Cutin

Metals used for food canning such as aluminum (Al), chromium-coated tin-free steel (TFS) and electrochemically tin-plated steel (ETP) were coated with a 2-3-µm-thick layer of polyaleuritate, the polyester resulting from the self-esterification of naturally-occurring 9,10,16-trihydroxyhexadecanoic (aleuritic) acid. The kinetic of the esterification was studied by FTIR spectroscopy; additionally, the catalytic activity of the surface layer of chromium oxide on TFS and, in particular, of tin oxide on ETP, was established. The texture, gloss and wettability of coatings were characterized by AFM, UV-Vis total reflectance and static water contact angle (WCA) measurements. The resistance of the coatings to solvents was also determined and related to the fraction of unreacted polyhydroxyacid. The occurrence of an oxidative diol cleavage reaction upon preparation in air induced a structural modification of the polyaleuritate layer and conferred upon it thermal stability and resistance to solvents. The promoting effect of the tin oxide layer in such an oxidative cleavage process fosters the potential of this methodology for the design of effective long-chain polyhydroxyester coatings on ETP.

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.

Elastomeric and pH-responsive hydrogels based on direct crosslinking of the poly(glycerol sebacate) pre-polymer and gelatin

The synthesis and biomedical applications of novel elastomeric, pH-responsive, biocompatible and biodegradable copolymer hydrogels based on poly(glycerol sebacate) and gelatin.

Synthesis of Glycerol-Based Biopolyesters as Toughness Enhancers for Polylactic Acid Bioplastic through Reactive Extrusion

The synthesis of polyesters based on glycerol, succinic acid [poly(glycerol succinate), PGS] and/or maleic anhydride [poly(glycerol succinate-co-maleate), PGSMA] was investigated aiming to produce a green product suitable for toughening of polylactic acid (PLA) using melt blending technologies. The molar ratio of reactants and the synthesis temperature were screened to find optimum synthesis conditions leading to the highest toughness enhancement of PLA. It was found that a molar ratio of reactants of 1:1 glycerol/succinic acid increases the effectiveness of PGS as a toughening agent for PLA, which correlates with the achievement of a higher molecular weight on the synthesis of PGS. The introduction of maleic anhydride as a comonomer for the synthesis of the partial replacement of succinic acid was advantageous for making PGS suitable for reactive extrusion (REX) mediated by free radical initiators. The tensile toughness of the REX PLA/PGSMA blends was improved by 392% compared with that of neat PLA, which was caused by the simultaneous cross-linking of PGSMA within the PLA matrix, and the in situ formation of PLA-g-PGSMA graft copolymers acting as interfacial compatibilizers. Two-dimensional nuclear magnetic resonance and Fourier transform infrared analysis confirmed the formation of PLA-g-PGSMA species on REX experiments. This in turn caused a decrease in the diameter of the PGS particles dispersed within the PLA matrix from >10 μm to approximately 2 μm as observed using scanning electron microscopy. A further increase of 1600% in the toughness of the blends was achieved by lowering the synthesis temperature of PGSMA from 180 to 150 °C. The optimum synthesis conditions for PGSMA leading to the highest increase in the toughness of 80/20 PLA/PGSMA blends were found to be 1:0.5:0.5 mol glycerol/succinic acid/maleic anhydride synthesized at a temperature of 150 °C for 5 h.

A conductive stretchable PEDOT-elastomer hybrid with versatile processing and properties

Herein we describe the use of vapour phase polymerisation (VPP) to form an elastomeric conducting hybrid, via the combination of poly(3,4-ethylene dioxythiophene) (PEDOT) and poly(glycerol sabecate) (PGS). The extent of PGS curing inversely affected the degree of PEDOT penetration in the material. At longer cure times, samples exhibited a negligible strain-resistance relationship. However, by reducing cure times and allowing greater penetration of PEDOT into PGS, more stable properties were observed over repeated deformation. The isolation of the PEDOT towards the surface allowed the use of laser engraving to pattern conducting tracks with ease. Such a benefit points to its potential for uninvolved, rapid manufacture of electrode arrays for biomedical devices or to allow precision cell interaction in tissue engineering.

Mechanical properties and degradation studies of poly(mannitol sebacate)/cellulose nanocrystals nanocomposites

Two pre-polymers with ad-mannitol : sebacic acid 1 : 1 and 1 : 2 ratios respectively were combined with cellulose nanocrystals (CNCs) and crosslinked applying different time–temperature profiles to obtain PMS/CNC nanocomposites with different properties.

Thermoresponsive, stretchable, biodegradable and biocompatible poly(glycerol sebacate)-based polyurethane hydrogels

This work reports the synthesis and characterization of thermoresponsive, stretchable, biodegradable and biocompatible poly(glycerol sebacate)-based polyurethane hydrogels.