Biocompatible Polyester Research Articles

Electrospun composite poly(lactic acid)/polyaniline nanofibers from low concentrations in CHCl3: Making a biocompatible polyester electro-active

Nanofibers of poly(lactic acid) (PLA) blended with polyaniline (PANi) were fabricated via electrospinning at much lower PLA concentrations (∼1wt%) in CHCl3 than reported before using a more efficient technique of preparing the solutions. The polymer nanofibers had diameters in the range 10 nm–300 nm. Nanofibers prepared with a 3 wt% PLA/PANi solution were conducting and were used to fabricate a diode which was electrically characterized and exhibited a low turn-on voltage and a rectification ratio of 500. The device characteristics were analyzed using the standard thermionic emission model of a Schottky junction and yielded an ideality factor of 1.6 and a barrier height of 0.49 eV. Using a simple circuit, the diode was able to rectify a low frequency alternating current signal with an efficiency of 10%. The ability to engineer insulating PLA into nanofibers that are electro-active extends the range of applications of this biocompatible and biodegradable polyester to include electronic devices that have reduced toxicity.

A New Strategy To Access Polymers with Aggregation-Induced Emission Characteristics

A highly efficient strategy for synthesizing the first biocompatible polyesters with AIE characteristics has been established via immortal ring-opening polymerizations of cyclic esters bearing nonluminophores. In the process, the large excess hydroxyl-modified AIE active compound, acting as the chain transfer agent, attaches to the active rare-earth metal catalyst via the rapid-reversible exchange reaction to initiate the polymerization. Thus, more polyester chains appear to grow from one active metal species, and the AIE fragments are incorporated into the polymer chains at specific sites, in situ. The resultant polyesters have linear, block, or star-shaped microstructures mimicking those of the modified AIE compounds. The polymerization solutions can be directly fabricated to large-area thin solid films. The obtained PLA, for instance, emits fluorescence in water/THF mixtures owing to aggregation, the intensity of which is 2850-fold stronger than that in THF solution. This strategy avoids complicated preparation of AIE-active monomers and/or usage of toxic metal reagents for catalyzing the coupling reactions in order to introduce AIE-active fragments, which provides a straightforward approach to access AIE active or other functional polymers from hardly modified monomers.

Crystallization Behaviors of Linear Polymers in Spin-coating Processes Traced by GISWAXS Measurements

The purpose of this study is clarification of crystallization behaviors of linear polymers in spin-coating film-forming processes on the molecular scale by time-resolved measurements of grazing-incidence small-angle and wide-angle X-ray scattering (GISAXS and GIWAXS: GISWAXS) measurements using synchrotron radiation. A sample used in this study was a commercially-available poly(3-hydroxybutyrate) (P3HB) (Sigma-Aldrich, Mw=437,000, Mw/Mn=1.67, Tg= 276 K) which was a biobased and biocompatible polyester. By spin-coating at rotational speeds of 1000 – 4000 rpm with using 0.49, 1.0, and 2.1wt% chloroform solutions of the P3HB, P3HB thin films with thicknesses of ca. 30 –600 nm were formed on silicon substrates. In these spin-coating processes at 296K, GISAXS and GIWAXS patterns from the sample on the substrate were simultaneously detected at BL45XU of SPring-8 (Hyogo, Japan). At the beginning of spin-coating, an isotropic scattering pattern from the solution was observed. Next, anisotropic Bragg reflections from oriented orthorhombic crystals of P3HB appeared and increased in intensity for several tens seconds. This indicated that P3HB chains crystallized as chloroform evaporated from the sample. It was also found that P3HB orthorhombic crystal having edge-on orientation was preferentially formed in thinner films. When the rotational speed of the substrate increased, the apparent induction period of crystallization slightly increased and the crystal growth rate decreased. This implied that the chain mobility of P3HB for crystallization might reduce due to a reduction in quantity of the solvent molecules and an increase in magnitude of the centrifugal force. These results obtained in this research would be important knowledge to improve film processing technologies for biobased polymeric materials.

Electrospinning/electrospraying vs. electrospinning: A comparative study on the design of poly(l-lactide)/zinc oxide non-woven textile

Abstract New hybrid fibrous materials from the biocompatible and biodegradable aliphatic polyester poly( l -lactide) (PLA) and pristine or surface-functionalized nanosized zinc oxide were prepared. The application of the techniques: (i) electrospinning of a suspension of ZnO in PLA solution, or (ii) simultaneous electrospinning of PLA solution and electrospraying of a ZnO suspension in PLA solution (at low PLA concentration) enabled the fabrication of hybrid materials of diverse design: non-woven textile consisting of fibers in which ZnO was deposited on the fibers’ surface (designated as type “on”) or was mainly in the fibers’ bulk (designated as type “in”). The photocatalytic activity of the new fibrous materials was estimated in respect to Methylene Blue (MB) and Reactive Red (RR) dyes. Type “on” hybrid materials had higher photocatalytic activity as compared to type “in” materials. It was shown that type “on” materials preserved their photocatalytic activity in respect to MB even after three repeated uses, while for the RR dye the same held true for ZnO-on-PLA mats only. The type “on” materials exhibited antimicrobial activity against the pathogenic microorganism Staphylococcus aureus as evidenced by the performed microbiological tests.

Microbial synthesis of functional homo-, random, and block polyhydroxyalkanoates by β-oxidation deleted Pseudomonas entomophila.

Functional polyhydroxyalkanoates (PHAs) allow chemical modifications to widen PHA diversity, promising to increase values of these biodegradable and biocompatible polyesters. Among functional PHAs, unsaturated PHA site chains can be easily grafted to add chemical groups, and to cross-link with other PHA polymer chains. However, it has been very difficult to obtain structurally controllable functional homo-, random, or block PHA. For the first time, a β-oxidation deleted Pseudomonas entomophila was used to successfully synthesize random copolymers of 3-hydroxydodecanoate (3HDD) and 3-hydroxy-9-decenoate (3H9D). Compositions of the random copolymers P(3HDD-co-3H9D) can be adjusted by ratios of dodecanoic acid (DDA) to 9-decenol (9DEO) fed to the culture of P. entomophila. Homopolymer P3H9D was formed when only 9DEO was added to the culture. Diblock copolymers of P3HDD-b-P3H9D were produced by feeding DDA as the first precursor to form a P3HDD block followed by adding 9DEO as the second precursor to form a second P3H9D block. It was demonstrated that random copolymers P(3HDD-co-3H9D) could be crossed-linked under UV-radiation due to the presence of the unsaturated bonds. Thermal and mechanical characterizations of the above homo-, random, and diblock PHA polymers were conducted. It was found that the diblock polymer P3HDD-b-P3H9D increased at least 2-fold on Young's modulus compared with its random copolymers consisting of similar 3HDD/3H9D ratios. This study demonstrates that PHA functionality could be controlled to meet various requirements.

Biocompatible multiblock aliphatic polyesters containing ether-linkages: influence of molecular architecture on solid-state properties and hydrolysis rate

A new class of biodegradable and biocompatible multiblock copolyesters containing butylene 1,4- cyclohexanedicarboxylate sequences is presented.

Development of poly(butylene succinate)/calcium phosphate composites for bone engineering

Bone tissue engineering offers the prospect of alternative therapies for clinically relevant skeletal defects. Poly(butylene succinate) (PBSu) is a biodegradable and biocompatible polyester which possesses some unfavorable biomaterial properties. In order to improve this limitation, we developed PBSu/hydroxyapatite (HA) and PBSu/β-tricalcium phosphate (TCP) composites to support the growth and osteogenic differentiation of human mesenchymal stem cells (hMSCs). The results showed that phase separation morphology of the composites were detected in both PBSu/HA and PBSu/TCP films where calcium phosphate (HA and TCP) dispersed thoroughly into PBSu. The addition of either HA or TCP increased the hydrophilicity of the resulting composites. All the materials appeared to be biocompatible and supported in vitro growth and osteoblast differentiation of hMSCs. In conclusion, the currently developed composite materials possess good biocompatibility and allow the growth and osteogenic differentiation of hMSCs in vitro, suggesting their potential application in stem cell-based bone engineering.

Functional Polyesters

SummaryThe present work aims to study the development of the production process of functionalized polyesters. By exploring materials produced by biological systems and modifying them by synthesis using renewable resources, a new class of biodegradable and biocompatible polyesters is being developed. The presence of specific functional groups opens up a wide range of possibilities for further modification of the polymer structure, and therefore of the respective final properties. Chemical modification of polyhydroxybutyrate (PHB) was carried out by partial glycolization to reduce the molecular weight. Subsequently esterification with maleic anhydride and glycols was performed to obtain unsaturated polyester backbones (UP). The UP was then blended with styrene and crosslinked with different initiating systems. The commercial PHB used possibly contained specific compounds to stabilize the polymer, which present an inhibitory effect on the radical polymerization. Moreover, characterization of this material and the functionalized products was performed as well as the optimization of the synthesis procedure.

Enhanced osteogenic activity of a poly(butylene succinate)/calcium phosphate composite by simple alkaline hydrolysis

Bone engineering offers the prospect of alternative therapies for clinically relevant skeletal defects. Poly(butylene succinate) (PBSu) is a biodegradable and biocompatible polyester which may possess some limitations in clinical use due to its hydrophobicity. In order to overcome these limitations and increase the bioactivity, a simple and convenient surface hydrolysis of PBSu, PBSu/hydroxyapatite and PBSu/β-tricalcium phosphate (TCP) films was performed. The resulting surfaces (i.e., HPBSu, HPBSu/HA and HPBSu/TCP) were tested for their physicochemical property, biocompatibility and osteogenic potency. The results showed that surface hydrolysis significantly increased surface roughness and hydrophilicity of the composites, with the HPBSu/TCP possessing the most pronounced results. All the materials appeared to be biocompatible and supported in vitro growth and osteoblast differentiation of hMSCs, and the alkaline hydrolysis significantly enhanced the hMSC cell proliferation and the osteogenic potency of PBSu/TCP compared with the non-hydrolyzed sample. In conclusion, the HPBSu/TCP possessed better hydrophilicity, biocompatibility and osteogenic potency in vitro, suggesting that this simple and convenient alkaline hydrolysis could be used to augment the biological property of PBSu-based composites for bone engineering in vivo.

The Analysis of Possibilities to Electrospin Nonwoven Mats from Pure PCL Nano/Micro Fibres

Electrospinning is a simple technique for the production of nano to micro scale fibers. Polycaprolactone (PCL) is biocompatible aliphatic polyester with many possible applications in the medical field. PCL nanofibres, produced by electrospinning, could provide new characteristics that are of interest for medical applications. The aim of this study is to estimate the influence of solvents, solution concentrations, distance between electrodes and stirring time of polymer solution on structure of electrospun PCL mats. To electrospun mats from PCL is possible, when PCL polymer is dissolved in chloroform and tetrahydrofuran solvents. It was investigated that structure of electrospun nonwoven mats from PCL nano, microfibers depends from the concentration of polymer solution. The distance between electrodes do not have influence on diameter of electrospun PCL nano/ microfibers, but has influence on structure of electrospun mats. Stirring time of PCL solution has no significant influence on structure of PCL electrospun mats, but it was noticed, that stirring time has influence on PCL nanofibers diameter. DOI: http://dx.doi.org/10.5755/j01.ms.19.3.1420

A prospective bifurcated biomedical stent with seamless woven structure

Bifurcated biomedical stents (BBSs) produced by three-dimensional tubular technology are typical substitutes for damaged tubular organs such as abdominal aorta branches, trachea branches, and esophagus branches in patients. They are generally made from thin cloth with stent-sutured method, by using manual loom or knitting loom. The existing BBSs may have some problems in busting strength, resistance to fatigue, porosity, and thickness. This paper proposes a novel method of performing design and fabrication for seamless woven BBSs with a modified rigid rapier-shuttle loom automatically. Seamless woven BBSs made from biocompatible polyester filaments were smoothly fabricated through the proposed method. The mechanical properties and water permeability of the resultant BBSs were analyzed by comparing commercial stents VP1200 K according to ISO 7198:1998. The result shows that the new BBS has better performance in terms of surface uniformity, mechanical properties, and water permeability.

Deep Eutectic Solvent-Assisted Synthesis of Biodegradable Polyesters with Antibacterial Properties

Bacterial infection related to the implantation of medical devices represents a serious clinical complication, with dramatic consequences for many patients. In past decades, numerous attempts have been made to develop materials with antibacterial and/or antifouling properties by the incorporation of antibiotic and/or antiseptic compounds. In this context, deep eutectic solvents (DESs) are acquiring increasing interest not only as efficient carriers of active principle ingredients (APIs) but also as assistant platforms for the synthesis of a wide repertoire of polymer-related materials. Herein, we have successfully prepared biodegradable poly(octanediol-co-citrate) polyesters with acquired antibacterial properties by the DES-assisted incorporation of quaternary ammonium or phosphonium salts into the polymer network. In the resulting polymers, the presence of these salts (i.e., choline chloride, tetraethylammonium bromide, hexadecyltrimethylammonium bromide, and methyltriphenylphosphonium bromide) inhibits bacterial growth in the early postimplantation steps, as tested in cultures of Escherichia coli on solid agar plates. Later, positive polymer cytocompatibility is expected to support cell colonization, as anticipated from in vitro preliminary studies with L929 fibroblasts. Finally, the attractive elastic properties of these polyesters permit matching those of soft tissues such as skin. For all of these reasons, we envisage the utility of some of these antibacterial, biocompatible, and biodegradable polyesters as potential candidates for the preparation of antimicrobial wound dressings. These results further emphasize the enormous versatility of DES-assisted synthesis for the incorporation, in the synthesis step, of a wide palette of APIs into polymeric networks suitable for biomedical applications.

Supercritical CO2 precipitation of poly(l-lactic acid) in a wide range of miscibility

Polymer microparticles are useful for numerous applications such as stationary phases in chromatography, adsorbents and catalyst supports, as well as for drug delivery systems. In recent decades the application of supercritical fluids for microparticle precipitation has been developed to a point where it is an ideal alternative to conventional processes. In this work poly(l-lactic acid) (PLLA), a biodegradable and biocompatible thermoplastic aliphatic polyester, has been processed using supercritical fluids, particularly by rapid expansion of supercritical solutions (RESS) and supercritical antisolvent (SAS) processes over a wide miscibility range. Particle morphology was greatly improved from irregular blocks to spherical microparticles on applying the SAS process. The effects of changes in polymer concentration, liquid flow rate, nozzle diameter, solvent, pressure and temperature have also been evaluated on the particle size of PLLA in the SAS precipitation. A higher concentration of the initial solution led to a decrease in particle size. Dichloromethane was the best of the chlorinated solvents investigated. The nozzle diameter had a negligible effect on particle size and the highest liquid flow rate gave the largest particle size. A larger particle size was also obtained on increasing the operating temperature. In contrast, the particle size decreased on increasing the operating pressure.

Tuning drug release in polyester thin films: terminal end-groups determine specific rates of additive-free controlled drug release

Modulating the drug release from polyester matrices independently of material properties would be beneficial to those designing biodegradable medical implants, such as drug delivery devices, stents and screws. However, the most common approaches use additives that often drastically alter the desired material properties. Recently, we have developed tools that allow gradient film formulations and high-throughput drug quantitation for the determination of parameter-specific correlations. We propose that modulated drug release can be obtained via additive-free mechanisms in polyesters by simply controlling polymer erosion through acidic terminal functional groups. Our results showed that drug release in poly(lactic-co-glycolic acid) (PLGA) formulations could be tuned to produce large ranges in drug release with relatively small changes in terminal acidic functional groups. For example, PLGA 53/47 thin films could be tuned to have 10–60% drug release at 14 days or 10–90% drug release at 20 days, depending on the PLGA/PLGA blend formulation and concentration of acidic terminal functional groups. A linear R-square correlation of up to 0.9 was observed for the acidic groups and percent drug release. Below a threshold of 1 part per thousand acidic groups, there was no increase in drug release, which has implications for polymer processing and film integrity. Biodegradable, biocompatible polyesters such as polyester poly(lactic-co-glycolic acid) (PLGA) are well suited to drug delivery: species ranging from small molecules to vaccines can be trapped within thin films or small particles of the material, and released on its degradation in the body. Control of the release rate is commonly achieved by incorporating additives to the polyester matrix, for example polyethylene glycol. However, this also affects other characteristics, such as the material's mechanical or swelling properties. To circumvent this issue, Terry Steele, Joachim Loo, Subbu Venkatraman and co-workers from Nanyang Technological University in Singapore have explored how the polyester's molecular weight and terminal functional groups could be used instead. Small variations in the PLGA terminal groups — replacing some of the standard ester group for more soluble carboxylic acid moieties — proved to have a significant effect on the material's degradation, and thus the release of drug molecules from thin films. Modulating the drug release from polyester matrices independently from the material properties would be beneficial to those designing biodegradable medical implants, such as drug delivery devices, stents and screws. We propose that modulated drug release can be obtained via an additive-free mechanism in polyesters by simply controlling polymer erosion through acidic terminal functional groups. The formulations can be tuned to produce large ranges in drug release with relatively small changes in terminal acidic functional groups. For example, poly(lactic-co-glycolic acid) (PLGA) 53/47 thin films could be tuned to have 10–90% drug release at 20 days, depending on the concentration of acidic terminal groups.

Second-generation functionalized medium-chain-length polyhydroxyalkanoates: the gateway to high-value bioplastic applications.

Polyhydroxyalkanoates (PHAs) are biodegradable biocompatible polyesters, which accumulate as granules in the cytoplasm of many bacteria under unbalanced growth conditions. Medium-chain-length PHAs (mcl-PHAs), characterized by C6-C14 branched monomer chains and typically produced by Pseudomonas species, are promising thermoelastomers, as they can be further modified by introducing functional groups in the side chains. Functionalized PHAs are obtained either by feeding structurally related substrates processed through the beta-oxidation pathway, or using specific strains able to transform sugars or glycerol into unsaturated PHA by de novo fatty-acid biosynthesis. Functionalized mcl-PHAs provide modified mechanical and thermal properties, and consequently have new processing requirements and highly diverse potential applications in emergent fields such as biomedicine. However, process development and sample availability are limited due to the toxicity of some precursors and still low productivity, which hinder investigation. Conversely, improved mutant strains designed through systems biology approaches and cofeeding with low-cost substrates may contribute to the widespread application of these biopolymers. This review focuses on recent developments in the production of functionalized mcl-PHAs, placing particular emphasis on strain and bioprocess design for cost-effective production.

Poly(L-lactic acid)/Hydroxyapatite Nanocylinders as Nanofibrous Structure for Bone Tissue Engineering Scaffolds

Poly (L-lactic acid) (PLLA), a biodegradable and biocompatible polyester, has been used as material of for tissue engineered scaffold and regenerative medicine. In this study, hydroxyapatite (HAp) and PLLA composite was electrospun. PLLA fibers were treated with an amino groups containing base in order to fabricate amino groups modified polymeric microcylinders. Simvastatin was loaded into the PLLA/HAp microcylinders. Our study focuses on the incorporation HAp and Simvastatin into the fibrous and cylindrical structure, its effects on the loading and release of simvastatin, and biological responses to osteoblast cells. The aspect ratio of microcylinders was tunable by varying the aminolysis treatment time and density of the base. The effects of the PLLA/HAp composites on osteoblast cell proliferation were evaluated. The PLLA/HAp may interact with osteoblast and obtain desired effects that were stimulating osteoblast function and restraining the osteoclast function for bone tissue regeneration. The potential of the developed composite microcylinders could be a promising way to fabricate the microfibrous structural scaffold that accelerates cell proliferation and functions for bone tissue engineering.

Heterogeneous mesoporous SBA-15 silica as catalyst towards the synthesis of various biodegradable aliphatic polyesters

Biocompatible and biodegradable polyesters have immense potential in medical applications as drug delivery vehicles and tissue engineering scaffolds. In this study, we synthesized biodegradable aliphatic polyesters, namely poly(butylene pimelate) (PBPi), poly(butylene succinate) (PBSu), and poly(butylene sebacate) (PBSe), by the polycondensation of equimolar quantities of dicarboxylic acid and diol using mesoporous SBA-15 silica as heterogeneous catalyst. We then compared its performance with a conventional homogenous catalyst, SnCl2·2H2O, which did not form these polymers. The synthesized SBA-15 catalyst was characterized by electron microscopy, nitrogen adsorption-desorption isotherm and infrared spectroscopy. The synthesized polyesters were evaluated using infrared spectroscopy, X-ray diffraction, nuclear magnetic resonance spectroscopy, differential scanning calorimetry, gel permeation chromatography, scanning electron microscopy and goniometry. The combined results demonstrate that the SBA-15 mesoporous catalyst formed higher molecular weight degradable polyesters in addition to higher yield and purity, thus confirming the superiority of the mesoporous silica catalyst for polymer formation. Open image in new window

Fabrication of well-controlled porous foams of graphene oxide modified poly(propylene-carbonate) using supercritical carbon dioxide and its potential tissue engineering applications

Poly(propylene carbonate) is a new amorphous, biodegradable and biocompatible aliphatic polyester. It has a potentially wide range of applications, such as packing materials and biomedical materials. However, the low glass transition temperatures (Tg) and poor mechanical property have limited its applications. In this paper, poly(propylene-carbonate)/graphene oxide nanocomposites with a 10°C increase in Tg and a 50 times increase in storage modulus at 30°C were firstly fabricated, then the nanocomposites were foamed using supercritical CO2 to widen their applications, particularly in the area of tissue engineering. It was demonstrated that the nanocomposite foams had good dimension stability and the final pore features were depended on supercritical CO2 saturation conditions. In addition, cytotoxicity and in vitro cell culturing tests of selected foams showed that the fabricated porous materials were non-cytotoxic and able to support cellular adhesion within the 3D structure, suggesting that these are promising materials for tissue engineering applications.

Recent Advances in the Production, Recovery and Applications of Polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polyesters that can potentially replace certain plastics derived from petroleum. PHAs can be produced using a combination of renewable feedstocks and biological methods. Native and recombinant microorganisms have been generally used for making PHAs via fermentation processes. As much as 90 % of the microbial dry mass may accumulate as PHAs. A range of PHAs has been produced using fermentation methods, including copolymers and block copolymers. Alternative production schemes based on genetically modified plants are becoming established and may become the preferred route for producing certain PHAs. Production in plants is likely to be inexpensive compared to production by fermentation, but it does not appear to be as versatile as microbial synthesis in terms of the range of products that may be generated. Cell-free enzymatic production of PHAs in vitro is receiving increasing attention and may become the preferred route to some specialty products. This review discusses the recent advances in production of polyhydroxyalkanoates by the various methods. Methods of recovering the polymer from microbial biomass are reviewed. Established and emerging applications of PHAs are discussed.

Reduction of suture associated inflammation using the novel biocompatible poly ester amide pseudo protein

Reduction of suture associated inflammation using the novel biocompatible poly ester amide pseudo protein