Biodegradable Thermoplastic Elastomers Research Articles

Stereocomplex formation of poly(l-lactide)-poly(ε-caprolactone) multiblock copolymers with Poly(d-lactide)

Stereocomplex formation is known to increase the melting temperature of poly(l-lactide) (PLLA). In this study, we investigate the stereocomplex formation of poly(l-lactide)-poly(ε-caprolactone) multiblock copolymers (PLLA-PCL MBCs) with poly(d-lactide) (PDLA). The stereocomplexed PLLA-PCL MBCs were readily synthesized by adding PDLA into PLLA-PCL MBCs solutions. X-ray diffraction and differential scanning calorimetry measurements indicate the preferential formation of stereocomplexes. Tensile moduli of PLLA-PCL MBCs increased after stereocomplex formation; however, they conserved their large elongation at break values even when the composition of hard segments (PLLA and PDLA) in the sample increased. The combination of high Young's modulus (>400 MPa) and large elongation (>400%) is high level reported for biodegradable thermoplastic elastomers. Dynamic mechanical analysis measurements suggest improved thermal-deformation stability in the stereocomplexes. Stereocomplex formation of PLLA-PCL random multiblock copolymers synthesized by the copolymerization of PLLA and PCL oligomers with PDLA also effectively increased the melting temperature and the Young's modulus. This simple strategy of adding PDLA into PLLA-segmented copolymers may be a useful method for the synthesis of any other stereocomplexed PLLA-segmented block copolymer.

Biodegradable Thermoplastic Elastomers Incorporating POSS: Synthesis, Microstructure, and Mechanical Properties

A need exists for biodegradable thermoplastic elastomers with tailorable mechanical and degradation properties. Toward meeting this need, we introduce a family of biodegradable thermoplastic elastomers that feature soft segments based on caprolactone–d,l-lactide or caprolactone–glycolide copolymers of low crystallinity, combined with a POSS-based hard segment with relatively low melting transition. Molecular characterization of the polyols and polyurethanes indicates good control over the composition and molecular weights, with high molecular weights for the polyurethanes, as desired. Thermal, mechanical, and microstructural characterization enabled establishment of structure–property relationships. Incorporation of two different comonomers was effective in diminishing soft segment crystallinity, positively impacting elasticity, while increasing POSS content proved effective in establishing thermally robust elastic behavior as well as mechanically reinforcing the polyurethanes. Prestraining the new thermo...

Thermoplastic polyester elastomer with controllable microstructure and biodegradability

Some aliphatic dibasic acid and dibasic alcohol were applied to synthesize the soft prepolyester and hard prepolyester by melting polycondensation, followed with chain extender methods to fabricate a series of biodegradable thermoplastic polyester elastomer (BTPE), which was identified by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H-NMR) and atomic force microscope (AFM). Experimental results showed that the BTPE has good mechanical properties with tensile strength up to 13 MPa while the elongation at break above 800%; the BTPE has good thermal stability with thermal decomposition temperature over 300°C and its melting point ( T m) over 100°C. Notably, the BTPE has good degradation properties, and the degree of degradation in lipase solution increases with the content of soft polyester increasing.

Synthesis and properties of ω-pentadecalactone-co-δ-hexalactone copolymers: a biodegradable thermoplastic elastomer as an alternative to poly(ε-caprolactone)

The copolymerization of ω-pentadecalactone with δ-hexalactone creates a new kind of low glass transition polyester that shows improved biodegradability and flexibility in comparison to poly(ε-caprolactone) (PCL).

The Synthesis of Hydroxybutyrate-Based Block Polyurethane from Telechelic Diols with Robust Thermal and Mechanical Properties

A series of novel amphiphilic block polyurethanes (PUHE) have been successfully synthesized by solution polymerization of the derived PHB-diol and poly(ethylene glycol) with a coupling agent of 1,6-hexamethylene diisocyanate (HDI), while the PHB-diol was prepared via the transesterification of PHB and ethylene glycol. The hydroxyl contents in PHB-diols range from 1.36 to 1.99 (the molar ratio) as determined by nonaqueous titration. The molecular weight and chemical compositions of PUHE and PHB-diol were investigated by GPC,1H NMR, and FTIR in detail, which confirm the successful synthesis of PUHE. The tensile strength and elongation at break of PUHE could reach as high as 20 MPa and 210%, as the content of PHB in PUHE is 33%. TGA curves indicate that block-bonding between PHB-diol and PEG increases the thermal stability of PHB-diol. Film degradation of PUHE was studied by weight loss and scanning electron microscope (SEM). It could be concluded that degradation occurred gradually from the surface to the inside and that the degradation rate could be controlled by adjusting the PHB/PEG ratios. These properties make PUHE able to be used as a biodegradable thermoplastic elastomer.

Synthesis of biodegradable thermoplastic elastomers from ε‐caprolactone and lactide

ABSTRACTThis article reports the synthesis and the properties of novel thermoplastic elastomers of A‐B‐A type triblock copolymer structure, where the hard segment A is poly(l‐lactide) (PLLA) and the soft segment B is poly(ε‐caprolactone‐stat‐d,l‐lactide) (P(CL‐stat‐DLLA)). The P(CL‐stat‐DLLA) block with DLLA content of 30 mol % was applied because of its amorphous nature and low glass transition temperature (Tg = approximately −40 °C). Successive polymerization of l‐lactide afforded PLLA‐block‐P(CL‐stat‐DLLA)‐block‐PLLAs, which exhibited melting temperature (Tm = approximately 150 °C) for the crystalline PLLA segments and still low Tg (approximately −30 °C) of the soft segments. The triblock copolymers showed very high elongation at break up to approximately 2800% and elastic properties. The corresponding d‐triblock copolymers, PDLA‐block‐P(CL‐stat‐DLLA)‐block‐PDLAs (PDLA = poly(d‐lactide)) were also prepared with the same procedure using d‐lactide in place of l‐lactide. When the PLLA‐block‐P(CL‐stat‐DLLA)‐block‐PLLA was blended with PDLA‐block‐P(CL‐stat‐DLLA)‐block‐PDLA, stereocomplex crystals were formed to enhance their Tm as well as tensile properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 489–495

Thermoplastic polyurethane elastomers from modified oleic acid

AbstractTwo novel potentially biodegradable thermoplastic polyurethane elastomers with unique structure and morphology were prepared from modified oleic acid. The hardness and mechanical properties were controlled by adjusting the soft segment concentration (SSC). Epoxidized methyl oleate was converted to methyl‐9‐ or −10‐hydroxystearate (hydroxystearate) by catalytic hydrogenation. The formed hydroxystearate was transesterified with 1,6‐hexanediol to obtain polyesterpolyol with molar mass 2500. Segmented polyurethanes with 50% and 70% SSC were prepared using the prepolymer method by reacting polyesterpolyol with diphenylmethane diisocyanate and 1,4‐butanediol as chain extender. Thermal and mechanical properties of the polymers indicated good micro‐phase separation. Both soft and hard segments displayed a certain degree of crystallization. Tensile strengths were 18 and 2.4 MPa for samples with 50% and 70% SSC, respectively. Elongations of 130% (50% SSC) and 43% (70% SSC) were somewhat lower than in comparable materials, presumably due to lower molar mass. © 2014 Society of Chemical Industry

Microstructural manipulation of electrospun scaffolds for specific bending stiffness for heart valve tissue engineering

Biodegradable thermoplastic elastomers are attractive for application in cardiovascular tissue construct development due to their amenability to a wide range of physical property tuning. For heart valve leaflets, while low flexural stiffness is a key design feature, control of this parameter has been largely neglected in the scaffold literature where electrospinning is being utilized. This study evaluated the effect of processing variables and secondary fiber populations on the microstructure, tensile and bending mechanics of electrospun biodegradable polyurethane scaffolds for heart valve tissue engineering. Scaffolds were fabricated from poly(ester urethane) urea (PEUU) and the deposition mandrel was translated at varying rates in order to modify fiber intersection density. Scaffolds were also fabricated in conjunction with secondary fiber populations designed either for mechanical reinforcement or to be selectively removed following fabrication. It was determined that increasing fiber intersection densities within PEUU scaffolds was associated with lower bending moduli. Further, constructs fabricated with stiff secondary fiber populations had higher bending moduli whereas constructs with secondary fiber populations which were selectively removed had noticeably lower bending moduli. Insights gained from this work will be directly applicable to the fabrication of soft tissue constructs, specifically in the development of cardiac valve tissue constructs.

Synthesis, characterization and degradation of biodegradable thermoplastic elastomers from poly(ester urethane)s and renewable soy protein isolate biopolymer

New biodegradable poly(ester urethane)/soy protein isolate (PEU/SPI) hybrids were prepared by in situ polymerization. The chemical incorporation of the SPI into the backbone chain of the PEU was facilitated by the reaction of the amine functional groups of SPI with methylene diphenyl diisocyanate (MDI). X-ray diffraction results showed that the chemical incorporation of SPI into PEU significantly changed the molecular structure of the PEU. The PEU/SPI hybrids exhibited higher thermal decomposition temperature and significant increase in the modulus compared with that of pure PEU. Microscopic examination of the morphology of PEU/SPI hybrids confirmed very fine and homogeneous SPI dispersion in PEU. The hydrolytic degradation of the PEU in a phosphate buffer solution was accelerated by incorporation of SPI, which was confirmed by water absorption and scanning electron microscopy of the samples after up to 10 weeks immersion in the buffer solution. This study provides a facile and innovative method of controlling the biodegradation rate of pure PEU with the additional advantage of environmentally-benign biodegradation of the hybrid PEU/SPI polymer, making the concept potentially widely applicable.

Biodegradable thermoplastic elastomer comprising PLLCA and CaCO3 whiskers: mechanical properties, thermal stability and shape memory properties

A biodegradable and thermoplastic elastomer—poly(L-lactide-co-e-caprolactone) (PLLCA)—was reinforced with 5, 10, 20, and 30 wt% of CaCO3 whiskers. We assessed the influence of the CaCO3 whisker content on the mechanical and thermal properties of the PLLCA/CaCO3 whisker composites. Scanning electron microscopy (SEM) revealed that the CaCO3 whiskers were uniformly distributed in the composite matrices. The results of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) showed that the glass transition temperatures (T g) of the composites increased slightly with increasing CaCO3 whisker content. At low CaCO3 whisker contents, the tensile strengths of the composites increased sharply with increasing CaCO3 content, the Young’s moduli also increased, and the elongation at break values gradually decreased. Thermogravimetric analysis (TGA) showed that the CaCO3 whiskers can promote the thermal degradation of PLLCA. Shape memory test results indicated that an appropriate amount of CaCO3 whiskers can improve the shape memory properties of PLLCA.

Synthesis of biodegradable thermoplastic elastomers (BTPE) based on ε-caprolactone

Aiming to mimic blood vessels, biodegradable thermoplastic elastomer (BTPE) is designed to be elastic, flexible and tough. A series of biodegradable triblock copolymers and poly(ester-urethanes) (PEU) based on e-caprolactone have been synthesized and studied. The crystallinity of the poly(e-caprolactone) used as soft segment has been disrupted by incorporating either L-lactide (L-LA) units or trimethylene carbonate (TMC) units. Our studies suggest that soft segment composition does affect the mechanical properties significantly.

Synthesis, characterization and properties of biodegradable poly(butylene succinate)‐block‐poly(propylene glycol) segmented copolyesters

AbstractBACKGROUND: To obtain a biodegradable thermoplastic elastomer, a series of poly(ester‐ether)s based on poly(butylene succinate) (PBS) and poly(propylene glycol) (PPG), with various mass fractions and molecular weights of PPG, were synthesized through melt polycondensation.RESULTS: The copolyesters were characterized using 1H NMR, gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, mechanical testing and enzymatic degradation. The results indicated that poly(ester‐ether)s with high molecular weights were successfully synthesized. The composition of the copolyesters agreed very well with the feed ratio. With increasing content of the soft PPG segment, the glass transition temperature decreased gradually while the melting temperature, the crystallization temperature and the relative degree of crystallinity decreased. Mechanical testing demonstrated that the toughness of PBS was improved significantly. The elongation at break of the copolyesters was 2–5 times that of the original PBS. Most of the poly(ester‐ether) specimens were so flexible that they were not broken in Izod impact experiments. At the same time, the enzymatic degradation rate of PBS was enhanced. Also, the difference in molecular weight of PPG led to properties being changed to some extent among the copolyesters.CONCLUSION: The synthesized poly(ester‐ether)s having excellent flexibility and biodegradability extend the application of PBS into the areas where biodegradable thermoplastic elastomers are needed. Copyright © 2009 Society of Chemical Industry

Preparation and characterization of biodegradable thermoplastic Elastomers (PLCA/PLGA blends)

A biodegradable elastomer (PLCA/PLGA blends) was prepared and characterized. First, poly(DL-lactide-co-e-caprolactone) (PLCA) and poly(DL-lactide-co-glycolide) (PLGA) were synthesized. Infrared (IR) spectroscopy, 1H nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC) were used to confirm the formation and structure of PLCA and PLGA. The solubility parameters of PLCA and PLGA were measured to estimate the miscibility between them. A series of PLCA/PLGA blends was prepared through solution blending. The morphology of all blends was examined by scanning electron microscope (SEM), and no obvious phase separation was detected at various ratios of PCLA and PLGA. Thermomechanical properties were characterized using thermogravimetry (TG), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA), the results showed that the PLCA/PLGA blends were a type of immiscible but compatible polymer blend. Mechanical properties, particularly stress-strain behavior, were examined; with an increase in PLGA content, the tensile strength and Young’s modulus of the blends increased dramatically, while elongation at break decreased.

Poly(CL/DLLA-b-CL) multiblock copolymers as biodegradable thermoplastic elastomers

Lactic acid and e-caprolactone based polymers and their derivates are widely used in biomedical applications. Different properties are introduced by modifying the composition. In this study, poly(e-caprolactone/D,L-lactide)-b-poly(ecaprolactone) multiblock copolymers were synthesized as poly(ester-urethane)s (PEUs) by polymerizing in two steps involving ring-opening polymerization of precursors and by diisocyanate linking of precursors to produce thermoplastic elastomers (TPEs). The precursors and products were characterized by SEC, 1H-NMR and DSC, and dynamic mechanical study (by dynamic mechanical analysis, DMA) as well as morphological characterization (by transmission electron microscopy, TEM) of the product TPEs was carried out. Tensile and creep recovery properties of them were also studied. According to the characterizations, all the polymerizations were successful, and the prepared TPEs showed clear elastic behavior. In the DMA scans, rubbery plateau in the storage modulus curves between Tg and terminal flow region was clearly detectable indicating elasticity. The TEM images demonstrated phase separation of amorphous and crystalline blocks when the degree of crystallinity of the hard blocks was high enough. The elongations of TPEs varied between 800–1800%, while the modulus was 7–66 MPa. Two different types of recovery tests indicated the creep properties of TPEs to be highly dependent on the degree of crystallinity.

Molecular Recognition in Poly(ε-caprolactone)-Based Thermoplastic Elastomers

The molecular recognition properties of the hydrogen bonding segments in biodegradable thermoplastic elastomers were explored, aiming at the further functionalization of these potentially interesting biomaterials. A poly(epsilon-caprolactone)-based poly(urea) 2 was synthesized and characterized in terms of mechanical properties, processibility and histocompatibility. Comparison of the data with those obtained from the structurally related poly(urethane urea) 1 revealed that the difference in hard segment structure does not significantly affect the potency for application as a biomaterial. Nevertheless, the small differences in hard block composition had a strong effect on the molecular recognition properties of the hydrogen bonding segments. High selectivity was found for poly(urea) 2 in which bisureidobutylene-functionalized azobenzene dye 3 was selectively incorporated while bisureidopentylene-functionalized azobenzene dye 4 was completely released. In contrast, the incorporation of both dyes in poly(urethane urea) 1 led in both cases to their gradual release in time. Thermal analysis of the polymers in combination with variable temperature infrared experiments indicated that the hard blocks in 1 showed a sharp melting point, whereas those in 2 showed a very broad melting trajectory. This suggests a more precise organization of the hydrogen bonding segments in the hard blocks of poly(urea) 2 compared to poly(urethane urea) 1 and explains the results from the molecular recognition experiments. Preliminary results revealed that a bisureidobutylene-functionalized GRGDS peptide showed more supramolecular interaction with the PCL-based poly(urea), containing the bisureidobutylene recognition unit, as compared to HMW PCL, lacking this recognition unit.

Effects of hydrolysis on a new biodegradable co-polymer

The aim of this study was to examine the feasibility of using a new low-modulus biodegradable thermoplastic elastomer for in vivo application as a stent cover. The new polymer, a thermoplastic elastomer, consists of a three-armed co-polymer of poly(lactide)acid (PLLA), poly(trimethylene carbonate) (PTMC) and poly(caprolactone) (PCL). A degradation study was performed in a buffer solution at 37°C for 4 and 6 weeks. The effect of degradation on mechanical properties was studied by stress-strain measurements and explained by using modulated DSC, GPC and mass measurements. A tapered block of PLLA and trimethylene carbonate connecting the crystalline outer part and the inner elastic part was highly susceptible to hydrolysis and caused rapid degradation and subsequent loss of mechanical properties. Random chain scission and homogenous hydrolysis resulted in a loss in mass and molecular weight. After 6 weeks of in vitro hydrolysis the molecular weight had decreased 54% and the elongation-at-break dropped from more than 300% to 90%. A medium free cell seeding study showed that endothelial cells adhered well to the polymeric material. An indicative animal study with the polymer acting as a stent cover showed very low levels of inflammation; however, pronounced neointima thickening was observed which was probably due to the premature failure of the material.

Zellproliferation und zelluläre Aktivität von Primärzellkulturen der Mundhöhle nach Oberflächenbesiedlung eines abbaubaren, thermoplastischen Blockcopolymers / Cell proliferation and cellular activity of primary cell cultures of the oral cavity after cell seeding on the surface of a degradable, thermoplastic block copolymer

Using standard cell biological and biochemical methods we were able to test the ability of a degradable, thermoplastic block copolymer to support the adhesion, proliferation, and the cellular activity of primary cell cultures of the oral cavity in vitro. The delicate balance between a group of endogenous enzymes, Matrix Metalloproteinases (MMPs), and their inhibitors (Tissue Inhibitor of MMPs, TIMPs) have a decisive function in the remodeling of the extracellular matrix during processes like wound healing or the integration of biomaterials in surrounding tissues after implantation. Recently developed, biodegradable thermoplastic elastomers with shape-memory properties may be the key to develop new therapeutical options in head and neck surgery. Primary cell cultures of the oral cavity of Sprague-Dawley rats were seeded on the surface of a thermoplastic block copolymer and on a polystyrene surface as control. Conditioned media of the primary cells were analyzed for MMPs and TIMPs after different periods of cell growth. The MMP and TIMP expression was analysed by zymography and a radiometric enzyme assay. No statistically significant differences in the appearance and the kinetic of MMP-1, MMP-2, MMP-9 and TIMPs were detected between cells grown on the polymer surface compared to the control. An appropriate understanding of the molecular processes that regulate cellular growth and integration of a biomaterial in surrounding tissue is the requirement for an optimal adaptation of biodegradable, polymeric biomaterials to the physiological, anatomical, and surgical conditions in vivo to develop new therapeutic options in otolaryngology and head and neck surgery.

Triblock Copolymers Based on 1,3‐Trimethylene Carbonate and Lactide as Biodegradable Thermoplastic Elastomers

AbstractSummary: Biodegradable triblock copolymers based on 1,3‐trimethylene carbonate (TMC) and different lactides (i.e. D,L‐lactide(DLLA), L‐lactide (LLA), D‐lactide (DLA)) designated as poly(DLLA‐TMC‐DLLA), poly(LLA‐TMC‐LLA) and poly(DLA‐TMC‐DLA) were prepared and their mechanical and thermal properties were compared with those of high molecular weight poly(TMC) and poly(TMC‐co‐DLLA) statistical copolymers. Triblock copolymers containing crystallizable LLA or DLA segments perform as thermoplastic elastomers (TPEs) when the poly(lactide) blocks are long enough to crystallize. In blends of poly(LLA‐TMC‐LLA) and poly(DLA‐TMC‐DLA) triblock copolymers, stereo‐complex formation between the enantiomeric poly(lactide) segments occurs as demonstrated by differential scanning calorimetry and light microscopy. These blends have good tensile properties and excellent resistance to creep under static and dynamic loading conditions.Permanent deformation (after 2 h recovery) of compression‐molded poly(TMC) and solvent‐cast poly(LLA‐TMC‐LLA) and poly(ST‐TMC‐ST) films.imagePermanent deformation (after 2 h recovery) of compression‐molded poly(TMC) and solvent‐cast poly(LLA‐TMC‐LLA) and poly(ST‐TMC‐ST) films.

Preparation and Properties of Poly(l-lactide)-block-poly(trimethylenecarbonate) as Biodegradable Thermoplastic Elastomer

Biodegradable ABA triblock copolymers of l-lactide and trimethylene carbonate with given compositions were prepared and chain-extended to produce high molecular weight polymer. The polymers were semicrystalline, and exhibited well microphase-segregated morphology with one crystalline poly(l-lactide) (PLLA) and the other soft and amorphous poly(trimethylene carbonate) (PTMC) block segments. The polymers could be cast into flexible and tough film, reversibly stretchable with elongation up to about 300%. This material may provide a novel thermoplastic elastomer possessing desirable properties including biodegradability, biocompatibility and good mechanical properties including two-phase morphology. Also a preliminary result on the hydrolytic degradation behavior was discussed.

Synthesis and characterization of hydroxy-terminated [RS]-poly(3-hydroxybutyrate) and its utilization to block copolymerization with l-lactide to obtain a biodegradable thermoplastic elastomer

A telechelic poly([RS]-3-hydroxybutyrate) ([RS]-PHB) was synthesized by the ring-opening polymerization of [RS]-β-butyrolactone (βBL) in the presence of 1,4-butanediol (BD) with distannoxane as the catalyst. This polymer was found to be terminated by secondary hydroxyl groups, having an (oxytetramethylen)oxy group in the main chain. It was subjected to block copolymerization with l-lactide by the catalysis of tin (II) octoate to obtain an A–B–A type triblock copolyester comprising poly(l-lactide) (A) and [RS]-PHB (B). In this block copolymerization, the molecular weight and the unit composition of the produced copolymer were successfully controlled by changing the l-lactide/[RS]-PHB ratio in feed. Its characterization revealed that this block copolymer has high potential for use as biodegradable thermoplastic elastomer.