PCL Segments Research Articles

Cartilage formation through alterations of amphiphilicity of poly(ethylene glycol)–poly(caprolactone) copolymer hydrogels

Hydrogels are of interest as scaffolds for cartilaginous tissue engineering due to their biocompatibility, swelling ratio, mechanical strength, and degradative behavior. This study was conducted to establish the most suitable poly(e-caprolactone)–poly(ethylene glycol)–poly(e-caprolactone) (PCL–PEG–PCL) triblock copolymer hydrogel for the optimal proliferation and differentiation of encapsulated chondrocytes for cartilage regeneration. PEG was copolymerized with PCL and then acrylated to confer photocrosslinking capacity. Chondrocytes were encapsulated within photocrosslinked triblock PEG-co-PCL hydrogels prepared with varying compositions. The effects of composition on the hydrogel properties and behavior of embedded cells were studied by varying the molecular weights, and thus the segment length, of the PEG and PCL blocks. Hydrogels with high-molecular-weight (10 000 Da) PEG were associated with higher swelling ratios (9.6 ± 0.2) and a reduced elastic modulus (0.223 ± 0.007 N mm−2). Biochemical analysis indicated a positive correlation between the swelling ratio and expression levels of glycosaminoglycans and total collagen. There was a 1.8-fold increase in glycosaminoglycan and 2.4-fold increase in total collagen content in hydrogels with the highest-molecular-weight (10 000 Da) PEG when compared to hydrogels with the low-molecular-weight (2000 Da) PEG after four weeks of culture. Histological examinations revealed more extensive collagen type II secretion and accumulation around chondrocytes when the molecular weight of the hydrophobic PCL segment increased. The lengths of the hydrophobic (PCL) and hydrophilic (PEG) segments resulted in changes in the properties of hydrogels that improved cellular proliferation and the production and distribution of extracellular matrix for cartilage regeneration.

Inorganic–Organic Shape Memory Polymer (SMP) Foams with Highly Tunable Properties

Thermoresponsive shape memory polymers (SMPs) are a class of smart materials that can return from a temporary to a permanent shape with the application of heat. Porous SMP foams exhibit unique properties versus solid, nonporous SMPs, enabling their utility in different applications, including some in the biomedical field. Reports on SMP foams have focused on those based on organic polymer systems. In this study, we have prepared inorganic-organic SMP foams comprising inorganic polydimethylsiloxane (PDMS) segments and organic poly(ε-caprolactone) PCL segments. The PCL segments served as switching segments to induce shape changing behavior whereas the length of the PDMS soft segment was systematically tuned. SMP foams were formed via the photochemical cure of acrylated (AcO) macromers AcO-PCL(40)-block-PDMS(m)-block-PCL(40)-OAc (m = 0, 20, 37, 66 and 130) using a revised solvent casting/particulate leaching (SCPL) method. By varying the PDMS segment length, PDMS-PCL foams having excellent shape memory behavior were obtained that exhibited highly tunable properties, including pore size, % porosity, compressive modulus, and degradation rate.

AB, BAB and (AB)3 poly(ε-caprolactone)-based block copolymers with functionalized poly(meth)acrylate segments

Linear and star-shaped poly(ε-caprolactone) (PCL) block copolymers containing poly(meth)acrylate segments with glycidyl, 2-(trimethylsilyloxy)ethyl and tert-butyl pendant groups were synthesized using mono-, di- and trifunctional PCL macroinitiators and appropriate (meth)acrylate monomers by controlled radical polymerization. The well-defined structures with narrow molecular weight distributions indicate the coexistence of semi-crystalline PCL and amorphous poly(meth)acrylic phases. The hydrophobic nature of the block copolymers can be easily converted to amphiphilic, which with biodegradable and biocompatible PCL segments are promising as polymeric carriers in drug delivery systems. © 2012 Society of Chemical Industry

Synthesis of pendent carboxyl-containing poly(ε-caprolactone-co-β-malic acid)-block-poly(l-lactide) copolymers for fabrication of nano-fibrous scaffolds

abstract Nano-fibrous scaffolds modified with biological peptides, which can mimic the physical and chemical characteristics of an extracellular matrix (ECM), have been considered good candidate matrices for cell culture in tissue engineering application. In this study, a series of semicrystalline block copolymers, specifically pendent carboxyl-containing poly(e-caprolactone-co-β-malic acid)-block-poly( l -lactide), were synthesized to fabricate nano-fibrous scaffolds via thermal induced liquid–liquid phase separation process. Random prepolymers P(CL-co-BMD) were first synthesized through ring-opening copolymerization of e-CL and 3(S)-[(benzyloxycarbony)methyl]-1,4-dioxane-2,5-dione (BMD) in the presence of dodecanol as initiator and stannous octoate(Sn(Oct)2) as catalyst. The terminal hydroxyl of P(CL-co-BMD)-OH was subsequently added to initiate the ring-opening of l -LA catalyzed by Sn(Oct)2. After deprotection, a series of block copolymers, poly(e-caprolactone-co-β-malic acid)-block-poly( l -lactide)(PCM-b-PLLA), were obtained and fabricated into nanofibrous scaffolds through thermally induced phase separation (TIPS) technique using tetrahydrofuran (THF) as solvent at a gelation temperature of −40 °C. The structure of the copolymers was characterized Nuclear Magnetic Resonance (1H NMR, 13C NMR), Gel Permeation Chromatography (GPC), and Differential Scanning Calorimetry (DSC). The crystallinity of the PCL segment generally decreased when the amount of BMD segment in P(CL-co-BMD) was increased. However, for PCM-b-PLLA, aside from the crystal melting peak of PLLA at 170 °C–180 °C, no indication of PCL section crystallization occurred because the crystallization of the PCL segment was interrupted by PLLA segment. The nanofiber size of the matrices was in the range of 180 nm–650 nm, similar to the architecture of ECM at the nanometer scale. These nanofibrous matrices have design potential to conjugate covalently to bioactive molecules for tissue engineering.

Synthesis, characterizations, and biocompatibility of block poly(ester‐urethane)s based on biodegradable poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB) and poly(ε‐caprolactone)

A type of block poly(ester-urethane)s (abbreviated as PUBC) based on bacterial copolyester poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3/4HB) and biodegradable poly(ε-caprolactone) (PCL) was synthesized by melting polymerization using 1,6-hexamethylene diisocyanate (HDI) as the coupling agent, with different 3HB, 4HB and PCL contents and segment lengths. Stannous octanoate (Sn(Oct)(2)) was used as catalyst. The chemical structure, molecular weight and thermal property were characterized by (1)H NMR, FTIR GPC, DSC and TGA. DSC analysis revealed that the PUBC polyurethanes exhibit amorphous to semi-crystalline (20.9% crystallinity degree) with T(g) range from -39.7 to -21.5 °C. The hydrophilicity was investigated by static contact angle of deionized water and CH(2)I(2). The obtained PUBCs are hydrophobic (water contact angle 73.7-90.2°). Platelet adhesion study and plasma recalcification time revealed that the block polyurethanes possess hemastasis ability. CCK-8 assay illuminated that the no cytotoxic polyurethanes maintain rat aortic smooth muscle cells (RaSMCs) good viability. It was found that the 4HB content in the materials is an important factor to affect the sustainable cell viability.

Multi-morphological self-assembled structures in water of a biodegradable β-cyclodextrin-based copolymer

A rigid-coil β-cyclodextrin-poly (ɛ-caprolactone) (CD-PCL) copolymer was synthesized in which biodegradable flexible multi PCL arms were selectively connected onto the wide side of the rigid torus-shaped β-CD through ring-opening polymerization (ROP) of ɛ-caprolactone (CL) and protection/deprotection technique of β-cyclodextrin (β-CD) via trimethylsilyl groups. 1H NMR, FT-IR, and GPC analysis confirmed the “jellyfish-like” branched architecture of CD-PCL copolymers. The self-assembled structures in water of the amphiphilic CD-PCL copolymer were investigated by transmission electron microscopy (TEM), dynamic light scattering (DLC) and viscometry. The results showed that CD-PCL could self-assemble into multi-morphological aggregates such as spheres, rods, vesicles, vesicular clusters and vesicular network in water. Interestingly, hierarchical stripe structure was observed in the formed vesicular network, which was driven by the crystallization of PCL segment in micelles. Moreover, the inclusion ability of copolymer micelles with ferrocenecarboxylic acid was investigated by UV.

Rheological and thermal properties of glycidyl azide polyol‐based energetic thermoplastic polyurethane elastomers

AbstractThe purpose of this study was to investigate the effects of polyol on glycidyl azide polyol (GAP)‐based energetic thermoplastic polyurethane elastomers (ETPEs). Briefly, a series of GAP/polyol‐based ETPEs (GAP/polyol ETPEs) with different copolyol ratios and hard segment contents were synthesized using GAP‐diol with common polyol and 4,4‐methylenebis(phenylisocyanate)‐extended 1,5‐pentanediol as soft and hard segments, respectively, by solution polymerization in dimethylformamide. The three types of polyols used were poly(tetramethylene ether) glycol (PTMG), polycarbonate‐diol (PCL‐diol) and polycaprolactone‐diol (PCD‐diol). The synthesized GAP/polyol ETPEs were identified and characterized using Fourier transform infrared and 1H NMR spectroscopy, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and rheometric mechanical spectrometry. For GAP/PCL ETPEs with lower hard segment content, DSC results showed that the GAP segment failed to interact with either the PCL segment or PCL melting. In addition, the results of DMA showed that the presence of PCL segments in ETPEs improved the storage modulus below the melting temperature of the PCL block. Further, the crystalline PCL segments were attributed to reinforcing the ETPEs in a manner similar to that of the hard domain. As the hard segment content increased in the GAP/polyol ETPEs, both GAP/PTMG ETPEs and GAP/PCL ETPEs exhibited microphase separation transitions, while rheological experiments demonstrated a sudden decrease in complex viscosity in neighboring microphase separation transitions. © 2012 Society of Chemical Industry

Novel Biodegradable and Double Crystalline Multiblock Copolymers Comprising of Poly(butylene succinate) and Poly(ε-caprolactone): Synthesis, Characterization, and Properties

A series of double crystalline multiblock copolymers composed of poly(butylene succinate) (PBS) and poly(ε-caprolactone) (PCL) have been successfully synthesized with hexamethylene diisocyanate (HDI) as a chain extender. The copolymers were systematically characterized by 1H NMR, GPC, TGA, DSC, WAXD, and mechanical testing. The results indicate that the PBS segment is immiscible with the PCL segment in the amorphous region. The copolymers follow a two-stage degradation behavior, and thermal stability increases with increasing PBS content. PBS and PCL in the copolymers crystallize and melt separately. The mechanical properties of the copolymers can be conveniently adjusted from rigid plastics to flexible elastomers by changing the feed composition. The impact strength is substantially improved by the incorporation of the PCL segment.

Synthesis and characterization of new biodegradable comb‐dendritic triblock copolymers

AbstractA series of well‐defined dumbbell‐shaped triblock copolymers consisting of linear poly(ethylene glycol) (PEG) and comb‐like poly(ε‐caprolactone) (PCL) with varied PCL arm lengths have been synthesized via the sequential preparation of different generation terminal dendronized PEG and ring‐opening polymerization of ε‐caprolactone. The copolymers were characterized using Fourier transform infrared, 1H NMR and 13C NMR spectroscopy and gel permeation chromatography. Differential scanning calorimetry was performed to measure the glass transition temperature, melting point and degree of crystallinity and the PEG segment and PCL segment crystallization temperatures. The crystallization of the copolymers was also studied using X‐ray diffraction. The dumbbell‐shaped copolymers were further used to construct microspheres using a double emulsion method. Scanning electron microscopy and dynamic light scattering results showed the size of the microspheres was about 2 to 4 µm and the size distribution was quite narrow. Copyright © 2012 Society of Chemical Industry

Synthesis, crystalline morphologies, self‐assembly, and properties of H‐shaped amphiphilic dually responsive terpolymers

AbstractNovel and well‐defined amphiphilic H‐shaped terpolymers poly(L‐lactide)‐block‐(poly(2‐(N,N‐dimethylamino)ethyl methacrylate) ‐block‐)poly(ε‐caprolactone)(‐block‐poly(2‐(N,N‐dimethylamino)ethyl methacrylate)) ‐b‐poly(L‐lactide) (PLLA‐b‐(PDMAEMA‐b‐)PCL(‐b‐PDMAEMA)‐b‐PLLA) were synthesized by the combination of ring‐opening polymerization, atom transfer radical polymerization, and click chemistry. The H‐shaped amphiphilic terpolymers can self‐assemble into spherical nano‐micelles in water. Because of the dually responsive (temperature and pH) properties of PDMAEMA segments, the hydrodynamic radius of the micelles of the H‐shaped terpolymer solution can be adjusted by altering the environmental temperature or pH values. The thermal properties investigation and the crystalline morphology analysis indicate that the branched structure of the H‐shaped terpolymers and the presence of amorphous PDMAEMA segments together led to the obvious decrease of PCL segments and the complete destruction of crystallinity of the PLLA segments in the H‐shaped terpolymers. In addition, the H‐shaped terpolymer film has better hydrophilicity than linear PCL or triblock polymer of PLLA‐b‐(N3)PCL(N3)‐b‐PLLA, due to the decrease or destruction of the crystallizability of the PCL or PLLA in the H‐shaped terpolymer and the presence of hydrophilic PDMAEMA segments. These unique H‐shaped amphiphilic terpolymers composed of biodegradable and biocompatible PCL and PLLA components and intelligent and biocompatible PDMAEMA component will have the potential applications in biomedical fields. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Hierarchical Mesoporous Silica Fabricated from an ABC Triblock Terpolymer as a Single Template

Hierarchical mesoporous silicas containing two kinds of mesoporous size are successfully synthesized using the simple evaporation-induced self-assembly (EISA) strategy. Two blocks of hydrophobic segments (PE and PCL) in the poly(ethylene-block-ethylene oxide-block-ϵ-caprolactone) (PE-PEO-PCL) triblock copolymer are involved in the two types of mesopore after calcination, the PE segment being attributed to the face-centered cubic (fcc) morphology (spherical pores) and the PCL segment attributed to the tetragonal cylinder structure (cylindrical pores).

An injectable biodegradable temperature-responsive gel with an adjustable persistence window

ɛ-Caprolactone (CL) and 3-benzyloxymethyl-6-methyl-1,4-dioxane-2,5-dion (fLA), with a benzyloxymethyl group at the 3-position of the lactide, were randomly copolymerized. The methoxy polyethylene glycol (MPEG)-b-[poly(ɛ-caprolactone)-ran-poly(3-benzyloxymethyl lactide) (PCL-ran-PfLA)] diblock copolymers were designed such that the PfLA content (0–15 mol%) in the PCL segment was varied. The MPEG-b-(PCL-ran-PfLA) diblock copolymers were derivatized by introducing a pendant benzyl group (MCxLy-OBn), hydroxyl group (MCxLy-OH), or carboxylic acid group (MCxLy-COOH) at the PfLA segment. The derivatized MPEG-b-(PCL-ran-PfLA) diblock copolymer solutions exhibited sol-to-gel phase transitions upon a temperature increase. The sol-to-gel phase transition depended on both the type of functional pendant group on the PfLA and the PfLA content in the PCL segment. MCxLy-COOH diblock copolymer solutions formed gels immediately after injection into Fischer rats. The gels gradually degraded over a period of 0–6 weeks after the initial injection, and the rate of degradation increased for higher concentrations of PfLA. Immunohistochemical characterization showed that the in vivo MPEG-b-(PCL-ran-PfLA) diblock copolymer gels provoked only a modest inflammatory response. These results show that the MPEG-b-(PCL-ran-PfLA) diblock copolymer gel described here may serve as a minimally invasive therapeutic, in situ-forming gel system with an adjustable temperature-responsive and in vivo biodegradable window.

Modifying the Hydrophilic–Hydrophobic Interface of PEG-b-PCL To Increase Micelle Stability: Preparation of PEG-b-PBO-b-PCL Triblock Copolymers, Micelle Formation, and Hydrolysis Kinetics

A set of PEG-b-PBO-b-PCL triblock copolymers were prepared for comparative studies of micelle formation and relative stability compared to the parent PEG-b-PCL diblock copolymers. Block copolymers that were characterized by 1H NMR and GPC were self-assembled in water by nanoprecipitation from organic solvents. Spherical micelles produced in near-quantitative yield were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The initial step in degradation of the block copolymers assembled in spherical micelles is shown by GPC and 1H NMR in acidic media to occur by hydrolysis of the interface ester group which cleaves the PCL segment in the core from the -PBOPEG and -PEG segments. Kinetics of hydrolysis of the ester groups that bind the hydrophobic PCL segment with either PEG or PBO units were followed by 1H NMR and demonstrate that the triblock has a reduced rate of hydrolysis. Inserting a short block of PBO between the PEG and PCL segments provides increased protection...

The degradation and biocompatibility of pH-sensitive biodegradable polyurethanes for intracellular multifunctional antitumor drug delivery

To obtain controllable stepwise biodegradable polymer for multifunctional antitumor drug carriers, pH-sensitive biodegradable polyurethanes were firstly synthesized using poly(ε-caprolactone) (PCL) and pH-sensitive poly(ε-caprolactone)–hydrazone–poly(ethylene glycol)–hydrazone–poly(ε-caprolactone) macrodiol (PCLH) as soft segment; l-lysine ethyl ester diisocyanate (LDI), l-lysine derivative tripeptide and 1,4-butandiol (BDO) as hard segment; and hydrazone-linked methoxyl-poly(ethylene glycol)(m-PEG-Hyd) as end-capper. Then, an extensive degradation process of the prepared pH-sensitive polyurethanes was investigated in vitro with proton nuclear magnetic resonance spectra (1H NMR), gel permeation chromatograph (GPC), scanning electron microscopy (SEM), and weight loss. It was found that the degradation of these polyurethanes occurred via the random hydrolytic ester cleavage along the PCL segments close to PEG segments in enzymatic solutions while the hydrazone bond in the polymer chain was more easily cleaved in acidic media, which was accelerated with decreasing pH value. Furthermore, the biocompatibility in vivo was evaluated in an intramuscular implantation model on Sprague–Dawley rats, using SEM and light microscopy. The result showed that the prepared polyurethanes can be easily degraded and the degradation products do not induce any adverse response from surrounding muscle tissues. Our work suggests that the prepared pH-sensitive polyurethanes could be promising materials as controllable biodegradable and non-cyctotoxic multifunctional carriers for active intracellular drug delivery.

Controlled thermal gelation of poly(ε-caprolactone)/poly(ethylene glycol) block copolymers by modifying cyclic ether pendant groups on poly(ε-caprolactone)

The control of the thermal gelation behavior of amphiphilic copolymers based on PEGylated hydrophobic polymers is important for applications in drug administration and controlled release. This paper studied a new method to control the thermal gelation behavior of the amphiphilic copolymers by structure modification of hydrophobic segments. A kind of triblock copolymer of PEG and modified poly(e-caprolactone) (PCL) with cyclic ether pendant groups, i.e. poly(e-caprolactone-co-1,4,8-trioxa[4.6]spiro-9-undecanone)-poly(ethylene glycol)-poly(e-caprolactone-co-1,4,8-trioxa[4.6]spiro-9-undecanone) triblock copolymers (PECT) were synthesized through the ring-opening copolymerization of e-caprolactone and 1,4,8-trioxa[4.6]spiro-9-undecanone (TOSUO) in the presence of poly(ethylene glycol). The structure and thermal gelation behavior of PECT were characterized by 1H NMR, FT-IR, GPC, XRD, DSC and DLS, etc. The study results indicated that the introduction of cyclic ether pendant groups on the PCL backbone not only reduced the crystallinity of PCL but also increased the hydrophilicity of the hydrophobic phase, which provides perfect dispersity of PECT in water and allows a more excellently controlled thermal gelation behavior than the PCL-PEG-PCL block copolymer. PECT powder can directly disperse in water to form a stable nanoparticle aqueous dispersion even with a high content of hydrophobic block (the weight ratio of PCL to PEG is nearly 3). Further, the PECT nanoparticle aqueous dispersion at higher concentration performed sol–gel–sol transition behavior with the temperature increasing from ambient or lower temperature, and the transition temperature and gelation behavior could be adjusted by the content of the cyclic ether pendant groups on the PCL segments. Significantly, avoiding the pre-quenching treatment that is needed for PCL-PEG-PCL gelation, the PECT nanoparticle aqueous dispersions, which are injectable fluids at ambient temperature and form a gel at 37 °C quickly, provide an injectable in situ gel system for clinical applications with the advantages of convenient dosage, administration, storage, and prescription. Therefore, the PECT thermal hydrogel system is expected to have potential applications in drug delivery and tissue engineering.

Dual-responsive crown ether-based supramolecular chain extended polymers

Based on the benzo-21-crown-7 (B21C7)/secondary ammonium salt molecular recognition motif, dual-responsive supramolecular chain extended polymers with a biodegradable poly(ε-caprolactone) (PCL) chain as the scaffold were successfully prepared by self-assembly of a heteroditopic macromonomer which was synthesized by a combination of ring-opening polymerization and click reaction. 1H NMR spectroscopy, FT-IR, solution viscometry, diffusion NMR and differential scanning calorimetry were employed to characterize these novel supramolecular chain extended polymers. Due to the environmental responsiveness of the recognition of the B21C7 host unit to the secondary ammonium salt guest moiety, the supramolecular chain extended polymers respond to pH and cation stimuli. The crystallization behavior of the PCL segments of the supramolecular chain extended polymers and the neutral counterpart were investigated by polarized optical microscopy. The B21C7/secondary ammonium salt host–guest interactions cause a decrease of the chain mobility of PCL and make the crystallization rate of PCL much slower in comparison with the case of the neutral counterpart.

Synthesis of functionalizable and biodegradable polymers via ring‐opening polymerization of 5‐benzyloxy‐trimethylene carbonate and ε‐caprolactone

AbstractThe biomedical applications of poly(ε‐caprolactone) (PCL) were limited for its high hydrophobicity and crystallinity. In this study, we copolymerized CL with amorphous 5‐hydroxyl‐trimethylene carbonate (HTMC) to solve the problem. The 5‐benzyloxy‐trimethylene carbonate (BTMC) was synthesized to copolymerize with CL, then hydrogenolyzed to obtain hydroxyl pendant groups. A serial of copolymers with different BTMC molar ratio were synthesized and their chemical structures and thermal properties were thoroughly studied with NMR, FT‐IR, GPC, XRD, DSC, and TGA. Finally we examined the water contact angle of the copolymers. DSC and XRD results showed that the PCL segments in the copolymers crystallized below 16.8%. BTMC molar content and the crystallinity of the copolymers increased after hydrolysis. With the introduced hydroxyl pendant groups, the deprotected copolymers improved their hydrophilic property significantly, and the copolymer with 9.3% HTMC molar content had static water contact angle as low as 36.5°. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Biodegradable Polyurethane Ureas with Variable Polyester or Polycarbonate Soft Segments: Effects of Crystallinity, Molecular Weight, and Composition on Mechanical Properties

Biodegradable polyurethane urea (PUU) elastomers are ideal candidates for fabricating tissue engineering scaffolds with mechanical properties akin to strong and resilient soft tissues. PUU with a crystalline poly(ε-caprolactone) (PCL) macrodiol soft segment (SS) showed good elasticity and resilience at small strains (<50%) but showed poor resilience under large strains because of stress-induced crystallization of the PCL segments, with a permanent set of 677 ± 30% after tensile failure. To obtain softer and more resilient PUUs, we used noncrystalline poly(trimethylene carbonate) (PTMC) or poly(δ-valerolactone-co-ε-caprolactone) (PVLCL) macrodiols of different molecular weights as SSs that were reacted with 1,4-diisocyanatobutane and chain extended with 1,4-diaminobutane. Mechanical properties of the PUUs were characterized by tensile testing with static or cyclic loading and dynamic mechanical analysis. All of the PUUs synthesized showed large elongations at break (800-1400%) and high tensile strength (30-60 MPa). PUUs with noncrystalline SSs all showed improved elasticity and resilience relative to the crystalline PCL-based PUU, especially for the PUUs with high molecular weight SSs (PTMC 5400 M(n) and PVLCL 6000 M(n)), of which the permanent deformation after tensile failure was only 12 ± 7 and 39 ± 4%, respectively. The SS molecular weight also influenced the tensile modulus in an inverse fashion. Accelerated degradation studies in PBS containing 100 U/mL lipase showed significantly greater mass loss for the two polyester-based PUUs versus the polycarbonate-based PUU and for PVLCL versus PCL polyester PUUs. Basic cytocompatibility was demonstrated with primary vascular smooth muscle cell culture. The synthesized families of PUUs showed variable elastomeric behavior that could be explained in terms of the underlying molecular design and crystalline behavior. Depending on the application target of interest, these materials may provide options or guidance for soft tissue scaffold development.

Synthesis, characterization, and properties of tunable thermosensitive amphiphilic dendrimer-star copolymers with Y-shaped arms

Novel and well-defined amphiphilic dendrimer-star copolymer poly(e-caprolactone)-block-(poly(2-(2-methoxyethoxy)ethylmethacrylate-co-oligo(ethylene glycol) methacrylate))2 with Y-shaped arms were synthesized by the combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The investigation of thermal properties and the analysis of crystalline morphology indicate that the high-branched structure of dendrimer-star copolymers with Y-shaped arms and the presence of amorphous P(MEO2MA-co-OEGMA) segments together led to the complete destruction of crystallinity of the PCL segments in the dendrimer-star copolymer. In addition, the hydrophilicity–hydrophobicity transition of the dendrimer-star copolymer film can be achieved by altering the external temperatures. The amphiphilic copolymers can self-assemble into spherical nanomicelles in water. Because the lower critical solution temperature of the copolymers can be adjusted by varying the ratio of MEO2MA and OEGMA, the tunable thermosensitive properties can be observed by transmittance, dynamic laser light scattering, and transmission electron microscopy (TEM). The release rate of model drug chlorambucil from the micelles can be effectively controlled by changing the external temperatures, which indicates that these unique high-branched amphiphilic copolymers have the potential applications in biomedical field. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis and characterization of novel urethane‐siloxane copolymers with a high content of PCL‐PDMS‐PCL segments

AbstractNovel polyurethane copolymers derived from 4,4′‐methylenediphenyl diisocyanate (MDI), 1,4‐butanediol (BD) and α,ω‐dihydroxy‐[poly(caprolactone)‐poly (dimethylsiloxane)‐poly(caprolactone)] (α,ω‐dihydroxy‐(PCL‐PDMS‐PCL); $ \overline M _{\rm{n}} $ = 6100 g mol−1) were synthesized by a two‐step polyaddition reaction in solution. In the synthesis of the polyurethanes, the PCL blocks served as a compatibilizer between the nonpolar PDMS blocks and the polar comonomers, MDI and BD. The synthesis of thermoplastic polyurethanes (TPU) with high soft segment contents was optimized in terms of the concentrations of the reactants, the molar ratio of the NCO/OH groups, and the time and temperature of the polyaddition reaction. The structure, composition, and hard MDI/BD segment length of the synthesized polyurethane copolymers were determined by 1H, 13C‐NMR, and two‐dimensional correlation (COSY, HSQC, and HMBC) spectroscopy, while the hydrogen bonding interactions in the copolymers were analyzed by FT‐IR spectroscopy. The influence of the reaction conditions on the structure, molecular weight, thermal, and some physical properties was studied at constant composition of the reaction mixture. A change in the molar ratio of the NCO/OH groups and the reaction conditions modified not only the molecular weight of the synthesized polyurethanes, but also the microstructure and therefore the thermal and physical properties of the copolymers. It was demonstrated that only PCL segments with high soft segment contents crystallize, thereby showing spherulitic morphology. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011