Syntheses and characterization of novel biostable polyisobutylene based thermoplastic polyurethanes

Quasiliving carbocationic polymerization of isobutylene using FeCl3 as an efficient and water-tolerant Lewis acid: synthesis of well-defined telechelic polyisobutylenes

A cost-efficient approach for the preparation of well-defined low molecular weight difunctional polyisobutulenes possessing an exo-olefin or hydroxyl group was developed in this study.

Synthesis of PLA-poly(ether urethane)-PLA copolymers and design of biodegradable anti-adhesive membranes for orthopaedic applications

Peritendinous adhesions cause chronic pain and disability. Leading causes are trauma to tendons and surrounding tissues and immobilization after surgery. Adhesions occur between 24 hours to 6 weeks after surgery. Anti-adhesion barriers are currently the best option available to prevent peritendinous adhesions, but are ineffective and difficult to use. We developed an anti-adhesive membrane that can be easily applied during tendon surgery and effectively prevent adhesions. The membrane is based on a new triblock copolymer, is non-toxic, can be bio-eliminated, and has a degradation rate of more than 6 weeks for optimal anti-adhesion effect. We synthesized and characterized poly(ether urethane) (PEU) from poly(ethylene glycol). Triblock copolymers poly(lactic acid)-PEU-poly(lactic acid) (PLA-PEU-PLA) were then synthesized from PEU with PLA blocks of different lengths, and characterized. The membranes were shaped by hot molding and their mechanical properties, contact angle, water uptake, the kinetics of in vitro degradation and cytotoxicity were studied. Mechanical properties were developed according to the needs of orthopaedic surgeons. Results showed that membranes maintained their filmogenic integrity, have a degradation rate for optimal adhesion prevention, can be bioeliminated and biocompatible suggesting that they could be safely and effectively used as anti-adhesion orthopaedic devices. These results support the use of PLA-PEU-PLA membranes as a medical device, however, the effectiveness of the membranes in vivo needs to be further evaluated. A future study using an in vivo rat model of postoperative peritendinous adhesions is currently being developed.

Synthesis and characterization of hydroxyl-terminated butadiene-end-capped polyisobutylene and its use as a diol for polyurethane preparation

Hydroxyl-terminated telechelic polyisobutylene (PIB) was prepared through living cationic polymerization. A living PIB chain was formed using the t-Bu-m-DiCuOMe/TiCl₄ initiating system and then capped with 1,3-butadiene (BD) to prepare chlorine-terminated telechelic PIB. The chlorine-terminated telechelic PIB was then hydrolysed with tetrabutylammonium hydroxide to form hydroxyl-terminated PIB. Nuclear magnetic resonance spectroscopy confirmed hydrolysis completion. The hydroxyl-terminated PIB was subsequently used as a diol to react with 4,4-methylenebis(phenylisocyanate) (MDI) and produce a PIB-based polyurethane, which showed stronger acid resistance, hydrolysis stability and thermal oxidation stability than a commercial polyurethane.

MECHANICAL PERFORMANCE OF NOVEL POLYISOBUTYLENE-BASED ELASTOMERIC POLYURETHANES BEFORE AND AFTER HYDROLYSIS

The mechanical performance of thermoplastic elastomeric polyurethanes (PUs) before and after hydrolysis is investigated. These new PUs were prepared with a new asymmetric polyisobutylene-diol (PIB-diol), without the use of solvents, and with short reaction times. The PUs were made with dicyclohexylmethane 4,4′-diisocyanate and 1,4-butanediol in the hard segments and poly(hexamethylene carbonate) (PC)-diol and polyisobutylene (PIB)-diol in the soft segments. The functionality of PIB-diol was verified by mass spectrometry. Optimum solventless synthesis conditions and performance were found with a mixture of 50/50 PIB-diol/PC-diol (28.9 wt% PIB in the PU). This PU had 26.03 ± 1.19 MPa tensile strength with 286.92 ± 12.17% elongation before and 16.22 ± 0.65 with 301.17 ± 15.08% elongation after American Society for Testing and Materials (ASTM) hydrolytic stability testing. Importantly, after the hydrolytic stability testing, the stress–strain plot of this PIB–PU was similar to that of the control PC–PU. The PU with 70/30 PIB-diol/PC-diol (41.2 wt% PIB in the PU) performed slightly better but needed solvent during synthesis because of the high viscosity of the mixtures.

Simultaneous Improvement of Oxidative and Hydrolytic Resistance of Polycarbonate Urethanes Based on Polydimethylsiloxane/Poly(hexamethylene carbonate) Mixed Macrodiols

The degradation behaviors including oxidation and hydrolysis of silicone modified polycarbonate urethanes were thoroughly investigated. These polyurethanes were based on polyhexamethylene carbonate (PHMC)/polydimethylsiloxane (PDMS) mixed macrodiols with molar ratio of PDMS ranging from 5% to 30%. It was proved that PDMS tended to migrate toward surface and even a small amount of PDMS could form a silicone-like surface. Macrophages-mediated oxidation process indicated that the PDMS surface layer was desirable to protect the fragile soft PHMC from the attack of degradative species. Hydrolysis process was probed in detail after immersing in boiling buffered water using combined analytical tools. Hydrolytically stable PDMS could act as protective shields for the bulk to hinder the chain scission of polycarbonate carbonyls whereas the hydrolysis of urethane linkages was less affected. Although the promoted phase separation at higher PDMS fractions lead to possible physical defects and mechanical compromise after degradation, simultaneously enhanced oxidation and hydrolysis resistance could be achieved for the polyurethanes with proper PDMS incorporation.

Smart and Biostable Polyurethanes for Long-Term Implants

This article reviews stimuli-responsive and biostable polyurethanes (PUs) and discusses biomedical applications of smart PUs with a particular focus on long-term implantable PU biomaterials such as PU generated artificial blood vessels, artificial intervertebral discs (IVDs), and intravaginal rings (IVRs). Recently, smart PUs have been actively researched to enhance bioactivity, biocompatibility, and reduce drug side effects. Although biodegradability is important in regenerative medicine, biostability of PU plays a key role for long-term implantable biomaterials. This article reviews recent publications of research and inventions of stimuli-responsive and biostable PUs. Applications of smart PUs in long-term implantable biomaterials are discussed and linked to the future outlook of smart biostable PU biomaterials.

Synthesis and shape memory property of segmented poly(ester urethane) with poly(butylene 1,4-cyclohexanedicarboxylate) as the soft segment

Shape memory property of segmented poly(ester urethane) with poly(butylene 1,4-cyclohexanedicarboxylate) as the soft segment.

Physical Characterization and Platelet Interactions under Shear Flows of a Novel Thermoset Polyisobutylene-based Co-polymer

Over the years, several polymers have been developed for use in prosthetic heart valves as alternatives to xenografts. However, most of these materials are beset with a variety of issues, including low material strength, biodegradation, high dynamic creep, calcification, and poor hemocompatibility. We studied the mechanical, surface, and flow-mediated thrombogenic response of poly(styrene-coblock-4-vinylbenzocyclobutene)-polyisobutylene-poly(styrene-coblock-4-vinylbenzocylcobutene) (xSIBS), a thermoset version of the thermoplastic elastomeric polyolefin poly(styrene-block-isobutylene-block-styrene) (SIBS), which has been shown to be resistant to in vivo hydrolysis, oxidation, and enzymolysis. Uniaxial tensile testing yielded an ultimate tensile strength of 35 MPa, 24.5 times greater than that of SIBS. Surface analysis yielded a mean contact angle of 82.05° and surface roughness of 144 nm, which was greater than for poly(ε-caprolactone) (PCL) and poly(methyl methacrylate) (PMMA). However, the change in platelet activation state, a predictor of thrombogenicity, was not significantly different from PCL and PMMA after fluid exposure to 1 dyn/cm(2) and 20 dyn/cm(2). In addition, the number of adherent platelets after 10 dyn/cm(2) flow exposure was on the same order of magnitude as PCL and PMMA. The mechanical strength and low thrombogenicity of xSIBS therefore suggest it as a viable polymeric substrate for fabrication of prosthetic heart valves and other cardiovascular devices.

Long-term in vitro hydrolytic stability of thermoplastic polyurethanes

Long-term in vitro stability of thermoplastic polyurethanes (TPUs) was studied for up to 52 weeks in phosphate buffer solution at 37, 55, and 80°C. Water uptake, molecular weights, and tensile properties were measured at regular intervals of 4, 8, 16, 32, and 52 weeks. The rate of molecular weight reduction increased with increasing temperature, and after 52 weeks at 80°C, all commercial polycarbonate (Bionate-55D, Quadrathane-80A, and Chronoflex-80A), poly(dimethylsiloxane) (ElastEon-2A) and polyether (Elasthane-55D) TPUs showed significant (43-51%) molecular weight (Mn ) reduction. The polyisobutylene (PIB)-based TPU exhibited a significantly lower decrease in Mn (26%) after 52 weeks at 80°C. For Bionate-55D and ElastEon-2A, at 80°C in dry nitrogen atmosphere substantial thermal degradation was observed, while for the other TPUs the effect of thermal degradation is small. The temperature dependent reduction of molecular weight was interpreted by simple second order kinetics. From the approximately linear Arrhenius plots the activation energies were calculated, which were highest for PIB-PU-020 and lowest for ElastEon-2A. For Elasthane-55D the in vitro molecular weight reduction was compared with that of explanted leads. The molecular weight reduction in vivo was much smaller than that predicted from in vitro data, which may suggest that the in vitro model does not adequately describe the hydrolysis in vivo. In the absence of validation for the other TPUs that in vitro methods closely reproduce in vivo degradation, it is unknown how these results correlate with in vivo performance.

Hydroxy-telechelic poly(ethylene-co-isobutylene) as a soft segment for thermoplastic polyurethanes

Facile preparation of linear amorphous hydroxy-telechelic poly(ethylene-co-isobutylene) (PEIB) was enabled by ROMP of a new monomer, (Z)-5,5-dimethylcyclooct-1-ene (Me₂COE).

Physical and thermal properties of thermoplastic poly(azo-urethane)s

New thermoplastic segmented poly(azo-urethane)s (PAUs) have been synthesized by one-step polycondensation from aromatic diazo-diol, ( E)-1-(4-(4-(3-hydroxypyridyl-azo)thiocarbamoylaminobenzyl)-phenyl)-3-(3-hydroxypyridylazo)thiourea, as chain extenders, phenylene diisocyanate and 20–60 mol % polyethylene glycol (PEG) with the molecular weight of 2000 g/mol. The effect of diazo-diol used in the structure and some physicochemical, thermal and mechanical properties of the segmented polyurethanes were studied. The structure was examined by proton nuclear magnetic resonance (1H NMR) and Fourier-transform infrared spectroscopy (FTIR) analyses. Polyazos were the products with good processability and high molar mass in the range 120 × 103–135 × 103 g/mol. Thermal properties, investigated by thermogravimetric analysis and differential scanning calorimetry indicated that PAUs up to 40 mol % polyol were fairly stable above 530°C, having initial weight loss of around 528–539°C, 10% gravimetric loss in the range 553–567°C and own high glass transition temperature 259–264°C. The polymers also demonstrated higher tensile strength (56.53–63.83 MPa) and elongation at break (1.58–1.63). However, compared with typical polyurethanes, PAUs with lower polyol content displayed higher Tgs, heat and mechanical stability owing to warily designed rigid hard segment structure.

An investigation on new high performance Schiff base polyurethanes

Novel poly(urethane-azomethine-thiourea)s (PUATs) were synthesized via one-step polymerization from newly prepared diol chain extender (1,4-phenylene bis((E)-1-(4-hydroxobenzylidene)thiourea) (PBHBT)), containing C=S and –C=N– linkages, along with 1,4-phenylene diisocyanate (PDI) as hard segments and 20, 40 and 60 mol.% polyethylene glycol (PEG) forming soft segments. The prepared chain extender and polymers were characterized via elemental, Fourier transform infrared, 1H- and 13C-NMR analyses, and physical properties such as ηinh, solubility, crystallinity, flame retardancy and thermal stability were studied. According to X-ray diffraction patterns, the Schiff base polymers exhibited amorphous morphologies and their molar masses were in the range of 148 × 103–163 × 103 g mol−1. Thermogravimetric analysis indicated that PUATs with 20 and 40 mol.% PEG were fairly stable above 500°C having T10 of 511–527°C and had high glass transition temperatures about 249–251°C. In comparison with typical polyurethanes, PUATs with lower polyol content exhibited better non-inflammability, Tg values, chemical and thermal stability owing to rigid hard segment structure.

Surface characterization and protein interactions of segmented polyisobutylene-based thermoplastic polyurethanes

The surface properties and biocompatibility of a class of thermoplastic polyurethanes (TPUs) with applications in blood-contacting medical devices have been studied. Thin films of commercial TPUs and novel polyisobutylene (PIB)-poly(tetramethylene oxide) (PTMO) TPUs were characterized by contact angle measurements, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM) imaging. PIB-PTMO TPU surfaces have significantly higher C/N ratios and lower amounts of oxygen than the theoretical bulk composition, which is attributed to surface enrichment of PIB. Greater differences in the C/N ratios were observed with the softer compositions due to their higher relative amounts of PIB. The contact angles were higher on PIB-PTMO TPUs than on commercial polyether TPUs, indicating lower surface energy. AFM imaging showed phase separation and increasing domain sizes with increasing hard segment content. The biocompatibility was investigated by quantifying the adsorption of fouling and passivating proteins, fibrinogen (Fg) and human serum albumin (HSA) respectively, onto thin TPU films spin coated onto the electrode of a quartz crystal microbalance with dissipation monitoring (QCM-D). Competitive adsorption experiments were performed with a mixture of Fg and albumin in physiological ratio followed by binding of GPIIb-IIIa, the platelet receptor ligand that selectively binds to Fg. The QCM-D results indicate similar adsorbed amounts of both Fg and HSA on PIB-PTMO TPUs and commercial TPUs. The strength of the protein interactions with the various TPU surfaces measured with AFM (colloidal probe) was similar among the various TPUs. These results suggest excellent biocompatibility of these novel PIB-PTMO TPUs, similar to that of polyether TPUs.

Hydroxyapatite Mineralization on the Calcium Chloride Blended Polyurethane Nanofiber via Biomimetic Method

Polyurethane nanofibers containing calcium chloride (CaCl2) were prepared via an electrospinning technique for the biomedical applications. Polyurethane nanofibers with different concentration of CaCl2 were electrospun, and their bioactivity evaluation was conducted by incubating in biomimetic simulated body fluid (SBF) solution. The morphology, structure and thermal properties of the polyurethane/CaCl2 composite nanofibers were characterized by means of scanning electron microscopy (SEM), field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetry. SEM images revealed that the CaCl2 salt incorporated homogeneously to form well-oriented nanofibers with smooth surface and uniform diameters along their lengths. The SBF incubation test confirmed the formation of apatite-like materials, exhibiting enhanced bioactive behavior of the polyurethane/CaCl2 composite nanofibers. This study demonstrated that the electrospun polyurethane containing CaCl2 composite nanofibers enhanced the in vitro bioactivity and supports the growth of apatite-like materials.