Synthesis and characterization of biocompatible, degradable, light-curable, polyurethane-based elastic hydrogels

A series of degradable polyurethane-based light-curable elastic hydrogels were synthesized from polycaprolactone diol, polyethylene glycol (PEG), lysine diisocyanate (LDI), and 2-hydroxyethyl methacrylate (HEMA) through UV light initiated polymerization reaction. LDI was used as hard segment and polycaprolactone (PCL) and/or PEG were used as soft segments. By changing the PCL to PEG ratio during the prepolymer synthesis, polyurethanes with different soft segmental structures, hydrophilicity, and cytophilicity were obtained after light-initiated polymerization. The chemical structures of the synthesized polymers were characterized using differential scanning calorimetry and Fourier transform infrared spectroscopy. Physical properties such as swelling, mechanical properties, and in vitro degradation were evaluated. Materials containing a higher ratio of PEG exhibit higher water absorbance, higher degradation rate in vitro, and lower mechanical strength in the hydrated state. Mouse embryonal carcinoma-derived clonal chondrocytes were used as a model cell type to study the cytocompatibility of the synthesized polymers. Chondrocyte attachment, proliferation rates, and morphologies varied with changes in the PCL/PEG ratio. With a higher PEG ratio, lower cell attachment and proliferation were observed. To improve the cell attachment and proliferation on high PEG content hydrogels, bioactive molecules, such as peptides and proteins, were conjugated or immobilized in the gel matrix during the light-curing process. In this study, a short peptide, Arg-Gly-Asp-Ser, was used as a model biomolecule and incorporated into the gels during the light-curing process and improved cell growth was observed. In summary, the use of PCL/PEG at different ratios, as well as the introduction of HEMA into polyurethane, allows the synthesis of a series of biocompatible elastic hydrogels with tunable physical and cytophilic properties through light-initiated polymerization. This series of materials also allows for controlling cell attachment and growth by incorporating bioactive molecules during the light-curing process.     

Self-association and micelle formation of biodegradable poly(ethylene glycol)-poly(L-lactic acid) amphiphilic di-block co-polymers

Di-block co-polymers of poly(ethylene glycol)-poly(L-lactic acid) (PEG-PLLA) were prepared by ring-opening polymerization, and their self-association and micelle formation were investigated. The block co-polymers have the same block length of the hydrophilic PEG segment (Mn = 2000), but different chain lengths of the hydrophobic PLLA segment (Mn = 700, 1000 and 1300, respectively). The di-block co-polymers synthesized were characterized by GPC, 1H-NMR, TGA and DSC. The critical micelle concentration (CMC) of the PEG-PLLA micelles was determined at various temperatures (5-45 degrees C) using a dye absorption technique involving fluorescence spectrophotometry with pyrene as a probe to monitor the change in the polarity of the microenvironment in the micelle. An increase in the molecular weight of the hydrophobic block decreases the CMC. The partition coefficients of pyrene between the micellar and aqueous phases range from 0.68 x 10(4 )to 1.76 x 10(4), depending on the PLLA content in the block co-polymers. An Arrhenius plot of ln(CMC) versus 1/T exhibited an almost constant CMC at low temperatures (<35 degrees C), followed by an increase of the CMC at higher temperatures (>35 degrees C). The increase of the CMC with temperature indicates the increase of the mobility of the hydrophobic PLLA core. These results were confirmed by 1H-NMR measurements. The micelle size and size distribution were determined by dynamic light scattering (DLS), and were in the range of 78-92 nm. A spherical micelle shape was confirmed by transmission electron microscopy. These results indicate that the CMC and the thermal characteristics of the core-forming segment of the block co-polymer play an important role in the properties of the polymer micelles used for drug delivery.     

Improving the elasticity and cytophilicity of biodegradable polyurethane by changing chain extender

Two types of biodegradable polyurethanes (PUs) were synthesized from methylene di-p-phenyl-diisocyanate (MDI), polycaprolactone diol (PCL-diol), and chain extenders of either butanediol (BD) or 2,2'-(methylimino)diethanol (MIDE). The effects of two types of chain extenders on the degradation, mechanical properties, hydrophilicity, and cytophilicity of PUs were evaluated. In vitro degradation studies showed that PU containing MIDE has a higher degradation rate than PU synthesized using BD as a chain extender. Mechanical testing on dry and wet samples demonstrated that PU containing MIDE has a much higher elongation in the elastic region than PU containing BD. PU containing MIDE is more hydrophilic and retains more liquid during in vitro culture. Furthermore, preliminary cytocompatibility studies showed that both types of degradable PU are nontoxic, and fibroblasts adhere better and proliferate faster on MIDE containing PU than BD containing PU. To compare the cytocompatibility and degradation behaviors of the synthesized PU with existing FDA approved biocompatible material, polylactide (PLA), with a similar degradation rate, was used as negative control. Two types of PU were shown to have similar cytocompatibility and degradation behaviors as those of the PLA material. To verify the effectiveness of the cytotoxicity assay, latex was used as a positive control. Latex samples showed toxicity to cultured cells as expected. In conclusion, by changing the type of chain extender used during the synthesis of degradable PUs, the degradation rate, mechanical properties, hydrophilicity, and cytophilicity can be adjusted for different tissue engineering applications.     

Synthesis and characterization of biodegradable elastomeric polyurethane scaffolds fabricated by the inkjet technique

Biodegradable polyurethanes (PUs) were synthesized from methylene di-p-phenyl-diisocyanate (MDI), polycaprolactone diol (PCL-diol) and N,N-bis (2-hydorxyethyl)-2-aminoethane-sulfonic acid (BES), serving as a hard segment, soft segment and chain extender, respectively. MDI was chosen due to its reactivity and wide application in synthesis of biomedical polyurethanes due to its reactivity; PCL-diol was chosen because of its biodegradability; and BES was chosen because it allowed the introduction sulfonic acid groups onto the polymer chains. We evaluated the polyurethanes' degradation rate, mechanical properties, hydrophilicity, antithrombogenecity, and ability to support fibroblast cell attachment and growth by comparing with polymers having a 2,2-(methylimino)diethanol (MIDE) chain extender. Mechanical testing demonstrated that the PU containing BES has tensile strengths of about 17 MPa and elongations up to 400%, about three times the strength and four times the elongation than the MIDE based PUs. The polymers showed decreased in vitro degradation rates, lower glass transition temperature (T(g)) and hydrophilicity possibly due to enhanced microphase separation. Preliminary cytocompatibility studies showed that all the PUs are non-toxic, but PU containing BES exhibited much lower cell attachment and proliferation than the MIDE chain extended polymers. An in vitro platelet adhesion assay showed lower platelet attachment on BES containing PU. Additionally, due to the existence of sulfonic acid groups, the BES extended PU became water soluble in basic condition and insoluble in acidic condition, a phenomenon that is reversible at pH value of 8.7, making this a pH sensitive polymer attractive for bioprinting applications. By adding acetic acid into an inkjet cartridge and printing it onto a PU solution with pH above 8.7, precision fabricated scaffolds can be obtained, suggesting that BES based PUs are promising candidates as synthetic inks used for customizable fabrication of tissue engineering scaffolds.     

Synthesis and Drug-Release Behavior of Porous Biodegradable Amphiphilic Co-polymeric Hydrogels

A series of amphiphilic random block co-polymers were synthesized by the condensation of hydrophobic polycaprolactone diol (PCL diol) with hydrophilic dicarboxy poly(ethylene glycol) (PEG-diacid), obtained by reacting poly(ethylene glycol) (PEG) with succinic anhydride. The PEG/PCL random block co-polymers were then acrylated with acryloyl chloride to form PEG/PCL diacrylates (PCEdA), and then characterized by FT-IR, ¹H-NMR and GPC. The porous biodegradable gels were prepared through photo-polymerization of the PCEdA dissolved in DMSO at low temperature. Thermal behavior, swelling ratio and morphological characteristics as well as biodegradability of the presented gels were investigated. Results showed that the swelling ratio of the gel in deionized water increased with an increase of the PEG chain length in the copolymeric gel. DSC thermograms indicated that the melting point of the PCEdA was lower than that of PCL and PEG blocks, but a new crystalline peak of the co-polymeric gel appeared with increasing of the segmental length of the PEG. Thermal stability of PCE gel was higher than that of PCE diol. The pore size of the gel was influenced by the concentration of PCEdA. The drug-release behavior of PCE gels was also investigated.     

Fabrication and characterization of hydrophilic electrospun membranes made from the block copolymer of poly(ethylene glycol-co-lactide)

To improve the hydrophilicity, pliability, and egradability of some biodegradable polymers such as polylactide (PLA), a triblock copolymer, and poly(ethylene glycol-co-lactide) (PELA) has been electrospun into fibrous membranes in the fiber sizes of 7.5 microm to 250 nm. The relationship between electrospinning parameters (such as voltage, concentration, and feeding rate) and the fiber diameters has been investigated. The characterizations for the structure and morphology of electrospun membranes were carried out using differential scanning calorimetry (DSC), (1)H NMR, and scanning electron microscopy (SEM). The hydrophilicity of the membrane was determined by contact angle measurements in bi-distilled water, and it was shown that the hydrophilicity of the copolymer could be adjusted by the content of the poly (ethylene glycol) (PEG) segment in the copolymer. The results of in vitro degradation study showed that the submicrostructure of the fibrous membrane and the incorporation of hydrophilic PEG into PLA block could accelerate the degradation of the membrane in regards to the changes of inherent viscosity, tensile strength, and weight loss.     

Degradation and cell culture studies on block copolymers prepared by ring opening polymerization of epsilon-caprolactone in the presence of poly(ethylene glycol)

Poly(epsilon-caprolactone) (PCL) and its block copolymers with poly(ethylene glycol) (PEG) were prepared by ring-opening polymerization of epsilon-caprolactone in the presence of ethylene glycol or PEG, using zinc metal as catalyst. The resulting polymers were characterized by various analytical techniques such as (1)H NMR, SEC, DSC, IR, X-ray, ESEM, and CZE. PCL/PEG copolymers with long PCL chains presented the same crystalline structure as PCL homopolymer, whereas PEG-bearing short PCL blocks retained the crystalline structure of PEG and exhibited an amphiphilic behavior in aqueous solutions. Degradation of PCL and PCL/PEG diblock and triblock copolymers was realized in a 0.13 M, pH 7.4 phosphate buffer at 37 degrees C. The results indicated that the copolymers exhibited higher hydrophilicity and degradability compared with the PCL homopolymer. Large amounts of PEG were released from the bulk after 60 weeks' degradation. In vitro cell culture studies were conducted on scaffolds manufactured via solid free form fabrication by using primary human and rat bone marrow derived stromal cells (hMSC, rMSC). Light, scanning electron, and confocal laser microscopy, as well as immunocytochemistry, showed cell attachment, proliferation, and extracellular matrix production on the surface, as well as inside the scaffold architecture. Copolymers showed better performance in the cell culture studies than the PCL homopolymer.     

Immobilization of poly(ethylene glycol) or its sulfonate onto polymer surfaces by ozone oxidation.

A novel surface modification method has been developed to improve biocompatibility of polymeric biomaterials. This approach involves ozonation and then followed by graft polymerization with acrylates containing PEG, sulfonated PEG or by coupling of PEG derivatives. All the reactions were confirmed by ATR FT-IR and ESCA. The degree of ozonation measured by the iodide method was dependent on the ozone permeability of the polymers used. Surface hydrophilicity was investigated by measuring the contact angles. Ozonation itself yielded a slight increase in hydrophilicity and a decrease in platelet adhesion, but PEG immobilization showed a significant effect on surface hydrophilicity and platelet adhesion to confirm well-known PEG's passivity which minimize the adhesion of blood components on polymer surfaces. Both graft polymerization and coupling were effective for PU. In contrast, only grafting gave enough yields for PMMA and silicone. Platelet adhesion results demonstrated that all PEG modified surfaces adsorbed lower platelet adhesion than untreated or ozonated ones. Polymers coupled with sulfonated PEG exhibited the lowest platelet adhesion when compared with control and PEG coupled ones by virtue of the synergistic effect of non-adhesive PEG and negatively charged SO3 groups. This PEG or sulfonated PEG immobilization technology using ozonation is relatively simple for introducing uniform surface modification and therefore very useful for practical application of blood contacting medical devices.     

Biodegradable poly(ether-ester) multiblock copolymers for controlled release applications

Multiblock poly(ether-ester)s based on poly(ethylene glycol), butylene terephthalate, and butylene succinate units were synthesized by a two-step melt polycondensation reaction, with the aim of developing a new series of degradable polymers for controlled release applications. The copolymers were characterized with respect to their composition (NMR), thermal properties (DSC), and swelling. The main focus was on the degradation kinetics and release properties of the copolymers. The crystallinity and swelling could be tailored by the PEG segment length and the ratio of the building units. With increasing mol fraction succinate in the hard segment, the swelling increased. The in vitro degradation was found to occur by molecular weight decrease and mass loss. Substitution of the aromatic terephthalate units by aliphatic succinate units increased the degradation rate of the copolymers. Polymers with PEG segments of 1000 kg/mol showed a more pronounced degradation than copolymers containing shorter and longer PEG segments. Model proteins were successfully incorporated and released from the poly(ether-ester) films. Depending on the size of the protein, the release mechanism was based on diffusion of the protein and degradation of the matrix.     

Cellulose Diacetate-g-poly(p-dioxanone) Co-polymer: Synthesis,Properties and Microsphere Preparation

A novel biodegradable graft co-polymer based on cellulose diacetate (CDA) and poly(p-dioxanone) was synthesized by ring-opening polymerization of p-dioxanone (PDO). The molecular structure of co-polymers was characterized by one- and two-dimensional NMR. The graft co-polymers with different lengths of PPDO side-chains could be controllably synthesized by changing the in-feed ratio of CDA/PDO. It was found that the PPDO content had great effect on the thermal transition behavior, crystallization ability and thermal stability of the graft co-polymer. The in vitro degradation rates of CDA-g-PPDO were higher than that of linear PPDO due to their lower crystallinity. Moreover, porous microspheres of graft co-polymers with a diameter of about 5 μm, prepared through the solvent evaporation of water-in-oil emulsion (W/O), indicated it may have potential applications in drug-delivery systems.     

Wound dressing with sustained anti-microbial capability

Amphiphilic poly(ether ester amide) (PEEA) multiblock copolymers were synthesized by polycondensation in the melt from hydrophilic poly(ethylene glycol) (PEG), 1,4-dihydroxybutane and short bisester-bisamide blocks. These amide blocks were prepared by reaction of 1,4-diaminobutane with dimethyl adipate in the melt. A range of multiblock copolymers were prepared, with PEG contents varying from 23-66 wt %. The intrinsic viscosity of the PEEA polymers varied from 0.58-0.78. Differential scanning calorimetry showed melting transitions for the PEG blocks and for the amide-ester blocks, suggesting a phase separated structure. Both the melting temperature and the crystallinity of the hard amide-ester segments decreased with increasing PEG content of the polymers. The equilibrium swelling ratio in phosphate buffered saline (PBS) increased with increasing amount of PEG in the polymers and varied from 1.7 to 3.7, whereas the polymer that contained 66 wt % PEG was soluble in PBS. During incubation of PEEA films in PBS, weight loss and a continuous decrease in the resulting inherent polymer viscosity was observed. The rate of degradation increased with increasing PEG content. The composition of the remaining matrices did not change during degradation. A preliminary investigation of the protein release characteristics of these PEEA copolymers showed that release of the model protein lysozyme was proportional to the square root of time. The release rate was found to increase with increasing degree of swelling of the polymers.     

Development of biodegradable and injectable macromers based on poly(ethylene glycol) and diacid monomers

Novel biodegradable injectable poly(ethylene glycol)-(PEG) based macromers were synthesized by reacting low-molecular weight PEG (MW: 200) and dicarboxylic acids such as sebacic acid or terephthalic acid. Chemical structures of the resulting polymers were confirmed by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy characterizations. Differential scanning calorimetry (DSC) showed that these polymers were completely amorphous above room temperature. After photopolymerization, dynamic elastic shear modulus of the crosslinked polymers was up to 1.5 MPa and compressive modulus was up to 2.2 MPa depending on the polymer composition. The in vitro degradation study showed that mass losses of these polymers were gradually decreased over 23 weeks of period in simulated body fluid. By incorporating up to 30 wt % of 2-hydroxyethyl methylmethacrylate (HEMA) into the crosslinking network, the dynamic elastic modulus and compressive modulus was significantly increased up to 7.2 and 3.2 MPa, respectively. HEMA incorporation also accelerated the degradation as indicated by substantially higher mass loss of up to 27% after 20 weeks of incubation. Cytocompatability studies using osteoblasts and neural cells revealed that cell metabolic activity on these polymers with or without HEMA was close to the control tissue culture polystyrene. The PEG-based macromers developed in this study may be useful as scaffolds or cell carriers for tissue engineering applications.     

A Library of L-Tyrosine-Derived Biodegradable Polyarylates for Potential Biomaterial Applications,Part I: Synthesis,Characterization and Accelerated Hydrolytic Degradation

A combinatorial library of biodegradable polyarylates derived from L-tyrosine was synthesized and characterized. These polyarylates are A–B-type co-polymers consisting of a cyclic dipeptide and a diacid. General structure–property correlations were established by comparing aryl diacid co-polymers and aliphatic diacid co-polymers. The synthesized polymers were characterized by FT-IR, ¹H-NMR, ¹³C-NMR for their chemical structure, by DSC and TGA for their thermal characteristics and by GPC for their molecular weight distribution. The T _g of polymers decreased and water absorption increased with increasing number of methylene groups in the polymer backbone. Using a cyclic peptide derived from L-tyrosine as co-monomer we obtained optimum bioactivity and biocompatibility. Combinatorial approaches of designing material increased effectively the number of available degradable polymers which can be used in different biomaterials applications. General structure–property correlation makes polymers' properties varied in a predictable and systematic fashion. Accelerated hydrolytic degradation studies of polyarylates were performed at 70°C in acid and alkali medium. The degradation rates of polymers were in accordance with their water absorption. The degradation rates of samples in acid medium were lower than those in alkali medium.     

Synthesis and characterization of poly(L-alanine)-block-poly(ethylene glycol) monomethyl ether as amphiphilic biodegradable co-polymers

Di-block co-polymers of poly(L-alanine) with poly(ethylene glycol) monomethyl ether (MPEG) were synthesized as amphiphilic biodegradable co-polymers. The ring-opening polymerization of N-carboxy-L-alanine anhydride (NCA) in dichloromethane was initiated by amino-terminated poly(ethylene glycol) monomethyl ether (MPEG-NH₂, M _n = 2000) to afford poly(L-alanine)-block-MPEG. The weight ratio of two blocks in the co-polymers could be altered by adjusting the feeding ratio of NCA to MPEG-NH₂. Their chemical structures were characterized on the basis of infrared spectrometry and nuclear magnetic resonance. According to circular dichroism measurement, the poly(L-alanine) chain on the co-polymers in an aqueous medium had a α-helix conformation. Two melting points from MPEG block and poly(L-alanine), respectively, could be observed in differential scanning calorimetry curves of the co-polymers, suggesting that a micro-domain phase separation appeared in their bulky states. The co-polymers could take up some water and the capacity was dependent on the ratio of poly(L-alanine) block to MPEG. Such co-polymers might be useful in drug-delivery systems and other biomedical applications.     

以聚乙二醇为软段的聚氨酯的合成及表征

利用本体法合成了以聚乙二醇(PEG M n=1000)为软段的聚氨酯(PU),硬段含量分别为40%,50%和55%,用PU-H 40、PU-H 50和PU-H 55表示。FT IR、DSC测试表明,随着硬段含量的增加,聚氨酯的微相分离程度逐渐增加;力学性能测试表明,以PU-H 50力学性能最好,达到了25 M Pa。通过在软段引入亲水性PEG,材料的表面亲水性也有较大的提高,PU-H 55的水接触角达到了33,°这是由于PU-H 55的微相分离好,软段的活动性增强而富集在材料表面。PU-H 55、PU-H 50及PU-H 40的水蒸气透过率分别为623、705和789 g/m2/24h,适合做防水透气型医用制品,如:医用手套、创伤敷料、医用防护服等,是一种具有广泛应用前景的防水透气型材料。     

Synthesis and characterization of poly(L-alanine)-block-poly(ethylene glycol) monomethyl ether as amphiphilic biodegradable co-polymers

Di-block co-polymers of poly(L-alanine) with poly(ethylene glycol) monomethyl ether (MPEG) were synthesized as amphiphilic biodegradable co-polymers. The ring-opening polymerization of N-carboxy-L-alanine anhydride (NCA) in dichloromethane was initiated by amino-terminated poly(ethylene glycol) monomethyl ether (MPEG-NH2, M(n) = 2000) to afford poly(L-alanine)-block-MPEG. The weight ratio of two blocks in the co-polymers could be altered by adjusting the feeding ratio of NCA to MPEG-NH2. Their chemical structures were characterized on the basis of infrared spectrometry and nuclear magnetic resonance. According to circular dichroism measurement, the poly(L-alanine) chain on the co-polymers in an aqueous medium had a alpha-helix conformation. Two melting points from MPEG block and poly(L-alanine), respectively, could be observed in differential scanning calorimetry curves of the co-polymers, suggesting that a micro-domain phase separation appeared in their bulky states. The co-polymers could take up some water and the capacity was dependent on the ratio of poly(L-alanine) block to MPEG. Such co-polymers might be useful in drug-delivery systems and other biomedical applications.     

Saccharide polymers, 1, Synthesis and polymerization of methyl 5-deoxy-2,3-O-iso-propylidene-ß-D-erythro-pent-4-enofuranoside

New “saccharide polymers” were synthesized. For this purpose the synthesis and the polymerization of an unsaturated sugar monomer, methyl 5-deoxy-2,3-O-isopropylidene-ß-D -erythro-pent-4-enofuranoside, briefly called “exo-ribene”, is described. All polymers, homo-and co-polymers, were synthesized under free radical conditions. The structures and compositions of the soluble “saccharide polymers” were established by elemental analysis, ¹H and ¹³C NMR, and FT-IR spectroscopy. Some characteristics e. g. molecular weights and optical rotations are reported. Depending on the comonomer reactivity and under optimized chain reaction conditions, saccharide polymers with various sugar content and high molecular weights have been obtained.     

Investigation on the properties of methoxy poly(ethylene glycol)/chitosan graft co-polymers

Methoxy poly(ethylene glycol)/chitosan graft co-polymers (CS-g-mPEGs) with different degrees of substitution were synthesized by reductive N-alkylation of chitosan with poly(ethylene glycol) aldehyde. The crystalline and thermal properties of CS-g-mPEGs were characterized by wide-angle X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetry (TG). The results indicate that CS-g-mPEG solids represent microphase separation morphology with mPEG crystal and CS domains coexistence and the introduction of PEG on CS improves the thermal decomposition. The hydrodynamic behavior of CS-g-mPEGs in aqueous solution and the influence of NaCl were investigated. The results indicate that the hydrodynamic behavior of CS-g-mPEGs in aqueous solution is significantly affected by the degree of substitution and the concentration of NaCl, which are quite different from that of CS. The results of this paper also certify that CS-g-mPEGs keep the property of complexation with a counter-ion, such as tripolyphosphate, to form nanoparticles through the electrostatic interaction.     

In Vitro Biocompatibility Evaluation of Novel Urethane–Siloxane Co-Polymers Based on Poly(ϵ-Caprolactone)-block-Poly(Dimethylsiloxane)-block-Poly(ϵ-Caprolactone)

Abstract

Novel polyurethane co-polymers (TPUs), based on poly(?-caprolactone)-block-poly(dimethylsiloxane)-block-poly(?-caprolactone) (PCL-PDMS-PCL) as soft segment and 4,4’-methylenediphenyl diisocyanate (MDI) and 1,4-butanediol (BD) as hard segment, were synthesized and evaluated for biomedical applications. The content of hard segments (HS) in the polymer chains was varied from 9 to 63 wt%. The influence of the content and length of the HS on the thermal, surface, mechanical properties and biocompatibility was investigated. The structure, composition and HS length were examined using ¹H- and quantitative ¹³C-NMR spectroscopy. DSC results implied that the synthesized TPUs were semicrystalline polymers in which both the hard MDI/BD and soft PCL-PDMS-PCL segments participated. It was found that an increase in the average HS length (from 1.2 to 14.4 MDI/BD units) was accompanied by an increase in the crystallinity of the hard segments, storage moduli, hydrophilicity and degree of microphase separation of the co-polymers. Depending on the HS content, a gradual variation in surface properties of co-polymers was revealed by FT-IR, AFM and static water contact angle measurements. The in vitro biocompatibility of co-polymers was evaluated using the endothelial EA.hy926 cell line and protein adsorption on the polyurethane films. All synthesized TPUs adsorbed more albumin than fibrinogen from multicomponent protein mixture, which may indicate biocompatibility. The polyurethane films with high HS content and/or high roughness coefficient exhibit good surface properties and biocompatible behavior, which was confirmed by non-toxic effects to cells and good cell adhesion. Therefore, the non-cytotoxic chemistry of the co-polymers makes them good candidates for further development as biomedical implants.     

Synthesis,Characterization, and Polymerization Kinetics of Novel Ladder‐Like Polysilsesquioxanes Containing Side‐Chain Propyl Methacrylate Groups

Three ladder‐like polysilsesquioxanes containing side‐chain propyl methacrylate groups have been synthesized successfully by stepwise coupling polymerization. The prepared ladder‐like polymers are polysilsesquioxanes containing 100 mol‐% propyl methacrylate side groups and two copolymers containing 70 mol‐% methyl or phenyl groups and 30 mol‐% propyl methacrylate side groups. They were characterized by FT‐IR, ¹H NMR, proton‐decoupled ¹³C NMR, and ²⁹Si NMR spectroscopies, gel‐permeation chromatography (GPC), wide‐angle X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and thermo‐gravimetric analysis (TGA). Characterization data indicate that these polymers have ordered ladder‐like structures with possible defects. At appropriate conditions, crystals of homopolymer were grown and are in the shape of a parallelogram. All three polymers were cured by 2,2′‐azoisobutyronitrile (1% w/w) and the kinetics for the bulk polymerization of these polysilsesquioxanes was followed by dynamic DSC method. Ozawa and Kissinger methods were used to calculate the activation energy for curing. Both the frequency factor and the activation energy of the homopolymer were found to be higher than the copolymers. Cured samples had a higher thermal stability than uncured samples.

Chemical structure of LPS.