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wo-, four-, and six-armed branched copolymers with electroactive and biodegradable properties were synthesized by coupling reactions between poly(l-lactides) (PLLAs) with different architecture and carboxyl-capped aniline trimer (CCAT). The aniline oligomer CCAT was prepared from amino-capped aniline trimer and succinic anhydride. FT-IR, NMR, and SEC analyses confirmed the structure of the branched copolymers. UV−vis spectra and cyclic voltammetry of CCAT and copolymer solution showed good electroactive properties, similar to those of polyaniline. The water contact angle of the PLLAs was the highest, followed by the undoped copolymer and the doped copolymers. The values of doped four-armed copolymers were 54−63°. Thermal properties of the polymers were studied by DSC and TGA. The copolymers had better thermal stability than the pure PLLAs, and the Tg between 48−58 °C and Tm between 146−177 °C of the copolymers were lower than those of the pure PLLA counterparts. This kind of electroactive and biodegradable copolymer has a great potential for applications in cardiovascular or neuronal tissue engineering., QC 20100519

A fundamental component of bone tissue engineering is an appropriate scaffold as a carrier for osteogenic cells. The aim of the study was to evaluate the response of human bone marrow stromal cells (BMSC) to scaffolds made of three biodegradable polymers: poly(L-lactide-co-epsilon-caprolactone) (poly(LLA-co-CL)), poly(L-lactide-co-1,5dioxepan-2-one) (poly(LLA-co-DXO)), and poly(L-lactide) (poly(LLA)). Cellular response was evaluated in terms of attachment, proliferation, and differentiation. SEM disclosed earlier cell attachment and better spreading on poly(LLA-co-CL) and poly(LLA-co-DXO) scaffolds than on poly(LLA) after 1 h. At 24 h and 14 days postseeding, BMSCs had spread well, forming multiple cellular layers on the scaffolds. Cell proliferation was higher on poly(LLA-co-CL) and on poly(LLA-co-DXO) than on poly(LLA) after 1 and 7 days. Cell growth cycles of BMSC were longer on the scaffolds than on coverslips. After 7 and 14 days cultivation on scaffolds, the expression of osteogenic markers such as ALP, Col I, OPN, and Runx2 were stimulated by BMSC, which indicating that poly(LLA-co-DXO), poly(LLA-co-CL), and poly(LLA) could support the osteogenic differentiation of BMSC in vitro. Poly(LLA-co-CL) and poly(LLA-co-DXO) promoted better attachment and growth of BMSC than poly(LLA). BMSC also retained their osteogenic differentiation potential, indicating biological activity of BMSC on the scaffolds. The promising results of this in vitro study indicate that these copolymers warrant further evaluation for potential application in bone tissue engineering., QC 20101210

QC 20111220

In this report, poly(L-lactide-co-epsilon-caprolactone), poly(LLA-co-CL) and poly(L-lactide-co-1,5-dioxepan-2-one), poly(LLA-co-DXO) were evaluated and compared for potential use in bone tissue engineering constructs together with bone marrow stromal cells (BMSC). The copolymers were tailored to reduce the level of harmful tin residuals in the scaffolding. BMSC isolated from Sprague-Dawley rats were seeded onto the scaffolds and cultured in vitro for up to 21 days. Cell spreading and proliferation was analyzed after 72 h by scanning electron microscopy and thiazolyl blue tetrazolium bromide (MTT) conversion assay. Osteogenic differentiation of BMSC was evaluated by real-time PCR after 14 and 21 days of culture. Hydrophilicity was significantly different between poly(LLA-co-CL) and poly(LLA-co-DXO) with the latter being more hydrophilic. After 72 h, both scaffolds supported increased cell proliferation and the mRNA expression of osteocalcin and osteopontin was significantly increased after 21 days. Further investigation of these constructs, with lower levels of tin residuals, are being pursued., QC 20110131

In this in vitro study, the initial response of human periodontal ligament (PDL) cells and alveolar osteoblast-like cells (HOB) to three biodegradable polymers with varying pore size and different mechanical properties were evaluated. Scaffolds were synthesized from poly(L-lactide), [poly(LLA)], poly(L-lactide-co-1,5-dioxepan-2-one), [poly(LLA-co-DXO)], poly(L-lactide-co-epsilon-caprolactone), and [poly(LLA-co-CL)] with pore sizes greater or less than 90 mm by salt leaching. Cells were obtained from patients undergoing routine oral surgery. After 2-4 passages, the cells were grown on scaffolds and in culture plates (control) for 3 h (PDL cells), 3 days (PDL cells and HOB), 10 and 14 days (HOB), respectively. The cellular morphology and spreading were determined by scanning electron microscopy (SEM) and the attachment and proliferation were evaluated by MTT assays. The SEM images revealed heterogeneous cellular morphology and good spreading. Cellular attachment and proliferation were significantly higher on poly(LLA-co-DXO) and poly(LLA-co-CL) than on poly(LLA) scaffolds (p = 0.003) and highest for poly(LLA-co-DXO). Expression of bone formation markers, collagen-I (COL-I), transforming growth factor-beta(1) (TGF-beta(1)), and osteocalcin (OCN), was determined by ELISA. The expression of COL-1 was similar for HOB and PDL cells, but significantly higher for pore size >90 mm while the HOB expression of TGF-beta(1) and OCN was greater on poly(LLA-co-CL) and poly(LLA-co-DXO) than on poly(LLA) scaffolds., QC 20101210

We present macromolecular architecture design as a useful tool to enhance the conductivity of degradable polymers. Linear and hyperbranched copolymers with electrical conductivity and biodegradability were synthesized by an "A(2) + B-n (n=2, 3, 4)" strategy using carboxyl-capped aniline pen tamer (CCAP) and branched poly(epsilon-caprolactone)s (PCLs) by coupling reactions. A more hydrophilic surface and lower crystallinity of the doped emeraldine state of aniline pentamer (EM A P) copolymer was achieved compared with PCLs, and TGA results demonstrated that the CCAP contents in the copolymers were almost the same. The structure of the polymers was characterized by FT-IR. NMR, and SEC. Good electroactivity of the copolymers was confirmed by UV and cyclic voltammetry (CV), and CV showed three pairs of redox peaks. The hyperbranched copolymers had a higher conductivity than the linear ones. It is suggested that the higher conductivity of the hyperbranched copolymer is due to the ordered distribution of peripheral EMAP segments that more easily form a conductive network. Therefore, the conductivity of the polymers is improved and controlled by the macromolecular architecture., QC 20110112

An unsaturated aliphatic polyester was synthesized by condensation polymerization to yield the pre-polymer, poly(but-2-ene-1,4-diyl malonate) (PBM), which is applicable as an elastomeric network and as a macroinitiator for the polymerization of cyclic ester monomers. The method of preparation was simple and straightforward with no need to purify the monomers or add a potentially harmful catalyst. The number average molecular weight of the pre-polymer could easily be increased from 5000 to 12000 by extending the reaction time. The pre-polymer PBM was successfully cross-linked with UV-radiation to form a clear, transparent, colorless, flexible, and strong film. PBM as a macroinitiator for L-lactide (LLA) and epsilon-caprolactone (CL) polymerizations highly increased the ductility of the LLA-polymer, while maintaining the strength, compared to PLLA polymerized with common initiators. The tensile properties of PCL were also improved. The linear PCL-PBM and PLLA-PBM polymers were easily cross-linked to give polymers with greater strength and higher modulus as the result., QC 20100525

The aim of this study was to evaluate the in vitro cytotoxicity and cytocompatibility of the developed aliphatic polyester co-polymer scaffolds: poly(L-lactide-co-epsilon-caprolactone) and poly(L-lactide-co-1,5-dioxepan-2-one). The scaffolds were produced by solvent casting and particulate leaching, and tested by direct and indirect contact cytotoxicity assays on human osteoblast-like cells and mouse fibroblasts. Cell morphology was documented by light and scanning electron microscopy. Viability was assessed by the MTT, neutral red uptake, lactic dehydrogenase and apoptosis assays. Extraction tests confirmed that the scaffolds did not have a cytotoxic effect on the cells. The cells grew and spread well on the test scaffolds with good cellular attachment and viability. The scaffolds are noncytotoxic and biocompatible with the two cell types and warrant continued investigation as potential constructs for bone tissue engineering., QC 20101210

Radical ring-opening polymerization has been efficiently used to copolymerize 2-methylene-1,3,6-trioxocane (MTC) and 2-methylene-1,3-dioxepane (MDO). The cyclic ketene acetal MTC was first synthesized and homopolymerized at different temperatures using either 2,2-azobisisobutyronitrile or dicumyl peroxide as initiator. The polymerization mechanism was not temperature-dependent, and the polymerization proceeded with 100% ring-opening at all the temperatures evaluated. The structures of MTC and PMTC were verified by H-1-nuclear magnetic resonance (NMR) and C-13-NMR spectroscopies. A number-average molecular weight of 6500 was obtained after 2 days at 70 degrees C in bulk, which was somewhat higher than the theoretical molecular weight. A significant amount of branching was detected from the high polydispersity index as well as the glass-transition temperatures. The polyester-ether was then successfully obtained by copolymerization of MTC with MDO. Different feed ratios and temperatures were used to map the reaction, and the copolymers were characterized by NMR, size exclusion chromatography, and differential scanning calorimetry. The amount of MTC within the polymer was independent of the feed ratio and always higher than the amount of MDO., QC 20101210

QC 20120214

A simple and effective method of fabricating scaffolds with open pore structures was successfully used on several copolymers. The method, which is straightforward and fast, was developed to overcome problems such as low pore interconnectivity and to achieve thick three-dimensional scaffolds. Copolymers are of particular interest because it is possible to tune their mechanical and degradable properties, and in this work, copolymers of L-lactide (LLA) and trimethylene carbonate (TMC) were synthesized through ring-opening polymerization. The copolymers formed had molecular weights ranging from close to 60000 g/mol to over 300000 g/mol and they were composed of 12-55 molar percentages of TMC and 88-45 molar percentages of LLA. The synthesized copolymers were evaluated as scaffold materials using a combined phase separation and particulate leaching technique, in which sugar templates were used as the leachable porosifiers. Differences in molecular weights, molar compositions, and degrees of crystallinity were all factors that influenced the properties of the prepared scaffolds. The copolymers with high LLA contents and high degrees of crystallinity were best suited for the scaffold fabrication technique used and gave degradable scaffolds with interconnected pores., QC 20100525

Radical ring-opening polymerization of cyclic ketene acetals is a means to achieve novel types of aliphatic polyesters. 2-methylene-1,3-dioxe-5-pene is a seven-membered cyclic ketene acetal containing an unsaturation in the 5-position in the ring structure. The double bond functionality enables further reactions subsequent to polymerization. The monomer 2-methylene-1,3-dioxe-5-pene was synthesized and polymerized in bulk by free radical polymerization at different temperatures, to determine the structure of the products and propose a reaction mechanism. The reaction mechanism is dependent on the reaction temperature. At higher temperatures, ring-opening takes place to a great extent followed by a new cyclization process to form the stable five-membered cyclic ester 3-vinyl-1,4-butyrolactone as the main reaction product. Thereby, propagation is suppressed and only small amounts of other oligomeric products are formed. At lower temperatures, the cyclic ester formation is reduced and oligomeric products containing both ring-opened and ring-retained repeating units are produced at higher yield., QC 20100805

By using less catalyst in the ring-opening polymerization of epsilon-caprolactone, a residual tin content of 5 ppm was reached without the need for additional purification. The initial amount of tin (II) 2-ethylhexanoate [Sn(Oct)(2)] was varied using catalyst:monomer ratios of 1:1000, 1:10,000, and 1:20,000. The impact on the final conversion, reaction control, average molecular weight, and polydispersity was studied. The amount of Sn(Oct)(2) could be significantly, reduced without influencing the reaction results. The residual amount of tin was reduced from 176 ppm with a catalyst:monomer ratio of 1:1000 in the polymer, to 5 ppm with the ratio 1:10,000. It was thus concluded that a catalyst:monomer ratio of 1:10,000 or lower is required to achieve a polymer with tin content Suitable for biomedical applications. The materials were also tested in a proliferation study with mesenchymal stem cells from mouse. Porous scaffolds were fabricated from the polymers, using a salt leaching technique, and the cell growth on the porous scaffolds as well as on homogeneous films was determined by light absorbance measurements. In this study, the cell proliferation results showed that cells could grow on all polymers with ail efficiency equal to or better than that on normal tissue Culture plastic., QC 20100922. Uppdaterad från Submitted till Published (20100922).

The influences of the stereochemical structure, the molecular weight, and the number of molecular branches for poly(lactide) (PLA) on enzymatic hydrolysis rates of PLA monolayers were studied by atomic force microscopy (AFM) and the Langmuir-Blodgett (LB) technique. Monolayers of six kinds of PLA with different molecular weights, stereochemical structure, and numbers of molecular branches were prepared by LB techniques and then characterized by AFM in air. The PLA molecules covered homogeneously with a silicon substrate and did not form lamellar crystals in the monolayer. We determined the initial hydrolysis rate of PLA monolayers in presence of proteinase K by volumetric analysis from the continuous AFM height images. The presence of D-lactyl unit reduced the hydrolysis rate of the monolayer. The hydrolysis rate for the linear PLLA samples increased with a decrease in the molecular weight. In contrast, the rates of erosion for branched PLLA monolayers were independent of the molecular weight of samples. The erosion rate of branched PLLA monolayers was found to be dependent on the average molecular weight of PLLA segment in branched molecules, not on. the overall molecular weight of samples. From these results, furthermore, the hydrolysis mode of PLAs by proteinase K is discussed., QC 20100525

Nanofibrous scaffolds of poly[(L-lactide)-co-(1,5-dioxepan-2-one)] generated by electrospinning have been compared with porous films obtained by solvent cast/salt leaching and homogeneous films. A comparison between the fibrous materials and the homogeneous solvent-cast films revelead that the surface of the nanofibers was more hydrophobic and that the nanofibers were degraded more rapidly in the presence of proteinase. It was obvious that the strain-to-break was reduced by the nanofiber formation, it decreased from 370% to 130% independent of fiber diameter. These values were however considerably higher than the strain-to-break of the solvent-cast/salt leaching scaffold. In addition, the nanofibrous material accelerated the adhesion and growth of the mesenchymal stem cell compared to the smooth material., QC 20100525

In this article the effects of the number of molecular branches (chain ends) and the stereochemistry of poly(lactide)s (PLAs) on the enzymatic degradation and alkaline hydrolysis are studied. Various linear and branched PLAs were synthesized using lipase PS (Pseudomonas fluorescens)-catalyzed ring-opening polymerization (ROP) of lactide monomers having different stereochemistries (L-lactide, D-lactide, and D,L-lactide). Five different alcohols were used as initiators for the ROP, and the monomer-to-initiator molar feed ratio was varied from 10 to 100 and 1000 for each branch in the polymer architecture. The properties of branched PLAs that would affect the enzymatic and alkaline degradations, i.e., the glass transition temperature, the melting temperature, the melting enthalpy, and the advancing contact angle, were determined. The PLA films were degraded using proteinase K or 1.0 M NaOH solution, and the weight loss and changes in the number average molecular weight (M-n) of the polymer were studied during 12 h of degradation. The results suggest that an increase in the number of molecular branches of branched PLAs enhances its enzymatic degradability and alkali hydrolyzability. Moreover, the change in M-n of the branched poly(L-lactide) (PLLA) by alkaline hydrolysis indicated that the decrease in M-n was in the first place dependent on the number of molecular branches and thereafter on the length of the molecular branch of branched PLA. The branched PLLA, poly(D-lactide) (PDLA), and poly(D,L-lactide) (PDLLA) differed in weight loss and change in M-n of the PLA segment during the enzymatic degradation. It is suggested that the branched PDLLA was degraded preferentially by proteinase K., QC 20100818

Poly(p-dioxanone) with an inherent viscosity of over 1 dL/g has been synthesized using the cyclic tin alkoxide 1-di-n-butyl-1-stanna-2,5-dioxacyclopentane as initiator. Poly(p-dioxanone) was synthesized in bulk and the results have been compared with polymerizations using tin (II) 2-ethylhexanoate (Sn(Oct)(2)) as catalyst. Sn(Oct)(2) has often been reported to be an effective catalyst for the synthesis of poly(p-dioxanone), but here it is compared with an initiator which is less prone to catalyze transesterification reactions. The results demonstrate that the cyclic tin initiator is a promising alternative for the synthesis of poly(p-dioxanone) with a high inherent viscosity. Poly(p-dioxanone) is a polymer with mechanical properties and a degradation rate suitable for tissue engineering applications. Both the cyclic tin initiator and Sn(Oct)(2) gave, under some reaction conditions, inherent viscosities around 1 dL/g. The best polymer synthesized using the cyclic tin initiator had a strain-at-break of 515% and a stress-at-break of 43 MPa. The inherent viscosity of this polymer was 1.16 dL/g, while Sn(Oct)(2) resulted in a polymer with an inherent viscosity less than 0.4 dL/g under the same reaction conditions., QC 20100525

By changing both the monomer composition and the polymer structure, we have varied the mechanical properties of resorbable polymers. The polymers were synthesized by ring-opening polymerization using L-lactide (LLA), epsilon-caprolactone (epsilon CL), trimethylene carbonate (TMC) and 1,5-dioxepan-2-one (DXO) as monomers. Well-defined triblock copolymers, microblock copolymers and networks have been evaluated, and comparisons between them show that it is possible to tune the mechanical properties. Triblock copolymers with an amorphous middle block of poly(1,5-dioxepan-2-one) (PDXO) and semi-crystalline end-blocks of poly(epsilon-caprolactone) (PCL) were stronger and had a higher strain at break than triblock copolymers with poly(L-lactide) (PLLA) as end-blocks. Polymers with both DXO and TMC in the amorphous middle-block and PLLA as end-blocks showed a lower stress at break, but the material gained elasticity, a property which is very valuable in tissue engineering. Mechanical properties of networks, synthesized by a novel method, containing PDXO and PCL are also presented. Although it is difficult to compare them with the uncross-linked polymers, this is an additional way to modify and widen the properties., Conference: International Symposium on Polymer Chemistry. Dalian, PEOPLES R CHINA

Conventional metal-catalyzed organic radical reactions and living radical polymerizations (LRP) performed in nonpolar solvents, including atom-transfer radical polymerization (ATRP), proceed by an innersphere electron-transfer mechanism. One catalytic system frequently used in these polymerizations is based on Cu(I)X species and N-containing ligands. Here, it is reported that polar solvents such as H2O, alcohols, dipolar aprotic solvents, ethylene and propylene carbonate, and ionic liquids instantaneously disproportionate Cu(I)X into Cu(0) and Cu(II)X-2 species in the presence of a diversity of N-containing ligands. This disproportionation facilitates an ultrafast LRP in which the free radicals are generated by the nascent and extremely reactive Cu(0) atomic species, while their deactivation is mediated by the nascent Cu(II)X-2 species. Both steps proceed by a low activation energy outer-sphere single-electron-transfer (SET) mechanism. The resulting SET-LRP process is activated by a catalytic amount of the electron-donor Cu(0), Cu2Se, Cu2Te, Cu2S, or Cu2O species, not by Cu(I) X. This process provides, at room temperature and below, an ultrafast synthesis of ultrahigh molecular weight polymers from functional monomers containing electronwithdrawing groups such as acrylates, methacrylates, and vinyl chloride, initiated with alkyl halides, sulfonyl halides, and N-halides., QC 20100525

QC 20190212

During the past decade, researchers in the field of polymer chemistry have developed a wide range of very powerful procedures for constructing ever-more-sophisticated polymers. These methods subsequently have been used in suitable systems to solve specific medical problems. This is complicated, and many key factors such as mechanical properties, biocompatibility, biodegradation, stability, and degradation profile must be considered. Colloid particle systems can be used to solve many biomedical- and pharmaceutical-related problems, and it is expected that nanotechnology can be used to develop these materials, devices, and systems even further. For example, an injectible scaffold system with a defined release and degradation profile has huge potential for the repair and regeneration of damaged tissues. This short, nonexhaustive review presents examples of polymer architecture in resorbable particles that have been compared and tested in biomedical applications. We also discuss the design of polymers for core-shell structures., QC 20100525

The challenges in finding a material with the proper characteristics for a given tissue engineering application are several. One solution is improving the ability to tailor the mechanical and physical properties along with the degradation profile of aliphatic polyesters, by for example alterations in their composition and architecture. In this study, well-defined star-shaped aliphatic polyesters constituted of four arms were synthesized. As a model system, L,L-lactide and a spirocyclic tin initiator was chosen and the affect of the solvent, temperature and monomer-to-initiator ratio on the number average molecular weight, the molecular weight distribution and the conversion of the polymers was shown. Consecutively, we proved that well-defined star-shaped block copolymers composed of 1,5-dioxepan-2-one and L,L-lactide with narrow molecular weight distributions and controlled block lengths can be synthesized using this system., QC 20120529