Controlled ring‐opening homo‐ and copolymerization of ɛ‐caprolactone and d,l‐lactide by iminophenolate aluminum complexes: An efficient approach toward well‐defined macromonomers

The aluminum complexes containing two iminophenolate ligands of the type (p‐XC₆H₄NCHC₆H₄O‐o)₂AlR' (R′=Me ( 3, 4 ) or R′=O(CH₂)₄OCH=CH₂ ( 5, 6 ), X=H ( 3, 5 ), F( 4, 6 )) were synthesized and characterized by ¹H, ¹³C NMR spectroscopy, and X‐ray crystallography. The reaction of AlMe₃ with two equivalents of substituted iminophenols gave five‐coordinated {ONR}₂AlMe ( 3, 4 ) complexes. Subsequent reaction of these methyl complexes with unsaturated alcohol, HO(CH₂)₄OCH=CH₂, resulted in target compounds 5 and 6 in a good yield. It was shown that the complexes ( 3 ‐ 6 ) are monomeric in solution (NMR) and in solid state (X‐ray analysis). The catalytic activity of the complexes 5 and 6 towards ring‐opening polymerization (ROP) of ?‐caprolactone and d,l ‐lactide was assessed. Complex 5 showed higher activity as compared with 6 , while both of these catalysts induced controlled homo‐ and copolymerization to afford the macromonomers with high content of vinyl ether end groups (F_n > 80%) in a broad range of molecular weights (M_n = 4000–30,000 g mol^?1) with relatively narrow MWD (M_w/M_n = 1.1–1.5). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1237–1250     

Ultralong Hydroxyapatite Nanowire/Collagen Biopaper with High Flexibility,Improved Mechanical Properties and Excellent Cellular Attachment

Highly flexible hydroxyapatite/collagen (HAP/Col) composite membranes are regarded to be significant for guided bone regeneration application owing to their similar chemical composition to that of natural bone, excellent bioactivity and good osteoconductivity. However, the mechanical strength of the HAP/Col composite membranes is usually weak, which leads to difficult surgical operations and low mechanical stability during the bone healing process. Herein, highly flexible ultralong hydroxyapatite nanowires/collagen (UHANWs/Col) composite biopaper sheets with weight fractions of UHANWs ranging from 0 to 100 % are facilely synthesized. The UHANWs are able to weave with each other to construct a three‐dimensional fabric structure in the collagen matrix, providing a strong interaction between UHANWs and an intermolecular force between UHANWs and the collagen matrix. The as‐prepared UHANWs/Col composite biopaper exhibits improved mechanical properties and high flexibility. More importantly, the as‐prepared highly flexible 70 wt % UHANWs/Col composite biopaper exhibits an excellent cytocompatibility and outstanding cellular attachment performance as compared with the pure collagen and 70 wt % HAP nanorods/Col membranes. In consideration of its superior mechanical properties and outstanding cellular attachment performance, the as‐prepared UHANWs/Col composite biopaper is promising for applications in various biomedical fields such as guided bone regeneration.     

Viscoelastic properties of poly(ε‐caprolactone) – hydroxyapatite micro‐ and nano‐composites

Various composites have been proposed in the literature for the fabrication of bioscaffolds for bone tissue engineering. These materials include poly(ε‐caprolactone) (PCL) with hydroxyapatite (HA). Since the biomaterial acts as the medium that transfers mechanical signals from the body to the cells, the fundamental properties of the biomaterials should be characterized. Furthermore, in order to control the processing of these materials into scaffolds, the characterization of the fundamental properties is also necessary. In this study, the physical, thermal, mechanical, and viscoelastic properties of the PCL‐HA micro‐ and nano‐composites were characterized. Although the addition of filler particles increased the compressive modulus by up to 450%, the thermal and viscoelastic properties were unaffected. Furthermore, although the presence of water plasticized the polymer, the viscoelastic behavior was only minimally affected. Testing the composites under various conditions showed that the addition of HA can strengthen PCL without changing its viscoelastic response. The results found in this study can be used to further understand and approximate the time‐dependent behavior of scaffolds for bone tissue engineering. Copyright © 2012 John Wiley & Sons, Ltd.     

Quantitative analysis of complex amino acids and RGD peptides by X‐ray photoelectron spectroscopy (XPS)

The C 1 s, N 1 s, and O 1 s core level binding energies (BEs) of the functional groups in amino acids (glycine, aspartic acid, glutamic acid, arginine, and histidine) with varied side‐chains and cell‐binding RGD‐based peptides have been determined and characterized by X‐ray photoelectron spectroscopy with a monochromatic Al K_α source. The zwitterionic nature of the amino acids in the solid state is unequivocally evident from the N 1 s signals of the protonated amine groups and the C 1 s signature of carboxylate groups. Significant adventitious carbon contamination is evident for all samples but can be quantitatively accounted for. No intrinsic differences in the XP spectra are evident between two polymorphs (α and γ) of glycine, indicating that the crystallographic differences have a minor influence on the core level BEs for this system. The two nitrogen centers in the imidazole group of histidine exhibit an N 1 s BE shift that is in line with previously reported data for theophylline and aqueous imidazole solutions, while the nitrogen and carbon chemical shifts reflect the unusual guanidinium chemical environment in arginine. It is shown that the complex envelopes of C 1 s and O 1 s photoemission spectra for short‐chain peptides can be analyzed quantitatively by reference to the less complex XP spectra of the constituent amino acids, provided the peptides are of high enough purity. The distinctive N 1 s photoemission from the amide linkages provides an indicator of peptide formation even in the presence of common impurities, and variations in the relative intensities of N 1 s were found to be diagnostic for each of the three peptides investigated (RGD, RGDS, and RGDSC). Copyright © 2013 John Wiley & Sons, Ltd.     

Enzymatic syntheses of unsaturated polyesters based on isosorbide and isomannide

The search for materials produced from renewable sources aiming at the substitution of petroleum‐based derivates is an area of intense investigation. In this work, the enzymatic copolymerization of isosorbide or isomannide with diethyl adipate and fractions of different unsaturated diesters (diethyl itaconate, diethyl fumarate, diethyl glutaconate, and diethyl hydromuconate) were examined using CAL‐B as catalyst. The polyesters prepared using one‐step syntheses were characterized by SEC, NMR, and MALDI‐TOF MS. In addition, syntheses with linear diols were carried out in bulk to evaluate the reactivity of cyclic diols in producing unsaturated polyesters using enzymatic catalysis, as well as to evaluate the occurrence of addition side reactions on the double bonds. Isosorbide and isomannide yielded unsaturated polymers with values in the order of 4,000‐16,000 when fumarate or glutaconate esters were added in 5 mol % ratio against adipate. In all cases MALDI‐TOF confirmed the presence of unsaturated units. Although these polyesters have unreacted double bonds they are prone to crosslinking and ready to further functionalization, like anchoring bioactive molecules. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3881–3891     

Synthesis of New Lipid‐Inspired Ionic Liquids by Thiol‐ene Chemistry: Profound Solvent Effect on Reaction Pathway

The synthesis of a series of new lipid‐inspired ionic liquids through thiol‐ene “click” reaction with a single‐step process. This synthesis offers considerable promise as an efficient and orthogonal method to construct structurally diverse imidazolium‐type ionic liquids with linear and branched cationic tails, as well as versatility in the placement of the sulfur heteroatom. Profound solvent effect in this ene reaction regioselectivity has been observed.     

Nanoarchitectonics beyond Self‐Assembly: Challenges to Create Bio‐Like Hierarchic Organization

Incorporation of non‐equilibrium actions in the sequence of self‐assembly processes would be an effective means to establish bio‐like high functionality hierarchical assemblies. As a novel methodology beyond self‐assembly, nanoarchitectonics, which has as its aim the fabrication of functional materials systems from nanoscopic units through the methodological fusion of nanotechnology with other scientific disciplines including organic synthesis, supramolecular chemistry, microfabrication, and bio‐process, has been applied to this strategy. The application of non‐equilibrium factors to conventional self‐assembly processes is discussed on the basis of examples of directed assembly, Langmuir–Blodgett assembly, and layer‐by‐layer assembly. In particular, examples of the fabrication of hierarchical functional structures using bio‐active components such as proteins or by the combination of bio‐components and two‐dimensional nanomaterials, are described. Methodologies described in this review article highlight possible approaches using the nanoarchitectonics concept beyond self‐assembly for creation of bio‐like higher functionalities and hierarchical structural organization.