Diels-Alder reactions as an efficient route to high purity cyclic polymers

A simple and efficient route for the synthesis of cyclic polymer systems is presented. Linear furan protected α-maleimide-ω-cyclopentadienyl functionalized precursors (poly(methyl methacrylate) and poly(tert-butyl acrylate)) were synthesized via atom transfer radical polymerization (ATRP) and subsequent substitution of the bromine end-group with cyclopentadiene. Upon heating at high dilution, deprotection of the dieneophile occurs followed by an intramolecular Diels–Alder reaction yielding a high purity cyclic product.

Photoinduced conjugation of Dithioester- and Trithiocarbonate-Functional RAFT polymers with alkenes

We report the photoinduced conjugation of polymers synthesized via reversible addition−fragmentation chain transfer (RAFT) polymerization with a number of low molecular weight (functional) olefins. Upon irradiation of a solution of an aliphatic alkene and the benzyl dithioacetic acid ester (CPDA) or dodecyl trithiocarbonate (DoPAT) functional poly(alkyl acrylate) at the absorption wavelength of the thiocarbonyl group (315 nm), incorporation of the alkene at the polymer chain-end occurred. The most efficient systems identified with regard to the rate of reaction and yield were poly(butyl acrylate)/CPDA/ethyl vinyl ether (78% monoinsertion product after 1 h) and poly(butyl acrylate)/CPDA/1-pentene (73% insertion product after 7 h) at ambient temperature. An in-depth analysis of the reaction mechanism by 1H NMR and online size-exclusion chromatography-electrospray ionization tandem mass spectrometry (SEC/ESI−MSn) revealed that a possible [2 + 2] photoaddition mechanism of conjugation does not take place. Instead, fast β-cleavage of the photoexcited RAFT-end group with subsequent radical addition of an alkene was observed for all employed systems. The presented reaction thus provides a means of spatial and temporal control for the conjugation of alkenes to thiocarbonyl thio-capped macromolecules via the use of UV radiation.

Chain scission resists for extreme ultraviolet lithography based on high performance polysulfone-containing polymers

A series of polymers with a comb architecture were prepared where the poly(olefin sulfone) backbone was designed to be highly sensitive to extreme ultraviolet (EUV) radiation, while the well-defined poly(methyl methacrylate) (PMMA) arms were incorporated with the aim of increasing structural stability. It is hypothesized that upon EUV radiation rapid degradation of the polysulfone backbone will occur leaving behind the well-defined PMMA arms. The synthesized polymers were characterised and have had their performance as chain-scission EUV photoresists evaluated. It was found that all materials possess high sensitivity towards degradation by EUV radiation (E0 in the range 4–6 mJ cm−2). Selective degradation of the poly(1-pentene sulfone) backbone relative to the PMMA arms was demonstrated by mass spectrometry headspace analysis during EUV irradiation and by grazing-angle ATR-FTIR. EUV interference patterning has shown that materials are capable of resolving 30 nm 1:1 line:space features. The incorporation of PMMA was found to increase the structural integrity of the patterned features. Thus, it has been shown that terpolymer materials possessing a highly sensitive poly(olefin sulfone) backbone and PMMA arms are able to provide a tuneable materials platform for chain scission EUV resists. These materials have the potential to benefit applications that require nanopattering, such as computer chip manufacture and nano-MEMS.

Additive manufacturing of tissues and organs

Additive manufacturing techniques offer the potential to fabricate organized tissue constructs to repair or replace damaged or diseased human tissues and organs. Using these techniques, spatial variations of cells along multiple axes with high geometric complexity in combination with different biomaterials can be generated. The level of control offered by these computer-controlled technologies to design and fabricate tissues will accelerate our understanding of the governing factors of tissue formation and function. Moreover, it will provide a valuable tool to study the effect of anatomy on graft performance. In this review, we discuss the rationale for engineering tissues and organs by combining computer-aided design with additive manufacturing technologies that encompass the simultaneous deposition of cells and materials. Current strategies are presented, particularly with respect to limitations due to the lack of suitable polymers, and requirements to move the current concepts to practical application.

Two-dimensional coordination polymers in rubidium and caesium complexes with orthanilic acid

The crystal structures of the rubidium and caesium complexes with 2-aminobenzenesulfonic acid (orthanilic acid), [Rb4(C6H6NO3S)4(H2O)]n (1) and [Cs(C6H6NO3S)]n (2) and have been determined at 200 K. Complex 1 has a repeating unit comprising four independent and different Rb coordination centres, (RbO8), (RbO7), (RbN2O4) and (RbO10), each having irregular stereochemistry and involving a number of bidentate chelate sulfonate-O,O’-metal and bridging interactions, giving a two-dimensional polymeric layered structure. Anhydrous complex 2 is also polymeric with the irregular (CsO7) coordination polyhedron comprising six sulfonate oxygen donors from three separate bidentate chelate sulfonate ligands and one monodentate bridging sulfonate oxygen, giving a two-dimensional layered structure.

Power-law viscous materials for analogue experiments: New data on the rheology of highly-filled silicone polymers

The selection of appropriate analogue materials is a central consideration in the design of realistic physical models. We investigate the rheology of highly-filled silicone polymers in order to find materials with a power-law strain-rate softening rheology suitable for modelling rock deformation by dislocation creep and report the rheological properties of the materials as functions of the filler content. The mixtures exhibit strain-rate softening behaviour but with increasing amounts of filler become strain-dependent. For the strain-independent viscous materials, flow laws are presented while for strain-dependent materials the relative importance of strain and strain rate softening/hardening is reported. If the stress or strain rate is above a threshold value some highly-filled silicone polymers may be considered linear visco-elastic (strain independent) and power-law strain-rate softening. The power-law exponent can be raised from 1 to ~3 by using mixtures of high-viscosity silicone and plasticine. However, the need for high shear strain rates to obtain the power-law rheology imposes some restrictions on the usage of such materials for geodynamic modelling. Two simple shear experiments are presented that use Newtonian and power-law strain-rate softening materials. The results demonstrate how materials with power-law rheology result in better strain localization in analogue experiments.

Electrospraying of polymers with therapeutic molecules : state of the art

The encapsulation and release of bioactive molecules from polymeric vehicles represents the holy grail of drug and growth factor delivery therapies, whereby sustained and controlled release is crucial in eliciting a positive therapeutic effect. To this end, electrospraying is rapidly emerging as a popular technology for the production of polymeric particles containing bioactive molecules. Compared with traditional emulsion fabrication techniques, electrospraying has the potential to reduce denaturation of protein drugs and affords tighter regulation over particle size distribution and morphology. In this article, we review the importance of the electrospraying parameters that enable reproducible tailoring of the particles' physical and in vitro drug release characteristics, along with discussion of existing in vivo data. Controlled morphology and monodispersity of particles can be achieved with electrospraying, with high encapsulation efficiencies and without unfavorable denaturation of bioactive molecules throughout the process. Finally, the combination of electrospraying with electrospun scaffolds, with an emphasis on tissue regeneration is reviewed, depicting a technique in its relative infancy but holding great promise for the future of regenerative medicine.

In vitro biocompatibility of different polyester membranes

Nowadays, synthetic biodegradable polymers, such as aliphatic polyesters, are largely used in tissue engineering. They provide several advantages compared to natural materials which use is limited by immunocompatibility, graft availability, etc. In this work, poly(L-lactic) acid (PLLA), poly(DL-lactic) acid (PDLA), poly-epsilon-caprolactone (PCL), poly(L-lactic)-co-caprolactone (molar ratio 70/30) (PLCL) were selected because of their common use in tissue engineering. The membranes were elaborated by solvent casting. Membrane morphology was investigated by atomic force microscopy. The membranes were seeded with human fibroblasts from cell line CRL 2703 in order to evaluate the biocompatibility by the Alamar blue test. The roughness of the membranes ranged from 4 nm for PDLA to 120 nm and they presented very smooth surface except for PCL which beside a macroscopic structure due to its hydrophobicity. Human fibroblasts proliferated over 28 days on the membranes proving the non-in vitro toxicity of the materials and of the processing method. A further step will be the fabrication of three-dimensional scaffold for tissue engineering and the treatment of the scaffolds to augment cell adhesion.

The incidence and predictors of lower limb split skin graft failure and primary closure dehiscence in day case surgical patients

This project was an observational study of outpatients following lower limb surgical procedures for removal of skin cancers. Findings highlight a previously unreported high surgical site failure rate. Results also identified four potential risk factors (increasing age, presence of leg pain, split skin graft and haematoma) which negatively impact on surgical site healing in this population.

Vascular remodeling in the internal mammary artery graft and association with in situ endothelin-1 and receptor expression

BACKGROUND: The vasoconstricting peptide endothelin-1 (ET-1) has been associated with atherosclerotic cardiovascular disease, vascular smooth muscle cell (VSMC) growth stimulation, and intimal thickening. ET-1 binds 2 receptor subtypes, endothelin A and B, and the ETA receptor mediates vasoconstriction and VSMC growth. This study aims to quantitatively assess arterial remodeling variables and compare them with changes in ET-1, ETA, and ETB expression in the internal mammary artery (IMA). METHODS AND RESULTS: Specimens from 55 coronary artery disease (CAD) patients (45 men, 10 women; mean age 65 years) and 14 control IMA specimens (from 7 men and 7 women; mean age 45 years) were collected. IMA cross sections were assessed by histochemical and immunohistochemical staining methods to quantify the levels of medionecrosis, fibrosis, VSMC growth, ET-1, ETA, ETB, and macrophage infiltration. The percentage area of medionecrosis in the patients was almost double that in the controls (31.85+/-14.52% versus 17.10+/-9.96%, P=0.0006). Total and type 1 collagen was significantly increased compared with controls (65.8+/-18.3% versus 33.7+/-13.7%, P=0.07, and 14.2+/-10.0% versus 4.8+/-2.8%, P=0.01, respectively). Despite ACE and/or statin therapy, ET-1 expression and cell cycling were significantly elevated in the patient IMAs relative to the controls (46.27+/-18.46 versus 8.56+/-8.42, P=0.0001, and 37.29+/-12.88 versus 11.06+/-8.18, P=0.0001, respectively). ETA and ETB staining was elevated in the patient vessels (46.88+/-11.52% versus 18.58+/-7.65%, P=0.0001, and 42.98+/-7.08% versus 34.73+/-5.20%, P=0.0067, respectively). A mild presence of macrophages was noted in all sections. CONCLUSIONS: Elevated distribution of collagen indicative of fibrosis coupled with increased cell cycling and high levels of ET-1 and ETA expression in the absence of chronic inflammation suggests altered IMA VSMC regulation is fundamental to the remodeling process.