Polyisobutylene: A most unusual polymer

ABSTRACT: The influence of molecular weight, M, on the fragility and fast dynamics in polyisobutylene (PIB) was studied using dielectric and mechanical relaxation spec-troscopies, calorimetry, and Raman spectroscopy. The measurements indicate a decrease in fragility with increasing M for shorter chains, in the range of M where Tg is M-dependent. Such behavior is not observed for other polymers and is at odds with traditional theoretical models that predict an increase in fragility with chain length. These results confirm the unusual character of PIB, as evident in various properties including extremely low gas permeability, a low fragility, and a segmental relaxation spectrum much broader than expected for a low-fragility material. The reason for this anomalous behavior remains unclear, but might be related to the sym-metric structure of the PIB repeat unit, together with comparable flexibility of both structural components, the backbone and side groups. VC 2008 Wiley Periodicals, Inc

Role of chemical crosslinking in material-driven assembly offibronectin (nano)networks: 2D surfaces and 3D scaffolds

Poly(ethyl acrylate) (PEA) induces the formation of biomimetic fibronectin (FN) (nano)networks uponsimple adsorption from solutions, a process referred to as material-driven FN fibrillogenesis. The ability ofPEA to organize FN has been demonstrated in 2D and 2.5D environments, but not as yet in 3D scaffolds,which incorporate three-dimensionality and chemical crosslinkers that may influence its fibrillogenicpotential. In this paper we show for the first time that while three-dimensionality does not interferewith PEA-induced FN fibrillogenesis, crosslinking does, and we determined the maximum amount ofcrosslinker that can be added to PEA to maintain FN fibrillogenesis. For this, we synthesised 2D substrateswith different amounts of crosslinker (1 10% of ethylene glycol dimethacrylate) and studied the role ofcrosslinking in FN organization using AFM. The glass transition temperature was seen to increase withcrosslinking density and, accordingly, polymer segmental mobility was reduced. The organization ofFN after adsorption (formation of FN fibrils) and the availability of the FN cell-binding domain werefound to be dependent on crosslinking density. Surface mobility was identified as a key parameter for FNsupramolecular organization. PEA networks with up to 2% crosslinker organize the FN in a similar way tonon-crosslinked PEA. Scaffolds prepared with 2% crosslinker also had FN (nano)networks assembled ontheir walls, showing PEA s ability to induce FN fibrillogenesis in 3D environments as long as the amountsof crosslinker is low enough.M.S.S. acknowledges funding from ERC (HealInSynergy 306990) and the UK MRC (MR/L022710/1). The support from the Ministry of Economy and Competitiveness-Spain (MAT2015-69315-C3-1-R Project) including the FEDER financial support, is gratefully acknowledged. CIBER-BBN is an initiative funded by the VI National R&D&I Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program. CIBER Actions are financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund. We are also grateful to the Electron Microscopy Service of Universitat Politecnica de Valencia for their valuable help.Sabater I Serra, R.; León-Boigues, L.; Sánchez Laosa, A.; Gómez Estrada, L.; Gómez Ribelles, JL.; Salmerón Sánchez, M.; Gallego Ferrer, G. (2016). Role of chemical crosslinking in material-driven assembly offibronectin (nano)networks: 2D surfaces and 3D scaffolds. Colloids and Surfaces B: Biointerfaces. 148:324-332. https://doi.org/10.1016/j.colsurfb.2016.08.044S32433214

Achieving an early pregnancy following allogeneic uterine transplantation in a rabbit model

[EN] Objective: Uterine transplantation (UTx) has been proposed as a treatment option for women diagnosed with absolute uterine factor infertility (AUFI). The goal of UTx remains achieving pregnancy and live birth of a healthy neonate following allogeneic UTx. Our aim was to assess whether fertility was possible following allogeneic uterine transplantation (UTx), when the recipient had demonstrated long-term survival and had been administered immunosuppression. Study design: Nine allogeneic UTx in New Zealand White rabbits were performed using a pre-determined protocol. Tacrolimus was the immunosuppressant selected. Embryos were transferred into both cornua of the sole living recipient via a mini-midline laparotomy. The pregnancy was monitored with regular reproductive profiles and serial trans-abdominal ultrasound to measure conceptus growth (gestation sac and crown rump length (CRL)). Results: In the sole surviving doe a gestation sac was visualised on ultrasound from Day 9 (D9) after embryo transfer. Gestation sac diameter and CRL increased from D9 to D16 but by D18 the gestation sac had reduced in size. The fetus was no longer visible, suggesting fetal resorption had occurred. Subsequent scans on D22 and D25 did not demonstrate a gestation sac. Scheduled necropsy on D27 and histopathology confirmed evidence of a gravid uterus and presence of a gestational sac. A single episode of acute rejection occurred on D13. Conclusion: Pregnancy was achieved after rabbit allogeneic UTx but serial ultrasound suggested that fetal demise occurred prior to scheduled necropsy. The study represents only the third example of conception and pregnancy following an animal allogeneic UTx.The authors would like to thank all the staff and veterinarians at the Royal Veterinary College (London, UK) who have been with us from the beginning and have worked tirelessly at ensuring we had the best possible conditions to carry out our transplant work. ALD receives funding at UCLH/UCL via the Department of Health's NIHR Biomedical Research Centres funding scheme.Saso, S.; Petts, G.; David, AL.; Thum, M.; Chatterjee, J.; Vicente Antón, JS.; Marco Jiménez, F.... (2015). Achieving an early pregnancy following allogeneic uterine transplantation in a rabbit model. European Journal of Obstetrics and Gynecology and Reproductive Biology. (185):164-169. doi:10.1016/j.ejogrb.2014.12.017S16416918