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Abstract: The mechanical behaviour, crystalline and macromorphology structure development during uniaxially deformation and annealing of poly-L- lactic acid (PLLA), with varying strain rate and draw temperatures, (Td) above Tg, have been investigated using Small- and wide-angle X-ray scattering (SAXS/WAXS), microscopy, thermal and mechanical techniques. The mechanical behaviour of PLLA, was strongly dependent on Td where embrittlement and eventual failure were observed as Td was increased, during uniaxial drawing of the amorphous polymer. This was mirrored in the bulk surface morphology where crazing, microvoiding and cavitation occurred with increasing Td. SAXS/WAXS data showed that strain-induced crystallization occurs on drawing, but crystallite orientation decreased with increasing Td, due to chain relaxation at temperatures ≥30 oC above Tg. However, no long-range oriented lamellar macromorphology was observed post-draw directly and only developed in the samples that were step annealed at temperatures above Td. Also, the disordered α’ crystal form was observed post-draw at Td between 60 – 80 oC, whereas Td ≥ 90 oC, resulted in the ordered α crystal form directly. However, on annealing at temperatures of ≥110 oC, the α’- α crystal transition ensued and in all samples, an oriented lamellar macromorphology developed. Therefore, Td and post-draw annealing, have a significant influence on the mechanical properties, crystallinity and crystalline phase transformation in PLLA, which in-turn, affects the polymers medical and industrial applications.

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Abstract: Monodisperse sequenced peptides and peptoids present unique nano-structures based on their self-assembled secondary and tertiary structures. However, the generation of peptide and peptoid hybrid oligomers in a sequence-defined manner via Ugi multicomponent reaction has not yet been studied. Herein, we report a synthetic strategy that enables both the modification of peptides as well as the generation of sequence-defined peptide-peptoid hybrid structures. Our synthetic methodology rests on the fusion of solid phase peptide synthesis with Ugi multicomponent reactions. We evidence that a diversity of chemical functionalities can be inserted into peptides or used in the design of peptide-peptoid hybrids exploiting a wide functional array including amines, carboxylic acids, hydrocarbons, carbohydrates as well as polymers, introducing a sequence-defined synthetic platform technology for precision peptoid hybrids.

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Abstract: We present a novel family of biocompatible hydrogels containing Nafion and poly(ethylene oxide) based block copolymers. In aqueous environment, thermodynamically stable ionomer-copolymer complexes are formed, as evident by light scattering and quartz crystal microbalance experiments. Moreover, incorporation of Nafion dramatically modifies the phase behaviour and the rheological properties of copolymer hydrogels. The hybrid systems not only undergo sharp and thermally reversible sol-gel transitions below the body temperature, thus retaining their injectable nature, but they also generate mechanically robust hydrogels. Moreover, ibuprofen was continuously released over a period of 26 days for the Nafion/Pluronic hydrogel, compared to only 3 days for the Nafion-free system. The hybrid gels are promising candidates for 3D-bioprinting and controlled drug release applications.

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Abstract: Simultaneous SAXS-WAXD measurements are carried out to gain information about the microstructure and the molecular orientation developed by polymeric chains during the electrospinning process. Three semicrystalline polymers were studied, namely polyacrylonitrile, Nylon 6,6, and poly(ethylene oxide), as non-woven mats with either randomly arranged or aligned electrospun fibers. Mat thermal and morphological properties are investigated, together with their structural details in order to derive their hierarchical structure from the macro to the nano-scale. SAXS patterns have an elliptical shape with the main axis along the equator direction. No reflections are noticeable along the meridional direction, suggesting that the investigated electrospun fibers have a fibrillar structure with no trace of lamellar morphology. Combining the values of the unit cell and of the crystal size it can be concluded that in the fibers the ordered domains are organized into a bundle of fibrils due to the lateral aggregation of roughly 10 unit cells and the regular ordering of about either 50 (Nylon 6,6 and polyacrylonitrile) or 25 (poly(ethylene oxide)) cells in the chain direction.

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Abstract: Amphiphilic diblock copolymer nano-objects can be readily prepared using reversible addition–fragmentation chain transfer (RAFT) polymerization. For example, poly(glycerol monomethacrylate) (PGMA) chain transfer agents (CTA) can be chain-extended using 2-hydroxypropyl methacrylate (HPMA) via RAFT aqueous dispersion polymerization to form well-defined spheres, worms or vesicles at up to 25% solids. The worm morphology is of particular interest, since multiple inter-worm contacts lead to the formation of soft free-standing gels, which undergo reversible degelation on cooling to sub-ambient temperatures. However, the critical gelation temperature (CGT) for such thermo-responsive gels is ≤20 °C, which is relatively low for certain biomedical applications. In this work, a series of new amphiphilic diblock copolymers are prepared in which the core-forming block comprises a statistical mixture of HPMA and di(ethylene glycol) methyl ether methacrylate (DEGMA), which is a more hydrophilic monomer than HPMA. Statistical copolymerizations proceeded to high conversion and low polydispersities were achieved in all cases (Mw/Mn < 1.20). The resulting PGMA-P(HPMA-stat-DEGMA) diblock copolymers undergo polymerization-induced self-assembly at 10% w/w solids to form free-standing worm gels. SAXS studies indicate that reversible (de)gelation occurs below the CGT as a result of a worm-to-sphere transition, with further cooling to 5 °C affording weakly interacting copolymer chains with a mean aggregation number of approximately four. This corresponds to almost molecular dissolution of the copolymer spheres. The CGT can be readily tuned by varying the mean degree of polymerization and the DEGMA content of the core-forming statistical block. For example, a CGT of 31 °C was obtained for PGMA59-P(HPMA91-stat-DEGMA39). This is sufficiently close to physiological temperature (37 °C) to suggest that these new copolymer gels may offer biomedical applications as readily-sterilizable scaffolds for mammalian cells, since facile cell harvesting can be achieved after a single thermal cycle.