All issues / Volume 13 (2019) / Issue 1 (January)
This is an editorial article. It has no abstract.
Adopting the beneficial chemical composition of mineral bone grafts and the interesting biomedical properties of the approved polycaprolactone, versatile manufacturing processes offering a near-net-shape fabrication and cost-effective scalability, has been used to fabricate highly porous polymer-ceramic biocomposite scaffolds with different amounts of the inorganic component CaCO3 by molded casting and fused deposition modelling. The mechanical properties and surface characteristics were evaluated after several steps of degradation by means of compression tests and scanning electron microscopy, respectively. Calcium release has been determined over a period of 4 weeks and the calcium phosphate phase formation on the surface was observed and validated by energy dispersive x-ray spectroscopy. The established production path and the use of the material combination polycaprolactone and calcium carbonate has enormous potential to manufacture individual and application-oriented open-porous scaffolds for hard tissue replacement.
Foamed poly(lactic acid) films reinforced with micro-crystalline cellulose (MCC), were uniaxially stretched to different ratios. At 10% (weight) loading MCC particles gave an approximately 3.5 times improvement in stiffness over unreinforced foams. X-ray tomography and image analysis showed that most MCC particles had low aspect ratios, were randomly oriented and well distributed. Stretching did not change the orientation of the MCC particles. Increases in stiffness with stretching were due to the alignment of the foam cell walls. Electron microscopy and image analysis showed that the foam cells were elongated and the walls aligned in the stretch direction. There was a good fit between measured stiffness and micro-mechanical modelling based on a variation of the Mori-Tanaka model for reinforcing particles randomly oriented in 3 dimensions.
Poly(propylene oxide)–poly(ethylene oxide)–poly(propylene oxide) (PPO–PEO–PPO) based bismaleimide (BMI) was employed as cross–linking agent for the synthesis of pH–sensitive clicked hydrogels by Diels–Alder (DA) reaction with furan–grafted chitosan in aqueous solution. The effect of the surrounding pH over the microstructure and the swelling ability of the hydrogels was evaluated depending on the initial composition. The results suggested that the hydrogels maintained the characteristic responsive properties of the original biopolymer even after the cross–linking reaction. The different macromolecular networks remarkably affected the final properties, especially when referring to pH–swelling sensitiveness and hydrogel porosity. In addition, the swelling parameters revealed that the hydrogels presented large liquid absorption capacity, showing excellent recovery properties and responsiveness at different pHs. The promising features of the ensuing hydrogels made them suitable as targeted pH–sensitive drug delivery systems.
Novel fluorescence and SERS encoded microspheres based on poly(glycidyl methacrylate) (PGMA) microspheres were developed by a controllable approach. The microspheres were encoded by four fluorescence dyes and three surface enhanced Raman spectra (SERS) probes. Multiple dyes could be simultaneously incorporated into the PGMA microspheres for encoding and the intensity of the fluorescence can be tuned by adjusting the feeding ratio. The PGMA microspheres were coated by silver nanoparticles and encoded by single and multiple SERS reporters. The fluorescence and SERS joint encoded PGMA microspheres were fabricated. All the fluorescence encoding signals can be excited at 488 nm. The fluorescent and SERS signals of dual-mode microspheres could be obtained from two optical channels and non-overlapping of emission spectra was observed in these encoded microspheres, which greatly increased the encoding capacity. The as prepared fluorescence and SERS encoded microspheres possess stable and distinct spectral encoding signals, large encoding capacity.
Efficient adhesion between polymers and two-dimensional materials, such as graphene, is fundamental and crucial for the development of flexible devices or special coating materials as well as defining the quality of the transfer processes for these materials. Here, contact angle (CA) measurements of four distinct polymers, low-density polyethylene – LDPE, polypropylene – PP, poly (butylene adipate-co-terephthalate) – PBAT and poly (vinylidene-fluoride-co-trifluoroethylene) – PVDF-TrFE, and graphene achieved by chemical vapor deposition (CVD) were used to understand the adhesion phenomena between such materials. The CA measurements were carried out at specific thermal conditions mimicking a transfer process that is based on direct contact of CVD graphene and polymers above their melting temperature (Direct Dry Transfer – DDT). Surface analysis allowed the efficiency of such transfer method to be pre-estimated owing to an understanding of the adhesion properties of both materials by comparing their polar and dispersive components values. However, rheological properties and chemical structures seemed to be equally important in this evaluation, either by molecular weight modification or introduction of chemical groups onto the surface of polymer films. The results allowed for an understanding of the role of the main factors in adhesion phenomena between graphene and polymers and how they can be used to improve graphene coating during transfer processes.
Thermally reversible light scattering (TRLS) materials based solely on benzoxazine-urethane (BA-a/PU) alloys were successfully fabricated and demonstrated in this work. The alloys displayed the opaque state below 40 °C. The alloys were transformed to the transparent state upon exposing to the transition temperature of 60–130 °C, depending on the molecular weights and mass concentrations of urethane prepolymers in the BA-a/PU alloys. The optical state transitions were reversible with small hystereses. BA-a/PU alloys exhibited a good optical contrast with 0%T at the light scattering state and almost 100%T at the transparent state. The alloys were glassy and form-stable up to 250 °C, due to the synergistic behavior in the glass transition temperatures. The reaction-induced phase separation effectuated by the incorporation of urethane prepolymer into thermosetting polybenzoxazine, the sizes and local concentrations of the phase-separated urethane microdomains in the supporting polybenzoxazine matrix, and the reversible dissolution and demixing of urethane microdomains and polybenzoxazine phase played crucial roles on TRLS properties of the developed benzoxazine-urethane alloys.
This work reports the preparation and testing of porous beds made from packed vinylated silica microparticles (SiMPs) grafted with thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) and exhibiting on demand thermally triggered permeability. PNIPAM-grafted hybrid SiMPs with diameters of 1.40–1.55 μm were synthesized and characterized with Attenuated Total Reflection Fourier Transform Infrared Spetroscopy (ATR-FTIR), Thermogravimetric Analysis (TGA), Flow Particle Image Analysis (FPIA) and Scannning Electron Miscroscopy (SEM) to elucidate their composition and morphology. The PNIPAM-grafted SiMPs were used to prepare thermoresponsive beds of dimensions 1×0.5×0.5 cm inside filtration tubes. The thermo-regulated permeability of solutions of selected model compounds, namely caffeine, ketoprofen, orange II, bromocresol green and cresol red across the hybrid beds was tested by calculating the retention percentage of the model compounds at temperatures below and above the lower critical solution temperature (LCST) of PNIPAM. The results showed a clear control over the permeability of the packed hybrid beds mediated by external temperature changes. This control was achieved by virtue of the switchable nanovalves created by the thermoresponsive PNIPAM present in the inter-particle voids of the packed beds.