4D printing has a great potential for the manufacturing of soft robotics and medical devices. The alliance of digital light processing (DLP) 3D printing and novel shape-memory photopolymers allows ...for the fabrication of smart 4D-printed medical devices in high resolution and with tailorable functionalities. However, most of the reported 4D-printed materials are nondegradable, which limits their clinical applications. On the other hand, 4D printing of biodegradable shape-memory elastomers is highly challenging, especially when transition points close to physiological temperature and shape fixation under ambient conditions are required. Here, we report the 4D printing of biodegradable shape-memory elastomers with tailorable transition points covering physiological temperature, by using poly(D,L-lactide-co-trimethylene carbonate) methacrylates at various monomer feed ratios. After the programming step, the high-resolution DLP printed stents preserved their folded shape at room temperature, and showed efficient shape recovery at 37 °C. The materials were cytocompatible and readily degradable under physiological conditions. Furthermore, drug-loaded devices with tuneable release kinetics were realized by DLP-printing with resins containing polymers and levofloxacin or nintedanib. This study offers a new perspective for the development of next-generation 4D-printed medical devices.
Digital light 4D printing of biodegradable drug-eluting elastomeric devices with tailorable thermal response at the physiological temperature and tunable drug release. Display omitted
•Biodegradable shape-memory elastomers were DLP printed.•The materials displayed elasticity below and above their transition temperatures.•4D printed elastomeric stents showed efficient shape recovery at 37 °C.•4D printed drug-loaded devices showed tuneable release kinetics.
In this paper two methods of preparation of yttrium orthovanadate nanopowders were presented: Solid State Reaction (top – down approach) and Solution Combustion Synthesis (bottom – up approach). For ...starting structural characterization, X – Ray Powder Diffraction (XPRD) and Field Emission Scanning Electron Microscopy (FESEM) were used. We report the change in reflection spectra in europium doped YVO4 nanopowders with comparison to its bulk analog. In UV–Vis reflection spectra we consider the change in values of band gap in these structures, after resizing it from bulk to nanomaterial. In Far – Infrared (FIR) reflection spectra, we registered the existence of Surface Optical Phonon (SOP) and different multi – phonon processes which alter the reflection spectra of bulk YVO4. The influence of Eu ions is reflected through multi – phonon processes that occur and are connected with energy transfer from YVO4 lattice to Eu ions. All IR spectra were modeled using classical oscillator model with Drude part added which takes into account the free carrier contribution. Since our samples are distinctively inhomogeneous materials, we use Effective Medium theory in Maxwell Garnett approximation to model its effective dieletric function.
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•Eu3+ doped YVO4 prepared by two methods: SCS and SSR.•We report the change in reflection spectra in europium doped YVO4 nanopowders.•We register the existence of Surface Optical Phonon (SOP) and multi – phonon processes.•SOP mode plays a role of longitudinal optical (LO) phonon.•SOP frequency has a linear dependence on filling factor.
Polycrystalline Bi1−xPr(Ce)xFeO3 ceramics (x = 0, 0.03, 0.05 and 0.10) were prepared by auto-combustion method using urea as a fuel. The influence of Pr(Ce) doping on structural, vibrational, ...morphological, dielectric and ferroelectric properties of BiFeO3 polycrystalline ceramics was investigated. From X-ray diffraction (XRD) and scanning electron microscopy measurements it was observed that Pr(Ce) doping generated a reduction of the crystallite (grain) size of BiFeO3 and contraction of the rhombohedral cell due to the increased compressive strain. The changes seen in the XRD and Raman spectra of 10% Pr(Ce)-doped samples, pointed to a probable appearance of orthorhombic (pseudotetragonal) crystal structure. The pristine BiFeO3 exhibited rounded shape, non-saturated ferroelectric hysteresis loop. The dielectric constant and dielectric loss have shown strong dispersion at lower frequencies, typical for conductive BiFeO3. Dielectric and ferroelectric properties at room temperature were improved with Pr doping. Concerning the Ce-doped samples, only the 3% Ce-doped sample exhibited a better shaped hysteresis loop and improved dielectric properties compared to the pristine BiFeO3. With further increase of Ce content the ferroelectric properties degraded.
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•Pr(Ce)-doped BiFeO3 ceramics were prepared by new auto-combustion method.•Structural, dielectric and ferroelectric properties were investigated.•Structural phase transition for the 10% Pr(Ce)-doped samples was observed.•Dielectric and ferroelectric properties were improved with increased Pr doping.•Dielectric and ferroelectric properties degraded with increasing Ce content.
► In this paper MnFe
2O
4 has been prepared by a soft mechanochemical synthesis in a planetary ball mill. ► The spinel phase was first observed for 12
h and completed for 25
h of milling in both case ...of synthesis. ► On the basis of Raman research is observed five first-order Raman active modes. ► Magnetic measurements after 25
h of milling show magnetization value of 70.4
emu/g and 71.1
emu/g. ► Mössbauer spectrometry reveals superparamagnetic particles.
Manganese ferrite, MnFe
2O
4 have been prepared by a soft mechanochemical route from mixture of (a) Mn(OH)
2 and α-Fe
2O
3 and (b) Mn(OH)
2 and Fe(OH)
3 powders in a planetary ball mill. The mixture was activated for varying duration. Soft mechanochemical reaction leading to formation of the MnFe
2O
4 spinel phase was followed by X-ray diffraction, Raman spectroscopy, scanning and transmission microscopy and magnetization measurements. The spinel phase formation was first observed after 12
h of milling and its formation was completed after 25
h in both cases. The synthesized MnFe
2O
4 ferrite has a nanocrystalline structure with a crystallite size of about 40 and 50
nm respectively for cases (a) and (b). There are five Raman active modes. Measurements after 25
h of milling show magnetization values of 70.4
emu/g and 71.1
emu/g respectively for cases (a) and (b). In order to understand better the whole process of phase formation, Mössbauer measurements were done.
Y-doped HfO2 nanopowders, produced by metathesis synthesis, exhibit ferromagnetism at room temperature. The X-ray diffraction and Raman measurements have shown that HfO2 nanopowders undergo phase ...transformation from monoclinic to tetragonal and cubic phase with increasing of Y content. The X-ray photoelectron spectroscopy and Raman analysis gave evidence that Y-doped HfO2 nanopowders are oxygen deficient. The ferromagnetic properties of Y-doped HfO2 nanocrystals are dependent on crystal structure changes. The structural transformation from monoclinic to tetragonal phase with Y doping is followed by increased ferromagnetic ordering because of the increased concentration of oxygen vacancies (VO) in different charge states. Higher Y content favors the formation of cubic phase and the ferromagnetism significantly weakens. In cubic hafnia phase, yttrium can form (VO–YHf) defect complexes in different charge states. The appearance of these complexes can be responsible for the degradation of ferromagnetic ordering.
The Solution Combustion Synthesis (SCS) method was used to prepare nanopowders of europium doped cubic Gd2Zr2O7 nanopowders. The surface of the samples have been investigated using atomic force ...spectroscopy (AFM) and far-infrared spectroscopy (FIR). Far-infrared reflectivity spectra of Eu3+ doped Gd2Zr2O7 nanopowders were measured at room temperature in spectral region between 80 and 650 cm−1. The Maxwell–Garnet formula was used to model dielectric function of Eu3+ doped Gd2Zr2O7 nanopowders as mixtures of homogenous spherical inclusions in air.
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•FIR measurements on Eu3+ doped Gd2Zr2O7 nanopowder.•Low frequency modes registered for the first time.•Phonons registered in both Gd2Zr2O7 isomeric structures.•Regarding isotopic shift, two previously unknown modes assigned.
Far-infrared spectroscopic study of CeO2 nanocrystals Popović, Z. V.; Grujić-Brojčin, M.; Paunović, N. ...
Journal of nanoparticle research : an interdisciplinary forum for nanoscale science and technology,
2015/1, Letnik:
17, Številka:
1
Journal Article
We present the far-infrared reflectivity spectra of 5 nm-sized pure and copper-doped Ce
1−
x
Cu
x
O
2−
y
(
x
= 0; 0.01 and 0.10) nanocrystals measured at room temperature in the 50–650 cm
−1
...spectral range. Reflectivity spectra were analyzed using the factorized form of the dielectric function, which includes the phonon and the free carriers contribution. Four oscillators with TO energies of approximately 135, 280, 370, and 490 cm
−1
were included in the fitting procedure. These oscillators represent local maxima of the CeO
2
phonon density of states, which is also calculated using the density functional theory. The lowest energy oscillator represents TA(L)/TA(X) phonon states, which become infrared-active
E
u
modes at the L and X points of the Brillouin zone (BZ). The second oscillator originates from TO(Γ) phonon states. The oscillator at ~400 cm
−1
originates from Raman mode phonon states, which at the L point of BZ also becomes infrared-active
E
u
mode. The last oscillator describes phonons with dominantly LO(Γ) infrared mode character. The appearance of phonon density of states related oscillators, instead of single
F
2u
infrared-active mode in the far-infrared reflectivity spectra, is a consequence of the nanosized dimension of the CeO
2
particles. The best fit spectra are obtained using the generalized Bruggeman model for inhomogeneous media, which takes into account the nanocrystal volume fraction and the pore shape.
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•YAG:Dy nanopowder was produced by Solution Combustion Synthesis (SCS) method.•Powders are composed by well-defined and separated nanoparticles.•Some particles are agglomerated but ...there are also separated particles.•The dielectric function was modeled by the Maxwell–Garnet formula.•Optical phonon confinement is registered.
The solution combustion synthesis was used to prepare nanopowders of yttrium aluminum garnet (YAG) and YAG doped with dysprosium ions, Dy3+, (YAG:Dy). The morphology, specific surface area, texture, and optical properties of the prepared materials were studied by the means of scanning electron microscopy (SEM), nitrogen adsorption method, and far-infrared spectroscopy at room temperature in the spectral region between 80 and 600cm−1. It was established that all the examined samples were microporous. The Maxwell–Garnet formula was used to model dielectric function of YAG and YAG:Dy nanopowders as mixtures of homogenous spherical inclusions in air.
BaTiO
3 ceramic powders were prepared by a complex method based on the Pechini type reaction route and mechanically assisted synthesis. In both ways BaTiO
3 ceramics were sintered after 120
min on ...1300
°C without pre-calcination steps. The crystal structure was investigated by the XRD, IR and Raman spectroscopy. The particle size and morphology of BaTiO
3 were examined by XRD and SEM. The XRD results of powders indicate the formation of cubic phase of BaTiO
3. It can be observed that in the case of Pechini process BaTiO
3 powder is well crystallized but in the case of mechanochemistry process, significant amount of amorphous phase was detected. The sintered BaTiO
3 ceramic sample prepared by Pechini process, shows the formation of tetragonal phase. However, IR and Raman spectrum showed a mixture of cubic and tetragonal for BaTiO
3 obtained by Pechini process and tetragonal for BaTiO
3 obtained by mechanically assisted synthesis.
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