In the present work polylactide (PLA)/15wt% hydroxyapatite (HA) porous scaffolds with pre-modeled structure were obtained by 3D-printing by fused filament fabrication. Composite filament was obtained ...by extrusion. Mechanical properties, structural characteristics and shape memory effect (SME) were studied. Direct heating was used for activation of SME. The average pore size and porosity of the scaffolds were 700μm and 30vol%, respectively. Dispersed particles of HA acted as nucleation centers during the ordering of PLA molecular chains and formed an additional rigid fixed phase that reduced molecular mobility, which led to a shift of the onset of recovery stress growth from 53 to 57°C. A more rapid development of stresses was observed for PLA/HA composites with the maximum recovery stress of 3.0MPa at 70°C. Ceramic particles inhibited the growth of cracks during compression-heating-compression cycles when porous PLA/HA 3D-scaffolds recovered their initial shape. Shape recovery at the last cycle was about 96%. SME during heating may have resulted in “self-healing” of scaffold by narrowing the cracks. PLA/HA 3D-scaffolds were found to withstand up to three compression-heating-compression cycles without delamination. It was shown that PLA/15%HA porous scaffolds obtained by 3D-printing with shape recovery of 98% may be used as self-fitting implant for small bone defect replacement owing to SME.
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•PLA/15%HA scaffolds with recovery stress of 3.0 MPa were obtained by 3D-printing.•HA particles act as nucleation centers and form an additional rigid fixed phase.•HA particles inhibit growth of cracks during compression-heating-compression cycles.•SME results in “self-healing” by narrowing the cracks with shape recovery of 98%.•PLA/15%HA porous scaffolds may be used as self-fitting bone implants.
In the present work PLA and PLA/15% wt. HA porous scaffolds for bone replacements with pre-modeled structure were obtained by 3D-printing by fused filament fabrication. The average pore size and ...porosity of the scaffolds were 700 μm and 30 vol. %, respectively. The modulus of elasticity, height of the samples, elastic deformation, accumulated energy and structural characteristics of 3D porous scaffolds were studied during the low-cycle tests. A decrease in the height, collapse of pores, delamination, bending and shear of the printed layers, growth and propagation of cracks during cyclic loading was observed. The introduction of dispersed HA particles reduced the rate of accumulation of defects. PLA/15%HA porous scaffolds with a larger crack resistance have the potential to be used as implants for trabecular bone replacement which are able to function under cyclic loading at a stress of 21 MPa for a long time without change.
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•Introduction of HA nanoparticles results in higher SME activation energy.•Shape programming at 64°C led to the maximum recovery stress.•Accumulation of defects led to decrease in ...shape recovery rate and recovery stresses.•3D-printed PLA/HA scaffolds support MSCs survival and stimulate active proliferation.
3D-printed porous scaffolds based on polylactide (PLA)/15% wt. nano-hydroxyapatite (HA) with shape memory effect (SME) for self-fitting implants were studied. Introduction of HA nanoparticles into the PLA matrix had an effect on the ordering of polymer molecular chains. The presence of HA nanoparticles caused a change in friction between molecular chains during the glass transition. Apparent activation energies of SME for PLA and PLA/HA 3D-printed samples were 490 and 555kJ/mol, respectively. HA nanoparticles acted as centers for the formation of additional rigid fixed phase that governed shape memory properties. The maximum recovery stress was observed in case of shape programming in the glass transition interval at 64°C. However, cyclic SME tests showed that the increase in number of cycles “programming – SME activation” led to decrease in shape recovery rate and recovery stresses due to accumulation of defects. It was demonstrated that 3D-printed porous PLA/HA scaffolds support mesenchymal stromal cells (MSCs) survival, and stimulate active proliferation of the cells as well. Such scaffolds with SME colonized by MSCs have the potential to be used as self-fitting implants for bone replacement and could also be beneficial in the engineering of complex tissues. MSCs colonization of scaffold favors vascularization of the implant, which is essential for the successful bone prosthesis.
Structural, mechanical and tribological properties of composite materials based on ultra-high molecular weight polyethylene reinforced with carbon fibers were investigated. The effect of surface ...modification of carbon fibers on the interaction at the fiber–matrix interface in UHMWPE based composites was studied. It was found that the thermal oxidation of carbon fibers by air oxygen at 500 °C can significantly enhance the interfacial interaction between the polymer matrix and carbon fibers. This allowed us to form composite materials with improved mechanical and tribological properties.
The microstructure, morphology, micro hardness and electrochemical properties of the deposited Ni-Al coating on the surface of hypoeutectoid steel, Nickle, Aluminum and Titanium substrates were ...analyzed by scanning electron microscopy, X-ray diffraction, micro hardness and electrochemical analysis. In this study the Ni-Al coating was produced by mechanical alloying method using a self-constructed vibratory ball mill with subsequent laser treatment. The approximate thickness of the coating was about 100 μm. The conditions of laser treatment, allowing to obtain Ni-Al intermetallic coating on the pre-alloyed by mechanical cladding substrates, were determined.
•Ni-Al intermetallic coatings were obtained by mechanical alloying (MA) and laser treatment.•The optimal regime of laser treatment of the obtained MA coating was determinated.•Process conditions of the MA method and laser treatment not involve the overheating of the substrate.•Synthesized NiAl intermetallic coating has relatively good electrochemical properties.
• Both chemical and thermal treatments of UKN 5000 carbon fibers allow one to obtain well-developed surface. • The changes of structure and properties of VMN-4 fibers after both thermal and chemical ...oxidation are insignificant due to more perfect initial structure of these fibers. • The oxidative treatment of carbon fibers allows one to improve the interfacial interaction in the UHMWPE-based composites. • The oxidative treatment of the fibers allows one to a triple increase of Young’s modulus of the modified fibers reinforced UHMWPE composites.
The PAN-based carbon fibers (CF) were subjected to thermal and chemical oxidation under various conditions. The variation in the surface morphology of carbon fibers after surface treatment was analyzed by scanning electron microscopy (SEM). It was found that the tensile strength of carbon fibers changed after surface modification. The interaction between the fibers and the matrix OF ultra-high molecular weight polyethylene (UHMWPE) was characterized by the Young modulus of produced composites. It was shown that the Young modulus of composites reinforced with modified carbon fibers was significantly higher than that of composites reinforced with non-modified fibers.
► By mechanical alloying method have been produced ternary TiFe-based compounds. ► The doped TiFe+5%Al and TiFe+4%Cr alloys demonstrated a simplified activation. ► The doped alloys demonstrated ...reversible hydrogen capacity of 0.7wt.%. ► TiFe+5%Al possessed the highest plateau in the two-phase region of the isotherms. ► The ternary compounds had a reduced hysteresis as compared with unalloyed TiFe.
A series of nanostructured alloys based on TiFe intermetallic compound were synthesized from the metallic elements in a planetary ball mill by solid state mechanical alloying. Al and Cr were added as doping components to a Fe-50% (at.) Ti powder mixture. Phase and structure transformations during mechanical alloying and subsequent annealing as well as hydrogen interaction with the alloys prepared were studied. It was shown that reversible hydrogen sorption capacity of the nanostructural alloys based on the TiFe intermetallic compound was of 0.7wt.% at room temperature. The alloys studied demonstrated a simplified activation of hydrogenation. A correlation between the alloys behavior in their reactions with hydrogen and structure parameters of the hydrogenated samples has been discussed.
► Radiation-protective composites were fabricated by solid state intermixing and thermal pressing. ► The composites based on UHMWPE contain В4С and W nanopowders as fillers. ► The mechanical and ...γ-radiation protective properties of the polymer-matrix nanocomposites were determined experimentally. ► For composites containing 12% B4C and 12% W the mechanical properties were studied prior to and after the irradiation with fast neutrons.
UHMWPE-based nanostructured composites containing B4C and W nanopowders were fabricated and studied. The mechanical and γ-radiation protective properties of the polymer-matrix nanocomposites were determined experimentally. For selected composites the mechanical properties were studied prior to and after the irradiation.
CF-PEEK composites were manufactured by 3D-printing using a novel FDM methodology and customized printer and were compared with their cast counterparts. The characterization of composite thermal ...properties in the range 25–300 °C revealed that 3D-printed CF-PEEK composites manifest 25–30% lower thermal conductivity than cast composites. Short carbon fibers used for reinforcement showed orientation along the polymer flow both in cast and 3-D printed samples causing the anisotropy of thermal properties. The hierarchical nature of 3DP CF-PEEK porosity was observed by SEM imaging, which allowed the identification of large scale inter-layer gaps and cracks, and fine scale intra-layer defects that are likely to be induced by the thermal and mechanical gradients within the deposit that arise during fabrication. Purposeful lay-up of long continuous carbon yarns during 3D-printing opens a way to fabricate tailored mechanical parts with desired anisotropy of properties.
•Successful 3D printing of continuous Carbon Fiber-reinforced PEEK matrix composites is reported.•Porosity caused by 3D printing reduces density and thermal conductivity compared to cast composites.•Large pores at the interfaces of deposited layers lead to damage localization and multiple crack formation under load.•Fine imperfections within individual layers caused by process-induced temperature gradients give rise to small-scale cracks.•Hierarchical porosity induces thermal conductivity anisotropy of 3DP CF-PEEK structures compared to their cast counterparts.
•Metal-polymer composite membranes have been prepared via MA.•Composite membranes consist of LaNi5-type alloy and polyethylene.•Addition of metal filler leads to a drop of the phase transition ...activation energy.•Hydrogen processing results in a shift of the internal friction peak.
In the present work, mechanical properties of metal-polymer composite membranes for hydrogen separation have been investigated by tensile test and mechanical spectroscopy methods. The membranes were prepared by high-energy ball milling and subsequent thermal pressing of a powder mixture of polyethylene with 10 wt% hydride-forming intermetallic compound LaNi2.5Co2.4Mn0.1. The membranes were then subjected to activation by long exposure in a hydrogen atmosphere. The static tensile test showed a slight decrease in membrane tensile strength after hydrogen activation that may be explained by intermetallic particle embrittlement. Mechanical spectroscopy study reveals a shift of the internal friction peak of the activated membrane by 22 K towards lower temperatures and a small decrease of the activation energy of polyethylene viscoelastic transformation from 144 kJ/mol to 138 kJ/mol.
