Ceramic-polymer Composites Research Articles

Relaxation processes and conduction behaviour in PVDF-TrFE and KNN-based composites

Polymer-ceramic composites have gained considerable attention in flexible electronic devices due to their uncommon features such as high dielectric constant, low conductivity, and good mechanical flexibility. The electrical and mechanical responses of various components (ceramic grain & grain boundary, polymer chains, and interface) need to be elucidated to rationally design high-performance polymer-ceramic composites. This paper provides a detailed analysis of dynamic mechanical and frequency-dependent dielectric behaviour with temperature to discern the various mechanisms responsible for the relaxations in the polyvinylidene fluoride-trifluoro ethylene/K0·5Na0·5NbO3–CaZn1/3Ta2/3O3 (PVDF-TrFE/KNN-1CZT) composite fabricated using solution casting technique. The FTIR spectra and x-ray diffraction patterns indicate the existence of the polar β-phase, confirming the ferroelectric nature of polymer films. The ferroelectric-paraelectric phase transition (TC ∼ 130 °C) of polymer film obtained from the DSC & DMA data was corroborated by the dielectric study. The introduction of ceramic fillers in polymer induces an additional relaxation in the 10 kHz to 1 MHz frequency range, owing to the ceramic-polymer interface formation, which is responsible for increment in the dielectric constant and storage capacity of the composites. The effective dielectric constant of the composite was modelled using the Maxwell-Garnet and Yamada models. The enhanced dielectric constant of composite films (εr ∼ 28) with the addition of dielectric filler qualifies these materials for flexible high-performance capacitive devices. Further, this study enables a better understanding of the various relaxation processes in the composite with dielectric fillers.

Enhancing functional properties of PVDF-HFP/BZT-BCT polymer-ceramic composites by surface hydroxylation of ceramic fillers

We report the mechanism to enhance the dielectric and ferroelectric behavior of polymer-ceramic composites through surface hydroxylation of 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-BCT) ceramic filler-particles embedded in PVDF-HFP copolymer matrix. Varying the hydroxylated h-(BZT-BCT) filler particle-content (φ = 0–40 wt%) in PVDF-HFP copolymer matrix, composite films (of ~75 μm thickness) were prepared. We observed that, with an increase in filler content up to an optimum concentration of 15 wt%, a microstructure with gradually denser particle-arrangement and enhanced particles-polymer surface interaction is exhibited, which leads to improved dielectric and ferroelectric behavior. The energy storage density (728 mJ/cm3 at an electric field of 750 kV/cm) of the composite with 15 wt% of h-(BZT-BCT) is found to be much higher than those of the pure BZT-BCT sample, pure PVDF-HFP copolymer and their composites. Our work demonstrates the method of enhancing the functional properties through a suitable microstructure of composite materials with surface-hydroxylation of filler particles.

Fabrication of fiber-reinforced polymer ceramic composites by wet electrospinning

We propose a novel approach of wet electrospinning to yield fiber-reinforced polymer ceramic composites, where a reactive ceramic precursor gel is used as a collector. We illustrate our approach by generating polyethylene oxide (PEO) fibers in a potassium silicate gel; the gel is later activated using metakaolin to yield a ceramic-0.5 wt% PEO fiber composite. An increase of 29% and 22% is recorded for the fabricated polymer ceramic composites in terms of indentation modulus and indentation hardness respectively. Our initial findings demonstrate the process viability and might lead to a potentially scalable manufacturing approach for fiber-reinforced polymer ceramic composites.

Hydroxyapatite Obtained via the Wet Precipitation Method and PVP/PVA Matrix as Components of Polymer-Ceramic Composites for Biomedical Applications.

The aspect of drug delivery is significant in many biomedical subareas including tissue engineering. Many studies are being performed to develop composites with application potential for bone tissue regeneration which at the same provide adequate conditions for osteointegration and deliver the active substance conducive to the healing process. Hydroxyapatite shows a great potential in this field due to its osteoinductive and osteoconductive properties. In the paper, hydroxyapatite synthesis via the wet precipitation method and its further use as a ceramic phase of polymer–ceramic composites based on PVP/PVA have been presented. Firstly, the sedimentation rate of hydroxyapatite in PVP solutions has been determined, which allowed us to select a 15% PVP solution (sedimentation rate was 0.0292 mm/min) as adequate for preparation of homogenous reaction mixture treated subsequently with UV radiation. Both FT-IR spectroscopy and EDS analysis allowed us to confirm the presence of both polymer and ceramic phase in composites. Materials containing hydroxyapatite showed corrugated and well-developed surface. Composites exhibited swelling properties (hydroxyapatite reduced this property by 25%) in simulated physiological fluids, which make them useful in drug delivery (swelling proceeds parallel to the drug release). The short synthesis time, possibility of preparation of composites with desired shapes and sizes and determined physicochemical properties make the composites very promising for biomedical purposes.

The influence of the chemical structure of selected polymers on the properties of ferroelectric ceramic-polymer composites

The paper presents research on ferroelectric ceramic-polymer composites based on barium-strontium titanate and water-thinnable polymeric dispersions, obtained by using tape casting method. Barium strontium titanate with the assumed stoichiometry Ba0,65Sr0,35TiO3 was synthesized by the high temperature solid-state reaction. Water-thinnable polymeric dispersions were synthesized from butyl acrylate, styrene and tert-butyl acrylate containing different amounts of individual monomers. Then, the ceramic-polymer composites were obtained by tape casting. The influence of the chemical structure of synthesized binders on the rheological properties of the slurries and on physicochemical and electrical properties (characterized by using Broadband Dielectric Spectroscopy, BDS) of ceramic-polymer composites were investigated.

Green electrospinning for biomaterials and biofabrication

Green manufacturing has emerged across industries, propelled by a growing awareness of the negative environmental and health impacts associated with traditional practices. In the biomaterials industry, electrospinning is a ubiquitous fabrication method for producing nano- to micro-scale fibrous meshes that resemble native tissues, but this process traditionally utilizes solvents that are environmentally hazardous and pose a significant barrier to industrial scale-up and clinical translation. Applying sustainability principles to biomaterial production, we have developed a ‘green electrospinning’ process by systematically testing biologically benign solvents (U.S. Food and Drug Administration Q3C Class 3), and have identified acetic acid as a green solvent that exhibits low ecological impact (global warming potential (GWP) = 1.40 CO2 eq. kg/L) and supports a stable electrospinning jet under routine fabrication conditions. By tuning electrospinning parameters, such as needle-plate distance and flow rate, we updated the fabrication of widely utilized biomedical polymers (e.g. poly-α-hydroxyesters, collagen), polymer blends, polymer-ceramic composites, and growth factor delivery systems. Resulting ‘green’ fibers and composites are comparable to traditional meshes in terms of composition, chemistry, architecture, mechanical properties, and biocompatibility. Interestingly, material properties of green synthetic fibers are more biomimetic than those of traditionally electrospun fibers, doubling in ductility (91.86 ± 35.65 vs. 45 ± 15.07%, n = 10, p < 0.05) without compromising yield strength (1.32 ± 0.26 vs. 1.38 ± 0.32 MPa) or ultimate tensile strength (2.49 ± 0.55 vs. 2.36 ± 0.45 MPa). Most importantly, green electrospinning proves advantageous for biofabrication, rendering a greater protection of growth factors during fiber formation (72.30 ± 1.94 vs. 62.87 ± 2.49% alpha helical content, n = 3, p < 0.05) and recapitulating native ECM mechanics in the fabrication of biopolymer-based meshes (16.57 ± 3.92% ductility, 33.38 ± 30.26 MPa elastic modulus, 1.30 ± 0.19 MPa yield strength, and 2.13 ± 0.36 MPa ultimate tensile strength, n = 10). The eco-conscious approach demonstrated here represents a paradigm shift in biofabrication, and will accelerate the translation of scalable biomaterials and biomimetic scaffolds for tissue engineering and regenerative medicine.

Compression fatigue properties and damage mechanisms of a bioinspired nacre-like ceramic-polymer composite

Fatigue resistance is invariably critical for structural materials, but is rarely considered in the development of new bioinspired materials. Here the fatigue behavior and damage mechanisms of a nacre-like ceramic (yttria-stabilized zirconia) - polymer (polymethyl methacrylate) composite, which resembles human tooth enamel in its stiffness and hardness, were investigated under cyclic compression to simulate potential service conditions. The composite has a brick-and-mortar structure which exhibits a staircase-like fracture behavior; it displays a transition in cracking mode from the fracture of the ceramic bricks to separation along the inter-brick polymer phase with increasing stress amplitude. The nacre-like structure functions to induce crack deflection, increase the roughness of the crack surfaces, and promote the mutual sliding between bricks during fracture; this results in high fatigue resistance, which enhances the potential of this composite for dental applications.

Preparation of zinc oxide/poly-ether-ether-ketone (PEEK) composites via the cold sintering process

Appropriate preparation routes allow designing and improving the performances of ceramic-based functional composites. In this work, two powder-preparation methods enabled by the cold sintering process are utilized to fabricate unique ZnO-based varistor composites. The thermoplastic polymer, poly-ether-ether-ketone (PEEK), has been successfully integrated with ZnO to form dense ZnO-PEEK composites. With a dissolution method, PEEK particles can be homogeneously dissolved by the mixed solution of tetrahydrofuran and toluene and then form nanoscale thin grain boundaries after cold sintering process. In the direct mixing method, large PEEK particles are observed in the cold sintered samples. A Finite Element Method (FEM) analysis indicates that von-mises stresses concentrate at the grain boundaries of ZnO and at the interfaces of ZnO and PEEK, and these can be increased with the increase of PEEK particle sizes. The electrical properties have been improved with the addition of PEEK, and the cold sintered 95ZnO-5PEEK shows a high breakdown electric field (0.1 mA/mm2) of 3070 V/mm, and a nonlinear coefficient of 5. In addition, the conduction mechanism of the composites has been investigated using impedance spectroscopy. Overall, our work provides a strategy for the development of high-performance ceramic-polymer composites via cold sintering process.

Development of novel bone-like nanocomposite coating of hydroxyapatite/collagen on titanium by modified electrophoretic deposition.

Electrophoretic deposition (EPD) is a simple, rapid, and inexpensive technique to accomplish uniform coatings with controlled thicknesses. The EPD using binders that do not require a thermal degreasing process, which also eliminates the polymer components of the composite, are required for coating polymer-ceramic composites. This study demonstrated the application of a modified EPD technique utilizing Mg2+ ions to coat a bone-like hydroxyapatite/collagen nanocomposite (HAp/Col) on a titanium (Ti) substrate. The coating thickness was successfully controlled by varying the applied voltage and/or the treatment time. The adhesive strength of the modified EPD coating, evaluated by the tape test, showed class 0 (coating was not peeled off) and drastically increased in comparison to that of the non-Mg2+ EPD coating, class 5 (coating was completely peeled off). The MG63 cells on the HAp/Col-coated Ti demonstrated similar proliferation to and superior alkaline phosphatase activity to that on the bare Ti. Thus, the HAp/Col-coated Ti is expected to facilitate the surrounding bone formation than the bare-Ti. The results of the study indicated the HAp/Col-coated Ti prepared by the modified EPD is effective for applications in novel instruments, such as, subperiosteal temporary anchorage devices, which strongly requires rapid osseointegration at the bone-implant surface.

Multifunctional lead-free K0.5Bi0.5TiO3-based ceramic reinforced PVDF matrix composites

This work aims for the experimental verification of the proposed models for the dielectric and piezoelectric behavior of the polymer-ceramic composites and designing a new composite material with excellent piezoelectric performance. The lead-free piezocomposites were fabricated via hot-press technique with various volume fraction of 0.95K0.5Bi0.5TiO3–0.05BiAlO3 (abbreviated as KBT-5BA) ceramic fillers embedded in polyvinylidene fluoride (PVDF) matrix. The fabricated composite system was further characterized for thermal, structural, and electrical properties. The addition of ceramic filler resulted in better thermal stability, an apparent evolution of ferroelectric β-phase over the other non electroactive phases due to electrostatic interaction at the ceramic-polymer interface, and a significant increase in the dielectric and piezoelectric performance. The dielectric permittivity of the composite with respect to filler volume was found to be well fitted by the Yamada model. Further, a noticeable change in the value of the shape parameter for composite with low and high volume fractions of the ceramic was discerned. The optimum dielectric response with εr ~112 at 1 MHz and piezoelectric coefficients d33 ~30 pC/N and g33 ~ 32 mV m/N were observed for the composite with optimized filler content. These results extend the feasibility of lead-free polymer ceramic composite materials for the development of piezoelectric devices.

Ceramic Powder Bed Laser Sintering (CPBLS) on copper-doped hydroxyapatite: Creation of thin (5–50 μm thick) consolidated ceramic patterns

Implants made of ceramics, and more particularly of calcium phosphates (hydroxyapatite: HA, mainly), promoting intimate contact with natural bone are nowadays merging. Addition of copper ions in bio-ceramics is expected to increase the biological compatibilities of bone graft substitutes. Previous works have shown that copper-doped hydroxyapatite (Cu-doped HA) ceramics can be prepared by solid-state sintering between HA and CuO powder mixtures at about 1100 °C; but, copper-substituted HA was found to be metastable leading to apatitic grains and Cu-rich grain boundaries during the sintering process. Ultra-rapid sintering is so needed. Selective laser sintering (SLS) is an additive manufacturing process that possesses the advantage to be based on ultra-fast sintering process under laser irradiation. SLS being used in literature for the application of laser on polymer-ceramic or poymer-metal composites the proper term all along the paper is Ceramic Powder Bed Laser Sintering (CPBLS). To achieve densification of Cu-doped HA ceramics from CPBLS process, one should control the composition/morphology/structure of the powder bed as well as three other important CPBLS parameters: (i) the applied energy from the laser beam, (ii) the laser power and the laser scanning speed, (iii) the distance between two successive lased lines. In this paper, the impact of all the main CPBLS parameters controlling the sintering of dip-coated Cu-doped HA layers on glass substrates is carefully investigated. Possibility of the creation of thin consolidated Cu-doped HA ceramic patterns, using the ultra-fast CPBLS process, is finally shown.

Cryo-Structured Materials Based on Polyvinyl Alcohol and Hydroxyapatite for Osteogenesis

The application of various materials in biomedical procedures has recently experienced rapid growth. One of the areas is the treatment of many of different types of bone-related diseases and disorders by using biodegradable polymer-ceramic composites. We have developed a material based on cryogel polyvinyl alcohol, mineralized with calcium phosphate. Composites were obtained by cyclic freezing-thawing, the synthesis of calcium phosphates was carried out in situ under the influence of microwave radiation with heating and stirring. The components of the composites were determined using the methods of IR-spectroscopy and scanning electron microscopy and electron probe microanalyzer, as well as their morphology and surface properties. The biological compatibility of the material was investigated in vivo for a Wistar rat. The assessment of the quality of bone formation between the cryogel-based implant and the damaged bone was carried out by computed tomography. An improvement in the consolidation of the bone defect is observed in the bone with the composite in comparison with the control bone.

Novel organic-inorganic polyphosphate based composite material as highly dense and robust electrolyte for low temperature fuel cells

Low temperature operating ceramic-based solid electrolytes are practical option to develop highly efficient energy conversion devices for next-generation energy demands. The present work provides a novel ceramic-polymer composite, where the host matrix of gadolinium doped cerium pyrophosphate (CGP) is reinforced by a non-toxic, biodegradable functionalized cellulose-based polymer (P), to achieve a highly dense and stable ionic conductor that can be applied in low temperature fuel cell (LTFC) application. This composite is examined for its phase identity, microstructure, and electrochemical properties. The composite is exposed to four different thermodynamic conditions i.e. dry air, humidified air (WA), D2O containing air (DA), and humidified H2 (WH2) to examine its ionic conductivity. To identify the responsible charge carrier and its mobility under different thermodynamic conditions complex impedance analysis has been used. A highly dense (apparent porosity~3%), and stable proton-conducting electrolyte was obtained by this reinforcement, with a remarkable proton conductivity of 13 and 29 mScm−1 under WA and WH2the atmosphere, respectively, where pH2O is maintained to 0.03 atm. The present composite is also found to be stable up to 100 h in terms of microstructure and ionic conductivity. Accounting all, the composite is suitable to be used as a solid electrolyte for LTFC application.

Deformation mechanisms in ice-templated alumina–epoxy composites for the different directions of uniaxial compressive loading

The ice-templating technique enables the fabrication of multilayered ceramic-based composite materials. Very little is known on the inelastic deformation mechanisms that evolve in this class of composite materials under compressive loading conditions and cause macroscopic failure. The current investigation is motivated by a recent study by the authors, which revealed that the uniaxial compressive response of ice-templated ceramic–polymer composites is strongly dependent on the loading direction relative to the layer orientation. The current investigation reveals that the inelastic deformation mechanisms in ice-templated alumina–epoxy composites are strongly influenced by the compressive loading orientation relative to the growth direction of ice crystals. The deformation mechanisms were investigated for the loading directions of 0° (parallel to the growth direction), 45° (to the growth direction), and 90° (to the growth direction). For 0°, kink band formation and longitudinal splitting were observed to be the primary strength limiting mechanisms. Kink band formation could be the primary strength limiting factor and responsible for the catastrophic-type compressive failure response. For the loading directions of 45° and 90°, interface delamination and fracture within the lamella walls and across the alumina–epoxy interfaces were the main deformation mechanisms. These mechanisms significantly reduced the compressive strength but attributed progressive-type failure behavior in ice-templated composites. The knowledge of the inelastic deformation mechanisms in ice-templated ceramic–polymer composites under compressive loading is vital for an improved understanding of structure–mechanical property relationships and hierarchical materials design.

Remarkably Elevated Permittivity Achieved in PVDF/1D La2TiO5 Composite Film Materials with Low-Level Dielectric Loss by Adding 2D V2C MXene Phase

High-dielectric-constant (high-k) polymer–ceramic composites with low-level dielectric loss are expected to enable excellent energy storage. However, high conductivity and high dielectric loss often occur simultaneously with high dielectric constant. To obtain a high dielectric constant but with low conductivity and low dielectric loss, in this work, we studied the ternary polyvinylidene fluoride (PVDF)/La2TiO5/V2C dielectric composite system, which takes advantage of the synergistic effect between the high content (0 wt.% to 40 wt.%) of pseudo-perovskite filler La2TiO5 and the low content (2 wt.%) of highly conductive two-dimensional filler V2C. Comparisons with the binary PVDF/La2TiO5 composite system revealed that the ternary PVDF/La2TiO5/V2C composite dielectric system enabled balance and optimization of the comprehensive electrical properties of the composite material. Significantly elevated permittivity as well as depressed low-level dielectric loss were obtained in the ternary composites. The optimized ternary composite with 40 wt.% La2TiO5 and 2 wt.% V2C exhibited high dielectric constant of 47 and low dielectric loss of 0.17 at 1 kHz. This work might enable facile fabrication of promising composite dielectric materials based on this excellent synergetic filler strategy.

Advances in Osteoporotic Bone Tissue Engineering.

The increase in osteoporotic fracture worldwide is urging bone tissue engineering research to find new, improved solutions both for the biomaterials used in designing bone scaffolds and the anti-osteoporotic agents capable of promoting bone regeneration. This review aims to report on the latest advances in biomaterials by discussing the types of biomaterials and their properties, with a special emphasis on polymer-ceramic composites. The use of hydroxyapatite in combination with natural/synthetic polymers can take advantage of each of their components properties and has a great potential in bone tissue engineering, in general. A comparison between the benefits and potential limitations of different scaffold fabrication methods lead to a raised awareness of the challenges research face in dealing with osteoporotic fracture. Advances in 3D printing techniques are providing the ways to manufacture improved, complex, and specialized 3D scaffolds, capable of delivering therapeutic factors directly at the osteoporotic skeletal defect site with predefined rate which is essential in order to optimize the osteointegration/healing rate. Among these factors, strontium has the potential to increase osseointegration, osteogenesis, and healing rate. Strontium ranelate as well as other biological active agents are known to be effective in treating osteoporosis due to both anti-resorptive and anabolic properties but has adverse effects that can be reduced/avoided by local release from biomaterials. In this manner, incorporation of these agents in polymer-ceramic composites bone scaffolds can have significant clinical applications for the recovery of fractured osteoporotic bones limiting or removing the risks associated with systemic administration.

Characterization of the interfacial Li-ion exchange process in a ceramic–polymer composite by solid state NMR

Li-ion exchange mechanism in ceramic–polymer composite electrolytes.

Three-dimensional printed poly (L-lactide) and hydroxyapatite composite for reconstruction of critical bone defect in rabbits.

ABSTRACTPurposeTo use a 3D printed poly (L-lactide) acid (PLLA) and hydroxyapatite (HA) composite as a bone substitute for reconstruction of a critical bone defect in the radius of rabbits.MethodsA 1.5 cm ostectomy was performed in the radial diaphysis of 60 New Zealand white rabbits. The rabbits were divided into three groups according to surgical treatment of the bone defect (group I – control, group II – bone graft, group III – 3D PLLA). Each group was divided into four subgroups with different radiographic and histopathologic evaluation times (T1 – 15 days, T2 – 30 days, T3 – 60 days, T4 – 90 days).ResultsThe implant group had greater clinically lameness (p = 0.02), edema (p = 0.007), pain (p = 0.04) and more complications at the surgical site (p = 0.03). Histologically, this group showed greater congestion (p = 0.04), hemorrhage (p = 0.04) and inflammation. Osteogenesis was microscopically similar between days (p = 0.54) and treatments (p = 0.17), even though radiographically, more effective bone healing occurred in the graft group (II), with more callus and bone bridge formation.ConclusionsThe customization of a 3D PLLA/HA scaffold was successful. However, in animals receiving the polymer-ceramic composite less bone callus and bone bridge was formed compared to the graft group.

Physicochemical and Biological Characterisation of Diclofenac Oligomeric Poly(3-hydroxyoctanoate) Hybrids as β-TCP Ceramics Modifiers for Bone Tissue Regeneration.

Nowadays, regenerative medicine faces a major challenge in providing new, functional materials that will meet the characteristics desired to replenish and grow new tissue. Therefore, this study presents new ceramic-polymer composites in which the matrix consists of tricalcium phosphates covered with blends containing a chemically bounded diclofenac with the biocompatible polymer—poly(3-hydroxyoctanoate), P(3HO). Modification of P(3HO) oligomers was confirmed by NMR, IR and XPS. Moreover, obtained oligomers and their blends were subjected to an in-depth characterisation using GPC, TGA, DSC and AFM. Furthermore, we demonstrate that the hydrophobicity and surface free energy values of blends decreased with the amount of diclofenac modified oligomers. Subsequently, the designed composites were used as a substrate for growth of the pre-osteoblast cell line (MC3T3-E1). An in vitro biocompatibility study showed that the composite with the lowest concentration of the proposed drug is within the range assumed to be non-toxic (viability above 70%). Cell proliferation was visualised using the SEM method, whereas the observation of cell penetration into the scaffold was carried out by confocal microscopy. Thus, it can be an ideal new functional bone tissue substitute, allowing not only the regeneration and restoration of the defect but also inhibiting the development of chronic inflammation.

Surface-modified Zn0.5Ti0.5NbO4 particles filled polytetrafluoroethylene composite with extremely low dielectric loss and stable temperature dependence

Polymer-ceramic composites are widely applied in microwave substrate materials due to the excellent dielectric properties and simple preparation process recently. Polytetrafluoroethylene-based (PTFE) composites filled with Zn0.5Ti0.5NbO4 (ZTN) ceramic particles were fabricated by hot-pressing. The particles were modified by C14H19F13O3Si to enhance the interface compatibility between PTFE and ZTN powders, which was characterized by X-ray photoelectron spectroscopy (XPS) and contact angle. The surface characteristic of particles transformed into hydrophobicity and tight microstructure as well as better dielectric properties were obtained after the surface modification. The microstructure, dielectric, thermal, mechanical properties, and water absorption of the composites concerning ZTN content were investigated. Modified ZTN/PTFE composites with 50 vol% ZTN particles exhibit excellent dielectric properties with a high dielectric constant of 8.3, an extremely low dielectric loss of 0.00055 at 7 GHz, and a stable temperature coefficient of the dielectric constant of −12.2 ppm/°C. All the properties show modified ZTN particles filled PTFE composite is the potential material for microwave substrate application.