Tetragonal to Cubic Transformation of SiO2-Stabilized ZrO2 Polymorph through Dysprosium Substitutions.

Partially stabilized tetragonal zirconia (t-ZrO2) is of particular interest for hard tissue replacements. Aging-related failures of the ceramic associated with the gradual transformation from t-ZrO2 to m-ZrO2 (monoclinic zirconia) can lead to its premature removal from the implant site. In addition, monitoring the satisfactory performance of the implant throughout its lifespan without invasive techniques is a challenging task. The magnetic resonance imaging (MRI) contrast ability of dysprosium (Dy3+) is well-established. To this aim, varied levels of Dy3+ additions in the ZrO2-SiO2 binary oxide system were explored. The results indicate the effective role of Dy3+ in the formation of thermally and mechanically stable c-ZrO2 (cubic zirconia) phase at higher temperatures. The presence of SiO2 influenced the t-ZrO2 stabilization, whereas Dy3+ tends to occupy the ZrO2 lattice sites to induce c-ZrO2 transition. Magnetic and MRI tests displayed the commendable contrast ability of Dy3+ stabilized ZrO2-SiO2 binary systems. Nanoindentation results demonstrate a remarkable enhancement of the mechanical properties.

Formation Mechanisms in ß-Ca3(PO4)2-ZnO Composites: Structural Repercussions of Composition and Heat Treatments.

Composites with varied proportions of ß-Ca3(PO4)2 and ZnO were obtained through an in situ aqueous precipitation method under slightly basic (pH ≈ 8) conditions. The formation of ß-Ca3(PO4)2 phase starts at an early heat-treatment stage (∼800 °C) and incorporates Zn2+ ions at both Ca2+(4) and Ca2+(5) sites of the lattice up to its occupancy saturation limit. The incorporation of Zn2+ in the ß-Ca3(PO4)2 lattice enhances its thermal stability delaying the allotropic ß-Ca3(PO4)2→α-Ca3(PO4)2 phase transformation. The excess zinc beyond the occupancy saturation limit precipitates as Zn(OH)2 and undergoes dehydroxylation to form ZnO at elevated temperatures. The presence of ZnO in the ß-Ca3(PO4)2 matrix yields denser microstructures and thus improves the mechanical features of sintered composites up to an optimal ZnO concentration beyond which it tends to exert an opposite effect.

Structural Perceptions and Mechanical Evaluation of ß-Ca3(PO4)2/c-CeO2 Composites with Preferential Occupancy of Ce3+ and Ce4.

The role of cerium in the formation of stable ß-Ca3(PO4)2/c-CeO2 composites and their structural analysis with varied compositional ratios were investigated. The composite formation was attempted through an in situ precipitation technique, and the gradual structural changes during heat treatments to yield the pure form of ß-Ca3(PO4)2/c-CeO2 composites was presented. The cerium was found in Ce3+ and Ce4+ oxidation states in composites. Ce3+ prefers to occupy the Ca2+(1), Ca2+(2), and Ca2+(3) sites of ß-Ca3(PO4)2, whereas, beyond the saturation occupancy limit, excess cerium prefers to crystallize in the form of thermodynamically stable cubic ceria (c-CeO2). A uniform expansion of the ß-Ca3(PO4)2 unit cell and the delayed allotropic conversion of ß-Ca3(PO4)2 → α-Ca3(PO4)2 have been detected due to the Ce3+ occupancy at the ß-Ca3(PO4)2 lattice. ß-Ca3(PO4)2/c-CeO2 composites exhibited a steady upsurge in the mechanical properties with consistent enhancement of c-CeO2 content in the composites. The overall results from the investigation imply the appropriateness of the ß-Ca3(PO4)2/c-CeO2 composites for applications in hard tissue replacements.

Mechanically tuned nanocomposite coating on titanium metal with integrated properties of biofilm inhibition, cell proliferation, and sustained drug delivery.

The clinical success of coated implants in executing biological functions inclusive of sustainable drug release and long term antibacterial activity without antibiotics is critical. To this aim, a nanohybrid of silver nanoparticles (AgNPs) cored in polyvinyl alcohol nanocapsules (Ag-PVA NCs) embedded in chitosan (CS) matrix loaded with anti-inflammatory drug naproxen was prepared. The synthesized nanohybrids that were subjected to coatings on (3-aminopropyl)triethoxysilane (APTES) treated titanium (Ti) metal exhibited dual role of excellent inhibition on biofilm formation and sustained drug release. These dual characteristics are achieved mainly based on intrinsic antibacterial property of AgNPs and differential entrapment of drug in PVA polymeric shell of AgNPs and CS matrix. The coatings also demonstrated enhanced mechanical properties with increasing inorganic filler and stress shielding on Ti metal. The biocompatibility tests involving adhesion, proliferation and differentiation of osteoblast cells demonstrated the efficacy of Ag-PVA NCs embedded in CS matrix as a suitable coating material for orthopedic applications.

Exploring the Biomedical Potential of PLA/Dysprosium Phosphate Composites via Extrusion-Based 3D Printing: Design, Morphological, Mechanical, and Multimodal Imaging and Finite Element Modeling.

The present investigation demonstrates the feasibility of dysprosium phosphate (DyPO4) as an efficient additive in polylactide (PLA) to develop 3D printed scaffolds through the material extrusion (MEX) principle for application in bone tissue engineering. Initially, uniform sized particles of DyPO4 with tetragonal crystal setting are obtained and subsequently blended with different concentrations of PLA to extrude in the form of filaments. A maximum of 20 wt % DyPO4 in PLA matrix has been successfully drawn to yield a defect free filament. The resultant filaments were 3D printed through material extrusion methodology. The structural and morphological analysis confirmed the successful reinforcement of DyPO4 throughout the PLA matrix in all of the 3D printed components. All of the PLA/DyPO4 composites exhibited magnetic resonance imaging and computed tomography contrasting properties, which were dependent on the dysprosium content in the PLA matrix. The detailed mechanical evaluation of the 3D printed PLA/DyPO4 composites ensured good strength accomplished by the reinforcement of 5 wt % DyPO4 in PLA matrix, beyond which a gradual decline in the strength is noticed. Representative volume elements models were developed to realize the intrinsic property of the PLA/DyPO4 composite, and finite element analysis under both static and dynamic loading conditions has been performed to account for the reliability of experimental results.

Structure, mechanical, optical, and imaging contrast features of Yb3+ , Dy3+ , Tb3+ , Gd3+ , Eu3+ , and Nd3+ substituted Y2 O3 -Ln2 O3 solid solution.

Bulk ceramic that possess the combined features of structural stability at elevated temperatures, appropriate mechanical stability, luminescence features, magnetic resonance (MR) and computed tomography (CT) imaging capacity in a single platform is considered an exciting prospect in biomedical applications. In this study, six different lanthanides (Ln3+ :Yb3+ , Dy3+ , Tb3+ , Gd3+ , Eu3+ , and Nd3+ ) were combined together to yield a Y2 O3 :Ln2 O3 solid solution and subsequently tested for the proposed application. Three different Y2 O3 :Ln2 O3 solid solutions were formed by varying the concentrations of Ln3+ precursors. A unique cubic crystal structure with Ia-3 (206) space setting is retained until 1500 °C and moreover an expanded lattice is accomplished with the gradual inclusion of six different Ln3+ . Optical analysis inferred the characteristic electronic transitions of all the Ln3+ and moreover up-conversion and down-conversion emission behavior were also attributed by the material during excitation at 795 and 350 nm. Nanoindentation studies exercised on the material envisaged reasonably enhanced hardness and Young's modulus values. Further, the enhanced CT imaging potential alongside in vitro MRI study deliberating the longitudinal (T1 ) and transverse (T2 ) relaxivity ability of the material is also established.

Investigation on the structural, mechanical and in vitro biocompatibility features of CaZr4 (PO4 )6 influenced by Zn2+ substitutions.

The present study explores the possibility of Zn2+ substituted calcium zirconium phosphate [CaZr4 (PO4 )6 ] as a potential replacement for the existing materials in load bearing orthopedic applications. Pure CaZr4 (PO4 )6 ) and wide range of Zn2+ substitutions in CaZr4 (PO4 )6 have been synthesized through citrate assisted sol-gel technique. The characterization results confirmed the extraordinary structural stability displayed by CaZr4 (PO4 )6 until 1,550°C. Further, the flexibility of CaZr4 (PO4 )6 lattice to accommodate 40 mol% of Zn2+ has been determined. The microstructures of CaZr4 (PO4 )6 and Zn2+ substituted CaZr4 (PO4 )6 demonstrated irregular sized grains and cracks alongside the negligence to obtain definite grain boundaries. This has been reflected in the moderate mechanical properties of the investigated specimen; nevertheless, Zn2+ substituted CaZr4 (PO4 )6 displayed enhanced mechanical stability. Further, in vitro tests signified the remarkable biocompatibility and alkaline phosphatase activity of Zn2+ substituted CaZr4 (PO4 )6 .

Structural, optical tuning, and mechanical behavior of zirconia toughened alumina through europium substitutions.

The structural and optical features of zirconia toughened alumina (ZTA) due to the assorted range of Eu3+ substitutions are demonstrated. The characterization studies affirm the pivotal role of Eu3+ on the improved structural stability of ZTA and associated tetragonal zirconia (t-ZrO2 ) → cubic zirconia (c-ZrO2 ) transformation. Eu3+ prefers accommodation at the lattice sites of ZrO2 and their gradual accumulation induces t- → c-ZrO2 transition. Beyond the substitution limit, Eu3+ reacts with Al2 O3 to form EuAlO3 . Optical studies validate typical Eu3+ emissions, and further, the emission spectrum also predicts the symmetry of Eu3+ coordination at the ZrO2 lattice. Uniform distribution of ZrO2 and Al2 O3 grains throughout the microstructures are evident from the morphological analysis. Further, the influence of Eu3+ on the enhanced mechanical stability of ZTA is ensured from indentation technique. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1170-1179, 2019.

Bulk Yttria as a Host for Lanthanides in Biomedical Applications: Influence of Concentration Gradients on Structural, Mechanical, Optical, and in Vitro Imaging Behavior.

The biomedical application of yttria (Y2O3) as a bulk material to host a series of rare earth elements (RE3+) has been explored in the current investigation. Dy3+, Gd3+, Tb3+, Yb3+, Eu3+, and Nd3+ were chosen for this purpose, and their corresponding concentrations in Y2O3 have been varied to obtain five different combinations. The results ascertain the potential of Y2O3 to host different RE3+ to retain a discrete cubic yttria (c-Y2O3) devoid of significant structural distortion until 1400 °C. Depending upon the size of RE3+, either a contracted or expanded cubic Y2O3 unit cell has been determined from the XRD and Raman analyses. Other than the typical vibrational modes of c-Y2O3, Raman spectra also unveiled characteristic emission features of RE3+ that were dependent on the excitation laser used to record the spectra. The characteristic absorption and emission characteristics depending on the type of RE3+ substitutions were determined from the optical measurements. Pore free microstructures determined from the morphological analysis are reflected in the enhanced mechanical behavior of RE3+ doped Y2O3 specimens. Dy3+ and Yb3+ substituted Y2O3 unveiled computed tomography (CT) imaging features. Dy3+, Tb3+, and Nd3+ dopant compositions delivered T2 magnetic resonance imaging (MRI) contrast features, while the specimen comprising Gd3+ revealed both T1 and T2 MRI characteristics.

Unveiling the Effects of Rare-Earth Substitutions on the Structure, Mechanical, Optical, and Imaging Features of ZrO2 for Biomedical Applications.

The impact of selective rare-earth (RE) additions in ZrO2-based ceramics on the resultant crystal structure, mechanical, morphological, optical, magnetic, and imaging contrast features for potential applications in biomedicine is explored. Six different RE, namely, Yb3+, Dy3+, Tb3+, Gd3+, Eu3+, and Nd3+ alongside their variations in the dopant concentrations were selected to accomplish a wide range of combinations. The experimental observations affirmed the roles of size and dopant concentration in determining the crystalline phase behavior of ZrO2. The significance of tetragonal ZrO2 (t-ZrO2) → monoclinic ZrO2 degradation is evident with 10 mol % of RE substitution, while RE contents in the range of 20 and 40 mol % ensured either t-ZrO2 or cubic ZrO2 (c-ZrO2) stability until 1500 °C. High RE content in the range of 80-100 mol % still confirmed the structural stability of c-ZrO2 for lower-sized Yb3+, Dy3+, and Tb3+, while the c-ZrO2 → RE2Zr2O7 phase transition becomes evident for higher-sized Gd3+, Eu3+, and Nd3+. A steady decline in the mechanical properties alongside a quenching effect experienced in the emission phenomena is apparent for high RE concentrations in ZrO2. On the one hand, the paramagnetic characteristics of Dy3+, Tb3+, Gd3+, and Nd3+ fetched excellent contrast features from magnetic resonance imaging analysis. On the other hand, Yb3+ and Dy3+ added systems exhibited good X-ray absorption coefficient values determined from computed tomography analysis.

Development and in vitro characterization of sol-gel derived CaO-P2O5-SiO2-ZnO bioglass.

A CaO-P(2)O(5)-SiO(2)-ZnO bioglass was formed by the sol-gel technique and characterized by Raman spectroscopy, X-ray diffraction, energy dispersive X-ray analysis (EDXA) and scanning electron microscopy (SEM). The surface reactivity of the resultant glass-ceramic specimens was analyzed by immersion studies in simulated body fluid (SBF). SEM-EDXS and inductively coupled plasma atomic emission spectrometry techniques were used to monitor changes in the glass surface and SBF composition. Osteoblast cell culture experiments were performed to assess the biocompatibility and the alkaline phosphatase activity. Cell counts of the osteoblasts cultured on the bioglass samples were studied and compared with the polystyrene plates. The cells cultured on the bioglass disks consistently showed a higher alkaline phosphatase activity and cell counts compared to cells cultured on either polystyrene plates or the base CaO-P(2)O(5)-SiO(2) bioglass. This was due to cell proliferation and differentiation promoted by the zinc-substituted bioglass.

Cryo-X-ray analysis-A novel tool to better understand the physicochemical reactions at the bioglass/biological fluid interface.

The present study deals with the short-term physicochemical reactions at the interface between bioactive glass particles [55SiO(2)-20CaO-9P(2)O(5)-12Na(2)O-4MgO. mol%] and biological fluid (Dulbecco Modified Eagle's Medium (DMEM)). The physicochemical reactions within the interface are characterized by scanning transmission electron microscopy (TEM) (STEM) associated with Energy-dispersive X-ray spectroscopy (EDXS). Microanalysis of diffusible ions such as sodium, potassium, or oxygen requires a special care. In the present investigation the cryo-technique was adopted as a suitable tool for the specimen preparation and characterization. Cryosectioning is essential for preserving the native distribution of ions so that meaningful information about the local concentrations can be obtained by elemental microanalysis. The bioglass particles immersed in biological fluid for 24 h revealed five reaction stages: (i) dealkalization of the surface by cationic exchange (Na(+), Ca(2+) with H(+) or H(3)O(+)); (ii) loss of soluble silica in the form of Si(OH)(4) to the solution resulting from the breakdown of Si--O--Si bonds (iii); repolymerization of Si(OH)(4) leading to condensation of SiO(2)); (iv) migration of Ca(2+) and PO(4) (3-) to the surface through the SiO(2)-rich layer to form CaO-P(2)O(5) film; (v) crystallization of the amorphous CaO-P(2)O(5) by incorporating OH-- or CO(3) (2-) anions with the formation of three different surface layers on the bioactive glass periphery. The thickness of each layer is approximately 300 nm and from the inner part to the periphery they consist of Si--OH, which permits the diffusion of Ca(2+) and PO(4) (3-) ions and the formation of the middle Ca--P layer, and finally the outer layer composed of Na--O, which acts as an ion exchange layer between Na(+) ions and H(+) or H(3)O(+) from the solution.