Functionalized-ferroelectric-coating-driven enhanced biomineralization and protein-conformation on metallic implants.

In the context of bone regeneration, it is important to have platforms that with appropriate stimuli can support the attachment and direct the growth, proliferation and differentiation of cells. In the orthopedic field, metals and alloys are still the dominant materials used as implants, though their bioinert character leads to failure or to the need for multiple revision procedures. To respond to this situation here we exploit an alternative strategy for bone implants or repairs, based on charge mediating signals for bone regeneration, envisaged as a type of biological micro-electromechanical system (BioMEM). This strategy includes coating metallic 316L-type stainless steel substrates with ferroelectric LiTaO3 layers functionalized via electrical charging or UV-light irradiation. We show that the formation of surface calcium phosphates and protein adsorption are considerably enhanced for 316L-type stainless steel functionalized ferroelectric coatings. Our findings go beyond the current knowledge and demonstrate that the protein conformation is sensitive to the type of charge functionalization of the ferroelectric coatings. Our approach can be viewed as a set of guidelines for the development of electrically functionalized platforms that can stimulate tissue regeneration, promoting direct integration of the implant in the host tissue and hence contributing ultimately to reducing implant failure.

Pairing High Piezoelectric Coefficients, d33, with High Curie Temperature (TC) in Lead-Free (K,Na)NbO3.

The largest piezoelectric properties, d33 = 416 pC/N and 490 pC/N, in KxNa1-xNbO3 ceramics have been reported for compositions close to polymorphic phase transition (PPT); however, they also have Curie temperatures, TC, of around 217-304 °C, considerably lower than those of undoped KNN ceramics (420 °C). High d33 along with high TC remains the ideal choice for applications but, unfortunately, not attained up to now. Here, we show that using KNN single crystals as seeds for template grain growth (TGG) of KNN ceramics enables dramatic improvements in the electromechanical properties while maintaining a high TC. The (001)-oriented (K0.5Na0.5)0.98Li0.02NbO3 ceramics engineered by TGG using (K0.5Na0.5)NbO3 crystals as templates exhibit a high d33 of 280 pC/N while maintaining the high TC of 430 °C. Enhanced piezoelectricity is attributed to long-range ordered ferroelectric domain patterns consisting of 90° and 180° domains, similar to single crystals. It is the first time that pairing high d33 and high TC in KNN, keeping a high PPT temperature, is achieved. This study is an unequivocal proof that it is possible to maximize d33, keeping a high TC in KNN without resorting to heavily doped compositions. This work opens the door to high-performance, rare-earth free, compositionally simple lead-free and low-cost electromechanical compounds, which can largely expand lead-free piezoelectrics applications.

Defects and charge transport in Mn-doped K0.5Na0.5NbO3 ceramics.

The relationship between charge transport, defects and ferroelectric response is established for K0.5Na0.5NbO3 (KNN) and Mn-doped KNN ceramics. At room temperature the conduction in KNN is associated with hole transport and can be suppressed by Mn doping. Because of that a less leaky ferroelectric hysteresis loop is obtained for Mn-doped KNN. At high temperatures the conduction is dominated by the motion of ionized oxygen vacancies, the concentration of which increases with Mn doping. This work adds relevant information on KNN and leverages its potential application.

Are lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) ferroelectrics bioactive?

The use of functional materials, such as ferroelectrics, as platforms for tissue growth in situ or ex situ, is new and holds great promise. But the usage of materials in any bioapplication requires information on biocompatibility and desirably on bioactive behavior when bone tissue engineering is envisaged. Both requirements are currently unknown for many ferroelectrics. Herein the bioactivity of LiNbO3 and LiTaO3 is reported. The formation of apatite-like structures on the surface of LiNbO3 and LiTaO3 powders after immersion in simulated body fluid (SBF) for different soaking periods indicates their bioactive potential. The mechanism of apatite formation is suggested. In addition, the significant release of lithium ions from the ferroelectric powders in the very first minutes of soaking in SBF is examined and ways to overcome this likely hurdle addressed.