Surface modification and enhanced photocatalytic CO2 reduction performance of TiO2: a review

Photoelectrochemical (PEC) water splitting is a promising approach for solar-driven hydrogen production with zero emissions, and it has been intensively studied over the past decades. However, the solar-to-hydrogen (STH) efficiencies of the current PEC systems are still far from the 10% target needed for practical application. The development of efficient photoelectrodes in PEC systems holds the key to achieving high STH efficiencies. In recent years, crystal facet engineering has emerged as an important strategy in designing efficient photoelectrodes for PEC water splitting, which has yet to be comprehensively reviewed and is the main focus of this article. After the Introduction, the second section of this review concisely introduces the mechanisms of crystal facet engineering. The subsequent section provides a snapshot of the unique facet-dependent properties of some semiconductor crystals including surface electronic structures, redox reaction sites, surface built-in electric fields, molecular adsorption, photoreaction activity, photocorrosion resistance, and electrical conductivity. Then, the methods for fabricating photoelectrodes with faceted semiconductor crystals are reviewed, with a focus on the preparation processes. In addition, the notable advantages of the crystal facet engineering of photoelectrodes in terms of light harvesting, charge separation and transfer, and surface reactions are critically discussed. This is followed by a systematic overview of the modification strategies of faceted photoelectrodes to further enhance the PEC performance. The last section summarizes the major challenges and some invigorating perspectives for future research on crystal facet engineered photoelectrodes, which are believed to play a vital role in promoting the development of this important research field.

Crystal facet engineering of photoelectrodes for photoelectrochemical water splitting

Surface and interface engineering of hierarchical photocatalysts

All implanted biomaterials are targets of the host's immune system. While the host inflammatory response was once considered a detrimental force to be blunted or avoided, in recent years, it has become a powerful force to be leveraged to augment biomaterial-tissue integration and tissue repair. In this review, we will discuss the major immune cells that mediate the inflammatory response to biomaterials, with a focus on how biomaterials can be designed to modulate immune cell behavior to promote biomaterial-tissue integration. In particular, the intentional activation of monocytes and macrophages with controlled timing, and modulation of their interactions with other cell types involved in wound healing, have emerged as key strategies to improve biomaterial efficacy. To this end, careful design of biomaterial structure and controlled release of immunomodulators can be employed to manipulate macrophage phenotype for the maximization of the wound healing response with enhanced tissue integration and repair, as opposed to a typical foreign body response characterized by fibrous encapsulation and implant isolation. We discuss current challenges in the clinical translation of immunomodulatory biomaterials, such as limitations in the use of in vitro studies and animal models to model the human immune response. Finally, we describe future directions and opportunities for understanding and controlling the biomaterial-immune system interface, including the application of new imaging tools, new animal models, the discovery of new cellular targets, and novel techniques for in situ immune cell reprogramming.

Immunomodulatory Biomaterials for Tissue Repair.

The demand for biomaterials that promote the repair, replacement, or restoration of hard and soft tissues continues to grow as the population ages Traditionally, smart biomaterials have been thought as those that respond to stimuli However, the continuous evolution of the field warrants a fresh look at the concept of smartness of biomaterials This review presents a redefinition of the term "Smart Biomaterial" and discusses recent advances in and applications of smart biomaterials for hard tissue restoration and regeneration To clarify the use of the term "smart biomaterials", we propose four degrees of smartness according to the level of interaction of the biomaterials with the bio-environment and the biological/cellular responses they elicit, defining these materials as inert, active, responsive, and autonomous Then, we present an up-to-date survey of applications of smart biomaterials for hard tissues, based on the materials' responses (external and internal stimuli) and their use as immune-modulatory biomaterials Finally, we discuss the limitations and obstacles to the translation from basic research (bench) to clinical utilization that is required for the development of clinically relevant applications of these technologies

/pdf/on-the-road-to-smart-biomaterials-for-bone-research-49pdoaival.pdf

On the road to smart biomaterials for bone research: definitions, concepts, advances, and outlook.

Excessive immune responses following the use of implantable, biomaterial-based medical devices represent a substantial challenge for treatment efficacy and patient well-being. Specifically, after implantation, pro-inflammatory M1 macrophages are activated by cytokines such as interferon-γ (IFN-γ) followed by anti-inflammatory M2 macrophages polarized by cytokines including interleukin-4 (IL-4), leading to healing and long-term stability of implants. Here, we report the loading of an immunomodulatory cytokine,IL-4, into TiO2 nanotubes (TNTs) followed by hydrogel coating on the TNTs for subsequent release of IL-4. Finally, IFN-γ was added onto the gel layer to effect rapid release. The release rates of both cytokines from the samples were monitored using an immersion test in phosphate-buffered solution. The cytocompatibility of the sample was evaluated using cultures of osteoblasts and macrophages. Macrophage phenotype switching in vitro was examined via cytokine secretion and gene expression analyses. In vitro testing showed that the sample could stimulate macrophage polarization from the M1 to M2 phenotype at the desired period owing to temporal release of IFN-γ and IL-4. Another biomaterial containing only IL-4 in TNTs was also able to modulate the transformation of M1 to M2 although with weaker effect than that containing IFN-γ and IL-4. The biomaterial may be useful as an osteoimplant in vivo owing to the inflammation caused by a wound or implantation. This study provided biomaterials capable of facilitating smooth M1 to M2 macrophages switching, which might be helpful to research immune responses of tissues to implants and will likely contribute to the development of bone substitute materials. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1878-1886, 2018.

Dual-inflammatory cytokines on TiO2 nanotube-coated surfaces used for regulating macrophage polarization in bone implants.

Surface properties such as physicochemical characteristics and topographical parameters are important considerations in the design of implant materials, as they determine interactions with living cells and tissues. Micro-/nanostructurization of Ti surfaces can enhance osteointegration, and strontium (Sr) is able to decrease osteoresorption. Sr loaded micro/-nanotubular structures that allow controlled and long-term Sr release are expected to yield favorable osteogenic effects. In this work, we constructed SrTiO 3 /TiO 2 nanoparticle-nanotube heterostructures on a microporous titanium (Ti) surface and characterized their properties. Ti plates were etched with acid to create a micro-rough surface (M) and then anodized to generate a surface layer of TiO 2 nanotubes (MN). Strontium (Sr) was loaded onto MN by hydrothermal treatment in Sr(OH) 2 solution (MN-Sr) for 1 or 3 h to obtain SrTiO 3 /TiO 2 nanotube heterostructures with different Sr contents. The in vitro biocompatibility of MN-Sr was investigated by evaluating protein adsorption, using osteoblast and osteoclast (RAW 264.7 cell) cultures. The micro-/nanostructured porous samples (MN and MN-Sr) promoted protein adsorption owing to their large specific surface area and high reactivity; the amount of protein adsorbed onto MN-Sr was independent of Sr content. Sr in SrTiO 3 /TiO 2 heterostructures exhibited controllable and sustained Sr 2 + ion release in phosphate-buffered saline. Moreover, heterostructures with an appropriate SrTiO 3 content promoted osteoblast adhesion, proliferation and differentiation, and inhibited osteoclast proliferation and differentiation. These results indicate that the micro-/nano heterostructure with an appropriate content of Sr has excellent osteogenic activity and anti-bone resorption ability.

Characterization and osteogenic activity of SrTiO3/TiO2 nanotube heterostructures on microporous titanium

Heterojunction of SrTiO3/TiO2 nanotubes with dominant (001) facets: Synthesis, formation mechanism and photoelectrochemical properties

Hierarchical fabrication of heterojunctioned SrTiO 3 /TiO 2 nanotubes on 3D microporous Ti substrate with enhanced photocatalytic activity and adhesive strength

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Papers

Dual-inflammatory cytokines on TiO2 nanotube-coated surfaces used for regulating macrophage polarization in bone implants.

Characterization and osteogenic activity of SrTiO3/TiO2 nanotube heterostructures on microporous titanium

Heterojunction of SrTiO3/TiO2 nanotubes with dominant (001) facets: Synthesis, formation mechanism and photoelectrochemical properties

Hierarchical fabrication of heterojunctioned SrTiO 3 /TiO 2 nanotubes on 3D microporous Ti substrate with enhanced photocatalytic activity and adhesive strength