Daqing Wei

High-yield synthesis of strong photoluminescent N-doped carbon nanodots derived from hydrosoluble chitosan for mercury ion sensing via smartphone APP.

Photoluminescent carbon nanodots (CNDs) have offered considerable potential to be used in biomedical and environmental fields including live cell imaging and heavy metal ion detection due to their superior quantum emission efficiencies, ability to be functionalized using a variety of chemistries and apparent absence of toxicity. However, to date, synthetic yield of CNDs derived from biomass via hydrothermal carbonization is quite low. We report here the synthesis of nitrogen-doped carbon nanodots (N-doped CNDs) derived from hydrosoluble chitosan via hydrothermal carbonization. The synthetic yield could reach 38.4% which is 2.2-320 times increase compared with that from other biomass reported so far. These N-doped CNDs exhibited a high quantum yield (31.8%) as a consequence of nitrogen incorporation coincident with multiple types of functional groups (C=O, O-H, COOH, and NH2). We further demonstrate applications of N-doped CNDs as probes for live cell multicolor imaging and heavy metal ion detection. The N-doped CNDs offered potential as mercury ion sensors with detection limit of 80nM. A smartphone application (APP) based on N-doped CNDs was developed for the first time providing a portable and low cost detection platform for detection of Hg(2+) and alert of heavy metal ions contamination.

Hydrosoluble, UV-crosslinkable and injectable chitosan for patterned cell-laden microgel and rapid transdermal curing hydrogel in vivo.

Natural and biodegradable chitosan with unique amino groups has found widespread applications in tissue engineering and drug delivery. However, its applications have been limited by the poor solubility of native chitosan in neutral pH solution, which subsequently fails to achieve cell-laden hydrogel at physiological pH. To address this, we incorporated UV crosslinking ability in chitosan, allowing fabrication of patterned cell-laden and rapid transdermal curing hydrogel in vivo. The hydrosoluble, UV crosslinkable and injectable N-methacryloyl chitosan (N-MAC) was synthesized via single-step chemoselective N-acylation reaction, which simultaneously endowed chitosan with well solubility in neutral pH solution, UV crosslinkable ability and injectability. The solubility of N-MAC in neutral pH solution increased 2.21-fold with substitution degree increasing from 10.9% to 28.4%. The N-MAC allowed fabrication of cell-laden microgels with on-demand patterns via photolithography, and the cell viability in N-MAC hydrogel maintained 96.3 ± 1.3% N-MAC allowed rapid transdermal curing hydrogel in vivo within 60s through minimally invasive clinical surgery. Histological analysis revealed that low-dose UV irradiation hardly induced skin injury and acute inflammatory response disappeared after 7 days. N-MAC would allow rapid, robust and cost-effective fabrication of patterned cell-laden polysaccharide microgels with unique amino groups serving as building blocks for tissue engineering and rapid transdermal curing hydrogel in vivo for localized and sustained protein delivery.

Synergistic effects of surface chemistry and topologic structure from modified microarc oxidation coatings on Ti implants for improving osseointegration.

Microarc oxidation (MAO) coating containing Ca, P, Si, and Na elements on a titanium (Ti) implant has been steam-hydrothermally treated and further mediated by post-heat treatment to overcome the compromised bone-implant integration. The bone regeneration, bone-implant contact, and biomechanical push-out force of the modified Ti implants are discussed thoroughly in this work. The best in vivo performances for the steam-hydrothermally treated one is attributed to the synergistic effects of surface chemistry and topologic structure. Through post-heat treatment, we can decouple the effects of surface chemistry and the nanoscale topologic structure easily. Attributed to the excellent in vivo performance of the surface-modified Ti implant, the steam-hydrothermal treatment could be a promising strategy to improve the osseointegration of the MAO coating covered Ti implant.

MC3T3-E1 cell response of amorphous phase/TiO2 nanocrystal composite coating prepared by microarc oxidation on titanium.

Bioactive amorphous phase/TiO2 nanocrystal (APTN) composite coatings were fabricated by microarc oxidation (MAO) on Ti. The APTN coatings are composed of much amorphous phase with Si, Na, Ca, Ti and O elements and a few TiO2 nanocrystals. With increasing applied voltage, the micropore density of the APTN coating decreases and the micropore size of the APTN coating increases. The results indicate that less MC3T3-E1 cells attach on the APTN coatings as compared to Ti. However, the APTN coatings greatly enhance the cell proliferation ability and the activity of alkaline phosphatase. The amorphous phase and the concentrations of the released Ca and Si from the APTN coatings during cell culture have significant effects on the cell response.

Structure, MC3T3-E1 Cell Response, and Osseointegration of Macroporous Titanium Implants Covered by a Bioactive Microarc Oxidation Coating with Microporous Structure

Macroporous Ti with macropores of 50-400 μm size is prepared by sintering Ti microbeads with different diameters of 100, 200, 400, and 600 μm. Bioactive microarc oxidation (MAO) coatings with micropores of 2-5 μm size are prepared on the macroporous Ti. The MAO coatings are composed of a few TiO2 nanocrystals and lots of amorphous phases with Si, Ca, Ti, Na, and O elements. Compared to compact Ti, the MC3T3-E1 cell attachment is prolonged on macroporous Ti without and with MAO coatings; however, the cell proliferation number increases. These results are contributed to the effects of the space structure of macroporous Ti and the surface chemical feature and element dissolution of the MAO coatings during the cell culture. Macroporous Ti both without and with MAO coatings does not cause any adverse effects in vivo. The new bone grows well into the macropores and micropores of macroporous Ti with MAO coatings, showing good mechanical properties in vivo compared to Ti, MAO-treated Ti, and macroporous Ti because of its excellent osseointegration. Moreover, the MAO coatings not only show a high interface bonding strength with new bones but also connect well with macroporous Ti. Furthermore, the pushing out force for macroporous Ti with MAO coatings increases significantly with increasing microbead diameter.

UV-crosslinkable and thermo-responsive chitosan hybrid hydrogel for NIR-triggered localized on-demand drug delivery

Innovative drug delivery technologies based on smart hydrogels for localized on-demand drug delivery had aroused great interest. To acquire smart UV-crosslinkable chitosan hydrogel for NIR-triggered localized on-demanded drug release, a novel UV-crosslinkable and thermo-responsive chitosan was first designed and synthesized by grafting with poly N-isopropylacrylamide, acetylation of methacryloyl groups and embedding with photothermal carbon. The UV-crosslinkable unit (methacryloyl groups) endowed chitosan with gelation via UV irradiation. The thermo-responsive unit (poly N-isopropylacrylamide) endowed chitosan hydrogel with temperature-triggered volume shrinkage and reversible swelling/de-swelling behavior. The chitosan hybrid hydrogel embedded with photothermal carbon exhibited distinct NIR-triggered volume shrinkage (∼42% shrinkage) in response to temperature elevation as induced by NIR laser irradiation. As a demonstration, doxorubicin release rate was accelerated and approximately 40 times higher than that from non-irradiated hydrogels. The UV-crosslinkable and thermal-responsive hybrid hydrogel served as in situ forming hydrogel-based drug depot is developed for NIR-triggered localized on-demand release.

Osseointegration of bioactive microarc oxidized amorphous phase/TiO2 nanocrystals composited coatings on titanium after implantation into rabbit tibia

The amorphous phase/TiO2 nanocrystals (APTN) composited coatings were prepared on Ti implants for biomedical applications. The Ti implants without and with the APTN composited coatings both do not cause any adverse effects after implantation into the rabbit tibia. The osseointegration of Ti implants after covering the APTN coatings is improved pronouncedly, greatly increasing the interface bonding strength between the implants and newly formed bones. In addition, it is interesting that the newly formed bone tissues appear in the micro-pores of the APTN coatings, promoting the interface bonding between the implants and new bones by the mechanical interlock. Moreover, the Ti implant with the APTN coatings formed at higher applied voltage exhibit higher shear strength and displacement during the pushing out experiment probably due to its better osseointegration.

Synergistic effects of elastic modulus and surface topology of Ti-based implants on early osseointegration

Early osseointegration plays a crucial role in determining the therapeutic efficacy of orthopedic implants. Some factors responsible for early osseointegration, such as inherent mechanical properties and surface topology of implants, are well-characterized. However, the synergistic effects of elastic modulus and surface topology of implants on the osteogenic differentiation of stem cells and early osseointegration have not been thoroughly investigated. In this study, the titanium (Ti) and β-titanium alloy Ti–24Nb–4Zr–8Sn (TNZS) were used to evaluate the synergistic effects of elastic modulus and surface topology on the biological performance of these materials in vitro and in vivo. Scanning electron microscopy imaging confirmed the presence of a micro-scale porous oxide layer on the Ti and TNZS surfaces upon treatment with microarc oxidation (MAO), which resulted in increased surface roughness, enhanced surface wettability and favourable mechanical properties. As compared with Ti-MAO, the TNZS-MAO samples with lower elastic modulus displayed increased cell attachment, alkaline phosphatase activity, collagen secretion, osteogenic marker expression, and mineralization of rat bone marrow mesenchymal stem cells. Upon implantation in rat femoral condylar defects, an inherently low elastic modulus could cooperatively accelerate early osseointegration and maturation of trabecular bone after 4 weeks implantation with the MAO modified surface. These results demonstrated that elastic modulus and the surface micro-scale topographical structure of Ti alloy implants have a synergistic effect on their osseointegration.

H2Ti5O11·H2O nanorod arrays formed on a Ti surface via a hybrid technique of microarc oxidation and chemical treatment

H2Ti5O11·H2O nanorod arrays deposited on a titanium (Ti) surface have been fabricated via a hybrid technique of microarc oxidation (MAO) and chemical treatment. After the MAO treatment, an amorphous phase composed porous coating containing Ca, P, Si and Na elements was formed on the Ti surface. At the beginning of the chemical treatment, the elements of Ca, P, Si and Ti dissolved from the MAO coating into the solution. With a prolonged treatment time, nanorod arrays with a long aspect ratio were formed on the coating surface instead of the porous surface. The results revealed that the formed nanorods on the Ti surface were H2Ti5O11·H2O with the growth direction of [010]. This as-prepared Ti plate with a nanorod array surface exhibits a super-hydrophilic property, an excellent apatite-inducing ability and photocatalytic properties due to the existence of OH groups in the atomic structure of H2Ti5O11·H2O. The incorporated elements of Ca, P, Si and Na, and the corrosive attack of OH groups are the two factors for the formation of H2Ti5O11·H2O. The long and thin nature of the nanorods is attributed to the anisotropy of the atomic structure of H2Ti5O11·H2O with the lowest strain energy along the [010] direction based on the solid phase transformation.

Conformal coating containing Ca, P, Si and Na with double-level porous surface structure on titanium formed by a three-step microarc oxidation

A bioactive coating containing Ca, P, Si and Na elements with a porous surface structure has been fabricated on a titanium (Ti) plate by a three-step microarc oxidation. Randomly distributed gouges (80–200 μm) have been observed from the conformal MAO coating (with micro-scale pore size of 0.6–2 μm in morphology) covered Ti surface which exhibits double-level porous structure. Meanwhile, it is noticed that Ca, P, Si and Na elements have been incorporated into the MAO coating but show different oxidation states of elements between the flat surface and gouge surface. The XPS results reveal that Ti–OH and SiO2 gel have only formed on the gouge surface because of the decreased microarc oxidizing ability in the local area. Besides, the bioactivity of the different MAO step prepared Ti plates has been examined by simulated body fluid (SBF) immersion. As expected, the three-step MAO prepared Ti with double-level porous surface structure exhibits the best apatite-inducing ability thanks to the as-introduced Ti–OH and Si–OH groups.