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Browsing by Author "Cheng, Gary J."
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Item Enhancement of osteoblast activity on nanostructured NiTi/hydroxyapatite coatings on additive manufactured NiTi metal implants by nanosecond pulsed laser sintering(Dove Press, 2018) Deng, Biwei; Bruzzaniti, Angela; Cheng, Gary J.; Biomedical Sciences and Comprehensive Care, School of DentistryBackground: The osteoinductive behaviors of nitinol (NiTi)-based metal implants for bone regeneration are largely dependent on their surface composition and topology. Continuous-mode laser sintering often results in complete melting of the materials and aggregation of particles, which lack control of heat transfer, as well as microstructural changes during sintering of the nanocomposite materials. Methods: In the current study, in situ direct laser deposition was used to additively manufacture three-dimensional NiTi structures from Ni and Ti powders. The mechanical property of NiTi has been shown to be similar to bone. Nanosecond pulsed laser sintering process was then utilized to generate a nanoporous composite surface with NiTi alloy and hydroxyapatite (HA) by ultrafast laser heating and cooling of Ni, Ti, and HA nanoparticles mixtures precoated on the 3D NiTi substrates; HA was added in order to improve the biocompatibility of the alloy. We then studied the underlying mechanism in the formation of NiTi/HA nanocomposite, and the synergistic effect of the sintered HA component and the nanoporous topology of the composite coating. In addition, we examined the activity of bone-forming osteoblasts on the NiTi/HA surfaces. For this, osteoblast cell morphology and various biomarkers were examined to evaluate cellular activity and function. Results: We found that the nanoscale porosity delivered by nanosecond pulsed laser sintering and the HA component positively contributed to osteoblast differentiation, as indicated by an increase in the expression of collagen and alkaline phosphatase, both of which are necessary for osteoblast mineralization. In addition, we observed topological complexities which appeared to boost the activity of osteoblasts, including an increase in actin cytoskeletal structures and adhesion structures. Conclusion: These findings demonstrate that the pulsed laser sintering method is an effective tool to generate biocompatible coatings in complex alloy-composite material systems with desired composition and topology. Our findings also provide a better understanding of the osteoinductive behavior of the sintered nanocomposite coatings for use in orthopedic and bone regeneration applications.Item Laser Shock Tuning Dynamic Interlayer Coupling in Graphene–Boron Nitride Moiré Superlattices(ACS, 2019) Kumar, Prashant; Liu, Jing; Motlag, Maithilee; Tong, Lei; Hu, Yaowu; Huang, Xinyu; Bandopadhyay, Arkamita; Pati, Swapan K.; Ye, Lei; Irudayaraj, Joseph; Cheng, Gary J.; Physics, School of ScienceIn the emergence of graphene and many two-dimensional (2D) materials, the most exciting applications come from stacking them into 3D devices, promising many excellent possibilities for neoteric electronics and optoelectronics. Layers of semiconductors, insulators, and conductors can be stacked to form van der Waals heterostructures, after the weak bonds formed between the layers. However, the interlayer coupling in these heterostructures is usually hard to modulate, resulting in difficulty to realize their emerging optical or electronic properties. Especially, the relationship between interlayer distance and interlayer coupling remains to be investigated, due to the lack of effective technology. In this work, we have used laser shocking to controllably tune the interlayer distance between graphene (Gr) and boron nitride (BN) in the Gr/BN/Gr heterostructures and the strains in the 2D heterolayers, providing a simple and effective way to modify their optic and electronic properties. After lase shocking, the reduction of interlayer distance is calculated by molecular dynamics (MD) simulation. Some atoms in Gr or BN are out-of-plane as well. In Raman measurements, the G peak in the heterostructure shows a red-shifted trend after laser shocking, indicating the strong phonon coupling in the interlayer. Moreover, the larger transparency after laser shocking also verifies the stronger photon coupling in the heterostructure. To investigate the effects of the interlayer coupling of heterostructure on its out-of-plane electronic behavior, we have investigated the electronic tunneling behavior. The heterostructure after laser shock reveals a lager tunneling current and lower tunneling threshold, proving an unexpected better electrical property. From DFT calculations, laser shocking can modulate the band gap structure of graphene in Gr/BN/Gr heterostructures; therefore, the heterostructures can be implemented as a unique photonic platform to modulate the emission characters of the anchored CdSe/ZnS core–shell quantum dots. Remarkably, the effective laser shocking method is also applicable to various otherwise noninteracting 2D materials, resulting in many new phenomena, which will lead science and technology to unexplored territories.Item Molecular-Scale Nanodiamond with High-Density Color Centers Fabricated from Graphite by Laser Shocking(Elsevier, 2020-05) Motlag, Maithilee; Liu, Xingtao; Nurmalasari, Ni Putu Dewi; Jin, Shengyu; Nian, Qiong; Park, Charles; Jin, Linrui; Huang, Libai; Liu, Jing; Cheng, Gary J.; Physics, School of ScienceNanodiamonds (NDs) with nitrogen vacancy (NV) color centers have the potential for quantum information science and bioimaging due to their stable and non-classical photon emission at room temperature. Large-scale fabrication of molecular-size nanodiamonds with sufficient color centers may economically promote their application in versatile multidisciplinary fields. Here, the manufacture of molecular-size NV center-enriched nanodiamonds from graphite powder is reported. We use an ultrafast laser shocking technique to generate intense plasma, which transforms graphite to nanodiamonds under the confinement layer. Molecular dynamics simulations suggest that the high pressure of 35 GPa and the high temperature of 3,000K result in the metaphase transition of graphite to nanodiamonds within 100 ps. A high concentration of NV centers is observed at the optimal laser energy of 3.82 GW/cm2, at which point molecular-size (∼5 nm) nanodiamonds can individually host as many as 100 NV centers. Consecutive melamine annealing following ultrafast laser shocking enriches the number of NV centers >10-fold and enhances the spontaneous decay rate of the NV center by up to 5 times. Our work may enhance the feasibility of nanodiamonds for applications, including quantum information, electromagnetic sensing, bioimaging, and drug delivery.