Yiwei Sun

Abstract Implant‐related infections are characterized by the formation of bacterial biofilms. Current treatments have various drawbacks. Nanozymes with enzyme‐like activity can produce highly toxic substances to kill bacteria and remove biofilms without inducing drug resistance. However, it is difficult for current monometallic nanozymes to function well in complex biofilm environments. Therefore, the development of multimetallic nanozymes with efficient multienzyme activities is crucial. In the present study, bimetallic nanozyme, ZnO‐CuS nanoflowers with peroxidase (POD), glutathione oxidase (GSH‐Px), and catalase (CAT) activity are successfully synthesized via calcination and loaded into F127 hydrogels for the treatment of implant‐related infections. The ability of ZnO‐CuS nanoflowers to bind bacteria is key for efficient antimicrobial activity. In addition, ZnO‐CuS nanoflowers with H 2 O 2 disrupt the metabolism of MRSA , including arginine synthesis, nucleotide excision repair, energy metabolism, and protein synthesis. ZnO‐CuS/F127 hydrogel in combination with H 2 O 2 has been demonstrated to be effective in clearing biofilm infection and facilitating the switch of M1 macrophages to M2‐repairative phenotype macrophages for the treatment of implant infections in mice. Furthermore, ZnO‐CuS/F127 hydrogels have favorable biosafety, and their toxicity is negligible. ZnO‐CuS/F127 hydrogel has provided a promising biomedical strategy for the healing of implant‐related infections, highlighting the potential of bimetallic nanozymes for clinical applications.

It is attractive to fabricate molds and dies using additive manufacturing (AM) technology because the increased freedom of design makes higher cooling efficiency possible. However, little is known so far about the thermal properties of the tool steels fabricated by AM, as well as how to balance between the thermal and mechanical properties. In this work, an H13 tool steel was processed by selective laser melting (SLM) followed by heat treatments and the thermal and mechanical properties in relation to microstructure were investigated. The as-built H13 showed lower thermal conductivities compared with conventional counterparts and exhibited anisotropy with a lower thermal conductivity along the building direction. Heat treatments generally increased the values of thermal conductivities and largely reduced anisotropy, but the final thermal conductivity differed when using different heat-treating schedules. It was found that porosity, retained austenite, the melt-pool structure and the ultra-fine cellular-columnar microstructure, which were functions of SLM and heat-treating parameters, were factors determining the thermal conductivity of H13. Based on the present study of SLMed H13, it is proposed that a trade-off is necessary between thermal and mechanical properties when designing the processing route.

Hybrid analog-digital precoding is challenging for broadband millimeter-wave (mmWave) massive MIMO systems, since the analog precoder is frequency-flat but the mmWave channels are frequency-selective. In this paper, we propose a principal component analysis (PCA)-based broadband hybrid precoder/combiner design, where both the fully-connected array and partially-connected subarray (including the fixed and adaptive subarrays) are investigated. Specifically, we first design the hybrid precoder/combiner for fully-connected array and fixed subarray based on PCA, whereby a low-dimensional frequency-flat precoder/combiner is acquired based on the optimal high-dimensional frequency-selective precoder/combiner. Meanwhile, the near-optimality of our proposed PCA approach is theoretically proven. Moreover, for the adaptive subarray, a low-complexity shared agglomerative hierarchical clustering algorithm is proposed to group the antennas for the further improvement of spectral efficiency (SE) performance. Besides, we theoretically prove that the proposed antenna grouping algorithm is only determined by the slow time-varying channel parameters in the large antenna limit. Simulation results demonstrate the superiority of the proposed solution over state-of-the-art schemes in SE, energy efficiency (EE), bit-error-rate performance, and the robustness to time-varying channels. Our work reveals that the EE advantage of adaptive subarray over fully-connected array is obvious for both active and passive antennas, but the EE advantage of fixed subarray only holds for passive antennas.