## Acoustic droplet–hydrogel composites for spatial and temporal control of growth factor delivery and scaffold stiffness

Fabiilli M L , Wilson C G , Frédéric Padilla, et al. Acta Biomaterialia, 2013, 9(7):7399-7409.
DOI：10.1016/j.actbio.2013.03.027

### Abstract:

Wound healing is regulated by temporally and spatially restricted patterns of growth factor signaling, but there are few delivery vehicles capable of the “on-demand” release necessary for recapitulating these patterns. Recently we described a perfluorocarbon double emulsion that selectively releases a protein payload upon exposure to ultrasound through a process known as acoustic droplet vaporization (ADV). In this study, we describe a delivery system composed of fibrin hydrogels doped with growth factor-loaded double emulsion for applications in tissue regeneration. Release of immunoreactive basic fibroblast growth factor (bFGF) from the composites increased up to 5-fold following ADV and delayed release was achieved by delaying exposure to ultrasound. Releasates of ultrasound-treated materials significantly increased the proliferation of endothelial cells compared to sham controls, indicating that the released bFGF was bioactive. ADV also triggered changes in the ultrastructure and mechanical properties of the fibrin as bubble formation and consolidation of the fibrin in ultrasound-treated composites were accompanied by up to a 22-fold increase in shear stiffness. ADV did not reduce the viability of cells suspended in composite scaffolds. These results demonstrate that an acoustic droplet–hydrogel composite could have broad utility in promoting wound healing through on-demand control of growth factor release and/or scaffold architecture.

Schematic representation of drug release by ADV in a hydrogel scaffold. Bottom: A water-in-PFC-in-water (W1/PFC/W2) double emulsion, containing a growth factor in the W1 phase, is encapsulated within the scaffold. Upon exposure to acoustic amplitudes greater than the ADV threshold of the emulsion, the PFC within the droplets is vaporized, thus releasing the W1 phase. Top left: confocal fluorescence image (fluorescein, shown in green) of a PFC double emulsion droplet (scale bar = 10 μm). Smaller aqueous droplets, containing a water-soluble payload such as fluorescein or bFGF, are enveloped by a larger PFC globule. Top right: visible image of a 10 mg ml−1 fibrin gel containing 5% (v/v) double emulsion after targeted exposure to ultrasound. The “block M” consists of gas bubbles generated by ADV. Scale bar = 4 mm.

## Direct Transmission of Digital Message via Programmable Coding Metasurface

Tie Jun Cui, Shuo Liu, Guo Dong Bai, and Qian Ma
DOI: 10.1155/2019/2584509

### Abstract:

In modern wireless communications, digital information is firstly converted to analog signal by a digital-analog convertor, which is then mixed to high-frequency microwave to be transmitted through a series of devices including modulator, mixer, amplifier, filter, and antenna and is finally received by terminals via a reversed process. Although the wireless communication systems have evolved significantly over the past thirty years, the basic architecture has not been challenged. Here, we propose a method to transmit digital information directly via programmable coding metasurface. Since the coding metasurface is composed of ‘0’ and ‘1’ digital units with opposite phase responses, the digital information can be directly modulated to the metasurface with certain coding sequences and sent to space under the illumination of feeding antenna. The information, being modulated in radiation patterns of the metasurface, can be correctly received by multiple receivers distributed in different locations. This method provides a completely new architecture for wireless communications without using complicated digital-analog convertor and a series of active/passive microwave devices. We build up a prototype to validate the new architecture experimentally, which may find promising applications where information security is highly demanded.

Schematic illustration of the working mechanism of the proposed DDM system.

### 推荐理由：

1. 首次提出将数字超表面用于无线信号传输，并且实验验证。
2. 解读超表面反射出的信息需要在特定方向接收信号，保证了信息的安全性。
3. 自适应调节算法解决传输信号被障碍物遮挡时传输受损的难题。

### 缺点：

1. 文中没有讨论这种数字超表面传递信息的速度，即通信领域的带宽，并且缺少与传统手段的比较。
2. 文中讨论的传输信号设备并没有给出信号在空间中的衰减。

## Broadband and wide-angle negative reflection at a phononic crystal boundary

Degang Zhao, Yangtao Ye, Shengjun Xu, Xuefeng Zhu, and Lin Yi
DOI: 10.1063/1.4863691

### Abstract:

We have theoretically and experimentally demonstrated the anomalous negative reflection at the boundary of a well-designed two-dimensional phononic crystal. This exotic phenomenon is attributed to the selective enhancement of −1st order diffraction mode with the zero-order diffraction mode being dramatically suppressed. After material and structural optimization, the negative reflection can be maintained in a broadband of frequencies and for a wide incident angle range. Our system can be employed to design Littrow configuration to realize perfect broadband and wide-angle blazing. The study gives a possibility to achieve greater flexibility and stronger effects in manipulating reflected acoustic waves, which has potential applications in underwater communication, medical ultrasonics, etc.

### 总结：

$P(r)=\sum_n{p_nexp(ik_n\cdot r)}, n=0,\pm1,\pm2,\cdots$

$k_n=(k_{nx},k_{ny}),k_{nx}=k_0 \sin \theta+n \frac{2\pi}{a},k_{ny}=\sqrt{k_0^2-k_{nx}^2}$

The schematic presentation of negative wave reflection at a phononic crystal boundary.

### 优点：

1. 利用声子晶体的禁带属性，实现了宽频宽角度范围的负反射
2. 实现了宽入射角度的完美$Littrow$结构，打破了传统光栅的发光角度依赖光栅表面构型的限制

### 不足：

1. 产生负反射是基于声子晶体禁带，这限制了产生负反射的频率范围在高频区
2. 宽入射角度范围能产生负反射对应的频率范围较窄
3. 该工作只关注了$-1$阶衍射模态，更高阶衍射模态对负反射是否存在影响呢