In this research, an in-plane hydrodynamically reconfigurable optofluidic microlens is porposed [1]. The microlens is formed by the laminar flow of a high-refractive-index stream and two low-refractive-index streams as shown in Figure 1. A mathematical model based on the quadrupolar flow theory is established for prediction of the stream dispersion and focal length [2-3]. The calculated streamlines are shown in Figure 2. These streamlines indicate the potential interface position of the cladding and core streams. By properly controlling the flow rate ratio of the streams, the shape of the high-refractive-index stream can be adjusted into biconvex, flat and biconcave, and the curvature of the stream interfaces can be precisely manipulated.

The fabricated microfluidic chip is shown in Figure 3. In the experiment, silicone oil (refractive index = 1.579) is selected as the high-refractive-index stream and 28.9% calcium chloride solution is used as the low-refractive-index stream. The refractive index of the calcium chloride solution is matched to that of PDMS (refractive index = 1.403) to avoid light scattering. Figure 4 shows the variation of the mircolens versus the flow rate ratio between calcium chloride solution and silicone oil. The interfaces between the fluids change with the adjustment of the flow rate of calcium chloride solution. When the flow rate ratio is low, the stream of silicone oil squeezes the streams of calcium chloride solution and forms a biconvex microlens. The curvatures of the interfaces between the fluids are symmetrical and positive and become small with the increase of the flow rate ratio. The interfaces turn to flat when the flow rate ratio is 0.45. If the flow rate ratio is kept increasing, the streams of calcium chloride solution expands and the stream of silicone oil shrinks. The interfaces become concave, resulting in negative curvatures. A biconcave microlens is formed. The output light beam is observed in the beam-tracing chamber, as shown in Figure 5. When the flow rate ratio is small, the shape of the microlens is biconvex and a focused beam can be observed in the beam-tracing chamber. With the increase of the flow rate ratio, the convergent angle shrinks. Afterward, the shape of the microlens gradually turns into biconcave and the output beam becomes divergent. Furthermore, the divergent angle expands with the flow rate ratio. The light beam is stable and no fluctuation is observed.

The proposed optofluidic microlens is a promising candidate for various microfluidic or lab-on-a-chip applications including biomedical sensing, cellular imaging and on-chip photonic signal processing.

We here propose a new experimental technique to modulate cortical neuronal activities by a combination of laser light irradiation and electrical microstimulation in the tissue slice perfused with artificial cerebro-spinal fluid. This technique enables one to both excite and inhibit the neuron populations in a spatially confined manner.

Setting a target on implantable medical devices such as respiration-supporting pacemaker for amyotrophic lateral sclerosis (ALS), we develop an energy harvester that could earn electrical power from the mechanical motion of liquid droplets on an electrical charged plate called “electret.” A PDMS sheet with micro fluidic channels is laminated onto a silicon substrate with built-in permanent electrical charges. A pair of capacitive electrodes is formed in the sealed fluidic channels, in which water droplets are displaced back and forth due to the applied pressure that simulates the motion of heartbeat. Typical output power of 0.17 µW/cm² is obtained at 0.47 Hz. Analytical model suggests that the extension of the electret plate to ~ 6 cm² delivers 1 mW power, which is sufficient to drive the implantable medical devices.

Aluminum-based localized surface plasmon resonance (LSPR) holds attractive properties including low cost, high natural abundance, and ease of processing by a wide variety of methods including complementary metal oxide semiconductor process, making it superior to conventional LSPR involving noble metals. It has great potential to be developed into large-scale arrays composed of highly miniaturized and uniform signal transducer elements, thereby widely used in the terminals of mobile healthcare, public health security and environmental monitoring.

In this presentation, we present an overview of our recent work on using aluminum nanostructured materials with LSPR for biosensing. Firstly, we introduce an aluminum nanopyramid array (NPA) with tunable ultraviolet-visible-infrared wavelength plasmon resonances. The Al NPA holds high RI sensitivity which is even comparable with that of noble metal, and can be used as a biosensor for rapid detection of carbohydrate antigen 199 (a biomarker specific to cancer exists in the digest system), with limit of detection determined to be 29 ng/mL. Secondly, we present a low-cost replication technique is introduced for the mass production of NPA. The method we developed has great potential in industrial production. Last, we apply the plasmonic nanostructures to real-time monitor the concentration change of hydrogen ion in saliva, and to rapidly determine the blood type and concentrations of red blood cells in human blood.

Recent research on medical implants has asked for more reliable and biocompatible hermetic packaging techniques with integrated circuits (IC). Besides, high-density multi-channel IC interconnects also become a major requirement to realize high-resolution application on electrical stimulation and recording. Previously proposed packaging methods are mostly based on wire bonding technique to bond pads on chip to pads on biocompatible ceramics substrate individually. However, the real medical implant product that are currently in use or under development still lack the high-density packaging techniques which limit the further development of application [1-3].

The development of film package in implantable electronic medical device is one of the major solution. Rodger et al [4] introduced a biocompatible interconnect film packaging method based on parylene film, which is already a huge achievement of high-density packaging techniques. Also, Rodger have demonstrated the parylene flex and high-density multi-channel retinal IC chip have a strong bonding to survive during surgical manipulation. Unfortunately, water penetration problem of parylene C film still exists in the in vivo corrosive body fluid environment that could not meet the requirement of long-term implantation in humans. Thus, A desired medical implants of lifetime 10 years are mostly depends on the packaging design protection on the device.

Thin film encapsulation has been studied on flexible OLED packaging using incompatible three layers MgF₂/ZnS film, which has a good water vapor and oxygen barrier capability that could substantial improvement in lifetime [5]. In this work, we built an ideal packaging design by introducing multiple biocompatible organic/inorganic film together on PI substrate. The water penetration route of multiple film will significantly enhanced due to the multiple films design. The fabrication and functional validation of the well designed multiple film are based on PI substrate of 1 µm organic parylene C (PA) and 50 nm inorganic aluminum oxide (Al₂O₃) film, which are five layers PA/Al₂O₃/PA/Al₂O₃/PA design structure (Fig. 1). PA and Al₂O₃ film are deposited using advanced chemical vapor deposition (CVD) and atomic layer deposition (ALD) technology, respectively. Specifically, the films packaging sample and the He leakage test sample are shown on fig.2a and fig.2b, respectively. The He leakage test pressure is 1×10^-10 Pa·m³/s, meeting FDA 10 year in vivo implantation standard. Furthermore, the in vivo biological compatibility results of cell relative growth rate (RGR) also demonstrate highly biocompatible level (0 level) in cell L929 (Fig. 3). 

In conclusion, the state-of-the-art multiple organic/inorganic film packaging has been successfully demonstrated as a useful package design. Thus, synergistic organic/inorganic packaging by “multiple PA and Al₂O₃ film” provides a promising film package design that ensures highly biocompatible and long-term implantable for medical implants market. Next, we will use this film packaging design in our 1024 high-density retinal product to achieve long time reliable implantation in vivo.