A local network of implants uses your body as the wiring
A local network of implants uses your body as the wiring
一种利用人体作为导线的植入式设备局域网
Most implants like pacemakers and insulin pumps work in isolation. To help them coordinate with each other, a team of Georgia Tech researchers built a networking system that sends signals through body tissue instead of antennas and radio waves. 大多数植入式设备（如心脏起搏器和胰岛素泵）都是独立工作的。为了帮助它们相互协作，佐治亚理工学院的研究团队构建了一种网络系统，该系统通过人体组织而非天线和无线电波来发送信号。
Radio problems
无线电带来的问题
Implants that communicate today mostly rely on radio protocols like Bluetooth Low Energy or near-field communication (NFC). Both are a poor fit for in-body data transfer, says Alex Abramson, a Georgia Tech engineer and co-author of the new study. The first problem is power. “If you want an implant to remain in an active state such that it can respond within milliseconds, it’s very difficult to do that with the Bluetooth system,” Abramson said. According to the paper, Bluetooth components, when they’re activated, can cut an implant’s battery life by up to 90 percent. 目前具备通信功能的植入式设备主要依赖蓝牙低功耗（BLE）或近场通信（NFC）等无线电协议。该研究的合著者、佐治亚理工学院工程师 Alex Abramson 表示，这两种技术都不太适合体内数据传输。首要问题是功耗。“如果你希望植入物保持活跃状态，以便在几毫秒内做出响应，使用蓝牙系统是非常困难的，”Abramson 说道。据论文显示，蓝牙组件一旦激活，可能会缩短植入设备高达 90% 的电池寿命。
The second problem is that radio waves don’t travel well through the body. “Bluetooth and near-field communication are attenuated quite a lot in the tissue,” Abramson said. He said that implant-to-implant radio communication systems run into attenuation issues if the signal has to travel more than one centimeter through the tissue. Then there’s size. Radio needs antennas, and commercial Bluetooth components require a device at least five millimeters wide. Implants thinner than three millimeters can be injected with a syringe at an outpatient clinic; bigger ones usually need surgery. 第二个问题是无线电波在人体内的传播效果不佳。“蓝牙和近场通信在组织中的衰减非常严重，”Abramson 说。他指出，如果信号必须穿过超过一厘米的组织，植入设备间的无线电通信系统就会遇到衰减问题。此外还有尺寸问题。无线电需要天线，而商用蓝牙组件要求设备宽度至少达到 5 毫米。直径小于 3 毫米的植入物可以在门诊通过注射器植入；而更大的设备通常需要手术。
The fix
解决方案
Abramson’s team came up is called SWANS (Smart Wireless Autonomous Networking System) and was inspired by the way body’s own internal communication networks. “The nervous system can take a lot of inputs from all over the body, harvest all that data, and make a specific decision. And our system mimics that,” Abramson said. SWANS relies on ionic conduction just like neurons, which communicate by shuttling sodium and potassium ions through their membranes, creating voltage differences. “But instead of using nerves, we use normal body tissue to send those signals,” Abramson said. Abramson 的团队提出了一种名为 SWANS（智能无线自主网络系统）的方案，其灵感来源于人体自身的内部通信网络。“神经系统可以接收来自全身的大量输入，收集所有数据并做出特定决策。我们的系统模仿了这一点，”Abramson 说。SWANS 像神经元一样依赖离子传导，神经元通过在细胞膜间穿梭钠离子和钾离子来通信，从而产生电压差。“但我们不是利用神经，而是利用正常的身体组织来发送这些信号，”Abramson 解释道。
Name calling
“点名”机制
The idea isn’t entirely new. A Food and Drug Administration-cleared pill called Abilify MyCite uses ionic conduction to tell a skin patch it was swallowed. But such systems typically link just two devices, while Abramson’s team wanted SWANS to connect many. The first SWANS component is a wearable hub. It’s a flexible circuit board that reads sensor data, runs decision-making algorithms, and emits voltage pulses of up to 12 volts. The second is a patch of stainless-steel microneedles that delivers those pulses into the body, bypassing the skin’s outermost, poorly conductive layer. The third is a network of syringe-injectable implants, each packing two receiving pads, a transistor switch, a battery, and either a sensor or an actuator such as a nerve stimulator. 这个想法并非完全创新。一种获美国食品药品监督管理局（FDA）批准的名为 Abilify MyCite 的药丸，就是利用离子传导来告知皮肤贴片它已被吞下。但此类系统通常只连接两个设备，而 Abramson 的团队希望 SWANS 能连接多个设备。SWANS 的第一个组件是一个可穿戴中心。它是一块柔性电路板，用于读取传感器数据、运行决策算法并发出高达 12 伏的电压脉冲。第二个组件是一块不锈钢微针贴片，将这些脉冲传导至体内，绕过皮肤最外层导电性差的屏障。第三个组件是一个可通过注射器植入的网络，每个植入物包含两个接收垫、一个晶体管开关、一个电池以及一个传感器或执行器（如神经刺激器）。
“We created all of the smarts in the wearable hub,” Abramson said. The wearable has more room and more battery power, so the implants could be kept small and simple. When the hub fires a pulse, it creates a brief electric field that spreads through the tissue in all directions. Every implant within range picks it up, but only the right one(s) react, a bit like people in a crowded room who turn around only when they hear their own name. The team achieved that by making each implant’s transistor switch on only when the incoming pulse crosses a specific threshold. Adding a resistor in front of the transistor raises the voltage needed to flip the switch. Adding a capacitor means the pulse must last long enough to charge it first. By mixing and matching these components, the team made implants that respond only to specific combinations of pulse strength and length. “我们将所有的智能处理功能都放在了可穿戴中心里，”Abramson 说。可穿戴设备有更多的空间和电池电量，因此植入物可以保持得非常小巧简单。当中心发出脉冲时，会产生一个短暂的电场，向四面八方穿过组织。范围内的每个植入物都能接收到信号，但只有特定的植入物会做出反应，这有点像在拥挤的房间里，人们只有听到自己的名字时才会回头。团队通过让每个植入物的晶体管仅在输入脉冲超过特定阈值时才开启来实现这一点。在晶体管前增加一个电阻可以提高开关所需的电压；增加一个电容器则意味着脉冲必须持续足够长的时间来为其充电。通过混合和匹配这些组件，团队制造出的植入物仅对脉冲强度和长度的特定组合做出响应。
This, the authors admit in the paper, means that voltage thresholds need to be tuned for each body and implant placement. Because SWANS implants are built from passive components, they draw almost no power while listening, extending battery life more than 15 times compared to Bluetooth and NFC. A complete implant with a battery measures 3 by 1.1 by 17 millimeters and fits through a 6-gauge needle. To test the system, Abramson and his colleagues installed it in chicken breasts, skin-on, bone-in pork bellies, and living rats. 正如作者在论文中所承认的，这意味着电压阈值需要针对每个人的身体和植入位置进行调整。由于 SWANS 植入物由无源组件构成，它们在监听时几乎不消耗电量，与蓝牙和 NFC 相比，电池寿命延长了 15 倍以上。一个完整的带电池植入物尺寸为 3 x 1.1 x 17 毫米，可以通过 6 号针头植入。为了测试该系统，Abramson 和他的同事将其安装在鸡胸肉、带皮带骨的猪腩肉以及活体大鼠身上。
Twitching legs
抽动的腿
“Pork belly is a very thick and heterogeneous tissue,” Abramson said. The signal had to get through fat, muscle, bone, and skin. A single 10-volt pulse produced a detectable voltage gradient more than 30 centimeters across the tissue and up to 14 centimeters deep—more than 10 times the coverage of Bluetooth or NFC. In live rats, the signals reached implants under the skin, in the abdominal cavity, and even in the stomach. Placement didn’t matter much either. “We put our wearable on the stomach of the rat, and then we were able to get actuation in the back of the rat,” Abramson said. “猪腩肉是一种非常厚且不均匀的组织，”Abramson 说。信号必须穿过脂肪、肌肉、骨骼和皮肤。单个 10 伏的脉冲在组织中产生了超过 30 厘米宽、深达 14 厘米的可检测电压梯度——覆盖范围是蓝牙或 NFC 的 10 倍以上。在活体大鼠身上，信号到达了皮下、腹腔甚至胃部的植入物。植入位置的影响也不大。“我们将可穿戴设备放在大鼠的胃部，然后就能在大鼠的背部实现驱动，”Abramson 说。
The most advanced experiment used strain sensors placed on the rats’ front legs. When a sensor detected the left or right forelimb moving, the hub sent a limb-specific pulse through the body that reached an implant on the corresponding hind leg, which stimulated the sciatic nerve and made that leg twitch. The team also built an implant-to-implant relay where a device with a temperature sensor passed a signal to a second implant only when it registered a fever above 40° C (104° F). Abramson notes that pacemakers and neurostimulators already use similar voltages and pulse lengths, so the team did not expect any major safety issues. In a two-month study in rats, scar tissue up to a millimeter thick grew around the implants, but by raising the voltage within safe limits, the team kept communication going throughout. The pulses didn’t stimulate nerves other than the targeted one, didn’t change the heart’s electrical activity, and caused no more cell death or oxidative stress than needles and implants that weren’t electrified. 最先进的实验使用了放置在大鼠前腿上的应变传感器。当传感器检测到左前肢或右前肢移动时，中心会通过身体发送一个特定肢体的脉冲，到达相应后腿上的植入物，从而刺激坐骨神经并使该腿抽动。团队还构建了一个植入物间的继电器，其中带有温度传感器的设备仅在记录到超过 40°C (104°F) 的发热时，才会向第二个植入物发送信号。Abramson 指出，心脏起搏器和神经刺激器已经在使用类似的电压和脉冲长度，因此团队预计不会有重大的安全问题。在一项为期两个月的大鼠研究中，植入物周围长出了厚达一毫米的疤痕组织，但通过在安全范围内提高电压，团队保持了全程通信。这些脉冲没有刺激目标神经以外的神经，没有改变心脏的电活动，并且造成的细胞死亡或氧化应激并不比未通电的针头和植入物多。