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General DESIGN
Superficial stimulation
DEEP brain stimulation
Introduction

BlueBerry Brain Implants
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BlueBerry’s 2×2 output connector allows for a wide range of custom implant designs, covering both superficial cortical and deep subcortical stimulation. In this section, we showcase two specific examples: a flexible PCB implant with micro-LEDs for cortical areas, and a fiber-coupled LED for deep brain stimulation. While these designs focus on bilateral barrel cortex and the ventral tegmental area (VTA), they can be adapted to suit many other regions. To maintain compatibility, implants must use a matching 2×2 1.27mm female Mill-Max connector and respect the polarity of the BlueBerry output channels.
Furthermore, ensure you have the correct resistor values on the BlueBerry board for your chosen LED color and application. For instance, in our default configuration (documented in the BlueBerry hardware section), we employ a zero-ohm resistor on each channel to drive blue LEDs in a pulsed mode. If you need continuous light delivery or plan to use LEDs with a different forward voltage (e.g., red), you must replace zero-ohm resistor it with a resistor that appropriately limits current. Alternatively, you can incorporate resistors on your custom implant PCB to match each LED’s requirements.
Although we are currently considering to develop more general-purpose implant designs to support various brain regions, the goal of this section is to illustrate how BlueBerry’s 2×2 connector can be leveraged for different experimental contexts. By following these guidelines; using a matching connector, respecting the polarity, and selecting suitable resistor values; you can create your own implants tailored to your specific neuroscience research needs.

Flexible implants design for BlueBerry wireless optogenetics system. Neuroscience application for closed-loop optogenetic stimulation covering superficial and deep-brain regions.
sUPERFICIAL/ CORTICAL IMPLANTS

Superficial Cortical Stimulation Implant

This section describes a flexible PCB implant that positions micro-LEDs directly over the brain’s surface. Our reference design targets the bilateral barrel cortex, but it can be modified for other cortical areas.

Required Materials:

  • Flexible PCB: Provided in the BlueBerry Implant Package. The full KiCad project is available so you can adjust and modify the design for your region of interest in the brain.
  • Double Row 1.27mm Mill-Max Connector (Through hole): For interfacing with BlueBerry’s output channels. Order from here.
  • Micro LEDs (Blue): Mounted onto the flexible PCB (one LED per side) Here we used the LA UB20FP1 led from Light Avenue. Link to the LED.

Assembly Steps

  1. Apply Solder Paste
    Place a small amount of solder paste using sharp Q-tips on the surface-mount pads of the flexible PCB (typically two sets of pads, one for each LED). This part has to be done under microscope.
  2. Place Micro LEDs
    Gently place the micro LEDs onto the pasted pads, ensuring correct polarity alignment (anode and cathode must match the PCB’s layout).
  3. Reflow
    Place the flexible PCB with the attached LEDs in a reflow oven according to standard soldering profiles. The LEDs will bond to the PCB during this process.
  4. Attach the 2×2 Mill-Max Connector
    First cut down a standard 20x2 Mill-Max female connector strip to the required 2×2 size. Align the female 2×2 connector with the through-holes on the PCB, then solder it in place. This connector ensures proper alignment and polarity when plugged into the BlueBerry device.

Once assembled, the flexible PCB implant can be attached onto the animal’s skull or over the cortical region of interest.

Instructions to assemble multichannel micro LED implant for superficial/cortical wireless optogenetic stimulation
DEEP BRAIN/ SUBCORTICAL IMPLANTS

Deep Brain Stimulation Implant

For deep brain targets such as the VTA, an LED-fiber coupling approach is typically used to direct light into subcortical regions. Below is a step-by-step guide to building a fiber-LED implant.

Required Materials

Assembly Steps

  1. Fiber Preparation
    Use a fiber stripper to remove approximately 10 mm of the protective coating (shield) from one end. Using a fiber optic scribe, make a clean cut leaving around 20 mm of total fiber length. Cut again from the shilded side to retain about 5–6 mm of shielded fiber. This shielded section will be entering the 3D printed LED-Fiber coupler). The unshielded section is the part inserting in the brain, therefor cut from the unsheilded side based on the region you will be targeting. In the example image below we kept ~5.5 mm for targeting the VTA. Finally, place the fiber ends (both ends) in a polishing disk and move them gently over polishing paper or film to create smooth, flat surfaces on both tips.‍
  2. Prepare the LED and Connector
    First cut down a standard 20x2 Mill-Max female (SMD) connector strip to the required 2×2 size. Solder the LED directly to the 2×2  female connector leads (the angled side as shown on image below), respecting the polarity of both the LED and the BlueBerry output. If only one LED channel is needed, trim the connector to 2×1; otherwise, keep 2×2 for multiple channels.‍
  3. Insert Fiber into the Coupler
    Feed the shielded side of the fiber through the bottom of the 3D-printed coupler. Place the surface-mount LED into the top circular area of the coupler, ensuring it is oriented to match the fiber’s core. Gently push the fiber so its polished tip touches the LED surface..‍
  4. Fix with UV-Curable Glue
    Add a small drop of Norland 61 (or similar UV-curable adhesive) around the LED and fiber interface in the coupler’s top recess. Expose the assembly to UV light until the glue solidifies, securely bonding the fiber tip to the LED. Place another small amount of glue on the shielded portion of the fiber, near the coupler’s base, and cure again under UV light. This final step ensures long-term mechanical stability.
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Instructions to fabricate fiber-LED coupled implant for deep brain optogenetic stimulation
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