Focal, remote-controlled, chronic chemical modulation of brain microstructures.

Direct delivery of fluid to brain parenchyma is critical in both research and clinical settings. This is usually accomplished through acutely inserted cannulas. This technique, however, results in backflow and significant dispersion away from the infusion site, offering little spatial or temporal control in delivering fluid. We present an implantable, MRI-compatible, remotely controlled drug delivery system for minimally invasive interfacing with brain microstructures in freely moving animals. We show that infusions through acutely inserted needles target a region more than twofold larger than that of identical infusions through chronically implanted probes due to reflux and backflow. We characterize the dynamics of in vivo infusions using positron emission tomography techniques. Volumes as small as 167 nL of copper-64 and fludeoxyglucose labeled agents are quantified. We further demonstrate the importance of precise drug volume dosing to neural structures to elicit behavioral effects reliably. Selective modulation of the substantia nigra, a critical node in basal ganglia circuitry, via muscimol infusion induces behavioral changes in a volume-dependent manner, even when the total dose remains constant. Chronic device viability is confirmed up to 1-y implantation in rats. This technology could potentially enable precise investigation of neurological disease pathology in preclinical models, and more efficacious treatment in human patients.

Steerable Microinvasive Probes for Localized Drug Delivery to Deep Tissue.

Enhanced understanding of neuropathologies has created a need for more advanced tools. Current neural implants result in extensive glial scarring and are not able to highly localize drug delivery due to their size. Smaller implants reduce surgical trauma and improve spatial resolution, but such a reduction requires improvements in device design to enable accurate and chronic implantation in subcortical structures. Flexible needle steering techniques offer improved control over implant placement, but often require complex closed-loop control for accurate implantation. This study reports the development of steerable microinvasive neural implants (S-MINIs) constructed from borosilicate capillaries (OD = 60 µm, ID = 20 µm) that do not require closed-loop guidance or guide tubes. S-MINIs reduce glial scarring 3.5-fold compared to prior implants. Bevel steered needles are utilized for open-loop targeting of deep-brain structures. This study demonstrates a sinusoidal relationship between implant bevel angle and the trajectory radius of curvature both in vitro and ex vivo. This relationship allows for bevel-tipped capillaries to be steered to a target with an average error of 0.23 mm ± 0.19 without closed-loop control. Polished microcapillaries present a new microinvasive tool for chronic, predictable targeting of pathophysiological structures without the need for closed-loop feedback and complex imaging.

Optical method for automated measurement of glass micropipette tip geometry.

Many experimental biological techniques utilize hollow glass needles called micropipettes to perform fluid extraction, cell manipulation, and electrophysiological recordings For electrophysiological recordings, micropipettes are typically fabricated immediately before use using a "pipette puller", which uses open-loop control to heat a hollow glass capillary while applying a tensile load. Variability between manufactured micropipettes requires a highly trained operator to qualitatively inspect each micropipette; typically this is achieved by viewing the pipette under 40-100x magnification in order to ensure that the tip has the correct shape (e.g., outer diameter, cone angle, taper length). Since laboratories may use hundreds of micropipettes per week, significant time demands are associated with micropipette inspection. Here, we have automated the measurement of micropipette tip outer diameter and cone angle using optical microscopy. The process features repeatable constraint of the micropipette, quickly and automatically moving the micropipette to bring its tip into the field of view, focusing on the tip, and computing tip outer diameter and cone angle measurements from the acquired images by applying a series of image processing algorithms. As implemented on a custom automated microscope, these methods achieved, with 95% confidence, ±0.38 µm repeatability in outer diameter measurement and ±5.45° repeatability in cone angle measurement, comparable to a trained human operator. Accuracy was evaluated by comparing optical pipette measurements with measurements obtained using scanning electron microscopy (SEM); optical outer diameter measurements differed from SEM by 0.35 ± 0.36 µm and optical cone angle measurements differed from SEM by -0.23 ± 2.32°. The algorithms we developed are adaptable to most commercial automated microscopes and provide a skill-free route to rapid, quantitative measurement of pipette tip geometry with high resolution, accuracy, and repeatability. Further, these methods are an important step toward a closed-loop, fully-automated micropipette fabrication system.

Actuated tissue engineered muscle grafts restore functional mobility after volumetric muscle loss.

Damage that affects large volumes of skeletal muscle tissue can severely impact health, mobility, and quality-of-life. Efforts to restore muscle function by implanting tissue engineered muscle grafts at the site of damage have demonstrated limited restoration of force production. Various forms of mechanical and biochemical stimulation have been shown to have a potentially beneficial impact on graft maturation, vascularization, and innervation. However, these approaches yield unpredictable and incomplete recovery of functional mobility. Here we show that targeted actuation of implanted grafts, via non-invasive transcutaneous light stimulation of optogenetic engineered muscle, restores motor function to levels similar to healthy mice 2 weeks post-injury. Furthermore, we conduct phosphoproteomic analysis of actuated engineered muscle in vivo and in vitro to show that repeated muscle contraction alters signaling pathways that play key roles in skeletal muscle contractility, adaptation to injury, neurite growth, neuromuscular synapse formation, angiogenesis, and cytoskeletal remodeling. Our study uncovers changes in phosphorylation of several proteins previously unreported in the context of muscle contraction, revealing promising mechanisms for leveraging actuated muscle grafts to restore mobility after volumetric muscle loss.

Platform for micro-invasive membrane-free biochemical sampling of brain interstitial fluid.

Neurochemical dysregulation underlies many pathologies and can be monitored by measuring the composition of brain interstitial fluid (ISF). Existing in vivo tools for sampling ISF do not enable measuring large rare molecules, such as proteins and neuropeptides, and thus cannot generate a complete picture of the neurochemical connectome. Our micro-invasive platform, composed of a nanofluidic pump coupled to a membrane-free probe, enables sampling multiple neural biomarkers in parallel. This platform outperforms the state of the art in low-flow pumps by offering low volume control (single stroke volumes, <3 nl) and bidirectional fluid flow (<100 nl/min) with negligible dead volume (<30 nl) and has been validated in vitro, ex vivo, and in vivo in rodents. ISF samples (<1.5 µL) can be processed via liquid chromatography-tandem mass spectrometry. These label-free liquid biopsies of the brain could yield a deeper understanding of the onset, mechanism, and progression of diverse neural pathologies.

Computationally Guided Intracerebral Drug Delivery via Chronically Implanted Microdevices.

Treatments for neurologic diseases are often limited in efficacy due to poor spatial and temporal control over their delivery. Intracerebral delivery partially overcomes this by directly infusing therapeutics to the brain. Brain structures, however, are nonuniform and irregularly shaped, precluding complete target coverage by a single bolus without significant off-target effects and possible toxicity. Nearly complete coverage is crucial for effective modulation of these structures. We present a framework with computational mapping algorithms for neural drug delivery (COMMAND) to guide multi-bolus targeting of brain structures that maximizes coverage and minimizes off-target leakage. Custom-fabricated chronic neural implants leverage rational fluidic design to achieve multi-bolus delivery in rodents through a single infusion of radioactive tracer (Cu-64). The resulting spatial distributions replicate computed spatial coverage with 5% error in vivo, as detected by positron emission tomography. COMMAND potentially enables accurate, efficacious targeting of discrete brain regions.