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

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Science Advances  25 Sep 2020:
Vol. 6, no. 39, eabb0657
DOI: 10.1126/sciadv.abb0657
  • Fig. 1 Design and characterization of a nitinol-activated nanofluidic pump.

    (A) Top: Schematic of nitinol wire–driven peristaltic pumping. Middle: Deformation of tubing (1 mm outer diameter, 0.5 mm inner diameter) in response to nitinol wire contraction (n = 3). Wire length = 14.6 mm. Wire diameter = 100 μm. Bottom: Images of nitinol wire–driven peristaltic pumping. Flow in one direction is driven by sequential contraction of wires in that direction. Scale bars, 2 mm. (B) Fluid displaced as a function of time in response to sequential wire contraction with 500-ms overlap between wires. Lack of overlap between the fourth and first wires between cycles results in backflow. (C) Fluid flow rate is influenced by wire pre-tension (n = 3), the percentage of its original width to which the tubing is compressed. Small values of pre-tension ensure that the wires do not slide along the tubing between contraction-relaxation cycles, increasing flow efficiency, while large values of pre-tension constrict the tube lumen and reduce flow rate. (D) Fluid flow rate is reduced to values commensurate with in vivo use (75.9 nl/min, 1.5 nl of backflow per pumping cycle) by using a custom-manufactured tubing (1 mm outer diameter, 0.1 mm inner diameter). (E) Fluid flow efficiency increases with increasing number of actuator wires, with flow rates and SDs matching our design requirements for flow driven by four wires (n = 3).

  • Fig. 2 Nanopump-driven infusion and sampling through a micro-invasive neural probe.

    (A) Fluid displacement tracking of nanopump-driven infusion through a borosilicate capillary (80 μm outer diameter, 50 μm inner diameter). (B) Fluid displacement tracking of nanopump-driven sampling through a borosilicate capillary (80 μm outer diameter, 50 μm inner diameter). (C) Infusion flow rate as a function of borosilicate capillary inner diameter (n = 3 per group). (D) Fluid displacement tracking of nanopump-driven infusion through a borosilicate capillary (80 μm outer diameter, 50 μm inner diameter) into an agarose gel brain phantom. (E) Fluid displacement tracking of nanopump-driven sampling through a borosilicate capillary (80 μm outer diameter, 50 μm inner diameter) from an agarose gel brain phantom. Sampling was performed after infusion.

  • Fig. 3 Miniaturization, optimization, and benchmarking of nanofluidic sampling platform.

    (A) Schematic of portable nanopump design, converting the benchtop prototype into a handheld battery-powered device, thereby enabling in vivo use. Photograph of manufactured portable nanopump in fig. S3. PCB, printed circuit board. (B) Fluid displaced as a function of time is a function of whether the nitinol wires operate on tubing filled with ambient air (trials 1, 2, and 3) or water (trials 1, 2, and 3). (C) Fluid displaced as a function of time for differing degrees of overlap (150 to 1000 ms) between wires during sequential contraction. (D) Fluid displaced as a function of time for optimized flow control code during infusion through and sampling from a borosilicate capillary (80 μm outer diameter, 50 μm inner diameter). Data from three separate trials are presented for both infusion and sampling. (E) MBP (~13 to 21 kDa) content in samples extracted using nanopump platform and standard microdialysis platform and compared to a control of known concentration. The nanopump-extracted sample significantly outperforms microdialysis in the measurement of this molecule, as it avoids sample extraction loss across a membrane. Samples were measured using a spectrophotometer. * represents analysis of variance (ANOVA) post hoc Tukey test, P ≤ 0.05. ** represents ANOVA post hoc Tukey test, P ≤ 0.01. (F) Hemoglobin (~64.5 kDa) content in samples extracted using nanopump platform and standard microdialysis platform and compared to a control of known concentration. The nanopump-extracted sample is not significantly different from the control and significantly outperforms microdialysis in the measurement of this molecule, as it avoids sample extraction loss across a membrane. n.s. represents ANOVA post hoc Tukey test P > 0.05. **** represents ANOVA post hoc Tukey test P ≤ 0.0001.

  • Fig. 4 Ex vivo characterization of nanofluidic sampling platform.

    (A) Schematic of sampling platform interfacing with rodent brain to collect samples of ISF. This methodology could potentially be adapted for chronic sampling (fig. S5D). (B) Scanning electron microscope image of borosilicate capillary. (C) Histological slice of rodent brain showing infusion of trypan blue into ex vivo tissue. (D) Fluorescent imaging of ex vivo brain showing a Genhance 750 dye bolus volume control as a function of infusion time (30 s right hemisphere, 60 s left hemisphere). Scale bar, 2 cm. (E) Time-lapse imaging (left) of fluorescent dye bolus volume in ex vivo brain showing linear increase (right) in volume as a function of infusion time. Scale bar, 2 cm. Data from two additional infusions are shown in fig. S6B.

  • Fig. 5 Biochemical characterization of in vivo samples of neural ISF.

    (A) MS/MS spectrum identifying MBP in in vivo sample. (B) MS/MS spectrum identifying BASP-1 in in vivo sample. (C) MS/MS spectrum identifying γ-enolase in in vivo sample. Fragment ions identified in the MS/MS spectrum are labeled, with b-type fragment ions containing the N terminus and y-type fragment ions containing the C terminus.

  • Fig. 6 Comparing biochemical profiles of in vivo samples of neural ISF. Middle:

    Venn diagram displaying the number of identified proteins in each of three in vivo samples from rat substantia nigra extracted using the nanopump. Top: MS/MS spectrum identifying transthyretin, found in all in vivo samples. Bottom: MS/MS spectrum identifying kinesin-like protein 15, found in all in vivo samples. Fragment ions identified in the MS/MS spectrum are labeled, with b-type fragment ions containing the N terminus and y-type fragment ions containing the C terminus. [M + 2H]2+ denotes precursor ion.

Supplementary Materials

  • Supplementary Materials

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

    Ritu Raman, Erin B. Rousseau, Michael Wade, Allison Tong, Max J. Cotler, Jenevieve Kuang, Alejandro Aponte Lugo, Elizabeth Zhang, Ann M. Graybiel, Forest M. White, Robert Langer, Michael J. Cima

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