3D-Printed Microneedles Create Precise Perforations in Human Round Window Membrane in Situ

Abstract

Hypothesis: Three-dimensional (3D)-printed microneedles can create precise holes on the scale of micrometers in the human round window membrane (HRWM). Background: An intact round window membrane is a barrier to delivery of therapeutic and diagnostic agents into the inner ear. Microperforation of the guinea pig round window membrane has been shown to overcome this barrier by enhancing diffusion 35-fold. In humans, the challenge is to design a microneedle that can precisely perforate the thicker HRWM without damage. Methods: Based on the thickness and mechanical properties of the HRWM, two microneedle designs were 3D-printed to perforate the HRWM from fresh frozen temporal bones in situ (n = 18 total perforations), simultaneously measuring force and displacement. Perforations were analyzed using confocal microscopy; microneedles were examined for deformity using scanning electron microscopy. Results: HRWM thickness was determined to be 60.1 ± 14.6 (SD) μm. Microneedles separated the collagen fibers and created slit-shaped perforations with the major axis equal to the microneedle shaft diameter. Microneedles needed to be displaced only minimally after making initial contact with the RWM to create a complete perforation, thus avoiding damage to intracochlear structures. The microneedles were durable and intact after use. Conclusion: 3D-printed microneedles can create precise perforations in the HRWM without damaging intracochlear structures. As such, they have many potential applications ranging from aspiration of cochlear fluids using a lumenized needle for diagnosis and creating portals for therapeutic delivery into the inner ear.

Ultrasound Microbubble–Facilitated Inner Ear Delivery of Gold Nanoparticles Involves Transient Disruption of the Tight Junction Barrier in the Round Window Membrane

“…Related studies have explored several strategies to increase the permeability of the RWM. Examples include using external magnetic forces to enhance transportation of superparamagnetic iron oxide NPs across an artificial RWM (Mondalek et al, 2006), manipulating drug solution osmolarity or benzyl alcohol content to alter the permeability properties of the RWM (Mikulec et al, 2008), and creating microperforations in the RWM to enhance diffusion across the membrane (Kelso et al, 2015;Chiang et al, 2020). All these attempts have focused on modifying the transcellular pathway of the RWM.…”

Inner ear delivery: Challenges and opportunities

“…40,41 To date, several needle designs have been fabricated with an assortment of unique characteristics. 39,[41][42][43][44][45] Microneedles fabricated using two-photon polymerization (2PP) are able to perforate guinea pig RWM reliably. 41,45 In the guinea pig, these perforations are not associated with any notable lasting effects on hearing, and the perforations also heal within a week after perforation.…”

“…Microneedles are designed with the microanatomic and mechanical properties of the RWM in mind, to create controlled and precise perforations in the membrane with minimal trauma (Figure ) . To date, several needle designs have been fabricated with an assortment of unique characteristics . Microneedles fabricated using two‐photon polymerization (2PP) are able to perforate guinea pig RWM reliably .…”

“…In the guinea pig, these perforations are not associated with any notable lasting effects on hearing, and the perforations also heal within a week after perforation . Microneedles can also create precise perforations in the human RWM . One of the challenges of microneedle use on the RWM is ensuring that the needle is inserted far enough to create a perforation but not so far as to cause damage to structures behind the RWM .…”

“…Microneedles can also create precise perforations in the human RWM . One of the challenges of microneedle use on the RWM is ensuring that the needle is inserted far enough to create a perforation but not so far as to cause damage to structures behind the RWM . Due to the anatomic constraints of RWM access in vivo, confirmation of microneedle perforation can be difficult; silver chloride‐plated microneedles can detect contact with perilymph based on changes in voltage …”