Introduction: Endovascular embolization is becoming an increasingly utilized method of treating a variety of neurovascular disorders, including aneurysms, arteriovenous malformations (AVMs), and tumors. Many of the existing limitations of this treatment are related to the embolization agents currently available, including material compaction or migration, disease recurrence, or off-target embolization. Hydrogels are a promising class of materials that may be utilized to address some of these concerns. Methods: We compounded hydrogel formulations that were low-viscosity, shear thinning, photo-sensitive, and radioopaque. We developed a method of intravascular micro-catheter hydrogel delivery with dynamic modulation of hydrogel physical characteristics at the tip of the catheter, via photo-crosslinking with an integrated UV emitting optical fibre. This allowed for rapid transition from liquid to solid state to block blood flow at the vascular target, as well as dynamic modulation to suit the needs of a variety of neurovascular disorders. We performed preliminary testing of this novel methodology in animal models of neurovascular disease. Results: With dynamic modulation of photo-crosslinking, we were able to deliver hydrogels with a viscosity range of up to 10^4 Pa*s. The technique allowed for successful deposition of the hydrogel precursor in animal models for aneurysms, AVMS, and tumors. Post-procedural angiography demonstrated satisfactory occlusion of target vessels without evidence of complications. Conclusions: This novel embolization method holds promise in improving the safety and efficacy of the endovascular treatment of a variety of different pathologies and should be investigated further with direct comparative studies.
Introduction: Photodynamic therapy (PDT) is a promising adjunctive treatment for high grade brain tumors. However, early clinical trials have utilized significant variations in the conditions of light delivery, including the type of fibre and diffusing fluid. Our goal of this study was to sweep these conditions to determine optimal parameters for light delivery to the tumor resection cavity using a 3D model. Method: A 3D model to mimic an intracranial cavity was created and a PDT device was assembled using multiple 2W output lasers connected to cylindrical diffusing fibres. A variety of light delivery conditions were tested, including the use of bare fibres versus fibres placed inside balloon catheters, with deionized water or intralipid solutions. India ink was utilized to mimic blood products in the resection cavity. Light intensity at the edge of the model, signifying incident intensity at the tissue surface, was measured in multiple axes to assess for strength and uniformity. Light intensity and uniformity were compared between groups using Kruskal-Wallis analysis of variance. Results: Light delivery was significantly higher with the bare fibre compared to the balloon catheter across all types of circulating fluid (34.2 ± 3.54 vs. 30.8 ± 1.31 mV/cm2, p<0.05), but less uniform. The light uniformity increased as the concentration of intralipid increased. In conditions with the addition of india ink, the bare fibre performed better than the balloon catheter. Conclusion: In this phantom model assessment, bare fibres with 0.1% or 0.5% intralipid solution led to improved light delivery compared to other parameters. Photodynamic therapy of the cavity following surgical resection of HGG should be performed with optimal light delivery parameters to ensure treatment efficacy.
Significance: Imaging of the spinal cord is challenging due to the surrounding bony anatomy, physiologic motion, and the small diameter of the spinal cord. This precludes the use of non-invasive imaging techniques in assessing structural changes related to trauma and evaluating residual function.
Aim: The purpose of our research was to apply endovascular technology and techniques and construct a preclinical animal model of intrathecal spinal cord imaging using optical coherence tomography (OCT).
Approach: Five animals (2 Yorkshire Swine and 3 New Zealand Rabbits) were utilized. Intrathecal access was gained using a 16-guage Tuohy, and an OCT catheter was advanced under roadmap technique into the cervical canal. The OCT catheter has a motorized pullback, and a total length of 54 mm of the spinal canal is imaged.
Results: Image acquisition was successful for all animals. There were no instances of difficult catheter navigation, enabling OCT imaging rostrally to C2. The thecal sac provided excellent thoroughfare for the OCT catheter. The clear cerebrospinal fluid also provided an excellent medium for image acquisition, with no detectable artifact from the contents of the cerebrospinal fluid. The anatomical space of the spinal canal could be readily appreciated including: dural lining of the thecal sac, epidural veins, pial lining of the spinal cord, arachnoid bands, dentate ligaments, and nerve rootlets/roots.
Conclusion: Minimally invasive intrathecal imaging using endovascular OCT was feasible in this preclinical animal study. The repurposing of an endovascular device for spinal imaging comes with limitations, and a spine-specific device is necessary.
Conducting polymer are a promising class of biomaterials owing to their mechanical compliance and energy density. However, slow electrochemical processes have hindered widespread application. In this work, we make microscopic arrays of fs/ps laser patterned holes in relatively thick, easy to handle conducting polymer films in order to reduce charging time. A single-step, top-down, non-contact and template-free approach is used, employing femto and picosecond lasers to texturize polypyrrole films while preserving the total capacitance. A wide range of hole separations and diameters (pitch/diameter from 9.75/5.17 μm to 24.7/13.2 μm) are explored to reduce the diffusion path length in the bulk polymer, which achieved a speed increase of between 2 and 30 times. Fast charging conducting polymer electrodes such as ones achieved in this work may be useful in creating highly efficient (extremely low impedance and high fidelity) implantable electrodes for neural monitoring/stimulating app
In this paper, beam-shifting optical coherence tomography (BSOCT) is presented for speckle reduction and flow rate measurement. The sample beam is rotated about the optical axis of the objective lens to modulate the incident angle on sample; 17 and 3 incident angles are respectively performed for speckle reduction and flow rate measurement. The performance of the proposed technique is investigated on both phantom and in vivo experiments. By combining a 2D micro-electro-mechanical system (MEMS) and a zigzag scanning protocol, the frame rates of 45.2 Hz for speckle reduction and 25.6 Hz for flow rate measurement are achieved. With beam-shifting angle of 4.76º, the speckle noise reduction of 91% and the flow rate measurement precision of 0.0019 μl/s are achieved.
Intraoperative characterization of blood flow and visualization of microvasculature can have a huge impact on surgical outcomes. Knowledge about vasculature can provide diagnostic leverage, reducing operating times and improving patient recovery. Currently used Doppler-based techniques suffer from various shortcomings such as poor spatial resolution, high susceptibility to motion artifacts, and the inability to detect longitudinal flows. Our aim is to develop a fast, non-invasive approach to intraoperative microvascular imaging of slow-moving blood. In this work, we present a spatio-temporal approach to detect blood flow in vessels on the order of 0.1 mm. Specifically, a speckle-variance flow processing algorithm is used to detect small changes in B-mode pixel intensity on a micro-ultrasound (μUS) system operating in the range of 22-70 MHz. Data used in this study was acquired intraoperatively for patients undergoing neurosurgical procedures. Microcirculation was clearly visible in various anatomical structures and the spatial resolution in flow detection was much superior in comparison to Doppler-based flow detection. Moreover, using infrared optical tracking (Northern Digital Inc., Waterloo, Canada), a three-dimensional reconstruction of the microvasculature was constructed. This 3D vessel map allows for better visualization of the vasculature in the surgical cavity – allowing surgeons to plan their incisions, minimizing blood loss and potentially improving patient outcomes. To our knowledge, this is the first implementation of a three-dimensional, intraoperative microcirculation imaging technique using statistical and optical methods, alongside a non-Doppler high frequency ultrasound.
There is increasing interest in creating bendable and stretchable electronic interfaces that can be worn or applied to virtually any surface. The electroactive polymer community is well placed to add value by incorporating sensors and actuators. Recent work has demonstrated transparent dielectric elastomer actuation as well as pressure, stretch or touch sensing. Here we present two alternative forms of sensing. The first uses ionically conductive and stretchable gels as electrodes in capacitive sensors that detect finger proximity. In this case the finger acts as a third electrode, reducing capacitance between the two gel electrodes as it approaches, which can be detected even during bending and stretching. Very light finger touch is readily detected even during deformation of the substrate. Lateral resolution is achieved by creating a sensor array. In the second approach, electrodes placed beneath a salt containing gel are able to detect ion currents generated by the deformation of the gel. In this approach, applied pressure results in ion currents that create a potential difference around the point of contact, leading to a voltage and current in the electrodes without any need for input electrical energy. The mechanism may be related to effects seen in ionomeric polymer metal composites (IPMCs), but with the response in plane rather than through the thickness of the film. Ultimately, these ionically conductive materials that can also be transparent and actuate, have the potential to be used in wearable devices.
A polyurethane hydrogel based touch sensor with high transparency and conformability is demonstrated. Polyurethane hydrogels swollen with various electrolytes were compressed at a pressure of 30 kPa, simulating a fingertap on a conventional touch screen device. Unlike ionic polymer metal composite and conducting polymer trilayer sensors, where electrodes render the sensors opaque and relatively rigid, the electrodes used in this work are metal wires or strips, separated from each other by regions of transparent film, enabling transparency and compliance. The voltages and currents observed when the perturbation is above one electrode are on the order of 10-2 V and 10-7 A, relative to a second electrode that is approximately 1 cm away. The sign of voltage and current signals detected from perturbations made between electrodes is determined by relative proximity to each electrode, and the magnitude appears to decrease with increasing distance from the electrodes. These observations suggest that it may be possible to discriminate the location of touch based on signals transmitted to the edges of an ionically conductive film. A model to describe the inhomogeneous ionic distribution and predict the resultant voltage and current is presented to qualitatively explain the sensing, based on the Donnan potential.
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