Biology subjects

Marr, D. W. M.

Publications and source records attributed to Marr, D. W. M..

3 recordsLinked to original sources

bioRxiv2023

Magnetically Powered Microwheel Thrombolysis of Occlusive Thrombi in Zebrafish

Tissue plasminogen activator (tPA) is the only FDA approved treatment for ischemic stroke but carries significant risks, including major hemorrhage. Additional options are needed, especially in small vessel thrombi which account for [~]25% of ischemic strokes. We have previously shown that tPA-functionalized colloidal microparticles can be assembled into microwheels ({micro}wheels) and manipulated under the control of applied magnetic fields to enable rapid thrombolysis of fibrin gels in microfluidic models of thrombosis. Providing a living microfluidic analog, transparent zebrafish larvae have a highly conserved coagulation cascade that enables studies of hemostasis and thrombosis in the context of intact vasculature, clotting factors, and blood cells. Here we show that tPA-functionalized {micro}wheels can perform rapid and targeted recanalization in vivo. This effect requires both tPA and {micro}wheels, as minimal to no recanalization is achieved with tPA alone, {micro}wheels alone, or tPA-functionalized microparticles in the absence of a magnetic field. We evaluated tPA-{micro}wheels in CRISPR-generated plasminogen (plg) heterozygous and homozygous mutants and confirmed that tPA-{micro}wheels are dose-dependent on plasminogen for lysis. We have found that magnetically powered {micro}wheels as a targeted tPA delivery system are dramatically more efficient at plasmin-mediated thrombolysis than systemic delivery in vivo. Further development of this system in fish and mammalian models could enable a less invasive strategy for alleviating ischemia that is safer than directed thrombectomy or systemic infusion of tPA.

bioengineering↗

bioRxiv2022

Magnetically powered chitosan milliwheels for rapid translation, barrier function rescue, and delivery of therapeutic proteins to the inflamed gut epithelium

Inflammatory bowel disease (IBD) is mediated by an overexpression of tumor necrosis factor- (TNF) by mononuclear cells in the intestinal mucosa. Intravenous delivery of neutralizing anti-TNF antibodies can cause systemic immunosuppression and up to one-third of people are non-responsive to treatment. Oral delivery of anti-TNF could reduce adverse effects; however, it is hampered by antibody degradation in the harsh gut environment during transit and poor bioavailability. To overcome these shortcomings, we demonstrate magnetically powered hydrogel particles that roll along mucosal surfaces, provide protection from degradation, and sustain local release of anti-TNF. Iron oxide nanoparticles are embedded into a crosslinked chitosan hydrogel and sieved to produce 100-200 m particles called milliwheels (m-wheels). Once loaded with anti-TNF, these m-wheels release 10% to 80% of their payload over one week at a rate that depends on crosslinking density and pH. A rotating magnetic field induces a torque on the m-wheels that results in rolling velocities greater than 500 m/s on glass and mucus-secreting cells. The permeability of TNF challenged gut epithelial cell monolayers was rescued in the presence of anti-TNF carrying m-wheels which both neutralized the TNF and created an impermeable patch over leaky cell junctions. With the ability to translate over mucosal surfaces at high speed, provide sustained release directly to the inflamed epithelium, and provide barrier rescue, m-wheels demonstrate a potential strategy to deliver therapeutic proteins for the treatment of IBD.

bioengineering↗

bioRxiv2021

Breaking the fibrinolytic speed limit with microwheel co-delivery of tissue plasminogen activator and plasminogen

Fibrinolysis is the enzymatic degradation of fibrin, the biopolymer that gives blood clots their mechanical integrity. To reestablish blood flow in vessels occluded by clots, tissue plasminogen activator (tPA) can be used; however, its efficacy is limited by transport to and into a clot and by the depletion of its substrate, plasminogen. To overcome these rate limitations, we design a platform to co-deliver tPA and plasminogen based on microwheels (wheels), wheel-like assemblies of superparamagnetic colloidal beads that roll along surfaces at high speeds and carry therapeutic payloads in applied magnetic fields. By experimentally measuring fibrinolysis of plasma clots at varying concentrations of tPA and plasminogen, the biochemical speed limit was first determined. These data, in conjunction with measurements of wheel translation, activity of immobilized tPA on beads, and plasminogen release kinetics from magnetic mesoporous silica nanoparticles (mMSN), were used in a mathematical model to identify the optimal tPA:plasminogen ratio and guide the coupling of plasminogen-loaded mMSN to tPA functionalized superparamagnetic beads. Once coupled, particle-bead assemblies form into a co-delivery vehicle that rolls to plasma clot interfaces and lyses them at rates comparable to the biochemical speed limit. With the addition of mechanical action provided by rotating wheels to penetrate clots, this barrier was exceeded by rates 40-fold higher lysis by 50 nM tPA. This co-delivery of an immobilized enzyme and its substrate via a microbot capable of mechanical work has the potential to target and rapidly lyse clots that are inaccessible by mechanical thrombectomy devices or recalcitrant to systemic tPA delivery.

bioengineering↗