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

Abstract

Background: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. Objectives:To overcome these rate limitations, a platform was designed to co-deliver tPA and plasminogen based on microwheels (µwheels), wheel-like assemblies of superparamagnetic colloidal beads that roll along surfaces at high speeds. Methods:The biochemical speed limit was determined by measuring fibrinolysis of plasma clots at varying concentrations of tPA (10-800 nM) and plasminogen (1-6 µM).Biotinylated magnetic mesoporous silica nanoparticles were synthesized and bound to streptavidin-coated superparamagnetic beads to make studded beads. Studded beads were loaded with plasminogen and tPA was immobilized on their surface.Plasminogen release and tPA activity were measured on the studded beads. Studded beads were assembled into µwheels with rotating magnetic fields and fibrinolysis of plasma clots was measured in a microfluidic device. Results:The biochemical speed limit for plasma clots was ~15 µm/min. Plasminogenloaded, tPA-immobilized µwheels lyse plasma clots at rates comparableto the biochemical speed limit. With the addition of a corkscrew motion, µwheels penetrate clots, thereby exceeding the biochemical speed limit (~20 µm/min) and achieving lysis rates 40-fold higher than 50 nM tPA. Conclusions: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.

Application of Nanotechnology in Thrombus Therapy

“…Taking the tissue plasminogen activator (tPA) as an example, its transport mode in occluded vessels with low or no blood flow is diffusion‐dominated, which greatly hinders its transport to the clot site. [ 54 ] Second, the half‐life of tPA‐derived rtPA in the blood is only a few minutes due to rapid receptor‐mediated endocytosis in the liver; so, the drug is usually eliminated before reaching the clot. [ 55 ] All of these greatly limit the therapeutic efficacy of fibrinolytic in arteriovenous thrombolysis.…”

“…The fibrinolysis rate of drug is limited by both transport processes and biochemical reactions. [54] Moreover, even if drugs are directly injected into the thrombus by intraarterial thrombolysis to improve the enrichment rate, or ultrasound mechanical thrombolysis is used to avoid the loss of delivery process, drugs or microbubbles often stay on the surface of the thrombus, making it difficult to penetrate; so, the efficiency of thrombolysis is still limited. [72,73] 3) The occurrence of side effects such as bleeding.…”

Magnetically Powered Chitosan Milliwheels for Rapid Translation, Barrier Function Rescue, and Delivery of Therapeutic Proteins to the Inflamed Gut Epithelium

“…23−25 Microbots designed to release a controlled amount of therapeutic often only do so over a period of hours rather than days due to payload limitations, which is suboptimal for treating chronic illness like IBD. 26 In previous work, we have shown that magnetic microwheels (μ-wheels), disk-like assemblies of superparamagnetic polystyrene microparticles, can translate at speeds of hundreds of μm/s along surfaces when driven by 1−10 mT rotating magnetic fields, 27−29 deliver therapeutic proteins, 30,31 and behave like swarms through complex vessels. 32 To build upon that work, we sought to create magnetically manipulated hydrogel-based milliwheels (m-wheels) designed for translation along mucosal tissues and controlled release of therapeutic proteins with swarm-like behavior.…”

An aquatic microrobot for microscale flow manipulation

“…Wang et al designed an electromagnetically actuated microrobot (EAM) as a mobile micromixer that can be moved to the targeted position in a start-shaped microfluidic chip and controlled to produce rotary motion, which helps in achieving considerable mixing enhancement 49 . In the field of clinical medicine, the microrobots were designed as several small microrods 24 , 50 , microswarm 51 , and microwheel 52 propelled by EMA that are employed to accelerate the t-PA by enhancing the convection induced by local vortex generation. Furthermore, to achieve localization mixing, several additional structures of high magnetic permeability, such as iron nails 24 and magnetic spacer 53 , are added in the microfluidic channel which help locate the microrobot at a targeted position.…”