Ultrasound angioplasty: an update review

In Vivo Polymer Mechanochemistry with Polynucleotides

Polymer mechanochemistry utilizes mechanical force to activate latent functionalities in macromolecules and widely relies on ultrasonication techniques. Fundamental constraints of frequency and power intensity have prohibited the application of the polymer mechanochemistry principles in a biomedical context up to now, although medical ultrasound is a clinically established modality. Here, a universal polynucleotide framework is presented that allows the binding and release of therapeutic oligonucleotides, both DNA- and RNA-based, as cargo by biocompatible medical imaging ultrasound. It is shown that the high molar mass, colloidal assembly, and a distinct mechanochemical mechanism enable the force-induced release of cargo and subsequent activation of biological function in vitro and in vivo. Thereby, this work introduces a platform for the exploration of biological questions and therapeutics development steered by mechanical force.

Sonopharmacology: controlling pharmacotherapy and diagnosis by ultrasound-induced polymer mechanochemistry

Active pharmaceutical ingredients are the most consequential and widely employed treatment in medicine although they suffer from many systematic limitations, particularly off-target activity and toxicity. To mitigate these effects, stimuli-responsive controlled delivery and release strategies for drugs are being developed. Fueled by the field of polymer mechanochemistry, recently new molecular technologies enabled the emergence of force as an unprecedented stimulus for this purpose by using ultrasound. In this research area, termed sonopharmacology, mechanophores bearing drug molecules are incorporated within biocompatible macromolecular scaffolds as preprogrammed, latent moieties. This review presents the novelties in controlling drug activation, monitoring, and release by ultrasound, while discussing the limitations and challenges for future developments.

Mechanochemical bond scission for the activation of drugs

Pharmaceutical drug therapy is often hindered by issues caused by poor drug selectivity, including unwanted side effects and drug resistance. Spatial and temporal control over drug activation in response to stimuli is a promising strategy to attenuate and circumvent these problems. Here we use ultrasound to activate drugs from inactive macromolecules or nano-assemblies through the controlled scission of mechanochemically labile covalent bonds and weak non-covalent bonds. We show that a polymer with a disulfide motif at the centre of the main chain releases an alkaloid-based anticancer drug from its β-carbonate linker by a force-induced intramolecular 5-exo-trig cyclization. Second, aminoglycoside antibiotics complexed by a multi-aptamer RNA structure are activated by the mechanochemical opening and scission of the nucleic acid backbone. Lastly, nanoparticle-polymer and nanoparticle-nanoparticle assemblies held together by hydrogen bonds between the peptide antibiotic vancomycin and its complementary peptide target are activated by force-induced scission of hydrogen bonds. This work demonstrates the potential of ultrasound to activate mechanoresponsive prodrug systems.

Toward Drug Release Using Polymer Mechanochemical Disulfide Scission

Traditional pharmacotherapy suffers from multiple drawbacks that hamper patient treatment, such as the buildup of antibiotic resistances or low drug selectivity and toxicity during systemic application. To overcome these challenges, drug activity can be controlled by employing delivery, targeting, or release solutions that mostly rely on the response to external physicochemical stimuli. Due to various technical limitations, mechanical force as a stimulus in the context of polymer mechanochemistry has so far not been used for this purpose, yet it has been proven to be a convenient and robust method to site-selectively rearrange or cleave bonds with submolecular precision in the realm of materials chemistry. Here, we present an unprecedented mechanochemically responsive system capable of successively releasing small furan-containing molecules, including the furylated fluorophore dansyl and the drugs furosemide as well as furylated doxorubicin, by ultrasound-induced selective scission of disulfide-centered polymers in solution. We show that mechanochemically generated thiol-terminated polymers undergo a Michael-type addition to Diels-Alder (DA) adducts of furylated drugs and acetylenedicarboxylate derivatives, initiating the downstream release of the small molecule drug by a retro DA reaction. We believe that this method can serve as a blueprint for the activation of many other small molecules.

How thrombus model impacts the in vitro study of interventional thrombectomy procedures

RATIONALE AND OBJECTIVES

Numerous experimental models are used to investigate the effectiveness of thrombectomy devices. We aimed to study the systematic effects of different in vitro thrombus models on the results of experimental thrombectomy and examined how thrombi formed in vitro and ex vivo differ.

METHODS

Three variables involved in human in vitro thrombogenesis were investigated: spontaneous or thrombin-induced clotting, age (1 or 5 days old), and storage temperature (4 degrees C or 21 degrees C). The fibrin content of in vitro and fresh or old ex vivo thrombi was measured by histologic studies. Ten experiments were performed with each of 8 different in vitro thrombus types using (1) ultrasound thrombolysis, (2) Oasis thrombectomy, (3) Amplatz thrombectomy, and (4) Straub-Rotarex catheters. Thrombus weight was measured after standardized treatment.

RESULTS

The fibrin content was markedly lower in all in vitro than in fresh and old ex vivo thrombi. In vitro thrombus type had no impact on the effectiveness of ultrasound thrombolysis and Amplatz thrombectomy. Thrombogenesis type affected Oasis and Straub-Rotarex catheter use. Storage temperature had a systematic impact on the outcome of Oasis thrombectomies.

CONCLUSION

The fibrin content of in vitro thrombi differs substantially from that of fresh and old ex vivo human thrombi. Experimental conditions may systematically impact experimental evaluation of thrombectomy procedures. In vitro thrombi with thrombin-induced thrombogenesis should be favored for use in thrombectomy experiments.

Ultrasound thrombolysis in hemodialysis access: in vitro investigation

PURPOSE

To evaluate the effectiveness of ultrasound thrombolysis in occluded hemodialysis access shunts using an in vitro model.

METHODS

Thrombosed hemodialysis accesses were simulated by clotted bovine blood in a flow model (silicone tubing; inner diameters 4, 6, and 9 mm). After retrograde and antegrade sheath placement (7 Fr), mechanical thrombolysis was performed using an ultrasound probe (Acolysis, Angiosonics, Morrisville, NC, USA). The tip of the device measured 2.2 mm in diameter. During sonication, the catheter was moved slowly back and forth using an over-the-wire system. Thirty complete occlusions [tubing diameters 4 mm (n = 12), 6 mm (n = 12), 9 mm (n = 6)] were treated. Initial thrombus weights were 3.5 (+/- 0.76) g, 7.7 (+/- 1.74) g, and 19.4 (+/- 2.27) g for the three diameters. Maximum sonication time was 15 min for each probe.

RESULTS

With this device, we were able to restore a continuous lumen in all 12 occluded 4 approximately mm silicone tubes. No wall-adherent thrombi remained after sonication for 3.5--9.6 min. In hemodialysis access models with diameters of 6 mm, thrombus fragments persisted in 25% (3/12 accesses). These were located in the medial portion of the access loop and near to the puncture sites. However, flow was re-established after 5.0--13.0 min of treatment in all settings. Mechanical dissolution of thrombus material failed in five of six access models with diameters of 9 mm, even though ultrasound energy was applied for the maximum of 15 min.

CONCLUSION

In a clotted hemodialysis shunt model, successful ultrasound thrombolysis was limited to small access diameters and small amounts of thrombus.