Ultrasound-Enabled Therapeutic Delivery and Regenerative Medicine: Physical and Biological Perspectives

The Complementary Roles of Neurological and Musculoskeletal Physical Therapy and Regenerative Medicine: A Comprehensive Review

Regenerative medicine, encompassing various therapeutic approaches aimed at tissue repair and regeneration, has emerged as a promising field in the realm of physical therapy. Aim: This comprehensive review seeks to explore the evolving role of regenerative medicine within the domain of physical therapy, highlighting its potential applications, challenges, and current trends. Researchers selected publications of pertinent studies from 2015 to 2024 and performed an exhaustive review of electronic databases such as PubMed, Embase, and Google Scholar using the targeted keywords "regenerative medicine", "rehabilitation", "tissue repair", and "physical therapy" to screen applicable studies according to preset parameters for eligibility, then compiled key insights from the extracted data. Several regenerative medicine methods that are applied in physical therapy, in particular, stem cell therapy, platelet-rich plasma (PRP), tissue engineering, and growth factor treatments, were analyzed in this research study. The corresponding efficacy of these methods in the recovery process were also elaborated, including a discussion on facilitating tissue repair, alleviating pain, and improving functional restoration. Additionally, this review reports the challenges concerning regenerative therapies, among them the standardization of protocols, safety concerns, and ethical issues. Regenerative medicine bears considerable potential as an adjunctive therapy in physiotherapy, providing new pathways for improving tissue repair and functional results. Although significant strides have been made in interpreting the potential of regenerative techniques, further research is warranted to enhance protocols, establish safety profiles, and increase access and availability. Merging regenerative medicine into the structure of physical therapy indicates a transformative alteration in clinical practice, with the benefit of increasing patient care and improving long-term results.

Ultrasound Pressure-Dependent Cytokine and Immune Cell Response Lost in Aged Muscle

OBJECTIVE

Therapeutic ultrasound remains a highly discussed topic in physical therapy due to uncertainty between treatment regimens and biological benefits. Its impact on aged populations, who are vulnerable to insufficient healing after muscle injury because of sarcopenia, is understudied. Despite the coupling between muscle inflammation and regeneration, research on the immune response after therapeutic ultrasound is limited. The objective of this study was to evaluate structure, inflammatory cytokine signaling and immune cell infiltration after therapeutic ultrasound in young and aging murine muscle.

METHODS

Young (6-week-old) and Adult (52-week-old) male and female mouse non-injured gastrocnemii were treated with either low-intensity pulsed ultrasound at 2 W/cm2 (∼0.243 MPa) or high-intensity pulsed focused ultrasound at 554 W/cm2 (∼5.96 MPa). Cytokine expression was evaluated at 1, 8 and 24 hours, cell infiltration was measured via flow cytometry at 1 and 24 hours and immunofluorescence assessed muscle fiber area, fibrosis and satellite cells at 24 hours after sonication.

RESULTS

Low-intensity pulsed ultrasound induced an early, transient inflammatory response where interleukin (IL)-15 and macrophages (M2 > M1) were increased 1 hour post-sonication. High-intensity pulsed focused ultrasound caused a late, extended immune response where monocyte chemoattractant protein 1 (MCP-1), neutrophils, monocytes and macrophages (M1 > M2) were increased 24 hours post-sonication. Notably, these changes manifested solely in Young gastrocnemius. The Adult gastrocnemius exhibited decreased cytokine expression (IL-1α, IL-6, IL-15, macrophage colony-stimulating factor [M-CSF]) and no alteration in immune cell recruitment post-sonication. There was no damage to muscle structure.

CONCLUSION

Therapeutic ultrasound induced a pressure-dependent inflammatory response that can augment or mitigate intrinsic muscle cytokine signaling and cell recruitment in adolescent or aged muscle, respectively.

Inducible endothelial leakiness in nanotherapeutic applications

All intravenous delivered nanomedicine needs to escape from the blood vessel to exert their therapeutic efficacy at their designated site of action. Failure to do so increases the possibility of detrimental side effects and negates their therapeutic intent. Many powerful anticancer nanomedicine strategies rely solely on the tumor derived enhanced permeability and retention (EPR) effect for the only mode of escaping from the tumor vasculature. However, not all tumors have the EPR effect nor can the EPR effect be induced or controlled for its location and timeliness. In recent years, there have been exciting developments along the lines of inducing endothelial leakiness at the tumor to decrease the dependence of EPR. Physical disruption of the endothelial-endothelial cell junctions with coordinated biological intrinsic pathways have been proposed that includes various modalities like ultrasound, radiotherapy, heat and even nanoparticles, appear to show good progress towards the goal of inducing endothelial leakiness. This review explains the intricate and complex biological background behind the endothelial cells with linkages on how updated reported nanomedicine strategies managed to induce endothelial leakiness. This review will also end off with fresh insights on where the future of inducible endothelial leakiness holds.

Ultrasound-Mediated Release of Gaseous Signaling Molecules for Biomedical Applications

Although nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂ S) have been considered as notorious gas pollutants for decades, they are considered as endogenous gaseous signaling molecules (GSMs), which have been widely recognized for their important signaling functions and prominent medical applications in human physiology. To achieve local delivery of GSMs to optimize therapeutic efficacy and reduce systemic side effects, stimuli-responsive nanocarriers have been successfully developed. Among them, ultrasound is considered as an attractive theranostic modality that can be used to track drug carriers, trigger drug release, and improve drug deposition, etc. In this minireview, we summarize recent achievements in designing ultrasound-responsive nanocarriers for the controlled delivery of GSMs and their biomedical applications. This emerging research direction enables the controlled delivery of GSMs to deep tissues, and the combination of ultrasound imaging techniques offers many possibilities for the fabrication of new theranostic platforms. This article is protected by copyright. All rights reserved.

Advances in Ultrasound-Responsive Hydrogels for Biomedical Applications

Various intelligent hydrogels have been developed for biomedical applications because they can achieve multiple, variable, controllable and reversible changes in their shape and properties in a spatial and temporal manner,...