While it is well known that mechanical signals can either promote or disrupt intervertebral disc (IVD) homeostasis, the molecular mechanisms for transducing mechanical stimuli are not fully understood. The transient receptor potential vanilloid 4 (TRPV4) ion channel activated in isolated IVD cells initiates extracellular matrix (ECM) gene expression, while TRPV4 ablation reduces cytokine production in response to circumferential stretching. However, the role of TRPV4 on ECM maintenance during tissue‐level mechanical loading remains unknown. Using an organ culture model, we modulated TRPV4 function over both short‐ (hours) and long‐term (days) and evaluated the IVDs' response. Activating TRPV4 with the agonist GSK101 resulted in a Ca2+flux propagating across the cells within the IVD. Nuclear factor (NF)‐κB signaling in the IVD peaked at 6 h following TRPV4 activation that subsequently resulted in higher interleukin (IL)‐6 production at 7 days. These cellular responses were concomitant with the accumulation of glycosaminoglycans and increased hydration in the nucleus pulposus that culminated in higher stiffness of the IVD. Sustained compressive loading of the IVD resulted in elevated NF‐κB activity, IL‐6 and vascular endothelial growth factor A (VEGFA) production, and degenerative changes to the ECM. TRPV4 inhibition using GSK205 during loading mitigated the changes in inflammatory cytokines, protected against IVD degeneration, but could not prevent ECM disorganization due to mechanical damage in the annulus fibrosus. These results indicate TRPV4 plays an important role in both short‐ and long‐term adaptations of the IVD to mechanical loading. The modulation of TRPV4 may be a possible therapeutic for preventing load‐induced IVD degeneration.
Therapeutic Low-intensity Pulsed Ultrasound (LIPUS) has been applied clinically for bone fracture healing and has been shown to stimulate extracellular matrix (ECM) metabolism in numerous soft tissues including intervertebral disc (IVD). In-vitro LIPUS testing systems have been developed and typically include polystyrene cell culture plates (CCP) placed directly on top of the ultrasound transducer in the acoustic near-field (NF). This configuration introduces several undesirable acoustic artifacts, making the establishment of dose-response relationships difficult, and is not relevant for targeting deep tissues such as the IVD, which may require far-field (FF) exposure from low frequency sources. The objective of this study was to design and validate an in-vitro LIPUS system for stimulating ECM synthesis in IVD-cells while mimicking attributes of a deep delivery system by delivering uniform, FF acoustic energy while minimizing reflections and standing waves within target wells, and unwanted temperature elevation within target samples. Acoustic field simulations and hydrophone measurements demonstrated that by directing LIPUS energy at 0.5, 1.0, or 1.5 MHz operating frequency, with an acoustic standoff in the FF (125–350 mm), at 6-well CCP targets including an alginate ring spacer, uniform intensity distributions can be delivered. A custom FF LIPUS system was fabricated and demonstrated reduced acoustic intensity field heterogeneity within CCP-wells by up to 93% compared to common NF configurations. When bovine IVD cells were exposed to LIPUS (1.5 MHz, 200 μs pulse, 1 kHz pulse frequency, and ISPTA = 120 mW cm−2) using the FF system, sample heating was minimal (+0.81 °C) and collagen content was increased by 2.6-fold compared to the control and was equivalent to BMP-7 growth factor treatment. The results of this study demonstrate that FF LIPUS exposure increases collagen content in IVD cells and suggest that LIPUS is a potential noninvasive therapeutic for stimulating repair of tissues deep within the body such as the IVD.
more » « less- NSF-PAR ID:
- 10303680
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Biomedical Physics & Engineering Express
- Volume:
- 6
- Issue:
- 3
- ISSN:
- 2057-1976
- Page Range / eLocation ID:
- Article No. 035033
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
Structural anisotropy, often observed in naturally occurring materials such as wood and human tissues, is central to the function in several engineered and non-engineered applications. In this study, we present the theory and proof-of-concept demonstration of an ultrasound-assisted non-contact manufacturing approach to create well-defined spatial patterns of micro-particles within a fluid matrix. A chamber with opposing pair of ultrasonic transducers was designed and prototyped based on standing bulk acoustic wave theory, and it was used to study the effects of ultrasound frequency (1, 1.5, 2, 3 MHz) and voltage amplitude (80, 160 mVpp) on alignment characteristics of polymer micro-particles (mean Ø = 8 μm) suspended in water (0.01 g/ml). The experimental results were consistent with theory in that the micro-particles aligned along linear strands, with the inter-strand spacing reducing with increasing frequency (p < 0.05). Increasing voltage amplitude reduced the time taken to align the particles, but it did not significantly change the observed spacing (p > 0.05). The observed spacing, however, was higher than the theoretical spacing of half-wavelength, for each frequency and amplitude. The alignment of living human adipose derived stem cells in viscous alginate hydrogel matrix was also successfully demonstrated. The approach presented herein can be scaled up into manufacturing processes, including layered manufacturing, to create highly functional mechanically and/or electrically anisotropic composites through controlled spatial geometry, as well as to biofabricate engineered tissues with aligned cells and extracellular matrix components to mimic natural tissues.more » « less
-
Ultrasonic (US) neuromodulation has emerged as a promising therapeutic means by delivering focused energy deep into the nervous tissue. Low-intensity ultrasound (US) directly activates and/or inhibits neurons in the central nervous system (CNS). US neuromodulation of the peripheral nervous system (PNS) is less developed and rarely used clinically. The literature on the neuromodulatory effects of US on the PNS is controversial, with some studies documenting enhanced neural activities, some showing suppressed activities, and others reporting mixed effects. US, with different ranges of intensity and strength, is likely to generate distinct physical effects in the stimulated neuronal tissues, which underlies different experimental outcomes in the literature. In this review, we summarize all the major reports that document the effects of US on peripheral nerve endings, axons, and/or somata in the dorsal root ganglion. In particular, we thoroughly discuss the potential impacts of the following key parameters on the study outcomes of PNS neuromodulation by US: frequency, pulse repetition frequency, duty cycle, intensity, metrics for peripheral neural activities, and type of biological preparations used in the studies. Potential mechanisms of peripheral US neuromodulation are summarized to provide a plausible interpretation of the seemly contradictory effects of enhanced and suppressed neural activities of US neuromodulation.more » « less
-
more » « less
Abstract Increased consumer interest in healthy‐looking skin demands a safe and effective method to increase transdermal absorption of innovative therapeutic cosmeceuticals. However, permeation of small‐molecule drugs is limited by the innate barrier function of the stratum corneum. Here, a conformable ultrasound patch (cUSP) that enhances transdermal transport of niacinamide by inducing intermediate‐frequency sonophoresis in the fluid coupling medium between the patch and the skin is reported. The cUSP consists of piezoelectric transducers embedded in a soft elastomer to create localized cavitation pockets (0.8 cm2, 1 mm deep) over larger areas of conformal contact (20 cm2). Multiphysics simulation models, acoustic spectrum analysis, and high‐speed videography are used to characterize transducer deflection, acoustic pressure fields, and resulting cavitation bubble dynamics in the coupling medium. The final system demonstrates a 26.2‐fold enhancement in niacinamide transport in a porcine model in vitro with a 10 min ultrasound application, demonstrating the suitability of the device for short‐exposure, large‐area application of sonophoresis for patients and consumers suffering from skin conditions and premature skin aging.
-
more » « less
Abstract Degeneration of fibrocartilaginous tissues is often associated with complex pro‐inflammatory factors. These include reactive oxygen species (ROS), cell‐free nucleic acids (cf‐NAs), and epigenetic changes in immune cells. To effectively control this complex inflammatory signaling, it developed an all‐in‐one nanoscaffold‐based 3D porous hybrid protein (3D‐PHP) self‐therapeutic strategy for treating intervertebral disc (IVD) degeneration. The 3D‐PHP nanoscaffold is synthesized by introducing a novel nanomaterial‐templated protein assembly (NTPA) strategy. 3D‐PHP nanoscaffolds that avoid covalent modification of proteins demonstrate inflammatory stimuli‐responsive drug release, disc‐mimetic stiffness, and excellent biodegradability. Enzyme‐like 2D nanosheets incorporated into nanoscaffolds further enabled robust scavenging of ROS and cf‐NAs, reducing inflammation and enhancing the survival of disc cells under inflammatory stress in vitro. Implantation of 3D‐PHP nanoscaffolds loaded with bromodomain extraterminal inhibitor (BETi) into a rat nucleotomy disc injury model effectively suppressed inflammation in vivo, thus promoting restoration of the extracellular matrix (ECM). The resulting regeneration of disc tissue facilitated long‐term pain reduction. Therefore, self‐therapeutic and epigenetic modulator‐encapsulated hybrid protein nanoscaffold shows great promise as a novel approach to restore dysregulated inflammatory signaling and treat degenerative fibrocartilaginous diseases, including disc injuries, providing hope and relief to patients worldwide.
