Convergence of Calcium Channel Regulation and Mechanotransduction in Skeletal Regenerative Biomaterial Design

Mature and Juvenile Neuromuscular Plasticity in Response to Unloading

The neuromuscular junction (NMJ) is the synapse that enables the requisite electrical communication between the motor nervous system and the myofibers that respond to such electrical stimulation with movement and force development. Changes in an NMJ's normal activity pattern have been demonstrated to remodel both the synapse and the myofibers that comprise the NMJ. Significant amounts of research have been devoted to the study of aging on the neuromuscular system. Far less, however, has been focused on revealing the effects of reduced activity on the NMJ and myofibers comprising juvenile neuromuscular systems. In the present investigation, the consequences of decreased activity imposed by muscle unloading (UL) via hindlimb suspension for 2 weeks (a period known to induce muscle remodeling) were examined in both young adult, that is, mature (8 mo), and juvenile (3 mo) neuromuscular systems. In total, 4 treatment groups comprised of 10 animals (Juvenile-Control, Juvenile-Unloaded, Mature-Control, and Mature-Unloaded) were studied. Immunofluorescent procedures, coupled with confocal microscopy, were used to quantify remodeling of both the pre- and postsynaptic features of NMJs, as well as assessing the myofiber profiles of the soleus muscles housing the NMJs of interest. Results of ANOVA procedures revealed that there were significant (p < 0.05) main effects for both treatment, whereby UL consistently led to expanded size of the NMJ, and Age where expanded NMJ dimensions were consistently linked with mature compared to juvenile neuromuscular systems. Moreover, only sporadically was interaction between the main effects of Age and Treatment noted. Importantly, one variable that remained impressively resistant to the effects of both Age and Treatment was the critical parameter of pre- to postsynaptic coupling suggesting stability in effective communication at the NMJ throughout the lifespan and despite changes in activity patterns. The data presented here suggest that further inquiry must be performed regarding disuse-related plasticity of the neuromuscular system in adolescent individuals as those individuals regularly suffer injuries resulting in periods of muscle UL.

MechanoBioCAD: a generalized semi-automated computational tool for mechanobiological studies

Soft micropillar arrays enable detailed studies of cellular mechanotransduction and biomechanics using traditional beam-bending models. However, they often rely on simplified assumptions, leading to significant errors in force estimation. We present MechanoBioCAD (MBC), a finite element method (FEM)-based tool designed specifically for micropillar research and error estimation. Unlike traditional methods, MBC leverages the principle of minimizing total potential energy, avoiding errors associated with beam bending assumptions. MBC automates FEM model generation, analysis, and post-processing, providing accurate force quantification based on deflection input. The tool addresses critical issues such as substrate deformation, interpillar interactions, improper load application heights, and nonlinear effects. Applied to fibroblast cell traction and Caenorhabditis elegans (C. elegans) thrashing cases, MBC recorded 23% and 34% errors in the estimated forces, respectively, compared to traditional methods. As an open-access tool with the Abaqus Student Edition, MBC democratizes rational design, analysis, and error estimation for researchers who are not subject matter experts in FEM.

3D-printed biomimetic bone scaffold loaded with lyophilized concentrated growth factors promotes bone defect repair by regulation the VEGFR2/PI3K/AKT signaling pathway

This study investigates the effects of concentrated growth factors (CGF) and bone substitutes on the proliferation and differentiation of bone marrow mesenchymal stem cells (BMSCs), as well as the development of a novel 3D-printed biomimetic bone scaffold. Based on the structure of cancellous bone, 3D-printed bionic bone with sustainable release of growth factors and Ca2+ was prepared. Using BMSCs and EA.hy926 in co-culture with the bionic bone scaffold, experimental results demonstrate that this bionic structural design enhances cell proliferation and adhesion, and that the bionic bone possesses the ability to promote bone and vascular regeneration directly. Transcriptomics, western blot analysis, and flow cytometry are employed to investigate the effects of CGF and Ca2+ on the signaling pathways of BMSCs. The study reports that vascular endothelial growth factor (VEGF) released by CGF activated VEGFR2 on BMSCs, leading to Ca2+ influx and activation of the PI3K/AKT signaling pathway, thereby influencing osteogenesis. Animal experiments confirm the ability of the bionic bone to promote osteogenesis in vivo, and its unique degradation pattern accelerates the in vivo repair of bone defects. In conclusion, this study presents a novel biomimetic strategy and, for the first time, explores the potential mechanism by which VEGF and Ca2+ regulate BMSCs differentiation through the VEGFR2/PI3K/AKT signaling pathway. These insights offer a new perspective for the development of innovative bone substitute materials.

Correlating Material Properties to Osteoprotegerin Expression on Nanoparticulate Mineralized Collagen Glycosaminoglycan Scaffolds

Precision material design directed by cell biological processes represents a frontier in developing clinically translatable regenerative technologies. While understanding cell-material interactions on multipotent progenitor cells yields insights on target tissue differentiation, equally if not more important is the quantification of indirect multicellular interactions. In this work, the relationship of two material properties, phosphate content and stiffness, of a nanoparticulate mineralized collagen glycosaminoglycan scaffold (MC-GAG) in the expression of an endogenous anti-osteoclastogenic secreted protein, osteoprotegerin (OPG) by primary human mesenchymal stem cells (hMSCs) is evaluated. The phosphate content of MC-GAG requires the type III sodium phosphate symporter PiT-1/SLC20A1 for OPG expression, correlating with β-catenin downregulation, but is independent of the effects of phosphate ion on osteogenic differentiation. Using three stiffness MC-GAG variants that do not differ significantly by osteogenic differentiation, it is observed that the softest material elicited ≈1.6-2 times higher OPG expression than the stiffer materials. Knockdown of the mechanosensitive signaling axis of YAP, TAZ, β-catenin and combinations thereof in hMSCs on MC-GAG demonstrates that β-catenin downregulation increases OPG expression by 1.5-fold. Taken together, these data constitute a roadmap for material properties that can used to suppress osteoclast activation via osteoprotegerin expression separately from the anabolic processes of osteogenesis.

Are Aminoglycoside Antibiotics TRPing Your Metabolic Switches?

Transient receptor potential (TRP) channels are broadly implicated in the developmental programs of most tissues. Amongst these tissues, skeletal muscle and adipose are noteworthy for being essential in establishing systemic metabolic balance. TRP channels respond to environmental stimuli by supplying intracellular calcium that instigates enzymatic cascades of developmental consequence and often impinge on mitochondrial function and biogenesis. Critically, aminoglycoside antibiotics (AGAs) have been shown to block the capacity of TRP channels to conduct calcium entry into the cell in response to a wide range of developmental stimuli of a biophysical nature, including mechanical, electromagnetic, thermal, and chemical. Paradoxically, in vitro paradigms commonly used to understand organismal muscle and adipose development may have been led astray by the conventional use of streptomycin, an AGA, to help prevent bacterial contamination. Accordingly, streptomycin has been shown to disrupt both in vitro and in vivo myogenesis, as well as the phenotypic switch of white adipose into beige thermogenic status. In vivo, streptomycin has been shown to disrupt TRP-mediated calcium-dependent exercise adaptations of importance to systemic metabolism. Alternatively, streptomycin has also been used to curb detrimental levels of calcium leakage into dystrophic skeletal muscle through aberrantly gated TRPC1 channels that have been shown to be involved in the etiology of X-linked muscular dystrophies. TRP channels susceptible to AGA antagonism are critically involved in modulating the development of muscle and adipose tissues that, if administered to behaving animals, may translate to systemwide metabolic disruption. Regenerative medicine and clinical communities need to be made aware of this caveat of AGA usage and seek viable alternatives, to prevent contamination or infection in in vitro and in vivo paradigms, respectively.

Remote coupling of electrical and mechanical cues by diurnal photothermal irradiation synergistically promotes bone regeneration

Recapitulating the natural extracellular physical microenvironment has emerged as a promising method for tissue regeneration, as multiple physical interventions, including ultrasound, thermal and electrical therapy, have shown great potential. However, simultaneous coupling of multiple physical cues to highly bio-mimick natural characteristics for improved tissue regeneration still remains formidable. Coupling of intrinsic electrical and mechanical cues has been regarded as an effective way to modulate tissue repair. Nevertheless, precise and convenient manipulation on coupling of mechano-electrical signals within extracellular environment to facilitate tissue regeneration remains challengeable. Herein, a photothermal-sensitive piezoelectric membrane was designed for simultaneous integration of electrical and mechanical signals in response to NIR irradiation. The high-performance mechano-electrical coupling under NIR exposure synergistically triggered the promotion of osteogenic differentiation of stem cells and enhances bone defect regeneration by increasing cellular mechanical sensing, attachment, spreading and cytoskeleton remodeling. This study highlights the coupling of mechanical signals and electrical cues for modulation of osteogenesis, and sheds light on alternative bone tissue engineering therapies with multiple integrated physical cues for tissue repair.

From electricity to vitality: the emerging use of piezoelectric materials in tissue regeneration

The unique ability of piezoelectric materials to generate electricity spontaneously has attracted widespread interest in the medical field. In addition to the ability to convert mechanical stress into electrical energy, piezoelectric materials offer the advantages of high sensitivity, stability, accuracy and low power consumption. Because of these characteristics, they are widely applied in devices such as sensors, controllers and actuators. However, piezoelectric materials also show great potential for the medical manufacturing of artificial organs and for tissue regeneration and repair applications. For example, the use of piezoelectric materials in cochlear implants, cardiac pacemakers and other equipment may help to restore body function. Moreover, recent studies have shown that electrical signals play key roles in promoting tissue regeneration. In this context, the application of electrical signals generated by piezoelectric materials in processes such as bone healing, nerve regeneration and skin repair has become a prospective strategy. By mimicking the natural bioelectrical environment, piezoelectric materials can stimulate cell proliferation, differentiation and connection, thereby accelerating the process of self-repair in the body. However, many challenges remain to be overcome before these concepts can be applied in clinical practice, including material selection, biocompatibility and equipment design. On the basis of the principle of electrical signal regulation, this article reviews the definition, mechanism of action, classification, preparation and current biomedical applications of piezoelectric materials and discusses opportunities and challenges for their future clinical translation.

Injectable ultrasound-powered bone-adhesive nanocomposite hydrogel for electrically accelerated irregular bone defect healing

The treatment of critical-size bone defects with irregular shapes remains a major challenge in the field of orthopedics. Bone implants with adaptability to complex morphological bone defects, bone-adhesive properties, and potent osteogenic capacity are necessary. Here, a shape-adaptive, highly bone-adhesive, and ultrasound-powered injectable nanocomposite hydrogel is developed via dynamic covalent crosslinking of amine-modified piezoelectric nanoparticles and biopolymer hydrogel networks for electrically accelerated bone healing. Depending on the inorganic-organic interaction between the amino-modified piezoelectric nanoparticles and the bio-adhesive hydrogel network, the bone adhesive strength of the prepared hydrogel exhibited an approximately 3-fold increase. In response to ultrasound radiation, the nanocomposite hydrogel could generate a controllable electrical output (-41.16 to 61.82 mV) to enhance the osteogenic effect in vitro and in vivo significantly. Rat critical-size calvarial defect repair validates accelerated bone healing. In addition, bioinformatics analysis reveals that the ultrasound-responsive nanocomposite hydrogel enhanced the osteogenic differentiation of bone mesenchymal stem cells by increasing calcium ion influx and up-regulating the PI3K/AKT and MEK/ERK signaling pathways. Overall, the present work reveals a novel wireless ultrasound-powered bone-adhesive nanocomposite hydrogel that broadens the therapeutic horizons for irregular bone defects.