Ultrasound-Activated Nanospheres Combine Ionic and Electrical Cues to Regrow Dental Tissue

When the dental pulp dies, the tooth loses far more than sensation. In immature permanent teeth, where root development is still underway, pulp necrosis halts root formation altogether, leaving thin, fragile dentinal walls and an incomplete apex that is dangerously prone to fracture. Conventional root canal therapy can eliminate infection, but it does so by removing the very living tissue that gives a tooth its long-term mechanical resilience and regenerative capacity. A study published in Materials Today Bio by Zuyong Wu, Jingjing Diao, Heng Zhang, and Naru Zhao now reports a biomaterial strategy that aims to rebuild the pulp–dentin complex rather than merely fill the space it once occupied, using nanospheres that respond to ultrasound by delivering both chemical and electrical signals to stem cells.

The central idea behind the new platform is that tissue regeneration is not only a matter of biochemistry. Mineralized tissues such as bone and dentin are rich in collagen, and collagen-bearing matrices exhibit piezoelectric behavior, generating electrical signals under physiological mechanical loading. These endogenous bioelectrical cues are known to influence cell migration, differentiation, extracellular matrix organization, and the growth of new blood vessels. Conventional bioactive glasses, which have long been favored in regenerative dentistry for their tunable degradation and their release of calcium and silicate ions that promote mineralization, exploit only the biochemical side of this picture. They lack any externally controllable physical or electromechanical signal that could be switched on or off to steer cellular behavior on demand.

Piezoelectric biomaterials offer a way to close that gap, because they can convert external mechanical stimulation into localized electrical signals that modulate cell activity. Low-intensity pulsed ultrasound, or LIPUS, is particularly attractive as the trigger: it is noninvasive, wireless, and capable of reaching deep tissues. But the most established piezoelectric ceramics come with drawbacks. Barium titanate and lead-based ceramics are poorly biodegradable and raise long-term biosafety concerns, while polymeric options such as polyvinylidene fluoride are biocompatible but produce relatively weak piezoelectric responses. Zinc oxide has emerged as a compelling alternative, combining useful piezoelectric properties with biodegradability and intrinsic biological activity, and the zinc ions released as it degrades have been reported to promote both angiogenesis and odonto/osteogenic differentiation. The catch is that zinc oxide degrades rapidly under physiological conditions, and excessive zinc ion release induces oxidative stress and cytotoxicity that have seriously limited its biomedical use.

The research team’s solution was a confinement-based nanocomposite they call Z-MBGNs: zinc oxide nanoparticles incorporated into mesoporous bioactive glass nanospheres. The nanospheres were synthesized through a sol–gel templating method in which cetyltrimethylammonium bromide served as the mesoporous template, tetraethyl orthosilicate supplied the silica, and calcium nitrate provided the calcium. Zinc species were then deposited under alkaline conditions and converted to crystalline zinc oxide by calcination at 600 degrees Celsius. By varying the zinc precursor concentration, the researchers produced three formulations containing 5.28, 10.24, and 15.22 weight percent zinc oxide, designated 5Z-, 10Z-, and 15Z-MBGNs. Transmission electron microscopy showed uniform spheres roughly 87 nanometers in diameter, and elemental mapping confirmed homogeneous co-distribution of zinc, silicon, calcium, and oxygen throughout the particles, supporting the interpretation that the zinc-containing phases are predominantly incorporated within the mesoporous matrix rather than simply sitting on the surface.

The mesoporous glass matrix plays a double role. It acts as a carrier for sustained ionic release, and it moderates the degradation of the embedded zinc oxide, taming the burst of zinc ions that makes the bare nanoparticles toxic. The safety advantage was striking in direct comparisons: in standardized L929 fibroblast cytotoxicity testing, cell viability in the 10Z-MBGN group reached 84.9 percent, whereas bare zinc oxide nanoparticles at equivalent zinc concentration dropped viability to 51.8 percent. At the highest loading, the nanocomposite still outperformed the bare nanoparticles by a wide margin, 48.3 percent versus 19.0 percent. Proliferation assays with human dental pulp stem cells and human umbilical vein endothelial cells showed that the 5Z and 10Z formulations significantly promoted growth, while the 15Z formulation inhibited it, likely because of excessive zinc ion exposure. The 10Z formulation was selected as the lead candidate because it balanced biological compatibility with the strongest ultrasound-responsive functionality.

That functionality was verified at two scales. Piezoresponse force microscopy revealed the characteristic signatures of a nanoscale electromechanical response, including a butterfly-shaped amplitude loop and phase switching under a DC bias sweep from minus ten to plus ten volts. More importantly, when the nanoparticle suspension was stimulated with LIPUS at 1 megahertz and a nominal 400 milliwatts per square centimeter with a 50 percent duty cycle, the 10Z-MBGN suspension generated a distinct electrical signal with a peak-to-peak voltage of about 600 millivolts, while plain buffer and zinc-free nanospheres showed only background fluctuations. Autoclave sterilization, a prerequisite for biological use, did not diminish this response, and it likewise preserved the mesoporous architecture, colloidal stability, and the sustained, burst-free release of calcium and zinc ions observed over 14 days.

With the material characterized, the team tested its effects on human dental pulp stem cells under a carefully optimized ultrasound protocol of 1 megahertz, 400 milliwatts per square centimeter, 50 percent duty cycle, and five minutes per day. Ultrasound-treated 10Z-MBGNs dramatically enhanced cell migration, closing 57.3 percent of a scratch wound within 12 hours compared with 26.7 percent for the nanospheres alone and 23.6 percent for untreated controls, a result that held even when proliferation was chemically suppressed with mitomycin C. Alkaline phosphatase activity, an early marker of odontogenic differentiation, was strongest in the ultrasound-treated group after 7 days. After 21 days of induction, Alizarin Red S staining and calcium quantification confirmed significantly greater mineralized matrix deposition. Gene expression analysis showed that the dentin matrix proteins DSPP and DMP-1 were significantly upregulated, with DMP-1 at day 14 roughly threefold higher than with nanospheres alone and ninefold higher than in controls. Western blotting additionally revealed increased expression of the mitochondrial calcium uniporter, MCU, hinting that mitochondrial calcium handling may participate in the cellular response, although the authors caution this remains a molecular readout rather than proof of a causal mechanism.

The angiogenic side of the story proved equally compelling. Human umbilical vein endothelial cells cultured with ultrasound-treated 10Z-MBGNs formed denser, more interconnected capillary-like networks on Matrigel, with significantly more branch points and greater total tube length. Expression of the angiogenic genes VEGF, bFGF, and CD31 rose over 7 days, and enzyme-linked immunosorbent assays confirmed increased secretion of VEGF and bFGF protein. To test whether these effects translate into tissue formation, the researchers implanted tooth-root-shaped beta-tricalcium phosphate scaffolds loaded with dental pulp stem cells, Matrigel, and 10Z-MBGNs subcutaneously in nude mice, applying LIPUS daily for the first 7 days. At 2 weeks, the ultrasound-treated constructs showed markedly larger VEGF- and bFGF-positive areas. At 6 weeks, they displayed increased DSPP and DMP-1 expression, and Masson’s trichrome staining revealed a collagen-positive area approximately 56-fold larger than in controls and 11-fold larger than in the non-ultrasound nanosphere group, alongside more organized tissue, odontoblast-like cells, mineralized tissue-like structures, and the greatest histologically identified vascular area.

The authors are appropriately measured about what these results do and do not establish. Because LIPUS-only and zinc-free nanosphere-plus-ultrasound control groups were not included, the relative contributions of direct ultrasound mechanotransduction and zinc oxide-associated electromechanical stimulation cannot yet be quantitatively separated, and phenomena such as acoustic streaming or electrokinetic effects may contribute to the measured electrical signal. The ectopic model is a proof of concept rather than a recapitulation of the native pulp–dentin complex, the vascular structures cannot yet be considered fully mature or perfused, and the animal sample size was small with no formal power analysis. Even so, the work demonstrates the feasibility of a growth-factor-free platform in which externally controllable ionic and electromechanical cues are combined in a single degradable nanomaterial. Before clinical translation, tooth-specific studies must determine how ultrasound transmits through enamel, dentin, and periodontal tissues, and how transducer design, coupling, intensity, and exposure should be tailored. If those hurdles are cleared, a five-minute daily ultrasound session activating piezoelectric nanospheres inside a treated tooth could one day offer a genuinely regenerative alternative to the root canal.

Subject of Research: Ultrasound-responsive piezoelectric zinc oxide bioactive glass nanospheres for dental pulp–dentin tissue regeneration

Article Title: Piezoelectric ZnO-incorporated bioactive glass nanospheres for enhanced odontogenic differentiation and angiogenesis

Article References: Wu, Z., Diao, J., Zhang, H., & Zhao, N. (2026). Piezoelectric ZnO-incorporated bioactive glass nanospheres for enhanced odontogenic differentiation and angiogenesis. Materials Today Bio, 41, Article 103731. https://doi.org/10.1016/j.mtbio.2026.103731

Image Credits: AI Generated

DOI: Not provided

Keywords: piezoelectric biomaterials, zinc oxide, bioactive glass, mesoporous nanospheres, low-intensity pulsed ultrasound, dental pulp stem cells, odontogenic differentiation, angiogenesis, regenerative endodontics, pulp-dentin complex, tissue engineering, VEGF