Methodology
The study tested injection protocols on 36 ovariectomized Wistar rats. The control injection was NaCl (control group) and the treatment injections were alendronate, or parathyroid hormone.
In addition to the systemic treatments (injections), the research team also delivered bilateral local injections of either their bioactive hydrogels or NaCl (control group) to metaphyseal trabecular bone.
The team then tracked bone changes using microCT scans over eight weeks. From those scans, the team identified areas of interest and quantified bone volume fraction, tissue mineral density, and trabecular morphology.
“The ovariectomized rat model is the standard model used by pharma companies to derisk their drugs,” said Régis Gauderon, CEO & co-founder of Lausanne, Switzerland-based flowbone Ltd.
At week eight, the team sacrificed the rats and performed histological analyses to assess bone structure and mineral inclusions.
Study Results
The control animals (received NaCl systemic and local injections) experienced substantial bone loss which led the research team to conclude that systemic treatments alone could only slow down the bone loss in this animal model.
The animals who received a systemic parathyroid hormone with a hydrogel containing Zoledronate got the best response, with bone volume fraction increasing up to 4.8-fold. The effects peaked at 2-4 weeks post-injection, followed by remodeling and restoration. Both local treatments increased trabecular thickness, with the gel with Zoledronate showing slower post-peak resorption.

Conclusions and Discussion
The research team concluded that local injections of both bioactive hydrogels significantly increased bone density up to three-fold—independent of systemic therapy. The addition of Zoledronate to the hydroxyapatite enhanced bone formation and delayed resorption in controls and animals receiving the parathyroid hormone—but offered no additional benefit when combined with systemic alendronate.
The authors also determined that these findings support the hypothesis of an additive effect, suggesting that injectable hydrogels with localized drug delivery can complement systemic therapies by rapidly increasing local bone density, thereby potentially preventing fractures in high-risk osteoporotic patients.
Discussing the “backstory” of the work was Régis Gauderon, CEO & co-founder of flowbone Ltd, makers of the injectable bioactive hydrogels used in the study. “The amazing properties of gels were discovered during the Ph.D. thesis of my co-founder and CTO, Dr. Ulrike Kettenberger at the Ecole Polytechnique Fédérale de Lausanne in Switzerland,” Gauderon told OTW.
“The first gel is composed of hydroxyapatite nanoparticles, a cross-linked hyaluronic acid matrix, and a contrast agent. The second gel has the same composition plus a very small dose of an antiresorptive drug for osteoporosis (Zoledronate) incorporated in it. Both involve leveraging nanobiology for a more natural mode of action, do not harden and turn directly into bone in a few weeks.”
“We also confirmed the effect of our gels in rabbits and sheep. However, there are no established osteoporotic models in these animals. The next step for us is to confirm the results in a first-in-human study.”
“Our gels work as a standalone solution or in combination with current drugs for osteoporosis where synergistic effects occur. The onset of action is very rapid, which is particularly important for patients with severe osteoporosis/those at very high risk of fractures.”

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