A Biodegradable Bioactive Glass-Based Hydration Sensor for Biomedical Applications

Abstract

Monitoring changes in edema-associated intracranial pressure that complicates trauma or surgery would lead to improved outcomes. Implantable pressure sensors have been explored, but these sensors require post-surgical removal, leading to the risk of injury to brain tissue. The use of biodegradable implantable sensors would help to eliminate this risk. Here, we demonstrate a bioactive glass (BaG)-based hydration sensor. Fluorine (CaF₂) containing BaG (BaG-F) was produced by adding 5, 10 or 20 wt.% of CaF₂ to a BaG matrix using a melting manufacturing technique. The structure, morphology and electrical properties of the resulting constructs were evaluated to understand the physical and electrical behaviors of this BaG-based sensor. Synthesis process for the production of the BaG-F-based sensor was validated by assessing the structural and electrical properties. The structure was observed to be amorphous and dense, the porosity decreased and grain size increased with increasing CaF₂ content in the BaG matrix. We demonstrated that this BaG-F chemical composition is highly sensitive to hydration, and that the electrical sensitivity (resistive-capacitive) is induced by hydration and reversed by dehydration. These properties make BaG-F suitable for use as a humidity sensor to monitor brain edema and, consequently, provide an alert for increased intracranial pressure.

Keywords: bioactive glass; biodegradable; brain edema; capacitive sensor; hydration monitoring.

Figure 1

Thermal cycles used for bioactive glass (BaG)-based sensor. Some icons were taken from Biorender.com.

Figure 2

Measurement setup for fluorine bioactive glass (BaG-F)-based sensors showing the conductivity changes induced by the humidity created by potassium sulfate solution (H₂SO₄). (a) Capacitive character in ambient. (b) Resistive capacitive in high humidity. (c) Reversal of capacitive character in ambient environment. The icons were taken from Biorender.com. Curves were derived from our study in the figure.

Figure 3

X-ray diffraction (XRD) patterns of fluorine bioactive glass (BaG-F_x).

Figure 4

Investigated three-dimensional (3D) structure of fluorine bioactive glass (BaG-F_x).

Figure 5

Scanning electron microscopy (SEM) images of fluorine bioactive glass (BaG-F_x).

Figure 6

Adsorption–desorption isotherms of fluorine bioactive glass (BaG-F_x). (a) Reference. (b) BaG-F₅. (c) BaG-F₁₀. (d) BaG-F₂₀.

Figure 7

Reversible resistive–capacitive behavior for a bioactive 10% fluorine glass-based sensor (BaG-F₁₀) during 30 min of measurement. (a) Capacitive character in ambient air. (b) Resistive–capacitive character in humidity (95% RH). (c) After the BaG-F₁₀ is moved to the ambient environment, the capacitive character returns within 5 s. (d) Its resistive–capacitance characteristics can be reversed by re-contacting BaG-F₁₀ with humidity. (f₀ = 1 Hz, |Z₀| = 1 Ohm).

Figure 8

Illustration of the physicochemical mechanism behind the resistiveؘ–capacitive behavior of biomaterials. Humidity-induced distortion of the vitreous network favors an unstable resistivity because of the screen effect. (f₀ = 1 Hz, |Z₀| = 1 Ohm).