Gel-saliva in the mouth: new polymer “drop by drop” moisturizes the mouth during xerostomia

A team from Purdue presented a rechargeable “saliva gel” based on the polymer PHEMA (poly(hydroxyethyl methacrylate)). It absorbs artificial saliva, and then releases it directly in the mouth for hours - at about the same rate as natural saliva at rest. In tests, the gel swelled by ~400% in 6 hours, released almost all of its supply in 4 hours at 37 °C, retained about 97% efficiency, and worked for at least 5 “charge-discharge” cycles. No mucosal toxicity was detected in cell cultures. The idea is aimed at patients with xerostomia (dry mouth) after radiation therapy, hemodialysis, and other conditions. The work was published in ACS Applied Polymer Materials.

Background

Xerostomia is a subjective sensation of dry mouth; often combined with objective hyposalivation (reduced salivation). Normal unstimulated salivary flow rate in healthy individuals is ~0.3–0.4 ml/min, and ≤0.1 ml/min indicates hyposalivation; the salivary glands secrete 0.5–1.5 l of saliva per day. Salivary deficiency leads to caries, candidiasis, taste, speech and swallowing disorders, pain and poor sleep.

• How common is it and who has it more often? In the general population, estimates vary widely (due to different methods), but xerostomia is a common symptom in the elderly. Particularly vulnerable are patients after radiation therapy of the head and neck (up to ~80% experience severe dryness during treatment, many persisting for months and years), people with Sjogren's syndrome, on polypharmacy (anticholinergic/psychotropic drugs), with diabetes, and on hemodialysis.
• Why "sprays" and rinses do not save for long. Most saliva substitutes are quickly washed off and provide short-term relief. Medicinal sialogogues (pilocarpine, cevimeline) are not effective for everyone and have side effects; neurostimulants and regenerative approaches are still limited by availability/data. Hence the demand for local moisture reservoirs that can maintain comfort for hours, dosing the output of liquid "like natural saliva."
• What "target delivery" is needed. In a healthy person, the unstimulated flow of saliva is exactly in the region of 0.3-0.4 ml/min; the desire to bring the release rate closer to these values makes the assistance natural in sensation (without "volleys" and overdrying).
• Why PHEMA was chosen. Poly(hydroxyethyl methacrylate) is a classic hydrogel with many –OH groups, biocompatible and long used in soft contact lenses (i.e. in constant contact with sensitive mucous membranes). It absorbs water/solutions, holds them with hydrogen bonds and can slowly release the contents – properties that are ideal for the role of a “saliva reservoir”.
• How does this fit into current practice? Today, the arsenal includes hygienic measures, frequent "top-up" with saliva substitutes, stimulation with chewing gum/sour, pilocarpine/cevimeline with intact gland function, prevention of caries and fungal infections. Rechargeable oral hydrogel logically complements this line as a long-lasting local remedy, especially for patients with post-radiation hyposalivation, night dryness or with long-term loads (travels, lectures, shifts).

What did they come up with?

Make a soft hydrogel reservoir that the patient places in the oral cavity (for example, near the cheek):

1. “charge” it with artificial saliva in advance;
2. let it slowly release liquid, maintaining comfortable moisture and lubrication.
   Material - PHEMA: a hydrophilic polymer with many -OH groups, is good "friends" with water, forms an elastic network and retains liquid due to hydrogen bonds.

How does this work

• PHEMA film absorbs artificial saliva and turns into a hydrogel state.
• In the mouth (≈37 °C), the gel gradually “shrinks” and releases its reserve. At the start, the release is faster (the authors estimate ~0.3 ml/min), then it levels out; the target corridor for comfort is 0.3–0.7 ml/min (this is approximately the rate of unstimulated salivation in healthy people).

What was measured?

• Swelling: up to ≈400% of the original volume in 6 hours.
• Recovery: Almost all stock in ≈4 h at 37°C; stability ≈97% over 5 consecutive cycles.
• Reuse: the gel was carefully “recharged” and comparable dynamics were again obtained.
• Biocompatibility: The conditioned medium of the gel did not inhibit the growth of oral keratinocytes; no significant cytotoxicity was found.
• Mechanics: the gel is much softer than the cheek (Young's modulus is hundreds of kPa versus megapascals for the mucous membrane) - an important hint for further adjustment of rigidity and comfort.

Why is this necessary?

Xerostomia (10–30% of adults, more common in the elderly; often after head and neck radiation therapy, chemotherapy, hemodialysis) impairs speech, swallowing, oral hygiene, and increases the risk of infections. Current solutions—sprays/rinses, chewing stimulants, neurostimulants, systemic drugs—either provide a short-term effect or are invasive/expensive. The hydrogel reservoir promises several hours of continuous hydration without the frequent “puff-puff.”

How is this different from regular "artificial saliva"

Classic substitutes are quickly washed off. Here, the material doses the liquid output and recharges, which potentially simplifies daily use (for example, during long classes, trips, sleep).

What's next?

So far, all tests are in the laboratory. The authors write directly that realistic tests in the mouth are ahead: with microbiota, temperature and pH swings, friction, conversations/food, with an assessment of the form factor (size, fixation, comfort), safety and service life. In parallel, it is necessary to understand what composition of artificial saliva is optimal, and whether the gel changes taste perception/diction.

Restrictions

• Not a clinic. Neither efficiency nor convenience for people has been demonstrated yet.
• Mechanics and ergonomics. The gel is noticeably softer than fabrics - comfortable, but can deform; the required geometry/holder is still being selected.
• Hygiene and maintenance: Reuse requires a clear cleaning/replacement regimen to avoid biofilm build-up.

Source: Debnath S. et al. Poly(hydroxyethyl methacrylate) Saliva-Gel: A Polymer-Based Solution for Xerostomia Treatment, ACS Applied Polymer Materials, online July 17, 2025. DOI: 10.1021/acsapm.5c00881