Research spotlight: Amila Peramune Arachchilage

Twenty-one days after mixing a paste from waste cattle bone and a layered clay mineral, researchers measured how much force it could withstand before failing: about 24 megapascals. That's not crown-grade strength, but it's enough for a material meant to sit against living tooth pulp — and the paste set in roughly 14 minutes. The composite, developed at the University of Otago's Sir John Walsh Research Institute, targets the most persistent gripes about the cements dentists use to keep damaged teeth alive.

Amila Peramune Arachchilage, a researcher at the institute, works two seams of science that rarely meet. In New Zealand, the focus is bioactive dental materials built from cheap, often discarded ingredients. In Sri Lanka, where the researcher also holds a post at the University of Sri Jayewardenepura, the subject is camptothecin, the natural compound behind two approved cancer drugs: irinotecan and topotecan. The connecting question is the same in both labs. How do you produce biologically active materials and molecules at scale without pricing people out — or stripping the source to extinction?

Why the current gold standard frustrates dentists

The benchmark in endodontics is mineral trioxide aggregate, better known as MTA. It's biocompatible, seals well and resists reinfection better than older zinc oxide–eugenol sealers. It also costs a lot, tugs at the dentist's patience in handling, can take hours to set, and sometimes stains a tooth grey. A 2025 review in Dentistry Journal, co-authored by Amila Peramune Arachchilage, argues that the literature has underplayed these flaws while overstating the benefits of bioceramic cements. That review points to calcium silicate, calcium phosphate and a family of bioactive glass formulations as the workhorses, then catalogues a familiar set of weaknesses: mediocre mechanical and handling properties, aesthetic problems from discolouration, limited antibacterial activity and price.

The new composite, reported in the International Endodontic Journal, swaps out the bismuth-based radiopacifier blamed for MTA's grey staining and uses zirconium oxide instead. Tricalcium silicate and dicalcium silicate do the setting. Three variants were tested, named for their loadings: B20 and B25 with 20 and 25 percent bovine hydroxyapatite, and M20 with 20 percent montmorillonite. Each was mixed with water into a hydraulic paste, then measured against commercial ProRoot MTA.

After 21 days, compressive strength reached 23.63 megapascals for B20, 21.2 for B25 and 23.8 for M20. Every variant pushed its pH above 11 within a day and held it there for three weeks — a strongly alkaline setting that discourages bacteria and encourages mineral deposition. Setting times landed between 13 and 14 minutes, a practical window for clinic work. Heavy metals sat within ISO limits, and radiopacity matched ISO recommendations, so the material shows up clearly on X-rays.

The biological behaviour split along the clay content. B20 and B25 showed good viability in cell culture. The M20 variant, carrying the most montmorillonite, triggered the most apatite formation and remineralisation — evidence that the clay does more than stiffen the matrix. "The montmorillonite does double duty," Amila Peramune Arachchilage said of the findings. "It reinforces the composite mechanically, and at the higher loading it drives apatite formation, which is what you want at the interface with living tissue." The authors still stop short of calling it a finished product; in vivo studies, they write, are needed before anyone reaches for it in a dental chair. The full study is open in the International Endodontic Journal.

A clay with a pharmacy pedigree

Montmorillonite's appeal is not new. A 2024 review from the same group in Materials Research Express details why the clay keeps showing up in experimental dental materials: a surface area of 700 to 800 square metres per gram, a cation exchange capacity up to 150 milliequivalents per 100 grams, and approval from the US Food and Drug Administration for drug delivery uses. That ion-swapping ability is what lets the clay hold calcium, silver or fluoride and release them slowly. The review also offers an honest caveat: work on finished montmorillonite dental products, and on in vivo performance, remains thin.

A plant molecule with a tree-shortage problem

Camptothecin was first isolated in the 1960s from the bark of a Chinese tree, Camptotheca acuminata. The molecule itself proved too toxic to use directly, but chemists built two approved cancer drugs from it: irinotecan, used mainly for colorectal cancer, and topotecan, used for ovarian and small-cell lung cancer. Both reached the US market in 1996, and by the early 2000s their combined sales were estimated at around a billion dollars a year. The supply chain, though, still leans on bark and seeds stripped from slow-growing trees such as Nothapodytes nimmoniana, a practice that threatens wild populations.

In 2024, a team that included Amila Peramune Arachchilage screened three Sri Lankan species of Ophiorrhiza, a genus of small herbaceous plants, and found a candidate answer. Ophiorrhiza mungos from the Deraniyagala and Bibile regions carried notably high camptothecin in its fruits and roots. Two relatives, O. rugosa variety angustifolia and O. pectinata, held camptothecin in their roots too, though at significantly lower concentrations (p below 0.005). Herbs regrow faster than trees, which makes them a more renewable source if cultivation can be tuned. The analytical methods passed validation for specificity, linearity, precision, accuracy and sensitivity against ICH guidelines. The study appears in Current Analytical Chemistry.

An earlier paper looked inside Nothapodytes nimmoniana itself, collected near Hakgala in Sri Lanka, to find where the plant stores camptothecin. Under ultraviolet light the compound fluoresces blue. The glow concentrated in the roots, with isolated strands in the petiole's phloem and clusters of idioblast cells in the cortex. Ultrasonic-assisted extraction with 90 percent methanol pulled the most from roots: 1.91 ± 0.02 milligrams per gram of dry weight. Leaves yielded roughly a hundredth of that, at 0.02 ± 0.01 milligrams per gram. Hot ethanol was better for twigs and leaves. No single extraction method wins everywhere, which means tissue-specific protocols matter. The paper is in Phytochemical Analysis.

The most unusual source is neither a plant part nor an herb. A fungus isolated from a Nothapodytes nimmoniana leaf in Sri Lanka — Diaporthe species F18, sharing 99 percent sequence similarity with Diaporthe guangxiensis — made camptothecin in submerged culture. Grown in Sabouraud dextrose broth at pH 5.6 and 30 degrees Celsius, shaken at 150 rpm for 14 days, the fungus produced 72.0 ± 0.2 micrograms per gram. Adding tryptophan multiplied the yield as much as 23-fold; ethanol gave an 8-fold boost. Production stayed fairly stable through six subculture generations. The Natural Product Research paper frames the fungus as a new microbial route, one that could sidestep tree felling altogether.

What the papers stop short of claiming

Every advance here is bench-level, and the authors say so plainly. The dental composite is an in vitro study; ethical approval was not required because no human tissue was involved, but that also means nobody has shown how the paste performs in a bleeding pulp chamber or after years of chewing. Compressive strength of around 24 megapascals is respectable for pulp capping, yet far below what load-bearing restorations demand. The montmorillonite review concedes that completed products and clinical studies are scarce. On the camptothecin side, the fungus makes micrograms per gram — orders of magnitude below what plant roots can provide — and subculture attenuation is a known industrial headache. Regional differences in camptothecin content also mean cultivation would have to be standardised site by site.

An independent materials scientist, asked for a cautionary view, put it bluntly: "In vitro bioactivity is a poor proxy for the messy biology of an inflamed pulp. Materials that look superb in cell culture have failed in the clinic because clinicians couldn't place them, or because patients rejected the way they set." The same scepticism applies to endophytic fungi, which are notoriously fickle at bioreactor scale.

Funding for the Sri Lankan camptothecin studies came from the National Research Council of Sri Lanka under grant 11-107. The dental papers did not name a funder in their abstracts, and the composite study states that ethical approval was not applicable for this laboratory work. No conflicts of interest surfaced in the abstracts reviewed.

What the next five years could bring

The dental projects are moving toward animal studies, and then, if those hold up, trials in humans. The plant work points a different way: identifying the highest-yielding Ophiorrhiza lines and the cultivation conditions that keep camptothecin levels high without raiding wild populations. The fungus route will live or die on whether fermentation engineers can push yields from micrograms toward the milligram scale cheaply enough to matter.

Across both countries and both subjects, the through-line is resourcefulness. Waste bones stand in for mined or imported minerals. A clay that costs little replaces a radiopacifier that stains teeth. A fungus and a fast-growing herb offer a quieter path to a cancer-drug precursor than felling a forest. None of it is ready for the clinic or the pharmacy shelf yet — and closing that gap is the point of the next decade of work.

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