Scientists Turn Plant Compound Into Material That May One Day Help Repair Bone

A Common Plant Compound Just Showed It Can Grow Bone Mineral in the Lab

Sorghum plants may have a hidden talent unrelated to feeding cattle. Buried inside their fibrous stems is a compound called lignin, the substance giving plants their structural backbone. New research out of the Hebrew University of Jerusalem suggests this humble plant material could one day contribute to materials for repairing bone.

A team led by postdoctoral researcher Dr. Srinath Palakurthy and Prof. Rivka Elbaum found that lignin extracted from sorghum stems can be coaxed into forming hydroxyapatite, the mineral that gives bones and teeth their strength, while supporting the growth of pre-osteoblast cells in laboratory tests. Published in ACS Biomaterials Science & Engineering, the findings point toward a possible plant-based alternative to bone graft materials, many of which come from animal tissue or synthetic sources.

A material derived from plants could offer a more sustainable starting point, though this study is still at an early laboratory stage.

Lignin’s Phenolic Groups Drive Mineral Growth

Lignin is everywhere. It ranks as the second most abundant natural polymer on Earth, trailing only cellulose, and gets discarded in huge volumes by farms and paper mills. Scientists have long known lignin has antioxidant and antibacterial properties, but its irregular, tangled structure has complicated medical development because lignin can vary depending on the plant source and how it is produced.

Palakurthy, Elbaum, and colleagues Christine Pilz-Allen and Peter Fratzl compared two structurally distinct forms of lignin, both extracted from sorghum stems. One came from ordinary sorghum plants that take up silica from soil, resulting in silica-rich lignin. The other came from a mutant strain absorbing far less silica, producing silica-poor lignin. Testing showed the silica-rich version contained substantially more of a chemical structure called a phenolic hydroxyl group. The researchers think these phenolic groups may act like molecular hooks for calcium, creating conditions that favor mineral growth.

That distinction mattered enormously. Researchers soaked samples of each lignin type in simulated body fluid, a solution engineered to mimic the mineral content of human blood plasma. Calcium began collecting on the silica-rich lignin’s surface within three days. By day 14, phosphorus joined it, and over two more weeks those elements organized into hydroxyapatite crystals, the main mineral found in bones and teeth. The silica-poor lignin showed no comparable mineral growth after 28 days, supporting the idea that the phenolic-rich structure played an important role.

Bone Cells Thrive at Low Doses of Lignin

Researchers also tested how the lignin interacted with living cells, using a standard lab cell line that models immature bone-building cells known as pre-osteoblasts. Small doses of lignin, 25 to 50 micrograms per milliliter, boosted cell growth beyond untreated controls. Viability remained above the study’s cytocompatibility threshold through 500 micrograms per milliliter, although the silica-rich lignin began to hinder cell growth at that concentration. At 1,000 micrograms per milliliter, the silica-rich lignin and its 10 percent silica composite were cytotoxic, while the blend containing 25 percent silica remained non-toxic even at that dose.

Degradation testing added another encouraging layer. For a future scaffold, gradual breakdown could be useful because the material would ideally make room for new tissue, though this study measured degradation in a laboratory solution, not alongside growing bone. The silica-rich lignin lost about 17 percent of its mass over three weeks in a simulated physiological buffer, while silica composites broke down faster, shedding more than 20 percent. The silica-poor lignin barely degraded at all, losing about 6 percent of its weight and then stabilizing.

Silica Exposure Shapes Lignin’s Bone-Building Power

Nature ran this experiment long before any lab did. Inside a growing sorghum stem, silica and lignin link up in the cell walls, part of what makes the stalk rigid enough to stand tall. Palakurthy and Elbaum had already shown that silica gets woven directly into lignin’s chemical structure, and this study tested that partnership outside a plant, using the material to grow bone-like mineral in a laboratory solution.

“Plants have evolved sophisticated strategies for building strong, functional structures, and we wanted to see whether we could borrow those structures, and adapt them for regenerative medicine,” Palakurthy said.

Elbaum framed the work as evidence that nature had already solved problems materials scientists still wrestle with. “Our work shows that plants have already solved many of the engineering challenges we face in designing regenerative materials,” she said. “By learning from the natural partnership between lignin and silica in plant tissues, we developed a sustainable material that supports bone mineral formation while remaining compatible with living cells.”

A Sustainable Alternative Still Years From the Clinic

None of this means a lignin bone graft is heading to hospitals soon. The study was conducted in laboratory dishes and simulated fluids, not in animals or people, and the authors are explicit that animal testing remains a necessary next step before clinical use becomes realistic, since bone healing in a living body involves blood flow, immune responses, and mechanical loads no lab bench can fully replicate.

Even so, the proof of concept matters, since farms and paper mills already generate enormous volumes of lignin as a byproduct, much of which remains a low-value resource. A biomedical use for a material this abundant could ease pressure on animal-derived grafts while giving leftover plant fiber a valuable second life.

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Disclaimer: This article describes early-stage laboratory research. The material has been tested only in simulated body fluid and with a single laboratory cell line, not in animals or people. Anyone considering treatment for a bone injury or condition should consult a qualified medical professional rather than relying on findings from preliminary research.

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