These Dissolvable Metal Implants Could Make Bone Surgery Safer And Stronger

MELBOURNE, Australia — Every year, millions of people get permanent metal implants for broken bones, knowing they might need painful removal surgeries later. But what if those implants could just disappear once the bone healed? Researchers from Monash University have created biodegradable zinc alloys that are finally strong enough to handle major fractures.

The study, published in Nature, revealed that making the tiny building blocks inside the metal—called grains—larger, not smaller, results in biodegradable implants that are nearly twice as strong as the magnesium-based screws and plates currently used in orthopedic surgery. These stronger materials actually become more stable at body temperature, solving a major durability problem that has long limited the use of dissolvable implants.

The Hall-Petch relationship is a fundamental principle in materials science that has guided metallurgy for over 70 years. However, this discovery opens up new possibilities for patients who need bone repair but want to avoid the complications and revision surgeries often required with permanent metal implants.

What This Means for Patients

Currently, when you break a bone that needs surgical repair, doctors typically use stainless steel or titanium screws and plates. While effective, these implants stay in your body forever, potentially causing problems like bone loss around the implant site and loosening that requires additional surgery to fix.

Biodegradable implants help bone heal and safely dissolve away, eliminating the need for removal surgery. However, existing biodegradable options made from magnesium alloys are relatively weak, limiting their use to non-load-bearing areas of the body.

The new zinc alloys developed by the Monash team achieve compressive yield strengths of over 400 MPa, making them comparable to high-strength medical-grade stainless steel and suitable for load-bearing uses like major bone fractures.

The research team was working with zinc-magnesium alloys when they noticed that samples with larger grain sizes, measured in micrometers (millionths of a meter), consistently outperformed those with smaller grains in strength tests.

To understand this phenomenon, researchers examined samples with grain sizes ranging from 11 micrometers to 47 micrometers. Using advanced electron microscopy and compression testing, they found that the way the metal bends and shifts changes a lot depending on the size of its grains.

In samples with smaller grains, the metal tends to bend and shift along the edges where the grains meet. But in samples with larger grains, the movement happens inside each grain itself, through a special type of crystal sliding and an unusual twisting effect the researchers called “accommodation twins.”

These accommodation twins work differently from the mechanical twins typically seen in metals. While mechanical twins help materials bend in response to external stress, accommodation twins help neighboring grains adapt to shape changes, keeping the overall structure intact.

Why is this Material Stronger?

Understanding this backward relationship comes down to zinc’s unique crystal structure. Zinc atoms arrange themselves in a hexagonal pattern, which makes the metal behave very differently in different directions, much more so than other metals like magnesium and titanium.

When pressure is applied, larger grains inside the metal respond differently than smaller ones, spreading out the stress more evenly and making the material stronger. The researchers tested their metals at room temperature and in extreme cold, and found that this “bigger is stronger” effect held up in both cases. In fact, at liquid nitrogen temperatures, the larger-grained samples were twice as strong as they were at room temperature.

Testing and Safety

Scientists tested the materials in both laboratory conditions and living rabbit models over six weeks to understand how the implants would behave in the human body.

Tests using human bone cells showed that when the metal was diluted, it had very little toxic effect, staying well within international safety limits. The materials only released tiny amounts of zinc, magnesium, copper, and manganese—much less than what people safely consume in a day.

In the animal studies, screws made from the new alloy degraded at a rate of 0.11 millimeters per year when implanted in rabbit femurs. This is similar to rates seen with clinically approved magnesium implants, but with significantly better mechanical properties.

The alloys are created through processes including melting, casting, and hot extrusion—techniques already used in medical device manufacturing. This means the technology could potentially be scaled up for commercial production without requiring entirely new manufacturing infrastructure.

Stronger biodegradable implants could expand treatment options for complex fractures, reduce the need for revision surgeries, and eliminate long-term complications associated with permanent implants.

Next steps involve optimizing alloy compositions for specific applications and conducting larger animal studies. If successful, these biodegradable zinc alloys could transform orthopedic medicine by providing the strength of permanent implants with the convenience of temporary ones. This could benefit millions of patients worldwide who need reliable, temporary solutions for bone repair.