Scientists develop implantable tiny sensors that help broken bones heal

By Stephen Beech

Tiny implantable sensors are helping to heal broken bones quicker.

The devices allow data-enabled resistance training to speed up the natural healing process in lab rats, say American scientists.

Researchers at the University of Oregon developed the miniature sensors that transmit real-time data about what’s happening at an injury site.

The team says that if applied in humans, the sensors could allow doctors to better tailor a rehab programme to an individual patient, monitoring their progress and adjusting exercises along the way.

They used the technology in a study, published in the journal npj Regenerative Medicine, to show that a resistance-training rehab program can "significantly improve" femur injuries in rats in just eight weeks.

Most femoral fractures take around four to six months to heal completely

But the sensors provide a window into the mechanical properties of the bone, giving scientists detailed ongoing information about the process of healing.

Study senior author Professor Bob Guldberg said: “Our data support early resistance rehabilitation as a promising treatment to increase bone formation, bone healing strength, and promote full restoration of mechanical properties to pre-injury levels."

It’s long been understood that post-injury exercise follows a "Goldilocks" principle: too little or too much can impede recovery, while just the right amount can enhance healing.

But pinpointing the exact type and intensity of exercise needed for the best recovery can be challenging, especially as it varies from patient to patient.

Now, the specialized sensors developed by the University of Oregon team could help change that by providing a window into what’s happening inside a healing bone throughout recovery.

The researchers aimed to test whether resistance running, which is a specific type of recovery exercise, could provide the right mechanical stimulation to improve bone recovery.

To do that, they built custom brakes for rodent exercise wheels, which added resistance similar to increasing the incline on a treadmill.

Rats with femur injuries and implanted sensors then ran on either a regular exercise wheel or the modified resistance exercise wheel.

The sensors transmitted strain data throughout the exercises, offering the research team a glimpse into the mechanical environment of bone cells during recovery.

Over the eight-week study, researchers monitored the healing process of the injured femurs and found that the resistance-trained rats displayed early signs of bone healing compared to those in sedentary or non-resistance conditions.

By the end of the eight-week recovery period, all groups - sedentary, non-resistance and resistance-trained - showed bone healing.

However, the resistance-trained animals had denser tissue, indicating that resistance rehab enhanced bone formation.

In fact, the injured bones of the resistance-trained rats exhibited mechanical properties, such as torque and stiffness, comparable to those of uninjured bones.

Guldberg says that indicates resistance training enhances recovery, even without any additional drugs or biological stimulants,

Biological agents such as BMP - a molecule that promotes bone growth - are often used in regeneration studies.

However, Guldberg’s team demonstrated complete functional recovery through resistance training alone, underscoring its potential for clinical application.

Study leader Dr. Kylie Williams, who further improved the prototype sensors, said: “One of the most impactful aspects of this work is that our resistance rehabilitation could regenerate the femur to normal strength within eight weeks without biological stimulants, and we’re really excited about that."

The research team said one limitation of the study is that all animals received a constant level of resistance throughout the experiment.

However, researchers in the Guldberg lab are now investigating how increasing or decreasing levels of rehabilitation intensity across weeks of healing may affect bone regeneration.

Although the research was conducted in rodents, the team hopes that data-enabled rehab can also be used to improve healing in human patients who sustain musculoskeletal injuries. T

Towards that goal, Penderia Technologies - a campus start-up company - is working on further improvements to the implantable sensors, including a battery-free design and wearable monitors to aid use in human patients.

Guldberg added: “We are hopeful this work can one day be translated to clinical settings, where these sensors can capture personalized measurements that account for injury type and severity to best inform rehabilitation decisions."