It’s time to treat our bones better, shape-memory polymers are here to help.

America’s population is increasingly getting older and more fragile which adds a great stress to our health care system. More than 53 million people in the United States have osteoporosis or are at high risk due to low bone mass. Luckily, we have a plethora of advanced treatment options. Yet, many patients return with problems and need revision. Wouldn’t it be great if there was a better option that was safe, efficient and cutting-edge?

Researchers suggest that shape-memory polymers could soon be an answer to it all.

Today, shape-memory polymers, a smart material that can return to an original state after being deformed with a stimulus, can be found in shrink wrap, combustion engines, and even foams that seal window frames. However, as close as even the next decade, the applications hopefully could spread into orthopedic practices and provide less invasive, intelligent medical devices such as self-fitting implants.

The practice of orthopedics extends far into history but the term “orthopedics” wasn’t coined until the 1700s and even then, it referred to correcting deformities in children. Since then, the practice is defined as the correction of deformities of bones or muscles and has had a plethora of advances like incorporating infection control (finally!!) and creating an entire hip out of metal.

Today, internal fixators—surgical implants for stabilizing bone— are the most common choice in orthopedic surgery and are generally composed of metals. Surgical grade stainless steel, cobalt-chromium alloys and pure commercial titanium/titanium alloys continue as the most commonly used variations. Yet, a controversy persists—there is a notable prevalence of metal sensitivity along with orthopedic implants.

Research has shown that prolonged contact with these metals can release carcinogens and produce allergic reactions. This is just one of the many postoperative complications that plague orthopedic surgery. Bone fracture repair is among the most common procedures, and unplanned re-operation falls shortly behind.

Researchers report that 81.8% of all unplanned re-operations occur after 30 days postoperative, which is the usual time frame utilized to measure surgical quality, a measurement of surgical care during and after operation. This raises the question of whether or not we are overestimating the caliber of current orthopedic treatments.

Shape memory polymers (SMPs) were introduced to mend the divide between the quality/longevity of orthopedic treatment and level of safety. Extensive research has already begun and application within orthopedics has been shown to have unlimited potential in changing how we treat patients from here on out. A focus has been placed on improving stabilization and grafting techniques within bone fracture repair.

Orthopedic surgery can come with implant failure, allergic reactions, further deformation of the bone, and a plethora of other risks. Re-operation on these problems can introduce even more troubles such as an on-site infection. The complications that come with current treatments after orthopedic surgeries often are dismissed as “rare” or insignificant in prevalence. But by understanding what new treatments have to offer, such as less invasive surgery through compacting larger devices before implantation, all the challenges become more substantial.

Current experiments are mostly designed to find what form and combination of materials are the best fit to address current challenges. The most popular forms being researched are SMPs with or without microscopic wells, foams, and 3-D printed scaffolds—structures that provide support during body tissue regeneration.

One study found that incorporating stem cells is one of the most promising breakthroughs. Researchers developed a dynamic sheet of SMPs with stem cells filled microscopic wells that mimicked the internal environment of a human body, much like the surrounding muscle.

Stem cells require stimuli similar to the body in order to activate their ability to turn into multiple cell types because they are, first and foremost, body cells. Using this method, differentiation into bone cells was excellent and promised high rates of stabilization. But the importance of these results really pertains to their bio-compatibility component.

One of the main issues with current orthopedic strategies is the exclusion of bio-compatibility, the metals seem to work great but they aren’t bone. SMPs are filling that gap.

To test how well SMPs performed within a living organism, researchers introduced SMPs in a foam form to live bone cells while measuring the toxicity and its shape-memory properties. They found that the cells were highly compatible with the polymer and the SMP’s porosity of 50-60% falling well within the optimal porosity for bone. Stress shielding tests looked promising as  they went through multiple cycles of temperature changes and compressive force. They remarkably acted in the same way as healthy bone, and withstood pressures up to 27 MPa. This is excellent since the average femur can withstand around 11.7 MPa.

In another attempt, scientists combined 3-D printing technology with SMPs which had a structure capable of housing stem cells. The SMPs incorporated the ability to form a perfect fit and the 3-D printing technique added a porous like structure that was much like bone. The attachment and viability of the stem cells was exceptional but the material’s ability to fully recover from stress needs further research. Despite the complication, this still can be interpreted as a step in the right direction since it has high potential in the orthopedic field for technologies such as self-fitting implants.

The ability shape-memory polymers to act as an actual bone and transform shapes is a remarkable aspect that we need to continue to experimentally test and apply in many other aspects such as self-tightening wires for orthodontic braces or biodegradable surgical sutures.

Once further research is initiated, especially in human trials and larger sample sizes, shape memory polymers can potentially be the new go-to material for any and all orthopedic surgeries. These smart materials are very promising in the orthopedic field and can not only improve patient’s quality of life but potentially remove the prevalence of revision surgery altogether.

By: A. Thompson

References:

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Image Credits

Fracture Trauma, Advance Ortho & Gynaec Center, http://www.orthogynaecenterindore.in/services/fracture-trauma/6

Low-Pressure One-Component Polyurethane Foam Sealant (OCF), Handifoam®, https://www.handifoam.com/product/handi-foam-window-door-west-low-pressure-one-component-polyurethane-foam-sealant-ocf/

Figure 4, Science Direct, https://www.sciencedirect.com/science/article/pii/S0142961215008741#fig4