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Biodegradable polymer grafts could grow to fix spine, biocompatible polymer 3D-printed into lifesaving implants

Biodegradable polymer grafts could grow to fix spine, biocompatible polymer 3D-printed into lifesaving implants

Biodegradable polymer grafts that, when surgically placed in damaged vertebrae, likely to grow to be just the right size and shape to fix the spinal column have been developed by  Rochester, Minn. based Mayo Clinic researchers scientists. These grafts fill the void to strengthen the spine, take on a spongy material that grows to the proper size and shape of damaged vertebrae to fix spinal columns. 
"The overall goal of this research is to find ways to treat people with metastatic spinal tumors," says Lichun Lu, Ph.D. "The spine is the most common site of skeletal metastases in cancer patients, but unlike current treatments, our approach is less invasive and is inexpensive." Often, removing extensive spinal tumors requires taking out the entire bone segment and adjacent intervertebral discs from the affected area. In this case, something must fill the large void to maintain the integrity of the spine and protect the spinal cord. There are typically two surgical choices in cases of extensive spinal metastases. In the more aggressive and invasive option, the surgeon opens the chest cavity from the front of the patient, which provides enough room to insert metal cages or bone grafts to replace the missing fragment. The other approach is less invasive, requiring just a small cut in the back or posterior, but only offers enough space for the surgeon to insert short expandable titanium rods, which are costly. To develop a less expensive graft compatible with the posterior spinal surgery option, Lu, who is at the Mayo Clinic, and her postdoctoral fellow, Xifeng Liu, Ph.D., sought a material that could be dehydrated down to a size compatible with posterior spinal surgery, and then, once implanted, absorb fluids from the body, expanding to replace the missing vertebrae.
The researchers started by crosslinking oligo [poly(ethylene glycol) fumarate] to create a hollow hydrophilic cage -- the scaffold of the graft -- which could then be filled with stabilizing materials, as well as therapeutics. "When we designed this expandable tube, we wanted to be able to control the size of the graft so it would fit into the exact space left behind after removing the tumor," Lu says. The researchers also needed to control the kinetics of the expansion, because if the cage expands too quickly, a surgeon may not have enough time to position it correctly, while a slow expansion could mean a longer-than-necessary surgery. Modifying the degree and timing of the polymer graft's expansion was a matter of chemistry, Liu says. "By modulating the molecular weight and charge of the polymer, we are able to tune the material's properties," he says. The researchers studied the effects of these chemical changes by observing the polymer grafts' expansion rates under conditions that mimic the spinal column environment in the lab. This information is key for determining the optimal size of a spinal implant for use in restorative surgery. The team identified a combination of materials that are biocompatible in animals and that they believe will work in humans. Lu says her lab's next step is to study the grafts in cadavers and simulate an in-patient procedure. Their goal is to initiate clinical trials within the next few years.

An adolescent girl has now joined a group of three baby boys and a baby girl who have received 3D-printed tracheal splints to treat a congenital breathing condition called tracheobronchomalasia (TBM). A partnership between University of Michigan and 3D priniting specialist EOS developed the life-saving implants. All five patients are progressing well thanks to the surgical procedures that have helped their collapsed airways function normally. The lifesaving procedures were conducted under US Food & Drug Administration Emergency Clearance. Additive manufacturing specialist company EOS provided technology solutions and expert.
Dr. Green  and Dr. Scott Hollister used Materialise’s Mimics Innovation Suite to model and construct these splints using CT scans of patient anatomy. The Suite was used to design the splint which is constructed from a bioresorbable technology platform licensed to Tissue Rigeneration Systems (TRS) by the University of Michigan in 2007. After several years refining fabrication methods, TRS received its first commercial product clearance from the FDA in 2013. The Materialise partnership is one of several co-development projects currently underway at TRS. Thanks to FDA approval for Expanded Access to an investigational medical device, the splints are now regularly used to treat TBM.  About 1 in 2,200 babies are born with TBM, which causes the trachea to periodically collapse. The tracheal splint, developed to save the lives of these children, is made with a biopolymer called polycaprolactone, a biodegradable material that is gradually absorbed into the infant’s body tissue over time.The U-M team now hopes to next year open a clinical trial for 30 patients with similar conditions at C.S. Mott Children’s Hospital. “We have continued to evolve and automate the design process for the splints, allowing us to achieve in two days what used to take us up to five days to accomplish,” adds Scott Hollister, Ph.D., professor of biomedical Engineering and mechanical engineering. “I feel incredibly privileged to be building products that surgeons can use to save lives.” We also feel privileged to report on how 3D printing can truly and practically save and change lives.

American scientists are hoping to mechanically reinforce worn-out cartilage by incorporating a biomimetic gel. As they report in the journal Angewandte Chemie, their technique results in extensive interpenetration of the cartilage's natural biopolymer network with the synthetic polymer network. Osteoarthritis does not only occur in older individuals. Young people are also affected, often as a result of a misalignment; an accident; or stress from competitive sport, excessive weight, or asymmetrical physical labor. Healthy cartilage acts as cushioning in the joint. If it wears out, the bones begin to rub against each other, causing pain and deformation of the joint. The cause of this wear is a depletion of glycosaminoglycans in the cartilage tissue. These polysaccharides carry a negative charge that allows them to bind to water molecules, which maintains the hydration of the tissue. In the early stages of osteoarthritis, the cartilage dries out and the "cushion" becomes thinner and less able to withstand load bearing. No treatments to regenerate cartilage are currently available.
Researchers from Boston University, the Beth Israel Deaconess Medical Center, and Boston Children's Hospital (Boston, USA) aim to change this. By incorporating a second polymer network that contains the necessary charged groups, they propose to re-establish the cartilage cushion and restore its mechanical stability. This should not just patch up individual damaged areas, but is designed to strengthen the entire tissue network. In this method, the tissue is infiltrated with monomers, which are polymerized in place by exposure to light.
The team, led by Mark. W. Grinstaff, chose to use zwitterions (ions with both positively and negatively charged groups) based on phosphorylcholine as their monomers. Phosphorylcholine is known for its biocompatibility. These monomers are able to penetrate into the biopolymer tissue of the cartilage. Further reagents are used to crosslink the synthetic polymer and to start the polymerization as soon as the area is irradiated with green laser light. This results in a gel in which the synthetic polymerchains are extensively entangled with the polymer chains of the cartilage. The gel binds water well, allowing the hydration of treated cartilage to be maintained longer under strain.
Compression tests with enzymatically degraded bovine cartilage showed that the gel can restore the original mechanical stability of the cartilage. The gel preferentially aggregates in areas that are particularly affected. A simulation of accelerated wear showed that healthy cartilage can also be effectively protected against degeneration by using this method. This new process thus seems to be highly promising for the treatment of osteoarthritis in its early stages.

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