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Chemical develops artificial meniscus from the prototyping technique

Prosthesis developed at the engineering school of the Unicamp can help treat patients with problems in the knee cartilage

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Foto: Antoninho Perri/Unicamp
Celio Hitoshi Wataya, a chemist at Unicamp, author of the research.
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Celio Hitoshi Wataya, a chemist at Unicamp, author of the research.

Patients with problems of meniscus cartilage in the human body located at the knee, were the target of attention of a doctoral research at the Faculty of Mechanical Engineering at Unicamp. This is because the chemical Celio Hitoshi Wataya has just developed an artificial meniscus from a technical adjustment in rapid prototyping, which allows the manufacture physical objects directly from data sources generated by computer-aided systems (CAD).

The differential of the work is to obtain a device of hydrogel crosslinked polymer capable of absorbing liquids without dissolving, from images of the knee by computed tomography, which can serve as a basis to construct an accurate modeling of the meniscus.

The result was a custom product and craft has been tested for cytotoxicity in animal models, aiming at applications in the medical field. He showed no local rejection, and the mechanical tests, showed a pattern on the tensile and compressive similar to that supported by a meniscus under the load. Is promising for this application, according to Celio.

The material used in the prosthesis, polyvinyl alcohol (PVA), is water soluble synthetic polymer used most of the world, found in items such as cosmetics, pharmaceuticals and clothing burned. It is found commercially as a powder or granules and has been extensively studied at the moment, although his knowledge already dates back to the 1920s, for its medicinal properties.

Importance <b> </ b>

According Célio two details were essential for the end product. The first treatment was given to computer tomography imaging of the knee with InVesalius and Rhinoceros, two free software.

The second was the use of dimethylsulfoxide (DMSO), a crosslinking agent employed in the arsenal of drugs, in the forms of gel and solution, indicated as anti-inflammatory and analgesic for topical use in trauma, bruises and edema.

Celio mind that thought of producing an artificial meniscus by the great social impact it would have on the lives of patients, since after injured the meniscus does not regenerate the original. The contact area of ​​the knee is reduced somewhere around 50%, subjecting the cartilage to a greater risk of injury.

As the author of the thesis, regeneration is complicated because the meniscus is poor in blood vessels and thus with minimal irrigation.

When regeneration occurs, the result is a fabric with poor mechanical properties, which when subjected to stresses may break easily, which would compromise its operation, since the meniscus acts as an absorber, preventing the friction between organs next, as the tibia and femur. Its primary function, including, is to absorb about 50% of the compressive load on the knee joint extension and 85% load in bending.

In the case of the existence of injuries, the procedure of choice in general is the removal of the meniscus, a meniscectomy, especially with a view to eliminating the pain, which is reported as severe by the patients. This is because the injury is still spreading and reaches a point that surgery is inevitable.

The biggest victims of torn meniscus are athletes, victims of car accidents and the elderly who have suffered falls.

<b> Tests </ b>

A study by Kobayashi, made in Japan, had already used the PVA in DMSO added to the knee of rabbits, Celio reports. The part of the fixation of the prosthesis was tested by the author with nylon and drilling on the tibia, made with drills.

There was still assessing the reaction of animals, noting, after a period of two years, that the agency had not caused local irritation. Was practically intact. The response was favorable, says the chemist, signaling its viability of use.

Based on this same investigation, Celio studied how to introduce the meniscus in humans. When you talk to experts at the Center for Information Technology Renato Archer (CTI), he found the alternative to customize the PVA from a sequence of computed tomography.

The researcher evaluated the three-dimensional images of the knee, which helped him play a mold of the meniscus to be filled with PVA. This meniscus shaped PVA and DMSO, passed by freezing and irradiation of gamma rays through multipurpose irradiator at the Institute of Nuclear and Energy Research (IPEN), USP, to reach the artificial meniscus.

Irradiated sample of this material was introduced into the skull of laboratory animals in order to ensure its biocompatibility. Similarly to the results of Kobayashi, and is not observed rejection of the material, no bleeding at the site after 12 days.

We also evaluated the reaction in the body of rats. For the blade, it was realized that there was no irritation. Rather, there was formation of a protective capsule of connective tissue involving this material, as expected, reports the PhD.

The material in vitro tests were performed at the Center for Experimental Medicine, Faculty of Medical Sciences (FCM) and in vivo at the Institute of Craniofacial Plastic Surgery (Sobrapar). Other laboratories were involved in the work of the Faculty of Mechanical Engineering (FEM), the Chemical Engineering Faculty (FEQ) and CTI.

<b> Process </ b>

Normally, the crosslinked PVA acts as a sponge capable of absorbing liquids, including synovial fluid, which is a mixture of water and mineral salts, Célio states. After it swells, it becomes more flexible, being able to damp the pressure from the members.

The virtual images of the meniscus undergo a rapid prototyping machine, which has similar functions to a printer. But instead of this printer has an ink container in its place accommodates other materials that can be metals, and other polymers.

In the case of this work, the technology has been adopted to obtain the mold of the meniscus and the device was prepared with the filling of the non-crosslinked polymer. Tomography was possible to visualize image multiple slices, with dimensions ranging from 1 to 4 mm. The thinner the layer, the more accurate is the final product, shows Célio.

In each case, he reveals, is made one meniscus, which takes about two to three hours to complete. According to the researcher, there are no proper equipment for this polymer. He tried to employ ultraviolet and infrared rays, but without achieving success.

The solution was left for molding and potting, with subsequent crosslinking, ie, formation of chemical bonds which prevent the dissolution of the polymer in the presence of synovial fluid. A rapid prototyping machine that can produce meniscus directly make the process faster, ensures a doctoral candidate.

   Palavras-chave:   Knee    Meniscus    Cartilage    Faculty of Engineering    Unicamp    Celio Hitoshi Wataya   
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