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Producing prostheses

Assai plastic

Seed of tropical fruit is raw material used to replace bones in the skull

Fabio ColombiniSeeds of the assai fruit treeFabio Colombini

Assai, the fruit of the Euterpe oleracea palm tree, is used to make juice, smoothies and ice cream. Now, recent studies have shown that it can be used to produce natural, renewable plastic to make bone prostheses, especially for the skull. Only the seeds are used for this purpose. This novelty was announced by a team of researchers headed by chemical engineer Rubens Maciel Filho, a professor at the State University of Campinas (Unicamp). The assai is native to the North of Brazil. The assai plastic was shown to have the same characteristics as those of petroleum-based polyurethane. In vitro tests have shown that the material is biocompatible and contains excellent mechanical and biological properties.

“According to recent research, the assai fruit has anti-oxidizing, anti-inflammatory and analgesic properties, among other features of interest in bioapplications,” Maciel explains. He is the coordinator of the Biomanufacturing Institute (Biofabris), one of the National Science and Technology Institutes (INCT), based in the school of Chemical Engineering (FEQ) at Unicamp. The research studies began in 2009 and the new polymer, which gave rise to a patent request, is the result of the master’s degree and doctoral studies of researcher Laís Gabriel, both of which were conducted under Maciel’s guidance.

Mechanical engineer André Jardini, a researcher at Biofabris, says that polyurethane is extensively used to manufacture orthopedic prostheses because it is compatible with live tissues. “In addition, it doesn’t release toxic substances when it is implanted,” he says. “There is another advantage of plant-originated polyurethane, which is the low cost of the raw material. This material is comparable to a bioceramic cranium prosthesis, which costs, on average, R$ 120 thousand. We believe that producing a similar prosthesis from assai will cost about five times less.”

The first step of the new material’s production process is to extract the fruit pulp with a special machine. Consumption of assai in the city of Belem generates 350 tons a day of pulped material (seeds and bagasse). “A humid mass and seeds covered in fibers and non-soluble particles are the left-overs,” explains professor Carmen Gilda Tavares Dias, from the Mechanical Engineering Laboratory of the Federal University of Pará (UFPA), who provided the pulped samples used by the researchers from Biofabris. “This biomass is put in a dryer to remove the dry seeds.”

Eduardo CesarLatticed prosthesisEduardo Cesar

The production of polyurethane comes after this step. Assai polyurethane is made from a substance called polyol, which is extracted from the seed. A chemical compound comprised of isocyanate (a viscous liquid) and hydrogen are added and placed inside a reactor. The next step is to add nanoparticles of hydroxyapatite, a substance comprised mostly of calcium phosphate, the main compound of bones, is absorbed by the body. Assai polymer is the final product; it is a porous, rigid foam that facilitates bone growth. According to the researchers, this material is more suitable for implants and prosthesis in parts of the body that do not require major mechanical effort, such as the skull and the face. “In the case of a prosthesis for a femur head, for example, it is better to use tougher materials, such as titanium,” says Jardini.

If approved in the clinical tests, the biopolyurethane developed at Biofabris with funding from FAPESP and from the National Council of Scientific and Technical Development (CNPq) could become a quick and specific alternative for creating prostheses or bone implants. Treatment can be customized, according to the needs of each patient. Based on a CAT scan of the injured area, processed by the InVesalius software (see Pesquisa FAPESP issue 148), developed by the Renato Archer Information Technology Center (CTI), in Campinas, it will be possible to manufacture a customized prosthesis. Jardini explains that the first step of this customization is to do the segmentation, by separating the soft tissue (skin, muscles, arteries) from the hard tissue (bone). “The next step is to produce a three-dimensional image of the hard tissue to show the missing part. Then, through mirroring, we ‘draw’ the prosthesis. The last step is to send this information to rapid prototyping equipment; this equipment will produce the identical anatomical prosthesis, layer by layer, of the missing bone.”

The area of biomaterials and biomanufacturing is a field of research that has been growing worldwide. “The field of biopolymers or polymeric biomaterials is quite extensive, due to the wide variety of plastics, such as acrylic, polyethylene, polypropylene, and PVC,” says Luís Alberto dos Santos, a professor at the Biomaterials Laboratory of the Federal University of Rio Grande do Sul (UFRGS). “Research studies have focused on two kinds of polymers: those with high mechanical resistance, placed in widely used areas (backbone, plates, screws), and absorbable polymers, that don’t have to be removed surgically and can be used to release drugs and antibiotics.”

Santos says that the word biopolymer has two broad meanings. “It can be a biomaterial for biomedical use or a polymer obtained from biological materials that is not necessarily used in human beings,” he explains. Concerning his own studies, Santos says that he is working on the development of a plastic derived from lactic acid, found for instance in meat or in milk and used for sutures and absorbable implants. Sodium alginate, derived from seaweed, is another biopolymer that we are working on,” he adds. “This material is a hydrogel that absorbs huge amounts of water; it can be used to cover the injuries of burn patients and diabetics, and in diapers and tampons. In addition, it can be used as support for cell culture.” The two research projects have resulted in submitting requests for patents.

The Project
Biofabris – Biomanufacturing Institute (nº 2008/57860-3); Modality Thematic Project – INCT; Coordinator Rubens Maciel Filho – Unicamp; Investment R$ 427,794.75 and US$ 766,420.83 (FAPESP)