L’accroissement de l’espérance de vie s’accompagne d’une détérioration de l’état de santé général des seniors et d’une recrudescence des maladies chroniques. Parmi les manifestations de la sénescence, l’atteinte de l’appareil locomoteur est particulièrement invalidante et accélère considérablement l’entrée en dépendance. C’est également le cas chez les plus jeunes lors d’atteintes traumatiques ou pathologiques. Ainsi, au niveau mondial 2,2 millions de greffes osseuses sont pratiquées chaque année, mais le taux de complications post-opératoires demeure élevé et est estimé à 15 % des interventions. Ces faits dessinent les contours d’un enjeu sociétal majeur ; les matériaux d’origine animale posent des problèmes d’histocompatibilité, de pathogénicité et donc de rejet. C’est pourquoi les efforts de recherche ciblent prioritairement le développement de biomatériaux synthétiques aptes à promouvoir la régénération osseuse. Actuellement les principaux substituts osseux sur le marché sont les « céramiques » bioactives (phosphates de calcium, verres bioactifs) qui présentent comme caractéristiques d’être biocompatibles, de se lier spontanément aux tissus osseux, de promouvoir l’adhésion des cellules osseuses et enfin d’être biorésorbables. Cependant, malgré cet ensemble de caractéristiques très satisfaisantes, la fragilité de ces matériaux en limite les applications. Pour pallier ce défaut, une solution ingénieuse est de s’inspirer de la structure particulière du tissu osseux. Celle-ci mêle intimement une phase inorganique, le minéral osseux constitué de cristaux d’apatite (phosphate de calcium résorbable), à une phase organique qui est majoritairement du collagène. De manière remarquable, une telle structure associe la rigidité de la partie inorganique à la ténacité des fibres de collagène. Pour obtenir des implants aux propriétés mécaniques proches du tissu osseux, la stratégie consiste donc à combiner céramiques bioactives et matière organique. À cette fin, l’équipe Biomatériaux du Laboratoire de Physique de Clermont (LPC) a récemment mis au point un procédé innovant qui permet la synthèse de matrices tridimensionnelles d’hybrides organique-inorganique à base de verre bioactif et de polymère biocompatible aux caractéristiques variées. Dans la continuité des travaux, il était alors question d’exploiter ce procédé afin de développer un substitut osseux hybride aux propriétés optimisées. Il s’agissait tout d’abord de sélectionner le polymère le plus adéquat pour la régénération osseuse, qui s’est avéré être le polycaprolactone, puis d’optimiser la synthèse (notamment la source de calcium), la structure macroporeuse et la proportion organique-inorganique. Le matériau hybride résultant a ensuite été dopé en éléments thérapeutiques à faible dose (< 5 % de la masse totale) avec des ions strontium ou des nutriments tels que la fisétine et l’hydroxytyrosol qui possèdent un effet ostéogénique. Les mousses hybrides ainsi développées ont finalement été caractérisées in vitro afin de déterminer leurs propriétés physico-chimiques et biologiques, et in vivo afin d’évaluer leur performance. Après 3 mois d’implantation dans un défaut critique de la calvaria de souris, les résultats démontrent le potentiel de ce substitut osseux: comparé au matériau commercial de référence (os bovin traité) qui conduit à une reconstruction osseuse de 16% (± 5%), l’hybride permet une reconstruction allant de 32% (± 3%) lorsqu’il n’est pas dopé, jusqu’à 55% (± 7%) voire 58% (± 7%) lorsqu’il est dopé respectivement en fisétine ou en strontium. Ces travaux de thèse laissent entrevoir des perspectives prometteuses telles que l’association des dopants et l’impression 3D des mousses hybrides polycaprolactone-verre bioactif. / The increase in life expectancy results in the decline of seniors’ health conditions and the resurgence of chronic diseases. Among the expressions of senescence, disorders of the musculoskeletal system are particularly disabling and considerably accelerate the state of dependency. This is also the case for young people who suffer from traumatic injuries or pathologic conditions. Thus, about 2.2 million bone grafts are performed worldwide every year. Yet, the level of postoperative complications remains high and is estimated at 15% of surgical operations. These facts outline a major societal concern: animal-based materials present a risk of histocompatibility issues and pathogenicity that may lead to implant failure. This is the reason why research efforts focus on the development of synthetic biomaterials capable of promoting bone regeneration. Currently, commercialised bone substitutes are mainly made of bioactive “ceramics” (calcium phosphates, bioactive glass) that are known to be biocompatible, to spontaneously bond to bone tissues, to promote bone cell adhesion and finally to be bioresorbable. However, despite these remarkable properties, the brittleness of these materials limits their applications. An ingenious solution to this brittleness can be learned from the particular structure of bone tissue. Bone tissue intimately blends an inorganic phase, the bone mineral, which is made of apatite crystals (resorbable calcium phosphates), with an organic phase that is mainly collagen. Such a structure associates the stiffness of the inorganic part with the toughness of collagen fibres. Therefore, in order to obtain implants with mechanical properties similar to that of bone, the strategy consists in combining bioactive ceramics with organic matter. To this end, the Biomatériaux team from the Laboratoire de Physique de Clermont (LPC) recently developed an innovative process that allows the synthesis of tridimensional organic-inorganic hybrids comprised of bioactive glass and biocompatible polymer. The objective of the thesis was to exploit this process in order to develop a hybrid bone substitute with optimal properties. First of all, polycaprolactone was selected as the polymer, especially because of its adequate degradation rate for long-term applications such as bone regeneration. Then, the synthesis process was improved (in particular, the calcium source was changed), the macroporous structure was optimised and the organic-inorganic ratio was chosen. Afterwards, elements that are known to induce an osteogenic effect were incorporated in the hybrid at low doses (< 5% of total weight): an inorganic doping was performed using strontium ions and an organic doping was performed using nutrients such as fisetin or hydroxytyrosol. The resultant hybrid scaffolds were eventually characterised in vitro in order to determine their physicochemical and biological properties and in vivo in order to evaluate their performance. After 3 months of implantation in a mouse calvarial critical defect, results demonstrate the potential of this bone substitute: compared to the reference commercial material (treated bovine bone) that leads to a bone reconstruction of 16% (± 5%), the hybrid allows a reconstruction going from 32% (± 3%) when it is not doped, to 55% (± 7%) and even 58% (± 7%) when it is doped respectively with fisetin or strontium. This thesis paves the way to promising perspectives like the association of doping agents and the 3D printing of polycaprolactone-bioactive glass hybrid scaffolds.

Made available in DSpace on 2014-07-29T15:07:31Z (GMT). No. of bitstreams: 1 Daniel Barbosa.pdf: 1143657 bytes, checksum: d56a1f0787d16e510afed007895c5973 (MD5) Previous issue date: 2010-10-24 / Abdominal wall defects may occur in fairly all animal species, and frequently demand corrective surgical treatment including implants of meshes, such as polypropylene. However, this biomaterial is not free from complications, what stimulates constant researches for new biomaterials that present certain advantages. Due to its well known biocompatibility, poliHEMA hydrogel was the chosen biomaterial for experimental abdominal wall implant associated to polypropylene mesh. This essay compared tissue responses to the employment of polypropylene mesh alone (group PP) and polyHEMA Hydrogel film associated to polypropylene mesh (group PH) on the correction of induced abdominal wall defects on bitches. Twelve mongrel adult female dogs, weighting from 10 to 20 kg, were divided in two equal groups. The animals from group PP received the polypropylene mesh implant whilst those from group PH received polyHEMA hydrogel coated polypropylene mesh to replace the abdominal transverse muscle. Six animals from each group were submitted to surgical procedure to remove the meshes at 30 and 60 days of the postoperative period. Tissue repairing phenomena such as: chronic inflammatory reaction, giant cell presence (foreign body chronic granulomatous inflammatory reaction) and connective tissue proliferation were microscopically evaluated. It may be concluded that polyHEMA hydrogel as a coating agent on polypropylene mesh implanted onto abdominal wall of female dogs triggers greater deposition of type I collagen, than polypropylene mesh alone. / Os defeitos na parede abdominal estão presentes em praticamente todas as espécies animais e não raro demandam tratamento cirúrgico corretivo com implantação de telas como a de polipropileno. Contudo esse biomaterial não é livre de complicações, o que impulsiona a constante pesquisa na busca de novos biomateriais que apresentem vantagens. O hidrogel de poliHEMA por ser reconhecidamente biocompatível foi o biomaterial de escolha para a implantação experimental em associação à tela de polipropileno na parede abdominal. Este estudo comparou as respostas teciduais do uso da tela de polipropileno isolada (grupo PP) e o filme de hidrogel de poliHEMA associado à tela de polipropileno (grupo PH) quando utilizados na correção de defeitos criados na parede abdominal de cadelas. Foram utilizadas 12 cadelas sem raça definida, adultas, pesando entre 10 e 20 kg, divididas em dois grupos de seis. Os animais do grupo PP receberam o implante da tela de polipropileno e os animais do grupo PH receberam a tela de polipropileno revestida de hidrogel de poliHEMA em substituição ao músculo transverso do abdome. Seis animais de cada grupo foram submetidos ao procedimento cirúrgico para a retirada das telas aos 30 e 60 dias do pós-operatório. Foram avaliados microscopicamente os fenômenos de reparo tecidual como: reação inflamatória crônica, presença de células gigantes (reação inflamatória crônica granulomatosa tipo corpo estranho), e proliferação conjuntiva. Conclui-se que o hidrogel de poliHEMA como agente de revestimento da tela de polipropileno quando implantado na parede abdominal de cadelas desencadeia maior deposição de colágeno tipo I quando comparado a tela de polipropileno isolada.