TYPE-I COLLAGEN IN XENOGENIC BONE-BIOMATE RIAL REGULATES ATTACHMENT AND SPREADING OF OSTEOBLAST VIA THE BETA-1 INTEGRIN SUBUNIT

Xenogenic bone biomaterials have been proposed as an alternative to au tografts or allografts in human bone restoring or in complement of pro sthetic surgery. When appropriate treatments were applied, immunologic al, inflammatory, bacteriological or virological adverse responses can be prevented. However, these treatments may interact with type I coll agen, the major component of the organic bone matrix. Type I collagen can bind osteoblasts via specific cell surface receptors, the integrin s. In this work, two different xenogenic biomaterials were studied. Bo th biomaterials have a bovine bone origin. They displayed similar arch itectural organization with connected plates and rods and similar surf ace topography and roughness. They differed by the presence or not of collagen type I. The first one was characterized by preservation of th e type I collagen matrix associated with spindle-shaped hydroxyapatite crystals and the sec end was solely composed by heal-modified apatite crystals. Osteoblast-like cells (Saos-2) were cultured on both biomat erials and examined in scanning and transmission electron microscopy a fter 7 and 14 days. Both biomaterials were cytocompatible as demonstra ted by good ultrastructural cell preservation. (1) At the surface of t he collagen containing biomaterial, cells were elongated in shape and oriented according to the trabecular architecture and to the superfici al collagen network. After 14 days of culture, cells were confluent an d the biomaterial surface was hidden by the cell sheet. The beta 1 int egrin subunit was detected by immunogold in transmission electron micr oscopy in close relationship with the superficial collagen fibres of t he biomaterial and with the outer cell surface. When cultures were car ried out in presence of anti beta 1 integrin subunit, cells were packe d and piled up with lack of specific orientation. (2) At the surface o f the deproteinized biomaterial, cells were globular without specific disposition and often partially attached to the surface. After 14 days of culture, large areas of the biomaterial surface remained uncovered . Anti beta 1 subunits conjugated with gold particles were detected ar ound the cells but with no specific association with the deproteinized biomaterial. These: results strongly suggest that presence of type I collagen fibres in the matrix of a bone biomaterial is of major intere st to determine cell attachment, spreading and orientation via interac tion between type I collagen and beta 1 integrin subunit of osteoblast s.