title: Collagen-hydroxyapatite composites with applications as bone substitutes: synthesis and characterisation.
abstract: The paper presents synthesis, swelling properties and in vitro degradation tests of collagen-hydroxyapatite composites, in the order to obtain new bone substitutes. Also, by using a 3D analysis with finite element the tension distribution at bone--synthesised substitute interface and in bone by comparing to bone substitute was determined.
  
  
  METHODS
  Collagen type I from tendon bovine source, provided from Sigma-Aldrich, has been used for materials synthesis. Composite materials have been obtained by hydroxyapatite (HA) precipitation from its precursors (aqueous solutions of CaCl2 and NaH2PO4), in the presence of NH4OH and process finalising at 37 degrees C. Three types of materials have been prepared: 75% collagen--25% HA(w/w)--Coll75-HA; 50% collagen--50% HA(w/w)--Coll50-HA; 25% collagen--75% HA(w/ w)--Coll25-HA. Swelling properties of the composite materials were evaluated gravimetrically and in vitro degradation in buffered collagenase was studied. The elasticity modulus was calculated from the dependence force versus material's strain. The 3D analysis with finite element at bone--synthesised substitute interface was performed for a right osteosynthesised fracture from femur.
  
  
  CONCLUSIONS
  Materials swelling in simulated body fluids revealed higher equilibrium swelling degree for HA-collagen composites with increased content of collagen. Materials are degraded by collagenase, the degradation rate being strongly dependent by composition; a higher content of collagen makes the composites more sensitive to the specific enzyme. SEM data have shown the forming of hydroxyapatite crystals onto collagen fibers. The mechanical characterisation has shown a limited elasticity at an increased value of the applied force for Coll25-HA. Over these forces the plasticity was observed. By using the 3D analysis with finite element at bone--synthesised substitute interface a higher strength was determined in the bone by comparison to bone substitute.
  
  
  CONCLUSIONS
  The superior elasticity properties of the synthesised collagen-HA by comparison to physiological biomechanical limits indicate a good behaviour as resistance bone substitute with applications in the extensive bones reconstruction (endoprosthesis revision, bone infections etc.).
authors.affiliation: Technical University Gh. Asachi Iaşi, School of Chemical Engineering and Environmental Protection, Department of Chemical Engineering.
authors.forename: Petruţa
authors.initials: P
authors.lastname: Flocea
authors.forename: M
authors.initials: M
authors.lastname: Popa
authors.forename: Fl
authors.initials: F
authors.lastname: Munteanu
authors.forename: Liliana
authors.initials: L
authors.lastname: Vereştiuc
mesh_terms: D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry*; D018786:Bone Substitutes / Q000138:chemical synthesis; D001842:Bone and Bones; D002417:Cattle; D003094:Collagen / Q000737:chemistry*; D019245:Compressive Strength; D017886:Durapatite / Q000737:chemistry*; D005264:Femoral Fractures / Q000628:therapy; D006801:Humans; D066298:In Vitro Techniques; D008422:Materials Testing / Q000379:methods; D008432:Mathematical Computing; D008953:Models, Anatomic; D013314:Stress, Mechanical
chemical_list: D001672:Biocompatible Materials; D018786:Bone Substitutes; D003094:Collagen; D017886:Durapatite