Investigation of the adsorption of tropocollagen type I on titanium and Ti6Al4V

The adsorption of tropocollagen type I on titanium and Ti6Al4V has been investigated using physicochemical (zeta potential measurements), biochemical (ELISA), and imaging methods (SEM, AFM). Zeta potential measurements on both materials showed isolectric points in the pH_iep range 4.3-4.8 if the metal surfaces were covered with amorphous oxide layers. Adsorption of both collagen molecules and fibrillar collagen led to a shift of about 0.5 pH units towards the alkaline region. From ELISA-based results it can be concluded that in the investigated concentration range of 0.01-0.5 mg/ml, the adsorption of collagen molecules leads to the formation of a rather uniform covering. The influence of pH and ionic strength on the adsorption behavior has been investigated. A model of the competitive adsorption of both tropocollagen molecules and in vitro reconstituted fibrils is presented. Based on this model, two methods are proposed for the improved adsorption of collagen fibrils: (i) adsorption from solutions that are essentially free from tropocollagen and oligomeric species; and (ii) use of already adsorbed tropocollagen as nucleation sites for further fibrillar growth.     

Versatile nanostructured processing strategy for bone grafting nanocomposites based on collagen fibrillogenesis

Abstract

Strong bone-like nanocomposites of collagen type I and hydroxyapatite were prepared by coupling the in situ synthesis, hybrid gel formation and subsequent dehydration consolidation. The calcium phosphate synthesis was initiated at 4°C in the concentrated collagen monomeric solutions. Under this condition collagen molecules inhibited the calcium phosphate uncontrollably rapid growth and the predominant collagen fibril aggregation was retarded. Elevating temperature induced collagen fibrillogenesis leading to the formation of elastic hybrid gels. The dehydration consolidation of the elastic gels gave rise to strong nanocomposites. The mechanical properties and bone-like characteristics of the prepared nanocomposites were explicated. The in situ formation of a hybrid gel together with its facile processing capability suggests the versatility of this biomimetic strategy either in fabricating different structural forms (films, scaffolds and monoliths) of bone grafts or in further inclusion of other biosubstance into the nanocomposites.     

Collagen immobilization onto the surface of artificial hair for improving the tissue adhesion

To improve the bonding ability of artificial hair towards soft tissue, type I atelocollagen was immobilized onto the hair surface. The artificial hair used was made of a poly(ethylene terephthalate) monofilament. Following photo-induced graft polymerization of a hydrophilic monomer onto the surface of artificial hair, collagen was complexed with the graft chains. Poly(acrylic acid) was selected as the polymer to be grafted onto the artificial hair because this synthetic polymer exhibited the greatest ability to form an interpolymer complex in solution with collagen among the three anionic polymers poly(acrylic acid), poly(2-acrylamido methylpropane sulfonic acid), and sodium poly(styrene sulfonic acid). When the surface of the poly(ethylene terephthalate) film used as a model substrate was grafted with poly(acrylic acid), the surface density of the collagen immobilized by interpolymer complexation was found to increase with increasing surface density of the graft chains. Immobilization of collagen onto the filament surface was confirmed by surface analysis with X-ray photoelectron spectroscopy and transmission electron microscopy. It was shown that in vitro degradation of the collagen immobilized onto poly(ethylene terephthalate) was suppressed by crosslinking the collagen molecules with glutaraldehyde. Cell culture tests revealed that L-cells were attached well to the surface of collagen-immobilized artificial hair. The surface-modified hairs were implanted percutaneously in the scalp of a human volunteer. Neither infection nor rejection of the hair filaments was observed after 1 year of implantation. It was found that the number of collagenimmobilized filaments remaining fixed in the scalp after 3 years of implantation was significantly larger than that of untreated filaments. These results indicate that surface-modified artificial hair is highly biosafe and shows excellent tissue adhesion.