Question

A hip implant failed two weeks after surgery. It was removed and the contact angle was found to have a value of 120o. A new implant that was coated with fibronectin (with a contact angle of 40o) was found to get integrated within three days! Provide an explanation for these observations.  

Answer 1

For dental or orthopedic implants to be osteoinductive, the implant material must support the long-term development, maturation, and function of osteoblasts attached to the metal surface. Unfortunately, titanium and its alloys often contain significant levels of inorganic surface contaminants, including metal ions silica and polishing agents, and other surface contaminants deposited by autoclaving procedures.The release of metal ions from titanium materials has been shown or suggested to diminish osteoblast gene expression, cellular function, and bone formation,while autoclaving can affect cellular responses to titanium materials,probably by introducing surface contaminants. Contaminants can also become attached to surface oxides during the sample preparation procedure and alter osteoblastic cell differentiation.

The Effects of the Fibronectin Coating on the Expression of Osteoblast Gene Markers

The fibronectin preadsorbed to titanium alloy can enhance the differentiation of osteoprogenitors. A previous study of fibronectin coatings on titanium disks revealed little or no evidence of cross-linking between adjacent homodimers at solution coating concentrations below 4 nmol/L. It has also been shown that the adsorption of fibronectin to titanium surfaces is essentially irreversible. These findings suggest that the incubation of disks with 1 nmol/L fibronectin as performed in the current study can produce a stable coating of fibronectin molecules on Ti-6Al-4V that are far enough apart to allow unrestricted spreading of individual molecules on the surface. It has been shown that the unimpeded spreading of adsorbed fibronectin on a surface facilitates an increase in the exposure of epitopes in the integrin-binding domain as the molecule unfolds to an extended conformation. At higher degrees of molecular packing, these epitopes are completely unavailable when the molecule assumes a more compact conformation. It was also found that fibronectin coated on the alloy produced a six- to eightfold stimulation of osteoblast cell attachment at the coating concentration of 1 nmol/L used in the current study. Therefore, the present procedure for incubating alloy disks with fibronectin in solution is likely to create a coating of fibronectin molecules capable of activating osteoblast integrin receptors.Even if the contact area of fibronectin coated implant is less compared to contact area of titanium implant its shown to provide a superior effect in terms of osteointegration.

Fibronectin coatings of titanium materials exert additional cellular actions that may increase the capacity of the implant material to support osteogenesis.

the stimulatory effects of fibronectin on osteoblast attachment provide an advantage over surface-roughening procedures, which have also been shown to inhibit osteogenic cell attachment.

The expression of osteoblast markers during the mineralization phase of osteoblastogenesis was increased by preadsorbed fibronectin

credits

Rapuano, B. E., Hackshaw, K. M., Schniepp, H. C., & MacDonald, D. E. (2012). Effects of coating a titanium alloy with fibronectin on the expression of osteoblast gene markers in the MC3T3 osteoprogenitor cell line. The International journal of oral & maxillofacial implants, 27(5), 1081–1090.

Rapuano, B. E., & MacDonald, D. E. (2011). Surface oxide net charge of a titanium alloy: modulation of fibronectin-activated attachment and spreading of osteogenic cells. Colloids and surfaces. B, Biointerfaces, 82(1), 95–103. https://doi.org/10.1016/j.colsurfb.2010.08.023

Ku Y, Chung CP, Jang JH. The effect of the surface modification of titanium using a recombinant fragment of fibronectin and vitronectin on cell behavior. Biomaterials. 2005 Sep;26(25):5153-7. doi: 10.1016/j.biomaterials.2005.01.060. PMID: 15792542.