Shear and Tensile Strength of Silk Coatings on Titanium Surfaces

Objectives: To develop a silk-based material that would provide an adhesive coating on dental implants and to assess the effectiveness of two silk coatings (silk and combination of silk and carbonate apatite) on three different surface treatments by comparing their shear and tensile strengths.

Methods: Sixty commercially pure titanium discs (7mm-diameter) were randomly divided into three groups: Group 1: Control (no surface treatment); Group 2: Sintered with apatite grit (MCD sand blasted); Group 3: Acid etched (3.5% HCl/H₂SO₄, 24hr). Using a patented process, silk fibroin was extracted and melted into e-gels. In each group, half of the samples were coated with silk only e-gel and the other half were coated with a combination of carbonate-apatite and silk in 1/5 ratio by volume. Two titanium studs were adhered using melted e-gel and allowed to dry overnight at room temperature. Tensile and shear tests were carried out with Universal testing machine with cross-head speed of 0.5mm/min. Statistical analysis was accomplished with one-way ANOVA. Significance was at p<.05

 

Results:

	Coating	Tensile (MPa±SD)	Shear (MPa±SD)
Group 1	Silk	0.34±0.11*	0.61±0.14*
	Silk+Ca-apatite	0.54±0.04*	0.75±0.18*
Group 2	Silk	0.82±0.12*	1.37±0.32
	Silk+Ca-apatite	0.64±0.04*	1.07±0.34
Group 3	Silk	0.43±0.18*	0.76±0.52*
	Silk+Ca-apatite	0.88±0.05*	0.97±0.52*

The silk coatings produced significantly different tensile strengths for all surface treatment groups. For shear strength, significant differences were seen between surface treatments Groups 1 & 3. MCD-blasted surface treatment on titanium with silk coating exhibited the highest shear strength. Acid etched surface treatment coated with combination of silk and Ca-apatite exhibited the highest tensile strength.

 

Conclusions: Melted e-gel silk coatings were successfully fabricated and adhered to titanium with various surface modifications. The mechanical properties of these coatings were comparable to current literature for coatings on titanium surfaces. This process shows promise for use as functional coatings on dental titanium implants.