Compressive Modulus Testing of Mineralized Silk-based Biomaterial

Objective:  The purpose of this study was to explore biopolymer based materials for potential application in dental restorations.  The compressive modulus of a non-mineralized silk-based biopolymer (NMSB) and a mineralized silk-based biopolymer (MSB) material was compared to that of a commercially available composite-resin (CR) material. 

Methods:  The silk-based biopolymer material was fabricated in both mineralized and non-mineralized forms by a patent pending protocol.  Cylinders of each type of silk material were formed with dimensions to have a length to diameter ratio of up to ~2:1 (NMSB: ~9-10mm height, ~4.5-5mm diameter, n=8; MSB: ~10.5-12.5mm height, ~6-7mm diameter, n=8).  Cylindrical specimens (~10-11mm height, ~5-5.5mm diameter, n=8) of light-cured Estelite Sigma PLT composite-resin (Tokuyama Dental) were also prepared. All specimens were stored in ~37˚ water for 24 hrs.  Compressive modulus testing was performed on an Instron 3366 using a 1kN load cell for the NMSB and MSB, and a 10kN load cell for the CR.  All specimens were tested with a crosshead speed of 1mm/min. 

Results:

Table 1: Compressive modulus testing of NMSB, MSB and CR (n=24, 8/group), analyzed by one-way ANOVA.

	NMSB	MSB	CR
Mean Compressive Modulus (MPa)	29.4	84.2	2793.1
Standard Deviation (MPa)	3.01	19.16	239.07
ANOVA F-test	1041.462    (p<0.0001)

Conclusions: The results indicate that the addition of mineral content improves the compressive modulus performance of the silk-based biopolymer.  However, they also demonstrate the need to further improve the strength of the silk biopolymer with modifications in mineral loading and other processing modes to reinforce the material's stiffness.  This study is an incremental step in further manipulation of the silk with the goal of producing a biomaterial for dental needs.     

This work was supported by NIH grants ED002520, EB003210.