SiO2-CaO-P2O5 (58S) sol gel glass applied onto surgical grade stainless steel by spray technique: morphological characterization by digital image processing

AISI 316L stainless steel is commonly used as a low-cost material for permanent implants. It can be protected for degradation and corrosion by applying a hybrid silica based coating. Also the bioactive response of the implant can only be achieved by functionalizing the coated implant surface. The aim of this work is to synthesize and characterize a sol-gel made glass particles from the system SiO2-CaO-P2O5 with potential as bone inductive material, with and without an aging treatment of the precursor solution. The glass was synthesized by sol-gel technique that, comparing with melt glasses, generates an open net structure that could lead to particle dissolution and apatite deposition for biological purposes. The synthesized glass is dispersed by spray onto AISI 316L protected by a hybrid silica based coating, generating deposits with different size and morphology. To characterize the particles composition, microRaman spectroscopy was applied. It showed that no significant changes were reached after aging or thermal treatment of the deposited particles. Image processing techniques based on Mathematical Morphology were used to analyze morphology and sizes of the deposits obtain with the different sols (aged and no aged). Aproximately 50% of the surface was covered with particles made with a glass aged, and a 25% of covered area was reached with no aged one. When no aged glass particles were deposited, the particle size distribution shows the presence of many big particles with a roundness factor between 0.8 and 1 in a high percentage, meaning that they are spherical due to the presence of solvent and with a more open glass structure in the no aged glass. The Digital Image Processing and Raman spectroscopy tools help to analyze, characterize and quantify the bioactive particles deposited onto coated surgical grade stainless steel in terms of morphology, distribution and composition.