Bioactive glass coating for hard and soft tissue bonding on Ti6Al4V and silicone rubber

using electron beam ablation


(by J. Schrooten, S.V.N. Jaecques, R.Eloy, C. Schultheiss, J. vn Humbeeck, J. vander Sloten)




In contrast to the bone bonding potential of existing implants, the adhesion of soft tissue with any commonly used implant material is poor. Therefore an important problem of percutaneous implants is the infectious passage of bacteria into the body at the interface between tissue and implant. Subcutaneous implants, e.g. access ports for injections used in chemotherapy, suffer under low fixation and should be anchored with the surrounding soft tissue.

The main objective of this research is to develop a method, which allows the growth of living soft tissue on medical implants ranging from metals to temperature sensitive polymers. The surface of the implant is to be coated with bioactive glass (BAG), which has proven bonding potential to hard and soft tissue. A new coating procedure based on electron beam ablation (ELBA) will be used.

A first project goal was to deliver a “proof of principle” of the ELBA technique by coating Ti6Al4V-alloy and silicone rubber (poly-dimethylsiloxane, PDMS) substrates with micrometer thin BAG layers.


Materials & Methods

BAG targets (Ć30mm, thickness d = 5-10mm) with the following composition (weight%) were produced: 60% SiO2, 9% CaO, 28% Na2O and 2% P2O5. Through ELBA this BAG was deposited on two different substrate materials: (i) Ti6Al4V, cylindrical disks (Ć10mm, d = 1mm), with a glass-blasted surface finish prior to coating and (ii) PDMS cylindrical disks (Ć10mm, d = 1mm), in as-received condition. The following properties of the coated samples were evaluated: composition, amorphous character, thickness, roughness, adhesion strength, short term (<24h) in vitro dissolution kinetics in Hanks’ solution and fibroblast cell adhesion with L929 mouse fibroblast cells (ISO-10993-5 standard). For the latter, tissue culture polystyrene (TCPS) was used as a control. The number of cells per ml medium in contact with the TCPS was taken as 100%.


Results & Discussion

The ELBA process changed the composition of the final BAG coating to 54% SiO2, 13% CaO, 31% Na2O and 2% P2O5. The deposited BAG layers, with a thickness ranging from 4 to 14 µm depending on the ELBA process parameters, were amorphous. The coating roughness had an Ra value of approximately 614 nm. The adhesion strength decreased with increasing coating thickness: 6.8 MPa for 2.4 µm thickness, versus 2.5 MPa for 8.3 µm. However, the adhesion strengths obtained with the thickest coatings are still sufficient for the intended use.

The in vitro dissolution experiments in Hanks’ solution showed a compositional change that is expected for BAG, related to leaching, dissolution and reprecipitation. After these in vitro tests the average coating roughness was significantly decreased  (from 882 nm Ra to 797 nm Ra, p<0.05 for Ti6Al4V substrates and from 1470 nm Ra to 531 nm Ra, p<0.01 for PDMS substrates) and crystalline phases (calcite) were formed.

The fibroblast cell adhesion test showed that after 24 hours, on the coated PDMS substrates 750% cells per ml medium were counted and 120% on the coated Ti6Al4V substrates, compared to 100% for the control. After 48 hours the results were 800% and 350% respectively. Afterwards the coating was completely covered with fibroblasts. There is good cell adhesion and proliferation on the treated PDMS samples and also on the treated Ti6Al4V samples, but on a lower level.



The coating of metallic and polymeric substrates with BAG of composition 54% SiO2, 13% CaO, 31% Na2O and 2% P2O5 was successful: the BAG coatings were amorphous, homogeneous and well adherent. In comparison to cell growth on untreated TCPS control surfaces, coated Ti6Al4V-alloy and PDMS samples showed an increased cell population at the surface after 48 hours. It can be concluded that the reported BAG coatings produced by ELBA have the ability to promote cell growth. These results will be used as a basis for investigating other BAG compositions more rigorously and understanding the reaction mechanism of thin BAG coatings with relation to soft and hard tissue bonding.