Immobilization of bone morphogenetic protein on DOPA- or dopamine-treated titanium surfaces to enhance osseointegration

Abstract

Titanium was treated with 3,4-dihydroxy-L-phenylalanine (DOPA) or dopamine to immobilize bone morphogenetic protein-2 (BMP2), a biomolecule. DOPA and dopamine solutions turned into suspensions, and precipitates were produced at high pH. Both treatments produced a brown surface on titanium that was thicker at high pH than low pH. Dopamine produced a thicker layer than DOPA. The hydrophobicity of the surfaces increased after treatment with dopamine independent of pH. Furthermore, there were more amino groups in the layers formed at pH 8.5 than pH 4.5 in both treatments. Dopamine treatment produced more amino groups in the layer than DOPA. BMP2 was immobilized on the treated surfaces via a coupling reaction using carbodiimide. More BMP2 was immobilized on surfaces treated at pH 8.5 than pH 4.5 in both treatments. The immobilized BMP induced specific signal transduction and alkali phosphatase, a differentiation marker. Thus, the present study demonstrates that titanium treated with DOPA or dopamine can become bioactive via the surface immobilization of BMP2, which induces specific signal transduction.

Figure 1

Photograph (a) and turbidity (b) of DOPA and dopamine solutions at different pH values. The turbidity data of dopamine solution are from Kang et al. [33].

Figure 2

Images (a) and water contact angle (b) of DOPA- and dopamine-treated titanium.

Figure 3

Amounts of amino groups on DOPA- and dopamine-treated titanium.

Figure 4

Amounts of BMP2 immobilized on DOPA- and dopamine-treated titanium.

Figure 5

The relationship between the amino groups (from Figure 3) and immobilized BMP2 (from Figure 4).

Figure 6

Induction of luciferase activity in BRE-Luc C2C12 cells by immobilized BMP2 on titanium.

Figure 7

Induction of alkaline phosphatase activity in BRE-Luc C2C12 cells by immobilized BMP2 on titanium.