3.1.2. X-ray Photoelectron Spectroscopy (XPS)

The surface chemical compositions of all Ti substrates determined by XPS are shown in Table 1. After anchoring Hepa-DOPA on the surface of Ti, C1s, and N1s peaks increased to compare with Ti alone. After immobilizing rhPDGF-BB and/or rhBMP-2 on the surface of Hepa/Ti disc, the N1s peak was increased and the S2p peak decreased versus Hepa/Ti. The amount of heparin anchored onto the Ti surface was 1.62 ± 0.32 μg/disc.


**Table 1.** Surface chemical compositions evaluated in 1 disc per group.

## *3.2. In Vitro rhPDGF-BB and rhBMP-2 Releases*

The release behaviors of rhPDGF-BB or rhBMP-2 from PDGF/Hepa/Ti, BMP/Hepa/Ti, and PDGF/BMP/Hepa/Ti are shown in Figure 4, respectively. The amounts of rhPDGF-BB released from PDGF/Hepa/Ti and PDGF/BMP/Hepa/Ti discs were 25.20 ± 6.48 ng and 15.56 ± 4.55 ng after 1 day, respectively. Over 28 days, the amounts of rhPDGF-BB released were 66.69 ± 5.81 ng for PDGF/Hepa/Ti and 34.52 ± 4.55 ng for PDGF/BMP/Hepa/Ti. In addition, on day 1, the amounts of rhBMP-2 that is released from BMP/Hepa/Ti and PDGF/BMP/Hepa/Ti were 27.46 ± 6.71 ng and 16.56 ± 4.48 ng, respectively. Over the 28-day period, the amount of rhBMP-2 released was 69.85 ± 7.43 ng for BMP/Hepa/Ti and 37.52 ± 4.26 ng for PDGF/BMP/Hepa/Ti.

**Figure 4.** In vitro releases of (**a**) rhPDGF-BB and (**b**) rhBMP-2 from PDGF/Hepa/Ti, BMP/Hepa/Ti and PDGF/BMP/Hepa/Ti.
