Calcium phosphate coated 3D printed porous titanium with nanoscale surface modification for orthopedic and dental applications

Abstract

This study aims to improve the interfacial bonding between the osseous host tissue and the implant surface through the application of doped calcium phosphate (CaP) coating on 3D printed porous titanium. Porous titanium (Ti) cylinders with 25% volume porosity were fabricated using Laser Engineered Net Shaping (LENS™), a commercial 3D Printing technique. The surface of these 3D printed cylinders was modified by growing TiO₂ nanotubes first, followed by a coating of with Sr²⁺ and Si⁴⁺ doped bioactive CaP ceramic in simulated body fluid (SBF). Doped CaP coated implants were hypothesized to show enhanced early stage bone tissue integration. Biological properties of these implants were investigated in vivo using a rat distal femur model after 4 and 10 weeks. CaP coated porous Ti implants have enhanced tissue ingrowth as was evident from the CT scan analysis, push out test results, and the histological analysis compared to porous implants with or without surface modification via titania nanotubes. Increased osteoid-like new bone formation and accelerated mineralization was revealed inside the CaP coated porous implants. It is envisioned that such an approach of adding a bioactive doped CaP layer on porous Ti surface can reduce healing time by enhancing early stage osseointegration in vivo.

Keywords: 3D printing; accelerated healing; in vivo osseointegration; porous cylinders; surface modification; titania nanotubes.

Figure 1

demonstrates the effects of combination of nanoscale surface modification with doped CaP coating on porous CpTi on in vivo osseointegration in a rat distal femur model

Figure 2:

Schematic representation of the LENS™ process [24].

Figure 3:

(a) Schematic of push-out test set-up. (b) Picture of push-out test set-up connected with the Instron. (c) Top view of the push-out test set-up with a sample attached.

Figure 4

(a-c):SEM and optical image [24] of the porous surface nature of LENS™ processed porous sample and porous Ti implant with fabrication of nanotubes with diameter 105±30nm and length 375±35nm using anodization method. (d): CaP and Sr-Si-CaP coating morphology on cylindrical LENS™ Porous Ti-NT samples at different magnifications showing the Sr and Si crystals on the cylinders. (e): CaP and Sr-Si-CaP coating thickness on cylindrical LENS™ Porous Ti-NT samples showing 120 nm and 170 nm thickness respectively.

Figure 5:

Signs of osteoid like new bone generation (in reddish orange color) in the histology images after 4 weeks (a, b, c, d) and 10 weeks (e, f, g, h). Modified Masson Goldner’s trichrome staining method was used, demonstrating enhanced bone formation in the doped coating at both the time points.

Figure 6

(a) shows total osteoid formation around the implant (200μms in radius) for the different compositions at two studied time points. (** means P value < 0.001, so statistically significant) (b) shows total amount of bone formation around the implant (200μms in radius) for the different compositions at two studied time points (** means P value < 0.001, so statistically extremely significant).

Figure 7:

CT scan images of implants after 10 weeks showing tissue ingrowth into the implants with no notable defects or gaps along the interface in the doped coating. (n=2)

Figure 8

(A):SEM images of stained porous Ti samples after 4 (a, b) and 10 (c, d) weeks showing the interfacial bonding between the implant and the tissue. (B): SEM images of stained porous Ti-NT samples after 4 (a, b) and 10 (c, d) weeks showing the interfacial bonding between the implant and the tissue. (C): SEM images of stained porous Ti-NT-CaP samples after 4 (a, b) and 10 (c, d) weeks showing the interfacial bonding between the implant and the tissue. (D): SEM images of stained porous Ti-NT-CaP-Sr-Si samples after 4 (a, b) and 10 (c, d) weeks showing the interfacial bonding between the implant and the tissue.

Figure 8

(A):SEM images of stained porous Ti samples after 4 (a, b) and 10 (c, d) weeks showing the interfacial bonding between the implant and the tissue. (B): SEM images of stained porous Ti-NT samples after 4 (a, b) and 10 (c, d) weeks showing the interfacial bonding between the implant and the tissue. (C): SEM images of stained porous Ti-NT-CaP samples after 4 (a, b) and 10 (c, d) weeks showing the interfacial bonding between the implant and the tissue. (D): SEM images of stained porous Ti-NT-CaP-Sr-Si samples after 4 (a, b) and 10 (c, d) weeks showing the interfacial bonding between the implant and the tissue.