Fabrication and Characterization of Bioactive Gelatin-Alginate-Bioactive Glass Composite Coatings on Porous Titanium Substrates

Abstract

In this research work, the fabrication of biphasic composite implants has been investigated. Porous, commercially available pure Ti (50 vol % porosity and pore distributions of 100-200, 250-355, and 355-500 μm) has been used as a cortical bone replacement, while different composites based on a polymer blend (gelatin and alginate) and bioactive glass (BG) 45S5 have been applied as a soft layer for cartilage tissues. The microstructure, degradation rates, biofunctionality, and wear behavior of the different composites were analyzed to find the best possible coating. Experiments demonstrated the best micromechanical balance for the substrate containing 200-355 μm size range distribution. In addition, although the coating prepared from alginate presented a lower mass loss, the composite containing 50% alginate and 50% gelatin showed a higher elastic recovery, which entails that this type of coating could replicate the functions of the soft tissue in areas of the joints. Therefore, results revealed that the combinations of porous commercially pure Ti and composites prepared from alginate/gelatin/45S5 BG are candidates for the fabrication of biphasic implants not only for the treatment of osteochondral defects but also potentially for any other diseases affecting simultaneously hard and soft tissues.

Keywords: bioactive coating; biopolymer composites; osteochondral defects; porous titanium; tribomechanical behavior.

Figure 1

Schematic of the fabrication process of biphasic coated substrates.

Figure 2

Microstructural characterization of porous c.p. Ti substrates: (a) density and total and interconnected porosity and (b) equivalent diameter and shape factor as well as mechanical behavior: (c) dynamic Young’s modulus (E_d) and yield strength (σ_y).

Figure 3

Characterization of polymeric coatings: (a,c) weight gain and (b,d) degradation rates of the different polymeric blends and composites.

Figure 4

SEM micrographs of composites prepared from (a) A, (b) 3A1G, and (c) 1A1G, showing different pore structures. Insets: higher-magnification images.

Figure 5

Optical images of the polymeric coatings onto metallic substrates. All samples contained 5 wt % BG 45S5.

Figure 6

(a) Cross section of a substrate coated with the 1A1G composite. (b) Schematic of the coated substrate, where a composite interface (I) is illustrated between the composite coating (C) and the metallic sample (M). (c,d) SEM micrographs of the different areas, at two magnifications. 1A1G composite-coated substrates with two different pore size distributions: (e) 200–355 and (f) 355–500 μm.

Figure 7

(a) Density and (b) total and interconnected porosity of the two tested materials: A and 1A1G. Note: the relative error of the density measurements varies between 2 and 4%.

Figure 8

SEM micrographs of composites (a,b) A and (c,d) 1A1G before and after 3 days of immersion in the SBF.

Figure 9

SEM images of composite A after (a) 7 and (b) 14 days of immersion in the SBF.

Figure 10

Chemical compositions, calculated by EDX–SEM, of two different surface areas of the coating obtained from A after 14 days in the SBF.

Figure 11

FTIR spectra of both composites, (a) one obtained from A and (b) one prepared from 1A1G, at different immersion times.

Figure 12

(a) Coefficient of friction and (b) LVDT vs distance of composites, obtained from 1A1G and a 5% BG for an initial spacer size of 355–500 μm and different applied loads of 1 and 3 N. The average COF, mass loss after tribomechanical tests, and absolute wear rates for composites are also presented.

Figure 13

(a) Coefficient of friction and (b) LVDT vs distance of composites obtained from A and 1A1G and 5% BG for a spacer size of 100–200 μm. The average COF, mass loss after tribomechanical tests, and absolute wear rates are also presented.

Figure 14

Influence of the pore size of the titanium substrate on the wear behavior (LVDT vs distance) of 1A1G + 5% BG. The mass loss after tribomechanical tests and absolute wear rates of composites are also presented.