Collagen as Coating Material for 45S5 Bioactive Glass-Based Scaffolds for Bone Tissue Engineering

Abstract

Highly porous 45S5 bioactive glass-based scaffolds were fabricated by the foam replica technique and coated with collagen by a novel method. After an initial cleaning step of the bioactive glass surface to expose reactive –OH groups, samples were surface functionalized by (3-aminopropyl)triethoxysilane (APTS). Functionalized scaffolds were immersed in a collagen solution, left for gelling at 37 °C, and dried at room temperature. The collagen coating was further stabilized by crosslinking with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS). Applying this coating method, a layer thickness of a few micrometers was obtained without affecting the overall scaffold macroporosity. In addition, values of compressive strength were enhanced by a factor of five, increasing from 0.04 ± 0.02 MPa for uncoated scaffolds to 0.18 ± 0.03 MPa for crosslinked collagen-coated scaffolds. The composite material developed in this study exhibited positive cell (MG-63) viability as well as suitable cell attachment and proliferation on the surface. The combination of bioactivity, mechanical competence, and cellular response makes this novel scaffold system attractive for bone tissue engineering.

Keywords: bioactive glass; bone tissue engineering; collagen; scaffolds; surface functionalization.

Figure 1

SEM images of as-fabricated bioactive glass-based scaffolds after sintering, at lower (A) and higher (B) magnifications. The hollow nature of the struts can be clearly seen (C) and can be attributed to the burn-out of the sacrificial polyurethane (PU) foam.

Figure 2

SEM images of uncrosslinked, collagen-coated bioactive glass-based scaffolds. The fibrous collagen layer can be clearly seen (B). After the coating process, the overall macroporosity of the scaffold is not affected (A). The collagen layer exhibits a thickness of a few micrometers (C). At the interface ((D–F), different magnifications), the rough bioactive glass surface can be clearly distinguished from the fibrous collagen layer.

Figure 3

XPS spectra of 45S5 bioactive glass (BG) surfaces before and after the silanization process in acetone +2 vol % APTS for 1 h.

Figure 4

FTIR spectra of 45S5 BG-based scaffolds and collagen-coated 45S5 BG-based scaffolds before and after crosslinking. Relevant peaks are discussed in the text.

Figure 5

Mass loss of uncrosslinked and crosslinked collagen on 45S5 BG-based scaffolds during TGA.

Figure 6

SEM images of as-fabricated 45S5 BG-based samples after immersion in simulated body fluid (SBF) for 1, 3, and 7 days (at different magnifications).

Figure 7

FTIR spectra of as-fabricated 45S5 BG-based samples after 0, 1, 3, 7, and 10 days of immersion in SBF. Relevant peaks are discussed in the text.

Figure 8

SEM images of collagen (Coll)-coated 45S5 BG-based scaffolds (cl) after immersion in SBF for 1, 3, 7, and 10 days (at different magnifications). The formation of a mineralized collagen layer can be observed.

Figure 9

FTIR spectra of collagen-coated 45S5 BG-based scaffolds (crosslinked) after 0, 1, 3, 7, and 10 days of immersion in SBF. Relevant peaks are discussed in the text.

Figure 10

Cumulative collagen release from different types of 45S5 BG-based scaffolds in PBS.

Figure 11

Cumulative collagen release from different types of 45S5 BG-based scaffolds in SBF.

Figure 12

Collagen release kinetics of collagen-coated 45S5 BG-based scaffolds in PBS (left) and SBF (right) before and after crosslinking.

Figure 13

Exemplary stress-displacement curves for 45S5 BG-based scaffolds with and without collagen coating.

Figure 14

Cell viability of MG-63 cells of different scaffold types (absorbance at 450 nm) after 7, 14, and 21 days. Significance levels: * p < 0.05, ** p < 0.01 (Bonferroni’s post-hoc test was used).

Figure 15

Relative proliferation of MG-63 cells on different scaffold types (absorbance at 450 nm) after 7, 14, and 21 days. Significance level: *** p < 0.001 (Bonferroni’s post-hoc test was used).

Figure 16

SEM images of seeded MG-63 cells on different types of scaffolds for 7, 14, and 21 days (at different magnifications).

Figure 17

Surface functionalization of 45S5 bioactive glass-based scaffolds with APTS divided into (I) hydrolysis, (II) condensation reaction, (III) hydrogen bonding, and (IV) bond formation [50,54,55,56].