Microgroove and Collagen-poly(ε-caprolactone) Nanofiber Mesh Coating Improves the Mechanical Stability and Osseointegration of Titanium Implants

Abstract

The effect of depositing a collagen (CG)-poly-ε-caprolactone (PCL) nanofiber mesh (NFM) at the microgrooves of titanium (Ti) on the mechanical stability and osseointegration of the implant with bone was investigated using a rabbit model. Three groups of Ti samples were produced: control Ti samples where there were no microgrooves or CG-PCL NFM, groove Ti samples where microgrooves were machined on the circumference of Ti, and groove-NFM Ti samples where CG-PCL NFM was deposited on the machined microgrooves. Each group of Ti samples was implanted in the rabbit femurs for eight weeks. The mechanical stability of the Ti/bone samples were quantified by shear strength from a pullout tension test. Implant osseointegration was evaluated by a histomorphometric analysis of the percentage of bone and connective tissue contact with the implant surface. The bone density around the Ti was measured by micro-computed tomography (μCT) analysis. This study found that the shear strength of groove-NFM Ti/bone samples was significantly higher compared to control and groove Ti/bone samples (p < 0.05) and NFM coating influenced the bone density around Ti samples. In vivo histomorphometric analyses show that bone growth into the Ti surface increased by filling the microgrooves with CG-PCL NFM. The study concludes that a microgroove assisted CG-PCL NFM coating may benefit orthopedic implants.

Keywords: bone; electrospun nanofiber; in vivo study; shear strength; titanium.

Figure 1

Scanning microscope image of the aligned poly-ε-caprolactone (PCL) nanofiber on a carbon type at (a) 1000× and (b) 1500× magnifications; (b) shows the diameter of the fiber and the distance between the fibers.

Figure 2

A fabricated (a) control; (b) groove, and (c) groove-NFM Ti samples.

Figure 3

Attachment of collagen-poly-ε-caprolactone nanofiber mesh (CG-PCL NFM) coating after in the vivo implantation of the Ti wire after eight weeks.

Figure 4

Load vs. displacement plot of a control, groove, and groove with NFM samples.

Figure 5

Pull out test results (in MPa) of different titanium samples after eight weeks of implantation. Bars represent mean ± SEM (n = 6). * represents statistical significant results compared to control samples for p < 0.05.

Figure 6

Stained images of decalcified Ti-bone samples: (a) groove and (b,c) groove-NFM. In the image, older cortical bone has a lighter pink color and newer cortical bone stains dark red, trabecular bone is stained in blue, while connective tissue is stained in white. In the above figures, the first, second, and third column images were taken at 0.5×, 4× and 20× magnifications. New cortical bone growth along the microgroove is visible from both groove-NFM samples, whereas connective tissues and trabecular bone growth along the microgroove is visible from groove sample.

Figure 8

Normalized bone density (total bone density/weight of the rabbit) belonging to the volume of the concentric cylindrical rings from the center axis of the implant. * represents statistically significant results compared to control samples for p < 0.05.

Figure 9

Schematic representation of the longitudinal section images of (a) control, (b) groove, and (c) groove-NFM samples.

Figure 10

Schematic representation of coating groove Ti samples by aligned electrospun nanofiber using an electrospin process.

Figure 11

X-ray image of femur after surgery.

Figure 12

Process to find the bone density from a selected region of interest (ROI) of a μ-CT image: (a) column selection around the center of the implant hole. Bottom of column is 500 μm from the bottom of the implant hole. The columns (represented by different color) were created by a transverse segmentation of the bone section into three rings. The inner section represents the holes created by an implant; (b) concentric ring creation around the hole of the implant. The three rings with radii of 2.25–1.75, 1.75–1.25, and 1.25–0.75 mm were represented by colored circles; (c) determination of CT threshold values to identify different types of bone tissue from a CT scan image of a rabbit femur bone before surgery (without implant). The CT scanning was conducted around the same location where the implant was inserted. (d) Use of density thresholds to assign portions of column to the specific bone tissue to generate 3D volume of the specified ROI.