Long-Term Stability and Osteogenic Activity of Recycled Polysulfone-Calcium Silicate Bone Implants In Vitro

Abstract

Environmental protection issues have received widespread attention, making material recycling increasingly important. The upcycling of polysulfone (PSF) medical waste, recognized as a high-performance plastic with excellent mechanical properties, deserves promotion. While PSF is suitable for use as an orthopedic implant material, such as internal fixation, its osteogenesis capabilities must be enhanced. Mechanical stability, particularly over the long term, is a significant concern for bone implants in load-bearing applications. This study recycled PSF medical waste to create bone composites by incorporating osteogenic calcium silicate (CaSi) at three different contents: 10%, 20%, and 30%. We evaluated the phase, morphology, weight loss, and three-point bending strength of the PSF-based composites after they were soaked in dynamic simulated body fluid (SBF) at pH levels of 7.4 and 5.0 for up to 12 months. Human mesenchymal stem cells (hMSCs) were utilized to assess the osteogenic activity of these composites. Our findings revealed that, while the bending strength of PSF-based composites declined with prolonged exposure to SBF, the dissolution of CaSi particles led to a manageable weight loss of about 4% after 12 months, regardless of pH 7.4 or 5.0. Importantly, the incorporation of CaSi into the PSF matrix exhibited a positive effect on the attachment and proliferation of hMSCs. The levels of alkaline phosphatase (ALP) and calcium deposits directly correlated with the CaSi content, indicating superior osteogenic activity. Considering biostability and osteogenic ability, the 20% CaSi-PSF composite demonstrated promise as a candidate for load-bearing implant applications.

Keywords: biostability; bone implant; calcium silicate; osteogenesis; polysulfone.

Figure 1

XRD patterns of three RFB composites with different CaSi content after soaking in an SBF solution at (a) pH 7.4 or (b) pH 5 for specified durations.

Figure 2

XRD patterns of three RNP composites with different CaSi content after soaking in an SBF solution at (a) pH 7.4 or (b) pH 5 for specified durations.

Figure 3

XRD patterns of three CNP composites with different CaSi content after soaking in an SBF solution at (a) pH 7.4 or (b) pH 5 for specified durations.

Figure 4

Surface SEM images of three RFB composites after being soaked in SBF solutions at pH levels of 7.4 and 5.0 for durations of 1 and 12 months. The scale bar represents two micrometers. Arrows indicate the solution-etched points surrounding the CaSi particle and the CaSi particles themselves.

Figure 5

Surface SEM images of three RNP composites after being soaked in SBF solutions at pH levels of 7.4 and 5.0 for durations of 1 and 12 months. The scale bar represents two micrometers. Arrows indicate the solution-etched points surrounding the CaSi particle and the CaSi particles themselves.

Figure 6

Surface SEM images of three CNP composites after being soaked in SBF solutions at pH levels of 7.4 and 5.0 for durations of 1 and 12 months. The scale bar represents two micrometers. Arrows indicate the solution-etched points surrounding the CaSi particle and the CaSi particles themselves.

Figure 7

The three-point bending strength of various PSF-based composites with different CaSi contents before and after soaking in an SBF solution at two pH levels: (a) pH 7.4 and (b) 5.0 for predetermined durations. Statistical comparisons were made between the different soaking time points for the same composite. Different capital letters indicate significant differences, with a significance level of p < 0.05 (n = 10).

Figure 8

Changes in weight loss of various PSF-based composites with different CaSi contents before and after soaking in an SBF solution at (a) pH 7.4 or (b) pH 5.0 for extended periods (n = 10).

Figure 9

(a) Cell attachment and (b) proliferation of hMSCs cultured on various composite surfaces at different time points. Statistical comparisons were made between samples incubated for the same duration. Different capital letters indicate significant differences at p < 0.05 (n = 3).

Figure 10

(a) The absorbance levels of (a) alkaline phosphatase activity and (b) mineralization expression in hMSCs cultured on various PSF-based composite surfaces. Samples that were incubated for the same duration were subjected to statistical analysis. Statistically significant differences are indicated using different capital letters, with a p-value of less than 0.05 (n = 3).

Scheme 1

A schematic diagram for understanding the impact of PSF types with 82 groups on mechanical properties, weight loss, and osteogenic activity.