PCL-Coated Multi-Substituted Calcium Phosphate Bone Scaffolds with Enhanced Properties

Bone scaffolds are engineered to support tissue regeneration and must closely mimic natural bone composition. Hydroxyapatite-based materials are commonly used due to their similarity to bone mineral. However, the mechanical and biological performance of these scaffolds can be limited. To address this, researchers have explored ionic substitutions within the hydroxyapatite lattice to improve scaffold properties. While prior studies have shown that substituting strontium or magnesium can alter scaffold characteristics, the combined effect of these substitutions remains unclear. Additionally, the role of the whitlockite phase in scaffold performance has not been fully established. The impact of surface coatings, such as poly(ε-caprolactone) (PCL), on scaffold mechanical properties and cell behavior is also an area of active investigation. This gap motivated the current study to examine how varying levels of strontium and magnesium substitution, along with PCL coating, influence scaffold structure, mechanical strength, and biological activity.

This study aimed to evaluate the effects of strontium and magnesium substitution in calcium phosphate scaffolds on their structural composition, mechanical properties, and biological performance. The specific problem addressed was the limited understanding of how combined ionic substitutions and surface coatings influence scaffold behavior. The motivation stemmed from the need to develop scaffolds that better mimic bone mineral and support cell differentiation. The study focused on using hydrothermal synthesis to create scaffolds with controlled substitution levels. It also sought to determine the role of the whitlockite phase in scaffold properties. Additionally, the study aimed to assess how PCL coating affects mechanical strength and whether strontium enhances stem cell differentiation. The goal was to provide insights into optimizing scaffold design for bone regeneration applications.

The researchers synthesized calcium phosphate scaffolds using a hydrothermal method at 200 °C. They used cuttlefish bone calcium carbonate, ammonium dihydrogenphosphate, strontium nitrate, and magnesium perchlorate as starting materials. They varied the substitution levels of strontium and magnesium to create different scaffold compositions. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were used to analyze scaffold structure and morphology. Whole powder pattern decomposition (WPPD) of XRD data was performed to determine phase composition and ionic substitutions. PCL-coated scaffolds were prepared using vacuum impregnation. Compression tests evaluated mechanical properties. Human mesenchymal stem cells (hMSCs) were cultured on scaffolds in osteogenic medium for 21 days. Immunohistochemical staining and RT-qPCR were used to assess collagen type I expression and osteogenic differentiation.

XRD and WPPD analysis showed that increased magnesium content correlated with a higher whitlockite (WH) phase proportion in biphasic hydroxyapatite (HAp)/WH scaffolds. Sr²⁺ ions were found to substitute Ca²⁺ sites in the WH phase. PCL-coated scaffolds with a 90:10 HAp:WH weight ratio showed improved mechanical properties in compression tests. Immunohistochemical staining revealed higher collagen type I expression in Mg-Sr-CaP/PCL scaffolds compared to Mg-CaP/PCL scaffolds, suggesting a positive effect of strontium on hMSC differentiation. RT-qPCR confirmed early osteogenic differentiation markers in cells cultured on the scaffolds. The combination of WH phase and PCL coating enhanced scaffold performance. Strontium substitution appeared to support cell differentiation more effectively than magnesium alone. These findings suggest that ionic substitutions and surface coatings can be used to tailor scaffold properties for bone regeneration.

The study demonstrated that strontium and magnesium substitutions in calcium phosphate scaffolds influence phase composition and mechanical performance. The whitlockite phase increased with higher magnesium content, and strontium ions successfully substituted calcium sites. PCL coating improved scaffold mechanical properties. Strontium substitution enhanced hMSC differentiation, as shown by increased collagen type I expression and RT-qPCR results. These findings suggest that combined ionic substitutions and surface coatings can be used to optimize scaffold performance. The results support the potential of these scaffolds for bone tissue engineering applications. The study provides evidence that scaffold composition directly affects cell behavior. The findings align with the authors' hypothesis that ionic substitutions and coatings can be used to improve scaffold functionality.