Investigating Ion Incorporation Strategies Onto Sintered Hydroxyapatite Scaffolds Fabricated Via Vat Photopolymerization
Swaminathan, Harish (2025)
2025
Master's Programme in Biomedical Sciences and Engineering
Lääketieteen ja terveysteknologian tiedekunta - Faculty of Medicine and Health Technology
Hyväksymispäivämäärä
2025-12-19
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-2025121911987
https://urn.fi/URN:NBN:fi:tuni-2025121911987
Tiivistelmä
Bone tissue engineering (BTE) research has produced several promising solutions in treating bone defects, and overcome the challenges faced by traditional grafting techniques (autograft, allograft and xenografts). There have been a number of biomaterials that have been investigated within BTE; however, hydroxyapatite (HAp) remains the most extensively studied biomaterial due to its chemical resemblance to the inorganic constituents of native bone tissue. In particular, ion-substituted HAp has been the focus of research because of its ability to replicate the non-stoichiometric chemical composition of native bone tissue and the therapeutic benefits it can offer. However, lattice-level substitutions during synthesis followed by high-temperature processing often produce undesirable phase transformations, such as α/β-tricalcium phosphate (α/β-TCP). These formed phases can compromise the mechanical and biological performance of the biomaterial in general. Thus, to address this challenge, this study investigated three different post-synthesis ion-incorporation techniques to introduce divalent cations such as strontium (Sr²⁺), magnesium (Mg²⁺), and zinc (Zn²⁺) onto the surface of sintered HAp scaffolds fabricated via vat photopolymerization (VPP). This fabrication technique was chosen due to its capability in reproducing the macroporous microstructure of the native bone in higher resolutions compared to other 3D printing tech-niques such as direct ink writing.
The first strategy involved direct immersion of sintered HAp macroporous scaffolds in cation-containing aqueous solutions under varying concentrations, temperatures, and immersion times. It was found that Mg²⁺ and Zn²⁺ adsorption was relatively consistent when compared with Sr²⁺, which lacked reproducibility. The second strategy involved immersing the scaffolds in the reaction medium, where the wet precipitation of cation-substituted HAp was occurring. This resulted in the deposition of a cation-substituted secondary HAp layer onto the sintered HAp scaffold surface. This approach yielded higher incorporation efficiency for Mg2+ and produced rough, irregular coatings, which are expected to enhance osseointegration. The third strategy utilized biomimetic coating methods by immersing the scaffolds in simulated body fluid (SBF) that is ten times more concentrated (10x SBF) and enriched with target cations. Sr²⁺ incorporation using this strategy was promising, and the molar substitu-tion percentages were found to increase over time, whereas Zn²⁺ incorporation was hindered by bulk precipitation and resulting in the formation of unintended phases.
Overall, the most effective technique for each cation was found to vary, with wet precipi-tation being the most effective for Mg²⁺ incorporation, biomimetic coating for Sr²⁺, and ion adsorption for Mg²⁺ and Zn²⁺. These findings demonstrate potential for functionalizing sin-tered HAp scaffolds with a variety of cations to improve their biological properties via the release of therapeutic ions without compromising their structural integrity. Although this in-vestigation serves only as a preliminary study that demonstrates the potential of post-synthesis ion-incorporation techniques, further investigations are needed to confirm their efficacy. Future work should focus on advanced characterization, ion release studies, and biological evaluations to validate their efficiency for use in manufacturing of scaffolds intended for clinical applications.
The first strategy involved direct immersion of sintered HAp macroporous scaffolds in cation-containing aqueous solutions under varying concentrations, temperatures, and immersion times. It was found that Mg²⁺ and Zn²⁺ adsorption was relatively consistent when compared with Sr²⁺, which lacked reproducibility. The second strategy involved immersing the scaffolds in the reaction medium, where the wet precipitation of cation-substituted HAp was occurring. This resulted in the deposition of a cation-substituted secondary HAp layer onto the sintered HAp scaffold surface. This approach yielded higher incorporation efficiency for Mg2+ and produced rough, irregular coatings, which are expected to enhance osseointegration. The third strategy utilized biomimetic coating methods by immersing the scaffolds in simulated body fluid (SBF) that is ten times more concentrated (10x SBF) and enriched with target cations. Sr²⁺ incorporation using this strategy was promising, and the molar substitu-tion percentages were found to increase over time, whereas Zn²⁺ incorporation was hindered by bulk precipitation and resulting in the formation of unintended phases.
Overall, the most effective technique for each cation was found to vary, with wet precipi-tation being the most effective for Mg²⁺ incorporation, biomimetic coating for Sr²⁺, and ion adsorption for Mg²⁺ and Zn²⁺. These findings demonstrate potential for functionalizing sin-tered HAp scaffolds with a variety of cations to improve their biological properties via the release of therapeutic ions without compromising their structural integrity. Although this in-vestigation serves only as a preliminary study that demonstrates the potential of post-synthesis ion-incorporation techniques, further investigations are needed to confirm their efficacy. Future work should focus on advanced characterization, ion release studies, and biological evaluations to validate their efficiency for use in manufacturing of scaffolds intended for clinical applications.