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Solution ripening of hydroxyapatite nanoparticles: effects on electrophoretic deposition
M Wei1, A J Ruys, B K Milthorpe
1School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia.
Journal of Biomedical Materials Research
|July 9, 1999
Summary
Developing crack-free hydroxyapatite (HAp) coatings for metal implants is crucial. Optimizing nanoparticulate HAp through aging or boiling in its mother liquor prevents cracking during low-temperature densification.
Area of Science:
- Biomaterials Engineering
- Materials Science
- Nanotechnology
Background:
- Electrophoretic deposition (EPD) is a cost-effective method for hydroxyapatite (HAp) coatings on metal implants.
- High-temperature sintering (≥1200°C) for densification causes detrimental reactions between HAp and metal substrates (e.g., titanium, stainless steel), degrading implant strength.
- Low-temperature sintering (900°C–1050°C) using nanoparticulate HAp leads to coatings prone to cracking due to high drying shrinkage.
Purpose of the Study:
- To develop a method for producing crack-free nanoparticulate HAp coatings suitable for low-temperature sintering.
- To investigate the effect of post-precipitation processing on the microstructure and coating integrity of HAp nanoparticles.
Main Methods:
- Precipitation of nanoparticulate HAp using a metathesis reaction: 10Ca(NO3)2 + 6NH4H2PO4 + 8NH4OH.
- Optimization of approximately 30 nm HAp nanoprecipitates via Ostwald ripening through boiling or ambient aging in the mother liquor.
- Evaluation of coating crack formation after drying and low-temperature sintering.
Main Results:
- As-precipitated HAp nanoparticles formed highly agglomerated, gel-like structures, resulting in severely cracked coatings after drying.
- Boiling for 2 hours or ambient aging for 10 days transformed the gel-like mass into unagglomerated nanoparticles.
- Ambient aging completely eliminated coating cracks, while boiling only reduced cracking, suggesting crack elimination is linked to deagglomeration rather than particle growth.
Conclusions:
- Optimizing nanoparticulate HAp via ambient aging in the mother liquor is a viable strategy to produce crack-free coatings for low-temperature sintering.
- This approach overcomes the limitations of traditional high-temperature sintering, preserving implant integrity.
- The findings enable the development of improved HAp-coated metal implants with enhanced biocompatibility and mechanical properties.