Abstract
Hierarchically porous hydroxyapatite (HHA) scaffolds were synthesized by template-assisted sol-gel chemistry. Polyurethane foam and a block copolymer were used as templates for inducing hierarchically porous structures. The HHA scaffolds exhibited open porous structures with large pores of 400–600 µm and nanoscale pores of ~75 nm. In comparison with conventional hydroxyapatite (CHA), HHA scaffolds exhibited significantly higher surface areas and increased protein adsorption for bovine serum albumin and vitronectin. Both the HHA and CHA scaffolds exhibited well in vitro biocompatibility. After 1 day, Saos-2 osteoblast-like cells bound equally well to both HHA and CHA scaffolds, but after 7 days in culture, cell proliferation was significantly greater on the HHA scaffolds (p < 0.01). High surface area and hierarchical porous structure contributed to the selective enhancement of osteoblast proliferation on the HHA scaffolds.
Highlights
Due to its chemical and biological similarity to the mineral phase of human bone, synthetic hydroxyapatite (HA) exhibits direct chemical bonding to hard tissue and is bioactive.HA has been widely used for a variety of biomedical applications, including mid-ear and bone implants, artificial vertebrae, and as orthopedic coatings [1,2,3,4]
Materials, calcium nitrate tetrahydrate (Ca(NO3 )·4H2 O, AR), triethyl phosphate (P(OC2 H5 )3, AR), diammonium hydrogen phosphate ((NH4 )2 HPO4, AR), Pluronic F127, polyvinyl alcohol (PVA), and 10× concentrated phosphate buffered saline (10× PBS) all came from Sigma-Aldrich, while anhydrous ethanol was from Merck (Darmstadt, Germany)
The Hierarchically porous hydroxyapatite scaffolds (HHA) scaffolds fabricated in this study showed a distribution of interconnected, open pores with diameters of 400–600 μm (Figure 1b,d), which are likely to be beneficial in facilitating cell infiltration, bone ingrowth and vascularization
Summary
Due to its chemical and biological similarity to the mineral phase of human bone, synthetic hydroxyapatite (HA) exhibits direct chemical bonding to hard tissue (osteointegration) and is bioactive.HA has been widely used for a variety of biomedical applications, including mid-ear and bone implants, artificial vertebrae, and as orthopedic coatings [1,2,3,4]. One popular technique to create open porosity in materials is to incorporate pore creating additives (porogens) These porogens can be crystals or particles of either volatile or soluble substances, such as paraffin [9], NaHCO3 [10,11], gelatin [12,13], or polymethylmethacrylate (PMMA) [14]. Open porosity may be created by replication [6], 3D printing techniques [8,15], a direct foaming technique, or hydrothermal conversion of cuttlebone. These methods inevitably lead to large crystal size and low surface area for various reasons.
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