Biomedical Engineering Reference
In-Depth Information
higher dosages of drugs, protein, or DNA molecules into the hierarchical
structures and release them at a controlled rate (Zhang, Cheng, et al. 2009;
Zhang, Yang, et al. 2009; Lin, Chang, and Zhu 2011; Lin, Zhou, et al. 2011;
Wu et al. 2011). Furthermore, the 3D architectured materials can be used as
injectable bone regeneration biomaterials and cell- or drug-loaded implants,
which are superior to particles. Therefore, the fabrication of nanostructured
biomaterials with novel 3D architectures is of great importance for enhancing
performances and expanding applications of them in biomedical fields. The
traditional strategy to synthesize the 3D architectured inorganic biomateri-
als is focused on the surfactant assistant assembled approach (He et al. 2007;
Ma and Zhu 2009; Wang et al. 2009; Zhang, Chang, et al. 2009; Zhang, Yang,
et al. 2009; Cheng et al. 2010; He et al. 2010). As a recently developed concept,
the self-assembly technologies using nanoparticles, nanorods, nanobelts, and
nanosheets as building blocks have been shown to be an efficient “bottom-
up” route to fabricate functional materials with different morphologies and
architectures (Corma et al. 2004; Lu et al. 2004). The surfactant assistant self-
assembly method has been considered the most effective method to control
the morphology and architectures of the functional materials. The surfactant
as a capping reagent plays an important role in the process of self-assembly or
oriented aggregation, facilitating the formation of special morphologies and
hierarchical superstructures to reduce the surface energy and thus the total
system energy, through the dipole-dipole interaction or van der Waals forces.
Moreover, it was revealed that the very short ligand greatly decreased the dis-
tance between the primary particles and thereby enhanced the dipole interac-
tion between them (Narayanaswamy et al. 2006; Lin, Chang, et al. 2009). On
the other hand, the van der Waals attractions between the surfactant and the
nanoparticles could also be responsible for the morphology evolution.
Using EDTA, Na 2 EDTA, and CA, for example, as the chelate and template-
directed reagents, and usually using urea as the homogeneous precipitate
reagent, the apatite materials with dandelion-like (Lak et al. 2008), porous
(He and Huang 2007, 2009), dumbbell-like (Chen et al. 2006), flowerlike
(Chen et al. 2006), and hollow nanostructures constructured by rods, whis-
kers, and nanosheets were successfully synthesized via the hydrothermal
process. The studies showed that the template and chelate type, pH values,
and temperatures play important roles in modulating the architectures of
the products. He and Huang (2009) found that the template Na 2 EDTA altered
the natural growth habit of carbonated HAp (CHAp) and induced the first
dendritic growth of CHAp nanoflakes on the surface of OCP, and the organic
conditioner glycerol controlled the second dendritic growth of CHAp nano-
flakes on the bigger ones. Higher concentrations of glycerol resulted in a
higher surface fractal dimension, smaller pore diameter, and greater specific
surface area. Chen et al. (2009) found that the morphology of fluorapatite
(FHAp) nanocrystal was highly dependent on the pH value and nature of
chelating reagent. In the case of CA, two main morphologies of FHAp nano-
crystals were observed as the pH value varied from 3.6 to 10.0. At low pH 3.6,
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