Porous hydroxyapatite scaffolds produced by the combination of the gel-casting and freeze drying techniques

Abstract

A technique combining gel-casting and freeze drying methods is introduced to prepare porous hydroxyapatite scaffolds which allow for better control of the scaffold microstructure and have improved mechanical properties. A monomeric system which is known to be a suitable gelling agent for setting ceramic suspensions into dense forms was selected to produce ceramic foams. Different concentrations of sodium lauryl sulphate solution were added into the hydroxyapatite gel suspension as a pore former. The effect of the solid content on the mechanical properties of the scaffold was also investigated. Rapid freezing with liquid nitrogen was performed according to the freeze drying technique and the porous structure and morphology of the scaffolds were analyzed by scanning electron microscopy. The mechanical properties of the hydroxyapatite scaffolds were determined by testing compressive strength using a universal testing machine. The prepared scaffolds were characterized by well-defined pore connectivity along with directional, uniform and completely open porosity. The maximum compressive strength of about 17 MPa obtained from the suspension consisted of 50% solid content with 20% concentration of sodium lauryl sulphate solution. The results show that sodium lauryl sulphate solution plays a significant role in changing the pore structure of hydroxyapaite scaffolds in systems having high solid content.

Structure control of hydroxyapatite ceramics via an electric field assisted freeze casting method

“…However, results indicated that the HA scaffolds with lamellar pores had a low adsorption rate of the bone cells [10]. To overcome this, HA scaffold with spherical pores was prepared by Monmaturapoj et al [11]. Unfortunately, the pores of the HA scaffolds with single spherical pores were poorly connected, limiting the growth and reproduction of bone cells [12].…”

Macroporous Ceramics by Gelation–Freezing Route Using Gelatin

“…[57] By using organic polymer in freeze casting routes, the ice crystal growth during freezing is adjustable, leading to the well-controlled pore size and morphology. Porous mullite, [60] porous yttria-stabilized ziroconia (YSZ) [14] porous alumina, [61,62] porous silicon nitride, [63] and porous hydroxyapatite [64] have been fabricated by freezedrying process with addition of polyvinyl alcohol (PVA), which suppresses ice crystal growth and reduces the pore sizes substantially. Tert-butyl alcohol (TBA) and acrylamide (AM) have been used as gelation agents for preparing porous alumina and silica via freeze-drying process; [57][58][59] TBA that freezes below 25°C and volatilizes rapidly above 30°C acts as the freezing vehicle and template for forming pores, while AM is polymerized in the slurry as the gelation agent, strengthening the green bodies substantially.…”

“…Tert-butyl alcohol (TBA) and acrylamide (AM) have been used as gelation agents for preparing porous alumina and silica via freeze-drying process; [57][58][59] TBA that freezes below 25°C and volatilizes rapidly above 30°C acts as the freezing vehicle and template for forming pores, while AM is polymerized in the slurry as the gelation agent, strengthening the green bodies substantially. Porous mullite, [60] porous yttria-stabilized ziroconia (YSZ) [14] porous alumina, [61,62] porous silicon nitride, [63] and porous hydroxyapatite [64] have been fabricated by freezedrying process with addition of polyvinyl alcohol (PVA), which suppresses ice crystal growth and reduces the pore sizes substantially. Porous alumina with oriented pore structures has been produced by freeze casting with a water-soluble polymer such as polyethylene glycol (PEG).…”

Inorganic Cryogels

“…Since the size of the pores can be varied by changing the crystallization conditions, the materials are suitable for the synthesis of ceramic scaffolds. The oriented character of the porosity leads to an anisotropy in the mechanical properties of such ceramics that is similar to the anisotropy of natural bones [132,[174][175][176][177][178]. The most significant progress in this direction was achieved by the development of hydroxyapatite (HAP) ceramics with a compression strength close to that of natural bone [179], and also by the development of tough Al 2 O 3 -PMMA layered nacre-like composites [180].…”