Hydroxyapatite scaffolds processed using a TBA-based freeze-gel casting/polymer sponge technique

Abstract

A novel freeze-gel casting/polymer sponge technique has been introduced to fabricate porous hydroxyapatite scaffolds with controlled "designer" pore structures and improved compressive strength for bone tissue engineering applications. Tertiary-butyl alcohol (TBA) was used as a solvent in this work. The merits of each production process, freeze casting, gel casting, and polymer sponge route were characterized by the sintered microstructure and mechanical strength. A reticulated structure with large pore size of 180-360 microm, which formed on burn-out of polyurethane foam, consisted of the strut with highly interconnected, unidirectional, long pore channels (approximately 4.5 microm in dia.) by evaporation of frozen TBA produced in freeze casting together with the dense inner walls with a few, isolated fine pores (<2 microm) by gel casting. The sintered porosity and pore size generally behaved in an opposite manner to the solid loading, i.e., a high solid loading gave low porosity and small pore size, and a thickening of the strut cross section, thus leading to higher compressive strengths.

Biomimetic Materials by Freeze Casting

“…Fu et al 42 proved that freeze-cast HA with lamellar ($25 lm wide) and cellular ($100 lm in diameter) architectures are able to support the proliferation of preosteoblastic cells (MC3T3-E1) in vitro. By investigating the two types of pore architectures, it was demonstrated that the scaffolds with cellular pores showed far better cell proliferation, differentiation, and migration, suggesting that larger pores (>50 lm) are [19,20,56,91,95,97,103]. Fig.…”

“…2i). 56,[78][79][80][81][82] Modifying the freeze conditions is another alternative to control the microstructures of freeze-cast scaffolds. Munch et al 71 showed that patterning the freezing surface can manipulate the long-range ordering of ice lamellae by controlling the initial direction of nucleation.…”

“…19 Figure 3d shows an artificial scaffold fabricated by a modified method that combines freeze gel casting and the polymer sponge technique, mimicking the trabecular architecture of cancellous bone. 56 Nacre is composed of $95 wt.% aragonite platelets (or tiles) embedded in an organic matrix of chitin. 94 Commonly described as a ''brick-and-mortar'' structure, the aragonite platelets are ''bricks'' that are self-assembled and ''glued'' together by the chitin biopolymer matrix.…”

Potential Bone Replacement Materials Prepared by Two Methods

“…water), is directionally frozen in a mold, then sublimated to remove the frozen liquid phase and sintered to densify the porous ceramics [16]. Several research groups have developed varying techniques for freeze-casting biocompatible ceramics, such as HA, for potential tissue engineering applications [17][18][19][20][21][22][23][24][25][26][27][28][29].…”

Untitled

“…The methods include uniaxial compaction [198,199], isostatic pressing (cold or hot) [200][201][202][203][204][205][206], granulation [207,208], loose packing [209], slip casting [210][211][212][213], gel casting [188,189,[214][215][216][217][218][219], pressure mold forming [220], injection molding [221], polymer replication [222][223][224][225], extrusion [226][227][228], slurry dipping and spraying [229], as well as to form ceramic sheets from slurries tape casting [124,216,230,231] doctor blade [232] and colander methods might be employed [194][195][196][197]233]. A combination of several techniques is also possible [216,234]. Furthermore, some of these processes might be performed under the magnetic field, ...…”