Biomedical Engineering Reference
In-Depth Information
It can be summarized from Table 4.3 that the variation in pore size and open porosity
directly affects the mechanical behavior of the prepared scaffold. The freeze-casting
method provides the highest compressive strength of around 40-145MPa. The lower
strength (
1MPa) of porous constructs was obtained in the polymer sponge method
and gas-foaming process. Recent investigations have shown that porous HA scaf-
folds, with a lamellar-type microstructure and unidirectional pores, can be obtained
by freeze casting of aqueous suspensions.
122,123
<
4.8 OVERVIEW OF BIOCOMPATIBILITY PROPERTIES: EVALUATION
OF POROUS SCAFFOLDS
Karageorgiou and Kaplan
145
investigated the influence of porosity on osteogenesis in
three-dimensional biomaterial scaffolds. It has been seen that the porosity and pore size
of biomaterial scaffolds play critical roles in bone formation in vitro and in vivo. The
minimum requirement for pore size is considered to be
100
m because of cell size
m
and migration requirements. However, pore sizes of
m are recommended
because of enhanced newbone formation and the formation of capillaries. The effect of
these morphological features on osteogenesis in vitro and in vivo, as well as relation-
ships to mechanical properties of the scaffolds, was addressed. In vitro, lower porosity
stimulates osteogenesis by suppressing cell proliferation and forcing cell aggregation.
In disparity, higher porosity and pore size result in greater bone ingrowth in vivo.
The kinetics of bone-like apatite formation on sintered hydroxyapatite in a
simulated body fluid was studied by Kim et al.
146
The surfaces of two HAs, which
have been sintered at different temperatures of 800
C and 1200
C, were investigated
as a function of soaking time in simulated body fluid (SBF) using transmission
electron microscopy (TEM) attached with energy-dispersive spectrometry (EDX)
and laser electrophoresis spectroscopy.
The synthesis of biomimetic Ca-hydroxyapatite powders at 37
C in synthetic
body fluids was reported by Tas.
147
300
m
Initially, HA was prepared as a nanosized
(
50 nm), homogeneous, and high-purity ceramic powder from calcium nitrate
tetrahydrate and diammonium hydrogen phosphate salts dissolved in modified SBF
solutions at 37
C and a pH of 7.4 using a novel chemical precipitation technique. The
synthesized precursors were found to reach a phase purity of 99% easily after 6 h of
calcination in air atmosphere at 900
C after oven-drying at 80
C.
Biocompatibility and osteogenicity of degradable Ca-deficient hydroxyapatite
(CDHA) scaffolds were investigated by Guo and coworkers.
148
They made scaffold
from calcium phosphate cement for bone tissue engineering with a particle-leaching
method. They demonstrated that the CDHA scaffolds with porosity of 81% showed
open macropores with pore sizes of 400-500
m. Thirty-six percent of these CDHA
scaffolds were degraded after 12 weeks in Tris-HCl solution. The results revealed
that the CDHA scaffolds were biocompatible and had no negative effects on the
mesenchymal stem cells (MSCs) in vitro. The CDHA scaffold, after 8 week
implantation in rabbit model shows good in vivo biocompatibility and extensive
osteoconductivity.
m
Search WWH ::
Custom Search