Biomedical Engineering Reference
In-Depth Information
220-240 °C and a glass transition temperature of 58-85 °C (
Tan et al
.
, 2005
). Polycaprolactone (PCL)
is also a semicrystalline polyester with a melting point of 55-60 °C and a glass transition temperature
of
−
60 °C. It could be hydrolytically degraded due to the presence of hydrolytically labile aliphatic
ester linkages. The degradation rate is about 2-3 years (
Nair and Laurencin, 2007
). Poly (L-lactic)
acid (PLLA) has a melting point of 172.2-186.8 °C and a glass transition temperature of 60.5 °C (
Tan
et al
.
, 2005
). The mineral component of bone is calcium phosphate. Hydroxyapatite (HA) is one of the
synthetic calcium phosphate ceramics. The bioceramic is widely used because it is chemically similar
to the inorganic component of hard tissues. HA theoretically consists of 39.68 wt% Ca and 18.45 wt%
P. It is more stable compared to other calcium phosphate ceramics within a pH range of 4.2-8.0 (
Best
et al
.
, 2008
).
Nanocomposites of bioceramic and biodegradable polymer are often sintered to facilitate prolif-
eration of and alkaline phosphatase activity expression by human osteoblast-like cells (SaOS-2). Poly
(hydroxybutyrate) (PHB) is a naturally occurring polyester by bacteria. The polymer has a melting point
of 160-180 °C. The copolymer of PHB and hydroxyvalerate is poly (hydroxybutyrate-co-hydroxyval-
erate) (PHBV), which is a semicrystalline polymer with a melting temperature lower than PHB. The
glass transition temperature of PHBV is in the range of
−
5-20°C (
Nair and Laurencin, 2007
). Calcium
phosphate (Ca-P)/PHBV and carbonated hydroxyapatite (CHA)/ PLLA nanocomposites have been em-
ployed to fabricate tissue engineering scaffolds (
Duan et al
.
, 2010
). In addition, titanium powder has
been sintered to form bone scaffolds (
Liu et al.
,
2013
).
2.3.2
GEL-BASED BIOMATERIALS
Gel-based biomaterials are widely used in additive biomanufacturing processes. Collagen gel or Matri-
gel
®
is coated on the substrate to help cells adhere to the substrate; for three-dimensional patterning,
Matrigel
®
is layered on top of the first pattern in the LGDW method (
Odde and Renn, 2000; Nahmias
et al.
,
2005; Nahmias and Odde, 2006; Narasimhan et al.
,
2004; Rosenbalm et al.
,
2006
). Alginate hy-
drogel is used in the LIFT method to encapsulate cells (
Koch et al.
,
2009, 2012; Gruene et al.
,
2010
).
MAPLEDW transfers biomaterials containing cells from transparent quartz support to a receiving
substrate. Matrigel
®
was used as the cell-containing matrix and laser absorptive layer (
Ringeisen
et al.
,
2004; Patz et al.
,
2006
). Bioceramic ribbon is also used by solvating hydroxyapatite and zirconia
powders in glycerol/water matrices and spin coating this solution (
Doraiswamy et al.
,
2007
). BioLP is
an improved version of MAPLEDW, since it employs quartz support coated by a metal or metal oxide,
which eliminates the direct interaction of laser and biomaterials. A ribbon consists of three layers, opti-
cal transparent quartz, metal or metal oxide laser absorptive layer, and cell solution having cells, cell
culture medium, and glycerol or methyl-cellulose. Glycerol and methyl-cellulose were used to reduce
evaporation of biological materials. Cell solution was transferred onto substrate coated by Matrigel
®
(
Barron et al.
,
2004, 2005; Pirlo et al.
,
2012; Othon et al.
,
2008
).
The types of hydrogels utilized for structure fabrication using light-assisted bioprinting include,
but are not limited to, poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) dimethacrylate
(PEGDMA), methacrylamide-modified gelatin (GelMOD), gelatin methacrylate (GelMA), and glyc-
idyl methacrylate modified hyaluronic acid (GMHA). Among these, PEGDA, GelMA, and GMHA are
the most extensively used (
Hribar et al.
,
2014
).
PEGDA hydrogels, with their superior biocompatibility, high water retention ability, and tunable
mechanical properties, in particular stiffness retention, serve as excellent candidates for synthetic
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