CRANIOFACIAL AND DENTAL TISSUE - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 197

9.4.1 SCAFFOLDS
Artificial scaffold materials for craniofacial/dental tissue regeneration may act like the extracellular
matrix of the desired tissue by supporting cell attachment, proliferation, and differentiation of host
or seeded cells in the presence of biological cues. The scaffolds are commonly resorbable and are ex-
pected to resorb at a rate similar to that of new bone formation ( Hutmacher, 2000 ). These scaffolds can
be used in different forms such as porous 3D solids ( Dean et al., 2012 ; Kim et al., 2011 ), nanofibers
( Gupte and Ma, 2012 ; Li et al., 2014 ), cement/putty ( Kim et al., 2012a ), among others . Various types
of scaffolds used for craniofacial/dental tissue regeneration can be divided into three main classes:
ceramic/bioactive glasses, natural/synthetic polymers, and composites ( Salgado et al., 2004 ). Illustra-
tions of all three scaffold material classes follow:
9.4.1.1 Ceramic/bioactive Glasses
The ceramic/bioactive glasses are a class of biomaterials made up of inorganic materials having high
compressive strength, but low tensile strength (brittle) characteristics. Calcium phosphate-based ma-
terials have been extensively used for craniofacial/dental tissue engineering in the form of injectable
calcium phosphate cement (CPC) ( Chen et al., 2014 ; Thein-Han et al., 2012 ) or implanted scaffolds
( Chan et al., 2009 ). Hydroxyapatite in the form of BoneSource ® cement (Stryker, Kalamazoo, MI)
has also been used for applications in craniofacial tissue engineering and reconstruction ( Costantino
et al., 1992 ; Friedman et al., 1998 ). Hydroxyapatite scaffolds prepared by additive manufacturing
(a.k.a. 3D printing) have been studied for their repair capability in minipig mandibular defects for 6
and 18 weeks ( Hollister et al., 2005 ). Bioactive glasses have also been studied as biomaterials for
craniofacial reconstruction ( Cho and Gosain, 2004 ; Gosain, 2004 ). One exciting new product which
promises to be quite adaptive is being developed by Filardo et al . Using a novel bioceramization pro-
cess, they have been able to turn wood into a strong, highly porous product with an elastic modulus that
approaches that of bone ( Filardo et al., 2014 ).
9.4.1.2 Natural/synthetic Polymers
Biopolymers can be prepared synthetically or from naturally occurring sources. Polymers tend to be more
flexible or ductile in nature than ceramics, although they usually have less compressive strength than
ceramics. Biopolymers derived from natural sources used for craniofacial regeneration include collagen
( Narotam et al., 2007 ), fibrin, hyaluronic acid ( Kretlow et al., 2009 ), alginate, silk ( Ye et al., 2011 ), and
chitosan ( Canter et al., 2010 ). Biopolymers of synthetic origin studied in bone tissue engineering ap-
plications include poly(propylene fumarate) (PPF) ( Dean et al., 2012, 2003b ), polylactic acid (PLA) ( Di
Bella et al., 2008 ), polyglycolic acid (PGA), poly(lactic-co-glycolic acid) (PLGA) ( Kaigler et al., 2006 ),
polycaprolactone (PCL) ( Schantz et al., 2003 ), and polyethylene glycol ( Terella et al., 2010 ). Most of
these biopolymers have also been used for dental tissue engineering ( Horst et al., 2012 ).
9.4.1.3 Composites
Blending ceramic, polymeric, and possibly metal or graft tissue components may result in an implant
with the desired material properties that is at least partially resorbable. Polymers and ceramics are
most likely to mimic bone extracellular matrix which in itself is a blend of inorganic (hydroxyapatite)
and organic (collagen type I) components. Some of the composites that have been used in various
combinations for craniofacial/dental tissue engineering are: beta-tricalcium phosphate, collagen, and
autologous bone fragments ( Kishimoto et al., 2006 ); polycaprolactone (PCL)-tricalcium phosphate