Artificial Scaffolds and Mesenchymal Stem Cells for Hard Tissues - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 166

Moroni and colleagues synthesized novel polyether-ester co-polymers, such as
poly(poly(ethylene oxide)terephthalate-co-(butylene) terephtalate) (PEOT/PBT),
and studied the influence of porosity, molecular network mesh size and swelling
on dynamic mechanical properties of the corresponding scaffold materials. PEOT/
PBT co-polymers are characterized by high elasticity, robustness, and strength.
In addition, they possess good processability due to a temperature-dependent
cross-linking of hydrophilic poly(ethylene oxide) (PEO) and semi-crystalline
poly(butylene terephthalate) segments. Mechanical properties and biodegradation
rate has been controlled via variation of the molecular weight of the starting
poly(ethylene glycol) segments and the weight ratio of PEO and PBT blocks.
These polyether-ester co-polymers have been investigated for tissue regeneration
and already tested for clinical applications (PolyActive TM , IsoTis Orthopaedics),
i.e., for bone filling materials [ 101 ]. Porous scaffold composite materials based on
synthetic PLA mineralized with calcium phosphate have been designed by Kim
and colleagues. Studies demonstrated a significant influence of scaffold compo-
sition on growth and differentiation of bone marrow-derived MSCs [ 102 ].
Recently, Li and colleagues reported in vitro mineralization and in vivo bone
regeneration studies performed in a rat calvarial defect model using novel
resveratrol-conjugated poly(e-caprolactone) (PCL) composites. The incorporation
of resveratrol results in increased alkaline phosphatase activity of rat bone marrow
stromal cells (BMSCs) and enhanced mineralization of the cell-scaffold com-
posites in vitro. The calvarial defects implanted with resveratrol-conjugated PCL
showed a higher X-ray density than the defects implanted with control PCL. Bone-
like structures, positively immunostained for bone sialoprotein, were shown to be
more extensively formed in the resveratrol-conjugated PCL. Thus, incorporation
of resveratrol into the acrylic acid-functionalized porous PCL scaffold led to a
significant increase in osteogenesis [ 103 ].
3.2 Conventional Scaffold Fabrication Methods
Well-established polymer processing techniques include various moulding and
casting processes, spinning, sintering, and extrusion techniques. The fabrication of
3D scaffolds includes the generation of pores via particle or selective leaching,
phase separation and different gas forming methods, and various textile formation
processes such as braiding, weaving, and knitting. Polymers have been investi-
gated in form of foams, sponges, gels, and hydrogels as scaffold and release
materials to deliver biologically active agents inducing tissue growth factors, as
reviewed in detail by Sachloz and Moroni [ 96 , 101 ].
Gels and Hydrogels are the most widely used scaffold materials providing the
possibility of encapsulating cells, i.e., to generate engineered cartilage or to protect
beta-cells against the immune system in type 1 diabetic patients. Hydrogels
made from both non-resorbable polymers such as polyesters and polyamides and
biodegradable polymers based on collagen, glycolic acid, lactic acid or hyaluronic