Inorganic and Composite Bioactive Scaffolds for Bone Tissue Engineering - Biomaterials Fabrication and Processing - page 4

1.4.2.4 Microsphere Sintering................................................................................... 31
1.4.2.5 Foam Coating................................................................................................ 31
1.5 Surface Functionalization ....................................................................................................... 32
1.5.1 Protein Adsorption ...................................................................................................... 32
1.5.2 Silane-Modifi ed Surfaces (Silanization Technique).................................................... 32
1.5.3 Topography (Roughness) Modifi cation ....................................................................... 33
1.5.4 Polymer Coatings ........................................................................................................ 33
1.6 Conclusions ............................................................................................................................. 33
References ........................................................................................................................................ 34

1.1 INTRODUCTION
Being a modern discipline, tissue engineering encounters various challenges, such as the develop-
ment of suitable scaffolds that temporarily provide mechanical support to cells at an early stage of
implantation until the cells are able to produce their own extracellular matrix (ECM) [1]. Numerous
biomaterials and techniques to produce three-dimensional (3-D) tissue-engineering scaffolds have
been considered; biomaterials include polymers, ceramics, and their composites, as discussed in the
literature [1-3]. In this chapter, we present an up-to-date summary of the fabrication technologies
for tissue-engineering scaffolds, including the choice of suitable materials and related fabrication
techniques, with a focus on the development of synthetic scaffolds based on bioceramics, glasses,
and their composites combined with biopolymers for bone regeneration. Being one of the most
promising technologies, the replication method for the production of highly porous, biodegrad-
able, and mechanically competent Bioglass ® -derived glass-ceramic scaffolds is highlighted. The
enhancement of scaffold properties and functions by surface modifi cation is also discussed, and
examples of novel approaches are given.

1.2 DESIGN OF 3-D SCAFFOLDS
In an organ, cells and their ECM are organized into 3-D tissues. Therefore, in tissue engineering
a highly porous 3-D matrix (i.e., scaffold) is necessary to accommodate cells and to guide their
growth and tissue regeneration in 3-D structures. This is particularly relevant in the fi eld of bone
tissue engineering and regeneration, bone being a highly hierarchical 3-D composite structure.
Moreover, the structure of bone tissue varies with its location in the body. So the selection of
confi gurations as well as appropriate biomaterials depends on the anatomic site for regeneration,
the mechanical loads present at the site, and the desired rate of incorporation. Ideally, the scaffold
should be porous enough to support cell penetration, tissue ingrowth, rapid vascular invasion, and
nutrient delivery. Moreover, the matrix should be designed to guide the formation of new bones in
anatomically relevant shapes, and its degradation kinetics should be such that the biodegradable
scaffold retains its physical (e.g., mechanical) properties for at least 6 months (for in vitro and in vivo
tissue regeneration) [1,3]. Important scaffold design parameters are summarized in Table 1.1.
The design of highly porous scaffolds involves a critical issue related to their mechanical prop-
erties and structural integrity, which are time dependent. For example, it has been reported that
the compressive strength of hydroxyapatite scaffolds increases from 30 MPa because of

tissue ingrowth in vivo [5]. This fi nding leads to a conclusion that it might not be necessary to have
a starting scaffold with a mechanical strength equal to that of a bone, because cultured cells on the
scaffold in vitro will create a biocomposite and increase the strength of the scaffold signifi cantly.
Another factor that affects scaffold design is the need for vascularization and angiogenesis
in the constructs [6]. In vitro engineering approaches face the problem of critical thickness while
regenerating tissue in the absence of true vascularization: mass transportation into tissue is dif-
fi cult beyond a thin peripheral layer of a tissue construct even if artifi cial means are used to supply
nutrients and oxygen [7]. Diffusion barriers that are present in vitro are most likely to become more

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