MICROENGINEERED POLYMER-AND CERAMIC-BASED BIOMATERIAL SCAFFOLDS: A TOPICAL REVIEW ON DESIGN, PROCESSING, AND BIOCOMPATIBILITY PROPERTIES - Micro and Nanotechnologies in Engineering Stem Cells and Tissues - page 86

TABLE 4.1 Pore Size Distribution for an Ideal Scaffold in Bone Tissue Engineering
Applications

Pore Size Biological Function

< 1 m m

Protein interaction; responsible for bioactivity

1-20 m Cell attachment; their orientation of cellular growth (directionally)

m

100-1000 m m Cellular growth and bone ingrowth

> 1000 m m

Shape and functionality of implant

Idea adapted from Ref. [29].

mechanical strength of pure HA has hampered its use as a bone implant material
because of conflicting requirements of porosity and strength.
Porous HA exhibits strong bonding to the bone; the pores provide a mechanical
interlock leading to a firm fixation of the material. Bone tissue grows well through
the pores, thus increasing strength of the HA implant in vivo. The ideal bone
substitute material should form a secure bond with the tissues by encouraging new
cells to grow and penetrate. New tissue and bone formation can easily take place on
osteophilic and porous implant and also helps to prevent loosening and movement of
the implant. When pore sizes exceed 100

m, the bone grows through the channels of
interconnected surface pores, thus maintaining the bone's vascularity and viability.
The application of implant depends on the pore size, as summarized in Table 4.1. 29
Because porous HA is more resorbable and more osteoconductive than dense HA,
there is an increasing interest in the development of synthetic porous HA bone
replacement material for the filling of both load-bearing and nonload-bearing
osseous defects. In terms of simulating the human bone structure, porous HA
scaffold has a large surface area, which is beneficial for adhesion of biological
cells and growth of new bone phase.

m

4.3 PROPERTY REQUIREMENT OF POROUS SCAFFOLD

Scaffold properties depend primarily on the nature of the biomaterial and the
fabrication process. The scaffolds are based on various materials, such as metals,
ceramics, glass, chemically synthesized polymers, natural polymers, and combina-
tions of these materials to form composites. The properties and requirements for
scaffolds in bone tissue engineering have been extensively reviewed; recent exam-
ples include aspects of degradation, 30-33 mechanical properties, 34-38

cytokine

delivery, 39-43 and combinations of scaffolds and cells. 44,45
Porosity is defined as the percentage of void space in a solid, 46 and it is a
morphological property, independent of the material. Pores are necessary for bone
tissue formation because they allow migration and proliferation of osteoblasts and
mesenchymal cells as well as vascularization. 47 In addition, a porous surface
improves mechanical interlocking between the implant biomaterial and the sur-
rounding natural bone, providing greater mechanical stability at the critical inter-
face. 48 The most common techniques used to create porosity in a biomaterial are salt