Table 1.

Design criteria for tissue engineering scaffolds.

Requirements	Description
(i) Geometry	It must initially fill complex 3-D defects, subsequently guiding the tissue to match the original 3-D anatomy
(ii) Bioactivity	Stimulation of rapid tissue attachment to the implant surface (without formation of scar/fibrous tissue) and creation of a stable long-term bonding that prevents micromotion at the interface and the onset of an inflammatory response
(iii) Biocompatibility	Ability to support normal cellular activity including molecular signaling systems without any local and/or systemic toxic effects to the host tissue
(iv) Chemical and biological stability/biodegradability	Depending on the specific application; if the scaffold must remain in situ indefinitely, materials with high stability must be selected; conversely, if it is intended to be a temporary device, the scaffold must degrade gradually over a predetermined period of time and be replaced by the natural host tissue
(v) Porous structure	The scaffold must possess an interconnected porous structure with a large surface-to-volume ratio and pore size of at least 100 μm in diameter (ideal for bone repair) to allow cell penetration, tissue in-growth, facilitate vascularization of the construct, and nutrient transport
(vi) Mechanical competence/compliance	The mechanical performance of the scaffold, which is determined by both the properties of the biomaterial and the porous structure, must be sufficient to withstand implantation handling and support the loads and stresses that the new tissue will ultimately bear. Adequate elastic compliance (low stiffness) with soft tissue is required for non-osseous applications
(vii) Biological properties	Special properties, such as the promotion of angiogenesis, stimulation of cell differentiation, and antibacterial effect, can be achieved by the release of appropriate ions from the scaffold material. These added values are typically imparted to bioactive glass scaffolds by carefully designing the glass composition
(viii) Fabrication	The scaffold should be easily tailored in size and shape to the diseased or injured area that the new tissue will replace
(ix) Commercialization potential	The scaffold should be produced with an automated technique in a reproducible manner; it should be fabricated and sterilized according to international standards for commercial production and clinical use