When using the SLA process based on a bottom-up projection approach to fabricate scaffold structures, the actual pores will be smaller than the desired size both in the *XY* plane and along the *Z* direction due to the overcure of liquid resin in both width and depth. For simplicity, assume the overcure along the *X*/*Y* direction in the *XY* plane is proportional to the feature's *XY* lengths with a ratio *η*_{xy}, and the overcure along the *Z* direction is equal to (*D*_{p} − *δ*), which occurs at the overhung features as shown in Fig. 3(b). *D*_{p} is the cure depth of the material and *δ* is the layer thickness. Accordingly, in the actually fabricated structures using the SLA process, the strut width will increase from *b* to *b*(1* + η*_{xy}), and the edge length of each pore will decrease from *a* to (*a* − *b η*_{xy}). The thickness of the first layer of the scaffold keeps constant at *b*, but all the other layers increase from *b* to *b + D*_{p} − *δ* and the distance between two neighboring layers decrease from *a* to (*a* − *D*_{p} + δ). Hence, the actual porosity of the fabricated scaffolds can be calculated as
Display Formula

(2)$\phi =(a\u2212b\eta xy)2(bn2+bn3+an3)+2(a\u2212Dp+\delta )(a\u2212b\eta xy)b(1+\eta xy)n2(n+1)(n\u22c5a+n\u22c5b+b+b\eta xy)2(n\u22c5a+n\u22c5b+b)$

The pore sizes used in scaffolds for tissue engineering are typically designed in the range of 100–600 *μ*m in order to obtain desired outcomes for tissue ingrowth and new bone formation [17]. Hence, the following constraints need to be satisfied for the designed scaffolds:
$a\u2212b\eta xy\u2208[100,600]\mu m$

$a\u2212Dp+\delta \u2208[100,600]\mu m$

$\eta xy\u2208[0,1]$

$\eta xy=f(b)$