We predicted and measured the evolution of smooth muscle cell (SMC) orientation in media-equivalents (MEs) for four fabrication conditions (F-, M-, F+, M+) under Free or Mandrel compaction (F/M) with and without magnetic prealignment of the collagen fibrils in the circumferential direction (+/-). Mandrel compaction refers to SMC-induced compaction of the ME that is constrained by having a nonadhesive mandrel placed in the ME lumen. Predictions were made using our anisotropic biphasic theory (ABT) for tissue-equivalent mechanics. Successful prediction of trends of the SMC orientation data for all four fabrication cases was obtained: maintenance of the initial isotropic state for F-, loss of initial circumferential alignment for F+, development of circumferential alignment for M-, and enhancement of initial circumferential alignment for M+. These results suggest two mechanisms by which the presence of the mandrel leads to much greater mechanical stiffness in the circumferential direction reported for mandrel compacted MEs relative to free compacted MEs: (1) by inducing an increasing circumferential alignment of the SMC and collagen, and (2) by inducing a large stress on the SMC, resulting in secretion and accumulation of stiffening components.