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Numerous organs in the bodies of animals, including the lung, kidney, and mammary gland, contain ramified networks of epithelial tubes. These structures arise during development via a process known as branching morphogenesis. Previous studies have shown that mechanical forces directly impact this process, but the patterns of mechanical stress exerted by branching embryonic epithelia are not well understood. This is, in part, owing to a lack of experimental tools. Traditional traction force microscopy assays rely on the use of compliant hydrogels with well-defined mechanical properties. Isolated embryonic epithelial explants, however, have only been shown to branch in three-dimensional matrices of reconstituted basement membrane protein, or Matrigel, a biomaterial with poorly characterized mechanical behavior, especially in the regime of large deformations. Here, to compute the traction stresses generated by branching epithelial explants, we quantified the finite-deformation constitutive behavior of gels of reconstituted basement membrane protein subjected to multi-axial mechanical loads. We then modified the mesenchyme-free assay for the ex vivo culture of isolated embryonic airway epithelial explants by suspending fluorescent microspheres within the surrounding gel and tracking their motion during culture. Surprisingly, the tracked bead motion was non-zero in regions of the gel far away from the explants, suggestive of passive swelling deformations within the matrix. To compute accurate traction stresses, these swelling deformations must be decomposed from those generated by the branching explants. We thus tracked the motion of beads suspended within cell-free matrices and quantified spatiotemporal patterns of gel swelling. Taken together, these passive swelling data can be combined with the measured mechanical properties of the gel to compute the traction forces exerted by intact embryonic epithelial explants.

Dermal sinus is more commonly associated with intradural dermoid than an epidermoid cyst. Conus epidermoid cyst with dermal sinus is a rare entity. We are presenting a rare case of infected conus epidermoid cyst along with the dermal sinus in an 18-month-old girl presented with flaccid paraparesis with sphincter dysfunction and timely intervention leads to complete recovery. We had searched PubMed for previously reported similar cases and did a case-based review of the literature. This 18-month-old girl with discharging lumbosacral sinus with fever since 3 days presented with flaccid paraparesis with sphincter dysfunction. Preoperative magnetic resonance imaging (MRI) showed a large enhancing lesion from L1-S1 along with the dermal sinus tract. Complete excision of the cyst along with the sinus tract, followed by long-term antibiotic therapy. The excision of the infected cyst was done through myelotomy under neuromonitoring, while some part of the capsule densely adherent to the neural tissue was left behind. The patient gradually improved following surgery and motor power of the lower limbs were $$ \raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$5$}\right. $$ while going home. Histopathology revealed epidermoid cyst with secondary inflammatory tissue. Follow-up MRI of the spine showed excision of the dermal sinus tract and cyst with postoperative changes. At 1-year follow-up, the patient was asymptomatic without any focal deficits. Early surgical intervention followed by long-term antibiotic therapy is a must for good functional recovery in patients of an infected dermal sinus tract with associated cyst. While excising cyst through myelotomy, some part of the capsule densely adherent to neural tissue may be left behind. Regular follow-up in the first year of surgery is essential to look for the recurrence of the lesion.