PLGA/PCL Micro-scaffold with Gradient Stiffness

The structural backbone of the engineered follicle is a melt-electrowritten (MEW) PLGA(75:25)/PCL biphasic micro-scaffold, fabricated as a cylindrical lattice 0.9 mm OD × 4 mm. The MEW process holds fiber diameter at 18 ± 3 µm and produces interconnected porosity in the 50–150 µm range, validated by micro-CT (Bruker SkyScan 1272, 2 µm voxel).

A graded stiffness profile is achieved by progressively decreasing the PCL fraction along the apico-basal axis (upper bulge region 25 % PCL → lower bulb region 5 % PCL). This produces a measured compressive modulus gradient from 1.8 MPa apically to 0.18 MPa basally, mimicking the natural mechano-environment between rigid outer root sheath and compliant papilla.

Encapsulated PLGA microspheres (Ø 12 µm) carrying VEGF-165, PDGF-BB, and TGF-β3 are embedded in the basal third of the scaffold during the post-print solvent-annealing step. Degradation in vivo proceeds biphasically: PLGA mass loss 50 % at ≈ 6 weeks, PCL skeleton persisting beyond 12 weeks to provide mechanical support during follicular maturation.