Demand for skin replacements is rapidly increasing as burn and full-thickness wounds are difficult to repair due to the low regeneration capability of innate tissues, as well as the physical drawbacks associated with currently available substitutes. To address this need, an emerging 3D printing technique, melt-electrowriting (MEW) was used to create novel bioactive scaffolds to promote skin regeneration. Polycaprolactone (PCL), a bioresorbable and biocompatible, synthetic polymer with Food and Drug Administration approval for use in the human body was selected as scaffold material due to its mechanical stability, flexibility, and superior melt processing properties. In order to increase PCL’s biological functionality bioactive milk proteins (MPs) were blended with PCL. To date, this is the first study of its kind detailing the tissue regenerative capacity of PCL containing MPs as bioactive additives for skin regeneration using MEW. The aim of this study was to MEW MP/PCL tissue engineered constructs (TEC) and assess their suitability for generating tissue in vitro. The MPs, lactoferrin (LF) and whey protein (WP), were mixed with PCL individually at varying concentrations (0.05%, 0.1%, 0.25%), and in combination (COMB) at concentrations of 0.25% each. TECs were characterised chemically, physically, and their biological activity assessed in vitro. Physical characterisation of MEW MP/PCL scaffolds showed that reproducible, layered micron range scaffolds could be fabricated; displaying high porosity, low degradation, and rapid protein release. Biological activity, determined via an in vitro skin model using human keratinocytes (HaCaTs) and normal human dermal fibroblasts cells, showed significantly increased cell growth, spreading, and infiltration into LF (0.25%) containing scaffolds and COMB scaffolds when compared to PCL alone (p ≤ 0.05). These findings demonstrated that the combined addition of LF and WP increased the biological activity of MEW PCL scaffolds and could be potentially used as a TEC for deep tissue dermal regeneration.

Figure S1. Schematic of two extrusion-based bioprinting methods. (A,B) The syringe and set of printers on the left are driven pneumatically by using air pressure and the associated syringes lack the graduations necessary for quantifying volumes dispensed. (C) The Hamilton syringe and Organovo bioprinter on the right is driven by direct mechanical force on the plunger. The Hamilton syringe features graduations for exact volume quantification, depicted on the right.