RESOURCES

Abstract
In this study, a novel hybrid scaffold comprising 3D-printed porous polyhydroxybutyrate (PHB), dextran (Dex), and magnesium-doped whitlockite (WL) nanoparticles was developed, which were further enhanced with an electrospun nanofibrous coating composed of Dex and Pluronic F127 (F127) loaded with Sildenafil (Sil) for use in craniofacial regeneration. This design was intended to improve the solubility of sildenafil and enable controlled release. Scanning electron microscopy (SEM) revealed a well-integrated structure between the 3D-printed strands and electrospun nanofibers. The scaffold exhibited sustained release of Sil over 28 days, with mechanical testing showing a compressive strength of 3.70 ± 0.33 MPa and an elastic modulus of 49.04 ± 4.62 MPa. Non-toxicity was confirmed via MTT assay on the MG63 cell line, and qRT-PCR results indicated significantly higher expression levels of collagen I, RUNX2, osteocalcin, VEGF, and CD31 markers associated with osteogenesis and angiogenesis. Following implantation in a rat calvarial defect model, the scaffold demonstrated robust osteogenic activity and new bone tissue formation over an eight-week period. This innovative scaffold design offers a promising solution for overcoming the challenges in craniofacial defect repair by integrating bioactive materials with advanced drug delivery systems, leading to more effective tissue regeneration strategies.

Abstract
Three-dimensional (3D) scaffolds are a critical component in guided-tissue regeneration strategies, particularly in cartilage engineering, by providing an adequate structural and physical environment for seeded cells to proliferate and eventually differentiate. Here we investigate the use of microbial poly(3-hydroxybutyrate-co-3-hydroxyexanoate) (PHBHHx) as polymeric inks for 3D printing of scaffolds and weigh their chondrogenic potential against commonly used poly(ε-caprolactone) (PCL). A set of processing parameters is first optimized for extrusion-based printing of porous PHBHHx and PCL scaffolds with well-defined architectures and without affecting the polymer's physicochemical properties. Mechanical testing results obtained under static compression confirm the fabrication of PHBHHx scaffolds with elastic modulus values comparable to those of human mature cartilage. LIVE/DEAD™ and AlamarBlue assays do not reveal any cytotoxic effect of PHBHHx scaffolds on primary human chondrocytes, which remain viable over 14 days of in vitro static culture. Additionally, real-time RT-qPCR analysis of key chondrogenic markers (i.e., SOX9, COL2A1 and ACAN) suggests chondrocytes retain their phenotype over the studied period, independently of the scaffolding material. Taken together, our results confirm the suitability of PHBHHx scaffolds to support the function of chondrocytes in vitro, opening new opportunities for their application in the field of cartilage tissue engineering.