3D printed bioinspired scaffolds integrating doxycycline nanoparticles: Customizable implants for in vivo osteoregeneration

3D printing has revolutionized pharmaceutical research, with applications encompassing tissue regeneration and drug delivery. Adopting 3D printing for pharmaceutical drug delivery personalization via nanoparticle-reinforced hydrogel scaffolds promises great regenerative potential. Herein, we engineered novel core/shell, bio-inspired, drug-loaded polymeric hydrogel scaffolds for pharmaceutically personalized drug delivery and superior osteoregeneration. Scaffolds were developed using biopolymeric blends of gelatin, polyvinyl alcohol and hyaluronic acid and integrated with composite doxycycline/hydroxyapatite/polycaprolactone nanoparticles (DX/HAp/PCL) innovatively via 3D printing. The developed scaffolds were optimized for swelling pattern and in-vitro drug release through tailoring the biphasic microstructure and wet/dry state to attain various pharmaceutical personalization platforms. Freeze-dried scaffolds with nanoparticles reinforcing the core phase (DX/HAp/PCL-LCS-FD) demonstrated favorably controlled swelling, preserved structural integrity and controlled drug release over 28 days. DX/HAp/PCL-LCS-FD featured double-ranged pore size (90.4 ± 3.9 and 196.6 ± 38.8 µm for shell and core phases, respectively), interconnected porosity and superior mechanical stiffness (74.5 ± 6.8 kPa) for osteogenic functionality. Cell spreading analysis, computed tomography and histomorphometry in a rabbit tibial model confirmed osteoconduction, bioresorption, immune tolerance and bone regenerative potential of the original scaffolds, affording complete defect healing with bone tissue. Our findings suggest that the developed platforms promise prominent local drug delivery and bone regeneration.

A vertical additive-lathe printing system for the fabrication of tubular constructs using gelatin methacryloyl hydrogel

Reproducing both the mechanical and biological performance of native blood vessels remains an ongoing challenge in vascular tissue engineering. Additive-lathe printing offers an attractive method of fabricating long tubular constructs as a potential vascular graft for the treatment of cardiovascular diseases. Printing hydrogels onto rotating horizontal mandrels often leads to sagging, resulting in poor and variable mechanical properties. In this study, an additive-lathe printing system with a vertical mandrel to fabricate tubular constructs is presented. Various concentrations of gelatin methacryloyl (gelMA) hydrogel were used to print grafts on the rotating mandrel in a helical pattern. The printing parameters were selected to achieve the bonding of consecutive gelMA filaments to improve the quality of the printed graft. The hydrogel filaments were fused properly under the action of gravity on the vertical mandrel. Thus, the vertical additive-lathe printing system was used to print uniform wall thickness grafts, eliminating the hydrogel sagging problem. Tensile testing performed in both circumferential and longitudinal direction revealed that the anisotropic properties of printed gelMA constructs were similar to those observed in the native blood vessels. In addition, no leakage was detected through the walls of the gelMA grafts during burst pressure measurement. Therefore, the current printing setup could be utilized to print vascular grafts for the treatment of cardiovascular diseases.

3D printable conductive composite inks for the fabrication of biocompatible electrodes in tissue engineering application

Native tissues are affected by the microenvironment surrounding the tissue, including electrical activities. External electrical stimulation, which is used in replicating electrical activities and regulating cell behavior, is mainly applied in neural and cardiac tissues due to their electrophysiological properties. The in vitro cell culture platform with electrodes provides precise control of the stimulation property and eases the observation of the effects on the cells. The frequently used electrodes are metal or carbon rods, but their risk of damaging tissue and their mechanical properties that are largely different from those of native tissues hinder further applications. Biocompatible polymer reinforced with conductive fillers emerges as a potential solution to fabricate the complex structure of the platform and electrode. Conductive polymer can be used as an ink in the extrusion-based printing method, thus enabling the fabrication of volumetric structures. The filler simultaneously alters the electrical and rheological properties of the ink; therefore, the amount of additional compound should be precisely determined regarding printability and conductivity. This review provides an overview on the rheology and conductivity change relative to the concentration of conductive fillers and the applications of printed electrodes. Next, we discuss the future potential use of a cell culture platform with electrodes from in vitro and in vivo perspectives.