From solvent-free microspheres to bioactive gradient scaffolds.

A solvent-free microsphere sintering technique was developed to fabricate scaffolds with pore size gradient for tissue engineering applications. Poly(D,L-Lactide) microspheres were fabricated through an emulsification method where TiO2 nanoparticles were employed both as particulate emulsifier in the preparation procedure and as surface modification agent to improve bioactivity of the scaffolds. A fine-tunable pore size gradient was achieved with a pore volume of 30±2.6%. SEM, EDX, XRD and FTIR analyses all confirmed the formation of bone-like apatite at the 14th day of immersion in Simulated Body Fluid (SBF) implying the ability of our scaffolds to bond to living bone tissue. In vitro examination of the scaffolds showed progressive activity of the osteoblasts on the scaffold with evidence of increase in its mineral content. The bioactive scaffold developed in this study has the potential to be used as a suitable biomaterial for bone tissue engineering and hard tissue regeneration.

3D Carbon-Based Porous Anode with a Pore-Size Gradient for High-Performance Lithium Metal Batteries.

Three-dimensional (3D) hosts have been identified as the most promising anode design for lithium metal batteries (LMBs). This has been previously demonstrated to be extremely effective at inhibiting the dendrite growth by reducing the local current densities, resulting in stable cycle performances. However, due to the complex synthetic procedures and low lithium utilization ratios, the practical application of the 3D host anode still remains a challenge. To address these issues, the current study reports the development and synthesis of a 3D-carbon-based porous anode (3D-CPA) with a pore-size gradient using a practical slurry-based process in which the pore sizes decrease from the top to bottom layer. The pore-size gradient design accomplished using carbon materials enables stable Li plating/stripping into the entire inner pores without the formation of dendrites and also confirms the high energy density of LMB. The as-prepared 3D-CPA with a pore-size gradient also demonstrated a higher average coulombic efficiency of 98.8% (250 cycles) than other 3D-CPAs with mono-pore sizes. Additionally, its symmetry cell had a prolonged lifespan of 660 hrs at 1 mAcm-2 (Li utilization ratio = 50%) and 680 hrs at 2 mAcm-2 (Li utilization ratio = 30%). Remarkably, a pouch full cell composed of LiNi0.6Co0.2Mn0.2 (NCM622) with 4 mA h cm-2/as-prepared 3D-CPA retained 87.2% of its capacity after 100 cycles, using a carbonate-based electrolyte. The current study, therefore, highly suggests the use of 3D host designs for the fabrication of LMBs to achieve reversible Li reactions, leading to long-term stability.

Effects of Shear Stress Gradients on Ewing Sarcoma Cells Using 3D Printed Scaffolds and Flow Perfusion.

In this work, we combined three-dimensional (3D) scaffolds with flow perfusion bioreactors to evaluate the gradient effects of scaffold architecture and mechanical stimulation, respectively, on tumor cell phenotype. As cancer biologists elucidate the relevance of 3D in vitro tumor models within the drug discovery pipeline, it has become more compelling to model the tumor microenvironment and its impact on tumor cells. In particular, permeability gradients within solid tumors are inherently complex and difficult to accurately model in vitro. However, 3D printing can be used to design scaffolds with complex architecture, and flow perfusion can simulate mechanical stimulation within the tumor microenvironment. By modeling these gradients in vitro with 3D printed scaffolds and flow perfusion, we can identify potential diffusional limitations of drug delivery within a tumor. Ewing sarcoma (ES), a pediatric bone tumor, is a suitable candidate to study heterogeneous tumor response due to its demonstrated shear stress-dependent secretion of ligands important for ES tumor progression. We cultured ES cells under flow perfusion conditions on poly(propylene fumarate) scaffolds, which were fabricated with a distinct pore size gradient via extrusion-based 3D printing. Computational fluid modeling confirmed the presence of a shear stress gradient within the scaffolds and estimated the average shear stress that ES cells experience within each layer. Subsequently, we observed enhanced cell proliferation under flow perfusion within layers supporting lower permeability and increased surface area. Additionally, the effects of shear stress gradients on ES cell signaling transduction of the insulin-like growth factor-1 pathway elicited a response dependent upon the scaffold gradient orientation and the presence of flow-derived shear stress. Our results highlight how 3D printed scaffolds, in combination with flow perfusion in vitro, can effectively model aspects of solid tumor heterogeneity for future drug testing and customized patient therapies.

Integration of PCL and PLA in a monolithic porous scaffold for interface tissue engineering.

A novel bi-layered multiphasic scaffold (BLS) have been fabricated for the first time by combining melt mixing, compression molding and particulate leaching. One layer has been composed by polylactic acid (PLA) presenting pore size in the range of 90-110µm while the other layer has been made of polycaprolactone (PCL) with pores ranging from 5 to 40µm. The different chemo-physical properties of the two biopolymers combined with the tunable pore architecture permitted to realize monolithic functionally graded scaffolds engineered to be potentially used for interface tissues regenerations. BLS have been characterized from a morphological and a mechanical point of view. In particular, mechanical tests have been carried out both in air and immersing the specimens in phosphate buffered saline (PBS) solution at 37°C, in order to evaluate the elastic modulus and the interlayer adhesion strength. Fibroblasts and osteoblasts have been cultured and co-cultured in order to investigate the cells permeation trough the different layers. The results indicate that the presented method is appropriate for the preparation of multiphasic porous scaffolds with tunable morphological and mechanical characteristics. Furthermore, the cells seeded were found to grow with a different trend trough the different layers thus demonstrating that the presented device has good potential to be used in interface tissue regeneration applications.

Preparation of three-layered porous PLA/PEG scaffold: relationship between morphology, mechanical behavior and cell permeability.

Interface tissue engineering (ITE) is used to repair or regenerate interface living tissue such as for instance bone and cartilage. This kind of tissues present natural different properties from a biological and mechanical point of view. With the aim to imitating the natural gradient occurring in the bone-cartilage tissue, several technologies and methods have been proposed over recent years in order to develop polymeric functionally graded scaffolds (FGS). In this study three-layered scaffolds with a pore size gradient were developed by melt mixing polylactic acid (PLA) and two water-soluble porogen agents: sodium chloride (NaCl) and polyethylene glycol (PEG). Pore dimensions were controlled by NaCl granulometry while PEG solvation created a micropores network within the devices. Scaffolds were characterized from a morphological and mechanical point of view in order to find a correlation between the preparation method, the pore architecture and compressive mechanical behavior. Biological tests were also performed in order to study the effect of pore size gradient on the permeation of different cell lines in co-culture. To imitate the physiological work condition, compressive tests were also performed in phosphate buffered saline (PBS) solution at 37°C. The presented preparation method permitted to prepare three-layered scaffolds with high control of porosity and pore size distribution. Furthermore mechanical behaviors were found to be strongly affected by pore architecture of tested devices as well as the permeation of osteoblast and fibroblast in-vitro.