Cell-secreted extracellular matrix formation and differentiation of adipose-derived stem cells in 3D alginate scaffolds with tunable properties.

Three dimensional (3D) alginate scaffolds with tunable mechanical and structural properties are explored for investigating the effect of the scaffold properties on stem cell behavior and extracellular matrix (ECM) formation. Varying concentrations of crosslinker (20 - 60%) are used to tune the stiffness, porosity, and the pore sizes of the scaffolds post-fabrication. Enhanced cell proliferation and adipogenesis occur in scaffolds with 3.52 ± 0.59 kPa stiffness, 87.54 ± 18.33% porosity and 68.33 ± 0.88 µm pore size. On the other hand, cells in scaffolds with stiffness greater than 11.61 ± 1.74 kPa, porosity less than 71.98 ± 6.25%, and pore size less than 64.15 ± 4.34 µm preferentially undergo osteogenesis. When cultured in differentiation media, adipose-derived stem cells (ASCs) undergoing terminal adipogenesis in 20% firming buffer (FB) scaffolds and osteogenesis in 40% and 60% FB scaffolds show the highest secretion of collagen as compared to other groups of scaffolds. Overall, this study demonstrates the three-way relationship between 3D scaffolds, ECM composition, and stem cell differentiation.

Bioactivated protein-based porous microcarriers for tissue engineering applications.

Microcarriers are commonly used in tissue engineering applications as they provide a large surface area for cell attachment. However, limited research has been done on ovalbumin (OVA), which is a relatively cheap protein found in avian egg white. Hence, in our current study OVA is fabricated into porous microcarriers and the effect of different OVA to alginate ratios on the properties of OVA microcarriers was investigated. Subsequently, in order to further improve cell-material interactions, the extracellular matrix (ECM) material isolated from the human lipoaspirate material was conjugated with the porous OVA microcarriers using carbodiimide chemistry. A waste-to-resource strategy was employed to obtain this ECM material from the human lipoaspirate material, which typically is discarded after surgery. This study illustrates the possibility of obtaining ECM material using a physical decellularization method as well as the novel application of ECM material as a coating to confer bioactivity to protein-based microcarriers such as OVA. The incorporation of lipoaspirate-derived ECM (LpECM) into the OVA microstructure has been shown to improve mechanical strength and promote cellular growth on the microcarriers. The resulting porous OVA-LpECM hybrid microcarriers with tunable mechanical properties are examples of bioactivated porous protein-based microcarriers that can be applied in the field of tissue engineering.

Three-dimensional scaffolds for tissue engineering applications: role of porosity and pore size.

Tissue engineering applications commonly encompass the use of three-dimensional (3D) scaffolds to provide a suitable microenvironment for the incorporation of cells or growth factors to regenerate damaged tissues or organs. These scaffolds serve to mimic the actual in vivo microenvironment where cells interact and behave according to the mechanical cues obtained from the surrounding 3D environment. Hence, the material properties of the scaffolds are vital in determining cellular response and fate. These 3D scaffolds are generally highly porous with interconnected pore networks to facilitate nutrient and oxygen diffusion and waste removal. This review focuses on the various fabrication techniques (e.g., conventional and rapid prototyping methods) that have been employed to fabricate 3D scaffolds of different pore sizes and porosity. The different pore size and porosity measurement methods will also be discussed. Scaffolds with graded porosity have also been studied for their ability to better represent the actual in vivo situation where cells are exposed to layers of different tissues with varying properties. In addition, the ability of pore size and porosity of scaffolds to direct cellular responses and alter the mechanical properties of scaffolds will be reviewed, followed by a look at nature's own scaffold, the extracellular matrix. Overall, the limitations of current scaffold fabrication approaches for tissue engineering applications and some novel and promising alternatives will be highlighted.

Preparation of a soft and interconnected macroporous hydroxypropyl cellulose methacrylate scaffold for adipose tissue engineering.

This study describes the preparation and characterization of a biodegradable 3D hydrogel constructed from hydroxypropyl cellulose (HPC), modified with bifunctional methacrylic anhydride (MA) to form hydroxypropyl cellulose methacrylate (HPC-MA), for adipose tissue engineering applications. The hydrogels were prepared from three different concentrations (10 wt%, 15 wt% and 20 wt%) of HPC-MA with 0.35 degree of substitution. HPC-MA hydrogel scaffolds with open biphasic features were prepared by exploiting the thermal responsive phase behavior of HPC and temperature mediated phase separation of HPC-MA. The resulting scaffolds exhibited pore sizes ranging from 30 to 300 µm and an interconnected porosity of ∼90%. The swelling ratio (SR) and storage modulus of HPC-MA scaffolds were in the range of 12.94 to 35.83 and 0.75 to 4.28 kPa, respectively. The swelling ratio and storage modulus suggested that the scaffold exhibits high water retention, allowing medium exchange during cell culturing and that it is suitable for adipose tissue regeneration. The HPC-MA scaffolds were found to be biocompatible to human adipose-derived stem cells (ASCs). ASCs were successfully differentiated into the adipocytes inside the scaffolds, and therefore demonstrated the potential application of these HPC-MA scaffolds for adipose tissue engineering.