Macroscale scaffolds created from cartilage-derived matrix (CDM) demonstrate chondroinductive or chondro-inductive properties, but many fabrication methods do not allow for control of nanoscale architecture. In this regard, electrospun scaffolds have shown significant promise for cartilage tissue engineering. However, nanofibrous materials generally exhibit a relatively small pore size and require techniques such as multilayering or the inclusion of sacrificial fibers to enhance cellular infiltration. The objectives of this study were (1) to compare multilayer to single-layer electrospun poly(ɛ-caprolactone) (PCL) scaffolds for cartilage tissue engineering, and (2) to determine whether incorporation of CDM into the PCL fibers would enhance chondrogenesis by human adipose-derived stem cells (hASCs). PCL and PCL–CDM scaffolds were prepared by sequential collection of 60 electrospun layers from the surface of a grounded saline bath into a single scaffold, or by continuous electrospinning onto the surface of a grounded saline bath and harvest as a single-layer scaffold. Scaffolds were seeded with hASCs and evaluated over 28 days in culture. The predominant effects on hASCs of incorporation of CDM into scaffolds were to stimulate sulfated glycosaminoglycan synthesis and COL10A1 gene expression. Compared with single-layer scaffolds, multilayer scaffolds enhanced cell infiltration and ACAN gene expression. However, compared with single-layer constructs, multilayer PCL constructs had a much lower elastic modulus, and PCL–CDM constructs had an elastic modulus approximately 1% that of PCL constructs. These data suggest that multilayer electrospun constructs enhance homogeneous cell seeding, and that the inclusion of CDM stimulates chondrogenesis-related bioactivity. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 3998–4008, 2014.

The development of synthetic biomaterials that possess mechanical properties mimicking those of native tissues remains an important challenge to the field of materials. In particular, articular cartilage is a complex nonlinear, viscoelastic, and anisotropic material that exhibits a very low coefficient of friction, allowing it to withstand millions of cycles of joint loading over decades of wear. Here, a three-dimensionally woven fiber scaffold that is infiltrated with an interpenetrating network hydrogel can build a functional biomaterial that provides the load-bearing and tribological properties of native cartilage. An interpenetrating dual-network “tough-gel” consisting of alginate and polyacrylamide was infused into a porous three-dimensionally woven poly(ϵ-caprolactone) fiber scaffold, providing a versatile fiber-reinforced composite structure as a potential acellular or cell-based replacement for cartilage repair.

Osmotic stress is a potent regulator of the normal function of cells that are exposed to osmotically active environments under physiologic or pathologic conditions. The ability of cells to alter gene expression and metabolic activity in response to changes in the osmotic environment provides an additional regulatory mechanism for a diverse array of tissues and organs in the human body. In addition to the activation of various osmotically- or volume-activated ion channels, osmotic stress may also act on the genome via a direct biophysical pathway. Changes in extracellular osmolality alter cell volume, and therefore, the concentration of intracellular macromolecules. In turn, intracellular macromolecule concentration is a key physical parameter affecting the spatial organization and pressurization of the nucleus. Hyper-osmotic stress shrinks the nucleus and causes it to assume a convoluted shape, whereas hypo-osmotic stress swells the nucleus to a size that is limited by stretch of the nuclear lamina and induces a smooth, round shape of the nucleus. These behaviors are consistent with a model of the nucleus as a charged core/shell structure pressurized by uneven partition of macromolecules between the nucleoplasm and the cytoplasm. These osmotically-induced alterations in the internal structure and arrangement of chromatin, as well as potential changes in the nuclear membrane and pores are hypothesized to influence gene transcription and/or nucleocytoplasmic transport. A further understanding of the biophysical and biochemical mechanisms involved in these processes would have important ramifications for a range of fields including differentiation, migration, mechanotransduction, DNA repair, and tumorigenesis. J. Cell. Biochem. 109: 460–467, 2010. © 2009 Wiley-Liss, Inc.

Adipose-derived stem cells (ASCs) are multipotent progenitors that can be chondrogenically induced by growth factors such as bone morphogenetic protein 6 (BMP-6). We hypothesized that nonviral transfection of a BMP-6 construct (pcDNA3-BMP6) would induce chondrogenic differentiation of ASCs encapsulated in alginate beads and that differentiation would be enhanced by the presence of the synthetic glucocorticoid dexamethasone (DEX) or the combination of epidermal growth factor (EGF), fibroblast growth factor-2 (FGF-2), and transforming growth factor beta-1 (TGF-β1), collectively termed expansion factors (EFs). Chondrogenesis was assessed using quantitative real-time polymerase chain reaction for types I, II, and X collagen, aggrecan, and BMP6. Immunohistochemistry was performed with antibodies for types I, II, and X collagen and chondroitin-4-sulfate. BMP6 overexpression alone induced a moderate chondrogenic response. The inclusion of EFs promoted robust type II collagen expression but also increased type I and X collagen deposition, consistent with a hypertrophic chondrocyte phenotype. Early gene expression data indicated that DEX was synergistic with BMP-6 for chondrogenesis, but immunohistochemistry at 28 days showed that DEX reduced glycosaminoglycan accumulation. These results suggest that chondrogenic differentiation of ASCs depends on complex interactions among various growth factors and media supplements, as well as the concentration and duration of growth factor exposure. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res, 2010