Stiffness-modulated water retention and neovascularization of dermal fibroblast-encapsulating collagen gel.

There is increasing evidence that matrix stiffness modulates various phenotypic activities of cells surrounded by a three-dimensional (3D) matrix. These findings suggest that matrix stiffness can also regulate dermal fibroblasts activities to remodel, repair, and recreate skin dermis, but this has not yet been systematically demonstrated to date. This study examines the effects of matrix rigidity on the morphology, growth rates, and glycosaminoglycan (GAG) production of dermal fibroblasts cultured in collagen-based hydrogels with controlled elastic moduli. The elastic moduli (E) of collagen hydrogels were increased from 0.7 to 1.6 and 2.2 kPa by chemically cross-linking collagen fibrils with poly(ethylene glycol) disuccinimidylester. Increasing E of the hydrogel led to decreases in cellular spreading, nuclear aspect ratio, and growth rate. In contrast, the cellular GAG production level was elevated by increasing E from 0.7 to 1.6 kPa. The larger accumulation of GAG in the stiffer hydrogel led to increased water retention during exposure to air, as confirmed with magnetic resonance imaging. Additionally, in a chicken chorioallantoic membrane, a cell-encapsulating hydrogel with E of 1.6 kPa created dermis-like tissue with larger amount of GAG and density of blood vessels, while a cell-hydrogel construct with E of 0.7 kPa generated scar-like tissue. Overall, the results of this study will be highly useful for designing advanced tissue engineering scaffolds that can enhance the quality of a wide array of regenerated tissues including skin.

Interplay of cell adhesion matrix stiffness and cell type for non-viral gene delivery.

Non-viral gene delivery has the potential to treat a wide array of diseases but has been hindered by limited expression in vivo, possibly due to complex cellular microenvironments at delivery sites. Previous studies have reported that extracellular matrix properties, including stiffness, influence non-viral gene transfection efficiencies. This study reports that the effect of matrix stiffness on non-viral gene delivery differs among cell types due to varying sensitivities to matrix rigidity. Plasmid DNA encoding bone morphogenetic protein (BMP)-2 was delivered to fibroblasts, bone marrow stromal cells, and myoblasts cultured on fibronectin-conjugated poly(ethylene glycol) diacrylate hydrogels with varied elastic moduli, and the cellular uptake and subsequent expression of plasmid DNA were examined. While exogenous BMP-2 expression increased with increasing matrix stiffness for all three cell types, the effects of matrix stiffness were most pronounced for fibroblasts. Mechanistic studies conducted in parallel indicate that matrix stiffness influenced the projected area and nuclear aspect ratio for fibroblasts but had minimal effects on the morphology of bone marrow stromal cells and myoblasts. Overall, we believe that the results of this study will be useful for developing advanced non-viral gene delivery strategies for improved therapeutic efficacy.

Three-dimensional synthetic niche components to control germ cell proliferation.

Spermatogonial stem cells (SSCs) are increasingly studied for potential use in tissue regeneration due to their ability to dedifferentiate into embryonic stem cell-like cells. For their successful therapeutic use, these cells must first be expanded in vitro using an appropriate culture system. We hypothesized that a hydrogel with proper biochemical and biomechanical properties may mimic the composition and structure of the native basement membrane onto which SSCs reside, thus allowing us to control SSC proliferation. This hypothesis was examined in two-dimensional (2D) and three-dimensional (3D) cultures using hydrogels formed from calcium cross-linked alginate molecules conjugated with synthetic oligopeptides containing the Arg-Gly-Asp sequence (RGD peptides). The RGD peptide density (N(RGD)) in gel matrices was controlled by mixing alginate molecules modified with RGD peptides and unmodified alginate molecules at varied ratios. The mechanical stiffness was controlled with the cross-linking density of gel matrices. Interestingly, the RGD peptide density modulated cell proliferation in both 2D and 3D cultures as well as the number and size of SSC colonies formed in 3D cultures. In contrast, cell proliferation was minimally influenced by mechanical stiffness in 2D cultures. Overall, the results of this study elucidate an important factor regulating SSC proliferation and also present a bioactive hydrogel that can be used as a 3D synthetic basement membrane. In addition, the results of this study will be broadly useful in controlling the proliferation of various stem cells.

Application of a two-dimensional model for predicting the pressure-flow and compression properties during column packing scale-up.

A two-dimensional model was formulated to describe the pressure-flow behavior of compressible stationary phases for protein chromatography at different temperatures and column scales. The model was based on the assumption of elastic deformation of the solid phase and steady-state Darcy flow. Using a single fitted value for the empirical modulus parameters, the model was applied to describe the pressure-flow behavior of several adsorbents packed using both fluid flow and mechanical compression. Simulations were in agreement with experimental data and accurately predicted the pressure-flow and compression behavior of three adsorbents over a range of column scales and operating temperatures. Use of the described theoretical model potentially improves the accuracy of the column scale-up process, allowing the use of limited laboratory scale data to predict column performance in large scale applications.

Paternal uniparental isodisomy for chromosome 14 in a patient with a normal 46,XY karyotype.

Chromosome 14 demonstrates imprinting with differing phenotypes for both maternal and paternal uniparental disomy (UPD). Although only 11 cases of paternal uniparental disomy 14 (patUPD14) have been reported, a distinct clinically recognizable syndrome has emerged. The major features are polyhydramnios, small thorax, mildly short limbs, abdominal wall defects, and characteristic face with short palpebral fissures, broad flat nasal bridge, prominent philtrum, and small ears. Radiographically, the chest is bell-shaped and the ribs are distinctive with caudal bowing anteriorly and cranial bowing posteriorly. Several affected infants have died from respiratory failure. The survivors have short stature and mental retardation. The initial cases were all recognized because of translocations involving chromosome 14. Subsequently, several patients with a similar phenotype and normal chromosomes have been reported, including two with mixed iso- and hetero-disomy as well as one with segmental UPD14. Our patient is the first with pure paternal isodisomy 14 in the absence of a translocation. We present additional clinical information, review the literature, and discuss mechanisms that may explain paternal isodisomy 14 in our chromosomally normal patient. Paternal UPD14 with normal karyotype may be more common than previously suspected and may be overlooked unless recognition of the clinical phenotype prompts investigation for UPD.