Although biochemical signals that modulate stem cell self-renewal and differentiation were extensively studied, only recently were the mechanical properties of a stem cell's microenvironment shown to regulate its behavior. It would be desirable to have independent control over biochemical and mechanical cues, to analyze their relative and combined effects on stem-cell function. We developed a synthetic, interfacial hydrogel culture system, termed variable moduli interpenetrating polymer networks (vmIPNs), to assess the effects of soluble signals, adhesion ligand presentation, and material moduli from 10-10,000 Pa on adult neural stem-cell (aNSC) behavior. The aNSCs proliferated when cultured in serum-free growth media on peptide-modified vmIPNs with moduli of >/=100 Pa. In serum-free neuronal differentiation media, a peak level of the neuronal marker, beta-tubulin III, was observed on vmIPNs of 500 Pa, near the physiological stiffness of brain tissue. Furthermore, under mixed differentiation conditions with serum, softer gels ( approximately 100-500 Pa) greatly favored neurons, whereas harder gels ( approximately 1,000-10,000 Pa) promoted glial cultures. In contrast, cell spreading, self-renewal, and differentiation were inhibited on substrata with moduli of approximately 10 Pa. This work demonstrates that the mechanical and biochemical properties of an aNSC microenvironment can be tuned to regulate the self-renewal and differentiation of aNSCs.

Hafnium oxide (HfO 2 ) is one of the most promising high-k materials to replace SiO 2 as a gate dielectric. Here we report material and electrical characterization of atomic layer deposition ͑ALD͒ hafnium oxide and the correlations between the results. The HfO 2 films were deposited at 200, 300, or 370°C and annealed in a nitrogen ambient at 550, 800, and 900°C. Results indicate that deposition temperature controls both the material and the electrical properties. Materials and electrical properties of films deposited at 200°C are most affected by annealing conditions compared to films deposited at higher temperatures. These films are amorphous as deposited and become polycrystalline after 800°C anneals. Voids are observed after a 900°C anneal for the 200°C deposited films. The 200°C deposited films have charge trapping and high leakage current following anneals at 900°C. The 300°C deposited films have lower chlorine content and remain void-free following high-temperature anneals. These films show a thickness-dependent crystal structure. Annealing the films reduces leakage current by four orders of magnitude. Finally, films deposited at 370°C have the highest density, contain the least amount of impurities, and contain more of the monoclinic phase of HfO 2 than those deposited at 300 and 200°C. The best electrical performance was obtained for films deposited at 370°C.

We have developed a synthetic polymer interface for the long-term self-renewal of human embryonic stem cells (hESCs) in defined media. We successfully cultured hESCs on hydrogel interfaces of aminopropylmethacrylamide (APMAAm) for over 20 passages in chemically-defined mTeSR™ 1 media and demonstrated pluripotency of multiple hESC lines with immunostaining and quantitative RT-PCR studies. Results for hESC proliferation and pluripotency markers were both qualitatively and quantitatively similar to cells cultured on Matrigel™ -coated substrates. Mechanistically, it was resolved that bovine serum albumin (BSA) in the mTeSR™ 1 media was critical for cell adhesion on APMAAm hydrogel interfaces. This study uniquely identified a robust long-term culture surface for the self-renewal of hESCs without the use of biologic coatings (e.g., peptides, proteins, or Matrigel™) in completely chemically-defined media that employed practical culturing techniques amenable to clinical-scale cell expansion.

A quartz crystal microbalance with dissipation monitoring (QCM-D) was used to assess the physical properties of interpenetrating polymer networks (IPNs) through swelling experiments in ambient humidity and in phosphate-buffered saline (PBS), pH 7.4. The IPNs, based on acrylamide (AAm) and poly(ethylene glycol) (pEG), swell from thin, rigid films when dry (16.7 +/- 5.2 nm on Si/SiO(2)) to expanded, viscoelastic films when hydrated (107 +/- 24.2 nm on Si/SiO2). The dry IPNs could be analyzed using the Sauerbrey relationship, but for the hydrated films it was necessary to interpret QCM-D data with a Kelvin-Voigt viscoelastic model. A complex modulus |G| of 116 +/- 38.1 kPa for the swollen IPN surface on Si/SiO2 was defined by the model. The QCM-D was also employed to quantify the adsorption of human fibrinogen, a protein important in thrombus formation, onto the IPNs. Fibrinogen adsorption studies demonstrated the sensitivity of the QCM-D, as well as confirmed the nonfouling nature of the IPN surface, where less than 5 ng/cm2 of fibrinogen was adsorbed.

Macrophage attachment and activation to implanted materials is crucial in determining the extent of acute and chronic inflammation, and biomaterials degradation. In an effort to improve implant performance, considerable attention has centered on altering material surface chemistry to modulate macrophage behavior. In this work, the influence of the modulus of a material on the behavior of model macrophages (i.e., human promonocytic THP-1 cells) was investigated. We synthesized interpenetrating polymer network (IPN) coatings with varying moduli to test the hypothesis that lower moduli surfaces attenuate THP-1 cell attachment and activation. The surface chemistry and moduli of the IPN coatings were characterized using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. THP-1 cells preferentially attached to stiffer coatings of identical surface chemistry, confirming that fewer macrophages attach to lower moduli surfaces. The secretion of human TNF-alpha, IL-10, IL-8 and IL-1beta from THP-1 cells attached to the IPNs was measured to assess the concentration of both pro- and anti-inflammatory cytokines. The global amount of TNF-alpha released did not vary for IPN surfaces of different moduli; however, the amount of the pro-inflammatory cytokine IL-8 released demonstrated a biphasic response, where lower (approx. 1.4 kPa) and very high (approx. 348 kPa) moduli IPN surfaces attenuated IL-8 secretion. The different trends for TNF-alpha and IL-8 secretion highlight the complexity of the wound healing response, suggesting that there may not be a unique surface chemistry and substratum modulus combination that minimizes the pro-inflammatory cytokines produced by activated macrophages.