Development of a bio-MEMS device for electrical and mechanical conditioning and characterization of cell sheets for myocardial repair

Here we propose a bio-MEMS device designed to evaluate contractile force and conduction velocity of cell sheets in response to mechanical and electrical stimulation of the cell source as it grows to form a cellular sheet. Moreover, the design allows for the incorporation of patient-specific data and cell sources. An optimized device would allow cell sheets to be cultured, characterized, and conditioned to be compatible with a specific patient's cardiac environment in vitro, before implantation. This design draws upon existing methods in the literature but makes an important advance by combining the mechanical and electrical stimulation into a single system for optimized cell sheet growth. The device has been designed to achieve cellular alignment, electrical stimulation, mechanical stimulation, conduction velocity readout, contraction force readout, and eventually cell sheet release. The platform is a set of comb electrical contacts consisting of three-dimensional walls made of polydimethylsiloxane and coated with electrically conductive metals on the tops of the walls. Not only do the walls serve as a method for stimulating cells that are attached to the top, but their geometry is tailored such that they are flexible enough to be bent by the cells and used to measure force. The platform can be stretched via a linear actuator setup, allowing for simultaneous electrical and mechanical stimulation that can be derived from patient-specific clinical data.     

A molecular marker confirms that the rate of adult maturation is largely independent of the rate of pre-adult development in Drosophila melanogaster

The separation of adult from pre-adult life seen with animals such as Drosophila melanogaster, which are holometabolous and undergo complete metamorphosis, provides the opportunity to examine the contribution of pre-adult rate of development on the rate of maturation and aging of the adult. Recent work has shown that when ambient temperature is used to alter the rate of development there is little effect on adult life span. From this work it has been concluded that the rate of aging is largely independent of the rate of pre-adult development. However, the techniques used to examine life span did not allow for the examination of the earliest events of adult life. Our experimental design used a molecular marker linked to life span as a sensitive measure of determining physiological age. In this way, we were able to evaluate the effect of pre-adult rate of development on the earliest events of adult life. Using ambient temperature to alter both the rate of development in the pre-adult and the rate of aging in the adult independently, we were able to show that it is the ambient temperature at which the adults are living that is the principle determinant of the rate of maturation and aging of the adult. Little effect was seen on the rate of adult maturation in response to an acceleration or a slowing down of the rate of pre-adult development as measured by our molecular marker. These data support the conclusions drawn by others who examined the effect of the rate of development on adult life expectancy. The timing mechanisms at work during pre-adult and adult life appear to be largely regulated separately. If there is such a thing as a physiological clock, it appears to be reset upon eclosion. © 1996 Wiley-Liss, Inc.     

Likelihoods and simulation methods for a class of nonneutral population genetics models

Methods for simulating samples and sample statistics, under mutation-selection-drift equilibrium for a class of nonneutral population genetics models, and for evaluating the likelihood surface, in selection and mutation parameters, are developed and applied for observed data. The methods apply to large populations in settings in which selection is weak, in the sense that selection intensities, like mutation rates, are of the order of the inverse of the population size. General diploid selection is allowed, but the approach is currently restricted to models, such as the infinite alleles model and certain K-models, in which the type of a mutant allele does not depend on the type of its progenitor allele. The simulation methods have considerable advantages over available alternatives. No other methods currently seem practicable for approximating likelihood surfaces.     

Potent and selective cathepsin L inhibitors do not inhibit human osteoclast resorption in vitro

Cathepsins K and L are related cysteine proteases that have been proposed to play important roles in osteoclast-mediated bone resorption. To further examine the putative role of cathepsin L in bone resorption, we have evaluated selective and potent inhibitors of human cathepsin L and cathepsin K in an in vitro assay of human osteoclastic resorption and an in situ assay of osteoclast cathepsin activity. The potent selective cathepsin L inhibitors (K(i) = 0.0099, 0.034, and 0.27 nm) were inactive in both the in situ cytochemical assay (IC(50) > 1 micrometer) and the osteoclast-mediated bone resorption assay (IC(50) > 300 nm). Conversely, the cathepsin K selective inhibitor was potently active in both the cytochemical (IC(50) = 63 nm) and resorption (IC(50) = 71 nm) assays. A recently reported dipeptide aldehyde with activity against cathepsins L (K(i) = 0.052 nm) and K (K(i) = 1.57 nm) was also active in both assays (IC(50) = 110 and 115 nm, respectively) These data confirm that cathepsin K and not cathepsin L is the major protease responsible for human osteoclastic bone resorption.