Dielectrophoresis-based analyte separation and analysis

Dielectrophoresis—the tendency of a material of high dielectric permittivity to migrate in an electrical field gradient to a region of maximum field strength—provides an ideal motive force for manipulating small volumes of biological analytes in microfluidic microsystems. The work described in this thesis was based on the hypothesis that dielectrophoresis could be exploited to provide high-resolution cell separations in microsystems as well as a means for the electrically-controllable manipulation of solid supports for molecular analysis. To this end, a dielectrophoretic/gravitational field-flow-fractionation (DEP/G-FFF) system was developed and the separation performance evaluated using various types and sizes of polystyrene microspheres as model particles. It was shown that separation of the polystyrene beads was based on the differences in their effective dielectrophoretic properties. The ability of an improved DEP/G-FFF system to separate genetically identical, but phenotypically dissimilar cell types was demonstrated using mixtures of 6m2 mutant rat kidney cells grown under transforming and non-transforming culture conditions. Additionally, a panel of engineered dielectric microspheres was designed with specific, predetermined dielectrophoretic properties such that their dielectrophoretic behaviors would be controllable and predictable. The fabrication method involved the use of gold-coated polystyrene microsphere cores coated with a self-assembled monolayer of alkanethiol and, optionally, a self-assembled monolayer of phospholipid to form a thin-insulating-shell-over-conductive-interior structure. The successful development of the DEP/G-FFF separation system and the dielectrically engineered microspheres provides proof-of-principle demonstrations of enabling dielectrophoresis-based microsystem technology that should provide powerful new methods for the manipulation, separation and identification of analytes in many diverse fields. ^

MEDICAL CARE UTILIZATION IN TIME AMONG ELDERLY MEDICARE ENROLLEES IN AN HMO

Investigation into the medical care utilization of elderly Medicare enrollees in an HMO (Kaiser - Portland, Oregon): The specific research topics are: (1) The utilization of medical care by selected determinants such as: place of service, type of service, type of appointment, physician status, physician specialty and number of associated morbidities. (2) The attended prevalence of 3 chronic diseases: hypertension, diabetes and arthritis in addition to pneumonias as an example of acute diseases. The selection of these examples was based on their importance in morbidity/or mortality results among the elderly. The share of these diseases in outpatient and inpatient contacts was examined as an example of the relation between morbidity and medical care utilization. (3) The tendency of individual utilization patterns to persist in subsequent time periods. The concept of contagion or proneness was studied in a period of 2 years. Fitting the negative binomial and the Poisson distributions was applied to the utilization in the 2nd year conditional on that in the 1st year as regards outpatient and inpatient contacts.^ The present research is based on a longitudinal study of 20% random sample of elderly Medicare enrollees. The sample size is 1683 individuals during the period from August 1980-December 1982.^ The results of the research were: (1) The distribution of contacts by selected determinants did not reveal a consistent pattern between sexes and age groups. (2) The attended prevalence of hypertension and arthritis showed excess prevalence among females. For diabetes and pneumonias no female excess was noticed. Consistent increased prevalence with increasing age was not detected.^ There were important findings pertaining to the relatively big share of the combined 3 chronic diseases in utilization. They accounted for 20% of male outpatient contacts vs. 25% of female outpatients. For inpatient contacts, they consumed 20% in case of males vs. 24% in case of females. (3) Finding that the negative binomial distribution fit the utilization experience supported the research hypothesis concerning the concept of contagion in utilization. This important finding can be helpful in estimating liability functions needed for forecasting future utilization according to previous experience. Such information has its relevance to organization, administration and planning for medical care in general. (Abstract shortened with permission of author.) ^