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Biomedical subjects

R G Pearson

Publications and source records attributed to R G Pearson.

16 recordsLinked to original sources
PubMed2002

Interactions of 3T3 fibroblasts and endothelial cells with defined pore features.

The colonization of biodegradable polymer scaffolds with cell populations has been established as the foundation for the engineering of a number of tissues, including cartilage, liver, and bone. Within these scaffolds, the cells encounter a porous environment in which they must migrate across the convoluted polymer surface to generate a homogenous cell distribution. Predicting the interactions between cells and pores is important if scaffold characteristics are to be optimized. Therefore, we investigated the behavior of two model cell types over a range of defined pore features. These pore features range from 5 to 90 microm in diameter and have been fabricated by photolithographic techniques. Quantitatively, the behavior of the cells is dependent on three factors: 1) percentage cell coverage of the surface; 2) pore size; and 3) cell type. Fibroblast cells displayed a co-operative pattern of cell spreading in which pores with diameters greater than the cell dimensions were bridged by groups of cells using their neighbors as supports. Endothelial cells were unable to use neighbors as support structures and failed to bridge pores greater than the cell diameter.

3T3 Cells↗
PubMed2002

Recent advances in tissue engineering: an invited review.

Tissue formation within the body, as part of a development or repair process, is a complex event in which cell populations self-assemble into functional units. There is intense academic, medical, and commercial interest in finding methods of replicating these events outside the body. This interest has accelerated with the demonstration of the engineering of skin and cartilage tissue in the laboratory and there is now worldwide activity in the in vitro regeneration of tissues including nerve, liver, bone, heart valves, blood vessels, bladder, and kidney. Approaches to tissue engineering center on the need to provide signals to cell populations to promote cell proliferation and differentiation. This review considers recent advances in methods of providing these signals to cells using examples of progress in the engineering of complex tissues.

Absorbable Implants↗
PubMed2001

A comparison of the adhesion of mammalian cells and Staphylococcus epidermidis on fibronectin-modified polymer surfaces.

The modification of polymer surfaces to mimic the extracellular matrix, and therefore, stimulate cell growth via receptor-mediated interactions, is one approach used to promote the integration of tissue-engineering scaffolds and biomaterials into the body. However, by optimizing surfaces for tissue integration it is likely that bacterial adhesion may also be affected, resulting in a greater risk of biomaterial-related infection. This could be detrimental to both the implant and the patient because biomaterial related infections are particularly resistant to host defenses and antibiotics. In this study, we analyzed the adhesion of a Staphylococcus epidermidis clinical isolate and 3T3 rat fibroblasts to tissue culture plastic coated with varying concentrations of fibronectin (Fn). Bacterial adhesion was always lower than tissue culture plastic and appeared to decrease with increasing Fn concentrations. Mammalian cell adhesion to Fn exceeded adhesion to tissue culture plastic but did not differ significantly over the range of protein concentrations or between 1 and 4 h of incubation. In most cases, the total surface coverage did not vary with time or Fn concentration, indicating that maximal cell adhesion and spreading occurred rapidly and at low protein concentrations. This study suggests that, by controlling the density of proteins or ligands on a surface, we can potentially optimize mammalian cell adhesion without stimulating bacterial adhesion, hence reducing the likelihood of infection.

3T3 Cells↗
PubMed1997

Historical rainforest contractions, localized extinctions and patterns of vertebrate endemism in the rainforests of Australia's wet tropics.

The spatial patterns in the distributions of vertebrates in the rainforests of the wet tropics biogeographic region of north-eastern Australia were examined to form hypotheses on the processes that have shaped vertebrate assemblages and patterns of species richness and regional endemism. These rainforests occur in a relatively narrow and discontinuous strip along the coast of north-eastern Australia. We found that the number of regionally endemic species and the proportion of regional endemics present in each subregion are both strongly related to the geographic shape of subregional patches of rainforest, independent of rainforest area, within Australian tropical rainforests. Shape has a more significant influence on regional endemism than area, and area has a stronger influence on species richness. These patterns were congruent for all terrestrial vertebrate classes manuals, birds, reptiles and frogst, and for the four groups combined. Our results suggest that the combination of current rainforest area and shape are an index of the relative susceptibility of each area of rainforest to historical contractions, with the implication that historical habitat fluctuations, coupled with subsequent localized extinctions species sifting; have been extremely important processes in determining current patterns of endemism in Australia's wet tropical rainforests. This hypothesis is supported by the highly nested structure of the subregional distribution patterns.

Animals↗
PubMed1991

Subjective evaluation of a prototype earmuff exhibiting flat and nonlinear attenuation characteristics.

Subjective user responses were obtained for a test earmuff exhibiting approximately flat (uniform) attenuation of about 25 dB from 500 to 8000 Hz for sound pressure levels (SPLs) less than 120 dB. At SPLs above 120 dB, the test earmuff exhibited nonlinear (level-dependent) attenuation characteristics such that noise reduction increased with increasing sound level. The study population consisted of police officers from the Raleigh, North Carolina, Police Department as they were performing arms requalification by executing a series of firing programs during two sequential and identical relays. The study subjects wore either the test earmuff or a comparable conventional earmuff during the first relay, then the alternate protector for the second relay with the order counterbalanced. Results indicated a significant preference for the test earmuff in three comparison areas: comfort, perceived hearing protection, and speech understanding. The study demonstrates that ammunition type and level of noise exposure contributed significantly to a preference in favor of the test earmuff. The subjects who used the quietest of the ammunition types rated the test earmuff significantly better than the remaining subjects with respect to speech understanding.

Adult↗
PubMed1990

Hearing conservation programs (HCPs): the effectiveness of one company's HCP in a 12-hr work shift environment.

An existing hearing conservation program (HCP), originally designed when an 8-hr work shift schedule was in effect, was evaluated at a plant site where a 12-hr work shift schedule is now utilized. The study included the following phases: a noise analysis of the work environment, HCP evaluation through the use of audiometric data base analysis (ADBA), applying ADBA procedures and a comparison of the shift in hearing threshold levels (HTLs) for the 8-hr and 12-hr work shifts, and an evaluation of the hearing protection devices (HPDs) being used at the facility over the 12-hr work shift by measuring temporary threshold shift (TTS). The mean measured employee time-weighted average (TWA) in the process area where the TTS study was conducted was 92 dBA. It was found that the existing HCP is at best marginal. The most likely causes of this less-than-desirable rating are inadequate audiometric testing procedures and inadequate HPD utilization. Furthermore, it was concluded that, at this time, the introduction of the 12-hr work shift has had no impact on the level of effectiveness of the HCP. In evaluating the three HPDs in use at the facility (3-M foam earplug, E-A-R foam earplug, and Bilsom Soft earplug), it was found that they all offered effective protection from noise at all audiometric test frequencies (0.5 to 6 kHz) except 0.5 kHz. All three HPDs exhibited TTS at 0.5 kHz with the TTS measured significant at the p less than 0.05 level for the E-A-R and 3-M wearer groups.

Audiometry↗
PubMed1987

The contribution of personal radios to the noise exposure of employees at one industrial facility.

An investigation of the contribution made to an employee's noise dose from the output of personal radios was performed at a North Carolina textile manufacturing facility where the daily time-weighted average sound level (TWA) was approximately 87 dB, A-weighted sound pressure level [dB(A)]. The measured mean equivalent diffuse field output level of the personal radios was determined to be 83 dB(A) with a range from 70 to 98 dB(A). The daily TWA of a typical employee who did not use a personal radio was determined to be 86.6 dB(A), whereas the exposure of personal radio users was 88.5 dB(A)--an increase of 1.9 dB(A). This increase in exposure was estimated to result in 4 dB of additional permanent noise-induced hearing loss at 4 kHz for the 5th percentile (most sensitive portion) of the population after 20 years of exposure beginning at age 20. The study concluded that the additional contribution of the personal radios to the employee's daily TWA did not pose a significant additional threat to their hearing. Specific hearing conservation criteria, however, were recommended for continuation of personal radio use at the facility.

Environmental Exposure↗
PubMed1986

Absolute electronegativity and hardness correlated with molecular orbital theory.

The concepts of absolute electronegativity, chi, and absolute hardness, eta, are incorporated into molecular orbital theory. A graphic and concise definition of hardness is given as twice the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Useful correlations can now be made between chemical behavior, visible-UV absorption spectra, optical polarizability, ionization potentials, and electron affinities.

Journal Article↗
PubMed1981

Semiclassical model for atoms.

The energies of several two- and three-electron atoms, in both ground states and excited states, are calculated by a very simple semiclassical model. The only change from Bohr's original method is to replace definite orbits by probability distribution functions based on classical dynamics. The energies are better than Hartree-Fock values. There is still a need for an exchange-energy correction.

Journal Article↗
PubMed1980

Electron density functions for simple molecules.

Trial electron density functions have some conceptual and computational advantages over wave functions. The properties of some simple density functions for H(+) (2) and H(2) are examined. It appears that for a diatomic molecule a good density function would be given by rho = N(A(2) + B(2)), in which A and B are short sums of s, p, d, etc. orbitals centered on each nucleus. Some examples are also given for electron densities that are appropriate for excited states.

Journal Article↗
PubMed1975

Concerning jahn-teller effects.

Jahn-Teller effects are grouped into two categories. The first arises from incomplete shells of degenerate orbitals. It includes the first-order Jahn-Teller effect, and the pseudo Jahn-Teller effect. The second arises from filled and empty molecular orbitals that are close in energy, and is the second-order Jahn-Teller effect. The two categories have quite different physical bases. As a result, geometric distortions produced by the first are quite small and normally lead to dynamic effects only. In favorable cases, the second-order Jahn-Teller effect produces very large distortions, including complete dissociation of a molecule. This can occur even when the relevant molecular orbitals are separated in energy by as much as 4 eV.

Journal Article↗