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Biomedical subjects

H Winet

Publications and source records attributed to H Winet.

At least 19 recordsLinked to original sources
PubMed1995

Incorporation of polylactide-polyglycolide in a cortical defect: neoangiogenesis and blood supply in a bone chamber.

Erodible polymers are an alternative to metals for fracture fixation (for example, in the malleolus) and for maxillofacial reconstruction. In this study, the vascular response to eroding polylactide-polyglycolide copolymer threads was observed chronically in a bone chamber implant, with use of intravital microscopy. A bone chamber implant loaded with 100 microns thick polylactide-polyglycolide threads was implanted into the right tibia in 15 mature female New Zealand White rabbits. Periodic intravital microscopic observations were performed from the third to the tenth or twelfth week after implantation. Vascularization, blood flow, and trabecular growth into the chambers from the medial cortex were recorded on videotape and analyzed using digital image processing. A statistically significant delay of neo-osteogenesis in the presence of this copolymer was described in an earlier report. The present report describes the measures of neoangiogenesis and blood supply; there was a significant delay in neoangiogenesis. It is suggested that both delayed angiogenesis and osteogenesis were secondary consequences of the macrophage response to slowly eroding poly-L-lactide crystal nanoparticles and the influence of reduced nutrient exchange. The lesser effect on blood supply and vascular volume fraction was seen to be linked to the slowing down of angiogenesis, as the latter allowed vessels to mature, with a widening of their calibers. This homeostatic adjustment was interpreted as being only partially successful in restoring control levels of oxygen delivery, because resulting increases in vessel surface area did not reach control levels. Thus, in the presence of eroding polylactide-polyglycolide, the oxygen supply and extravasation of other nutrients may be below normal during healing phases when the need is critical.

Analysis of Variance↗
PubMed1990

A control model for tibial cortex neovascularization in the bone chamber.

Neovascularization across a gap defect in a rabbit tibial cortex was monitored using the optical bone chamber implant (BCI). Cortical bone growing by apposition as trabeculae was observed weekly as it penetrated a slit into a tissue space in vivo and in situ. Each rabbit was viewed weekly with an intravital microscope from 3 to 8 weeks postimplantation. The constant field of view was the slit-gap tissue space, which was 100 microns thick and 2 mm in diameter. Vessels were imaged with epi-illuminated fluorescence microscopy as they carried FITC-dextran 70 that had been injected into an aural vein. Observations were videotaped and photographed. Videotape frames were analyzed with a digital image processing system to obtain measures of vessel length per unit volume (L/V) of fibroblastic granular tissue and trabeculae, caliber C, and flow velocity u, all as functions of time. Observations supported the conclusions that (1) neovascularization precedes neo-osteogenesis, (2) major vessels tend to align with the tibial axis, (3) bone apposition-generated destruction of fibrous granular tissue vessels stimulates fibrous granular tissue angiogenesis, which keeps its L/V constant, (4) L/V in trabeculae increases with time, and (5) blood supply (Q) and nutrient exchange in healing trabeculae are not positively correlated. Thus, O2 supply to the trabeculum cannot be predicted from Q alone because the nutrient exchange area is not constant. It was noted that an increase in the potential nutrient exchange area occurred in both fibrous granular tissue and osseous vessels and the volume fraction of blood decreased in the fibrous granular tissue and remained constant in the trabeculae.

Animals↗
PubMed1990

Neo-osteogenesis of haversian trabeculae through a bone chamber implanted in a rabbit tibial cortex: a control model.

Neo-osteogenesis of cortical bone trabecular was observed as they regenerated into a bone chamber implant by appositional growth. Measures of change in bone area were obtained from 13 rabbits each week starting the third and ending the eighth week postimplantation. Observations were made using intravital microscopy and were analyzed using digital image processing. Images were computer-captured video frames equivalent to 78 (6 x 13) separate observations. They were measured by tracing the trabecular outlines with a digitizing crosshair each week and comparing changes in area as a percent of the circular field-of-view ("slit-gap") filled. Data supported the hypothesis that trabecular regeneration week 3 to week 8 followed the logistic growth curve regression: A% 100%/1 + 9.47e-0.7747(t-3) where A% is the percent of slit-gap area covered by bone and t is time, at a very high significance level. Nevertheless, a highly significant linear regression fit the data. Statistical analysis showed that the regression line could be fit to bone area measurements from weeks 3 to 8 (W3-W8) postimplantation, giving a constant neo-osteogenesis rate of 7.42 +/- 0.67 X 10(4) microns 2/day and a decreasing linear neo-osteogenesis rate from 73 microns/day at W4 to 21 microns/day at W8; the latter is based on a circle-segment approximation of trabeculum shape. This range approximated a bridge between ranges for cortical gap defect healing and porous ingrowth healing reported by other workers and supported the hypothesis that the BCI control model was a cross between gap healing and porous ingrowth.

Air Pressure↗
PubMed1989

A horizontal intravital microscope-plus-bone chamber system for observing bone microcirculation.

A horizontal intravital microscope has been built which utilizes the telescope optics format with infinity-corrected objectives. The intravital stage accomodates a rabbit into which a tibial bone chamber has been implanted. The chamber is itself an optical component and is considered an integral part of the system. Each animal is observed in supine position with its implanted leg held in an adjustable spring-loaded yoke which aligns the bone chamber in the optical axis. Long working-distance objectives and condensers allow for viewing of the slit-gap tissue in the bone chamber with both transmitted and epi-illumination; the latter being applied for fluorescence studies. A unique feature of the system is a transfer lens holder which can be relocated within the microscope tube. This adjustable lens holder allows for changing of transfer lenses, thereby freeing the investigator to utilize objective lenses with preferred numerical apertures for a given image size.

Animals↗
PubMed1988

Wound healing in the bone chamber 1. Neoosteogenesis during transition from the repair to the regenerative phase in the rabbit tibial cortex.

The optical bone chamber technique that includes intravital microscopy is described and is then applied to measuring primary wound healing neoostogenesis in rabbit tibia cortical bone during the period when fibrovascular tissue is being replaced by regenerating osteovascular tissue. The small population of rabbits sampled allowed only tentative conclusions. The quantitative measurements, a direct from of histomorphometry, are applied to determine the consistency of observations, with the hypothesis that healing into the bone chamber slit-gap follows the pattern of primary bone regeneration established as "characteristic" by other studies. The results supported the hypothesis and showed that bony ingrowth started during the third postoperative week (W3) with a maximum linear growth rate of 85.5 micron/day for a bone front. Evidence for remodeling by W6 was also obtained. While the bone chamber environment for tissue ingrowth is artificial, it can generate quantitative data that may provide a statistically valid basis for modeling pathophysiologic processes associated with bone wound healing.

Animals↗
PubMed1987

The role of the periciliary fluid in mucociliary flows: flow velocity profiles in frog palate mucus.

Observations of flow velocity profiles over frog mucociliated palate are used to estimate viscosity, shear rate and shear stress in the periciliary flow field. The ability of cilia to generate significant shear stress at long distances and their utility as rhoeometers are examined. It is proposed that the depth of significant ciliary shear penetration into the periciliary fluid is sufficient to move mucus masses well beyond the ciliary tips, obviating the need for tip penetration where anchoring phenomena are sufficiently reduced.

Animals↗
PubMed1984

On the mechanics of mucociliary flows. III. Flow-velocity profiles in frog palate mucus.

Flow-velocity profiles over excised frog ciliated epithelium were obtained for the region within about 600 micron of the mucosa. Fluorescent particles were used as flow tracers. Both a control and an autologous mucus suspension were observed. The control culture medium was bounded by the walls of the observation chamber, and mucus was deposited on the epithelium as a blob after mixing it with tracers. In spite of the difference in boundary conditions the two profiles, normalized to maximum particle velocity and solution depth, were indistinguishable at heights over 60 micron from the mucosa. The near-mucosa profiles in contrast were unalike with mucus exhibiting a greater shear gradient than the control culture medium. It was concluded that ciliary contact is not necessary for generation of mucus flow provided the ciliary shear is not negated by the mucus "flake" or "slab" being in simultaneous contact with significant ciliostatic patches which would act as anchors.

Animals↗
PubMed1984

Observations on the response of human spermatozoa to gravity, boundaries and fluid shear.

Human sperm motility response to three mechanical stimuli, gravity, fluid flow shear and rigid boundaries, was measured in a tube of 310 X 400 microns calibre. Data were gathered by cine recordings at various focussing levels d across the tube and analysed with a computerized image analysis system. The most influential stimulus was the tube wall near (more than 'at') which the swimmers tended to accumulate, leaving the fluid beyond 100 microns from the wall (d = 100) vacant of motile spermatozoa. The boundary effect was evident as soon as the spermatozoa could be viewed after loading, and accumulation, measured as frequency, as a function of d did not change with time t. This response was not significantly altered by the addition of laminar flow with a centre line velocity of about 400 microns/sec. In flow shear, spermatozoa aligned positively (in the flow direction) at the wall but negatively by about 30 microns from the wall where the velocity gradient (= shear rate) was about 3.5 sec-1. The response to gravity was relatively weak with 11 spermatozoa positive (swimming downwards) for each 9 negative. Neither the boundary effect nor the 'rheotaxic' effect were influenced by gravity as there was no statistical difference in orientation or distribution patterns between vertically and horizontally flowing suspensions. It is suggested that the boundary effect cannot be ignored in in-vitro manipulations, particularly when spermatozoa are observed or extracted. Its importance in vivo lies in the degree to which the tubes transporting motile spermatozoa seem to have mechanisms for reversing the wall accumulation tendency.

Computers↗
PubMed1983

A model of ovum transport.

A theoretical fluid dynamical model of ovum transport in the oviduct incorporating transport mechanisms due to ciliary activity, muscular activity and an applied pressure drop across the oviduct is developed. Theory suggests that the cilia provide the steady component of ovum transport whereas muscular activity results in highly oscillatory motion. If muscular activity is to provide transport in a pro-uterine direction, a coordinated sequence of muscular activity with a strong pro-uterine bias is needed. Changes in pressure are highest in the narrowest sections. The highly convoluted rugae may allow "leakback" around the ovum so relieving the pressure drop across the ovum in narrower sections of the oviduct.

Animals↗
PubMed1976

Ciliary propulsion of objects in tubes: wall drag on swimming Tetrahymena (Ciliata) in the presence of mucin and other long-chain polymers.

The lubrication effect of three long-chain polymers - mucin, methylcellulose and Ficoll - on ciliary propulsion in tubes is measured by plotting the relative velocities of swimming cilitates as a function of the tube bore diameter. Mucin shows the most unequivocal lubrication, which is found at concentrations between 0% and 9.1% (w/v). This observation, coupled with viscometric measurements which show that ciliary tip shear rates are sufficient to solate mucin, serve as the groundwork for a model of mucin lubrication which explains the optimized lubrication behaviour of thixotropic gelating polymers as an expression of the response to shear by the various stages of polymer clustering during the gelatin process. In addition to the lubricative effect, another wall drag reduction effect by mucin was measured in the clearance region beyond the lubrication layer. This apparent viscosity reduction is optimized in the concentration range between I.7% and 4.I% mucin and may also be explained in terms of the properties of gel clustering.

Animals↗
PubMed1976

Spirillum swimming: theory and observations of propulsion by the flagellar bundle.

The hydrodynamics and energetics of helical swimming by the bacterium Spirillum sp. is analysed using observations from medium speed cine photomicrography and theory. The photographic records show that the swimming organism's flagellar bundles beat in a helical fashion just as other bacterial flagella do. The data are analysed according to the rotational resistive theory of Chwang & Wu (1971) in a simple-to-use parametric form with the viscous coefficients Cs and Cn calculated according to the method of Lighthill (1975). Results of the analysis show that Spirillum dissipated biochemical energy in performing work against fluid resistance to motion at an average rate of about 6 X 10(-8) dyne cm s-1 with some 62-72% of the power dissipation due to the non-contractile body. These relationships yield a relatively low hydromechanical efficiency which is reflected in swimming speeds much smaller than a representative eukaryote. In addition the Cn/Cs ratio for the body is shown to lie in the range 0-86-1-51 and that for the flagellar bundle in the range 1-46-1-63. The implications of the power calculations for the Berg & Anderson (1973) rotating shaft model are discussed and it is shown that a rotational resistive theory analysis predicts a 5-cross bridge M ring for each flagellum of Spirillum.

Energy Metabolism↗