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At least 199 records · Page 11Linked to original sources
PubMed2002

A biologically active VEGF construct in vitro: implications for bioengineering-improved prosthetic vascular grafts.

Prosthetic arterial grafts are unable to develop an intact endothelial lining after implantation, predisposing them to fail. Strategies have been sought to enhance endothelialization using growth factors and cytokines. This study assessed the biologic activity of vascular endothelial growth factor (VEGF) covalently linked to bovine serum albumin (BSA). Native and modified VEGF were assayed for endothelial cell migration and proliferation. Migration assays were performed comparing the effects of 2% fetal bovine serum (FBS), 50 ng/mL, 100 ng/mL, and 200 ng/mL of native VEGF and VEGF-BSA. Proliferation assays were performed by using Alamar Blue comparing cellular growth in 1% FBS, 10% FBS, 100 ng/mL unbound VEGF, and 100 ng/mL VEGF-BSA. VEGF is a potent chemotactic agent for endothelial cells in both unbound and bound states. Native VEGF solutions (50 ng/mL, 100 ng/mL, and 200 ng/mL) stimulated 23.9 cells/high power field (HPF), 35.3 cells/HPF, and 49.1 cells/HPF (p < 0.005). VEGF-BSA solutions stimulated 25.9 cells/HPF, 39.1 cells/HPF, and 69.0 cells/HPF (p < 0.001). VEGF-BSA and native VEGF supported similar increased cellular proliferation compared with 1% FBS media (p < 0.002). Modified VEGF retains its chemotactic and proliferative properties in vitro. These findings suggest that bare prosthetic surfaces lined with VEGF bound to a "basecoat" albumin may support endothelial cell proliferation and migration and thereby offer new strategies to improve graft patency.

Blood Vessel Prosthesis↗
PubMed2003

Bioengineered human bone tissue using autogenous osteoblasts cultured on different biomatrices.

Surgical treatment of critical-size posttraumatic bone defects is still a challenging problem, even in modern bone and joint surgery. Progress in cellular and molecular biology during the last decade now permits novel approaches in bone engineering. Recent conceptual and technical advances have enabled the use of mitotically expanded, bone-derived cells as a therapeutic approach for tissue repair. Using three different tissue carrier systems, we successfully cultivated human osteoblasts in a newly developed perfusion chamber. We studied cell proliferation and the expression of osteocalcin, osteopontin, bone morphogenetic protein-2A, alkaline phosphatase, and vascular endothelial growth factor as parameters for osteoblast function and viability. Adherence of highly enriched human osteoblasts had already started after 1 h and resulted in completely overgrown human bone pieces after 10 days. Expression analysis of bone-specific alkaline phosphatase indicated differentiating osteoblasts, whereas the high mRNA expression of osteocalcin and osteopontin revealed terminally differentiated osteoblasts and the process of mineralization. Additionally, gene expression was significantly higher when demineralized bone was used as biomatrix, compared to autoclaved bone and hydroxyapatite ceramics. We conclude that with our newly developed perfusion culture system, vital autogenous bone implants of clinically applicable size can be generated within 17 days in order to manage critical-size bone defects.

Animals↗
PubMed2001

Functional examination of microencapsulated bioengineered insulin-secreting beta-cells.

Clonal insulin-secreting BRIN-BD11 cells engineered by electrofusion were encapsulated inside natrium alginate beads and cultured in RPMI 1640 culture media. Acute insulin secretory responses to glucose and amino acids were compared between microencapsulated cells and non-encapsulated cells maintained in monolayer culture. Encapsulated cells exhibited a 1.5-fold, 2.9-fold and 4.2-fold increase (P< 0.001) in insulin release in response to 16.7 mmol/l glucose, 10 mmol/l L-arginine and 10 mmol/l L-alanine respectively. Insulin output by non-encapsulated cells was approximately 30% greater but the relative magnitudes of responses were similar. This is the first study to demonstrate the stability of cellular engineered insulin-secreting cells encapsulated in alginate beads, illustrating the utility of this approach for cellular engineering and potential transplantation in diabetes.

Alanine↗
PubMed1986

Application of bioengineering to disease diagnosis.

Traditional approaches to diagnosing disease include clinical observations, pathological changes in tissues, and searches for the etiology, by isolation, or identification of microorganisms, or by serological methods. Development of techniques for studying the molecular biology of microorganisms, manipulation of cellular systems, and improved immunoassays have contributed to better diagnostic technology. Recombinant DNA technology has made it possible to apply highly specific probes consisting of nucleotide sequences that hybridize with complementary sequences of microorganisms. The specific techniques utilized include Southern, northern, and dot blot hybridization and in situ hybridization. Identification of proteins of microorganisms is done by western blot, dot blot, and in situ peroxidase-antiperoxidase techniques. These techniques have the promise of being highly specific and rapid methods for diagnosis of disease.

Animal Diseases↗
PubMed1988

Bioengineering issues related to in situ remediation of contaminated soils and groundwater.

This chapter presents some of the engineering challenges in biological degradation of organic contaminants in surface soils and the subsurface environment. Extraction of contaminants from the subsurface is generally costly, slow, and difficult. This has led to an interest in using in situ techniques for biodegradation of contaminants. For some contaminants that can be readily used as primary energy sources for bacteria with or without the presence of oxygen, bacterial removal is relatively simple and, in some situations, occurs naturally. In other cases, such as hydrocarbon spills, in situ treatment is still attractive, but has the added cost and difficulty of supplying required oxygen and nutrients for the fairly efficient aerobic oxidation. There are some indications that hydrocarbons may be biodegraded in the absence of oxygen; but, in these cases, the rates of degradation appear to be slow. More research in this area is desirable. The major challenge to both engineers and scientists lies in the decomposition of hazardous chemicals that appear to be transformed by the process of co-metabolism, or else are so low in concentration that they can only serve as secondary substrates. In either case, primary substrates are required to supply the major energy requirements for bacterial growth and/or for activation of enzymes necessary for the transformation. Engineering experience in the utilization of such processes for degradation of contaminants in the environment is very limited. Little is currently known about substrate interactions and how to optimize the bacterial transformations. Chemical requirements for achieving co-metabolism are high. In addition, knowledge is lacking about methods for getting the correct amounts of chemicals to the locations where needed and in the form needed. The solution of these important issues presents a significant challenge to the engineering and science communities, requiring both basic laboratory studies and field demonstrations in well-characterized environments.

Bacteria↗
PubMed2002

Fundamental structural aspects and features in the bioengineering of the gas exchangers: comparative perspectives.

Over its life, an organism's survival and success are determined by the inventory of vital adaptations that its progenitors have creatively appropriated, devised and harnessed along the evolutionary pathway. Such conserved attributes provide the armamentarium necessary for withstanding the adverse effects of natural selection. Refinements of the designs of the respiratory organs have been critical for survival and phylogenetic advancement of animal life. Gas exchangers have changed in direct response to the respiratory needs of whole organisms in different environmental states and conditions. Nowhere else is the dictum that in biology 'there are no rules but only necessities' more manifest than in the evolutionary biology of the gas exchangers. The constructions have been continually fashioned and refined to meet specific needs. Solutions to common respiratory needs have been typified by profound structural convergence. Over the evolutionary continuum, as shifts in environmental situations occurred, infinitely many designs should theoretically have emerged. Moreover, without specific selective pressures and preference for certain designs, considering that there are only two naturally occurring respirable fluid media (air and water), air-lungs, water-lungs, air-gills and water-gills would have formed to similar extents. Factors such as body size, phylogenetic level of development, respiratory medium utilized and habitats occupied have permutatively prescribed the design of the gas exchangers. The construction of the modern gas exchangers has eventuated through painstaking cost-benefit analysis. Trade-offs and compromises have decreed only a limited number of structurally feasible and functionally competent outcomes. The morphological congruity (analogy) of the gas exchangers indicates that similar selective pressures have compelled the designs. Solutions to metabolic demands for molecular O2 have only differed in details. Passive physical diffusion, for example, is the ubiquitous method of transfer of O2 across biological tissues. Gills, evaginated gas exchangers, were the primordial respiratory organs that evolved for water breathing, whereas lungs (invaginated gas exchangers) developed for terrestrial (air) breathing. Transitional (= bimodal = amphibious) breathing has evolved in animals with specialized organs that extract O2 from both water and air. Lungs are tidally (= bidirectionally) ventilated, while gills are unidirectionally ventilated, a feature that allows the highly efficient counter-current disposition between blood and water. Since animals occupy inconstant environmental milieus and their metabolic states vary, gas exchangers are designed to operate optimally across a spectrum of conditions that range from resting to exercise and even under hypoxia. Inbuilt structural and functional flexibility provides the requisite safety factors that allow adjustments to modest pressures. The fundamental structural features that determine the respiratory function of a gas exchanger are respiratory surface area, thickness of the blood-water/gas (tissue) barrier and volume of the pulmonary capillary blood. The diffusing capacity of a gas exchanger correlates directly with the surface area and inversely with the thickness of the blood-water/gas (tissue) barrier. An extensive surface area is generated in gills by extensive stratification of the gas exchanger and in lungs by profuse internal subdivision. Compartmentalization yields small terminal gas exchange compartments that compel greater commitment of energy to ventilate. The surfactant, a phospholipid lining, reduces the forces of surface tension at the air-water interface. This attenuates the propensity of physical collapse of the minute gas exchange units and minimizes the cost of ventilation. The surfactant characterizes all the gas exchangers derived from the piscine air bladder. In the lower air-breathing vertebrates, such as the lungfishes (Dipnoi), amphibians and certain reptiles, the pneumocytes are not differentiated into type I and II cells, as is the case in the lungs of the higher vertebrates-birds and mammals. It is envisaged that in endotherms, the overall numerical density of the pneumocytes and hence the O2 consumption of the gas exchangers may be reduced and a thin blood-gas (tissue) barrier generated, factors that enhance respiratory efficiency. The thin blood-gas (tissue) barriers, for example, those of the mammalian (in the respiratory sections of the interalveolar septum) and avian lungs, consist of an epithelial cell and an endothelial cell with a common basement membrane. An interstitial space occurs in the blood-air/water (tissue) barriers of the gas exchangers of fish gills and lungs of lungfishes, amphibians, reptiles and in the supportive parts of the interalveolar septum of the mammalian lung. Collagen, elastic tissue, nerves, lymphatic vessels and smooth muscle elements are found in the interstitial space. The thickness of the blood-air/water (tissue) barrier allometrically changes very little. This suggests that the thicknesses of the blood-water/air (tissue) barriers have been optimized. The presentation and exposure to the gas exchange media (water/air to blood), features dictated by the geometry and arrangements of the structural components of the gas exchangers, contribute greatly to respiratory efficiency. The countercurrent presentation between water and blood in fish gills is the most efficient design in the evolved gas exchangers: It was imperative for survival in water, a medium that contains relatively less O2 and is more expensive to breathe. In the evolved vertebrate gas exchangers, the exposure of blood to air is best manifested in the diffuse design of the avian lung, where the capillary blood is literally suspended in a three-dimensional air space, the blood being exposed to air virtually across the entire blood-gas (tissue) barrier. A double capillary design occurs in the lungs of amphibians and generally those of reptiles, whereas a single capillary design commonly occurs in those of adult mammals. The capillary loading (the ratio of the volume of the capillary blood to the surface area across which blood is exposed to air) in lungs with a double capillary arrangement is high and manifests a poor design. On the other hand, the low capillary loading that characterizes the single capillary system indicates better exposure of blood to air and greater respiratory capacity. Fractal geometry features in the construction of the gas exchangers. The highly versatile design allows the gas exchangers to function optimally under different conditions and circumstances and to maintain congruent morphologies over a wide range of body size, shape and metabolic capacities. At the gas exchange level, sheet-flow design preponderates in the evolved gas exchangers; blood is efficiently exposed to the external respiratory medium. The respiratory capacity of a gas exchanger is comprehensively granted by refinements of structural features and functional processes. Modelling, mathematical integration of structural and functional parameters, provides a holistic view of the essence of the design of a gas exchanger.

Animals↗
PubMed1984

Impact of bioengineering on noninvasive diagnostics.

Out of a number of important methods used in laboratory angiology, only a limited group was selected to be discussed in this symposium. Phonoangiography is reviewed from the qualitative and quantitative viewpoint for its practical value and accessibility. Various aspects of pressure and volume detection of the eye pulse are discussed from the viewpoint of carotid artery disease and its noninvasive diagnosis, with special reference to oculoplethysmography as well as the Gee-pneumooculoplethysmography. Impedance plethysmography (IPG) is one of the controversial techniques used in laboratory angiology, with its main application currently in the area of diagnosis of venous obstructive disease. The dilemma of application of IPG in the diagnosis of arterial disease is discussed mainly from an engineering point of view. Spectral analysis will be covered in view of the fast emergence of Doppler Duplex scanning as the major diagnostic mode in extracranial carotid artery disease.

Auscultation↗
PubMedDate not supplied

Images from Waves--photoelastic modelling of bones. 8th Samuel Haughton Lecture, Bioengineering Section of Royal Academy of Medicine in Ireland. January 2002.

BACKGROUND: This paper cites the development of the principles of photoelastic stress analysis, contemporary to the life of Samuel Haughton. Subsequent studies of bone and joint replacements are discussed, with reference to hypotheses regarding bone, including the coincidence of trabecular structure with principal stresses. Issues regarding assumptions of homogeneous and isotropic properties in photoelastic modelling are acknowledged. AIM: Awareness of photoelastic methods is often through the visual appeal of the coloured fringe patterns. The aim of this paper is to complement this awareness by demonstration of the quantitative analyses that may be conducted through biomechanical examples. METHODS: Examples of new pseudo three-dimensional model analyses are presented together with a method for photoelastic study of cancellous bone, which entails novel procedures for preparation of replicate models and for optical evaluation of fringes. CONCLUSION: Photoelastic analysis offers novel solutions to studies in biomechanics, which are facilitated by contemporary modelling materials.

Animals↗