Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Engineering”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19Linked to original sources
PubMed2006

Preliminary experience with tissue engineering of a venous vascular patch by using bone marrow-derived cells and a hybrid biodegradable polymer scaffold.

OBJECTIVE: Currently available synthetic polymer vascular patches used in cardiovascular surgery have shown serious shortcomings, including thrombosis, calcification, infection, and lack of growth potential. These problems may be avoided by vascular patches tissue-engineered with autologous stem cells and biodegradable polymeric materials. The objective of this study was to develop a tissue-engineered vascular patch by using autologous bone marrow-derived cells (BMCs) and a hybrid biodegradable polymer scaffold. METHODS: Hybrid biodegradable polymer scaffolds were fabricated from poly(lactide-co-epsilon-caprolactone) (PLCL) copolymer reinforced with poly(glycolic acid) (PGA) fibers. Canine bone marrow mononuclear cells were induced in vitro to differentiate into vascular smooth muscle cells and endothelial cells. Tissue-engineered vascular patches (15 mm wide x 30 mm long) were fabricated by seeding vascular cells onto PGA/PLCL scaffolds and implanted into the inferior vena cava of bone marrow donor dogs. RESULTS: Compared with PLCL scaffolds, PGA/PLCL scaffolds exhibited tensile mechanical properties more similar to those of dog inferior vena cava. Eight weeks after implantation of vascular patches tissue-engineered with BMCs and PGA/PLCL scaffolds, the vascular patches remained patent with no sign of thrombosis, stenosis, or dilatation. Histological, immunohistochemical, and scanning electron microscopic analyses of the retrieved vascular patches revealed regeneration of endothelium and smooth muscle, as well as the presence of collagen. Calcium deposition on tissue-engineered vascular patches was not significantly different from that on native blood vessels. Immunofluorescent double staining confirmed that implanted BMCs survived after implantation and contributed to regeneration of endothelium and vascular smooth muscle in the implanted vascular patches. CONCLUSIONS: This study demonstrates that vascular patches can be tissue-engineered with autologous BMCs and hybrid biodegradable polymer scaffolds.

Absorbable Implants↗
PubMed2003

Cell sheet engineering for myocardial tissue reconstruction.

Myocardial tissue engineering has now emerged as one of the most promising treatments for the patients suffering from severe heart failure. Tissue engineering has currently been based on the technology using three-dimensional (3-D) biodegradable scaffolds as alternatives for extracellular matrix. According to this most popular technique, several types of 3-D myocardial tissues have been successfully engineered by seeding cardiomyocytes into poly(glycolic acid), gelatin, alginate or collagen scaffolds. However, insufficient cell migration into the scaffolds and inflammatory reaction due to scaffold biodegradation remain problems to be solved. In contrast to these technologies, we now propose novel tissue engineering methodology layering cell sheets to construct 3-D functional tissues without any artificial scaffolds. Confluent cells on temperature-responsive culture surfaces can be harvested as a viable contiguous cell sheet only by lowering temperature without any enzymatic digestions. Electrical communications are established between layered cardiomyocyte sheets, resulting in simultaneous beating 3-D myocardial tissues. Layered cardiomyocyte sheets in vivo present long survival, macroscopic pulsation and characteristic structures of native heart tissue. Cell sheet engineering should have enormous potential for fabricating clinically applicable myocardial tissues and should promote tissue engineering research fields.

Animals↗
PubMed2004

Skeletal tissue engineering-from in vitro studies to large animal models.

Bone is a tissue with a strong regenerative potential. New strategies for tissue engineering of bone should therefore only focus on defects with a certain size that will not heal spontaneously. In the development of tissue-engineered constructs many variables may play a role, e.g. the source of the cells used, the design and mechanical properties of the scaffold and the concentration and mode of application of growth factor(s). Models for studying new strategies for tissue engineering of bone should be based on the target tissue to be restored. However, in light of the many potential variables, which may also interact if used in combination(s), there is also a large need for relatively simple models in which variables can be tested in a limited number of animals. Moreover, in compromised bone there may be a problem with the load-bearing capacity of the remaining healthy bone. In this light, an important prerequisite for tissue-engineering constructs is that they can be tested in loaded conditions. Particularly, this latter prerequisite is very difficult to achieve. Therefore, in vitro tests for mechanical stability are very useful for evaluating the mechanical consequences of a particular reconstruction procedure prior to the animal experiment. Before a tissue-engineered construct can be introduced into a clinical trial, a final test should be available in a large animal model that is as close and relevant to a particular problematic clinical situation as possible.In the past, a series of models were developed in our laboratory that are very useful for testing tissue-engineered constructs. In this paper, we focus on the use of relatively new simple in vitro and in vivo models for hip revision surgery, segmental bone defect restoration and tumour surgery.

Animals↗
PubMed2004

Engineered heart tissue for regeneration of diseased hearts.

Cardiac tissue engineering aims at providing contractile heart muscle constructs for replacement therapy in vivo. At present, most cardiac tissue engineering attempts utilize heart cells from embryonic chicken and neonatal rats and scaffold materials. Over the past years our group has developed a novel technique to engineer collagen/matrigel-based cardiac muscle constructs, which we termed engineered heart tissue (EHT). EHT display functional and morphological properties of differentiated heart muscle and can be constructed in different shape and size from collagen type I, extracellular matrix proteins (Matrigel((R))), and heart cells from neonatal rats and embryonic chicken. First implantation studies in syngeneic Fischer 344 rats provided evidence of EHT survival and integration in vivo. This review will focus on our experience in tissue engineering of cardiac muscle. Mainly, EHT construction, matrix requirements, potential applications of different cell types including stem cells, and our first implantation experiences will be discussed. Despite many critical and unresolved questions, we believe that cardiac tissue engineering in general has an interesting perspective for the replacement of malfunctioning myocardium and reconstruction of congenital malformations.

Animals↗
PubMed2003

Normal features of tissue-engineered auricular cartilage by flow cytometry and histology: patient safety.

BACKGROUND: Cytokinetic abnormalities in DNA content, such as aneuploidy, haploidy, and tetraploidy, have been found to occur in human cartilaginous tumors. The high number of chondrocytes needed for tissue-engineered cartilaginous implants requires the cells to be passaged repeatedly. The theoretical risk of changes in the normal diploid state of these cells during their growth in vitro and after generation of tissue-engineered cartilage in vivo is not known. Materials and methods Auricular chondrocytes were obtained from 6 patients and cultured in vitro. Chondrocyte number was increased by repeated passaging. The passaged cells were implanted in nude mice for 8 weeks to generate tissue-engineered cartilage. Fresh control chondrocytes along with the passaged cells and cells obtained from the tissue-engineered constructs were collected and compared for DNA content by flow cytometry. RESULTS: Flow cytometry demonstrated 100% diploidy with no evidence of aneuploidy, haploidy, or tetraploidy in all groups of cells. Histology of the tissue-engineered cartilage also showed no evidence of cellular atypia. CONCLUSION: The number of human auricular chondrocytes can be increased by repeated passaging and passaged chondrocytes can be safely used for implantation to generate tissue-engineered constructs without a change in the normal diploid state of the cells. Histology of the cartilage generated showed normal features without atypia.

Aneuploidy↗
PubMed2002

A new source for cardiovascular tissue engineering: human bone marrow stromal cells.

OBJECTIVE: Vascular-derived cells represent an established cell source for tissue engineering of cardiovascular constructs. Previously, cell isolation was performed by harvesting of vascular structures prior to scaffold seeding. Marrow stromal cells (MSC) demonstrate the ability to differentiate into multiple mesenchymal cell lineages and would offer an alternative cell source for tissue engineering involving a less invasive harvesting technique. We studied the feasibility of using MSC as an alternative cell source for cardiovascular tissue engineering. METHODS: Human MSC were isolated from bone marrow and expanded in culture. Subsequently MSC were seeded on bioabsorbable polymers and grown in vitro. Cultivated cells and seeded polymers were studied for cell characterization and tissue formation including extracellular matrix production. Applied methods comprised flow cytometry, histology, immunohistochemistry, transmission (TEM) and scanning electron microscopy (SEM), and biochemical assays. RESULTS: Isolated MSC demonstrated fibroblast-like morphology. Phenotype analysis revealed positive signals for alpha-smooth muscle actin and vimentin. Histology and SEM of seeded polymers showed layered tissue formation. TEM demonstrated formation of extracellular matrix with deposition of collagen fibrils. Matrix protein analysis showed production of collagen I and III. In comparison to vascular-derived cell constructs quantitative analysis demonstrated comparable amounts of extracellular matrix proteins in the tissue engineered constructs. CONCLUSIONS: Isolated MSC demonstrated myofibroblast-like characteristics. Tissue formation on bioabsorbable scaffolds was feasible with extracellular matrix production comparable to vascular-cell derived tissue engineered constructs. It appears that MSC represent a promising cell source for cardiovascular tissue engineering.

Actins↗
PubMed2002

A novel small animal model of left ventricular tissue engineering.

BACKGROUND: Complex congenital cardiac anomalies involving ventricular hypoplasia require either staged palliative reconstruction, converting the circulatory system to a single ventricle based pump, or allogeneic transplantation. Tissue engineering offers the potential for complete reconstruction of these defects, but is limited by the inability to model myocardial tissue engineering in a small animal. Our goal was to develop a small animal model for ventricular tissue engineering using rat heterotopic heart transplantation. METHODS: Donor hearts were explanted after cardioplegic arrest and the left ventricular volume was augmented by the implantation of a biodegradable engineered construct. The heart was then transplanted heterotopically into syngeneic recipients creating either a volume loaded, functioning left ventricle, or a non-functioning left ventricle. Some of the engineered constructs were seeded with multipotent bone marrow-derived mesenchymal progenitor cells before implantation. Animals were evaluated by echocardiography, morphology, histology, and immunohistochemistry after 1 month. RESULTS: A scaffolding constructed from polytetrafluoroethylene, polylactide mesh, and type I and IV collagen hydrogel resulted in minimal intracardiac inflammation without aneurysmal dilatation. Successful transplantation and differentiation of mesenchymal progenitor cells was accomplished using this scaffolding. No ventricular arrhythmias resulted from this surgical manipulation and echocardiography revealed both end systolic and diastolic volume augmentation with ventricular expansion. CONCLUSION: We have developed an in vivo model of ventricular tissue engineering using heterotopic heart transplantation. Future work will focus on construction of ventricular tissue around pre-fabricated vascular networks in order increase cellular engraftment for ventricular reconstruction.

Animals↗
PubMed2001

Physics and engineering: milestones in medicine.

The history of the development of the applications of physics and engineering in medicine provides an insight into contemporary practice and can help to mould the future. Physics and engineering form a continuum, and, in the present context, engineering is indistinguishable from applied physics. The modern scientific era, which extends over 500 years, is characterised by numerous significant developments: for example, the Nobel prizes which most closely relate to physics and engineering in medicine were for X-rays and radioactivity, the electrocardiogram, the scattering of radiation, the cyclotron, nuclear magnetic resonance, the transistor, radioimmunoassay and computed tomography; and a medical physicist has received the Peace Prize. The origins and development of nuclear medicine, magnetic resonance and ultrasonic imaging are representative of the whole field. Physics and engineering rank alongside other medical sciences and underpin many of their applications. In what is now the developed world, human life expectancy has increased dramatically, but the costs and risks of modern medicine have meanwhile become a huge problem. The growing divergence of rich and poor is now arguably the greatest challenge. The future cannot be predicted, but the potential of physics and engineering to improve medicine has never been greater.

Biomedical Engineering↗
PubMedDate not supplied

Engineering the E. coli UDP-glucose synthesis pathway for oligosaccharide synthesis.

A metabolic engineering strategy was successfully applied to engineer the UDP-glucose synthesis pathway in E. coli. Two key enzymes of the pathway, phosphoglucomutase and UDP-glucose pyrophosphorylase, were overexpressed to increase the carbon flux toward UDP-glucose synthesis. When additional enzymes (a UDP-galactose epimerase and a galactosyltransferease) were introduced to the engineered strain, the increased flux to UDP-glucose synthesis led to an enhanced UDP-galactose derived disaccharide synthesis. Specifically, close to 20 mM UDP-galactose derived disaccharides were synthesized in the engineered strain, whereas in the control strain only 2.5 mM products were obtained, indicating that the metabolic engineering strategy was successful in channeling carbon flux (8-fold more) into the UDP-glucose synthesis pathway. UDP-sugar synthesis and oligosaccharide synthesis were shown to increase according to the enzyme expression levels when inducer concentration was between 0 and 0.5 mM. However, this dependence on the enzyme expression stopped when expression level was further increased (IPTG concentration was increased from 0.5 to 1 mM), indicating that other factors emerged as bottlenecks of the synthesis. Several likely bottlenecks and possible engineering strategies to further improve the synthesis are discussed.

Carbon↗
PubMed2001

Tissue engineering: implications in the treatment of organ and tissue defects.

The loss or failure of organs and tissues due to injury/trauma or ageing is one of the major causes for concern in human health care. Tissue engineering, a new emerging field in modern biomedical sciences, promises a new ray of hope for transplantation biology by creating viable substitutes for such failing organs or tissues. Tissue engineering is rapidly growing in both scope and importance within biomedical engineering. It represents the marriage of rapid developments in cellular and molecular biology on the one hand and materials, chemical and mechanical engineering on the other. The ability to manipulate and reconstitute tissue function has tremendous clinical implications and is likely to play a key role in cell and gene therapies in the coming years. This article discusses the basic principles of tissue engineering and some of the attempts made to provide solutions by engineering tissues in vitro.

Aged↗
PubMed2000

Improving lycopene production in Escherichia coli by engineering metabolic control.

Metabolic engineering has achieved encouraging success in producing foreign metabolites in a variety of hosts. However, common strategies for engineering metabolic pathways focus on amplifying the desired enzymes and deregulating cellular controls. As a result, uncontrolled or deregulated metabolic pathways lead to metabolic imbalance and suboptimal productivity. Here we have demonstrated the second stage of metabolic engineering effort by designing and engineering a regulatory circuit to control gene expression in response to intracellular metabolic states. Specifically, we recruited and altered one of the global regulatory systems in Escherichia coli, the Ntr regulon, to control the engineered lycopene biosynthesis pathway. The artificially engineered regulon, stimulated by excess glycolytic flux through sensing of an intracellular metabolite, acetyl phosphate, controls the expression of two key enzymes in lycopene synthesis in response to flux dynamics. This intracellular control loop significantly enhanced lycopene production while reducing the negative impact caused by metabolic imbalance. Although we demonstrated this strategy for metabolite production, it can be extended into other fields where gene expression must be closely controlled by intracellular physiology, such as gene therapy.

3-Deoxy-7-Phosphoheptulonate Synthase↗
PubMed2006

Molecular engineering approaches to peptide, polyketide and other antibiotics.

Molecular engineering approaches to producing new antibiotics have been in development for about 25 years. Advances in cloning and analysis of antibiotic gene clusters, engineering biosynthetic pathways in Escherichia coli, transfer of engineered pathways from E. coli into Streptomyces expression hosts, and stable maintenance and expression of cloned genes have streamlined the process in recent years. Advances in understanding mechanisms and substrate specificities during assembly by polyketide synthases, nonribosomal peptide synthetases, glycosyltransferases and other enzymes have made molecular engineering design and outcomes more predictable. Complex molecular scaffolds not amenable to synthesis by medicinal chemistry (for example, vancomycin (Vancocin), daptomycin (Cubicin) and erythromycin) are now tractable by molecular engineering. Medicinal chemistry can further embellish the properties of engineered antibiotics, making the two disciplines complementary.

Anti-Bacterial Agents↗
PubMed2005

Harnessing wound healing and regeneration for tissue engineering.

Biomedical science has made major advances in understanding how cells grow into functioning tissue and the signalling mechanisms used to achieve this are slowly being dissected. Tissue engineering is the application of that knowledge to the building or repairing of organs, including skin, the largest organ in the body. Generally, engineered tissue is a combination of living cells and a supporting matrix. Besides serving as burn coverings, engineered skin substitutes can help patients with diabetic foot ulcers. Today, most of these ulcers are treated with an approach that includes antibiotics, glucose control, special shoes and frequent cleaning and bandaging. The results of such treatments are often disappointing and ineffectual, and scarring remains a major problem, mechanically, cosmetically and psychologically. Within our group we are attempting to address this by investigating novel approaches to skin tissue engineering. We are identifying novel therapeutic manipulations to improve the degree of integration between a tissue engineered dermal construct and the host by both molecular manipulation of growth factors but also by understanding and harnessing mechanisms of regenerative biology. For the purpose of this summary, we will concentrate primarily on the latter of these two approaches in that we have identified a novel mouse mutant that completely and perfectly regenerates skin and cartilaginous components following ear injury. This experimental animal will allow us to characterize not only novel genes involved in the regeneration process but also to utilize cells from such animals in artificial skin equivalents to assess their behaviour compared with normal cells. This approach should allow us to create a tissue-engineered substitute, which more closely resembles the normal regional microanatomy and physiology of the skin, allowing better integration to the host with minimal or no scarring.

Animals↗
PubMed2001

Fetal tissue engineering: diaphragmatic replacement.

BACKGROUND/PURPOSE: Prosthetic repair of congenital diaphragmatic hernia has been associated with high complication rates. This study was aimed at applying fetal tissue engineering to diaphragmatic replacement. METHODS: Fetal lambs underwent harvest of skeletal muscle specimens. Once expanded in vitro, fetal myoblasts were suspended in a collagen hydrogel submitted to controlled radial tension. The construct was then placed in a bioreactor. After birth, all animals underwent creation of 2 diaphragmatic defects. One defect was repaired with the autologous-engineered construct placed in between 2 acellular supporting membranes and the other with an identical construct but without any cells. Each animal was its own control (graft, n = 10). Animals were killed at different time-points postimplantation for histologic examination. Statistical analysis was by analysis of variance (ANOVA). RESULTS: Fetal myoblasts expanded up to twice as fast as neonatal cells. Hydrogel-based radial tension enhanced construct architecture by eliciting cell organization within the scaffold. No eventration was present in 4 of 5 engineered constructs but in 0 of 5 acellular grafts (P<.05). At harvest, engineered constructs were thick and histologically resembled normal skeletal muscle, whereas acellular grafts were thin, floppy, and showed low cell density with increased fibrosis. CONCLUSIONS: Unlike acellular grafts, engineered cellular diaphragmatic constructs are anatomically and histologically similar to normal muscle. Fetal tissue engineering may be a viable alternative for diaphragmatic replacement.

Analysis of Variance↗
PubMed2002

Engineering growing tissues.

Regenerating or engineering new tissues and organs may one day allow routine replacement of lost or failing tissues and organs. However, these engineered tissues must not only grow to fill a defect and integrate with the host tissue, but often they must also grow in concert with the changing needs of the body over time. We hypothesized that tissues capable of growing with time could be engineered by supplying growth stimulus signals to cells from the biomaterial used for cell transplantation. In this study, chondrocytes and osteoblasts were cotransplanted on hydrogels modified with an RGD-containing peptide sequence to promote cell multiplication. New bone tissue was formed that grew in mass and cellularity by endochondral ossification in a manner similar to normal long-bone growth. Transplanted cells organized into structures that morphologically and functionally resembled growth plates. These engineered tissues could find utility in treating diseases and injuries of the growth plate, testing the effect of experimental drugs on growth-plate function and development, and investigating the biology of long-bone growth. Furthermore, this concept of promoting the growth of engineered tissues could find great utility in engineering numerous tissue types by way of the transplantation of a small number of precursor cells.

Alginates↗
PubMedDate not supplied

A model of tissue-engineered ventral hernia repair.

We have developed a tissue-engineered ventral hernia repair system using our novel aligned collagen tube and autologous skeletal muscle satellite cells. In this model system, skeletal muscle satellite cells were isolated from a biopsy, expanded in culture, and incorporated into our collagen tube scaffold, forming the tissue-engineered construct. We characterized the results of the repaired hernias on both the gross and microscopic scales and compared them to an unrepaired control, an autologous muscle repair control, and a collagen-tube-only repair. Untreated animals developed a classic hernia sac, devoid of abdominal muscle and covered only with a thin layer of mesothelial tissue. Significant muscle, small-diameter blood vessels, and connective tissue were apparent in both the autologous control and the engineered muscle repairs. The engineered muscle repairs became cellularized, vascularized, and integrated with the native tissue, hence becoming a "living" repair. A tissue-engineered construct repair of ventral hernias with subsequent incorporation and vascularization could provide the ultimate in anterior wall myofascial defect repair and would further the understanding of striated muscle engineering. The knowledge gained from our model system would have immediate application to mangled extremities, maxillofacial reconstructions, and restorative procedures following tumor excision in other areas of the body.

Animals↗
PubMed2002

An evaluation of retrofit engineering control interventions to reduce perchloroethylene exposures in commercial dry-cleaning shops.

Real-time monitoring was used to evaluate the ability of engineering control devices retrofitted on two existing dry-cleaning machines to reduce worker exposures to perchloroethylene. In one dry-cleaning shop, a refrigerated condenser was installed on a machine that had a water-cooled condenser to reduce the air temperature, improve vapor recovery, and lower exposures. In a second shop, a carbon adsorber was retrofitted on a machine to adsorb residual perchloroethylene not collected by the existing refrigerated condenser to improve vapor recovery and reduce exposures. Both controls were successful at reducing the perchloroethylene exposures of the dry-cleaning machine operator. Real-time monitoring was performed to evaluate how the engineering controls affected exposures during loading and unloading the dry-cleaning machine, a task generally considered to account for the highest exposures. The real-time monitoring showed that dramatic reductions occurred in exposures during loading and unloading of the dry-cleaning machine due to the engineering controls. Peak operator exposures during loading and unloading were reduced by 60 percent in the shop that had a refrigerated condenser installed on the dry-cleaning machine and 92 percent in the shop that had a carbon adsorber installed. Although loading and unloading exposures were dramatically reduced, drops in full-shift time-weighted average (TWA) exposures were less dramatic. TWA exposures to perchloroethylene, as measured by conventional air sampling, showed smaller reductions in operator exposures of 28 percent or less. Differences between exposure results from real-time and conventional air sampling very likely resulted from other uncontrolled sources of exposure, differences in shop general ventilation before and after the control was installed, relatively small sample sizes, and experimental variability inherent in field research. Although there were some difficulties and complications with installation and maintenance of the engineering controls, this study showed that retrofitting engineering controls may be a feasible option for some dry-cleaning shop owners to reduce worker exposures to perchloroethylene. By installing retrofit controls, a dry-cleaning facility can reduce exposures, in some cases dramatically, and bring operators into compliance with the Occupational Safety and Health Administration (OSHA) peak exposure limit of 300 ppm. Retrofit engineering controls are also likely to enable many dry-cleaning workers to lower their overall personal TWA exposures to perchloroethylene.

Air Pollutants, Occupational↗
PubMed1992

Process safety management: resources from the American Institute of Chemical Engineers for use by industrial hygienists.

Industrial hygienists often work closely with engineers to control occupational safety and health hazards. This working relationship involves an educational process in which both engineers and industrial hygienists learn from one another. The Center for Chemical Process Safety (CCPS) of the American Institute of Chemical Engineers (AIChE) is expanding the opportunity for interdisciplinary cooperation and education by producing a series of guidelines publications on the technical and scientific issues critical to preventing and mitigating major releases of toxic materials. Examples of these guidelines include Hazard Evaluation Procedures; Technical Management of Chemical Process Safety; Chemical Process Quantitative Risk Analysis; and Safe Storage and Handling of Highly Toxic Hazardous Materials. Additional topics are addressed in the 8 guidelines in print and the 15 others in preparation. Several guidelines contain specific examples that illustrate how industrial hygienists, engineers, and other readers can use the guidelines to help address chemical process safety problems. Another CCPS activity involves an effort to include an awareness of health, safety, and loss prevention as an integral part of undergraduate chemical engineering education. For practicing engineers and industrial hygienists, a number of continuing education courses on topics such as process hazard analysis, process risk assessment, and process safety are offered by the AIChE. All of these resources are particularly timely in light of the Occupational Safety and Health Administration's recently enacted rule on Process Safety Management of Highly Hazardous Chemicals.

Academies and Institutes↗