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PubMedDate not supplied

Functional engineered channels and pores (Review).

Significant progress has been made in membrane protein engineering over the last 5 years, based largely on the re-design of existing scaffolds. Engineering techniques that have been employed include direct genetic engineering, both covalent and non-covalent modification, unnatural amino acid mutagenesis and total synthesis aided by chemical ligation of unprotected fragments. Combinatorial mutagenesis and directed evolution remain, by contrast, underemployed. Techniques for assembling and purifying heteromeric multisubunit pores have been improved. Progress in the de novo design of channels and pores has been slower. But, we are at the beginning of a new era in membrane protein engineering based on the accelerating acquisition of structural information, a better understanding of molecular motion in membrane proteins, technical improvements in membrane protein refolding and the application of computational approaches developed for soluble proteins. In addition, the next 5 years should see further advances in the applications of engineered channels and pores, notably in therapeutics and sensor technology.

Animals↗
PubMed2004

Effects of diesel engine speed and water content on emission characteristics of three-phase emulsions.

The effects of water content of three-phase emulsions and engine speed on the combustion and emission characteristics of diesel engines were investigated in this study. The results show that a larger water content of water-in oil (W/O) and oil-in-water-in-oil (O/W/O) emulsion caused a higher brake specific fuel consumption (bsfc) value and a lower O2, as well as a lower NOx emission, but a larger CO emission. The increase in engine speed resulted in an increase of bsfc, exhaust gas temperature, fuel-to-air ratio, CO2 emission and a decrease of NOx, CO emission, and smoke opacity. Because of the physical structural differences, the three-phase O/W/O emulsions were observed to produce a higher exhaust gas temperature, a higher emulsion viscosity and a lower CO emission, in comparison with that of the two-phase W/O emulsion. In addition, the use of W/O emulsions with water content larger than 20% may cause diesel engines to shut down earlier than those running on O/W/O emulsions with the same water content. Hence, it is suggested that the emulsions with water content larger than 20% are not suitable for use as alternative fuel for diesel engines.

Air Pollutants↗
PubMed2002

Gene transfer of a human insulin-like growth factor I cDNA enhances tissue engineering of cartilage.

The repair of articular cartilage lesions remains a clinical problem. Two novel approaches to cartilage formation, gene transfer and tissue engineering, have been limited by short-term transgene expression in transplanted chondrocytes and inability to deliver regulatory signals to engineered tissues according to specific temporal and spatial patterns. We tested the hypothesis that the transfer of a cDNA encoding the human insulin-like growth factor I (IGF-I) can provide sustained gene expression in cell-polymer constructs in vitro and in vivo and enhance the structural and functional properties of tissue-engineered cartilage. Bovine articular chondrocytes genetically modified to overexpress human IGF-I were seeded into polymer scaffolds, cultured in bioreactors in serum-free medium, and implanted subcutaneously in nude mice; constructs based on nontransfected or lacZ-transfected chondrocytes served as controls. Transgene expression was maintained throughout the duration of the study, more than 4 weeks in vitro followed by an additional 10 days either in vitro or in vivo. Chondrogenesis progressed toward the formation of cartilaginous tissue that was characterized by the presence of glycosaminoglycans, aggrecan, and type II collagen, and the absence of type I collagen. IGF-I constructs contained increased amounts of glycosaminoglycans and collagen and confined-compression equilibrium moduli as compared with controls; all groups had subnormal cellularity. The amounts of glycosaminoglycans and collagen per unit DNA in IGF-I constructs were markedly higher than in constructs cultured in serum-supplemented medium or native cartilage. This enhancement of chondrogenesis by spatially defined overexpression of human IGF-I suggests that cartilage tissue engineering based on genetically modified chondrocytes may be advantageous as compared with either gene transfer or tissue engineering alone.

Animals↗
PubMed2000

Morphogenesis and tissue engineering of bone and cartilage: inductive signals, stem cells, and biomimetic biomaterials.

Morphogenesis is the developmental cascade of pattern formation, body plan establishment, and the architecture of mirror-image bilateral symmetry of many structures and asymmetry of some, culminating in the adult form. Tissue engineering is the emerging discipline of design and construction of spare parts for the human body to restore function based on principles of molecular developmental biology and morphogenesis governed by bioengineering. The three key ingredients for both morphogenesis and tissue engineering are inductive signals, responding stem cells, and the extracellular matrix. Among the many tissues in the human body, bone has considerable powers for regeneration and is a prototype model for tissue engineering based on morphogenesis. Implantation of demineralized bone matrix into subcutaneous sites results in local bone induction. This model mimics sequential limb morphogenesis and permitted the isolation of bone morphogens. Although it is traditional to study morphogenetic signals in embryos, bone morphogenetic proteins (BMPs), the inductive signals for bone, were isolated from demineralized bone matrix from adults. BMPs and related cartilage-derived morphogenetic proteins (CDMPs) initiate, promote, and maintain chondrogenesis and osteogenesis and have actions beyond bone. The symbiosis of bone inductive and conductive strategies are critical for tissue engineering, and is in turn governed by the context and biomechanics. The context is the microenvironment, consisting of extracellular matrix, which can be duplicated by biomimetic biomaterials such as collagens, hydroxyapatite, proteoglycans, and cell adhesion proteins including fibronectins. Thus, the rules of architecture for tissue engineering are an imitation of the laws of developmental biology and morphogenesis, and thus may be universal for all tissues, including bones and joints.

Adult↗
PubMed2002

A glimpse of tissue engineering in China.

Tissue engineering activities in China have expanded and advanced to the extent that it is not possible to acknowledge all of the work in one review. Substantial progress has been made in the development of novel biomaterial scaffolds and in the genetic manipulation of cells in vitro. Moreover, certain aspects of tissue engineering strategies have begun to undergo clinical trial. A glimpse of tissue engineering in China was afforded at the First International Conference on Biomaterials (China) held in Beijing, July 24-26, 2001. Several papers presented at the meeting, which was conducted in English only, reflected many of the tissue engineering activities in the country. A brief summary of some of the papers may begin to suggest possibilities for collaboration between tissue engineers inside and outside of China, as well as to facilitate dissemination of important findings.

China↗
PubMed2002

Composition options for tissue-engineered bone.

The logical assembly of tissue-engineered bone is ultimately directed by the clinical status of the patient. The basic elements for tissue-engineered bone should include signaling molecules, cells, and extracellular matrix. The assembly of these basic elements may need to be modified by tissue engineers to account for patient variables of age, gender, health, systemic conditions, habits, and anatomical implant. Moreover, different regions of the body will have different functional loads and vascularity. This review discusses several basic options that may be necessary to engineer bone, including spatial and temporal assembly of signaling factors, cells, and biomimetic extracellular matrices. Moreover, the importance of the health care status of the patient who may be receiving the tissue-engineered composition is emphasized.

Bone Marrow Cells↗
PubMed2002

Repairing large porcine full-thickness defects of articular cartilage using autologous chondrocyte-engineered cartilage.

Large full-thickness defects of articular cartilage remain a major challenge to orthopedic surgeons because of unsatisfactory results of current therapy. Many methods, such as chondrectomy, drilling, cartilage scraping, arthroplasty, transplantation of chondrocytes, periosteum, perichondrium, as well as cartilage and bone, have been tried to repair articular cartilage defects. However, the results are far from satisfactory. In this study, we applied a tissue-engineering approach to the repair of articular cartilage defects of knee joints in a porcine model. Using isolated autologous chondrocytes, polyglycolic acid (PGA), and Pluronic, we have successfully in vivo-engineered hyaline cartilage and repaired articular cartilage defects. The surface of the repaired defects appeared smooth at 24 weeks postrepair. Histological examination demonstrated a typical hyaline cartilage structure with ideal interface healing between the engineered cartilage and the adjacent normal cartilage and underlying cancellous bone. In addition, glycosaminoglycan (GAG) levels in the engineered cartilage reached 80% of that found in native cartilage at 24 weeks postrepair. Biomechanical analysis at 24 weeks demonstrated that the biomechanical properties of the tissue-engineered cartilage were improved compared with those at an earlier stage. Thus, the results of this study may provide insight into the clinical repair of articular cartilage defects.

Animals↗
PubMed2003

Precursor tissue analogs as a tissue-engineering strategy.

Natural tissues are composed of functionally diverse cell types that are organized in spatially complex arrangements. Organogenesis of complex tissues requires a coordinated sequential transformation process, with individual stages involving time-dependent expression of cell-cell, cell-matrix, and cell-signal interactions in three dimensions. The common theme of temporal-spatial patterning of these cellular interactions is also observed in other physiological processes, such as growth and development, wound healing, and tumor migration. The "precursor tissue analog" (PTA) applies the temporal-spatial patterning theme to tissue engineering. The goal of PTA in tissue engineering is not to fabricate the final transplantable tissue but rather to guide the dynamic organization, maturation, and remodeling leading to the formation of normal and functional tissues. We describe the critical design principles of PTA. First, structural, mechanical, and physiological requirements of the PTA as a temporary scaffold must be met by a fabrication method with flexibility. The fabrication potential incorporating biological materials such as living cells and plasmid DNA has been addressed. Second, the PTA concept is considered suitable for future tissue engineering in light of the use of undifferentiated stem cells, and may possess a capability to guide stem cells toward diverse differentiation characteristics in situ. To this end, the behavior of the engineered cell and tissue must be monitored in detail. The development of a practical phenotype monitoring system such as a DNA microarray may be integral to the fabrication strategies of PTA. Third, the microtopographical and microenvironmental control on the liquid-solid interaction may lead to a critical design for PTA to provide soluble factors, nutrients, and gases to the cells embedded within the scaffold. We suggest that the level set numerical simulation method may be utilized to engineer the consistent circulation of bioactive liquid throughout the PTA microenvironment.

Animals↗
PubMed2003

Angiogenesis in tissue-engineered small intestine.

Tissue-engineered intestine offers promise as a potential novel therapy for short bowel syndrome. In this study we characterized the microvasculature and angiogenic growth factor profile of the engineered intestine. Twenty-three tissue-engineered small intestinal grafts were harvested from Lewis rat recipients 1 to 8 weeks after implantation. Architectural similarity to native bowel obtained from juvenile rats was assessed with hematoxylin and eosin-stained sections. Capillary density, measured after immunohistochemical staining for CD34, was expressed as number of capillaries per 1000 nuclei. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) tissue levels were measured by ELISA and normalized to total protein. Over the 8-week period cysts increased in volume (0.5 cm(3) at week 1 versus 12.6 cm(3) at week 8) and mass (1.30 +/- 0.29 versus 9.74 +/- 0.3 g; mean +/- SEM). Muscular and mucosal layers increased in thickness, but capillary density remained constant (82.95 +/- 4.81 capillaries per 1000 nuclei). The VEGF level was significantly higher in juvenile rat bowel than in engineered cyst (147.6 +/- 23.9 versus 42.3 +/- 3.4 pg/mg; p < 0.001). Tissue bFGF levels were also higher (315 +/- 65.48 versus 162.3 +/- 15.09 pg/mg; p < 0.05). The mechanism driving angiogenesis differs in engineered intestine and in normal bowel. VEGF and bFGF delivery may prove useful for bioengineering of intestine.

Aging↗
PubMed2003

Engineering of vaginal tissue in vivo.

Congenital vaginal anomalies and cloacal malformations may require extensive surgical reconstruction. Surgical challenges are often encountered because of the limited amounts of native tissue available. We investigated the feasibility of using vaginal epithelial and smooth muscle cells for the engineering of vaginal tissues in vivo. Vaginal epithelial and smooth muscle cells of female rabbits were grown, expanded in culture, and characterized immunocytochemically. Vaginal epithelial and smooth muscle cells were seeded on polyglycolic acid (PGA) scaffolds at 10 x 10(6) and 20 x 10(6) cells/cm(3), respectively. The cell-seeded scaffolds were subcutaneously implanted into nude mice. The animals were killed 1, 4, and 6 weeks after implantation. Immunocytochemical and histochemical analyses were performed with pancytokeratins AE1/AE3 and with smooth muscle-specific alpha-actin antibodies to confirm the reconstituted tissue phenotype. Western blot analyses and electrical field stimulation studies were also performed to further characterize the tissue-engineered constructs. Vaginal epithelial cells were serially identified with anti-pancytokeratins AE1/AE3 at all culture stages. Smooth muscle cells in culture stained positively with alpha-smooth muscle actin antibodies. One week after implantation in vivo, the retrieved polymer scaffolds demonstrated multilayered tissue strips of both cell types, and penetrating native vasculature was also noted. Increased organization of the smooth muscle and epithelial tissue was evident by 4 weeks. There was no evidence of tissue formation in the controls. Immunocytochemical analyses using anti-pancytokeratins confirmed the presence of vaginal epithelial cells in each of the constructs. Anti-alpha-actin smooth muscle antibodies also confirmed the presence of multilayered smooth muscle fibers and tissue at each time point. Western blot analyses of the scaffolds confirmed the expression of cytokeratin and smooth muscle actin proteins when compared with controls. The contractile properties of the tissue-engineered vaginal constructs in response to electrical field stimulation were similar to those of normal vaginal tissue. Vaginal epithelial and smooth muscle cells can be easily cultured and expanded in vitro. Cell-seeded polymer scaffolds are able to form vascularized vaginal tissue in vivo that have phenotypic and functional properties similar to those of normal vaginal tissues. This is the first demonstration in tissue engineering wherein vaginal epithelial and smooth muscle cells are reconstituted in vivo into vaginal tissue. This technology may be pursued further experimentally in order to achieve the engineering of vaginal tissues for clinical applications.

Actins↗
PubMedDate not supplied

Tissue engineering: the end of the beginning.

This study was undertaken to assess the impact of current economic conditions and recent disappointing product launches on the field of tissue engineering. Data were collected on all firms known to be active in the field, analyzed, and compared with analogous data collected in 1995, 1998, and 2000. As of December 31, 2002, more than 2600 full-time equivalents (FTEs) in 15 countries and 89 firms were engaged in tissue-engineering research and development. Annual spending was US dollars 487 million, down about 20% since 2000-a reasonable performance in the face of a stagnant economy and difficult capital markets. Individual sectors proved far more volatile. Activity in skin, cartilage, and other structural applications declined by more than 50% with a loss of 800 FTEs. This downsizing was somewhat counterbalanced by a 42% increase in stem cell firms, which added more than 300 employees. Consistent with general disenchantment with technology sector equities, capital value of publicly traded tissue-engineering corporations has decreased by almost 90% from US dollars 2.5 billion at the end of 2000 to US dollars 300 million at the end of 2002. The United States' fraction of the total workforce declined from 80% in 2000 to 54% in 2002. By the close of 2002, twenty tissue-engineered products had entered Food and Drug Administration clinical trials. Four were approved but none of these are yet commercially successful. Six other applications were either abandoned or failed to achieve product approval. Ten products were still in clinical trials, some of which were investigator sponsored, and most of which were at the phase I/phase II stage. The field has yet to produce a profitable product despite an aggregate research and development investment exceeding US dollars 4.5 billion. Tissue engineering is clearly having difficulty transitioning from a development stage industry to one with a successful product portfolio. This is often the case for breakthrough medical technologies.

Clinical Trials as Topic↗
PubMed1999

End-to-end anastomosis between tissue-engineered intestine and native small bowel.

The purpose of this study was to demonstrate the feasibility of end-to-end anastomosis between tissue-engineered intestine and native small bowel and to investigate the effect of this anastomosis on their growth. Microporous biodegradable polymer tubes were created from a fiber mesh of polyglycolic acid sprayed with 5% polylactic acid. Intestinal epithelial organoid units were harvested from neonatal Lewis rats and seeded onto polymers. These constructs were implanted into the omentum of adult Lewis rats. Three weeks after the implantation, the constructs (n = 7) were anastomosed to the native jejunum in an end-to-end fashion. Ten weeks after implantation, the tissue-engineered intestine was harvested. Four of 7 rats survived for 10 weeks and the overall patency rate of the anastomosis was 78% (11 of 14 anastomosis). The maximal length of the tissue-engineered intestine at week 3 and 10 was 1.80 +/- 0.32 and 1.93 +/- 0.39 cm (mean +/- SD). Histologically, the tissue-engineered intestine was lined with a well-developed neomucosal layer that was continuous with the native intestine. We conclude that anastomosis between tissue-engineered intestine and native small bowel had a moderately high patency rate and had a positive effect on maintenance of the size of the neointestine and development of the neomucosa.

Anastomosis, Surgical↗
PubMed2006

Localization of type VI collagen in tissue-engineered cartilage on polymer scaffolds.

Together, the chondrocyte and its pericellular matrix have been collectively termed the chondron. Current opinion is that the pericellular matrix has both protective and signalling functions between chondrocyte and extracellular matrix. Formation of a native chondrocyte pericellular matrix or chondron structure might therefore be advantageous when tissue engineering a functional hyaline cartilage construct. The presence of chondrons has not been previously described in cartilage engineered on a scaffold. In this paper, we describe a modified immunochemical method to detect collagen VI, a key molecular marker for the pericellular matrix, and an investigation of type VI collagen distribution in engineered hyaline cartilage constructs. Cartilage constructs were engineered from adult human or bovine hyaline chondrocytes cultured on sponge or nonwoven fiber based HYAFF 11 scaffolds. Type VI collagen was detected in all constructs, but a distinctive, high-density, chondron-like distribution of collagen VI was present only in constructs exhibiting additional features of hyaline cartilage engineered using nonwoven HYAFF 11. Chondron structures were localized in areas of the extracellular matrix displaying strong collagen II and GAG staining of constructs where type II collagen composed a high percentage (over 65%) of the total collagen.

Animals↗
PubMed2004

Functional innervation in tissue engineered models for in vitro study and testing purposes.

The biotechnology industry is rapidly expanding and the emerging field of tissue engineering is projected to have a high impact in the near future. Recently the field of cellular, drug, and prosthetic delivery has melded with the field of tissue engineering to make simulated tissues. In addition to their roles as tissue substitutes for transplantation, these simulated tissues may provide more accurate models and environments for toxicology testing and the study of peripheral nerves. The current study demonstrates the importance of innervation, in general, for the function of engineered tissues. We observe that the presence of nerves in a tissue engineered (TE) human cornea model enhances the growth of the epithelium and the formation of its protective mucin layer. Innervation also confers protection to the epithelium from chemical insult, as determined by the level of post-treatment epithelial cell death. We demonstrate differential responses of the nerves to chemical stimuli by changes in intracellular sodium as measured by 2-photon microscopy. The 2-photon imaging techniques also allow for the visualization and study of the fine sensory axon fibers within the 3-dimensional tissue. This work demonstrates a role for innervation in the protective quality and function of the engineered tissue, and the potential to use the nerves themselves as indicators of the severity of an insult. These results are important to consider for the development of any optimized TE models for in vitro study and testing purposes.

Animals↗
PubMedDate not supplied

Health care engineering management.

Today, health care engineering management is merely a concept of dreamers, with most engineering decisions in health care being made by nonengineers. It is the purpose of this paper to present a rationale for an integrated hospital engineering group, and to acquaint the clinical engineer with some of the salient features of management concepts. Included are general management concepts, organization, personnel management, and hospital engineering systems.

Maintenance and Engineering, Hospital↗
PubMedDate not supplied

1988 survey of hospital salaries & job responsibilities for clinical engineers & biomedical technicians.

The Journal of Clinical Engineering has conducted its third survey of the salaries paid to Clinical Engineers and Biomedical Engineering Technicians in U.S. hospitals. This paper reports the salary and work responsibility data obtained from 1,420 professionals in relationship to: Certification; Region of the U.S.; Teaching Versus Nonteaching Facilities; Years of Experience; Education; Union Membership; and Gender. Data are included on Wage Increases and Job Responsibilities. This was the largest salary survey ever obtained in this field. The average BMET I has 2.4 years of experience and earns $19,400 +/- $3,400 (Std. Dev.). The average BMET II has 5.6 years of experience and earns $24,400 +/- $4,700. The average BMET III has 10.2 years of experience and earns $29,300 +/- $5,300. The average BMET Supervisor has 13.1 years of experience and earns $33,600 +/- $5,600. The average Clinical Engineer has 9.4 years of experience and earns $33,500 +/- $7,400. CE Supervisors are the highest paid in the field with an average 13.2 years of experience and an average salary of $43,900 +/- $11,400. Wages remain the highest on the West Coast and lowest in the Southeast. From 1986 to 1987, the nationwide average wages increased for CE Supervisors (+6.6%), BMET Supervisors (+3.1%) and BMET Is (+2.1%) but decreased for nonsupervisory Clinical Engineers (-2.1%), BMET IIs (-.4%) and BMET IIIs (-.7%). the highest quartile of CE Supervisors now earns between $48,900 and $99,000 per year. While certified individuals earn from $532 to $10,670 more than noncertified, a part of this difference is attributable to additional years of experience.

Biomedical Engineering↗
PubMed2002

Tissue-engineered small intestine: ontogeny of the immune system.

BACKGROUND: Using tissue-engineering techniques, we have developed a that regenerates structural and transporter properties of native jejunum. The purpose of this study was to characterize the mucosal immune system of the engineered neointestine. We hypothesized that the neointestinal mucosa is capable of developing a mature immunocyte population and that exposure to luminal stimuli is critical to this development. METHODS: Neointestinal cysts were engineered by implanting polymer-organoid constructs into syngeneic adult recipients. Neointestine (cysts left nonanastomosed [NA] and cysts anastomosed to native bowel [AN]) and native jejunum were harvested serially (3-56 weeks postoperatively). Immune cell subsets were characterized by the immunohistochemical detection of cell-specific antigens (T cells [CD3], B cells [CD32], NK cells [CD56], and macrophages [CD68]) combined with computer-based morphometry. RESULTS: Intraepithelial and lamina propria immunocyte population densities and subset distributions were identical in AN cysts harvested 20 weeks postoperatively and in native jejunum. Mucosal immunocyte population densities were lower in AN cysts harvested 10 weeks postoperatively and only rudimentary in NA cysts, even those harvested 20 weeks postoperatively. CONCLUSIONS: These results suggest that tissue-engineered intestine has the capacity to develop a mucosal immune system with an immunocyte population similar to that of native small intestine. The development of this immune system is a function of both exposure to luminal stimuli and the duration of this exposure. Tissue-engineered intestine offers promise as a new therapeutic approach for patients who have intestinal insufficiency.

Anastomosis, Surgical↗
PubMed2003

Tissue engineering: current state of clinical application.

Despite several, mostly isolated successes, few controlled, prospective trials have yet validated clinical tissue engineering applications. Although this may, at least in part, be explained by the very young age of this field, tissue engineering involves the need for an elaborate and expensive infrastructure, not to mention qualified personnel. This translates into an inherent difficulty in establishing multicenter trials. Moreover, companies mostly devoted to tissue engineering have yet to prove themselves economically viable. On the other hand, although very few engineered tissues have been approved by the US Food and Drug Administration (FDA), more than 70 companies have recently been developing new products. Many challenges are yet to be overcome before "off-the-shelf" tissues can be offered commercially. Nevertheless, given the scientific promise, potential social impact, and young age of the field, many believe that it should be only a matter of time until tissue engineering reaches the mainstream of surgical practice.

Humans↗