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PubMed2002

In vivo evaluation of a bioactive scaffold for bone tissue engineering.

Revision cases of total hip implants are complicated by the significant amount of bone loss. New materials and/or approaches are needed to provide stability to the site, stimulate bone formation, and ultimately lead to fully functional bone tissue. Porous bioactive glasses (prepared from 45S5 granules, 45% SiO2, 24.5% Na2O, 24.5% CaO, and 6% P2O5) have been developed as scaffolds for bone tissue engineering and have been studied in vitro. In this study, we investigated the incorporation of tissue-engineered constructs utilizing these scaffolds in large, cortical bone defects in the rat simulating revision conditions. With implantation times of 2, 4, and 12 weeks the results were compared to those using the bioactive ceramic scaffold alone. Two tissue-engineered constructs were studied: osteoprogenitor cells that were either seeded onto the scaffold prior to implantation ("primary") or those that were culture expanded to form bonelike tissue on the scaffold prior to implantation ("hybrid"). Defects treated with the hybrid had the greatest amount of bone in the available pore space of the defect over all other groups at 2 weeks (p < 0.05). For both the primary and hybrid groups, woven and lamellar bone was present along the interface of the scaffold and the host cortex and within the porous space of the scaffold at 2 weeks. By 4 weeks, very uniform, lamellar bone was present throughout the scaffold for both tissue-engineered groups. The amount of bone significantly increased over time for all groups while the bioactive ceramic gradually resorbed by 40% at 12 weeks (p < 0.05). Structural properties of the treated long bones improved over time. Long bones treated with the hybrid had an early return in torsional stiffness by 2 weeks. Both tissue-engineered constructs achieved normal torsional strength and stiffness by 4 weeks as compared to the scaffold alone, which achieved this by 12 weeks. Porous, surface modified bioactive ceramic is a promising scaffold material for tissue-engineered bone repair.

Animals↗
PubMed2001

Flux estimation using isotopic tracers: common ground for metabolic physiology and metabolic engineering.

Metabolic physiologists and metabolic engineers share the need to estimate flux. However, the physiologist often works with systems that do not maintain steady state for long. Many sites cannot be sampled, and calculating mass and isotopic balance for the entire system may not be feasible. To deal with these constraints, metabolic physiologists have developed specialized isotopic techniques that may be unfamiliar to metabolic engineers. A selection of these techniques is presented here, not because it is anticipated that they would be used by engineers exactly as in the physiologist's setting, but because they illustrate novel applications of tracer methodology. Creative engineers may find new adaptations of these tools in metabolic engineering and opportunities to increase redundancy. Physiologists, entering into a dialog with engineers, may see more clearly the potential of comprehensive models and revisit the impediments to a more complete analysis of human metabolic systems.

Animals↗
PubMed1986

Legal and regulatory aspects of genetically engineered animals.

The commercialization of genetically engineered food animals will pose a number of legal and regulatory questions. These may be grouped into questions of process and questions of products. The process of animal genetic engineering with artificially constructed vectors will probably be regulated in much the same manner as other veterinary procedures. There may be some discussion, however, as to whether animal drug or animal biologic regulations are more applicable. The products of animal genetic engineering, i.e., transgenic food animals and food products made from them, also raise important questions about product safety and identity. These include whether and how genetically engineered food animals will be subject to federal inspection for wholesomeness, whether artificial vectors, foreign genes, or gene products will adulterate recipient animal tissues, and how food products made from such animals will be labeled. Prior federal experience with the inspection of interspecific hybrids of cattle and buffalo provides a useful basis for further policy developments in the inspection and labeling of genetically engineered food animals. In particular, the inspection of cattle/buffalo hybrids has established a phenotypic (based on appearance) criterion for deciding how novel food animals should be inspected. As the genetic engineering of food animals on a production basis draws nearer, it may be necessary to supplement the phenotypic criterion with genetic (based on pedigree) criteria to assure that the essential characteristics of animals slaughtered under current food statutes are maintained.

Animal Husbandry↗
PubMed1992

Opportunities for the cellular approach in biomedical engineering.

This review is a commentary on recent, altered perspectives about biomedical engineering and its role in medicine. It is argued that, rather than being a peripheral specialty, medical engineering and engineering principles in general have a direct application to biochemical medicine and cell biology. A brief description is given of the cell as a compartmentalised reactor system, and the ways in which it is possible to replace lost or aberrant cell function. Specific topics are then covered to illustrate the general thesis. These are: polymers for cell mimicry, cell-surface interactions, biomolecule transport, cell transport phenomena, cell signalling, harnessing of cells for therapy and microbial interactions. These disparate subject areas have a common thread of interest for the biomedical engineer, and are presented here in a way which highlights key points of relevance for engineering. Though necessarily brief, the various descriptions in this review provide a film indication that a rigorous approach to the assessment, modelling and use of cells along sound engineering lines is vital for the future. It is concluded that, without this approach, our understanding of cell biology will remain semiquantitative and semiempirical.

Biological Transport↗
PubMed2005

Dendritic cells engineered to express CD40L continuously produce IL12 and resist negative signals from Tr1/Th3 dominated tumors.

TNFalpha-matured dendritic cells (DCs) pulsed with tumor antigens are being evaluated as cancer vaccines. It has been shown that DCs produce IL12 during a limited time span and subsequently enter a stage of IL12 exhaustion. If DCs are generated ex vivo, the patient could receive IL12-exhausted DCs which may be detrimental for stimulating anti-tumor Th1 responses. Furthermore, many cancer patients exhibit a cytokine profile skewed toward IL10 and TGFbeta. This immunological profile, called the Tr1/Th3 response, is associated with the presence of regulatory T-cells. Tr1/Th3 responses potently inhibit DC maturation, thereby regulating Th1 responses. In the present study, we produced genetically engineered DCs that continuously express Th1-related cytokines such as IL12, and resist negative signals from Tr1/Th3-dominated bladder carcinoma cells. Human immature DCs were genetically engineered by adenoviral vectors to express CD40L, or were treated with TNFalpha as a positive control for maturation. The expression of different Th1/Th3 and inflammatory cytokines was monitored. IL12 and IFNgamma were expressed by CD40L-engineered DCs, while TNFalpha-matured DCs lacked IFNgamma and exhibited low IL12 expression. The addition of recombinant IL10 to genetically engineered DCs did not abolish their Th1 profile. Likewise, coculture with tumor cell lines expressing TGFbeta with or without recombinant IL10 did not revert to the engineered DCs. We further demonstrate that the resistance of CD40L-expressing DCs to TGFbeta and IL10 may be due to decreased levels of TGFbeta and IL10 receptors. Thus, CD40L-engineered DCs are robust Th1-promoting ones that are resistant to Tr1/Th3-signaling via IL10 and TGFbeta.

CD40 Ligand↗
PubMed2003

Clinical aspects and strategy for biomaterial engineering of an auricle based on three-dimensional stereolithography.

At the present time, the partial and/or complete reconstruction of an auricle from autologous rib cartilage is one of most widely published techniques. In the field of tissue engineering, different techniques have been described to generate cartilage tissue using isolated chondrocytes. The basis of these tissue-engineering techniques is bioresorbable or non-bioresorbable biomaterials, which serve as a three-dimensional cell carrier. Tissue engineering of an auricle requires preformed bioresorbable biomaterials designed to fit the form of a patient's auricular defect. Three-dimensional imaging acquired from computed tomography scans or laser surface scanning has become an important tool in modern medicine. This study represents the preoperative procedures for the reconstruction of an auricle through tissue engineering in accordance with the clinical aspects. Hyaff 11, a hyaluronic acid derivative, was used as a three-dimensional cell carrier for isolated human nasoseptal chondrocytes. The chondrocytes were amplified in a conventional monolayer culture before the cells were seeded on a hyaluronic non-woven mesh and cultured in vitro for 4 weeks. The chondrogenic potential of human nasal chondrocytes in Hyaff 11 was investigated by confocal laser scanning microscopy, histology (toluidine blue) and immunohistochemistry (collagen type II). Computer-aided design (CAD) and manufacture of an auricle model with stereolithographical methods were used for the prefabrication of a bioresorbable three-dimensional cell carrier designed in the form of a patient's auricular defect. The cell carrier used was Hyaff 11, a fully benzyl-esterified hyaluronic acid derivative. Confocal laser scanning microscopy has shown good cell attachment, a homogenous distribution of amplified chondrocytes and a viability of more than 90%. After 4 weeks in vitro culture the human nasoseptal chondrocytes synthesized new cartilage with the expression of cartilage-specific collagen type II. In order to shape a patient's designed scaffold the auricle model was fitted exactly and symetrically to the contralateral side. Subsequently, the mirror image patient-specific model was used to prepare an identical scaffold model made of a fully benzyl-esterified hyaluronic acid derivative. The bioresorbable scaffold that was produced gave a satisfactory representation of auricle structure. Bioresorbable preformed biomaterials in the form of a patient's auricle defect represent an important prerequisite for the tissue engineering of autologous auricle grafts. Hyaff 11 seems to be a promising material for tissue engineering of cartilage transplants, and the application of this approach will improve conventional reconstructive surgery in the future.

Absorbable Implants↗
PubMed2006

Biomedical engineering and the whitaker foundation: a thirty-year partnership.

The Whitaker Foundation, established in 1976, will close in 2006. It will have made awards totaling 805 million US dollars, with over 710 million US dollars in biomedical engineering. Close to 1,500 faculty members received research grants to help them establish academic careers in biomedical engineering, and over 400 graduate students received fellowship support. The Foundation also supported the enhancement or establishment of educational programs in biomedical engineering, especially encouraging the formation of departments. The number of biomedical engineering departments almost tripled during the past 10 years, now numbering close to 75. Leveraging of grants enabled the construction of 13 new buildings. With the field firmly established, the grant program supporting new faculty members will be the one missed the most. New opportunities, however, are emerging as interdisciplinary research is being embraced by both public and private funding sources. The life sciences will be increasingly incorporated into all areas of engineering, and it is expected that such "biofication" will pose both opportunities and challenges to biomedical engineering.

Biomedical Engineering↗
PubMed2001

Tissue engineering in urology.

Congenital abnormalities, cancer, trauma, infection, inflammation, iatrogenic injuries, and other conditions may lead to genitourinary organ damage or loss, requiring eventual reconstruction. Tissue engineering follows the principles of cell transplantation, materials science, and engineering toward the development of biological substitutes that would restore and maintain normal function. Tissue engineering may involve matrices alone, wherein the body's natural ability to regenerate is used to orient or direct new tissue growth, or the use of matrices with cells. Both synthetic (polyglycolic acid polymer scaffolds alone and with co-polymers of poly-1-lactic acid and poly-DL-lactide-coglycolide) and natural biodegradable materials (processed collagen derived from allogeneic donor bladder submucosa and intestinal submucosa) have been used, either alone or as cell delivery vehicles. Tissue engineering has been applied experimentally for the reconstitution of several urologic tissues and organs, including bladder, ureter, urethra, kidney, testis, and genitalia. Fetal applications have also been explored. Recently, several tissue engineering technologies have been used clinically, including the use of cells as bulking agents for the treatment of vesicoureteral reflux and incontinence, urethral replacement, and bladder reconstruction. Recent progress suggests that engineered urologic tissues may have clinical applicability in the future.

Humans↗
PubMed2003

The social ascription of obligations to engineers.

Discovering obligations that are ascribed to them by others is potentially an important element in the development of the moral imagination of engineers. Moral imagination cannot reasonably be developed by contemplating oneself and one's task alone: there must be some element of discovering the expectations of people one could put at risk. In practice it may be impossible to meet ascribed obligations if they are completely general and allow no exceptions--for example if they demand an unlimited duty to avoid harm. But they can still serve to modify engineers' prior ethics, for example by limiting a purely utilitarian approach to deciding who should bear risk and how much risk they should bear. Ascribed obligations can also give engineers insight into the public reaction to risks that arise from engineered systems, and the consequent expectations that the public have about how much protection is desirable and where the responsibility for this protection lies. This article analyses the case for taking ascribed obligations seriously, and reviews some of the obligations that have been ascribed in the aftermath of recent engineering failures. It also proposes ways in which ascribed obligations could be used in engineers' moral development.

Engineering↗
PubMed2004

A psychological model that integrates ethics in engineering education.

Ethics has become an increasingly important issue within engineering as the profession has become progressively more complex. The need to integrate ethics into an engineering curriculum is well documented, as education does not often sufficiently prepare engineers for the ethical conflicts they experience. Recent research indicates that there is great diversity in the way institutions approach the problem of teaching ethics to undergraduate engineering students; some schools require students to take general ethics courses from philosophical or religious perspectives, while others integrate ethics in existing engineering courses. The purpose of this paper is to propose a method to implement the integration of ethics in engineering education that is pedagogically based on Kohlberg's stage theory of moral development.

Curriculum↗
PubMed2004

Teaching engineering ethics to first-year college students.

One of the methods used at Penn State to teach engineering students about ethics is a one-credit First-Year Seminar entitled "How Good Engineers Solve Tough Problems." Students meet in class once a week to understand ethical frameworks, develop ethical problem-solving skills, and to better understand the professional responsibilities of engineers. Emphasis is on the ubiquity of ethical problems in professional engineering. A learning objective is the development of moral imagination, similar to the development of technical imagination in engineering design courses. Making sound arguments is also addressed in the process of reasoning through cases, and critiquing other's arguments. Over the course of the semester, students solve five engineering ethics cases. Each week, a student team of four people is responsible for reading the assigned section of the text, developing a summary, and leading the class discussion.

Engineering↗
PubMed1994

Perception of risks and benefits of in vitro fertilization, genetic engineering and biotechnology.

The use of new biotechnology in medicine has become an everyday experience, but many people still express concern about biotechnology. Concerns are evoked particularly by the phrases genetic engineering and in vitro fertilization (IVF), and these concerns persist despite more than a decade of their use in medicine. Mailed nationwide opinion surveys on attitudes to biotechnology were conducted in Japan, among samples of the public (N = 551), high school biology teachers (N = 228), scientists (N = 555) and nurses (N = 301). People do see more benefits coming from science than harm when balanced against the risks. There were especially mixed perceptions of benefit and risk about IVF and genetic engineering, and a relatively high degree of worry compared to other developments of science and technology. A discussion of assisted reproductive technologies and surrogacy in Japan is also made. The opinions of people in Japan were compared to the results of previous surveys conducted in Japan, and international surveys conducted in Australia, China, Europe, New Zealand, U.K. and U.S.A. Japanese have a very high awareness of biotechnology, 97% saying that they had heard of the word. They also have a high level of awareness of IVF and genetic engineering. Genetic engineering was said to be a worthwhile research area for Japan by 76%, while 58% perceived research on IVF as being worthwhile, however 61% were worried about research on IVF or genetic engineering. Japanese expressed more concern about IVF and genetic engineering than New Zealanders. The major reason cited for rejection of genetic manipulation research in Japan and New Zealand was that it was seen as interfering with nature, playing God or as unethical. The emotions concerning these technologies are complex, and we should avoid using simplistic public opinion data as measures of public perceptions. The level of concern expressed by scientists and teachers in Japan suggest that public education "technology promotion campaigns" will not reduce concern about science and technology. Such concern should be valued as discretion that is basic to increasing the bioethical maturity of a society, rather than being feared.

Adult↗
PubMed2004

Human umbilical cord cells for cardiovascular tissue engineering: a comparative study.

OBJECTIVE: Tissue engineering of viable, autologous cardiovascular replacements with the potential to grow, repair and remodel represents an attractive approach to overcome the shortcomings of available replacements for the repair of congenital cardiac defects. Currently, vascular myofibroblast cells represent an established cell source for cardiovascular tissue engineering. Cell isolation requires the invasive harvesting of venous or arterial vessel segments prior to scaffold seeding, a technique which may not be preferable, especially in pediatric patients. This study evaluates cells isolated from human umbilical cord artery, umbilical cord vein and whole cord as alternative autologous cell sources for cardiovascular tissue engineering. METHODS: Cells were isolated from human umbilical cord artery (UCA), umbilical cord vein (UCV), whole umbilical cord (UCC) and saphenous vein segments (VC), and were expanded in culture. All three expanded cell groups were seeded on bioabsorbable copolymer strips and grown in vitro for 28 days. Isolated cells were characterized by flow cytometry, histology, immunohistochemistry, proliferation assays and compared to VC. Morphological analysis of the seeded polymer strips included histology, immunohistochemistry, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and uniaxial stress testing. RESULTS: UCA, UCV and UCC demonstrated excellent cell growth properties comparable to VC. Following isolation, all three cell groups showed myofibroblast-like morphology and characteristics by staining positive for alpha-smooth muscle actin (ASMA) and vimentin. Histology and immunohistochemistry of seeded polymers showed good tissue and extracellular matrix formation containing collagen I, III and elastin. TEM showed viable myofibroblasts and the deposition of collagen fibrils and progressive growing tissue formation, with a confluent surface, was observed in SEM. No difference was found among the mechanical properties of UCA, UCV, UCC and VC tissue engineered constructs. CONCLUSIONS: Tissue engineering of cardiovascular constructs by using UCA, UCV and UCC is feasible in an in vitro environment. Cell growth, morphology, characteristics and tissue formation were comparable between UCA, UCV, UCC and VC. UCC represent an attractive, readily available autologous cell source for cardiovascular tissue engineering offering the additional benefits of utilizing juvenile cells and avoiding the invasive harvesting of intact vascular structures.

Absorbable Implants↗
PubMed2006

Cellular therapy and myocardial tissue engineering: the role of adult stem and progenitor cells.

Acquired cardiovascular diseases and complex congenital heart diseases are leading causes of morbidity and mortality. Cellular therapy and tissue engineering are emerging as promising alternative approaches to treat cardiovascular diseases. Cellular therapy involves isolating cells and delivering the cells to the site of cardiac injury to restore blood flow and contractility to previously infarcted, scarred or dysfunctional heart. Myocardial tissue engineering, engineered heart tissue by seeding cells in three-dimensional matrices of biodegradable polymers or cell sheet engineering without artificial scaffolds to form new myocardial constructs. Questions are common to both these approaches, such as the best cell source and optimal conditions for therapeutic application. The capabilities of stem cells for pluripotency and long-term self-renewal make it an ideal source for myocardial tissue engineering and cell therapy. We review the current understanding of postnatal adult stem and progenitor cells in cellular therapy and myocardial tissue engineering from a surgical view point, and highlight the latest advances in these exciting fields.

Adult↗
PubMed2005

Prediction of vascular tissue engineering results with artificial neural networks.

Tissue engineers are often confused on finding the most successful strategy for specific patient. In this study, we used artificial neural networks to predict the outcomes of different vascular tissue engineering strategies, thus providing advisory information for experimental designers. Over 30 variables were used as features of the tissue engineering strategies. Different architectures of artificial neural networks with back propagation algorithm were tested to obtain the best model configuration for the prediction of the tissue engineering strategies. In the computational experiments, the artificial neural networks with one and two hidden layers could, respectively, detect unsuccessful strategies with the highest predictive accuracy of 91.45 and 94.24%. In conclusion, artificial intelligence has great potential in tissue engineering decision support. It can provide accurate advisory information for tissue engineers, thus reducing failures and improving therapeutic effects.

Animals↗
PubMed2006

Development of a model system for preliminary evaluation of tissue-engineered vascular conduits.

BACKGROUND/PURPOSE: The ability to construct tissue-engineered neovessels for use as arterial or venous grafts holds great promise for the advancement of pediatric surgical disciplines. Although the feasibility of tissue engineering vascular grafts has been demonstrated, the long-term function, safety, and efficacy of these grafts as well as their capacity to grow and adapt remain largely unknown. In an attempt to further characterize and develop this technology, we used severe combined immunodeficiency beige (SCID/bg) mouse recipients, chosen because such animals accept xenogenic human cells, to create a small animal model that would allow a rapid and cost-effective preliminary evaluation of the function of tissue-engineered vascular grafts. METHODS: Eight CB-17 SCID/bg female mice underwent vascular graft placement. Four of these mice received aortic interposition grafts, 1 mouse received an inferior vena cava interposition graft, and 3 mice underwent aortocaval graft insertion. All grafts were fashioned from decellularized ovine arteriole tissue engineering scaffolds. Grafts were evaluated for patency using clinical examination, ultrasound interrogation, and micro-computed tomography. Animals were killed at various time points after implantation, and grafts were harvested and analyzed histologically using standard hematoxylin and eosin staining. RESULTS: All grafts were patent based on clinical examination for up to 35 days. Patency was confirmed in 5 grafts using ultrasound interrogation. Patency was confirmed in 4 grafts using micro-computed tomography. One animal that underwent arteriovenous grafting had to be euthanized secondary to high-output cardiac failure on postoperative day 2. The remaining animals were killed between postoperative days 12 and 35. Histologic evaluation of the specimens demonstrated patent grafts with cellular ingrowth into the tissue engineering scaffold. CONCLUSIONS: From these results, we conclude that the use of the SCID/bg mouse model for preliminary evaluation of new tissue engineering methodologies for construction of vascular conduits is feasible. Use of this model has the added advantage of evaluating nonautologous and even xenograft tissues, including human cells.

Animals↗
PubMed2006

A comparison of engineered urinary bladder and intestinal smooth muscle for urinary bladder wall replacement in a rabbit model.

BACKGROUND/PURPOSE: The small intestine is the most common resource for bladder augmentation. Little is known whether intestinal smooth muscle cells (SMCs) may be engineered into bladder tissue. We investigated the phenotypic and functional characteristics of engineered bladder and intestinal SMCs as bladder wall replacement in a rabbit model. METHODS: One month after an initial 70% partial cystectomy, 3 autoaugmentation surgeries were performed, including traditional autoaugmentation (TA, n = 6), TA using engineered bladder SMCs (TA + B, n = 6), and TA using intestinal SMCs (TA + I, n = 6). All were followed up by bladder volume measurement and retrieved on the first, third, and sixth month. The grafts and the native bladder wall were evaluated with immunocytochemistry and electrical field stimulation (EFS). Statistical analysis was performed using analysis of variance. RESULTS: Both the TA + I and TA + B groups showed significant and similar bladder capacity increment in all time points. The engineered muscle cells demonstrated the typical "contraction-relaxation" response to supramaximal EFS. There were no statistical differences in both the TA + I and TA + B groups in contractility force. CONCLUSION: Engineered SMCs derived from urinary bladder and small intestine could retain their phenotype after implantation in vivo. Both exhibited a similar degree of contractility to EFS. These results suggest that there are no phenotypic or functional differences between muscle cells obtained from the 2 different organs. Both have the potential to be engineered into normal bladder tissues.

Animals↗
PubMed2004

Tissue-engineered trachea from sheep marrow stromal cells with transforming growth factor beta2 released from biodegradable microspheres in a nude rat recipient.

OBJECTIVE: The purpose of this study was to evaluate the feasibility of using autologous sheep marrow stromal cells cultured onto polyglycolic acid mesh to develop helical engineered cartilage equivalents for a functional tracheal replacement. We also explored the potential benefit of local delivery of transforming growth factor beta 2 with biodegradable gelatin microspheres. METHODS: Bone marrow was obtained by iliac crest aspiration from 6-month-old sheep and cultured in monolayer for 2 weeks. At confluence, the cells were seeded onto nonwoven polyglycolic acid fiber mesh and cultured in vitro with transforming growth factor beta 2 and insulin-like growth factor 1 for 1 week. Cell-polymer constructs were wrapped around a silicone helical template. Constructs were then coated with microspheres incorporating 0.5 microg transforming growth factor beta 2. The cell-polymer-microsphere structures were then implanted into a nude rat. On removal, glycosaminoglycan content and hydroxyproline were analyzed in both native and tissue-engineered trachea. Histologic sections of both native and tissue-engineered trachea were stained with hematoxylin and eosin, safranin-O, and a monoclonal anti-type II collagen antibody. RESULTS: Cell-polymer constructs with transforming growth factor beta 2 microspheres formed stiff cartilage de novo in the shape of a helix after 6 weeks. Control constructs lacking transforming growth factor beta 2 microspheres appeared to be much stiffer than typical cartilage, with an apparently mineralized matrix. Tissue-engineered trachea was similar to normal trachea. Histologic data showed the presence of mature cartilage. Glycosaminoglycan and hydroxyproline contents were also similar to native cartilage levels. CONCLUSIONS: This study demonstrates the feasibility of engineering tracheas with sheep marrow stromal cells as a cell source. Engineering the tracheal equivalents with supplemental transforming growth factor beta 2 seemed to have a positive effect on retaining a cartilaginous phenotype in the newly forming tissue.

Absorbable Implants↗