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PubMed2004

Biological and biophysical principles in extracorporal bone tissue engineering. Part I.

Advances in the field of bone tissue engineering have encouraged physicians to introduce these techniques into clinical practice. Bone tissue engineering is the construction, repair or replacement of damaged or missing bone in humans or animals. Engineering of bone can take place within the animal body or extracorporal in a bioreactor for later grafting into the body. Appropriate cell types and non-living substrata are minimal requirements for an extracorporal tissue engineering approach. This review discusses the biological and biophysical background of in vitro bone tissue engineering. Biochemical and biophysical stimuli of cell growth and differentiation are regarded as potent tools to improve bone formation in vitro. The paper focuses on basic principles in extracorporal engineering of bone-like tissues, intended to be implanted in animal experiments and clinical studies. Particular attention is given in this part to the contributions of cell and material science to the development of bone-like tissues. Several approaches are at the level of clinical applicability and it can be expected that widespread use of engineered bone constructs will change the surgeon's work in the near future.

Animals↗
PubMed2003

Diversity and dynamics of microbial communities in engineered environments and their implications for process stability.

The availability of molecular biological tools for studying microbial communities in bioreactors and other engineered systems has resulted in remarkable insights linking diversity and dynamics to process stability. As engineered systems are often more manageable than large-scale ecosystems, and because parallels between engineered environments and other ecosystems exist, the former can be used to elucidate some unresolved ecological issues. For example, the process stability of methanogenic bioreactors containing well-defined trophic groups appears to depend on the diversity of the functional groups within each trophic level as well as on how these functional groups complement each other. In addition to using engineered systems to study general ecological questions, microbial ecologists and environmental engineers need to investigate conditions, processes, and interactions in engineered environments in order to make the ecological engineering of bioreactor design and operation more practicable.

Bacterial Physiological Phenomena↗
PubMed2004

Characterization of diesel particles: effects of fuel reformulation, exhaust aftertreatment, and engine operation on particle carbon composition and volatility.

Diesel exhaust particles are the major constituent of urban carbonaceous aerosol being linked to a large range of adverse environmental and health effects. In this work, the effects of fuel reformulation, oxidation catalyst, engine type, and engine operation parameters on diesel particle emission characteristics were investigated. Particle emissions from an indirect injection (IDI) and a direct injection (DI) engine car operating under steady-state conditions with a reformulated low-sulfur, low-aromatic fuel and a standard-grade fuel were analyzed. Organic (OC) and elemental (EC) carbon fractions of the particles were quantified by a thermal-optical transmission analysis method and particle size distributions measured with a scanning mobility particle sizer (SMPS). The particle volatility characteristics were studied with a configuration that consisted of a thermal desorption unit and an SMPS. In addition, the volatility of size-selected particles was determined with a tandem differential mobility analyzer technique. The reformulated fuel was found to produce 10-40% less particulate carbon mass compared to the standard fuel. On the basis of the carbon analysis, the organic carbon contributed 27-61% to the carbon mass of the IDI engine particle emissions, depending on the fuel and engine operation parameters. The fuel reformulation reduced the particulate organic carbon emissions by 10-55%. In the particles of the DI engine, the organic carbon contributed 14-26% to the total carbon emissions, the advanced engine technology, and the oxidation catalyst, thus reducing the OC/EC ratio of particles considerably. A relatively good consistency between the particulate organic fraction quantified with the thermal optical method and the volatile fraction measured with the thermal desorption unit and SMPS was found.

Aerosols↗
PubMed2001

Tissue engineering research in oral implant surgery.

In this article, we introduce some of the more extensively evaluated technologies using concepts of tissue engineering. We report on hard tissue engineering and soft tissue engineering and their utility for dental implant therapy. For hard tissue engineering, we evaluated human recombinant bone morphogenetic protein-2 and marrow mesenchymal stem cells using a model of sinus augmentation procedure in rabbit. We also describe distraction osteogenesis as another category for hard tissue engineering. In addition, we evaluate soft tissue management using cultured epithelial grafting for soft tissue engineering. The results of our tissue regeneration materials and methods in this study are positive. When the tissue engineering materials are used in clinics in the future, implant surgery could be the leading field.

Absorbable Implants↗
PubMed2004

Emissions and demonstration of an emission control technology for small two-stroke utility engines.

Small utility engines represent an important contribution to the emissions inventory and have been subjected to increasingly stringent regulations in recent years. For this project, a Tanaka two-stroke engine was tested in its original condition and with a modified fuel/oil injection system. The modified fuel/oil injection system applied to the Tanaka two-stroke engine resulted in significant emissions reductions of approximately 52% for carbon monoxide (CO), 70% for total hydrocarbons (THC), 70% for particulate matter (PM), and 67% for the regulated THC + nitrogen oxides metric. This technology met the California Air Resources Board's 2000 model-year regulations for all pollutants, with the exception of slightly higher PM emissions. Two additional two-stroke engines were tested under a new condition and after at least 100 hr of use to examine the effects of deterioration on in-use, two-stroke engines. For one engine, CO and PM emissions more than tripled after 162 hr of operation in the field, with smaller increases also observed for THC (20%). For the second engine, significant repairs were required throughout the 100 operating hours, which counteracted the effects of the emissions deterioration and resulted in lower CO and THC emissions.

Air Pollutants↗
PubMed2000

Combining chondrocytes and smooth muscle cells to engineer hybrid soft tissue constructs.

Engineering new tissues using cell transplantation may provide a valuable tool for reconstructive surgery applications. Chondrocyte transplantation in particular has been successfully used to engineer new tissue masses due to the low metabolic requirements of these cells. However, the engineered cartilaginous tissue is too rigid for many soft tissue applications. We propose that hybrid tissue engineered from chondrocytes and smooth muscle cells could reflect mechanical properties intermediate between these two cell types. In this study, rat aortic smooth muscle cells and pig auricular chondrocytes were co-cultured on polyglycolic acid fiber-based matrices to address this hypothesis. Mixed cell suspensions were seeded by agitating the polymer matrices and a cell suspension with an orbital shaker. After seeding, cell-polymer constructs were cultured in stirred bioreactors for 8 weeks. The cell density and extracellular matrix (collagen, elastin, and glycosaminoglycan) content of the engineered tissues were determined biochemically. After 8 weeks in culture, the hybrid tissue had a high cell density (5.8 x 108 cells/cm(3)), and elastin (519 microg/g wet tissue sample), collagen (272 microg/g wet tissue sample), and glycosaminoglycan (GAG; 10 microg/g wet tissue sample) content. Mechanical testing indicated the compressive modulus of the hybrid tissues after 8 weeks to be 40.8 +/- 4.1 kPa and the equilibrium compressive modulus to be 8.4 +/- 0.8 kPa. Thus, these hybrid tissues exhibited intermediate stiffness; they were less stiff than native cartilage but stiffer than native smooth muscle tissue. This tissue engineering approach may be useful to engineer tissues for a variety of reconstructive surgery applications.

Animals↗
PubMed2002

Three-dimensional tissue engineering of hyaline cartilage: comparison of adult nasal and articular chondrocytes.

Adult chondrocytes are less chondrogenic than immature cells, yet it is likely that autologous cells from adult patients will be used clinically for cartilage engineering. The aim of this study was to compare the postexpansion chondrogenic potential of adult nasal and articular chondrocytes. Bovine or human chondrocytes were expanded in monolayer culture, seeded onto polyglycolic acid (PGA) scaffolds, and cultured for 40 days. Engineered cartilage constructs were processed for histological and quantitative analysis of the extracellular matrix and mRNA. Some engineered constructs were implanted in athymic mice for up to six additional weeks before analysis. Using adult bovine tissues as a cell source, nasal chondrocytes generated a matrix with significantly higher fractions of collagen type II and glycosaminoglycans as compared with articular chondrocytes. Human adult nasal chondrocytes proliferated approximately four times faster than human articular chondrocytes in monolayer culture, and had a markedly higher chondrogenic capacity, as assessed by the mRNA and protein analysis of in vitro-engineered constructs. Cartilage engineered from human nasal cells survived and grew during 6 weeks of implantation in vivo whereas articular cartilage constructs failed to survive. In conclusion, for adult patients nasal septum chondrocytes are a better cell source than articular chondrocytes for the in vitro engineering of autologous cartilage grafts. It remains to be established whether cartilage engineered from nasal cells can function effectively when implanted at an articular site.

Animals↗
PubMed2003

A closer view of tissue engineering in China: the experience of tissue construction in immunocompetent animals.

Tissue engineering started in late 1980s and is now well established and progressing rapidly in Western developed countries. However, the development of tissue-engineering research in China remains relatively unknown to the international society of tissue engineering. Although involved in all areas of tissue-engineering research, including the creation of new scaffold materials, in vitro studies of seed cells, application of growth factors, and modification of seed cells and scaffold materials, China has put special emphasis on tissue construction in large mammalian animals in order to establish a solid scientific basis for clinical application of engineered tissues. To provide a closer view of tissue-engineering research in China, this article reviews our experience in tissue construction and tissue repair using immunocompetent animals such as sheep, pig, and dog as well as hen and rabbit. The engineered tissues include bone, cartilage, tendon, skin, blood vessels, cornea, and peripheral nerves.

Animals↗
PubMed2003

Motivation, characterization, and strategy for tissue engineering the temporomandibular joint disc.

The purpose of this review is to serve as the standard point of reference in guiding researchers investigating the tissue engineering of the temporomandibular joint (TMJ) disc. Tissue engineering of the TMJ disc is in its infancy, and currently there exists a gap between the tissue engineering community and the TMJ characterization community. The primary goal is to help bridge that gap by consolidating the characterization studies here as a reference to researchers attempting to tissue engineer the TMJ disc. A brief review of TMJ anatomy is provided, along with a description of relevant pathology, current treatment, and a rationale for engineering the TMJ disc. The biochemical composition and organization of the disc are reviewed, including glycosaminoglycan (GAG) and collagen content. The collagen of the disc is almost exclusively type I and primarily runs anteroposteriorly through the center and in a ringlike fashion around the periphery. The GAG content is approximately an order of magnitude less than that of hyaline cartilage, and although the distribution is not entirely clear, it seems as though chondroitin and dermatan sulfate are by far the primary GAGs. Cellular characterization and mechanical properties under compression, tension, and shear are reviewed as well. The cells of the disc are not chondrocytes, but rather resemble fibrocytes and fibrochondrocytes and may be of the same lineage. Mechanically, the disc is certainly anisotropic and nonhomogeneous. Finally, a review of efforts in tissue engineering and cell culture studies of the disc is provided and we close with a description of the direction we envision/propose for successful tissue engineering of the TMJ disc.

Animals↗
PubMedDate not supplied

ProteinChip system technology: a powerful tool to analyze expression differences in tissue-engineered blood vessels.

At the time of implantation, tissue-engineered constructs should resemble native tissues as closely as possible. At present, histology and biochemical methods are commonly used to compare tissue-engineered constructs with native tissue. A ProteinChip system based on surface-enhanced laser desorption/ionization time of flight mass spectrometry (SELDI) has been developed that allows visualization of complex protein profiles from biological samples. The aim of this study was to determine whether the ProteinChip system is a suitable tool with which to compare the protein expression profiles of tissue-engineered aortic blood vessels with native tissues. Tissue-engineered blood vessel substitutes were fabricated with poly-4-hydroxybutyrate scaffolds, ovine vascular cell seeding, and dynamic tissue culture conditions. Engineered, ovine aortic, and carotid tissues were homogenized and total protein was extracted. Samples were analyzed on ProteinChip arrays. Analysis yielded reproducible protein profiles from all samples. About 150 distinct protein peaks were detected. Comparative analysis with ProteinChip software revealed that the protein profiles from native aorta and native carotid arteries were similar whereas early tissue-engineered samples displayed more distinct deviations. In conclusion, ProteinChip system technology is rapid, reproducible, and highly sensitive in highlighting differentially expressed proteins in tissue-engineered blood vessel substitutes.

Animals↗
PubMed2000

Tissue engineering of artificial organs.

Tissue engineering efforts are currently being undertaken for every type of tissue and organ within the urinary system. Most of the effort expended to engineer genitourinary tissues has occurred within the last decade. Tissue engineering techniques require expertise in growth factor biology, a cell culture facility designed for human application, and personnel who have mastered the techniques of cell harvest, culture, and expansion. Polymer scaffold design and manufacturing resources are essential for the successful application of this technology. In order to apply these engineering techniques to humans, further studies need to be performed with many of the tissues described. The first human application of cell-based tissue engineering technology for urologic applications took place at our institution, with the injection of autologous cells for the correction of vesicoureteral reflux in children. The same technology has been expanded to treat adult patients with urinary incontinence. Trials of urethral tissue replacement with processed collagen matrices are in progress, and bladder replacement using tissue engineering techniques are currently being arranged. Recent progress suggests that engineered urologic tissues may have clinical applicability in the future.

Artificial Organs↗
PubMed2002

Autologous penile corpora cavernosa replacement using tissue engineering techniques.

PURPOSE: The availability of engineered tissues would be beneficial to patients undergoing penile reconstruction. We explored the possibility of replacing an entire cross-sectional segment of both corporal bodies with autologous engineered tissues in rabbits, and investigated the structural and functional integrity of the neo-corpora. MATERIALS AND METHODS: Acellular corporal collagen matrices were obtained from donor rabbit penis. Autologous corpus cavernosal smooth muscle and endothelial cells were harvested, expanded and seeded on the matrices. An entire cross-sectional segment of protruding rabbit phallus was excised, leaving the urethra intact. A total of 26 matrices, including 18 seeded with cells and 8 without cells, were interposed into the excised corporal space. An additional 4 rabbits that did not undergo surgical intervention served as normal controls. Functional and structural parameters (cavernosography, cavernosometry, mating behavior and sperm ejaculation) were followed for 6 months. Gross examination, and histochemical, immunocytochemical and Western blot analyses were performed at 3 and 6 months after implantation. RESULTS: The experimental corporal bodies demonstrated intact structural integrity on cavernosography and decreased maximal intracavernosal pressures on cavernosometry compared to normal controls. Mating activity in animals with engineered corpora normalized by 3 months postoperatively. The presence of sperm was confirmed during mating and was present in all rabbits with engineered corpora but in only 2 with the matrix alone. Histologically sinusoidal spaces and walls lined with endothelial and smooth muscle cells were observed in the engineered grafts. Each cell type was identified immunocytochemically. Grafts without cells contained fibrotic tissue and calcifications with sparse corporal elements. Western blot analysis of engineered grafts showed nitric oxide synthase activity similar to normal controls. CONCLUSIONS: Autologous corpus cavernosal smooth muscle and endothelial cells seeded on collagen matrices can form corpora cavernosa tissue structures in a rabbit model. Engineered corpora cavernosa achieved adequate structural and functional parameters. This technology may be applicable to patients who require additional tissue for phallic reconstruction.

Animals↗
PubMed2004

Microtia chondrocytes as a donor source for tissue-engineered cartilage.

OBJECTIVES/HYPOTHESIS: Current surgical techniques for the correction of microtia are challenging. Research in the field of tissue engineering is providing insight into chondrocyte behavior for a possible future treatment of microtia. The authors wished to evaluate the biological potential of chondrocytes isolated from microtia cartilage as compared with normal auricular cartilage as a source of tissue-engineered cartilage. STUDY DESIGN: A comparative research design to study the potential of microtia cartilage chondrocytes with normal auricular chondrocytes as a source of tissue-engineered cartilage. METHODS: Cartilage specimens from 12 pediatric patients (six normal auricular specimens and six auricular specimens with microtia) were obtained. The chondrocytes were isolated and cultured in vitro; chondrocyte number was increased by passaging. Each type of cell was implanted in nude mice to generate tissue-engineered cartilage. Eight weeks after implantation the specimens were dissected and removed. Results were compared between the normal auricular and microtia specimens in regard to cell number expansion in vitro and generation of tissue-engineered cartilage in vivo. RESULTS: An initial mean cell number of 150,000 cells in each group (normal and microtia) increased to an average cell number of 120 million cells/mL in the normal and 130 million cells in the microtia subgroups, respectively, at the end of the second passage. Histologically, both types of chondrocytes generated normal elastic cartilage. CONCLUSION: The study demonstrated the potential of cells isolated from microtia cartilage to generate tissue-engineered cartilage. Microtia cartilage represents an important additional donor source for the possible generation of a human tissue-engineered auricle.

Case-Control Studies↗
PubMed2002

Bridging tendon defects using autologous tenocyte engineered tendon in a hen model.

Tendon defects remain a major concern in plastic surgery because of the limited availability of tendon autografts. Whereas immune rejection prohibits the use of tendon allografts, most prosthetic replacements also fail to achieve a satisfactory long-term result of tendon repair. The tissue engineering technique, however, can generate different tissues using autologous cells and thus may provide an optimal approach to address this concern. The purpose of this study was to test the feasibility of engineering tendon tissues with autologous tenocytes to bridge a tendon defect in either a tendon sheath open model or a partial open model in the hen. In a total of 40 Leghorn hens, flexor tendons were harvested from the left feet and were digested with 0.25% type II collagenase. The isolated tenocytes were expanded in vitro and mixed with unwoven polyglycolic acid fibers to form a cell-scaffold construct in the shape of a tendon. The constructs were wrapped with intestinal submucosa and then cultured in Dulbecco's Modified Eagle Medium plus 10% fetal bovine serum for 1 week before in vivo transplantation. On the feet, a defect of 3 to 4 cm was created at the second flexor digitorum profundus tendon by resecting a tendon fragment. The defects were bridged either with a cell-scaffold construct in the experimental group ( n= 20) or with scaffold material alone in the control group ( n= 20). Specimens were harvested at 8, 12, and 14 weeks postrepair for gross and histologic examination and for biomechanical analysis. In the experimental group, a cordlike tissue bridging the tendon defect was formed at 8 weeks postrepair. At 14 weeks, the engineered tendons resembled the natural tendons grossly in both color and texture. Histologic examination at 8 weeks showed that the neo-tendon contained abundant tenocytes and collagen; most collagen bundles were randomly arranged. The undegraded polyglycolic acid fibers surrounded by inflammatory cells were also observed. At 12 weeks, tenocytes and collagen fibers became longitudinally aligned, with good interface healing to normal tendon. At 14 weeks, the engineered tendons displayed a typical tendon structure hardly distinguishable from that of normal tendons. Biomechanical analysis demonstrated increased breaking strength of the engineered tendons with time, which reached 83 percent of normal tendon strength at 14 weeks. In the control group, polyglycolic acid constructs were mostly degraded at 8 weeks and disappeared at 14 weeks. However, the breaking strength of the scaffold materials accounted for only 9 percent of normal tendon strength. The results of this study indicated that tendon tissue could be engineered in vivo to bridge a tendon defect. The engineered tendons resembled natural tendons not only in gross appearance and histologic structure but also in biomechanical properties.

Animals↗
PubMed2002

Tissue engineering of the lymphatic system.

The field of tissue engineering has seen tremendous expansion in the last decade. In the last several years, tissue-engineering strategies to treat diseases of skin, cartilage, bone, bladder, blood vessel, tendon, and other tissues have been described. However, tissue-engineering approaches to treat diseases of the lymphatic system are currently nonexistent. We propose that acellular tissues, either native or engineered, could be exploited as a platform for the study of lymphatic biology, and for lymphatic tissue engineering. While speculative, this type of experimental model system could prove powerful for dissecting molecular and cellular events surrounding tumor invasion of lymphatics, as well as lymphangiogenesis. Scaffolds seeded with genetically engineered lymphatic cells could also be implanted to repopulate lymphatic vasculature. In the future, the lymphatic system will surely be added to the list of tissues and organs that prove amenable to tissue-engineering therapies.

Animals↗
PubMed2003

Tissue engineering therapy for cardiovascular disease.

The present treatments for the loss or failure of cardiovascular function include organ transplantation, surgical reconstruction, mechanical or synthetic devices, or the administration of metabolic products. Although routinely used, these treatments are not without constraints and complications. The emerging and interdisciplinary field of tissue engineering has evolved to provide solutions to tissue creation and repair. Tissue engineering applies the principles of engineering, material science, and biology toward the development of biological substitutes that restore, maintain, or improve tissue function. Progress has been made in engineering the various components of the cardiovascular system, including blood vessels, heart valves, and cardiac muscle. Many pivotal studies have been performed in recent years that may support the move toward the widespread application of tissue-engineered therapy for cardiovascular diseases. The studies discussed include endothelial cell seeding of vascular grafts, tissue-engineered vascular conduits, generation of heart valve leaflets, cardiomyoplasty, genetic manipulation, and in vitro conditions for optimizing tissue-engineered cardiovascular constructs.

Animals↗
PubMed2000

Ethical considerations for biomedical scientists and engineers: issues for the rank and file.

Biomedical science and engineering is inextricably linked with the fields of medicine and surgery. Yet, while physicians and surgeons, nurses, and other medical professionals receive instruction in ethics during their training and must abide by certain codes of ethics during their practice, those engaged in biomedical science and engineering typically receive no formal training in ethics. In fact, the little contact that many biomedical science and engineering professionals have with ethics occurs either when they participate in government-funded research or submit articles for publication in certain journals. Thus, there is a need for biomedical scientists and engineers as a group to become more aware of ethics. Moreover, recent advances in biomedical technology and the ever-increasing use of new devices virtually guarantee that biomedical science and engineering will become even more important in the future. Although they are rarely in direct contact with patients, biomedical scientists and engineers must become aware of ethics in order to be able to deal with the complex ethical issues that arise from our society's increasing reliance on biomedical technology. In this brief communication, the need for ethical awareness among workers in biomedical science and engineering is discussed in terms of certain conflicts that arise in the workaday world of the biomedical scientist in a complex, modern society. It is also recognized that inasmuch as workers in the many branches of bioengineering are not regulated like their counterparts in medicine and surgery, perhaps academic institutions and professional societies are best equipped to heighten ethical awareness among workers in this important field.

Authorship↗
PubMed1998

1998 ARRS President's Award. The potential of in vivo vascular tissue engineering for the treatment of vascular thrombosis: a preliminary report. American Roentgen Ray Society.

OBJECTIVE: Current gene therapy and tissue engineering protocols suffer from a number of inherent limitations. In this study, we examine the feasibility of a new approach for the treatment of vascular thrombosis: in vivo tissue engineering. MATERIALS AND METHODS: Rabbit femoral veins were transfected in situ with either a previously characterized adenoviral-construct-expressing tissue plasminogen activator or a viral (adenoviral-construct-expressing beta-galactosidase) or nonviral (buffer) control and used as cross sections (n = 3). Treated veins were then harvested and grafted into the ipsilateral common femoral artery as an interposition vein graft. A potent stimulus for thrombus formation was then introduced into the recipient artery downstream of the graft. Six days later, the rabbits were sacrificed, and the grafts and downstream arteries were harvested. Vessel segments were then examined for thrombus according to defined anatomic zones. Transfection efficiency and presence of smooth muscle cells in the vein graft were also evaluated. RESULTS: The engineered vein graft showed a significant reduction in thrombus formation within both the graft and the downstream artery relative to nonviral (buffer) and viral (adenoviral-Rous sarcoma virus beta-galactosidase [Adv/RSV-betagal]) controls. Underlying endothelial cell transfection efficiency of 90% was observed in viral controls (Adv/RSV-betagal). A 2.4-fold increase in smooth muscle alpha-actin positive cells in the engineered vein graft was seen compared with nonviral (phosphate-buffered saline) controls. A 10-fold increase in smooth muscle alpha-actin-positive cells in the engineered vein graft relative to viral (Adv/RSV-betagal) controls was also observed. CONCLUSION: In vivo tissue engineering is a new paradigm in molecular medicine that is a viable alternative to conventional gene therapy and tissue engineering for the treatment of vascular thrombosis.

Animals↗