Gastric epithelium under organotypic perfusion culture

Bridging the gap between traditional cell cultures and bioreactors applied in regenerative medicine: practical experiences with the MINUSHEET perfusion culture system

To meet specific requirements of developing tissues urgently needed in tissue engineering, biomaterial research and drug toxicity testing, a versatile perfusion culture system was developed. First an individual biomaterial is selected and then mounted in a MINUSHEET(®) tissue carrier. After sterilization the assembly is transferred by fine forceps to a 24 well culture plate for seeding cells or mounting tissue on it. To support spatial (3D) development a carrier can be placed in various types of perfusion culture containers. In the basic version a constant flow of culture medium provides contained tissue with always fresh nutrition and respiratory gas. For example, epithelia can be transferred to a gradient container, where they are exposed to different fluids at the luminal and basal side. To observe development of tissue under the microscope, in a different type of container a transparent lid and base are integrated. Finally, stem/progenitor cells are incubated in a container filled by an artificial interstitium to support spatial development. In the past years the described system was applied in numerous own and external investigations. To present an actual overview of resulting experimental data, the present paper was written.

Development of 3D in vitro technology for medical applications

In the past few years, biomaterials technologies together with significant efforts on developing biology have revolutionized the process of engineered materials. Three dimensional (3D) in vitro technology aims to develop set of tools that are simple, inexpensive, portable and robust that could be commercialized and used in various fields of biomedical sciences such as drug discovery, diagnostic tools, and therapeutic approaches in regenerative medicine. The proliferation of cells in the 3D scaffold needs an oxygen and nutrition supply. 3D scaffold materials should provide such an environment for cells living in close proximity. 3D scaffolds that are able to regenerate or restore tissue and/or organs have begun to revolutionize medicine and biomedical science. Scaffolds have been used to support and promote the regeneration of tissues. Different processing techniques have been developed to design and fabricate three dimensional scaffolds for tissue engineering implants. Throughout the chapters we discuss in this review, we inform the reader about the potential applications of different 3D in vitro systems that can be applied for fabricating a wider range of novel biomaterials for use in tissue engineering.

Supportive development of functional tissues for biomedical research using the MINUSHEET® perfusion system

Functional tissues generated under in vitro conditions are urgently needed in biomedical research. However, the engineering of tissues is rather difficult, since their development is influenced by numerous parameters. In consequence, a versatile culture system was developed to respond the unmet needs.

Optimal adhesion for cells in this system is reached by the selection of individual biomaterials. To protect cells during handling and culture, the biomaterial is mounted onto a MINUSHEET® tissue carrier. While adherence of cells takes place in the static environment of a 24 well culture plate, generation of tissues is accomplished in one of several available perfusion culture containers. In the basic version a continuous flow of always fresh culture medium is provided to the developing tissue. In a gradient perfusion culture container epithelia are exposed to different fluids at the luminal and basal sides. Another special container with a transparent lid and base enables microscopic visualization of ongoing tissue development. A further container exhibits a flexible silicone lid to apply force onto the developing tissue thereby mimicking mechanical load that is required for developing connective and muscular tissue. Finally, stem/progenitor cells are kept at the interface of an artificial polyester interstitium within a perfusion culture container offering for example an optimal environment for the spatial development of renal tubules.

The system presented here was evaluated by various research groups. As a result a variety of publications including most interesting applications were published. In the present paper these data were reviewed and analyzed. All of the results point out that the cell biological profile of engineered tissues can be strongly improved, when the introduced perfusion culture technique is applied in combination with specific biomaterials supporting primary adhesion of cells.

Tissue engineering of composite grafts: Cocultivation of human oral keratinocytes and human osteoblast-like cells on laminin-coated polycarbonate membranes and equine collagen membranes under different culture conditions

In complex craniomaxillofacial defects, the simultaneous reconstruction of hard and soft tissue is often necessary. Until now, oral keratinocytes and osteoblast-like cells have not been cocultivated on the same carrier. For the first time, the cocultivation of human oral keratinocytes and human osteoblast-like cells has been investigated in this study. Different carriers (laminin-coated polycarbonate and equine collagen membranes) and various culture conditions were examined. Human oral keratinocytes and human osteoblast-like cells from five patients were isolated from tissue samples, seeded on the opposite sides of the carriers and cultivated for 1 and 2 weeks under static conditions in an incubator and in a perfusion chamber. Proliferation and morphology of the cells were analyzed by EZ4U-tests, light microscopy, and scanning electron microscopy. Cocultivation of both cell-types seeded on one carrier was possible. Quantitative and qualitative growth was significantly better on collagen membranes when compared with laminin-coated polycarbonate membranes independent of the culture conditions. Using perfusion culture in comparison to static culture, the increase of cell proliferation after 2 weeks of cultivation when compared with the proliferation after 1 week was significantly lower, independent of the carriers used. In conclusion, the contemporaneous cultivation of human oral keratinocytes and human osteoblast-like cells on the same carrier is possible, a prerequisite for planned in vivo studies. As carrier collagen is superior to laminin-coated polycarbonate membranes. Regarding the development over time, the increase of proliferation rate is lower in perfusion culture. Examinations of cellular differentiation over time under various culture conditions will be subject of further investigations.

Ectopic bone formation in collagen sponge self-assembled peptide–amphiphile nanofibers hybrid scaffold in a perfusion culture bioreactor

The objective of this study was to enhance ectopic bone formation in a three-dimensional (3-D) hybrid scaffold in combination with bioreactor perfusion culture system. The hybrid scaffold consists of two biomaterials, a hydrogel formed through self-assembly of peptide-amphiphile (PA) with cell suspensions in media, and a collagen sponge reinforced with poly(glycolic acid) (PGA) fiber incorporation. PA was synthesized by standard solid-phase chemistry that ends with the alkylation of the NH2 terminus of the peptide. A 3-D network of nanofibers was formed by mixing cell suspensions in media with dilute aqueous solution of PA. Scanning electron microscopy (SEM) observation revealed the formation of fibrous assemblies with an extremely high aspect ratio and high surface areas. Osteogenic differentiation of mesenchymal stem cells (MSC) in the hybrid scaffold was greatly influenced by the perfusion culture method compared with static culture method. When the osteoinduction activity of hybrid scaffold was studied following the implantation into the back subcutis of rats in terms of histological and biochemical examinations, significantly homogeneous bone formation was histologically observed throughout the hybrid scaffolds when perfusion culture was used compared with static culture method. The level of alkaline phosphatase activity and osteocalcin content at the implanted sites of hybrid scaffolds were significantly high for the perfusion group compared with those in static culture method. We conclude that combination of MSC-seeded hybrid scaffold and the perfusion method was promising to enhance in vitro osteogenic differentiation of MSC and in vivo ectopic bone formation.

Perfusion culture enhances osteogenic differentiation of rat mesenchymal stem cells in collagen sponge reinforced with poly(glycolic Acid) fiber

The objective of this study was to obtain fundamental knowledge about in vitro culture systems to enhance the proliferation and differentiation of mesenchymal stem cells (MSCs) in collagen sponge reinforced by the incorporation of poly(glycolic acid) (PGA) fiber. A collagen solution with PGA fiber homogeneously localized at PGA:collagen weight ratios of 0.67, 1.25, 2.5, and 5 was freezedried, followed by cross-linking of combined dehydrothermal, glutaraldehyde, and ultraviolet treatment. Scanning electron microscopy revealed that collagen sponges exhibited homogeneous and interconnected pore structures with an average size of 180 microm, irrespective of PGA fiber incorporation. When rat MSCs were seeded into collagen sponge with or without PGA fiber incorporation, more attached cells were observed in collagen sponge incorporating PGA fiber than in collagen sponge without PGA fiber incorporation, irrespective of the PGA:collagen ratio. The proliferation and osteogenic differentiation of MSCs in PGA-reinforced sponge at a weight ratio of 5 were greatly influenced by the culture method and growth conditions. Alkaline phosphatase (ALP) activity and osteocalcin content of MSCs cultured in PGA-reinforced sponge by the perfusion method became maximum at a flow rate of 0.2 mL/min, although they increased with culture time period. It may be concluded that appropriate perfusion conditions enable MSCs to positively improve the extent of proliferation and differentiation.

Impregnation of Plasmid DNA into Three-Dimensional Scaffolds and Medium Perfusion Enhancein VitroDNA Expression of Mesenchymal Stem Cells

This article describes the development of an in vitro culture system to enhance the expression of a plasmid DNA for mesenchymal stem cells (MSCs) by a combination of plasmid DNA impregnation into three-dimensional cell scaffolds and culture methods. Gelatin was cationized by introducing spermine to the carboxyl groups for complexation with the plasmid DNA. As the MSC scaffold, poly(glycolic acid) (PGA) fiber fabrics, collagen sponges, and collagen sponges reinforced by incorporation of PGA fibers were used. A complex of cationized gelatin and plasmid DNA encoding bone morphogenetic protein 2 (BMP-2) was impregnated into the scaffolds. Plasmid DNA was released from PGA-reinforced collagen sponge for longer than from the other scaffolds. MCS were seeded into each type of scaffold and cultured by static, stirring, and perfusion methods. When MSCs were cultured in PGA-reinforced sponge, the level of BMP-2 expression was significantly enhanced by perfusion culture compared with the other culture methods, and the time of expression was prolonged. Irrespective of the culture method, the expression level was significantly higher from plasmid DNA impregnated in scaffold than by plasmid DNA in medium. The alkaline phosphatase activity and osteocalcin content of MSCs cultured in PGA-reinforced sponge by the perfusion method were significantly higher compared with those of other methods, and a significantly higher amount of plasmid DNA internalized into MSCs was observed. We conclude that a combination of plasmid DNA-impregnated PGA-reinforced sponge and the perfusion method was promising to promote in vitro gene expression for MSCs.

Stable ciliary activity in human nasal epithelial cells grown in a perfusion system

PURPOSE

Explore the usefulness of a perfusion system in order to establish human nasal epithelial cell cultures suitable for long-term in vitro ciliary beat frequency (CBF) and cilio-toxicity studies.

METHODS

The cells were obtained by protease digestion of nasal biopsy material. The cells were plated at a density of 0.8-1 x 10(6)/cm2 on Vitrogen-coated polyethylene terephthalate membranes, and cultured under submerged conditions in a CO2 incubator or in a perfusion system (initiated on days 8-9 after plating). The CBF was determined at 24.1 +/- 0.8 degrees C by a computerized microscope photometry system. The morphology of the cultured cells was characterized by transmission electron microscopy (TEM).

RESULTS

Under CO2 incubator culture conditions, stable ciliary activity was expressed and maintained from day 2 to day 24. Under perfusion system culture conditions, the CBF (mean+/-S.D., n = 4) amounted to 8.4 +/- 0.9 and 8.8 +/- 0.4 Hz on days 7 and 14, respectively. These values were lower as compared to the corresponding CBF obtained in the CO2 incubator cultures (9.5 +/- 0.6 and 9.9 +/- 1.0 Hz, respectively). Reference cilio-stimulatory (glycocholate) and cilio-inhibitory (chlorocresol) compounds were used to assess CBF reactivity. In the CO2 incubator and 7- and 14-days perfusion system cultures, glycocholate (0.5%) showed a reversible cilio-stimulatory effect of 23, 26 and 21%, respectively, while chlorocresol (0.005%) exerted a reversible cilio-inhibitory effect of 36, 40 and 36%, respectively. TEM revealed polarized cuboidal to columnar epithelial morphology, with well-differentiated ciliated cells under CO2 and perfusion system conditions (up to day 23).

CONCLUSION

Culturing human nasal epithelial cells on Vitrogen-coated polyethylene terephthalate membranes in submerged conditions in a CO2 incubator and in a perfusion system offers the possibility for long-term preservation (up to 22-24 days) of stable and reactive CBF in vitro.

Application of Perfusion Culture System Improves in Vitro and in Vivo Osteogenesis of Bone Marrow-Derived Osteoblastic Cells in Porous Ceramic Materials

Composites of bone marrow-derived osteoblasts (BMOs) and porous ceramics have been widely used as a bone graft model for bone tissue engineering. Perfusion culture has potential utility for many cell types in three-dimensional (3D) culture. Our hypothesis was that perfusion of medium would increase the cell viability and biosynthetic activity of BMOs in porous ceramic materials, which would be revealed by increased levels of alkaline phosphate (ALP) activity and osteocalcin (OCN) and enhanced bone formation in vivo. For testing in vitro, BMO/beta-tricalcium phosphate composites were cultured in a perfusion container (Minucells and Minutissue, Bad Abbach, Germany) with fresh medium delivered at a rate of 2 mL/h by a peristaltic pump. The ALP activity and OCN content of composites were measured at the end of 1, 2, 3, and 4 weeks of subculture. For testing in vivo, after subculturing for 2 weeks, the composites were subcutaneously implanted into syngeneic rats. These implants were harvested 4 or 8 weeks later. The samples then underwent a biochemical analysis of ALP activity and OCN content and were observed by light microscopy. The levels of ALP activity and OCN in the composites were significantly higher in the perfusion group than in the control group (p < 0.01), both in vitro and in vivo. Histomorphometric analysis of the hematoxylin- and eosin-stained sections revealed a higher average ratio of bone to pore in BMO/beta-TCP composites of the perfusion group after implantation: 47.64 +/- 6.16 for the perfusion group and 26.22 +/- 4.84 for control at 4 weeks (n = 6, p < 0.01); 67.97 +/- 3.58 for the perfusion group and 47.39 +/- 4.10 for control at 8 weeks (n = 6, p < 0.05). These results show that the application of a perfusion culture system during the subculture of BMOs in a porous ceramic scaffold is beneficial to their osteogenesis. After differentiation culture in vitro with the perfusion culture system, the activity of the osteoblastic cells and the consequent bone formation in vivo were significantly enhanced. These results suggest that the perfusion culture system is a valuable and convenient tool for applications in tissue engineering, especially in the generation of artificial bone tissue.

Tissue engineering in otorhinolaryngology

Tissue engineering is a field of research with interdisciplinary cooperation between clinicians, cell biologists, and materials research scientists. Many medical specialties apply tissue engineering techniques for the development of artificial replacement tissue. Stages of development extend from basic research and preclinical studies to clinical application. Despite numerous established tissue replacement methods in otorhinolaryngology, head and neck surgery, tissue engineering techniques opens up new ways for cell and tissue repair in this medical field. Autologous cartilage still remains the gold standard in plastic reconstructive surgery of the nose and external ear. The limited amount of patient cartilage obtainable for reconstructive head and neck surgery have rendered cartilage one of the most important targets for tissue engineering in head and neck surgery. Although successful in vitro generation of bioartificial cartilage is possible today, these transplants are affected by resorption after implantation into the patient. Replacement of bone in the facial or cranial region may be necessary after tumor resections, traumas, inflammations or in cases of malformations. Tissue engineering of bone could combine the advantages of autologous bone grafts with a minimal requirement for second interventions. Three different approaches are currently available for treating bone defects with the aid of tissue engineering: (1) matrix-based therapy, (2) factor-based therapy, and (3) cell-based therapy. All three treatment strategies can be used either alone or in combination for reconstruction or regeneration of bone. The use of respiratory epithelium generated in vitro is mainly indicated in reconstructive surgery of the trachea and larynx. Bioartificial respiratory epithelium could be used for functionalizing tracheal prostheses as well as direct epithelial coverage for scar prophylaxis after laser surgery of shorter stenoses. Before clinical application animal experiments have to prove feasability and safety of the different experimental protocols. All diseases accompanied by permanently reduced salivation are possible treatment targets for tissue engineering. Radiogenic xerostomia after radiotherapy of malignant head and neck tumors is of particular importance here due to the high number of affected patients. The number of new diseases is estimated to be over 500,000 cases worldwide. Causal treatment options for radiation-induced salivary gland damage are not yet available; thus, various study groups are currently investigating whether cell therapy concepts can be developed with tissue engineering methods. Tissue engineering opens up new ways to generate vital and functional transplants. Various basic problems have still to be solved before clinically applying in vitro fabricated tissue. Only a fraction of all somatic organ-specific cell types can be grown in sufficient amounts in vitro. The inadequate in vitro oxygen and nutrition supply is another limiting factor for the fabrication of complex tissues or organ systems. Tissue survival is doubtful after implantation, if its supply is not ensured by a capillary network.

Physiological and cell biological aspects of perfusion culture technique employed to generate differentiated tissues for long term biomaterial testing and tissue engineering

Optimal results in biomaterial testing and tissue engineering under in vitro conditions can only be expected when the tissue generated resembles the original tissue as closely as possible. However, most of the presently used stagnant cell culture models do not produce the necessary degree of cellular differentiation, since important morphological, physiological, and biochemical characteristics disappear, while atypical features arise. To reach a high degree of cellular differentiation and to optimize the cellular environment, an advanced culture technology allowing the regulation of differentiation on different cellular levels was developed. By the use of tissue carriers, a variety of biomaterials or individually selected scaffolds could be tested for optimal tissue development. The tissue carriers are to be placed in perfusion culture containers, which are constantly supplied with fresh medium to avoid an accumulation of harmful metabolic products. The perfusion of medium creates a constant microenvironment with serum-containing or serum-free media. By this technique, tissues could be used for biomaterial or scaffold testing either in a proliferative or in a postmitotic phase, as is observed during natural development. The present paper summarizes technical developments, physiological parameters, cell biological reactions, and theoretical considerations for an optimal tissue development in the field of perfusion culture.

Polar application of test substances in an organotypic environment and under continuous medium flow: a new tissue-based test concept for a broad range of applications in pharmacotoxicology

We have established a new test concept for in vitro pharmacological trials. Our model employs tissue explants to test compounds for toxicity which arises with the metabolic interactions among different cell types. Microsurgical preparation of tissue explants avoids the destruction of the organ-specific tissue architecture. Explants were mounted in tissue carriers to improve nutrition and handling of the sample. To allow for the omission of serum supplementation of the culture medium, explants were cultured under continuous medium flow. Test substances are applied considering the polar architecture of most tissues in vivo, for example, covering the apical aspect of epithelia. In principal, all tissues obtained from any species, including man, can be used in this system. A trial application was performed with vitreous body substitutes, substances used in ophthalmology. One compound had passed cell culture tests, but caused massive blood vessel deterioration in vivo. Using our test system based on the developing renal vessel system, we could confirm, within 24 hours, severe vessel damage which resembles the injury suffered by the rabbit retina. We demonstrate that an improved tissue culture assay is a suitable tool for the detection of toxicity that remained unidentified in cell culture tests.