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The Masquelet procedure or induced membrane technique presents a treatment option for relatively large osseous defects, e.g. after trauma, tumour resection or osteomyelitis even in the presence of unfavourable soft tissues. Initially developed at the end of the last century by the French surgeon Masquelet, the technique relies on a bioactive membrane that forms a foreign body reaction around a cement spacer. This spacer is implanted in the residual defect after rigorous debridement of bone and soft tissue during a first-stage procedure. A second-stage intervention is performed 1-2 months later with removal of the spacer under preservation of the membrane that has since formed around the cement. The membrane acts as an internal bioreactor exerting its effect via a rich vascularization and secretion of growth and differentiation factors. The void within the membrane is filled with an autologous cancellous graft. After adequate stabilisation using standard techniques, a gradual corticalisation of the graft can be observed over the duration of several months, with remodelling in the long-term course.The following article describes the original technique, our preferred approach including indication, surgical technique and postoperative follow-up. Additionally, the biological background and clinical tips and tricks are presented.

"Keep up with today's single-use technology standard but also remain one step ahead" – that could have been the motto of the BioTech 2016 conference at ZHAW Waedenswil on September 5 and 6, which brought together manufacturers, suppliers, users, regulatory specialists and representatives of organizations in this field to implement single-use devices all over the world. It was an effectiveness analysis of the trend to replace reusable equipment in production facilities with single-use components.

The ability of selected manganese peroxidase (MnP) yeast strains, isolated from the mixed liquor of an activated sludge bioreactor treating melanoidins wastewater, was investigated in this work, aiming to examine the degradation potential of melanoidins, in the presence or absence of nutrients. Ten yeast strains were initially isolated from the mixed liquor; four yeast strains (Y1, Y2, Y3 and Y4) were selected for further studies, based on their tolerance towards synthetic melanoidins (SMs) degradation and MnP activity onto solid agar medium. The Y1 strain exhibited almost 98% homology to Candida glabrata yeast, based on 28S rRNA identification studies. During experiments carried out using SM at 30 °C, the four isolated yeast cultures showed a noticeable organic matter reduction and decolorization capacity reaching up to 70% within 2–5 days. However, the corresponding yeast cultures grown in glucose peptone yeast extract medium using real melanoidin wastewater at 30°C showed lower organic matter and color removal capacity, reaching about 60% within 2–5 days. Nevertheless, it was found that the removal of real and synthetic melanoidins could be carried out by these strains under non-aseptic conditions, without requiring further addition of nutrients.

Biological and physical characteristics of matrices are one essential factor in creating bioartificial tissue. In this study, a new 3-dimensional cellulose matrix (Xellulin(®)) was tested in terms of biocompatibility and applicability for tissue engineering in vitro and in vivo.The tested matrix Xellulin(®) is a natural hydrological gel-matrix containing bacterial cellulose and water. To evaluate the cell biocompatibilty, cell adherence and proliferation characteristics in vitro, the matrix was cultured with human fibroblasts. Further in vivo studies were carried out by transplanting preadipocytes of 4- to 6-week-old Wistar rats with 3 different conditions: a) Xellulin(®) including 500 000 preadipocytes subcutaneous, b) Xellulin(®) including 500 000 preadipocytes within an in vivo bioreactor chamber, c) Xellulin(®) without cells subcutaneous as control. After explantation on day 14 histomorphological and immunohistochemical evaluations were performed.In vitro study revealed an excellent biocompatibility with good cell adherence of the fibroblasts on the matrix and evidence of cell proliferation and creation of a 3-dimensional cell network. In vivo neocapillarisation could be shown in all groups with evidence of erythrocytes (H/E staining) and endothelial vascular cells (RECA-1-staining). A significantly higher vascular density was shown in vascularised bioreactor group (18.4 vessels/100 000 µm(2) (group b) vs. 8.1 (group a), p0.05). Cell density was the highest in the vascularised group, but without significant values. No immunogenic reaction to the matrix was noticed.The promising in vitro results concerning cell adherence and proliferation on the tested matrix could be confirmed in vivo with an evidence of 3-dimensional neocapillarisation. Cell survival was higher in the vascularised group, but without significance. Long-term tests (28-42 days) need to be carried out to evaluate long-term cell survival and the matrix stability. Furthermore, studies concerning the implementation of the matrix within anatomic structures as well as long-term biocompatibility are needed.

Interaction between platelets and artificial materials within cardiovascular devices triggers blood coagulation and represents a frequent adverse response to implant deployment. Avoidance of this interaction is obtained through the generation and sustenance under flow of a confluent and stable endothelial monolayer covering the luminal device surface, altogether defined as the process of endothelialization. Supraphysiological wall shear stress (WSS) levels generated within vascular assist devices (VADs) constitute a major challenge toward endothelialization. Here we report the experimental demonstration that stable endothelialization can be achieved at supraphysiological WSS levels by pure means of appropriate surface micro-structuring. Using a custom-designed flow bioreactor we exposed endothelial monolayers to physiological and supraphysiological WSS levels and investigated the resulting integrity of cell-to-cell junctions, the cell density and the cell polarization. At physiological WSS levels, optimal endothelialization was obtained independently from surface topography. However, at higher WSS levels, only monolayers grown on appropriately micro-structured surfaces preserved optimal integrity. Under these flow conditions, endothelial cells polarized by the contact with the micro-structure and, interestingly, oriented themselves in the direction perpendicular to flow. Such endothelial layers withstood WSS levels exceeding of 100% or more the thresholds detected on flat substrates.

With the advent of the era of tissue engineering (TE), experimental settings have been developed that allow for a defined environment with optimised cell growth conditions and/or the production of specific substitutes. These isolated systems have been termed "bioreactors". By translating the principles of bioreactors into an in vivo context, advances in biomaterial sciences and cell biology have been merged into an integrative research concept. Even today, in the age of regenerative Medicine (RegMed) the transfer of experimental in vitro findings into a clinical in vivo approach still remains a vast challenge. In order to fulfil these specific requirements bioreactors had to be defined anew. Latest advances in areas like reconstructive medicine (the arteriovenous loop as a means of organogenesis) or modern wound management (topical negative pressure therapy as a perfusion bioreactor) give new impulses towards the translation of Reg-Med concepts into the clinical routine.

Vascular tissue engineering represents a new but rapidly growing field due to the need for better vascular prostheses for coronary or peripheral revascularization procedures. Current synthetic prostheses have a high incidence of failure due to thrombosis and/or intimal hyperplasia especially in small caliber artificial vascular prostheses. New approaches such as decellularized, natural or synthetic, 3-D stable/degradable scaffolds are being developed for acellular or cell-based vascular replacements. The drawbacks of cellular bioreactor matured prostheses are delayed availability and that they are, labor and cost-intensive. However, some research groups have shown limited clinical applications. The acellular approach is based on a biodegradable, electrospun, porous 3-D structure made of nano- and micro-sized polycaprolactone fibers. Animal studies in rats and pigs have shown good short and long-term results after arterial replacement with autologous cellular and matrix ingrowth, angiogenesis, confluent endothelialization and absence of occlusions or aneurysm formation. Therefore, the in vivo vascular tissue engineering approach produces shelf-ready biodegradable vascular prostheses which might be an option for future clinical applications.

Innovative mixing principles in bioreactors, for example using the rocking of a platform to induce a backwards and forwards 'wave' , or using orbital shaking to generate a 'wave' that runs round in a cylindrical container, have proved to be successful for the suspension cultures of cells, especially when combined with disposable materials. This article presents an overview of the engineering characteristics when these new principles are applied in bioreactors, and case studies covering scales of operation from milliliters to 1000 liters.

Cardiac function, including the heart muscle and valves, can be severely altered by congenital and acquired heart diseases. Several graft materials are currently used to replace diseased cardiac tissue and valvular segments. Implantable grafts are either non-vital or can trigger an immune response which leads to graft calcification and degeneration. None of the existing grafts have the ability to remodel and grow in tandem with the physiological growth of a child and therefore require re-operation. Novel approaches such as tissue engineering have emerged as possible alternatives for cardiac reconstruction. The main concept of tissue engineering includes the use of biological and artificial scaffolds that form the shape of the organ structures for subsequent tissue replacement, which will provide absolute biocompatibility, no thrombogenicity, no teratogenicity, long-term durability and growth.Heart valve tissue engineering represents an important field especially in pediatric patients with valve pathologies. In order to create an autologous valve equivalent myofibroblasts and/or endothelial cells are seeded on specially designed scaffolds. Here we describe the different types of cell sources and different types of matrices currently used in heart valve tissue engineering. Valve manufacture is carried out in specially designed bioreactors providing physiological conditions. The number of clinical studies using tissue engineered valves is still limited; however, several promising results have already demonstrated their durability and ability to grow.Myocardial tissue engineering aims to repair, replace and regenerate damaged cardiac tissue using tissue constructs created ex vivo. Conceivable indications for clinical application of tissue engineered myocardial-implant substitutes include ischemic cardiomyopathies, as well as right ventricular outflow tract reconstruction in patients with congenital heart diseases. Therapeutic application of functional (contractile) tissue engineered heart muscle appears feasible once key issues such as identification of the suitable human cell source, large scale expansion and suitable scaffolds are solved. In addition, the present article discusses the importance of vascularization as an important prerequisite for successful bio-artificial myocardial tissue.Further experimental and clinical research on cardiovascular tissue engineering is felt to be of great importance for others as well as for us in order to create an ideal heart valve/myocardial substitute and help our patients with advanced cardiac pathologies.

The main problem in the treatment of orthopaedic joint-surface defects will be solved by tissue engineering of cartilage implants. Entire biological osteochondral implants can be grown from autologous cells of the patient. The nutrition of articular cartilage is by diffusion only. Therefore the chondrocyte as the unique cell type is perfectly dedicated to the tissue culture approach. Engineering techniques of bioreactors are prerequisite for these biological and medical solutions. With our tissue engineering project for the generation of osteochondral constructs we demonstrate possibilities and characteristics of bioreactors for the modification of cell culture techniques and mechanical conditioning of cartilage tissue for fully operable implants.

Today liver transplantation is the only curative option for the treatment of end-stage liver diseases. A major limitation of liver transplantation is the donor organ shortage. Therefore, tissue engineering based cell transplantation is currently under investigation with the aim to replace liver tissue and function. The principle of tissue engineering is the notion of an interaction between a cell and a three-dimensional matrix. The matrix serves as a scaffold and guides a three-dimensional cell assembly. In addition, the matrix provides for a regulation of cell proliferation and function by cell-matrix interactions. In cultures of hepatocytes a regulation of cell proliferation and specific function by using three-dimensional matrices and by modifying the surface with isolated molecules of the extracellular matrix has been demonstrated. Furthermore, a beneficial effect of a flow bioreactor system on cell viability and function was observed. In addition, a system for heterotopic hepatocyte transplantation on polymeric matrices was developed in an animal model. In this transplantation model a long-term proliferation and function of transplanted hepatocytes was shown. The major limitation of matrix-based transplantation systems is the high initial cell loss, most probably due to an insufficient vascularisation. Thus, the development of vascularised matrices and the creation of bile ducts remain major problems in the technologies of hepatic tissue engineering and have to be addressed to enable further advances towards clinical applications.

Um ein standardisiertes und praxistaugliches Verfahren zur „direkten Prozessprüfung“ sowohl für große kommunale als auch für kleinere landwirtschaftliche Kofermentations-anlagen zu erarbeiten, wurden zunächst in anaerob mesophil und thermophil betriebenen Laboranlagen sowie in einem Pasteurisierungsbehältnis (70 90 °C) geeignete Prüfkörper getestet sowie die Tenazität unterschiedlicher Prüforganismen untersucht. Dabei galt es einen Indikatororganismus zu finden, der mit konventionellen Techniken, schnell und kostengünstig nachzuweisen ist, eine hohe Thermoresistenz und epidemiologische Bedeutung besitzt. In thermophil betriebenen Laboranlagen (55 °C) wurde daher die Tenazität von Salmonella Senftenberg W 775, Ascaris suum, Campylobacter jejuni, Coliphagen „Wildstamm“ sowie Coliphage T1 und Enterococcus faecalis untersucht. Während Salmonella Senftenberg W 775, Ascaris suum und Campylobacter jejuni bereits innerhalb einer Stunde inaktiviert werden konnten, überlebten Enterococcus faecalis 3 Stunden und ein Coliphagen „Wild- stamm“ wurde noch nach mehr als 24 Stunden nachgewiesen. Tenazitätsversuche in den mesophil betriebenen Laboranlagen (35 °C) führte bei keinem der untersuchten Prüforganismen zu einer Inaktivierung innerhalb von 24 Stunden. Bei der Erhitzung in einem Pasteurisierungsbehältnis (70 - 90 °C) zeigte sich, dass Myco-bacterium avium ssp. paratuberculosis als auch Ascaris suum innerhalb 30 Minuten bei 70 °C zu eliminieren sind. Enterococcus faecalis, Coliphage „Wildstamm“ und Salmonellen waren bei 70 °C nach einer Stunde Einwirkzeit nicht mehr nachweisbar. Der Coliphage T1 konnte bei 70 °C erst nach 90 Minuten nicht mehr nachgewiesen werden. Diese Ergebnisse wurden durch die Untersuchungen in acht Praxisanlagen weitestgehend bestätigt, mit der Ausnahme, dass sowohl der Coliphage „Wildstamm“ als auch der Coliphage T1 unter Praxisbedingungen bei der Pasteurisierung von 70 °C eine Stunde lang zu inaktivieren ist. Die alleinige thermophile Faulung (52 – 55 °C) reicht jedoch nicht aus, um Coliphage T1 innerhalb von 24 Stunden zu inaktivieren. Coliphage T1 stellt einen Prüforganismus dar, der in seiner Thermoresistenz über Salmonella Senftenberg W 775 und Enterococcus faecalis einzu¬stufen ist. Er ist leicht handhabbar und innerhalb von einem Tag steht ein Ergebnis fest. Sein Einsatz als „Prüforganismus“ zur Prozessvalidierung ist, vor allem vor dem Hintergrund der Verordnung (EG) Nr. 1774/2002 (ANONYM, 2002) bei der Verwertung von Kategorie-3-Material zu diskutieren, wobei in diesem Zusammenhang noch weiterer Forschungsbedarf besteht. Um ein seuchenhygienisch unbedenkliches Produkt zu erzielen, wird vorgeschlagen, im Rahmen einer direkten Prozesskontrolle in Anaerobanlagen folgende Temperatur-/Zeit- kombinationen zu wählen: -Thermophile Anlagen: 55 °C/22 - 24 Stunden -Pasteurisierung: 70 °C/1 Stunde. Sollte allerdings zukünftig als Prüforganismus der Coliphage T1 relevant werden, müssen nach den vorliegenden Ergebnissen aus den Laboranlagen in der Erhitzung 70 °C/90 Minuten bzw. 80 °C/30 Minuten gefordert werden. Die thermophile Betriebsweise bei 55 °C und einer garantierten Aufenthaltszeit von 22 - 24 Stunden reicht nicht aus, um Coliphage T1 zu eliminieren. Im Hinblick auf thermophil betriebene Nassvergärungsverfahren ohne Vor- oder Nach-erhitzungseinrichtungen, die nachweislich keine Pfropfenströmung (Durchflussströmung) gewährleisten können, ist es unerlässlich, exakte Daten zur „tatsächlichen“ Aufenthaltszeit (Mindestverweilzeit) von Substratpartikeln oder der Flüssigphase zu erhalten. Durch die Bestimmung der tatsächlichen Aufenthalts¬zeit von Partikeln in einer thermophil betriebenen Anaerobanlage wird die Möglichkeit ein¬geräumt, an jeder Anlage individuell die Kontaktzeiten der Indikatororganismen bei der Durchführung der direkten Prozessprüfung auf die vorher ermittelten Aufenthaltszeiten zu begrenzen. Die strikte Vorgabe der vorgegebenen Aufenthaltszeit bei der Prozessprüfung von 22 - 24 Stunden bei 55 °C kann damit unterschritten werden. Als „biologischer Tracer“ wurde eine Bacillus globigii-Sporensuspenison angewandt, da zunächst in Laboranlagen sicher gewährleistet werden konnte, dass dieses thermo-resistente Bakterium nicht in der natürlichen Flora des Substrates von Anaerobanlagen vorkommt, sich optimal mit dem Beschickungsmaterial vermischen lässt und die Prozess-einflüsse in Anaerobanlagen nicht in der Lage sind, Bacillus globigii zu eliminieren. Der Einsatz einer Bacillus globigii-Sporensuspenison wurde an 3 ausgewählten Praxisanlagen überprüft. Ihre Verwendung als „biologischer Tracer“ zur Bestimmung der realen Aufenthaltszeit hat sich u. a. auch in einer großen kommunalen Anaerobanlage (>3.000 m3) sowie u.a. auch in einer Mischtrommel zur Klärschlammtrocknung bewährt. Zusätzlich zu der „direkten Prozessprüfung“ wurden die Substrate der unterschiedlichen Biogasanlagen vor und nach der thermischen Behandlung („Input- und Outputkontrolle“) auf ihren Gehalt an Salmonellen, Enterokokken und Gesamtcoliforme sowie Fäkalcoliforme untersucht. Das Ziel der Untersuchungen lag darin, die Effektivität der in den untersuchten Biogasanlagen ablaufenden Prozesse zu überprüfen. Daraus wurde ersichtlich, dass eine Inaktivierung von Mikroorganismen im thermophilen Bereich (55°C) eher gewährleistet war als im mesophilen Bereich (35°C). Jedoch ist eine vollständige Abtötung der Mikroorganismen ohne zusätzliche Hygienisierung nicht zu erreichen., In order to establish a standardised and practice relevant method for ‘direct process control’, which is suitable for large communal as well as smaller agricultural co-fermentation plants, we first analysed the suitability of germ carriers and the tenacity of various test organisms. These analyses were conducted in anaerobic mesophilic and thermophilic lab-scale fermenters and in a pasteurising container (70-90°C). The aim was to identify an indicator organism that can be detected quickly and inexpensively by conventional techniques, and which is also highly thermoresistant and has epidemiological relevance. In thermophilic lab-scale fermenters (55 °C), the tenacity of Salmonella Senftenberg W775, Ascaris suum, Campylobacter jejuni, ‘wild type’ coliphage, as well as coliphage T1, and Enterococcus faecalis was investigated. Whereas Salmonella Senftenberg W775, Ascaris suum, and Campylobacter jejuni could be inactivated within 3 hours, Enterococcus faecalis survived for more than 3 hours, and a wild type coliphage could be detected even after more than 24 hours. Tenacity experiments in mesophilic lab-scale fermenters (35 °C) showed no inactivation of any of the test organisms within 24 hours. Heating to temperatures between 70-90°C showed that both Mycobacterium avium ssp. paratuberculosis and Ascaris suum were eliminated within 30 minutes at 70°C. Enterococcus faecalis, wilde type coliphage, and Salmonellae could not be detected after 1 hour of incubation at 70°C. The coliphage T1 could be eliminated only after 90 minutes at 70°C. For the most part, these results were confirmed by investigations in operating fermentation plants, with the exception that, under practice conditions, wild type coliphage as well as coliphage T1 need to be pasteurised for 1 hour at 70°C to be inactivated. The thermophilic fermentation alone (52 – 55 °C) is not enough to inactivate coliphage T1 within 24 hours. Coliphage T1 presents a test organism that, with regard to its thermoresistance, should be placed above Salmonella Senftenberg W775 and Enterococcus faecalis. Its handling is unproblematic and results can be obtained within a day. Its use as a ‘test organism’ should be discussed, especially in relation to the regulation (EC) no. 1774/2002 (ANONYM, 2002), for usage of category III material, whereby further research is needed in this context. In order to obtain a product, which is safe with regard to health risks, it is suggested to choose the following temperature/ time combinations for direct process control in anaerobic fermenters: -Thermophilic fermenters: 55 °C/ 22 - 24 hours -Pasteurising: 70 C/ 1 hour. However, if the coliphage T1 will become relevant as a test organism in the future, the present results show that heating to 70°C/ 2 hours or 80°C/ 1 hour are required. The thermophilic processes at 55°C and an assured retention time of 22-24 hours are not sufficient to eliminate coliphage T1. With regard to thermophilic wet fermentation processes without pre- or post heating steps, which do not warrant plug flow, it is absolutely necessary to obtain data for the exact retention times (minimum retention time) of substrate particles or the liquid phase. Establishing the exact retention time of particles in a thermophilic fermentation plant offers the possibility to limit the contact times of indicator organisms to predetermined retention times of a particular fermenter during the conduct of direct process monitoring. The strict demand of the required incubation times during process monitoring of 22-24 hours could thus be shortened. A Bacillus globigii spore suspension was used as a biological tracer because it could previously be shown in lab-scale fermenters that this thermoresistant bacterium, which is not present in the natural flora of substrates used in anaerobic fermenters, can be optimally mixed with infeed materials, and the influences of processes in anaerobic fermenters are unable to eliminate Bacillus globigii. The use of a Bacillus globigii spore suspension was investigated in 3 selected treatment plants. Its value as a biological tracer to determine absolute retention times was, amongst other things, also seen in a large communal anaerobic fermentation plant (>3.000 m3), as well as in a mixing drum for drying sewage sludge. In addition to the ‘direct process control’, the substrate from the different biogas plants, was examined for its Salmonella, enterococci and total and faecal coliforms content before and after the thermal treatment. The purpose of these assays was to ensure the efficiency of the process used in the biogas plants. According to the results of this study, thermophilic anaerobic digestion ensures better inactivation of microorganisms than anarerobic digestion at mesophilic temperatures. However, the complete inactivation of microorganisms was not possible without additional pasteurisation. It is advisable to still call for the so-called ‘direct process control’ even under an amended bio-waste regulation (BioAbfV). For it provides a definite indication that the processes in a particular plant, with its given technical set-up by using defined substrates, are principally able to yield a hygienically risk-free end product. This study was carried out in 2002. According to Regulation (EC) No. 2008/2006 (Anonymus, 2006a) from February 2006, the validation of biotechnological processes in composting and biogas plants must to be carried out using two test organisms: Salmonella Senftenberg H2S negative and Enterococcus faecalis.

Tissue engineering is a young, multidisciplinary scientific field which aims at generating bioartificial tissues in vitro to restore diseased human organs. This fledgling sector of biosciences emerged few years ago but draws scientific and public attention increasingly, as the recent accomplishments are impressive and promise alternative therapeutic concepts to replace or enhance failing human organs. Tissue engineering using either polymers or decellularized native allogeneic or xenogeneic matrices may provide the techniques to develop the ideal graft. The matrix scaffold can be seeded with cells that organise and develop into tissue prior to or following implantation. This review surveys upon recent developments in the field of in vitro tissue engineering (skin, heart, heart valves, blood vessels, liver, kidney, urogenital, and nerves), without claiming completeness, thus providing an insight into what has been attempted and what may be possible in the near future.

The engineering ex vivo of cartilage tissue of predefined size and shape starting from autologous cells has the potential to provide orthopaedic surgeons with functional grafts for the repair of joint injuries. Despite the progress made in the generation and validation of engineered cartilage starting from animal cells, serveral challenges remain to be faced to extend these results to human chondrocytes. This review highlights the need for a highly interdisciplinary approach to effectively introduce engineered cartilage grafts in the routine clinical practice. Issues to be addressed include those related to the biology of chondrocytes, the properties of porous 3D scaffolds, the application of physical stimuli, and the development of economically viable manufacturing systems.

Postnatal stem cells play a decisive role in cell-based therapies due to their high proliferation activity and functional plasticity. On the one hand, basic research in cell biological processes of adult stem cells is crucial in order to establish them as therapeutic tools. On the other hand, development and enhancements of appropriate techniques are required: we need to establish defined technologies for extraction and differentiation of stem cells and to develop adequate cell carrier devices, scaffolds, and bioreactors for in vitro purposes. Furthermore, it is an interdisciplinary challenge to consider logistical aspects concerning isolation, transport, and storage of stem cells in order to use them in a wide range of activities in regenerative medicine. In this review we present the current methods of work and research on adult stem cells. We explain their therapeutic use and define requirements for future technological developments for work with postnatal stem cells.

Reconstruction of tendon tissue is problematic in many cases. Since direct tendon suture is often impossible, major reconstruction with the use of free tendon transplants or tendon transposition is necessary. Important motor units often have to be sacrificed for reconstructive purposes. In this study we investigated whether long tendon-like substitutes can be fabricated in vitro from human mesenchymal stem cells (MSCs) and a collagen type I gel when cultured under cyclic stretching conditions.MSCs were obtained from bone marrow aspirates of the iliac crest. Cells were suspended in a collagen type I gel and polymerized in a glass-cylinder with defined size. The fabricated tendon substitutes underwent static stretching for 14 days followed by cyclic stretching for 21 days in a special manufactured bioreactor. Non-stretched substitutes served as a control.Macroscopically the stretched tendon substitutes showed an increased opacity and a smoother surface structure compared to the non-stretched control. The stretched substitutes displayed more spindle-shaped, longitudinal orientated cells, a tendon-like organization of the collagen matrix, and a parallel organization of the collagen fibers when stained with Hematoxylin/Eosin and Elastica.Long tendon substitutes could be fabricated from MSCs and a collagen type I gel by cyclic stretching and showed tendon-like parallel collagen fibers and spindle-shaped cells. The use of MSCs in combination with adequate scaffold materials has great therapeutic potential for the development of autologous transplantable tendon substitutes.

For the cultivation of animal cells perfused cell culture systems are advantageous. The measurement of the process parameters for the check of the culture is difficult through the small volumes and dimensions. A developed measuring system allows the measuring of the parameters temperature, pH-value and dissolved oxygen.

An important consideration for the utilisation of in vitro culture models for studies on drug metabolism as an alternative to animal testing is the maintenance of a defined degree of cell differentiation. Thus, in vitro conditions reflecting as near as possible the in vivo situation of the cells within the whole organ are required. A bioreactor was developed for the cultivation of liver cells which allows the reorganisation of hepatocytes and non-parenchymal cells of the liver in coculture to form three-dimensional, tissue-like structures including extracellular matrix components produced by the cells. In this study, the vitality and metabolic activity of isolated rat hepatocytes was investigated over a two week culture period in bioreactors. The results show that after a reorganisation phase, the cells preserve specific functions, such as protein and urea synthesis capacity and specific cytochrome P450 activities during the culture period, with maximal values during the first week. Possible applications of the model in pharmaceutical industry are studies on metabolite patterns, enzyme induction, drug-drug-interactions, first pass effects and long-term toxicity of drugs.