Design and performance of a bioreactor system for mechanically promoted three-dimensional tissue engineering

There is currently considerable interest in increasing the response of mesenchymal cells to physical forces, and numerous loading devices have been used to increase the formation of skeletal tissue in vivo and in vitro. We have developed a bioreactor system to apply cyclic strains on three-dimensional specimens over a range of 0-20,000 mustrain. The piezoelectric-driven mechanism allows the precise adjustment and control over load-related deformations of tissue, as shown by finite-element calculations of deformation of a collagen gel under load. We present the design of the bioreactor and its performance in specimens of tissue containing activated osteoblasts and chondrocytes. Biaxial tissue straining at 2,000 mustrain led to a substantial increase in the number of both types of cell compared with unstimulated controls. The synthesis of cell-specific extracellular matrix proteins increased when physiological loads (2,000 mustrain) were applied in the bioreactor, whereas higher deformations (20,000 mustrain) resulted in a reduction in proliferation and differentiation of cells. The mechanisms whereby mechanical stimulation leads to a defined cell reaction are not known, but the application of physiological micromovements in extracorporeal tissue chambers is a promising approach to the formation of hard tissue.

[Fritz hauschild (1908-1974) and drug research in the 'German Democratic Republic' (GDR)]

The chemist and pharmacologist Fritz Hauschild developed the sympathomimetic agent Pervitin (metamphetamin) in the 1930s. Not only because of the abuse of the stimulant during the Second World War ("pilot's chocolate") it is one of the most controversial substances in drug history. Nearly forgotten are Hauschild's contributions to build up the drug system in the GDR. Although he was a convinced communist, the skilful pharmacologist gave very early warning of the imminent lack of innovation in the GDR pharmaceutical industry. A letter which he addressed to the Minister of Health, Max Sefrin (born 1913), did not lack explicitness.

Basic reactions of osteoblasts on structured material surfaces

In order to assess how bone substitute materials determine bone formation in vivo it is useful to understand the mechanisms of the material surface/tissue interaction on a cellular level. Artificial materials are used in two applications, as biomaterials alone or as a scaffold for osteoblasts in a tissue engineering approach. Recently, many efforts have been undertaken to improve bone regeneration by the use of structured material surfaces. In vitro studies of bone cell responses to artificial materials are the basic tool to determine these interactions. Surface properties of materials surfaces as well as biophysical constraints at the biomaterial surface are of major importance since these features will direct the cell responses. Studies on osteoblastlike cell reactivity towards materials will have to focus on the different steps of protein and cell reactions towards defined surface properties. The introduction of new techniques allows nowadays the fabrication of materials with ordered surface structures. This paper gives a review of present knowledge on the various stages of osteoblast reactions on material surfaces, focused on basic cell events under in vitro conditions. Special emphasis is given to cellular reactions towards ordered nano-sized topographies.

Branched chain amino acids as a parameter for catabolism in treated phenylketonuria

This study was performed to study an association between nutritional status on one hand and BCAA- and Phe-concentrations on the other hand in PKU patients free of infection. AA profiles from 70 PKU patients were measured. 9 patients (subgroup I) with elevated Phe- and BCAA-concentrations as well as 23 patients (subgroup II) with only elevated Phe-levels were included. Dietary records were obtained from both groups; low caloric intake in subgroup I was increased with Duocal or p-am ANAMIX without modifying total protein- and Phe-intake. AA profiles were controlled after 2 weeks. Additionally, we investigated AA profiles from 26 liver transplanted patients with increased carbohydrate and caloric intake as an example for anabolism. In subgroup I Phe- and Isoleu-concentrations decreased sign. After dietary intervention. Leu, Val and Tyr levels decreased not sign. Initial Phe-levels correlated negatively with protein and caloric intake. BCAA concentrations of liver transplanted patients receiving high amounts of carbohydrates were in the lower range of normal. Increased caloric intake lowered most of the elevated Phe- and BCAA- concentrations.

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

Over the last decade extracorporal bone tissue engineering has moved from laboratory to clinical application. The restoration of maxillofacial bones from cell harvesting through product manufacture and end-use has benefited from innovations in the fields of biomechanical engineering, product marketing and transplant research. Cell/scaffold bone substitutes face a variety of unique clinical challenges which must be addressed. This overview summarises the recent state of the art and future anticipations in the transplantation of extracorporally fabricated bone tissues.

Biological and biophysical principles in extracorporal bone tissue engineering

The aim of this review is to characterise the biological and biophysical background of in vitro bone tissue engineering. The paper focuses on basic principles in extracorporal engineering of bone-like tissues, considering parameters such as scaffold design, tissue construction, bioreactors, and cell stimulation in vivo and in vitro. Scaffolds have a key function concerning cellular invasion and bone formation. The intra-architectural scaffold geometry, as well as the scaffold material, play an important role in the process of bone regeneration. Various types of bioreactors have been tested for their utility in bone substitute fabrication that is clinically effective and reproducible. Sophisticated bioreactor systems are those that mimic the three-dimensional morphology and the mechanical situation of bones. Mechanical stimulation as well as other biophysical stimuli appear to be critical factors for proliferation and differentiation of bone cells and for bone mineral and structure formation. Furthermore an enhancement of bone regeneration by application of chemical stimulation factors is discussed.

Tierexperimentelle Evaluation des periimplant�ren Knochens bei zylindrischen gegen�ber konischen Implantattypen

BACKGROUND

The treatment of patients with early or immediately loaded dental implants has renewed interest in the behavior of osseointegration at the implant surface. Whereas it is generally accepted that peri-implant tissue formation and mineralization are dependent on the local mechanical environment in the interface zone, controversies exist concerning the impact of implant design on peri-implant bone formation. The aim of the present study was the in vivo evaluation of peri-implant bone formation by two different implant systems: cylindrical (ITI) versus conical (ILI).

MATERIAL AND METHOD

A total of 60 implants (30 ITI and 30 ILI) were placed in the cranial and caudal part of the tibia of eight Göttinger minipigs. Half of the minipigs were sacrificed at 7 days and 28 days of osseointegration. Implant-containing bone specimens were prepared for histological and ultrastructural investigations.

RESULTS

Histological and scanning electron-microscopic investigations showed a direct contact of bone-like minerals over the whole implant surface from day 7 of implant/bone interaction. Whereas the ILI implant showed direct contact up to the top of the crestal bone, ITI implants demonstrated a crestally located narrow gap without ossification over the whole experimental period.

CONCLUSION

Our investigations support the hypothesis of an implant design-inherent emergence and maintenance of crestal bone.

Biological and biophysical principles in extracorporal bone tissue engineering

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.

Ultrastructural characterization of the implant/bone interface of immediately loaded dental implants

Primary stability and an optimized load transfer are assumed to account for an undisturbed osseointegration process of implants. Immediate loaded newly designed titanium dental implants inserted in the mandible of minipigs were used for the characterization of the interfacial area between the implant surface and the surrounding bone tissue during the early healing phase. Histological and electron microscopical studies were performed from implant containing bone specimens. Two different load regimens were applied to investigate the load related tissue reaction. Histological and electron microscopical analysis revealed a direct bone apposition on the implant surfaces, as well as the attachment of cells and matrix proteins in the early loading phase. A striking finding of the ultrastructural immunocytochemical investigations was the synthesis and deposition of bone related proteins (osteonectin, fibronectin, fibronectin receptor) by osteoblasts from day one of bone/biomaterial interaction. Calcium-phosphate needle-like crystallites were newly synthesized in a time-related manner directly at the titanium surface. No difference in the ultrastructural appearance of the interface was found between the two loading groups. Our experimental data suggest that loading of specially designed implants can be performed immediately after insertion without disturbing the biological osseointegration process.

Dissemination of the entomopathogenic fungus verticillium lecanii (Zimmermann) Viégas (Hyphomycetales: Moniliaceae) in a population of Frankliniella occidentalis (Pergande, 1895) (Thysanoptera: Thripidae)

Tests were carried out to investigate the dissemination of the entomopathogenic fungus Verticillium lecanii (Zimmermann) Viégas in a population of Frankliniella occidentalis. The tested factors, which influence the efficacy of the fungus against the pest insect, have been the population density of the thrips at the application moment as well as the temperature. The population density influenced the dissemination of the fungal spores in the population. The higher the density has been, the higher the insetting control effect has been as well. The temperature influenced the speed of the fungal effect, too. The higher the temperature has been, the earlier the control effect started. However, an increase of the natural mortality was found as well.

Aspects of collagen mineralization in hard tissue formation

Collagen is the dominant fibrous protein not only in connective tissues but also in hard tissues, bone, dentin, cementum, and even the mineralizing cartilage of the epiphyseal growth plate. It comprises about 80-90% (by weight) of the organic substance in demineralized dentin and bone. When collagen fibers are arranged in parallel to form thicker bundles, as in lamellar bone and cementum, interior regions may be less mineralized; in dentin, however, the collagen fibers form a network and collagen fibers are densely filled with a mineral substance. In the biomineralization of collagen fibers in hard tissues, matrix vesicles play a fundamental role in the induction of crystal formation. The mineralization of matrix vesicles precedes the biomineralization of the collagen fibrils and the intervening ground substance. In addition, immobilized noncollagenous fibrous macromolecules, bound in a characteristic way to the fibrous collagen surface, initiate, more intensely than collagen, mineral nucleation in the hard tissue matrix.

Are collimated low-dose digital radiographs valid for performing Delaire's architectural analysis?

Computed radiography (CR) provides the dynamic exposure range to reveal objects in film areas exposed by very low X-ray exposure. Conventional cephalometric radiographs are normally beam limited to the facial skeleton. The cranial vault and cervical vertebra are collimated and only exposed by extra-focal radiation and scatter. We hypothesize that, on conventional cephalometric radiographs obtained with CR, image data of collimated film areas can be enhanced for reliable performance of Delaire's cephalometric analysis of the entire skull. Therefore the aim of the present study was to compare the reproducibility of landmark placement on normal and underexposed film areas of CR images. Intra- and inter-observer reproducibility of landmark identification was evaluated on 200 randomly selected radiographs by calculating the error radius of repeated landmark placements. A paired-samples t-test revealed differences (P< 0.001) between intra- and inter-observer reproducibility. Intra-observer accuracy was influenced (P< 0.001) by variability of suture obliteration (bregma). Identification of landmarks in areas of extra-focal radiation showed no difference (P> 0.05) from that of landmarks inside the normally exposed area. CR offers the opportunity to perform of a full cranial analysis on a cephalometric radiograph collimated to the facial region.

Primäre Implantatstabilität bei unterschiedlichen Knochenaufbereitungstechniken

The treatment concept of osseointegration is based on a stable embodiment of implants in bone and the maintenance of stability during functional load. A goal of the surgical preparation technique is therefore to obtain a stable and firm implant anchorage. The aim of this study was to evaluate implant stability after different surgical treatment of the bony implantation bed. Thirty cylindrical solid-screw-shaped implants with standard SLA ITI configuration were implanted into the explanted mandibles of five minipigs. The implant sites were prepared either by a conventional burr technique (group A), by burr technique with additional thread cutting (group B), or by the osteotome technique (group C). Primary implant stability was evaluated by resonance frequency analysis and removal torque test. The average value of the resonance frequency analysis (RFA) was 6000+/-469 cycles/s in group A, 5700+/-557 cycles/s in group B, and 5540+/-527 cycles/s in group C. Removal torque values of group A (507+/-57 Nmm) were significantly higher than those of group B (466+/-45 Nmm) and group C (240+/-31 Nmm) (between group A and C p<0.05, group A to B p=0.39, and B to C p<0.05). It can be concluded from this study that the conventional burr technique achieves a statistically significantly better primary bone anchorage than the osteotome technique.

Experimentelle und klinische Studie zur Stabilität einer Osteosyntheseplatte für den atrophen Unterkiefer

BACKGROUND

The high rate of complications led us to develop a new osteosynthesis plate for the treatment of the fractured atrophied mandible. The development of the new so-called pencil-bone plate is based on the 2.0 mini-plate system manufactured by the Medartis Company.

MATERIAL AND METHODS

Finite elements (FE) analysis of the new plate as well as flexibility experiments were undertaken, and 14 patients with 16 fractures of the atrophied mandible were treated with the pencil-bone plate between October 2000 and November 2001.

RESULTS

The results clearly show that the pencil-bone plate reacted in both the FE model and the static flexibility experiment in a more stable way than a standard 2.0 plate. In 13 patients, healing proceeded without serious complications; all of the patients showed subjective, nearly unchanged chewing, speaking, and swallowing abilities and no complications occurred when wearing dentures. One patient underwent surgical intervention after a new trauma.

CONCLUSION

The clinical outcome of the treated fractures confirmed the experimental results, which proved the high stability of the plate in the area of the fracture site. Due to the mini-plate format the intraoral application of the plate is possible without problems. The intraoral access allows rapid operation followed by a minimum of morbidity. A great advantage of the small dimension system is the unrestricted wearing of dentures after the application.

Intraoral sebaceous carcinoma

Sebaceous carcinoma in the oral cavity is extremely rare, and we have found only four previously reported cases. We describe a fifth case. A wide surgical excision seems to be the correct treatment and estimation of serum carcinoembryonic antigen (CEA) may be a useful tumour marker in the follow-up of intraoral sebaceous carcinomas.

Evaluation of accuracy of insertion of dental implants and prosthetic treatment by computer-aided navigation in minipigs

The survival of loaded implants is critically dependent on their biomechanical stability. We have used a computer-guided navigation technique to evaluate the accuracy of computer-assisted insertion for immediately-loaded implants in minipigs. On the basis of computed tomographical data, the Robodent system was used for preoperative planning and guidance of inserting the implant. An optical tracking system allowed positioning of the implant and immediate prosthetic rehabilitation by inserting it in a plaster model and during the operation. Postoperative computed tomograms (CT) showed that the implants were placed precisely in the preoperatively planned position. The accuracy achieved corresponded well with the spatial resolution of the CT used. Immediate placement of the prefabricated crowns resulted in favourable occlusal positioning. Histological cross-sections showed that the implants were biomechanically stable. The accuracy of insertion of oral implants illustrated here suggests that insertion and prosthetic modelling of implants may benefit from computer-assisted navigation.

Incidence of tumor lysis syndrome in children with advanced stage Burkitt's lymphoma/leukemia before and after introduction of prophylactic use of urate oxidase

To evaluate the clinical benefit of the prophylactic use of urate oxidase in children with non-Hodgkin's lymphoma (NHL), we analyzed the incidence and complications of tumor lysis syndrome (TLS) in children with B-cell acute lymphoblastic leukemia (B-ALL) or stage III/IV Burkitt's lymphoma and a lactate dehydrogenase (LDH) level > or =500 U/l before and after the introduction of a protocol amendment to use urate oxidase for the prophylaxis of TLS. Data from 1791 children with NHL enrolled in the two subsequent multicenter studies NHL-BFM 90 and 95 were evaluated. The presence of the side effects TLS, anuria, sepsis, and other complications during the first 2 weeks after admission were registered. Until March 1996, no urate oxidase was used (period 1). From November 1997 all children with B-ALL or stage III and IV B-NHL and LDH > or =500 U/l should receive urate oxidase prophylactically (period 3). In between (period 2), urate oxidase was given in a minority of hospitals therapeutically. Initial chemotherapy was identical. Altogether, 78 children (4.4%) developed a TLS. Patients with B-ALL had the highest risk to develop a TLS (26.4%) followed by B-ALL/Burkitt's lymphoma and a LDH > or =500 U/l (14.9%). In period 1, 16.1% and 9.2% of the latter children developed a TLS or anuria, respectively, compared to 12.3% and 6.2% in period 3 ( p=NS). The incidence of sepsis remained unchanged (5.0% vs 4.6%). In children with B-ALL the differences in the incidence of TLS and anuria between period 3 and period 1 were more pronounced, reaching significance for anuria (15.4% vs 3.8%, p=0.03). Our results suggest that patients with the highest risk to develop a TLS might benefit from the prophylactic use of urate oxidase.

[Experimental study on the biomechanical stability of different internal fixators for use in the mandible]

BACKGROUND

Comparative studies of different forms of osteosynthesis require that biomechanical and biological criteria be observed. The conditions in experimental studies should be as close as possible to the in vivo situation. The aim of our study was to develop a fracture model that would allow determination of the micromovements in the gap tissue following different forms of internal fixation in fractured human mandibles.

METHODS

Micromovements in the gap tissue of five human mandibles treated with different osteosynthetic systems (DCP, EDCP, Miniplates, 3-D systems) following osteotomy or fracture in the region of the corpus and median region were investigated by means of strain gauges. By fitting the human mandibles in plaster according to a method of our own it was possible to create fractures at predictable and comparable localizations.

RESULTS

Our investigations show that the micromovements in the gap tissue of osteotomied and fractured mandibles are different and not dependent on the form of osteosynthesis applied. Physiological micromovements in the gap tissue were found under strain for all osteosynthetic systems used in fractured and congruently reset mandibles.

DISCUSSION

Our fracture and osteosynthesis model allows the quantitative determination of micromovements in the gap tissue and shows the importance of ideal realignment, which has a decisive influence on micromovements in the gap tissue.

A new method for the fast determination of kinetic parameters in anaerobic digestion processes and application to textile wet processing wastewater

A new method for the fast and efficient determination of the anaerobic degradability and for the calculation of kinetic parameters is proposed. It is based on the idea that monitoring of the acidification step in the anaerobic degradation cascade is sufficient, as the subsequent steps (acetogenesis, methanogenesis) are well known processes dependent on the intermediate concentrations and not on the original substrate used. The investigation of the acidification is subdivided into two steps. In the first step, biomass is adapted to the new substrate in a continuously operated bioreactor. The second step, the only step monitored, is the acidification of the substrate (or wastewater) in a batch experiment. Three different methods to monitor the acidification were tested: gas chromatography (offline), on-line titration and monitoring of the base consumption (direct titration). The results of these methods were compared to "traditional" batch tests. It is shown that the simplest method (direct titration) revealed the most important information. The investigated substrates were selected pollutants of textile wet processing wastewater.

Factors affecting constancy of acetate concentration and correct determination of methanogenic activity in pH-stat experiments

The determination of methanogenic activity with a pH-stat titration bioassay is evaluated utilising a mathematical model of this system. For given kinetic parameters and experimental conditions the model calculates the development of titrant flow and acetate concentration during experiments. Simulations of experiments under various conditions are compared. They show that the original method inherently causes a strong drift of acetate concentration during the experiments and a misestimation of methanogenic activity. As a solution to these disadvantages the addition of sodium hydroxide to the titrant and a careful control of pH during flushing the reactor with gas prior to the experiment are recommended. In this way a better constancy of acetate concentration and a more accurate determination of methanogenic activity should be achievable. The accuracy of this method is limited by the stability of pH-electrode calibration parameters.

Fuzzy-control for improved nitrogen removal and energy saving in WWT-plants with pre-denitrification

In the last few years, numerous studies were carried out, dealing with the application of fuzzy-logic to improve the control of the activated sludge process. In this paper, fuzzy-logic based control strategies for wastewater treatment plants with pre-denitrification are presented that should lead to better effluent quality and, in parallel, to a reduction of energy consumption. Extensive experimental investigations on a large scale pilot plant as well as simulation studies (ASM1 with SIMBA) were carried out in order to design, evaluate and compare different fuzzy-controllers with each other and with comparable conventional control systems. The fuzzy-controllers were designed as high-level controllers that determine the DO-setpoints in the aerated zones and the ratio between aerated and non-aerated zones. Conventional PI-controllers were used to maintain the DO-concentration at the set-point levels. The ammonia and nitrate concentration in the effluent and the ammonia load in the influent were considered as input variables for the different fuzzy-controllers. Compared to the operation with fixed nitrification/denitrification zones and constant DO concentrations, the required air-flow could be reduced up to 24% by using fuzzy-logic based control strategies. In comparison with a more advanced conventional control strategy (relay controller with two thresholds and the NH4-N concentration in the effluent as single control variable) a reduction of air-flow-rate up to 14% could be achieved. At the same time, NH4-N peaks in the effluent that are normally caused by peak flow conditions could be reduced significantly. The large scale experiments show that the fuzzy-controllers can be easily implemented in modern control and supervision systems and that the control characteristics can be followed and modified during operation. It therefore can be expected that the developed fuzzy-control systems will be accepted by the operating personnel in wastewater treatment plants.