[Does heparin coating improve the biocompatibility poly(D,L)lactide?].
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Animals↗
Biomedical subjects
E Wintermantel
Publications and source records attributed to E Wintermantel.
[Failure conditions of glass filament yarns: a contribution to the valuation of carcinogenic potentials of fiber fragments].
Failure of glass filament yarns results in the formation of many fragments. Through inhalation, these particles can intrude into the human body. If the fragments are sufficiently bioresistant and have a fiber dust geometry, according to the MAK-values (6), i.e. if they are longer than 5 microns and thinner than 3 microns and show an aspect ratio greater than 3, they have a carcinogenic potential. Since the glass filaments show a diameter greater than 3 microns, no fiber dust particles will be formed if transversal fiber failure occurs without crack-branching. In the present study the geometric distribution of fragments after failure of glass filament yarns under combined stress was investigated in order to estimate the carcinogenic potential of the fragments. The knot tension test was shown to be a suitable method for this investigation. A defined fraction of the total amount of fragments were analysed with scanning electron microscopy (SEM) by measuring their length and diameter. To investigate whether the analysed particles are fragments of the glass filament yarns, chemical analysis was performed with energy dispersive X-ray analysis (EDX). Morphologically, two different fragment types were observed: a) Fragments with their entire filament cross-section which were formed by transversal fiber fraction. b) Smaller fragments which were formed through crack-branching. These smaller fragments were observed to adhere on the bigger fragments due to high surface forces. During each knot tension test, 5-60 fragments per filament were formed. However, the fraction of fiber dust particles was very low and showed a maximum of 1.5%. Only in one of the four tested yarn types (high temperature yarn HT 75) the formation of fiber dust particles was observed. The other yarns showed fragments with dimensions close to fiber dust geometry. Therefore, it cannot be excluded that some fragments with fiber dust geometry may have been formed during mechanical testing. Fragment distribution of the studied E-glass yarns was shown to be dependent on the modification method. To date, it cannot be excluded that there are types of glass filament yarns forming a major quantity of fiber dust particles during failure. The fragments of type b such as fiber dust particles were observed to adhere on bigger fragments which are themselves too big to reach the alveoli. In the present study the stability of these agglomerates under various environmental conditions was not investigated. Moreover, fragment agglomerates should not be considered on their own but in connection with the application. The presented tests were carried out with simple yarns and, therefore, represent isolated observations.
Air Pollutants↗
Autosterilization of biodegradable implants by injection molding process.
Sterilization of degradable implants by standard procedures may damage the parts due to the labile chemical nature of the polymers. This study examined whether the injection molding process used for the production of polymeric parts may itself sterilize the implant due to high temperature, pressure, and shear forces applied. Poly-D,L-lactic acid (PDLLA) and poly-L-lactic acid (PLLA) granules were contaminated with thermoresistant spores of Bacillus stearothermophilus (>10(5) spores/g). Sterile and contaminated granules of both polymers were injection molded and tested for sterility. All 27 samples produced with sterile PDLLA and processed at 120 degrees C and all 18 samples produced with sterile PLLA at 200 degrees C remained sterile after injection molding and handling. However, in five out of 28 PDLLA samples and in one out of 26 PLLA samples produced with contaminated material, spores had survived the process. In conclusion, the injection molding process could not reliably sterilize parts produced with polylactic acid granules that were heavily contaminated with thermoresistant organisms. However, the number of viable spores was significantly reduced by more than 99.99%. Thus, the injection molding process might allow the autosterilization of parts produced with raw material that is not heavily contaminated.
Biocompatible Materials↗
Tissue engineering scaffolds using superstructures.
Here, scaffolds as cell and tissue carriers are approached from an engineering point of view, emphasizing material superstructuring in the design of supports. Superstructure engineering provides optimal spatial and nutritional conditions for cell maintenance by the arrangement of structural elements (e.g. pores or fibres) so as to vary the order of cell to cell contact. This approach is illustrated in the design of several scaffolds: knitted fabrics as three-dimensional superstructures for optimized osteosynthesis implants, a new injectable open porous implant system, an angiopolar non-degradable ceramic cell carrier, and an injectable or microsurgically implantable entangled carrier system. The implications for tissue engineering are discussed.
Anisotropy↗
Angiopolarity of cell carriers: directional angiogenesis in resorbable liver cell transplantation devices.
The purpose of this study was to obtain directional angiogenesis of small blood vessels and capillaries to an implant made from a resorbable polymer for hepatocyte transplantation. It was intended to mimic the native acinar structure of the liver in order to facilitate replication of the cells and organ growth. The implant device structure was designed for injection to minimize surgical trauma. Hollow microspheres with an open porous wall structure and one large central opening were made from poly(d,l-lactic-co-glycolic acid) (85:15 lactic:glycolic). This polymeric scaffold was seeded with hepatocytes and implanted into the abdominal wall muscle of syngeneic Fisher rats. Specimens explanted up to 56 days p.o. showed hepatocyte survival and the development of a directional blood supply. This phenomenon is coined "angiopolarity". The study should help in addressing the issue as to whether avascular cell implants with post-transplantation organ growth should be attempted. Processing options in applying heat to the polymer solution allow manufacturing of larger microspheres with different diameters of central openings. This would allow the use of the scaffold for other cell transplantations than hepatocytes.
Animals↗
Future directions in biomaterials.
Biomaterials have made a great impact on medicine. However, numerous challenges remain. This paper discusses three representative areas involving important medical problems. First, drug delivery systems; major considerations include drug-polymer interactions, drug transformation, diffusion properties of drugs and, if degradation occurs, of polymer degradation products through polymer matrices developing a more complete understanding of matrix degradation in the case of erodible polymers and developing new engineered polymers designed for specific purposes such as vaccination or pulsatile release. Second, cell-polymer interactions, including the fate of inert polymers, the use of polymers as templates for tissue regeneration and the study of polymers which aid cell transplantation. Third, orthopaedic biomaterials, including basic research in the behaviour of chondrocytes, osteocytes and connective tissue-free interfaces and applied research involving computer-aided design of biomaterials and the creation of orthopaedic biomaterials.
Biocompatible Materials↗
Intradiscal collagenase for treatment of lumbar disc herniations. A comparison of clinical results and computed tomography follow-up.
In a series of 34 patients with herniated lumbar discs, treated by intradiscal injection of highly purified collagenase, the post-treatment course has been followed-up clinically and by repeated computed tomographies (CT). Good or excellent results have been achieved in 17 patients. An only slight improvement of pain was noted in 2 patients. Fifteen patients had to be operated on due to not improved or worsened clinical symptoms. The most striking result of our CT follow-up was a tendency of the disc herniation to increase initially after collagenase injection. About two thirds of the patients had such an increase at the one week after injection control. After 6 weeks this rate had decreased to only about one quarter, but in the meantime 13 patients had to be operated. Only after 6 months most hernias of the up till then not operated patients were smaller and none were larger than before treatment. There was also a transient density decrease of the treated disc, most pronounced one week after collagenase injection. At controls 6 months later density had reached again pre-treatment levels. It is likely that the volume increase tendency of the disc material after collagenase injection is responsible for a worsening of the clinical symptoms, which not seldomly occurs during the initial post-treatment period, and in some patients makes an operation necessary.
Back Pain↗
The thermic vascular anastomosis (TVA). IV. Analysis by scanning electron microscopy.
In the present study 48 thermic vascular anastomoses performed in Sprague Dawley Wistar rats were subjected to analysis by scanning electron microscopy. Depending on the period of postoperative survival (up to 18 months) normal smooth endothelium, dissected cuffs and aneurysms were seen. Endothelial damage through heat application following bipolar coagulation was only slight. In one 18 months old anastomosis an aneurysm with a delicate network of endothelialized filaments was seen leaving a free passage for the blood flow centrally. A comparison of the literature describing the healing processes of intima following various traumas is made.
Animals↗
The thermic vascular anastomosis (TVA). II. Microvascular auscultation applied to thermic vascular anastomoses.
The study shows that microvascular auscultation with a diplomicrophone is a useful method in recording and analyzing the blood flow in nonsuture thermic vascular anastomoses. In 320 anastomoses on the rat carotid artery microvascular auscultation was found to be applicable immediately after performing an anastomosis and up to 30 days postoperatively. Records of sound tracks made at various periods of postoperative survival of the animals are presented and analyzed. A comparison with auscultation results of sutured microvascular anastomoses and of ligated arteries is made.
Animals↗
The thermic vascular anastomosis (TVA). III. Analysis by histology.
In 48 Sprague Dawley Wistar rats Thermic Vascular Anastomoses were analyzed by histology 1, 10, and 30 days, 6 and 18 months postoperatively. Fibrin glue turned out to be a valuable additional fixative, effective in preventing ruptures of the anastomoses. It did not modify the formation of a pseudo-intimal layer of connective tissue between the original vascular ends. The healing process of TVAs is worked out; references to earlier studies describing microvascular procedures with fibrin glue application are made.
Animals↗
The thermic vascular anastomosis (TVA). A new nonsuture method. I. History, instruments, and microsurgical technique.
In order to unite blood vessels in a split second during a total clamping time of less than three minutes a new microsurgical technique has been developed. Heat from a frequency electric current applied to calibrated metal loops unites the cuffs of the vessel ends instead of sutures. As a model for vascular anastomoses the new technique was used in an experiment with 320 rats. Two energy output adjustments of the power source combined with application of fibrin glue on the anastomosis are compared. The new instruments developed for this technique and the operation method are presented with reference to earlier vascular surgical procedures, and the results of patency controls of the anastomoses one day, 10 days, and 30 days postoperatively are listed. Preliminary findings of a long term study are added. This study shows that fully patent anastomoses can be obtained with this technique in much less time than with suturing.
Angiography↗
[Carbohydrate metabolism in brain and liver tissue following experimental vascular suturing of the right carotid artery (author's transl)].
Experiments with Wistar rats have been performed in order to analyse brain and liver metabolism after suturing of the rats right carotid artery. It should be figured out how much an interruption of the bilateral blood supply of the brain during end-to-end-anastomosis of a carotid artery would interfere with normal brain and liver metabolism. General anaesthesia of all animals was obtained with pentobarbital. The vascular anastomoses have been performed by using the microsurgical technique. Groups of animals were formed in order to analyse metabolism after various periods of postoperative survival. Brain and liver tissue was removed and the metabolism stopped immediately by freezing the tissue in liquid nitrogen. Biochemical analysis showed several highly significant changes of levels of values indicating hypoxia. Additional experiments have been carried out in order to find out whether hypoxia could be detected in other organs of the body such as the liver after performing the same microsurgical procedure on a carotid artery and how pronounced these changes would be compared to those of brain metabolism. Results of experiments performed up to now indicate that hypoxia also develops in liver tissue.
Animals↗
Microvascular auscultation. A new technique, using a diplo-microphone, for analysis of blood flow at suture lines in small arteries.
A new atraumatic method for patency and blood flow control of microvascular anastomoses has been developed. Sounds proximal and distal to a suture line are separately detected by means of two specially modified miniature microphones built together as an auscultation unit and named a diplo-microphone. Transmission of the two amplified signals to a loudspeaker as well as to an oscilloscope screen allows analysis of patency at the anastomosis. Photos taken of the sound waves are individual records characterizing blood flow on both sides of the suture line. The new method has been tested in carotid arteries of Wistar rats. Sounds at stenoses and end-to-end anastomoses have been detected, and several characteristics of postoperative sound waves have been worked out. The new method has turned out to be more sensitive in detecting medium-sized stenoses than radical pressure tests performed with forceps. Construction and application of a diplo-microphone are described. Auscultation results of normal and stenosed arteries are discussed.
Amplifiers, Electronic↗
A new gearing approximator for microsurgical vascular anastomoses.
A new gearing approximator for microsurgical vascular anastomoses is described. A highly precise and smoothly working robust gearing in connection with an asymmetrically notched key allows quick application of the approximator and an exactly adjustable interclip distance. By means of a combined handling and gearing screw and exchangeable 30 degrees-angled clips the instrument can easily be applied in narrow operating fields, and it can be handled under vision through the operating microscope without change in magnification adjustment. A quickly increasing platelt aggregation at the suture line and an early "slow flow" can be achieved by gradual opening of the clips. The ease of approximator application may contribute to shortening operation times.
Neurosurgery↗
Angiopolarity: a new design parameter for cell transplantation devices and its application to degradable systems.
The purpose of this study was to obtain directional angiogenesis of small blood vessels and capillaries to an implant made from a resorbable polymer for hepatocyte transplantation. It was intended to mimic the native acinar structure of the liver in form to facilitate replication of the cells and organ growth. The implant device structure was designed for injection to minimize surgical trauma. Hollow microspheres with an open porous wall structure and one large central opening were made from poly(d,1-lactic-co-glycolic acid) (85:15 lactic:glycolic). This polymeric scaffold was seeded with hepatocytes and implanted into the abdominal wall muscle of syngeneic Fisher rats. Specimens explanted up to 56 days postoperatively showed hepatocyte survival and the development of a directional blood supply, a phenomenon known as "angiopolarity." This study should help in addressing the issue as to whether vascular cell implants with posttransplantation organ growth should be attempted.
Animals↗