Detlef Behrend

Structural alterations of adhesion mediating components in cells cultured on poly-β-hydroxy butyric acid

Polymers may serve as a biodegradable material in tissue engineering. To assess the biocompatibility of poly-beta-hydroxy butyric acid (PHB), we studied the structural organization of cellular molecules involved in adhesion using osteoblastic and epithelial cell lines. On PHB, both cell lines revealed a rounded cell shape due to reduced spreading. The filamentous organization of the actin cytoskeleton was impaired. In double immunofluorescence analyses we demostrated that the colocalization of the fibronectin fibrils with the actin filaments was lost in cultures on PHB. Similarly, collagen II distribution was altered, whereas the organization of collagen I was not obviously affected. Further evidence for impaired structural organization was obtained for the beta1-integrin receptor and vinculin which mediate the interaction of the cytoskeleton with the extracellular matrix. In confluent epithelial cells, the tight junction protein ZO-1 showed a larger lateral extension in the cell-cell contacts when cells were grown on PHB. Because structural organization of components which mediate cell-matrix and cell-cell adhesion controls cell physiology these parameters could be a sensitive indicator for the biocompatibility of implant materials.

Optical coherence tomography as an orientation guide in cochlear implant surgery

Conclusion: With optical coherence tomography (OCT) it is basically possible to reveal parts of the cochlear morphology without opening its enveloping membranes. Thus, it may serve as a helpful guide for the surgeon to localize the scala tympani precisely before opening the fluid-filled inner ear to insert the electrode array. Objective: To improve anatomical orientation in cochlear implant surgery before definitively opening the fluid-filled inner ear. The question was whether a new imaging technique, OCT, might provide information about the site of the underlying inner ear structures (scala tympani, scala vestibuli) and could, consequently, guide the surgeon towards the scala tympani. Materials and methods: In a preliminary study, OCT was carried out on human temporal bone preparations, in which a cochleostomy (‘fenestration’) was performed leaving the endosteum and the fluid-filled inner ear intact. OCT was applied via a prototype of a specially equipped operating microscope. The mode of OCT used in this context was spectral-domain (SD)-OCT. Results: On scans, which can be read analogous to B-mode sonography, OCT provides information about structures on the inner surface of the partly exposed but still intact membranous cochlear lining – such as scala tympani or scala vestibuli.

Laser cutting: influence on morphological and physicochemical properties of polyhydroxybutyrate

Polyhydroxybutyrate (PHB) is a biocompatible and resorbable implant material. For these reasons, it has been used for the fabrication of temporary stents, bone plates, nails and screws (Peng et al. Biomaterials 1996;17:685). In some cases, the brittle mechanical properties of PHB homopolymer limit its application. A typical plasticizer, triethylcitrate (TEC), was used to overcome such limitations by making the material more pliable. In the past few years, CO2-laser cutting of PHB was used in the manufacturing of small medical devices such as stents. Embrittlement of plasticized PHB tubes has been observed, after laser machining. Consequently, the physicochemical and morphological properties of laser-processed surfaces and cut edges of plasticized polymer samples were examined to determine the extent of changes in polymer properties as a result of laser machining. These studies included determination of the depth of the laser-induced heat affected zone by polariscopy of thin polymer sections. Molecular weight changes and changes in the TEC content as a function of distance from the laser-cut edge were determined. In a preliminary test, the cellular response to the processed material was investigated by cell culture study of L929 mouse fibroblasts on laser-machined surfaces. The heat-affected zone was readily classified into four different regions with a total depth of about 60 to 100 microm (Klamp, Master Thesis, University of Rostock, 1998). These results correspond well with the chemical analysis and molecular weight measurements. Furthermore, it was found that cells grew preferentially on the laser-machined area. These findings have significant implications for the manufacture of medical implants from PHB by laser machining.

Poly(3-hydroxybutyrate) (PHB) patches for covering anterior skull base defects – an animal study with minipigs

Conclusion: We conclude that PHB patch material may fulfil the specific requirements that are necessary for a dural substitute, including defect closure, stability and biocompatibility. Our results support the assumed positive influence of PHB on bone regeneration. Objectives: Although many experimental and clinical studies have been performed to identify a suitable material to repair defects of the dura mater, no ideal dural substitute is currently available. PHB is a biodegradable and biocompatible polymer that might serve as dural substitute and osteosynthesis material in cranial bone defects. Materials and methods: Different standardized PHB patches were used in six minipigs for covering defined bone defects in the anterior skull base including a dura mater lesion as well as in the frontal sinus front wall. After a defined time of implantation of 3, 6, and 9 months PHB patches were explanted and examined for clinical findings, biodegradation, presence of microorganisms, histological findings, and electron microscopy. Results: The examinations revealed an increasing closure of bone defect corresponding with time. The anterior skull base bone defect was completely closed after 9 months. The histological findings revealed a connective tissue and callus formation around the PHB patches with fibroblasts and foreign body/giant cell reaction growing through PHB membrane pores. There were no reactions or adhesions between brain and PHB or dura mater and PHB, respectively. Investigations of biodegradation and electron microscopy revealed a continuous breakdown of PHB in the course of time with variations due to different PHB structures. Microbiological investigations could not detect any florid intracranial infection.

An "endosteal electrode" for cochlear implantation in cases with residual hearing? Feasibility study: preliminary temporal bone experiments.

Background: Over the years, an increasing number of patients with some degree of residual hearing have received cochlear implants. In these cases, the marginal benefit provided by hearing aids alone is not sufficient; however, as experience has already shown, when hearing aids are used in combination with a cochlear implant, more benefit may be obtained. As a prerequisite, this requires that residual hair cell function must remain intact postoperatively. One of the European pioneers of cochlear implants, Ernst Lehnhardt, questioned whether residual hearing might better be preserved if the implanted electrode permits the fluid-filled inner ear space to remain intact. Subsequently, he proposed insertion of a very flat electrode array design into the extraluminal space between the spiral ligament and the bony cochlear wall (endosteum). Objective: Our study aimed to determine whether it is feasible to insert an endosteal electrode model intracochlearly but extraluminarily, anatomically, and ultimately surgically and to determine the impact on surrounding intracochlear structures. Methods: Insertion of two silicon models of an endosteal electrode were carried out in 15 human temporal bones. Histologic examination of the temporal bones after electrode insertion was performed on both fresh and fixed specimens to determine whether the desired anatomic site of insertion was achieved. In combination with light reflected and electron microscopic techniques, the extent to which the surrounding structures were impacted was also examined. Results: Successful insertion of the prototype silicon endosteal electrodes was performed intracochlearly and extraluminarly in 11 of the 15 temporal bone specimens, confirming the anatomic feasibility of insertion into the crevice between the spiral ligament and endosteum. Conclusions: On the basis of the anatomy of the human temporal bone, insertion of an “endosteal electrode” is feasible. Subsequently, in vivo animal studies are needed to determine the physical effects of insertion of an endosteal electrode design prototype upon the functionality of the surrounding intracochlear structures and in particularly the ability to preserve hearing function.

The loss of stiffness as osteoporosis progresses.

The routine diagnosis of osteoporosis is based on radiological measurements of bone mineral content. An osteoporotic failure is influenced both by a loss of mineralized bone and internal bone structure. The structure cannot be estimated by bone reconstruction based on standard radiological equipment. To investigate the influence of structure on cancellous bone stiffness, a new finite element model of cancellous bone is developed. The model describes a cancellous bone unit as an open-celled structure. Trabecular length, trabecular thickness, diameter of trabecular connections, relative lattice disorder and relative bone loss determine the real architecture. Using this model, the loss of stiffness as a result of trabecular thinning and loss of trabecular connections is estimated. The volume fraction as a scalar value for a volume can not be a marker for orthotropic stiffness changes. A formula in the form Y = e(a *1 n(X) + b) can describe the correlation between cancellous bone stiffness and volume fraction. These formulas are appropriate for those cases, when the loss of bone mineral (decrease in trabecular thickness) is closely connected to a loss of structure (increasingly perforated trabecular network).

Temporal bone investigations on landmarks for conventional or endosteal insertion of cochlear electrodes

Conclusion. Our anatomical findings place special emphasis on the requirement to follow an infero-anterior approach to the round window, to expose the scala tympani safely for ‘normal’ cochlear implantation. It is also known how easily the basilar membrane may be accidentally damaged, despite exercising considerable caution in the approach used. With regard to an ‘endosteal electrode’ it can be stated that there are no really specific indicators to locate the spiral ligament, or each of the scalae, on the lateral aspect of the tissue layer encasing the cochlea. For the concept of an endosteal electrode, however, the soft tissue layer of the lateral aspect of the cochlea is considered to be sufficiently thick to serve as a physical barrier between the electrode and the inner ear fluid. Objectives. To re-evaluate surgical techniques of gaining access to the scala tympani for cochlear implantation (cochleostomy, ‘fenestration’). There are two reasons for this study. First, recent publications show that in a significant number of patients the electrode array was unintentionally inserted into the ‘wrong’ scala (sc. vestibuli). Second, dealing with an alternative concept proposed by Lehnhardt for patients with residual hearing (‘endosteal electrode’), the anatomical site of the spiral ligament should be known. In a study on human temporal bones the topography of the middle and inner ear is revised with regard to the presence of anatomical or surgical landmarks that may guide the surgeon. Materials and methods. Anatomical examinations were performed on 10 temporal bones (5 fresh specimens and 5 fixed in formalin), in which the bone of the promontory was carefully milled. The consistency of identification and the relative location of specific surgical indicators or landmarks such as ‘blue lines’ and ‘gray lines’ were evaluated for 10 temporal bones. Furthermore, the projection of the lateral attachment of the basilar membrane on the promontory was determined with regard to round window anatomy. Results. In all cases, a major blue line indicated the lateral aspect of the basal cochlear turn while milling the promontorial bone. In a limited number of cases (20%), an additional gray line potentially indicated the spiral ligament before the last shell of bone was removed. In 80% of the cases it was possible to remove the bony layer and leave the endosteum intact as a precondition for a potential endosteal electrode insertion. In addition, through the examination of these models, the relative anatomical location of structures, such as the scala vestibuli, scala tympani, spiral ligament, and basilar membrane, is reviewed.

Development of a biodegradable tissue adhesive based on functionalized 1,2-ethylene glycol bis(dilactic acid). I.

Tissue adhesives are a valuable alternative for mechanical tissue fixation by sutures or staples. Adhesives are desirable in body regions where damage and bleeding must be avoided. Tissue adhesives provide easy and fast handling. This study reports the development of a tissue adhesive based on 1,2-ethylene glycol bis(dilactic acid) (ELA) functionalized with hexamethylene diisocyanate (HDI) to produce isocyanate terminated ELA-NCO which was characterized by NMR and FTIR spectroscopy. ELA-NCO together with chain elongation agents forms an adhesive system suitable for tissue fixation. Several biodegradable polymers, such as hyaluronic acid, gelatin, chitosan acetate, and chitosan chloride were tested as chain elongation agents to obtain an adhesive system and studied on bovine muscle tissue to evaluate their adhesive strength and compared to fibrin glue. Tensile strength of glued joints was determined by a Zwick universal testing machine at ambient temperature. Mixtures of ELA-NCO and chitosan acetate or chloride, showed significantly higher adhesive strength than fibrin glue. Reaction between ELA-NCO and chitosan chloride produced polyurethane was traced by FTIR spectroscopy. NMR, FTIR, and rheological measurements demonstrated that ELA-NCO and chitosan chloride can be sterilized by gamma-rays or superheated water vapor without alterations, respectively. A mixture of ELA-NCO and chitosan chloride can be useful as medical tissue adhesive.

Electromyographical recording of the electrically elicited stapedius reflex via a bipolar hook electrode.

Objective: To prove the feasibility of recording stapedius reflexes by bipolar electromyography intra-operatively during cochlea implant via a bipolar hook needle electrode. Study Design: Prospective study. Setting: Tertiary referral center. Patients: Adults receiving a MED-EL cochlear implant. Intervention: Diagnostic. Main Outcome Measures: Stapedius reflex responses can be recorded by electromyography. Results: A double hook electrode could be inserted into the muscle tissue via the natural opening of the pyramid process along with the stapedius tendon. In 7 out of 10 patients supplied with MED-EL CIs (PULSARCI100 or SONATATI100), electrically elicited stapedius reflex potentials were recorded after eliminating stimulation artifacts caused by electromagnetic fields during electical stimulation by low pass filtering. Conclusion: Intraoperative stapedius reflex recording by bipolar electromyography via a hook electrode is feasible. Further research will show whether these signals may be used for establishing a self-adjusting speech processor.

Drug-eluting stent technologies for vascular regeneration

Abstract Currently, first generation drug-eluting stents are widely used in clinical practice to revascularize stenotic arterial vessel segments, and to prevent in-stent restenosis and other shortcomings of conventional bare metal stents. However, clinically relevant risks associated with current drug-eluting stents, such as delayed healing, late thrombosis and hypersensitivity, as well as the permanent nature of the stents represent challenges for further development in this field. This paper reviews current drug-eluting stent technology, and describes recent advances towards a second generation of drug-eluting stents. Particular emphasis is put on the development of stents from bioabsorbable materials as a temporary alternative to permanent stent implants.