In vivo testing of a bioabsorbable magnesium alloy serving as total ossicular replacement prostheses.

Magnesium alloys have been investigated in different fields of medicine and represent a promising biomaterial for implants due to characteristics like bioabsorbability and osteoinduction. The objective of this study was to evaluate the usability of magnesium as implant material in middle ear surgery. Magnesium implants were placed into the right middle ear of eighteen New Zealand White rabbits. Nine animals were euthanized after four weeks and nine animals after three month. The petrous bones were removed and embedded in epoxy resin. The specimens were then polished, stained and evaluated with the aid of a light microscope. The histological examination revealed a good biocompatibility. After four weeks, a beginning corrosion of the implant's surface and low amount of trabecular bone formation in the area of the stapes base plate was observed. A considerable degradation of implants and obvious bone formation was found three month after implantation. The magnesium alloy used in the present study partly corroded too fast, so that a complete bone reconstruction could not be established in time. The increased osteoinduction on the stapes base plate resulted in a tight bone-implant bonding. Thus, a promising application of magnesium could be a coating of biomaterials in order to improve the bony integration of implants.

Nanoporous silica coatings as a drug delivery system for ciprofloxacin: outcome of variable release rates in the infected middle ear of rabbits.

HYPOTHESIS: The present study was performed to examine the impact of the release rate of ciprofloxacin from prostheses coated with nanoporous silica layers on the outcome of an acute bacterial infection of the middle ear of rabbits. BACKGROUND: Middle ear prostheses are often implanted in an infectious environment because of chronic otitis media and cholesteatoma. Bacterial colonization leads to healing disorders after surgery and may lead to the extrusion of the implants. Nanoporous silica layers appear promising as a drug delivery system for antibiotics placed on implants. Before clinical applications can be envisioned, it is necessary to find an optimal release rate. METHODS: White New Zealand rabbits were provided unilaterally with either a "slow release" or a "burst release" ciprofloxacin-containing middle ear Bioverit II prosthesis. After implantation, the middle ears were infected with a solution of Pseudomonas aeruginosa. Afterwards, animals were monitored clinically and, after 3 months, sacrificed to perform necropsy and microbiologic examinations. RESULTS: In the "slow release" group, 7 of 12 animals had to be euthanized preterm because of their poor clinical condition compared with 2 of 12 animals of the "burst release" group (p < 0.05). Clinical and microbiologic examination also showed a better outcome for animals of the burst release group. CONCLUSION: A burst release of ciprofloxacin from middle ear implants is important to combat a perioperative infection with Ps. aeruginosa in the middle ear model of the rabbit.

Mesoporous silica films as a novel biomaterial: applications in the middle ear.

In this tutorial review we present the process of the development of functional implants using mesoporous silica. The different steps from chemical synthesis and physicochemical characterization followed by in vitro testing in cell culture assays to clinically relevant in vivo animal studies are examined. Since the end of the 1990s, mesoporous silicas have been considered as biomaterials. Numerous investigations have demonstrated their non-toxic and biocompatible properties. These qualities in combination with the unique properties of high surface area and pore volume, uniform and tunable pore sizes and chemical modifiability are the reasons for the great scientific interest in this field. Here we show that besides bulk materials or mesoporous silica nanoparticles, mesoporous silica films are highly promising as coatings on medical prostheses or implants. We report on the development of functionalized mesoporous silica materials specifically for middle ear applications. Middle ear prostheses are used to restore the sound transmission through this air-filled cavity when the small bones of the middle air (the ossicular chain) have been destroyed by disease or by accidents. In addition to optimal restoration of sound transmission, this technique bears several challenges, e.g. an ongoing bacterial infection or the displacement of the prosthesis due to insufficient fixation. To improve the healing process, a mesoporous silica coating was established on ceramic middle ear prostheses, which then served as a base for further functionalizations. For example, the bone growth factor BMP2 was locally attached to the coating in order to improve the fixation of the prosthesis by forming a bony connection to the remainder of the ear bones. Further, an implant-based local drug delivery system for the antibiotic ciprofloxacin was developed with the aim of fighting bacterial infections. Further possibilities using mesoporous silica nanoparticles as part of a composite on an implant are briefly discussed.

Efficacy of nanoporous silica coatings on middle ear prostheses as a delivery system for antibiotics: an animal study in rabbits.

Nanoporous silica layers are able to host molecules and release them over a certain period of time. These local drug delivery systems for antibiotics could be a new approach in the treatment of chronic otitis media. The aim of this study was to examine the efficacy of nanoporous silica coatings on middle ear prostheses as a delivery system for antibiotics in vivo. Pseudomonas aeruginosa was inoculated into the middle ear of rabbits to induce an otitis media. The control group received coated Bioverit®II implants without antibiotics. Coated prostheses with loaded ciprofloxacin were implanted into the middle ears of the study group. After 1 week, the rabbits were sacrificed. The clinical examination as well as the microbiological and histological examinations of organs and middle ear irrigation revealed clear differences between the two groups. P. aeruginosa was detected in every middle ear of the control group and was almost completely eliminated in the study group. Organ examinations revealed the presence of P. aeruginosa in the control group and a prevention of a bacterial spread in the study group. The nanoporous silica layer as antibiotic delivery system showed convincing efficacy in induced pseudomonal otitis media in the rabbit.

Layered double hydroxides as efficient drug delivery system of ciprofloxacin in the middle ear: an animal study in rabbits.

Chronic otitis media is a common disease often accompanied by recurrent bacterial infections. These may lead to the destruction of the middle ear bones such that prostheses have to be implanted to restore sound transmission. Surface coatings with layered double hydroxides (LDHs) are evaluated here as a possibility for drug delivery systems with convenient advantages such as low cytotoxicity and easy synthesis. Male New Zealand White rabbits were implanted with Bioverit(®) II middle ear prostheses coated with the LDH Mg(4)Al(2)(OH)(12)(SO(4))(2)·6H(2)O impregnated with ciprofloxacin. 12 (group 1) were directly infected with Pseudomonas aeruginosa and another 12 (group 2) 1 week after the implantation. Clinical outcome, blood counts, histological analyses and microbiological examination showed an excellent antimicrobial activity for group 1, whereas this effect was attenuated in animals where infection was performed 1 week after implantation. This is the first study to demonstrate an efficient drug delivery system with an LDH coating on prostheses in the middle ear.

Amino-modified silica surfaces efficiently immobilize bone morphogenetic protein 2 (BMP2) for medical purposes.

Due to its ability to induce de novo bone formation the differentiation factor bone morphogenetic protein 2 (BMP2) is often used to enhance the integration of bone implants. With the aim of reducing possible high dose side-effects and to lower the costs, in order to produce affordable implants, we developed a simple and fast method for the immobilization of BMP2 on silica-based surfaces using silane linkers which carry amino or epoxy functions. We put an especial emphasis on the influence of the nanoscale surface topography of the silica layer. Therefore, we chose glass (for control experiments) and Bioverit® II (as a typical implant base material) as support materials and coated these substrates with unstructured or nanoporous amorphous silica layers for comparison. Immobilized BMP2 was quantified by two different methods: by ELISA and by a cell-based assay for active BMP2. These tests probe for immunologically and biologically active BMP2, respectively. The results show that the amino functionalization is better suited for immobilizing the protein. Strikingly, a considerably higher amount of BMP2 could be immobilized on coated Bioverit® II surfaces compared with coated glass substrates, which was presumably due to the macroscopic roughness of the Bioverit® II substrates. In addition, it was found that the nanoporous silica coatings on Bioverit® II substrates were able to bind more BMP2 than the unstructured ones.

Evaluation of madurahydroxylactone as a slow release antibacterial implant coating.

Madurahydroxylactone (MHL), a secondary metabolite with antibacterial activity was evaluated for its suitability to generate controlled drug release coatings on medical implant materials. A smooth and firmly attached layer could be produced from a precursor solution on various metallic implant materials. In physiological salt solutions these coatings dissolved within a time period up to one week. A combination of MHL with a broad spectrum fluoroquinolone antibiotic was used to create a coating that was active against all bacterial strains tested. The time period during which the coating remained active against Pseudomonas aeruginosa was investigated. The results indicated a delayed drug release from single layer coatings in the course of seven days. MHL was biocompatible in cell culture assays and could after a delay even serve as a cell adhesion substrate for human or murine cells. The findings indicate a potential for MHL for the generation of delayed release antimicrobial implant coatings.

A biomechanical ear model to evaluate middle-ear reconstruction.

In order to evaluate the efficiency of middle-ear prostheses in near-real conditions, an artificial model was developed that approximately simulates the actual geometrical and biomechanical properties of the ear system (excluding the ossicular chain). The sound transmission characteristics of selected commercial middle-ear prostheses and of a synthetic test material were measured using laser Doppler vibrometry (LDV) in this model. The model's realistic properties enabled clinical tympanometry to be used to control the stiffness. In addition the influences of the implant mass on transmission characteristics were investigated. With an averaged displacement between 10 and 100 nm/Pa up to 2000 Hz, the transmission characteristic of the model was comparable with data obtained from the intact middle ear in temporal bone experiments. From the acoustical point of view, no significant material-specific differences could be found. Increasing the mass of the implants to more than 50 mg results in poorer acoustic transmission. In general, changes to the stiffness involving compliance values greater than 3.5 ml and smaller than 0.2 ml led to poorer acoustic transmission.

Management of choanal atresia in cases of craniofacial malformation.

OBJECTIVE: To report the method and results of endonasal endoscopic approach in congenital choanal atresia in cases of craniofacial malformation. PATIENTS: The pathology of unilateral and bilateral choanal atresia and the treatment results in seven children treated between 1999 and 2006 are presented. 5 infants suffering from bilateral atresia also had severe malformations (Charge syndrome [2 patients], trisomy 18, microcephalus, central cranioschisis, cleft lip and anophthalmia 9). The surgical intervention was carried out immediately after birth. 2 patients with unilateral atresia were treated in their second and sixth year of life respectively. CT scan was the diagnostic procedure of choice. Intraoperative endoscopy showed both membraneous and osseous atresia. SURGICAL PROCEDURE: Trocars of different sizes were used to open the atresia plate, while the osseous parts were removed with diamond drills. Silicone tubes were inserted transnasally and remained in place for several months to improve the infants'ability to breath and drink. RESULTS: In all cases of bilateral atresia the tubes either had to be changed repeatedly or replaced with larger tubes due to dislocation and head growth. The septum was perforated in one case. No further stenoses were detected following the removal of the tubes (after 3-6 months). CONCLUSION: The transnasal access is particularly suited to newborns and infants because it induces a minor surgical trauma and carries a low risk of bleeding if endoscopes are used. The results show that the risk of restenoses can be minimised with sufficient fixating and in-patient care.

Free Bioverit II implants coated with a nanoporous silica layer in a mouse ear model-- a histological study.

The objective of this study is to evaluate the suitability of a mouse middle ear model for testing ossicular replacement materials. Twenty-four BALB/c mice are implanted with the bioglass-ceramic Bioverit II which is coated with a silica-nanostructure or with plain Bioverit II as a control. After 2, 6, and 12 weeks, 4 mice per group are sacrificed and both complete petrous bones are analyzed histologically. All implants revealed in situ an incipient growth of thin connective tissue layers over the surface, followed by a spreading of epithelial cells. The osseogenic response which is increasing with time is more intense in the coated Bioverit II specimens. The absence of inflammatory cells suggests an excellent biocompatibility of the silica nano structure. As the results are comparable to a study with the same materials in rabbits, the mouse model described is highly suitable for evaluation of new ossicular replacement materials. Additionally, by gene expression analysis a more detailed insight into cellular interactions of the middle ear is offered.

Normative data of multifrequency tympanometry in rabbits.

In an experimental study, we evaluated acoustic immittance in rabbits in order to use these data as normative values for further experimental investigations. This study is the first experimental evaluation of both conventional 226 Hz and multifrequency tympanometry (MFT) in rabbits. For the investigation, we used 33 female New Zealand rabbits weighing 3.2-4.4 kg and aged six months. Bilateral measurements using conventional 226 Hz and MFT were performed under general anaesthetic. A 226 Hz tympanogram was recorded for all animals by conducting an air pressure sweep from +200 to -400 daPa at a rate of 50 daPa/s. Subsequent tympanograms were recorded over a wide frequency range from 250 to 2000 Hz. The acoustic impedance device used in this study provided reproducible and evaluable tympanograms. The applied tone frequency of 226 Hz proved to be especially suitable for determining compliance. Normative data obtained from our study reveal the resonance frequency to be 1368 +/- 205 standard deviation (SD) for the right side and 1413 +/- 216 SD for the left side. The values for physiological acoustic immittance of the middle ear in the rabbit obtained here can serve as normative data in subsequent experimental animal studies.

A comparative study of the audiological outcomes with Retro-X (semi-implantable hearing aid system) and conventional open fitting hearing aids.

The objective of this study was to compare the results of hearing augmentation with the Retro-X semi-implantable hearing aid to a conventional non-implantable open canal hearing aid using the same software technology (Titan-X, auric Hearing Systems, HiKaNo.:13.20.03.0047). Nineteen subjects (20 ears) with mild to moderate high-frequency sensory-neural hearing loss were included in this clinical study. All the subjects were first fitted with a conventional open canal hearing aid (Titan-X). After a period of 4-6 weeks audiological evaluations were performed using standardized speech tests in quiet and noise. Subjective evaluation was performed with the help of standardized questionnaires. After this phase the patients received the semi-implantable Retro-X device under local anaesthesia and 4 weeks later were fitted with a hearing module with the same software technology as the conventional Titan-X hearing aid. Four weeks following the first fitting the same audiological evaluations were performed under similar conditions and the patients were evaluated again using the same questionnaires in order to compare the results of the Retro-X semi-implantable system with the conventional open canal hearing aid. Audiological evaluations revealed better results with the semi-implantable Retro-X in the adaptive speech in noise test; however, the results of the monosyllabic word test in quiet were similar for the Retro-X and conventional open canal hearing aid. The patients subjectively preferred the improved wearing comfort of the semi-implantable device. The Retro-X semi-implantable hearing aid provides better speech perception in noise and higher wearing comfort in comparison to the conventional open canal hearing aids. Considering the simple implantation procedure under local anaesthesia with low complication rate, Retro-X is an alternative to the conventional open canal hearing aids in patients with mild to moderate high frequency sensory-neural hearing loss.

A comparison of different nanostructured biomaterials in subcutaneous tissue.

The nanostructured surface of a material can improve its interaction with cells and its acceptance as an implant. We compared two novel biomaterials with different nanostructures: Bioverit II with a coating of nanoporous silica and chitosan-hydroxyapatite composite materials. Pure Bioverit II served as a control. Platelets of these materials were implanted for 28, 85 and 300 days in the subcutaneous tissue in the neck of 38 rabbits. After excising the specimens they were fixed, embedded in epoxy resin and analyzed histologically. All coated Bioverit II implants showed a thin capsule of connective tissue. After 300 days, these capsules tended to be thicker than in pure Bioverit II. No signs of inflammation were observed and the materials appeared unaltered by visual inspection. In case of chitosan-hydroxyapatite composites, massive capsules consisting of dense connective tissue were found, and the material showed signs of biodegradation in form of fissures and cavities. In conclusion, the nanoporous coating showed no obvious positive effect with regard to capsule formation; the chitosan-hydroxyapatite implants provoked a stronger interaction between cells and material. However, most Bioverit II implants showed no alterations optically, whereas chitosan-hydroxyapatite was partly degraded in all cases.

Multifrequency tympanometry: experimental application after implantation of ossicular replacement prosthesis in rabbits.

HYPOTHESIS: We used multiple-frequency tympanometry (MFT) to evaluate the influence of a newly developed ossicular replacement prosthesis on transmission characteristics of middle ear. BACKGROUND: Multiple-frequency tympanometry is a technique for evaluating the emittance of the middle ear over a wide frequency range. It has been shown to be sensitive to certain middle ear conditions that are not detected by conventional 226-Hz tympanometry. In the field of experimental evaluation, MFT has been shown in certain animal studies to be useful in monitoring diseases. METHODS: Thirty-six prostheses composed of titanium dioxide ceramic were implanted into the right middle ear of female rabbits. Bilateral measurements using conventional 226-Hz and MFT were performed before implantation and after 28, 84, and 300 days postoperatively. The results of the preoperative examinations yielded reference values for physiological resonance frequency. After dissecting the temporal bone, we opened the middle ear and analyzed both the surrounding tissue and the position of the prosthesis. RESULTS: The constant values for compliance revealed by both preoperative and postoperative measurements indicate good reproducibility of 226-Hz tympanometry. Postoperatively, resonance frequency increased continuously up to the 300th day. The observation supports the assumption that the higher stiffness level of connective tissue influenced resonance frequency. CONCLUSION: The reference values in this study can serve as guidelines for further experimental trials.

Histological evaluation of novel ossicular chain replacement prostheses: an animal study in rabbits.

CONCLUSION: The improved biocompatibility of Bioverit II coated with a nanostructured surface shows promising qualities for use in human reconstructive middle ear surgery. In the case of chitosan-hydroxyapatite composite prostheses, further investigations regarding composition of the material, degree of purity and design are necessary before clinical application. OBJECTIVE: The selection of optimal materials for reconstructive middle ear surgery continues to be a problem. In the present study novel materials were tested as total ossicular replacement prostheses (TORPs) in an animal model. MATERIALS AND METHODS: Bioverit II coated with a nanostructured surface and chitosan-hydroxyapatite composites were placed in the middle ear of 40 rabbits. Uncoated Bioverit II was used as control. After an implantation period of 28, 84 or 300 days petrous bones were extracted, embedded in epoxy resin and examined by light microscopy. RESULTS: Uncoated and coated Bioverit prostheses revealed a mucosal coverage and a little osseogenic response after 28 days. The results of the coated Bioverit prostheses slightly surpassed those of the plain prostheses. Chitosan-hydroxyapatite composite prostheses were mostly found to be dislocated after 28 days. Formations of granulation tissue and fibrotic capsules were observed around these implants. This reaction could be caused by the instability of the composite material or may be due to impurities present in the chitosan.

Three-dimensional visualization of the nasal cavity and paranasal sinuses. Clinical results of a standardized approach using multislice helical computed tomography.

OBJECTIVE: The aim of this study was to introduce 3-dimensional (3D) visualization of the nasal cavity and paranasal sinuses as a diagnostic tool and to examination the clinical results of its standardized application. METHODS: One hundred sixty patients with chronic or acute nasal symptoms underwent helical computed tomography scanning and fiberoptic endoscopy of the sinuses, and 120 of them underwent endoscopic sinus surgery. The 3D images were compared with the axial and multiplanar reconstructed images using a checklist comprising important anatomic landmarks. After qualitative assessment of the representation of anatomic structures in healthy subjects, the method was applied to pathologic cases. The 3D images of these patients were correlated with the preoperative and intraoperative findings. RESULTS: Six hundred virtual endoscopies (VEs) were performed. The VE views allowed a realistic illustration of the various pathologic findings, except from cases with highly obstructive sinonasal disease. The correlation between the preoperative fiberoptic endoscopy and the intraoperative findings was significant (r = 0.83, P = 0.001). CONCLUSION: The standardized clinical application of this method serves as an important supplement to 2-dimensional slices and conventional endoscopy.

Limitations of titanium dioxide and aluminum oxide as ossicular replacement materials: an evaluation of the effects of porosity on ceramic prostheses.

BACKGROUND: Because the performance of titanium dioxide (TiO2) has not yet been assessed in the unique environment of the middle ear, its role as an ossicular replacement prototype in the form of a total ossicular replacement prosthesis (TORP) was tested and compared with aluminum oxide (Al2O3), once considered to be a suitable implant material. METHODS: Ossiculoplasty was performed by implanting TORPs into the tympanic cavities of rabbits. After an implantation period of 28, 84, or 300 days, the petrous bones were extracted, whereby the biocompatibility of the prostheses was examined using light microscopy and scanning electron microscopy to determine morphologic changes in situ. Proper implant placement and functionality was tested via manual manipulation. RESULTS: Mucosa was seen covering most of the implants by day 84. Inflammatory cells were not observed in any of the specimens examined. The macroporous TiO2 TORPs were subjected to osseous infiltration, material dissolution, and fragmentation, whereas the microporous TiO2 implants were subjected to an increasing frequency of fissure formations. The Al2O3 prostheses demonstrated signs of material dissolution by producing encapsulated aggregates during the experimental trial period. CONCLUSIONS: Neither the macroporous nor microporous oxide ceramics were able to withstand the oscillatory stress to which they were continually subjected. Although porosity allows for the rapid integration of an implant material into a biological environment, its properties are not suited to fulfill the requirements of strength and long-term stability, which are demanded of middle ear prostheses.