J. J. Grote

Macropore tissue ingrowth: a quantitative and qualitative study on hydroxyapatite ceramic

The aim of this study was to obtain more information about macropore tissue ingrowth into the pores of sintered hydroxyapatite implanted in the rat middle ear, for the assessment of the usefulness of this material in reconstructive middle-ear surgery. The exudate filing the pores during the early post-operative period was gradually replaced by equal amounts of fibrous tissue and bone. The percentage of the macropore area occupied by bone was directly correlated with the macropore size. Bone was deposited not only from the pore wall towards the pore centre, but also in the opposite direction. Bonding osteogenesis was demonstrated. At sites of mechanical irritation, the presence of multinucleated cells and proliferatively active mononuclear phagocytes persisted for as long as a year. Under appropriate conditions hydroxyapatite seems to be a promising material for bone substitution in reconstructive middle-ear surgery.

Bioreactions at the tissue/ hydroxyapatite interface

The events at the hydroxyapatite implant material/tissue interface in the rat middle ear were studied by light microscopy, autoradiography, morphometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray microanalysis. Deposition of calcium, partially in the form of calcium phosphate, was found at the interface. Resorption of the implant material occurred as the result of mono- and multinuclear phagocyte activity. Resorption decreased 6 mnth after the operation, possibly due to the decreasing number of phagocytes at the interface and the increasing amount of bone in the macropores.

Effect of implantation site on phagocyte/polymer interaction and fibrous capsule formation

Implants of Silastic, Estane, polypropylene oxide and an HPOE/PBT segmented polyether polyester copolymer were qualitatively and quantitatively evaluated, with respect to interaction with mononuclear and multinucleated phagocytes as well as fibrous capsule formation, after implantation at three sites in the rat middle ear. The volume of the phagocyte exudate surrounding the implants, the degree of implant degradation and fragmentation and the thickness of the fibrous capsules were found to be correlated with the implantation site. From these findings, it can be concluded that it is important to assess the biological performance of a biomaterial at carefully chosen implantation sites.

Use of Sintered Hydroxylapatite in Middle Ear Surgery

The behavior of a ceramic, sintered hydroxylapatite in animal experiments and clinical trials is reported. This material demonstrates its usefulness in the reconstruction of bony defects in the external ear canal and as replacement of the bony ear canal in a total alloplastic middle ear prosthesis.

Acute Otitis Media: An Animal Experimental Study

This paper describes an investigation performed to study the middle ear events ensuing from Staphylococcus aureus induced infection in the middle ear cavity of the rat. To obtain an evaluation at both the cell and the tissue level, scanning electron microscopy, transmission electron microscopy and histology were used. Staphylococcus aureus infection appears to be characterized by five major events: (i) cellular response, (ii) humoral response, (iii) mucociliary response, (iv) fibroblastic response, (v) bony response. Since these occurrences correspond to the events witnessed in the human middle ear affected by acute otitis media, S. aureus achieved infection might prove a useful tool for the further study of this disease, by means of animal experiments.

Tympanic membrane structure during a Staphylococcus aureus-induced middle ear infection. A study in the rat middle ear.

In response to a Staphylococcus aureus-induced middle ear infection the tympanic membrane showed infiltration of polymorphonuclear granulocytes, lymphocytes, and macrophages and increased areas covered by ciliary and secretory epithelium. These reactions, which were comparable to the cellular and mucociliary responses seen in the middle ear mucosa during infection, were restricted to the pars flaccida and to predominantly the annular and manubrial regions of the pars tensa. This showed that the greater part of the tympanic membrane, where the lamina propria is composed of collagenous bundles and only very thin layers of loose connective tissue, is hardly affected by or barely responds to the inflammatory stimulus.

Epithelial Reactions to Hydroxyapatite: An in Vivo and in Vitro Study

The intention of this study was to investigate the epithelial reactions to hydroxyapatite ceramic in vivo and in vitro. Shortly after implantation in the rat middle ear, hydroxyapatite was found covered by a mucosal layer. In the early postoperative period the implant was almost completely covered by epithelial cells, which were found to proliferate and also showed migratory activity. After longer intervals the implant was completely covered by epithelium, which was composed predominantly of flat polygonal cells and a relatively small number of ciliated epithelium and goblet cells. All cells showed normal morphology. In vitro experiments showed preservation of the morphology of rat middle-ear mucosa explants with good outgrowth of epithelial cells. In these outgrows, the majority of the cells were flat polygonal, but ciliated epithelium was also seen. No difference was found between the absence and presence of hydroxyapatite. Serially cultured cells displayed normal polygonal morphology, but no ciliated cells were found. Ciliated cells were also absent in control experiments without hydroxyapatite. Growth curves obtained in the absence and presence of hydroxyapatite did not differ significantly from each other.

Cytokeratin Expression in Cholesteatoma Matrix, Meatal Epidermis and Middle Ear Epithelium: A Preliminary Report

The cytokeratin expression of cholesteatoma matrix, meatal epidermis and middle ear epithelium was investigated with six anticytokeratin monoclonal antibodies. One of these was broad specific and the other antibodies were directed against cytokeratins 4, 8, 10, 18 and 19 respectively. Immunoperoxidase staining of cryosections revealed the presence of cytokeratin 10 in cholesteatoma matrix and meatal epidermis. In contrast, middle ear epithelium was characterized by cytokeratins 4, 8, 18 and 19 and not by cytokeratin 10. An infrequent focal presence of cytokeratins 4, 18 and 19 was found in cholesteatoma. In general, the divergence between the cytokeratin expression of middle ear epithelium versus that of cholesteatoma and meatal epidermis suggests an epidermal origin of cholesteatoma. However, a metaplastic origin of cholesteatoma cannot be excluded because of the infrequent focal presence of cytokeratins 4, 18 and 19 in cholesteatoma.

Osteoinduction within PEO/PBT copolymer implants in cranial defects using demineralized bone matrix

This study was undertaken to assess the osteoinductive effect addition of demineralized bone matrix (DBM) gel has, on the behaviour of osteoconductive bone-bonding PEO/PBT copolymer (PolyactiveR) implants. Cranial defects in rats were filled with these composites to study bone formation in comparison with several controls after 2 and 8 weeks survival time. Osteogenesis was qualitatively evaluated by using light- and transmission electron microscopy as well as backscatter electron imaging. Quantification of the amount of bone ingrowth was performed by using a computerized image analysis system. Initially, rapid calcification was observed in the polymer and DBM, followed by formation of new trabecular bone around the demineralized bone fragments. Bone ingrowth in implants consisting of plain copolymer was less than expected based on previous research, but the addition of demineralized bone matrix gel resulted in a significantly greater amount of new bone formation in the defects. We concluded that the application of DBM-gel to PolyactiveR implants had a beneficial effect on the amount of new bone formation in this material. This procedure combines the osteoinductive potential of DBM with the mechanical and bone-bonding properties of a copolymer, thus opening the way to the development of a line of osteoactive composite implants with good surgical handling properties.

Hydroxyapatite in the Infected Middle Ear

In order to test the suitability of hydroxyapatite implants for use in tympanoplasty, a study was performed in which the behaviour of these biomaterials was observed in the infected middle ear of the rat. Infection was induced by means of intratympanical injection of a Staphylococcus aureus suspension. The reactions observed show great resemblance with the events witnessed in the middle ear infected without implant. Another similarity can be demonstrated between the implant inserted in the infected tympanon and the implant remaining in the non infected middle ear cavity. All implants are characterized by a mucosal and bony lining. Macropores, when present, become filled with fibrous tissue, gradually replaced by bone. The bonding between the tissue and the implant appears to be tight.