Tympanic membrane (TM) perforations lead to significant hearing loss and may promote infection of the middle ear (ME). Myringoplasty is commonly performed to repair chronic perforations, with the primary goals of perforation closure and hearing restoration. Although various grafts and materials have been used to promote TM regeneration, all have associated limitations. Recent experimental studies have shown the potential of silk fibroin scaffold (SFS) and porcine-derived acellular collagen type I/III scaffold (ACS) as onlay graft materials for TM perforation repair. The aims of this study were to evaluate the in vivo safety and efficacy of SFS and ACS, compared with two commonly used graft materials (paper patch and Gelfoam®) for the promotion of TM regeneration.
In this thesis, a general overview of different types of biological and synthetic scaffolds for TM regeneration was provided, and evidence of scaffolds’ function in TM wound healing was described. Furthermore, a brief review of ME packing agents and a discussion on the potential benefits of no packing also was supplied.
Firstly, the in vivo biocompatibility of SFS and ACS were characterised and compared with Gelfoam and paper in a rat model. The scaffolds were implanted in subcutaneous (SC) tissue and ME cavity followed by histological and otoscopic evaluation for up to 26 weeks. Our results revealed that SFS and ACS were well tolerated and compatible in rat SC and ME tissues throughout the study. The tissue response adjacent to the implants evaluated by histology and otoscopy showed that SFS and ACS have a milder tissue response with minimal inflammation as compared to paper control. Gelfoam gave similar results to SFS and ACS after SC implantation, but it was found to be associated with pronounced fibrosis and osteoneogenesis after ME implantation. It is concluded that SFS and ACS both were biocompatible and could serve as scaffolds for tissue engineering in the ear.
In an acute TM perforation rat model, these scaffolds were implanted using onlay myringoplasty. Surface morphology of the scaffolds was observed prior to implantation with scanning electron microscopy (SEM). The morphology of the TM was assessed at various time points postimplantation using otoscopy, light and electron microscopy, and functional outcomes by auditory brainstem responses (ABR). We found that SFS and ACS significantly accelerated the TM perforation closure, produced optimal TM thickness, and resulted in better trilaminar morphology with well-organised collagen fibres and early restoration of hearing. By contrast, paper and Gelfoam lost their scaffold function in the early stages and showed an inflammatory response, which may have contributed to delayed healing. This study indicates that compared with paper and Gelfoam, SFS and ACS are more effective in promoting an early TM regeneration and an improved hearing.
In addition, the efficacy of SFS and ACS for the repair of TM was further confirmed using a guinea pig acute TM perforation model. The perforations were repaired with SFS, ACS, and paper using onlay myringoplasty, or they were allowed to heal spontaneously (control). TM structural healing was evaluated by otomicroscopy and histology, and functional hearing was analysed by ABR. Prior to the study, mechanical properties of SFS and ACS were also investigated. Tensile strength and elasticity of SFS and ACS were within the known range for human TM. Based on otologic and histologic evaluation, TMs treated with SFS or ACS showed complete closure of the perforation at an earlier stage, with a trilaminar structure and more uniform thickness compared to paper and control treated groups. ABR assessment demonstrated that SFS or ACS treatment facilitated a faster restoration of hearing function compared to paper and control groups. The results of this study substantiate that SFS and ACS are effective graft materials for myringoplasty and may be utilised as alternatives to current grafts for TM repair.
In summary, the results in this thesis indicate that compared to paper and Gelfoam, SFS and ACS are safe and effective in promoting early TM regeneration and improved hearing, suggesting that these novel scaffolds may be potential substitutes for clinical use.
|Qualification||Doctor of Philosophy|
|Publication status||Unpublished - 2014|