Tissue-material interactions : bioadhesion and tissue response

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 159-162).Diverse interactions between soft tissues and implanted biomaterials directly influence the success or failure of therapeutic interventions. The nature and extent of these interactions strongly depend on both the tissue and material in question and can presumably be characterized for any given clinical application. Nevertheless, optimizing biomaterial performance remains a challenge in many implant scenarios due to complex relationships between intrinsic material properties and tissue response. Soft tissue sealants are clinically-relevant biomaterials which impart therapeutic benefit through adhesion to tissue, thus exhibiting a direct functional dependence on tissue-material reactivity. Because adhesion can be rigorously quantified and correlated to the local tissue response, sealants provide an informative platform for studying material properties, soft tissues, and their interplay. We developed a model hydrogel sealant composed of aminated polyethylene glycol and dextran aldehyde (PEG:dextran) that can possess a wide range of bulk and adhesive properties by virtue of constituent polymer modifications. Through comparison to traditional sealants, we established that highly viscoelastic adhesion promotes tissue-sealant interfacial failure resistance without compromising underlying tissue morphology.(cont.) We analyzed multiple soft tissues to substantiate the notion that natural biochemical variability facilitates the design of tissue-specific sealants which have distinct advantages over more general alternatives. We confirmed that hydrogel-based materials are an attractive material class for ensuring sealant biocompatibility, but found that a marked reduction in adhesive strength following characteristic swell can potentially limit clinical efficacy. To mitigate the swell-induced loss of hydrogel-based sealant functionality, a biomimetic conjugation strategy derived from marine mussel adhesion was applied to PEG:dextran and shown to favorably modulate adhesion. In all phases of this research, we defined material design principles that extend beyond the immediate development of PEG:dextran with potential to enhance the clinical performance of a range of biomaterials.by Tarek Shazly.Ph.D

Property determinants of dextran:polyethylene glycol adhesive sealants

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Includes bibliographical references (leaves 98-100).Internal surgical intervention necessitates the intentional wounding of tissue. In certain clinical procedures, the desired wound healing response requires the use of closure techniques, such as suturing or stapling of disjoined tissues. Risk factors associated with these techniques are largely attributed to the discrete nature of the mechanical forces arising in the tissues. Adhesive sealants can mitigate risk by imparting a continuous stress distribution to tissues upon closure, as opposed to destructive stress concentrations. A novel class of dextran:polyethylene glycol hydrogels are a potential alternative to the limited selection of available adhesive sealants. Multiple compositional variations are available for both the dextran and polyethylene glycol components, making a wide range of clinically relevant material properties achievable. Key material properties determining sealant efficacy include hydration and degradation in an aqueous medium, elastic modulus, adhesion strength to tissue, and biocompatibility. Relationships between these pertinent properties and available compositional variations are determined for dextran:polyethylene glycol materials.(cont.) Gravimetric, mechanical and biological testing reveal the following compositional determinants of material properties in dextran:polyethylene glycol copolymers: constituent molecular complexity dictates material hydration and degradation, solid content dictates elastic modulus, available aldehyde groups dictate adhesion strength, and material solid content and reactive group ratio dictate induced cell proliferation and cytotoxicity. Knowledge of these property determinants facilitates development of an optimal dextran:polyethylene glycol material in a small bowel resection model for adhesive sealants, and furthers the understanding of these complex copolymers for other sealant applications. Generalization of the identified property determinants to other material classes provides a vehicle for advancement of adhesive sealant technologies.by Tarek Shazly.S.M

Severe pediatric ocular injury due to explosion of a firecracker inside a soda bottle

This case report describes a penetrating ocular injury, followed by endophthalmitis, in a four-year-old girl, resulting from explosion of a small K0201 match-cracker inside a soda bottle. The patient presented with two corneal lacerations, ruptured crystalline lens, multiple intraocular foreign bodies, and hyphema of the right eye, for which immediate surgical exploration and repair was performed. The patient developed aggressive endophthalmitis that led to atrophy of the eye within a few weeks. Severe ocular injuries can result from small, relatively “safe” firecrackers. Therefore, this type of firework should not be used, especially by minors

Long-term safety and efficacy of selective laser trabeculoplasty as primary therapy for the treatment of pseudoexfoliation glaucoma compared with primary open-angle glaucoma

Tarek A Shazly1,2, Jan Smith3, Mark A Latina41Ophthalmology Department, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, MA, USA; 2Ophthalmology, Assiut University Hospital, Assiut, Egypt; 3Oslo Eye Institute, Oslo, Norway; 4Reading Health Center, Reading, MA, USAPurpose: To investigate the safety and efficacy of selective laser trabeculoplasty (SLT) to reduce intraocular pressure (IOP) in patients with pseudoexfoliation glaucoma (PXFG) compared with primary open-angle glaucoma (POAG).Design: Non-randomized, prospective, clinical trial.Methods: Nineteen eyes of 13 patients with POAG and 18 eyes of 13 patients with PXFG were treated with SLT. Patients were followed without antiglaucoma medications until additional medical, laser, or surgical intervention was initiated, at which time they were considered failures, had withdrawn from the study, or underwent a second SLT.Results: The POAG and PXFG eyes showed similar reductions of IOP over the 49 months of follow-up. At 30 months of follow-up the POAG group showed a mean IOP of 17.6 ± 2.8 mmHg and a mean IOP reduction of 5.7 ± 2.1 mmHg; the PXFG group showed a mean IOP of 18.3 ± 4.7 and a mean IOP reduction of 5.3 ± 3.0 mmHg. Four eyes in the PXFG group and three eyes in the POAG group failed by 30 months. The cumulative probability of success was 74% for the PXFG group and 77% for the POAG group. Four PXFG eyes underwent a second SLT after 30 months of follow-up with a final IOP of 17.6 ± 2.8 mmHg. There were no serious adverse events.Conclusion: SLT is a safe and effective method to lower IOP in patients with PXFG as initial glaucoma therapy. Both groups showed similar IOP reductions and failure rates.Keywords: glaucoma, selective laser trabeculoplasty, primary open angle glaucoma, pseudoexfoliation glaucoma, intraocular pressure, laser, trabecular meshwor

Combining Baerveldt Implant with Trabectome Negates Tube Fenestration: A Coarsened-matched Comparison

Purpose: To assess the efficacy and survival rate of the Trabectome-mediated ab interno trabeculectomy combined with non-fenestrated Baerveldt glaucoma implant compared with the Baerveldt glaucoma implant alone. Method: In this retrospective comparative case series, 175 eyes undergoing primary glaucoma surgery (Baerveldt–Trabectome [BT] group: 60 eyes and Baerveldt [B] group: 115 eyes) were included. Participants were identified using the procedural terminology codes. Groups were then matched by Coarsened Exact Matching that resulted in the inclusion of 51 eyes in each group. The primary outcome measure was surgical success defined as 5 mmHg < intraocular pressure (IOP) ≤ 21 mmHg, and IOP reduction ≥ 20% from baseline, and no need to reoperation for glaucoma. Secondary outcome measures were IOP, number of glaucoma medications, and best-corrected visual acuity (BCVA). Results: The cumulative probability of success at one year was 61% in the BT group and 50% in the B group. IOP decreased from 23.5 ± 2.4 mmHg at baseline to 14.1 ± 2.7 mmHg at the final follow-up in the BT group (P = 0.001). The corresponding values for the B group were 23.2 ± 2.0 mmHg and 13.9 ± 1.6 mmHg, respectively (P = 0.001). There was no significant difference between the groups in terms of IOP at the final follow-up (P = 0.56). The number of medications at baseline was 2.3 ± 0.3 in both groups. However, the BT group needed fewer drops at all postoperative time intervals and used 1.1 ± 0.3 versus 2.0 ± 0.4 eye drops (group B) at the final follow-up visit (P = 0.004). Eyes in B with phacoemulsification had a significantly higher IOP on day 1 compared to B (23.2 ± 14.3 versus 17.9 ± 11.4, P = 0.041). During the one-year follow-up, 7 (13.7%) patients in BT group and 18 (35.2%) in B group experienced hypotony (P = 0.04). No dangerous hypotony or hypertension occurred in BT group. The mean BCVA at baseline was 0.64 ± 0.85 logMAR and changed to 0.55 ± 0.75 logMAR in BT and B groups, respectively (P = 0.663). The corresponding numbers for the final follow-up visit was 0.72 ± 1.07 and 0.63 ± 0.97 logMAR, respectively (P = 0.668). Conclusion: We observed similar rates of success and IOP reduction using BT and B techniques. BT group needed fewer glaucoma medications. Tube fenestration was unnecessary in BT group resulting in less postoperative ocular hypotony and hypertension. The results of our study indicate that additional trabectome procedure makes Baerveldt glaucoma implant safer, easier to handle, and more predictable in the most vulnerable patients with advanced glaucoma

Trabectome Surgery Combined with Baerveldt Glaucoma Implantation Negates Tube Fenestration

Purpose: To evaluate the efficacy and survival rates of the same session ab interno trabeculectomy with trabectome and Baerveldt glaucoma implant (BT) compared to Baerveldt implant alone (B). Method: A total of 175 eyes undergoing primary glaucoma surgery were enrolled in this retrospective comparative case series, including 60 eyes which underwent BT and 115 eyes which received B alone. Participants were identified using the procedural terminology codes, and their medical records were reviewed. The primary outcome measure was surgical success defined as 5 mmHg > IOP ≤ 21 mmHg and IOP reduction ≥ 20% from baseline, no reoperation for glaucoma, and no loss of light perception vision. Secondary outcome measures were intraocular pressure, the number of glaucoma medications, and best corrected visual acuity (BCVA). Results: The cumulative probability of success at 1 year was 61% in BT, and 50% in B. IOP decreased significantly from 23.6±8.9 mmHg at baseline to 13.7±3.9 mmHg at the final follow up in BT (P= 0.001). The corresponding numbers for B were 23.3±7.5 and 14.2±4.5, respectively (P= 0.001). There was no significant difference in IOP at the final follow-up (P=0.56). The number of medications at baseline was comparable in both groups (2.1±1.1 in BT versus 2.4±1 in B, p=0.07). However, BT needed statistically significant fewer drops in all postoperative time intervals and used 0.9±0.9 (BT) and 1.6±1.2 eyedrops (B) at the final follow-up visit (P= 0.004). No dangerous hypertony or hypertension occurred in BT. Conclusion: Similar rates of success and IOP reduction were observed in BT and B. Eyes who underwent trabectome surgery needed significantly fewer glaucoma medications during 1-year follow-up period while tubes did not require fenestration resulting in fewer postoperative hypotony or hypertension