Neil G. Fairbairn

Augmenting peripheral nerve regeneration using stem cells: A review of current opinion

Outcomes following peripheral nerve injury remain frustratingly poor. The reasons for this are multifactorial, although maintaining a growth permissive environment in the distal nerve stump following repair is arguably the most important. The optimal environment for axonal regeneration relies on the synthesis and release of many biochemical mediators that are temporally and spatially regulated with a high level of incompletely understood complexity. The Schwann cell (SC) has emerged as a key player in this process. Prolonged periods of distal nerve stump denervation, characteristic of large gaps and proximal injuries, have been associated with a reduction in SC number and ability to support regenerating axons. Cell based therapy offers a potential therapy for the improvement of outcomes following peripheral nerve reconstruction. Stem cells have the potential to increase the number of SCs and prolong their ability to support regeneration. They may also have the ability to rescue and replenish populations of chromatolytic and apoptotic neurons following axotomy. Finally, they can be used in non-physiologic ways to preserve injured tissues such as denervated muscle while neuronal ingrowth has not yet occurred. Aside from stem cell type, careful consideration must be given to differentiation status, how stem cells are supported following transplantation and how they will be delivered to the site of injury. It is the aim of this article to review current opinions on the strategies of stem cell based therapy for the augmentation of peripheral nerve regeneration.

The clinical applications of human amnion in plastic surgery

Since the early 1900s, human amnion has been applied to a wide variety of clinical scenarios including burns, chronic ulcers, dural defects, intra-abdominal adhesions, peritoneal reconstruction, genital reconstruction, hip arthroplasty, tendon repair, nerve repair, microvascular reconstruction, corneal repair, intra-oral reconstruction and reconstruction of the nasal lining and tympanic membrane. Amnion epithelial and mesenchymal cells have been shown to contain a variety of regulatory mediators that result in the promotion of cellular proliferation, differentiation and epithelialisation and the inhibition of fibrosis, immune rejection, inflammation and bacterial invasion. The full repertoire of biological factors that these cells synthesise, store and release and the mechanisms by which these factors exert their beneficial effects are only now being fully appreciated. Although many commercially available biological and synthetic alternatives to amnion exist, ethical, religious, and financial constraints may limit the widespread utilisation of these products. Amnion is widely available, economical and is easy to manipulate, process and store. Although many clinical applications are of historical interest only, amnion offers an alternative source of multi-potent or pluripotent stem cells and therefore may yet have a great deal to offer the plastic surgery and regenerative medicine community. It is the purpose of this article to review the clinical applications of human amnion relevant to plastic surgery.

Light-Activated Sealing of Nerve Graft Coaptation Sites Improves Outcome following Large Gap Peripheral Nerve Injury.

Background: Nerve repair using photochemically bonded human amnion nerve wraps can result in superior outcomes in comparison with standard suture. When applied to nerve grafts, efficacy has been limited by proteolytic degradation of bonded amnion during extended periods of recovery. Chemical cross-linking of amnion before bonding may improve wrap durability and efficacy. Methods: Three nerve wraps (amnion, cross-linked amnion, and cross-linked swine intestinal submucosa) and three fixation methods (suture, fibrin glue, and photochemical bonding) were investigated. One hundred ten Lewis rats had 15-mm left sciatic nerve gaps repaired with isografts. Nine groups (n = 10) had isografts secured by one of the aforementioned wrap/fixation combinations. Positive and negative control groups (n = 10) were repaired with graft and suture and no repair, respectively. Outcomes were assessed using sciatic function index, muscle mass retention, and histomorphometry. Statistical analysis was performed using analysis of variance and the post hoc Bonferroni test (p < 0.05). Results: Cross-linking improved amnion durability. Photochemically bonded cross-linked amnion recovered the greatest sciatic function index, although this was not significant in comparison with graft and suture. Photochemically bonded cross-linked amnion recovered significantly greater muscle mass (67.3 ± 4.4 percent versus 60.0 ± 5.2 percent; p = 0.02), fiber diameter, axon diameter, and myelin thickness (6.87 ± 2.23 &mgr;m versus 5.47 ± 1.70 &mgr;m; 4.51 ± 1.83 &mgr;m versus 3.50 ± 1.44 &mgr;m; and 2.35 ± 0.64 &mgr;m versus 1.96 ± 0.47 &mgr;m, respectively) in comparison with graft and suture. Conclusion: Light-activated sealing of cross-linked human amnion results in superior outcomes when compared with conventional suture.

Improving Outcomes in Immediate and Delayed Nerve Grafting of Peripheral Nerve Gaps Using Light-Activated Sealing of Neurorrhaphy Sites with Human Amnion Wraps.

Background: Photochemical tissue bonding uses visible light to create sutureless, watertight bonds between two apposed tissue surfaces stained with photoactive dye. When applied to nerve grafting, photochemical tissue bonding can result in superior outcomes compared with suture fixation. Our previous success has focused on immediate repair. It was the aim of this study to assess the efficacy of photochemical tissue bonding when performed following a clinically relevant delay. Methods: Forty male Lewis rats had 15-mm left sciatic nerve gaps repaired with reversed isografts immediately (n = 20) or after a 30-day delay (n = 20). Repairs were secured using either suture or photochemical tissue bonding. Rats were killed after 150 days. Outcomes were assessed using monthly Sciatic Function Index evaluation, muscle mass retention, and nerve histomorphometry. Statistical analysis was performed using analysis of variance and the post hoc Bonferroni test. Results: In both immediate and delayed groups, photochemical tissue bonding showed a trend toward greater recovery of Sciatic Function Index, but these results were not significant. The Sciatic Function Index was significantly greater when performed immediately. Significantly greater muscle mass retention occurred following photochemical tissue bonding in both immediate and delayed repairs. Values did not differ significantly between immediate and delayed groups. Histomorphometric recovery was greatest in the immediate photochemical tissue bonding group and poorest in the delayed suture group. Fiber diameter, axon diameter, myelin thickness, and G-ratio were not significantly different between immediate suture and delayed photochemical tissue bonding. Conclusions: Light-activated sealing of nerve grafts results in significantly better outcomes in comparison with conventional suture. The technique not only remains efficacious but may also help ameliorate the detrimental impacts of surgical delay.

Light-Activated Sealing of Acellular Nerve Allografts following Nerve Gap Injury

Introduction Photochemical tissue bonding (PTB) uses visible light to create sutureless, watertight bonds between two apposed tissue surfaces stained with photoactive dye. In phase 1 of this two-phase study, nerve gaps repaired with bonded isografts were superior to sutured isografts. When autograft demand exceeds supply, acellular nerve allograft (ANA) is an alternative although outcomes are typically inferior. This study assesses the efficacy of PTB when used with ANA. Methods Overall 20 male Lewis rats had 15-mm left sciatic nerve gaps repaired using ANA. ANAs were secured using epineurial suture (group 1) or PTB (group 2). Outcomes were assessed using sciatic function index (SFI), gastrocnemius muscle mass retention, and nerve histomorphometry. Historical controls from phase 1 were used to compare the performance of ANA with isograft. Statistical analysis was performed using analysis of variance and Bonferroni all-pairs comparison. Results All ANAs had signs of successful regeneration. Mean values for SFI, muscle mass retention, nerve fiber diameter, axon diameter, and myelin thickness were not significantly different between ANA + suture and ANA + PTB. On comparative analysis, ANA + suture performed significantly worse than isograft + suture from phase 1. However, ANA + PTB was statistically comparable to isograft + suture, the current standard of care. Conclusion Previously reported advantages of PTB versus suture appear to be reduced when applied to ANA. The lack of Schwann cells and neurotrophic factors may be responsible. PTB may improve ANA performance to an extent, where they are equivalent to autograft. This may have important clinical implications when injuries preclude the use of autograft.

Abstract P22: Photochemical Tissue Bonding Improves Outcomes for Acellular Nerve Allograft

PURPOSE: Photochemical tissue bonding (PTB) creates sutureless, watertight bonds between two apposed tissue surfaces that have been stained with photoactive dye and illuminated with a 532nm laser. When applied to nerve repairs wrapped with human amnion, this approach resulted in superior outcomes in comparison to conventional suture fixation. This technique remained efficacious when applied to isograft repair of sciatic nerve injury in a rodent model. Following major injury, demand for autogenous nerve graft may exceed that which can be supplied by the patient. Acellular nerve allograft (ANA) is an option in these circumstances, although outcomes are typically inferior to autograft. This study assesses the efficacy of PTB when used with ANA in a 15mm sciatic nerve gap in the rat.

Abstract P6: A Photochemical Tissue Bonding Approach for Sutureless Microvascular Anastamosis in an Arterial Graft Model

PurPose: Microvascular repair with suture remains the gold standard, but can lead to inflammation and thrombosis, especially in small peripheral vessels. Use of clips, couplers, and rings can assist with technical difficulties but do not minimize risk of thrombosis or endothelial damage. Photochemical tissue bonding (PTB) is a technique that covalently links protein to create an immediate watertight bond, and has been employed by our group for wound closure in several tissues including cornea, skin, tendon, and peripheral nerve. We hypothesize that use of PTB in conjunction with a biocompatible intraluminal stent would result in a watertight seal with minimal endothelial inflammation.