Photochemical Tissue Bonding Research Articles

Photochemical Tissue Bonding of Amnion Allograft Membranes for Peripheral Nerve Repair: A Biomechanical Analysis.

Photochemical tissue bonding (PTB) is a technique for peripheral nerve repair in which a collagenous membrane is bonded around approximated nerve ends. Studies using PTB with cryopreserved human amnion have shown promising results in a rat sciatic nerve transection model including a more rapid and complete return of function, larger axon size, and thicker myelination than suture repair. Commercial collagen membranes, such as dehydrated amnion allograft, are readily available, offer ease of storage, and have no risk of disease transmission or tissue rejection. However, the biomechanical properties of these membranes using PTB are currently unknown in comparison to PTB of cryopreserved human amnion and suture neurorrhaphy. Rat sciatic nerves (n = 10 per group) were transected and repaired using either suture neurorrhaphy or PTB with one of the following membranes: cryopreserved human amnion, monolayer human amnion allograft (crosslinked and noncrosslinked), trilayer human amnion/chorion allograft (crosslinked and noncrosslinked), or swine submucosa. Repaired nerves were subjected to mechanical testing. During ultimate stress testing, the repair groups that withstood the greatest strain increases were suture neurorrhaphy (69 ± 14%), PTB with crosslinked trilayer amnion (52 ± 10%), and PTB with cryopreserved human amnion (46 ± 20%), although the differences between these groups were not statistically significant. Neurorrhaphy repairs had a maximum load (0.98 ± 0.30 N) significantly greater than all other repair groups except for noncrosslinked trilayer amnion (0.51 ± 0.27 N). During fatigue testing, all samples repaired with suture, or PTBs with either crosslinked or noncrosslinked trilayer amnion were able to withstand strain increases of at least 50%. PTB repairs with commercial noncrosslinked amnion allograft membranes can withstand physiological strain and have comparable performance to repairs with human amnion, which has demonstrated efficacy in vivo. These results indicate the need for further testing of these membranes using in vivo animal model repairs.

Need for innovation: laser sutures

In this modern era there is dire need of awareness regarding sutureless surgical procedures. Globally 310 million surgeries are performed each year1. Using thread and needle for suturing is still as common as using legs to walk. This method is not near to ideal because of risk of contamination, infections, scar marks, needle trauma, and reopening of tissues if the stitches are not held tight2. The prevention of wound infections after surgical procedures is of great interest for every surgical discipline, in order to improve the quality of patient care. And the best way to prevent suture-related complications is to have sutureless procedures. A number of sutureless methods have developed over the time which includes fibrin glue, cyanoacrylates, scaffolds and bio-inspired adhesives3. The sutureless technique which is receiving increasing attention is Photochemical Tissue Bonding (PTB), which can also be called laser sutures. PTB is a novel tissue repair technique that causes the proteins on tissue surfaces to crosslink by using visible light and a photosensitizing dye. This technique has been successfully demonstrated in a number of tissue repair models4. This suture-replacement technique is able to close incisions nearly instantaneously without damaging tissue. It gives minimum scar, is time saving, has more accuracy, causes less infections and is less user dependent as compared with typical sutures. This technique does not provide promising results on the skin but also has been tested for vascular and nervous repairs5. Therefore I think it’s high time that surgeons should consider using this in their practice. Ethical approval None. Sources of funding None. Author contribution Misbah Kaleem: Conception of work along with final draft. Musaddiq Kaleem: Editing draft and reviewed article. Conflict of interest disclosure The authors declare that they have no financial conflict of interest with regard to the content of this report. Research registration unique identifying number (UIN) None. Guarantor None.

Controlled afterglow luminescent particles for photochemical tissue bonding

Upconversion materials (UCMs) have been developed to convert tissue-penetrating near-infrared (NIR) light into visible light. However, the low energy conversion efficiency of UCMs has limited their further biophotonic applications. Here, we developed controlled afterglow luminescent particles (ALPs) of ZnS:Ag,Co with strong and persistent green luminescence for photochemical tissue bonding (PTB). The co-doping of Ag+ and Co2+ ions into ZnS:Ag,Co particles with the proper vacancy formation of host ions resulted in high luminescence intensity and long-term afterglow. In addition, the ALPs of ZnS:Ag,Co could be recharged rapidly under short ultraviolet (UV) irradiation, which effectively activated rose bengal (RB) in hyaluronate-RB (HA-RB) conjugates for the crosslinking of dissected collagen layers without additional light irradiation. The remarkable PTB of ZnS:Ag,Co particles with HA-RB conjugates was confirmed by in vitro collagen fibrillogenesis assay, in vivo animal wound closure rate analysis, and in vivo tensile strength evaluation of incised skin tissues. Taken together, we could confirm the feasibility of controlled ALPs for various biophotonic applications.

Light-Activated Vascular Anastomosis.

Background. There have been few advances in technique since vascular anastomosis was performed with silk suture on a curved needle in 1902. This technique results in disruption of the endothelium with exposed intraluminal suture, both of which may lead to thrombocyte aggregation, intimal hyperplasia, and vascular stenosis. A variety of alternative techniques have been explored, with limited success. Photochemical tissue bonding (PTB) is a light-activated methodology of rapidly cross-linking tissue interfaces at the molecular level. Herein, we describe a new technique for anastomosis of venous interposition graft in an ovine model of femoral artery bypass utilizing PTB. Methods. Polypay specific pathogen free sheep (n = 5; 40-45kg) underwent femoral artery bypass utilizing saphenous vein. The femoral artery was transected and reversed saphenous vein was implanted as an interposition graft. The proximal anastomosis was created as a vein-over-artery cuff utilizing PTB, and the distal anastomosis was created with standard interrupted 8-0 polypropylene suture. Four weeks post-index operation, femoral angiogram was performed to evaluate patency, tortuosity, and luminal diameter. All bypass grafts were harvested and longitudinal and transverse histological sections from the proximal anastomosis were analyzed. Results. The PTB anastomoses (n = 5) were immediately watertight and patent. All animals survived the 28-day study duration. Angiography revealed patent grafts with no aneurysm or stenosis (n = 5). Histologic examination revealed integration of the venous endothelium with the arterial adventitia. Conclusion. Photochemical tissue bonding creates an immediate strong, watertight vascular anastomosis that can withstand physiologic arterial pressure and remains patent at 28days without the need for intraluminal suture.

A review on Light-initiated crosslinking of biomaterials stained with Rose Bengal for “Nanosuturing” Macromolecular interfaces

The prospect of utilizing light to photochemically induce or enhance the adhesion of tissue surfaces has been scientifically investigated for over 20 years. During this time, two slightly different approaches have emerged. On one hand, a photochemically active molecule, eg. Rose Bengal (RB) can be applied as a dye on the tissue to be bonded and then exposed to appropriate light for crosslinking. On the other hand, the possibility of embedding the photochemically active molecule inside an exogenous carrier matrix and then bringing the stained material in contact with the tissue has only been investigated more recently. While the photochemical tissue bonding (PTB) with RB via direct staining of the tissue has been reviewed, we found no reviews analyzing the results obtained when exogenous biomaterials are stained and then bonded to the tissue by the photochemical process. Here, we aim at providing a short review of the use of exogenous materials dyed with RB as candidates for PTB and evaluate the reported bonding strengths as a function of materials chemistry and crosslinking parameters. PTB with RB has been tested in biomaterials like chitosan and human amniotic membrane yielding a water-tight seal after activation with green light. The key variables and conditions of this technique were summarized, including light source, fluence, composition of the RB staining solution and molecular structure of the biomaterial. Lastly, reported photo- and cytotoxicity results are briefly discussed to provide an outlook into the promising future of PTB in photomedicine.

Noninvasive Photochemical Sealing for Achilles Tendon Rupture by Combination of Upconversion Nanoparticles and Photochemical Tissue Bonding Technology.

Photochemical tissue bonding (PTB), based on photosensitizer rose bengal (RB) and green light, has been regarded as an effective alternative to surgical suture and has been reported to provide benefits for Achilles tendon repair. Limited to the poor penetration of green light, secondary damage still exists while applying PTB for closed Achilles tendon rupture. This study is aimed at exploring the effects of noninvasive photochemical sealing on Achilles tendon rupture by the combination of PTB and upconversion nanoparticles (UCNPs). The rare-earth UCNPs of NaYF4 : Yb/Er (Y : Yb : Er = 78 : 20 : 2) were fabricated and then loaded into Chitosan/β-GP hydrogel containing RB to prepare UCNPs@RB/Chitosan/β-GP hydrogel. The properties of UCNPs and UCNP/Chitosan/β-GP hydrogel were characterized by TEM, SEM, DLS, and FTIR analysis. The effects of UCNP and PTB combination were evaluated in an Achilles tendon rupture rat model using histological analysis. Bioluminescence imaging of ROS was performed to explore the potential mechanism. UCNPs had a uniform shape with a diameter of 29.7 ± 2.6 nm. The UCNPs@RB/Chitosan/β-GP hydrogel could upconvert the near-infrared light into green light. The results of histological assessment showed that compared with traditional suture repair, the rats injected with UCNPs@RB/Chitosan/β-GP hydrogel followed by irradiating with near-infrared light and the rats treated with RB solution followed by irradiating with green light had better effects on Achilles tendon repair. The benefits might be related to the generation of ROS in the PTB process. These findings indicated that the combination of PTB and UCNPs@RB/Chitosan/β-GP hydrogel could be used as a noninvasive photochemical sealing for Achilles tendon rupture.

Photo-oxidation of lysozyme triggered by riboflavin is O2-dependent, occurs via mixed type 1 and type 2 pathways, and results in inactivation, site-specific damage and intra- and inter-molecular crosslinks

Photosensitized protein oxidation is a promising tool for medical procedures such as photochemical tissue bonding (PTB). We have recently reported that the binding of rose Bengal, a sensitizer employed in PTB, to lysozyme modulates the photooxidation and crosslinking of this protein. In this work we examined the photooxidation and crosslinking of lysozyme mediated by riboflavin (RF) an endogenous sensitizer also employed in PTB. We hypothesized that since RF does not bind strongly to proteins, the mechanism(s) and extent of enzymatic inactivation, amino acid modification and protein crosslinking would be dependent on the presence of O2, and differ to that induced by rose Bengal. This hypothesis was tested using UV–visible spectrophotometry, isothermal titration calorimetry (ITC), SDS-PAGE gels, quantification of amino acid consumption, and LC-MS analysis of sites of modification and crosslinks. Under N2, limited damage was detected arising from type 1 (radical) chemistry with formation of specific intra- (Tyr20-Tyr23) and inter- (Tyr23-Trp108) molecular crosslinks. In contrast, the presence of O2 triggered extensive protein damage through mixed type 1 and type 2 (1O2) mechanisms leading to Trp, Met, Tyr and His oxidation, loss of enzymatic activity and protein dimerization. LC-MS analysis provided evidence for crosslinking via radical-radical recombination reactions (Trp28-Tyr53), and secondary reactions involving nucleophilic attack of the side-chain amine of Lys116 on carbonyl groups. Overall, this behavior is in marked contrast to that detected with rose Bengal indicating that the mechanisms and sites of photo-oxidative damage, and consequences for protein function, can be modulated by the choice of sensitizing dye.

Porous chitosan adhesives with L-DOPA for enhanced photochemical tissue bonding

L-3,4-dihydroxyphenylalanine (L-DOPA) is a naturally occurring catechol that is known to increase the adhesive strength of various materials used for tissue repair. With the aim of fortifying a porous and erodible chitosan-based adhesive film, L-DOPA was incorporated in its fabrication for stronger photochemical tissue bonding (PTB), a repair technique that uses light and a photosensitiser to promote tissue adhesion. The results showed that L-DOPA did indeed increase the tissue bonding strength of the films when photoactivated by a green LED, with a maximum strength recorded of approximately 30 kPa, 1.4 times higher than in its absence. The addition of L-DOPA also did not appreciably change the swelling, mechanical and erodible properties of the film. This study showed that strong, porous and erodible adhesive films for PTB made from biocompatible materials can be obtained through a simple inclusion of a natural additive such as L-DOPA, which was simply mixed with chitosan without any chemical modifications. In vitro studies using human fibroblasts showed no negative effect on cell proliferation indicating that these films are biocompatible. The films are convenient for various surgical applications as they can provide strong tissue support and a microporous environment for cellular infusion without the use of sutures. Statement of significanceTissue adhesives are not as strong as sutures on wounds under stress. Our group has previously demonstrated that strong sutureless tissue repair can be realised with chitosan-based adhesive films that photochemically bond to tissue when irradiated with green light. The advantage of this technique is that films are easier to handle than glues and sutures, and their crosslinking reactions can be controlled with light. However, these films are not optimal for high-tension tissue regenerative applications because of their non-porous structure, which cannot facilitate cell and nutrient exchange at the wound site. The present study resolves this issue, as we obtained a strong and porous photoactivated chitosan-based adhesive film, by simply using freeze drying and adding L-DOPA.

Abstract 14: Large Gap Peripheral Nerve Repair in a Non-Human Primate Model: Improving Outcomes Utilizing Photochemical Tissue Bonding (PTB) with Acellular Nerve Allograft (ANA)

PURPOSE: Segmental peripheral nerve deficits are challenging injuries associated with poor outcomes. While these injuries afflict civilians (e.g. Boston Marathon Bombing), they have become increasingly prevalent in combat trauma since the advent of improvised explosive devices. Standard of care large-gap (>3cm) reconstruction requires nerve autograft. Alternatives are sought in clinical scenarios where donor limb is not available (e.g. multiple extremity trauma) or donor site morbidity (e.g. painful neuroma formation, loss of function) makes autograft use suboptimal. A variety of alternatives have been proposed including allografts and conduits. Photochemical tissue bonding (PTB) as an alternative to traditional suture neurorrhaphy has been extensively studied in the rodent sciatic nerve model. PTB carries several advantages: reduction of needle trauma, prevention of axonal escape, and a water-tight seal to contain neuroregenerative factors and exclude inflammatory invasion. We report a non-human primate study which recapitulates human anatomy, allows for objective quantitative functional outcomes testing, electrophysiology and histomorphometry. The purpose of this study is to evaluate whether PTB can elevate the performance of acellular nerve allograft (ANA) to that of standard of care autograft/suture. METHODS: Nineteen rhesus macaques underwent 4cm proximal radial nerve defect creation in the right upper extremity, the radial nerve transected proximally at the humeral spiral groove, distally prior to the branch to brachioradialis. The radial nerve was selected as it is responsible for an isolated function with no input from other nerves. Three repair techniques were evaluated: n=6 autograft/suture, n=6 ANA/suture, n=7 ANA photosealed in place with light-activated human amnion wraps (PTB). An objective functional outcome test was conceived using an apparatus that accurately measured the degree of wrist extension as a function of time after surgery. Electromyography (EMG) was performed at 0, 120, 240, and 365 days (euthanasia). Histomorphometry and muscle mass retention were analyzed at euthanasia. RESULTS: Average loss of wrist extension was 88.3 ± 8.2° after radial nerve defect creation. Autograft group animals recovered 82.0° of extension by 7 months. Wrist extension recovery was modestly slower, as expected, in the ANA groups, however, by 8 months the ANA/PTB group recovered 63.0° of extension with no difference in recovery of baseline EMG amplitude as compared to controls (Avance/PTB=75.81% vs. autograft/suture=65.06%). If recovery follows current trajectory, we expect ANA/PTB to demonstrate equivalent outcomes to the autograft/suture group at one year. CONCLUSION: This radial nerve defect model improves upon existing animal models by allowing for large nerve gap testing in a primate model more analogous to the clinical large nerve gap injury in humans. ANA/PTB group functional recovery lagged modestly behind autograft/suture (by as long as 8 weeks) but is approaching equivalence at 8 months. EMG recovery is similar at 8 months. This preliminary data confirms PTB as a promising technique to improve outcomes of large nerve gap reconstruction in combination with autograft (previously demonstrated) and with acellular nerve allograft.

Photochemical Tissue Bonding Technique for Improving Healing of Hand Tendon Injury

We utilized a novel approach of combined photochemical tissue bonding (PTB) and human amniotic membrane (HAM) to improve hand tendon repair and also evaluated its efficacy. Subei chickens underwent surgical transection of the flexor digitorum profundus tendons and repair by (1) SR (standard Kessler suture; n = 24; 6-0 prolene) and (2) HAM/PTB (n = 24), where a section of HAM was stained with 0.1% Rose Bengal, wrapped around the ruptured tendon and bonded with 532 nm light (0.5 W/cm2, 200 J/cm2). Total active motion, gross appearance, extent of adhesion formation, biochemical properties, and inflammatory cells of the repaired tendon were evaluated on days 3, 7, 14, and 28 postoperatively. PTB strongly bonded HAM with flexor digitorum profundus tendon surface. No significant difference was observed between the tensile properties of either group on all postoperative time points. The joint activities and the adhesion formation levels were significantly better in the HAM/PTB group compared with those in the SR group on day 14. Histological examination revealed drastically reduced number of inflammatory cells in the HAM/PTB group than in the SR group on days 7 and 14 after surgery. These findings revealed that PTB sealing of HAM around the tendon repair site provided considerable benefits for hand tendon repair by eliminating technical difficulties and obvious contraindications. Thus, this novel procedure has considerable benefits in repairing hand tendon damage.

Photochemical tissue bonding promotes the proliferation and migration of injured tenocytes through ROS/RhoA/NF‐κB/Dynamin 2 signaling pathway

Photochemical tissue bonding (PTB) has been found to promote the healing of Achilles tendon tissue injury and to reduce postoperative complications. However, the underlying cellular and molecular mechanisms are not clear. In this study, the cell proliferation, ROS generation, migration and the protein expression of DNM2, NF-κB p65, TGF-β1 and VEGF in tenocytes after PTB treatment were measured by CCK-8, flow cytometry, Transwell and western blot assay, respectively. And those in tenocytes after DNM2 silencing or overexpressing or treatment with inhibitors of NF-κB, ROS and RhoA were also measured. Our results showed that 10 mW PTB treatment for 80 and 120 s significantly increased cell proliferation and increased ROS generation in tenocytes. 10 mW PTB treatment for 40 and 80 s significantly activated RhoA and increased the protein expression of DNM2, NF-κB p65, TGF-β1 and VEGF, but 10 mW PTB treatment for 120 s decreased the protein expression of those. DNM2 silencing significantly suppressed cell migration and the expression of DNM2, TGF-β1, and VEGF in tenocytes after PTB treatment (10 mW, 80 s), which was inhibited by DNM2 overexpression. Individual treatment with inhibitor of NF-κB, ROS, and RhoA in tenocytes showed decreased protein expression of DNM2, TGF-β1, and VEGF. Moreover, in vivo experiment found that PTB treatment significantly inhibited cell apoptosis and the expression of DNM2, NF-κB p65, RhoA, TGF-β1, and VEGF in a time-dependent manner. Taken together, our results suggest that PTB promotes the proliferation and migration of injured tenocytes through ROS/RhoA/NF-κB/DNM2 signaling pathway.

An intraluminal stent facilitates light-activated vascular anastomosis.

Photochemical tissue bonding (PTB) is a sutureless, light-activated technique that produces a watertight, microvascular repair with minimal inflammation compared to standard microsurgery. However, it is practically limited by the need for a clinically viable luminal support system. The aim of this study was to evaluate a hollow biocompatible stent to provide adequate luminal support to facilitate vascular anastomosis using the PTB technique. Forty rats underwent unilateral femoral artery transection. Five rats were used to optimize the stent delivery method, and the remaining 35 rats were randomized into three groups: (1) standard suture repair with 10-0 nylon microsuture (SR), (2) standard suture repair over the stent (SR + S), or (3) PTB repair over stent (PTB + S). For the PTB group, a 2-mm overlapping cuff was painted with 0.1% (wt/vol) Rose Bengal then illuminated for 30 seconds on each side (532 nm, 0.5 W/cm, 30 J/cm). Anastomotic leak and vessel patency (immediate, 1 hour, and 1 week postoperatively) were assessed. Vessels in all three groups were patent immediately and at 1 hour postoperatively. After 1 week, all animals displayed patency in the SR group, while only 5 of 14 and 2 of 8 surviving animals had patent vessels in the PTB + S and SR + S groups, respectively. This study demonstrated successful use of an intraluminal stent for acute microvascular anastomosis using the PTB technique. However, the longer-term presence of the stent at the anastomotic site led to thrombosis in multiple cases. A rapidly dissolvable stent should facilitate a light-activated microvascular anastomosis with excellent long-term patency.

From Bench to Bedside: No Need to be Nervous About Microsuturing?

Peripheral nerve injuries, whether sustained through avulsive neurotmesis, sharp or projectile penetrating mechanisms, or iatrogenic injury, can be devastating. Ignoring for a moment the miraculous physiologic complexities of our muscular and skeletal symptoms, individual muscles and bones are, quite frankly, “dumb,” providing a specific and limited set of mechanical functions. Peripheral nerves, on the other hand, are dizzyingly complex—carrying critical afferent and efferent information along a living system of electrical circuits that we take for granted during any activity we do, and even during our periods of inactivity. Despite the perceived predilection to injury, our nerves are quite robust—the majority of nerve tissue being biological insulation in the form of myelin sheaths and vascularized connective tissue that supports and nourishes our nerves, allowing them to glide within our limbs so that we don't cause a nerve palsy during strenuous or contorted activities. Historically, the prognosis for complete nerve injuries (either internal or external transections) has not been spectacular. Yes, direct repairs can sometimes restore nerve function rather dramatically, particularly for distal injuries in younger patients. However, proximal injuries, in mixed motor and sensory nerves, and/or involving “critical-sized” defects of 4 cm to 7 cm or longer, continue to be challenging, and the prognosis remains poor for most patients who experience these injuries. Numerous advances in the last two decades have finally started to “move the needle” and improve the prognosis for the surgical management of peripheral nerve injuries. Viable off-the-shelf surgical conduits for short-segment gaps (or for overwrapping repair sites to limit scarring and axonal escape) have become widely available, and offer results comparable to direct repair for short-segment deficits, particularly for sensory nerves [4, 6]. Perhaps better still, decellularized human allograft nerve grafts (Avance, AxoGen, Inc, Alachua, FL, USA) have demonstrated meaningful sensory and motor recovery (M4-M5, representing near-normal to normal strength against resistance), potentially equivalent to autograft (or even direct repair [10]) without donor site limitations or morbidity, for defects as long as 5 cm [1, 6, 7]. Investigators have focused with renewed enthusiasm on the immunosuppressant FK506 (tacrolimus) based on better-than expected neurologic recovery in patients undergoing whole-hand transplants [2]. Tacrolimus appears to enhance nerve regeneration through a noncalcineurin dependent pathway, and has been studied intermittently for decades for this purpose [12, 13]. Perhaps most exciting, we may finally be approaching the event horizon of the era of sutureless (or minimal-suture) nerve repair. Why the need for minimal suture nerve repair? Microsuturing of nerves is fraught with difficulty, and can result in undesired complications such as scarring, fascicle ligation by the suture, or gapping and axonal escape resulting in a neuroma in continuity, particularly when not augmented with a nerve conduit, vein graft, or similar envelope. An alternative approach like fibrin glue has demonstrated equivalent or superior results to suture repair in numerous animal studies and one human study [11], but concerns about lack of tensile strength and secondary nerve gapping persist [11]. Beyond fibrin glue, we have seen poly(ethylene glycol [PEG]) hydrogel improve resistance to gapping, show equivalence to suture, and demonstrate better results than fibrin sealant [8]. The use of photochemical tissue bonding (PTB) represents an even-more-promising technique using a nonthermal, Nd/YAG laser, nonimmunogenic amnion-derived wrap, and a photoactive dye. Animal studies [5, 9] suggest improved electrophysiological outcomes, histologic recovery, and even gait compared to direct suture repair. A more-recent study [3] created a 15 mm defect in rat sciatic nerves and repaired the defect with reversed isografts. PTB repairs outperformed suture repair for both immediate and delayed (30 days) reconstruction with regard to muscle mass retention and histomorphometric recovery [3]. Animal studies of escalating complexity continue to be performed for this technique, with the hope of human trials commencing shortly. Other interventions to improve nerve repair and reconstruction outcomes are being investigated, as well, and those mentioned above are by no means an exhaustive list. It also seems likely that no single modality will lead us to the holy grail of normal (or nearly normal) function following proximal or long-segment peripheral nerve injury. Perhaps most importantly, many of these newer techniques can be used concurrently and may ultimately prove complimentary. For example, one can imagine using PTB with allografts, reinforced with fibrin or PEG hydrogel glue, in a patient treated with low-dose tacrolimus postoperatively to improve overall recovery. Ultimately, we need to ask ourselves “if this injury happened to me, could I still be an orthopaedic surgeon?” Until the answer is yes, we need to keep pushing the clinical and translational research envelope. But someday soon, stitching up a nerve repair or reconstruction may not require a stitch at all.

A light-activated amnion wrap strengthens colonic anastomosis and reduces peri-anastomotic adhesions.

Colonic anastomotic failure is a dreaded complication, and multiple surgical techniques have failed to eliminate it. Photochemical tissue bonding (PTB) is a method of sealing tissue surfaces by light-activated crosslinking. We evaluated if a human amniotic membrane (HAM), sealed over the anastomotic line by PTB, increases the anastomotic strength. Sprague-Dawley rats underwent midline laparotomy followed by surgical transection of the left colon. Animals were randomized to colonic anastomosis by one of the following methods (20 per group): single-layer continuous circumferential suture repair (SR); SR with a HAM wrap attached by suture (SR+ HAM-S); SR with HAM bonded photochemically over the anastomotic site using 532 nm light (SR+ HAM-PTB); approximation of the bowel ends with only three sutures and sealing with HAM-PTB (3+ HAM-PTB). A control group underwent laparotomy alone with no colon resection (NR). Sub-groups (n = 10) were sacrificed at days 3 and 7 post-operatively and adhesions were evaluated. A 6 cm section of colon was then removed and strength of anastomosis evaluated by burst pressure (BP) measurement. A fourfold increase in BP was observed in the SR+ HAM-PTB group compared to suture repair alone (94 ± 3 vs. 25 ± 8 mm Hg, P < 0.0001) at day 3. At day 7 the burst pressures were 165 ± 40 and 145 ± 31 mm Hg (P = 1), respectively. A significant decrease in peri-anastomotic adhesions was observed in the SR+ HAM-PTB group compared to the SR group at both time points (P < 0.001). Sealing sutured colonic anastomotic lines with HAM-PTB increases the early strength of the repair and reduces peri-anastomotic adhesions. Lasers Surg. Med. 48:530-537, 2016. © 2016 Wiley Periodicals, Inc.

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.

Bioabsorbable polymer optical waveguides for deep-tissue photomedicine.

Advances in photonics have stimulated significant progress in medicine, with many techniques now in routine clinical use. However, the finite depth of light penetration in tissue is a serious constraint to clinical utility. Here we show implantable light-delivery devices made of bio-derived or biocompatible, and biodegradable polymers. In contrast to conventional optical fibres, which must be removed from the body soon after use, the biodegradable and biocompatible waveguides may be used for long-term light delivery and need not be removed as they are gradually resorbed by the tissue. As proof of concept, we demonstrate this paradigm-shifting approach for photochemical tissue bonding (PTB). Using comb-shaped planar waveguides, we achieve a full thickness (>10 mm) wound closure of porcine skin, which represents ∼10-fold extension of the tissue area achieved with conventional PTB. The results point to a new direction in photomedicine for using light in deep tissues.

The safety of photochemical tissue bonding for treating damaged corneal epithelium using limbal stem cells pre-cultured on human amniotic membrane

We previously demonstrated the feasibility of treating limbal stem cell deficiency (LSCD) with limbal stem cells (LSCs) pre-cultured on human amniotic membrane (HAM), using a suture-free technique called photochemical tissue bonding (PTB). However, important issues regarding the safety and the influence of PTB on LSCs have not been elucidated. In this study, LSCs, isolated from rabbit eyes and identified by cell markers, were labeled with BrdU prior to cultivation on de-epithelialized HAM to fabricate grafts. Rabbit LSCD models were created and randomly divided into groups for transplantation of fabricated grafts using sutures or PTB (n=10). Possible phototoxicity of PTB to LSCs was analyzed in vitro and in vivo. Restoration of corneal epithelium was evaluated at 28days after grafting. Our results showed that phototoxicity did not occur in the LSCs cultured on HAM after PTB in vitro. Transplantation of grafts with PTB restored the damaged cornea epithelium effectively and no significant influences on LSC characteristics were found in both sutured and PTB groups. BrdU positive cells were tracked at 28days post grafting suggesting that the restored epithelium was derived from the in vitro fabricated HAM/LSC graft. These data suggest that PTB is a safe and potential strategy for securing LSC/HAM grafts that produces with better outcomes than sutured attachment.

Improving outcome following large deficit peripheral nerve injury: The application of a human amnion nerve wrap and photochemical tissue bonding (PTB)

Improving outcome following large deficit peripheral nerve injury: The application of a human amnion nerve wrap and photochemical tissue bonding (PTB)

Outcomes comparisons between civilian and military trauma patients undergoing limb salvage

INTRODUCTION: Microvascular repair with suture is pro-thrombotic and inflammatory in nature, especially in vessels measuring <2mm in diameter. Photochemical tissue bonding (PTB) is a technique that crosslinks collagen to create an immediate watertight bond with minimal inflammation. We hypothesize that use of PTB with a biocompatible intraluminal stent will result in a rapid microvascular seal with minimal endothelial inflammation.

Long term recovery of median nerve repair using laser‐activated chitosan adhesive films

Sutures remain the standard peripheral nerve repair technique, whether applied directly or indirectly to nerve tissue. Unfortunately, significant postoperative complications can result, such as inflammation, neuroma formation and foreign body reactions. Photochemical-tissue-bonding (PTB) using rose Bengal (RB) integrated into a chitosan bioadhesive is an alternative nerve repair device that removes the need for sutures. Rats were arranged into three groups: RB-chitosan adhesives-repair, end-to-end epineural suture-repair (surgical standard) and sham laser-irradiated control. Groups were compared through histological assessment, electrophysiological recordings and grip motor strength. RB-chitosan adhesive repaired nerves displayed comparable results when compared to the standard suture-repair based on histological and electrophysiological findings. Functionally, RB-chitosan adhesive was associated with a quicker and more pronounced recovery of grip force when compared to the suture-repair.