Photochemical Tissue Bonding: A Promising Technique for Peripheral Nerve Repair

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

BACKGROUND

 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.

METHODS

 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.

RESULTS

 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%.

CONCLUSION

 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.

Advancements and applications of upconversion nanoparticles in wound dressings

Wound healing is a complex process that requires effective management to prevent infections and promote efficient tissue regeneration. In recent years, upconversion nanoparticles (UCNPs) have emerged as promising materials for wound dressing applications due to their unique optical properties and potential therapeutic functionalities. These nanoparticles possess enhanced antibacterial properties when functionalized with antibacterial agents, helping to prevent infections, a common complication in wound healing. They can serve as carriers for controlled drug delivery, enabling targeted release of therapeutic agents to the wound site, allowing for tailored treatment and optimal healing conditions. These nanoparticles possess the ability to convert near-infrared (NIR) light into the visible and/or ultraviolet (UV) regions, making them suitable for therapeutic (photothermal therapy and photodynamic therapy) and diagnostic applications. In the context of wound healing, these nanoparticles can be combined with other materials such as hydrogels, fibers, metal-organic frameworks (MOFs), graphene oxide, etc., to enhance the healing process and prevent the growth of microbial infections. Notably, UCNPs can act as sensors for real-time monitoring of the wound healing progress, providing valuable feedback to healthcare professionals. Despite their potential, the use of UCNPs in wound dressing applications faces several challenges. Ensuring the stability and biocompatibility of UCNPs under physiological conditions is crucial for their effective integration into dressings. Comprehensive safety and efficacy evaluations are necessary to understand potential risks and optimize UCNP-based dressings. Scalability and cost-effectiveness of UCNP synthesis and manufacturing processes are important considerations for practical applications. In addition, efficient incorporation of UCNPs into dressings, achieving uniform distribution, poses an important challenge that needs to be addressed. Future research should prioritize addressing concerns regarding stability and biocompatibility, efficient integration into dressings, rigorous safety evaluation, scalability, and cost-effectiveness. The purpose of this review is to critically evaluate the advantages, challenges, and key properties of UCNPs in wound dressing applications to provide insights into their potential as innovative solutions for enhancing wound healing outcomes. We have provided a detailed description of various types of smart wound dressings, focusing on the synthesis and biomedical applications of UCNPs, specifically their utilization in different types of wound dressings.

Photosealing of dural defects using a biocompatible patch

PURPOSE

Photosealing of many biological tissues can be achieved using a biocompatible material in combination with a dye that is activated by visible light to chemically bond over the tissue defect via protein cross-linking reactions. The aim of this study was to test the efficacy of photosealing using a commercially available biomembrane (AmnioExcel Plus) to securely close dural defects in comparison to another sutureless method (fibrin glue) in terms of repair strength.

METHODS

Two-millimeter diameter holes were created in dura harvested from New Zealand white rabbits and repaired ex vivo using one of two methods: (1) in n = 10 samples, photosealing was used to bond a 6-mm-diameter AmnioExcel Plus patch over the dural defect, and (2) in n = 10 samples, fibrin glue was used to attach the same patch over the dural defect. Repaired dura samples were then subjected to burst pressure testing. Histological analysis was also performed of photosealed dura.

RESULTS

The mean burst pressures of rabbit dura repaired with photosealing and fibrin glue were 302 ± 149 mmHg and 26 ± 24 mmHg, respectively. The increased repair strength using photosealing was statistically significant and considerably higher than the normal intracranial pressure of ~ 20 mmHg. Histology demonstrated a tight union at the interface between the dura surface and patch with no disruption of the dura structure.

CONCLUSION

The results of this study suggest that photosealing performs better than fibrin glue for the fixation of a patch for ex vivo repair of small dural defects. Photosealing is worthy of testing in pre-clinical models for the repair of dural defects.

Upconversion nanomaterials and delivery systems for smart photonic medicines and healthcare devices

In the past decade, upconversion (UC) nanomaterials have been extensively investigated for the applications to photomedicines with their unique features including biocompatibility, near-infrared (NIR) to visible conversion, photostability, controllable emission bands, and facile multi-functionality. These characteristics of UC nanomaterials enable versatile light delivery for deep tissue biophotonic applications. Among various stimuli-responsive delivery systems, the light-responsive delivery process has been greatly advantageous to develop spatiotemporally controllable on-demand "smart" photonic medicines. UC nanomaterials are classified largely to two groups depending on the photon UC pathway and compositions: inorganic lanthanide-doped UC nanoparticles and organic triplet-triplet annihilation UC (TTA-UC) nanomaterials. Here, we review the current-state-of-art inorganic and organic UC nanomaterials for photo-medicinal applications including photothermal therapy (PTT), photodynamic therapy (PDT), photo-triggered chemo and gene therapy, multimodal immunotherapy, NIR mediated neuromodulations, and photochemical tissue bonding (PTB). We also discuss the future research direction of this field and the challenges for further clinical development.

Self-Organization Dynamics of Collagen-like Peptides Crosslinking Is Driven by Rose-Bengal-Mediated Electrostatic Bridges

The present work focuses on the computational study of the structural micro-organization of hydrogels based on collagen-like peptides (CLPs) in complex with Rose Bengal (RB). In previous studies, these hydrogels computationally and experimentally demonstrated that when RB was activated by green light, it could generate forms of stable crosslinked structures capable of regenerating biological tissues such as the skin and cornea. Here, we focus on the structural and atomic interactions of two collagen-like peptides (collagen-like peptide I (CLPI), and collagen-like peptide II, (CLPII)) in the presence and absence of RB, highlighting the acquired three-dimensional organization and going deep into the stabilization effect caused by the dye. Our results suggest that the dye could generate a ternary ground-state complex between collagen-like peptide fibers, specifically with positively charged amino acids (Lys in CLPI and Arg in CLPII), thus stabilizing ordered three-dimensional structures. The discoveries generated in this study provide the structural and atomic bases for the subsequent rational development of new synthetic peptides with improved characteristics for applications in the regeneration of biological tissues during photochemical tissue bonding therapies.

A Photosealed Cap Prevents Disorganized Axonal Regeneration and Neuroma following Nerve Transection in Rats

Neuroma is a common sequela of traumatic peripheral nerve injury that can result in pain and decreased quality of life for patients. Neuromas result from axonal outgrowth in an attempt to reestablish continuity with the disrupted distal nerve end. Photosealing is a light-activated technique whereby tissues can be securely isolated in a strong and secure manner. This study investigated whether photosealing of autologous vein and crosslinked human amniotic membrane (xHAM) to cap the proximal stump of transected sciatic nerve would prevent disorganized axonal regeneration and neuroma in a rat model.

Light-activated photosealing with human amniotic membrane strengthens bowel anastomosis in a hypotensive, trauma-relevant swine model

BACKGROUND

Gastrointestinal anastomotic leakage is a dreaded complication despite advancements in surgical technique. Photochemical tissue bonding (PTB) is a method of sealing tissue surfaces utilizing photoactive dye. We evaluated if crosslinked human amniotic membrane (xHAM) photosealed over the enteroenterostomy would augment anastomotic strength in a trauma-relevant swine hemorrhagic shock model.

METHODS

Yorkshire swine (40-45 kg, n = 14) underwent midline laparotomy and sharp transection of the small intestine 120 cm proximal to the ileocecal fold. Immediately following intestinal transection, a controlled arterial bleed was performed to reach hemorrhagic shock. Intestinal repair was performed after 60 minutes and autotransfusion of the withdrawn blood was performed for resuscitation. Animals were randomized to small intestinal anastomosis by one of the following methods (seven per group): suture repair (SR), or SR with PTB augmentation. Animals were euthanized at postoperative Day 28 and burst pressure (BP) strength testing was performed on all excised specimens.

RESULTS

Mean BP for SR, PTB, and native tissue groups were 229 ± 40, 282 ± 21, and 282 ± 47 mmHg, respectively, with the SR group statistically significantly different on analysis of variance (p = 0.02). Post-hoc Tukey all-pairs comparison demonstrated a statistically significant difference in burst pressure strength between the SR only and the PTB group (p = 0.04). All specimens in SR group ruptured at the anastomosis upon burst pressure testing, while all specimens in the PTB group ruptured at least 2.5 cm from the anastomosis.

CONCLUSION

Photosealing with xHAM significantly augments the strength of small intestinal anastomosis performed in a trauma porcine model.

Lanthanide-Doped Nanoparticles for Near-Infrared Light Activation of Photopolymerization: Fundamentals, Optimization and Applications

Photopolymerization refers to a type of polymerization process in which light is utilized as excitation source to initiate polymerization of monomers and oligomers. Despite great progress, photopolymerization is typically induced by ultraviolet or visible light, which still greatly restrains its applications. Upconversion nanoparticles (UCNPs) represent a class of optical nanomaterials that are able to convert low-energy near-infrared (NIR) light into high-energy ultraviolet (or visible light) emissions. In this context, UCNP-assisted photopolymerization has recently attracted extensive attentions due to its unique advantages. In this account, recent advances in the fundamentals, optimization and emerging applications of UCNP-based photopolymerization are reviewed. Fundamental theories of upconversion luminescence and photopolymerization will be introduced first. Various optimization approaches to improve UCNP-assisted photopolymerization are then summarized, followed by diverse emerging applications. Challenges and future perspectives in this area will be provided as a conclusion.

Negative Pressure Neurogenesis: A Novel Approach to Accelerate Nerve Regeneration after Complete Peripheral Nerve Transection

Various modalities to facilitate nerve regeneration have been described in the literature with limited success. We hypothesized that negative pressure applied to a sectioned peripheral nerve would enhance nerve regeneration by promoting angiogenesis and axonal lengthening.

METHODS

Wistar rats' sciatic nerves were cut (creating ~7 mm nerve gap) and placed into a silicone T-tube, to which negative pressure was applied. The rats were divided into 4 groups: control (no pressure), group A (low pressure: 10 mm Hg), group B (medium pressure: 20/30 mm Hg) and group C (high pressure: 50/70 mm Hg). The nerve segments were retrieved after 7 days for gross and histological analysis.

RESULTS

In total, 22 rats completed the study. The control group showed insignificant nerve growth, whereas the 3 negative pressure groups showed nerve growth and nerve gap reduction. The true nerve growth was highest in group A (median: 3.54 mm) compared to group B, C, and control (medians: 1.19 mm, 1.3 mm, and 0.35 mm); however, only group A was found to be significantly different to the control group (**P < 0.01). Similarly, angiogenesis was observed to be significantly greater in group A (**P < 0.01) in comparison to the control.

CONCLUSIONS

Negative pressure stimulated nerve lengthening and angiogenesis within an in vivo rat model. Low negative pressure (10 mm Hg) provided superior results over the higher negative pressure groups and the control, favoring axonal growth. Further studies are required with greater number of rats and longer recovery time to assess the functional outcome.

Influence of Rose Bengal Dimerization on Photosensitization

Protein crosslinking photosensitized by rose Bengal (RB^2- ) has multiple medical applications and understanding the photosensitization mechanism can improve treatment effectiveness. To this end, we investigated the photochemical efficiencies of monomeric RB^2- (RB_M ^2- ) and dimeric RB^2- (RB_D ^2- ) and the optimal pH for anaerobic RB^2- photosensitization in cornea. Absorption spectra and dynamic light scattering (DLS) measurements were used to estimate the fractions of RB_M ^2- and RB_D ^2- . RB^2- self-photosensitized bleaching was used to evaluate the photoactivity of RB_M ^2- and RB_D ^2- . The pH dependence of anaerobic RB^2- photosensitization was evaluated in ex vivo rabbit corneas. The 549 nm/515 nm absorption ratio indicated that concentrations > 0.10 mm RB contained RB_D ^2- . Results from DLS gave estimated mean diameters for RB_M ^2- and RB_D ^2- of 0.70 ± 0.02 nm and 1.75 ± 0.13 nm, respectively, and indicated that 1 mm RB^2- contained equal fractions of RB_M ^2- and RB_D ^2- . Quantum yields for RB^2- bleaching were not influenced by RB_D ^2- in RB^2- solutions although accounting for RB^2- concentration effects on the reaction kinetics demonstrated that RB_D ^2- is not a photosensitizer. Optimal anaerobic photosensitization occurred at pH 8.5 for solutions containing 200 mm Arg. These results suggest potential approaches to optimizing RB_M ^2- -photosensitized protein crosslinking in tissues.

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.

Laryngeal adductor function following potassium titanyl phosphate laser welding of the recurrent laryngeal nerve

OBJECTIVES/HYPOTHESIS

Recurrent laryngeal nerve (RLN) transection injuries may occur during thyroidectomy and other surgical procedures. Laser nerve welding has been shown to cause less technique-related axonal damage than the traditional suture method. We compared functional adductor results using these two methods of RLN repair.

STUDY DESIGN

Animal model.

METHODS

Canine hemilarynges underwent pretreatment testing of laryngeal adductor function, followed by RLN transection and repair using potassium titanyl phosphate (KTP) laser welding (n = 8) or microneural suture (n = 16) techniques. Six months later, adductor function was measured again and expressed as a proportion of the pretreatment value.

RESULTS

The mean laryngeal adductor pressure ratios were 82.4% (95% confidence interval [CI]: 72.8%-92.0%) for the laser repair group and 55.5% (95% CI: 49.4%-61.6%) for the suture control group, with a difference of 26.9% (95% CI: 15.3%-38.5%). Both spontaneous and stimulated glottic closure was observed in the laser welding and microsuture repair groups.

CONCLUSIONS

Laser nerve welding resulted in greater strength of adduction than suture repair of an acutely transected RLN. Suture anastomosis may traumatize more axons than the laser. Stronger vocal fold adduction is associated clinically with better protection from aspiration and improved voice outcomes. KTP laser welding should be considered for anastomosis of the RLN and other nerves.

LEVEL OF EVIDENCE

NA Laryngoscope, 130:1764-1769, 2020.

Nanotransducers for Near-Infrared Photoregulation in Biomedicine

Photoregulation, which utilizes light to remotely control biological events, provides a precise way to decipher biology and innovate in medicine; however, its potential is limited by the shallow tissue penetration and/or phototoxicity of ultraviolet (UV)/visible light that are required to match the optical responses of endogenous photosensitive substances. Thereby, biologically friendly near-infrared (NIR) light with improved tissue penetration is desired for photoregulation. Since there are a few endogenous biomolecules absorbing or emitting light in the NIR region, the development of molecular transducers is essential to convert NIR light into the cues for regulation of biological events. In this regard, optical nanomaterials able to convert NIR light into UV/visible light, heat, or free radicals are suitable for this task. Here, the recent developments of optical nanotransducers for NIR-light-mediated photoregulation in medicine are summarized. The emerging applications, including photoregulation of neural activity, gene expression, and visual systems, as well as photochemical tissue bonding, are highlighted, along with the design principles of nanotransducers. Moreover, the current challenges and perspectives in this field are discussed.

Photochemical Tissue Bonding Technique for Improving Healing of Hand Tendon Injury

PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Photocrosslinkable Gelatin/Tropoelastin Hydrogel Adhesives for Peripheral Nerve Repair

Suturing peripheral nerve transections is the predominant therapeutic strategy for nerve repair. However, the use of sutures leads to scar tissue formation, hinders nerve regeneration, and prevents functional recovery. Fibrin-based adhesives have been widely used for nerve reconstruction, but their limited adhesive and mechanical strength and inability to promote nerve regeneration hamper their utility as a stand-alone intervention. To overcome these challenges, we engineered composite hydrogels that are neurosupportive and possess strong tissue adhesion. These composites were synthesized by photocrosslinking two naturally derived polymers, gelatin-methacryloyl (GelMA) and methacryloyl-substituted tropoelastin (MeTro). The engineered materials exhibited tunable mechanical properties by varying the GelMA/MeTro ratio. In addition, GelMA/MeTro hydrogels exhibited 15-fold higher adhesive strength to nerve tissue ex vivo compared to fibrin control. Furthermore, the composites were shown to support Schwann cell (SC) viability and proliferation, as well as neurite extension and glial cell participation in vitro, which are essential cellular components for nerve regeneration. Finally, subcutaneously implanted GelMA/MeTro hydrogels exhibited slower degradation in vivo compared with pure GelMA, indicating its potential to support the growth of slowly regenerating nerves. Thus, GelMA/MeTro composites may be used as clinically relevant biomaterials to regenerate nerves and reduce the need for microsurgical suturing during nerve reconstruction.

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.

Semitransparent bandages based on chitosan and extracellular matrix for photochemical tissue bonding

BACKGROUND

Extracellular matrices (ECMs) are often used in reconstructive surgery to enhance tissue regeneration and remodeling. Sutures and staples are currently used to fix ECMs to tissue although they can be invasive devices. Other sutureless and less invasive techniques, such as photochemical tissue bonding, cannot be coupled to ECMs because of their intrinsic opacity to light.

RESULTS

We succeeded in fabricating a biocompatible and adhesive device that is based on ovine forestomach matrix (OFM) and a chitosan adhesive. The natural opacity of the OFM has been overcome by adding the adhesive into the matrix that allows for the light to effectively penetrate through it. The OFM-chitosan device is semitransparent (attenuation length ~ 106 µm) and can be photoactivated by green light to bond to tissue. This device does not require sutures or staples and guarantees a bonding strength of ~ 23 kPa.

CONCLUSIONS

A new semitransparent and biocompatible bandage has been successfully fabricated and characterized for sutureless tissue bonding.

Upconversion Nanoparticles/Hyaluronate-Rose Bengal Conjugate Complex for Noninvasive Photochemical Tissue Bonding

The recent progress in photonic nanomaterials has contributed greatly to the development of photomedicines. However, the finite depth of light penetration is still a serious limitation, constraining their clinical applications. Here, we developed a poly(allylamine) (PAAm)-modified upconversion nanoparticle/hyaluronate-rose bengal (UCNP/PAAm/HA-RB) conjugate complex for photochemical bonding of deep tissue with near-infrared (NIR) light illumination. Compared to the conventional invasive treatment via suturing and stapling, the UCNP/PAAm/HA-RB conjugate complex could be noninvasively delivered into the deep tissue and accelerate the tissue bonding upon NIR light illumination. HA in the outer layer of the complex facilitated the penetration of RB into the collagen layer of the dermis. The NIR light triggered UCNP of NaYF₄: Yb/Er (Y:Yb:Er = 78:20:2) in the complex to illuminate visible green light under the skin tissue. The activated RB in the HA-RB conjugate by the green light induced radical formation for the cross-linking of incised collagen matrix. An in vitro light propagation test and collagen fibrillogenesis analysis, an in vivo animal tissue bonding test, and an ex vivo tensile strength test of dissected skin tissues confirmed the successful photochemical tissue bonding effect of the UCNP/PAAm/HA-RB conjugate complex.

Photochemical Cross-Linking for Penetrating Corneal Wound Closure in Enucleated Porcine Eyes

PURPOSE

To compare the efficacy of photochemical-induced tissue cross-linking (PCL), utilizing Rose Bengal (RB) and 532 nm green light irradiation (RB-PCL), with standard sutures for closure of penetrating corneal incision in porcine cadaver eyes.

METHODS

A full-thickness penetrating incision, 3 mm in length parallel to the limbus and perpendicular to the corneal surface, was made in the enucleated porcine cornea. Photochemical cross-linking was performed with tropical RB application and irradiation of 532 nm green light (0.6 W/cm²) for 200, 250, and 300 seconds at laser fluences of 120, 150, and 180 J/cm², respectively, which was compared with the standard 10-0 nylon suture group. Following treatment, intraocular pressure to the point where wound leakage occurred (IOP_L) was measured. Corneal central thickness and surface temperature before and after PCL treatment were recorded. Optical coherence tomography (OCT) and scanning electron microscopy (SEM) were utilized to evaluate wound closure.

RESULTS

The mean corneal central thickness was increased from 812.0 ± 47.0 to 838.0 ± 45.6 µm after the incision as a result of cornea aqueous humor infiltration. RB penetrated approximately 140 μm into the porcine corneal stroma. The mean IOP_L for untreated blank group after incision was 4.27 ± 0.36 mmHg. Increased laser fluences produced increased IOP_L of 27.02 ± 3.01 (PCL₁₂₀), 31.60 ± 3.67 (PCL₁₅₀) and 36.73 ± 3.25 mmHg (PCL₁₈₀), which were statistically different from the control intact group. The mean IOP_L in the sutured cornea was 57.30 ± 4.59 mmHg. The average surface temperature difference before and after PCL treatment was 2.03 ± 0.45-2.47 ± 0.79°C. OCT demonstrated not only complete but also improved closure in comparison with disorganized collagen fibers after conventional suturing, which is further confirmed by SEM.

CONCLUSIONS

Complete and clinically relevant seal of full-thickness porcine corneal incision was achieved using PCL method ex vivo, which provides potential application of this technique in ocular wound closure.

A novel experimental rat model of peripheral nerve scarring that reliably mimics post-surgical complications and recurring adhesions

Inflammation, fibrosis and perineural adhesions with the surrounding tissue are common pathological processes following nerve injury and surgical interventions on peripheral nerves in human patients. These features can reoccur following external neurolysis, currently the most common surgical treatment for peripheral nerve scarring, thus leading to renewed nerve function impairment and chronic pain. To enable a successful evaluation of new therapeutic approaches, it is crucial to use a reproducible animal model that mimics the main clinical symptoms occurring in human patients. However, a clinically relevant model combining both histological and functional alterations has not been published to date. We therefore developed a reliable rat model that exhibits the essential pathological processes of peripheral nerve scarring. In our study, we present a novel method for the induction of nerve scarring by applying glutaraldehyde-containing glue that is known to cause nerve injury in humans. After a 3-week contact period with the sciatic nerve in female Sprague Dawley rats, we could demonstrate severe intra- and perineural scarring that resulted in grade 3 adhesions and major impairments in the electrophysiological peak amplitude compared with sham control (P=0.0478). Immunohistochemical analysis of the nerve structure revealed vigorous nerve inflammation and recruitment of T cells and macrophages. Also, distinct nerve degeneration was determined by immunostaining. These pathological alterations were further reflected in significant functional deficiencies, as determined by the analysis of relevant gait parameters as well as the quantification of the sciatic functional index starting at week 1 post-operation (P<0.01). Moreover, with this model we could, for the first time, demonstrate not only the primary formation, but also the recurrence, of severe adhesions 1 week after glue removal, imitating a major clinical challenge. As a comparison, we tested a published model for generating perineural fibrotic adhesions, which did not result in significant pathological changes. Taken together, we established an easily reproducible and reliable rat model for peripheral nerve scarring that allows for the effective testing of new therapeutic strategies.

Silkworm Gut Fiber of Bombyx mori as an Implantable and Biocompatible Light-Diffusing Fiber

This work describes a new approach to the delivery of light in deeper tissues, through a silk filament that is implantable, biocompatible, and biodegradable. In the present work, silkworm gut fibers (SGFs) of Bombyx mori L., are made by stretching the silk glands. Morphological, structural, and optical properties of the fibers have been characterized and the stimulatory effect of red laser light diffused from the fiber was assayed in fibroblast cultures. SGFs are formed by silk fibroin (SF) mainly in a β-sheet conformation, a stable and non-soluble state in water or biological fluids. The fibers showed a high degree of transparency to visible and infrared radiation. Using a red laser (λ = 650 nm) as source, the light was efficiently diffused along the fiber wall, promoting a significant increment in the cell metabolism 5 h after the irradiation. SGFs have shown their excellent properties as light-diffusing optical fibers with a stimulatory effect on cells.

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

BACKGROUND AND OBJECTIVE

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.

STUDY DESIGN

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.

RESULTS

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).

CONCLUSION

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.

Photochemistry of rose bengal in water and acetonitrile: a comprehensive kinetic analysis

A comprehensive investigation of the photophysical properties and the photochemistry of rose bengal provided detailed information about the kinetics and the optical properties of all major intermediates involved.

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 μm versus 5.47 ± 1.70 μm; 4.51 ± 1.83 μm versus 3.50 ± 1.44 μm; and 2.35 ± 0.64 μm versus 1.96 ± 0.47 μm, 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.

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 28 days 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 28 days 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.

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.

Photoactive fluoropolymer surfaces that release sensitizer drug molecules

We describe a physical-organic study of two fluoropolymers bearing a photoreleasable PEGylated photosensitizer that generates (1)O2((1)Δg) [chlorin e6 methoxy tri(ethylene glycol) triester]. The surfaces are Teflon/poly(vinyl alcohol) (PVA) nanocomposite and fluorinated silica. The relative efficiency of these surfaces to photorelease the PEGylated sensitizer [shown previously to be phototoxic to ovarian cancer cells (Kimani, S. et al. J. Org. Chem 2012, 77, 10638)] was slightly higher for the nanocomposite. In the presence of red light and O2, (1)O2 is formed, which cleaves an ethene linkage to liberate the sensitizer in 68-92% yield. The fluoropolymers were designed to deal with multiple problems. Namely, their success relied not only on high O2 solubility and drug repellency but also on the C-F bonds, which physically quench little (1)O2, for singlet oxygen's productive use away from the surface. The results obtained here indicate that Teflon-like surfaces have potential uses in delivering sensitizer and singlet oxygen for applications in tissue repair and photodynamic therapy (PDT).

Light-activated sealing of skin wounds

BACKGROUND AND OBJECTIVES

We have developed a light-activated technology for rapidly sealing skin surgical wounds called photochemical tissue bonding (PTB). The goals of this study were to evaluate parameters influencing PTB in order to optimize its clinical efficacy and to determine whether PTB can be used to seal wounds in moderately to highly pigmented skin.

STUDY DESIGN/MATERIALS AND METHODS

Application of Rose Bengal (RB) followed by exposure to 532 nm was used to seal linear incisions (1.5 mm deep, 2 cm long) in lightly pigmented (Yorkshire) and darkly pigmented (Yucatan) swine skin. The force required to open the seal (the bonding strength) was measured by in situ tensiometry. Reflectance spectra, epidermal transmission spectra, and histology were used to characterize the skin. The relationships of RB concentration and fluence to bonding strength were established in Yorkshire skin. Surface temperature was measured during irradiations and cooling was used while sealing incisions in Yucatan skin. Monte Carlo simulations were carried out to estimate the effect of epidermal melanin on the power absorbed in the dermis at the incision interface.

RESULTS

The lowest fluence, 25 J/cm(2), delivered at an irradiance of 0.5 W/cm(2) substantially increased the bonding strength (∼ 10-fold) compared to controls in Yorkshire swine skin. Increasing the fluence to 100 J/cm(2) enhanced bonding strength by a further 1.5-fold. Application of 0.1% RB for 2 minutes produced the greatest bonding strength using 100 J/cm(2) and limited the penetration of RB to an ∼ 50 μm band on the dermal incision wall. Reflectance spectra indicated that Yorkshire skin had minimal melanin and that Yucatan skin was a good model for highly pigmented human skin. In Yucatan skin, the bonding strength increased 1.7-fold using 0.1% RB and 200 J/cm(2) at 1.5 W/cm(2) with cooling and epinephrine. Monte Carlo simulation indicated that absorption of 532 nm light by epidermal melanin in dark skin decreased the power absorbed along the incision in the dermis by a factor of 2.7.

CONCLUSIONS

These results suggest that in lightly pigmented skin the PTB treatment time can be shortened without compromising the bonding strength. Sealing incisions using PTB in moderately and highly pigmented skin will require a careful balance of irradiance and cooling.

Peripheral nerve reconstruction after injury: a review of clinical and experimental therapies

Unlike other tissues in the body, peripheral nerve regeneration is slow and usually incomplete. Less than half of patients who undergo nerve repair after injury regain good to excellent motor or sensory function and current surgical techniques are similar to those described by Sunderland more than 60 years ago. Our increasing knowledge about nerve physiology and regeneration far outweighs our surgical abilities to reconstruct damaged nerves and successfully regenerate motor and sensory function. It is technically possible to reconstruct nerves at the fascicular level but not at the level of individual axons. Recent surgical options including nerve transfers demonstrate promise in improving outcomes for proximal nerve injuries and experimental molecular and bioengineering strategies are being developed to overcome biological roadblocks limiting patient recovery.

Peripheral nerve reconstruction after injury: a review of clinical and experimental therapies

Unlike other tissues in the body, peripheral nerve regeneration is slow and usually incomplete. Less than half of patients who undergo nerve repair after injury regain good to excellent motor or sensory function and current surgical techniques are similar to those described by Sunderland more than 60 years ago. Our increasing knowledge about nerve physiology and regeneration far outweighs our surgical abilities to reconstruct damaged nerves and successfully regenerate motor and sensory function. It is technically possible to reconstruct nerves at the fascicular level but not at the level of individual axons. Recent surgical options including nerve transfers demonstrate promise in improving outcomes for proximal nerve injuries and experimental molecular and bioengineering strategies are being developed to overcome biological roadblocks limiting patient recovery.

Nerve repair: toward a sutureless approach

Peripheral nerve repair for complete section injuries employ reconstructive techniques that invariably require sutures in their application. Sutures are unable to seal the nerve, thus incapable of preventing leakage of important intraneural fluids from the regenerating nerve. Furthermore, sutures are technically demanding to apply for direct repairs and often induce detrimental scarring that impedes healing and functional recovery. To overcome these limitations, biocompatible and biodegradable glues have been used to seal and repair peripheral nerves. Although creating a sufficient seal, they can lack flexibility and present infection risks or cytotoxicity. Other adhesive biomaterials have recently emerged into practice that are usually based on proteins such as albumin and collagen or polysaccharides like chitosan. These adhesives form their union to nerve tissue by either photothermal (tissue welding) or photochemical (tissue bonding) activation with laser light. These biomaterial adhesives offer significant advantages over sutures, such as their capacity to unite and seal the epineurium, ease of application, reduced invasiveness and add the potential for drug delivery in situ to facilitate regeneration. This paper reviews a number of different peripheral nerve repair (or reconstructive) techniques currently used clinically and in experimental procedures for nerve injuries with or without tissue deficit.

Laser-activated adhesive films for sutureless median nerve anastomosis

A novel chitosan adhesive film that incorporates the dye 'Rose Bengal' (RB) was used in conjunction with a green laser to repair transected rat median nerves in vivo. Histology and electrophysiological recording assessed the impact of the laser-adhesive technique on nerves. One week post-operatively, the sham-control group (laser-adhesive technique applied on un-transected nerves) conserved the average number and size of myelinated fibres in comparison to its contralateral side and electrophysiological recordings demonstrated no significant difference with un-operated nerves. Twelve weeks after the laser-adhesive anastomoses, nerves were in continuity with regenerated axons that crossed the anastomotic site.

A photoactivated nanofiber graft material for augmented Achilles tendon repair

BACKGROUND AND OBJECTIVE

Suture repair of Achilles tendon rupture can cause infection, inflammation and scarring, while prolonged immobilization promotes adhesions to surrounding tissues and joint stiffness. Early mobilization can reduce complications provided the repair is strong enough to resist re-rupture. We have developed a biocompatible, photoactivated tendon wrap from electrospun silk (ES) to provide additional strength to the repair that could permit early mobilization, and act as a barrier to adhesion formation.

STUDY DESIGN/MATERIAL AND METHODS

ES nanofiber mats were prepared by electrospinning. New Zealand white rabbits underwent surgical transection of the Achilles tendon and repair by: (a) SR: standard Kessler suture + epitendinous suture (5-0 vicryl). (b) ES/PTB: a single stay suture and a section of ES mat, stained with 0.1% Rose Bengal (RB), wrapped around the tendon and bonded with 532 nm light (0.3 W/cm(2) , 125 J/cm(2) ). (c) SR + ES/PTB: a combination of (a) and (b). Gross appearance, extent of adhesion formation and biomechanical properties of the repaired tendon were evaluated at Days 7, 14, or 28 post-operatively (n = 8 per group at each time point).

RESULTS

Ultimate stress (US) and Young's modulus (E) in the SR group were not significantly different from the ES/PTB group at Days 7 (US, P = 0.85; E, P = 1), 14 (US, P = 0.054; E, P = 1), and 28 (US, P = 0.198; E, P = 0.12) post-operatively. Adhesions were considerably greater in the SR group compared to the ES/PTB group at Days 7 (P = 0.002), 14 (P < 0.0001), and 28 (P < 0.0001). The combination approach of SR + ES/PTB gave the best outcomes in terms of E at 7 (P < 0.016) and 14 days (P < 0.016) and reduced adhesions compared to SR at 7 (P < 0.0001) and 14 days (P < 0.0001), the latter suggesting a barrier function for the photobonded ES wrap.

CONCLUSION

Photochemical sealing of a ES mat around the tendon repair site provides considerable benefit in Achilles tendon repair. Lasers Surg. Med. 44: 645-652, 2012. © 2012 Wiley Periodicals, Inc.

Semi-interpenetrating network of polyethylene glycol and photocrosslinkable chitosan as an in-situ-forming nerve adhesive

An ideal adhesive for anastomosis of severed peripheral nerves should tolerate strains imposed on rejoined nerves. We use blends of photocrosslinkable 4-azidobenzoic acid-modified chitosan (Az-C) and polyethylene glycol (PEG) as a new in-situ-forming bioadhesive for anastomosing and stabilizing the injured nerves. Cryo-scanning electron microscopy suggests that the polymer blends form a semi-interpenetrating network (semi-IPN), where PEG interpenetrates the Az-C network and reinforces it. Az-C/PEG semi-IPN gels have higher storage moduli than Az-C gel alone and fibrin glue. Nerves anastomosed with an Az-C/PEG gel tolerate a higher force than those with fibrin glue prior to failure. A series of ex vivo and in vitro cell experiments indicate the Az-C/PEG gels are compatible with nerve tissues and cells. In addition, Az-C/PEG gels release PEG over a prolonged period, providing sustained delivery of PEG, a potential aid for nerve cell preservation through membrane fusion. Az-C/PEG semi-IPN gels are promising bioadhesives for repairing severed peripheral nerves not only because of their improved mechanical properties but also because of their therapeutic potential and tissue compatibility.

Photo-oxidation of proteins

Photo-induced damage to proteins occurs via multiple pathways. Direct damage induced by UVB (λ 280-320 nm) and UVA radiation (λ 320-400 nm) is limited to a small number of amino acid residues, principally tryptophan (Trp), tyrosine (Tyr), histidine (His) and disulfide (cystine) residues, with this occurring via both excited state species and radicals. Indirect protein damage can occur via singlet oxygen ((1)O(2)(1)Δ(g)), with this resulting in damage to Trp, Tyr, His, cystine, cysteine (Cys) and methionine (Met) residues. Although initial damage is limited to these residues multiple secondary processes, that occur both during and after radiation exposure, can result in damage to other intra- and inter-molecular sites. Secondary damage can arise via radicals (e.g. Trp, Tyr and Cys radicals), from reactive intermediates generated by (1)O(2) (e.g. Trp, Tyr and His peroxides) and via molecular reactions of photo-products (e.g. reactive carbonyls). These processes can result in protein fragmentation, aggregation, altered physical and chemical properties (e.g. hydrophobicity and charge) and modulated biological turnover. Accumulating evidence implicates these events in cellular and tissue dysfunction (e.g. apoptosis, necrosis and altered cell signaling), and multiple human pathologies.

Photochemical crosslinked electrospun collagen nanofibers: synthesis, characterization and neural stem cell interactions

Currently available crosslinking methods for electrospun collagen nanofibers do not preserve the fibrous architecture over prolonged periods of time. In addition, electrospinning of collagen often involves solvents that lead to extensive protein denaturation. In this study, we demonstrate the advantage of acetic acid over 1,1,1,3,3,3 hexafluoroisopropanol (HFP) in preventing collagen denaturation. A novel photochemical crosslinking method using rose bengal as the photoinitiator is also introduced. Using circular dichorism analyses, we demonstrate the fraction of collagen helical structure to be significantly greater in acetic acid-spun fibers than HFP-spun fibers (28.9 +/- 5.9% vs. 12.5 +/- 2.0%, p < 0.05). By introducing 0.1% (w/v) rose bengal into collagen fibers and subjecting these scaffolds to laser irradiation at a wavelength of 514 nm for 100 sec, biodegradable crosslinked scaffolds were obtained. Scaffold degradation as evaluated by soaking crosslinked collagen scaffolds in PBS at 37 degrees C, indicated a mass loss of 47.7 +/- 7.4% and 68.9 +/- 24.7% at day 7 and day 15, respectively. However, these scaffolds retained fibrous architecture for at least 21 days under physiological conditions. Neural stem cell line, C17.2, cultured on crosslinked collagen scaffolds proliferated after 7 days by forming a confluent layer of cells with extensive cellular projections that were indicative of neurite outgrowth. Taken together, these findings support the potential of acetic acid-electrospun photochemical crosslinked collagen nanofibers for neural tissue engineering.

Improving electrophysiologic and histologic outcomes by photochemically sealing amnion to the peripheral nerve repair site

BACKGROUND

The surgical approach used today in the repair of peripheral nerve injuries rarely achieves full functional recovery. This study determines whether isolation of the nerve repair site using photochemical tissue bonding (PTB) in combination with human amniotic membrane can improve both functional and histologic recovery.

METHODS

New Zealand white rabbits (n = 24) underwent transection of the right common peroneal nerve. Epineural nerve repair was performed using 10-0 nylon sutures. The repair site was then wrapped in a cuff of human amniotic membrane, which either was secured with sutures or sealed using PTB. Standard neurorrhaphy alone was assessed as a control group. Functional recovery was recorded at 30-day intervals postoperatively by electrophysiologic assessment. At 120 days, animals were killed humanely and nerves harvested for histomorphometry.

RESULTS

Nerves treated with amnion wraps and sealed with PTB demonstrated a statistically significant improvement across both functional and histologic parameters. Functional recovery, as measured by repeated electrophysiologic studies over time, revealed a 26.2% improvement over standard neurorrhaphy alone (P < .05). Nerves treated with PTB-sealed amnion wraps had significantly greater (P < .001) axon (5.08 +/- 1.06 microm) and fiber diameters (7.46 +/- 1.37 microm), as well as myelin thickness (2.39 +/- 0.7 microm) and the g ratio (axon diameter/fiber diameter ratio; 0.68 +/- 0.07) distal to the repair site compared to standard neurorrhaphy alone (4.98 +/- 1.81 microm, 6.77 +/- 1.94 microm, 1.79 +/- 0.42 microm, and 0.71 +/- 0.09, respectively).

CONCLUSION

Isolation of the repair site using a photochemically sealed amnion wrap improves electrophysiologic and histologic recovery compared to standard suture neurorrhaphy.