Graft Regeneration Research Articles

Regeneration of partially decellularized tracheal scaffolds in a mouse model of orthotopic tracheal replacement

Decellularized tracheal scaffolds offer a potential solution for the repair of long-segment tracheal defects. However, complete decellularization of trachea is complicated by tracheal collapse. We created a partially decellularized tracheal scaffold (DTS) and characterized regeneration in a mouse model of tracheal transplantation. All cell populations except chondrocytes were eliminated from DTS. DTS maintained graft integrity as well as its predominant extracellular matrix (ECM) proteins. We then assessed the performance of DTS in vivo. Grafts formed a functional epithelium by study endpoint (28 days). While initial chondrocyte viability was low, this was found to improve in vivo. We then used atomic force microscopy to quantify micromechanical properties of DTS, demonstrating that orthotopic implantation and graft regeneration lead to the restoration of native tracheal rigidity. We conclude that DTS preserves the cartilage ECM, supports neo-epithelialization, endothelialization and chondrocyte viability, and can serve as a potential solution for long-segment tracheal defects.

Masseter nerve-based facial palsy reconstruction.

Facial paralysis is a devastating disease, the treatment of which is challenging. The use of the masseteric nerve in facial reanimation has become increasingly popular and has been applied to an expanded range of clinical scenarios. However, appropriate selection of the motor nerve and reanimation method is vital for successful facial reanimation. In this literature review on facial reanimation and the masseter nerve, we summarize and compare various reanimation methods using the masseter nerve. The masseter nerve can be used for direct coaptation with the paralyzed facial nerve for temporary motor input during cross-facial nerve graft regeneration and for double innervation with the contralateral facial nerve. The masseter nerve is favorable because of its proximity to the facial nerve, limited donor site morbidity, and rapid functional recovery. Masseter nerve transfer usually leads to improved symmetry and oral commissure excursion due to robust motor input. However, the lack of a spontaneous, effortless smile is a significant concern with the use of the masseter nerve. A thorough understanding of the advantages and disadvantages of the use of the masseter nerve, along with careful patient selection, can expand its use in clinical scenarios and improve the outcomes of facial reanimation surgery.

Perilipin2 is an Earlier Marker Than Perilipin1 for Identifying Adipocyte Regeneration in Fat Grafts.

Both perilipin1 (Plin1) and perilipin2 (Plin2) play a crucial role in regulating lipid droplet (LD) formation in fat cells. Plin2 is expressed early in the adipocyte differentiation process but is replaced by Plin1 after cell maturation. In free fat grafts, only a small number of adipocytes remain alive or are replaced by newly regenerated fat cells. It is known that Plin1-positive adipocytes participate in regeneration, but the characteristics of Plin2 expression during this process are still poorly understood. The aim of this study was to investigate whether Plin2 is a more precise early marker for detecting adipocyte regeneration in fat grafts than Plin1. Autologous fat tissue (120 mg) harvested from inguinal fat pads was injected under the scalps of C57 mice. Samples were explanted at days 3, 7, 15, and 30 after transplantation. Changes in sample size and weight were evaluated. Hematoxylin-eosin staining, real-time polymerase chain reaction, and immunostaining of Plin1 and Plin2 expression were performed. Plin1, but not Plin2, expression was detected in the freshly harvested fat, but the latter was activated after grafting. Newly regenerated Plin2-positive adipocytes increased from day 3 to day 7 and then declined, whereas the number of Plin1-positive fat cells decreased first and began to increase after day 15. The expression levels of Plin1 and Plin2 mRNA demonstrated similar changes over time. At day 30, adipocytes lost Plin2 expression and were positive for Plin1 again. Our experiments showed convincing evidence that Plin2 expression could be used to detect early adipocyte regeneration in grafted fat tissue.

Long-term results of triple-layered small diameter vascular grafts in sheep carotid arteries

There is an urgent clinical for small diameter vascular grafts (SDVGs) for use in the treatment of coronary artery disease. Moreover, biodegradable SDVGs are drawing increasing attention because they have the potential to restore vascular function with the degradation of vascular graft and tissue regeneration. In this study, we designed triple-layered SDVGs to mimic the native arterial structure, with each layer contributing its unique porosity to the porous structure. We evaluated triple-layered SDVGs in a sheep carotid arterial replacement model. After implantation for 12 months, two grafts were patent and indicated the feasibility of using grafts in large animals. Nevertheless, it was determined that both grafts formed aneurysms at the proximal end. The prevention of such aneurysms remains a challenge for future investigation.

Life-Threatening Portal Flow Steal Reappearing Under Increased Intrahepatic Vascular Resistance After Living Donor Liver Transplantation

Maintenance of adequate portal inflow is crucial for graft regeneration in adult living donor liver transplantation (ALDLT) to allow the recipients to meet their early metabolic demands. A persistent large spontaneous portosystemic shunt can divert portal flow away from the liver graft, leading to impaired or delayed graft regeneration and subsequent graft failure. The importance of obliterating huge portosystemic shunt during liver transplantation is obvious for successful ALDLT. However, in partial liver graft with a relatively small graft-to-recipient weight ratio (GRWR) (compared with deceased donor whole graft liver transplantation), even the persisting small portosystemic shunt may result in repeated portal flow steal when a liver graft faces increased intrahepatic vascular resistance caused by rejection or graft congestion with hepatic venous outflow stenosis. We present 2 complicated cases of reappearing portal flow steal that were derived from the remaining small portosystemic shunt under the increased vascular resistance of the liver graft, even after interruption of a large portosystemic shunt during ALDLT. Because ALDLT is always a partial liver graft, even when GRWR is over 1%, it is much more vulnerable to hemodynamic changes in portal flow by rejection or graft congestion by hepatic venous outflow obstruction. Therefore, a comprehensive understanding of complex portosystemic shunt and complete reinterruption of reappearing portosystemic shunt, even though small and insignificant, during ALDLT is important for graft salvage procedures before irreversible liver graft damage.

Is there any correlation between liver graft regeneration and recipient's pretransplant skeletal muscle mass?-a study in extended left lobe graft living-donor liver transplantation.

The end-stage liver disease causes a metabolic dysfunction whose most prominent clinical feature is the loss of skeletal muscle mass (SMM). In living-donor liver transplantation (LDLT), liver graft regeneration (GR) represents a crucial process to normalize the portal hypertension and to meet the metabolic demand of the recipient. Limited data are available on the correlation between pre-LDLT low SMM and GR. Retrospective study on a cohort of 106 LDLT patients receiving an extended left liver lobe graft. The skeletal muscle index (SMI) at L3 level was used for muscle mass measurement, and the recommended cut-off values of the Japanese Society of Hepatology guidelines were used as criteria for defining low muscularity. GR was evaluated as rate of volume increase at 1 month post-LT [graft regeneration rate (GRR)]. The median GRR at 1 month post-LT was 91% (IQR, 65-128%) and a significant correlation with graft volume-to-recipient standard liver volume ratio (GV/SLV) (rho -0.467, P<0.001), graft-to-recipient weight ratio (GRWR) (rho -0.414, P<0.001), donor age (rho -0.306, P=0.001), 1 month post-LT cholinesterase serum levels (rho 0.397, P=0.002) and pre-LT low muscularity [absent vs. present GRR 97.5% (73.1-130%) vs. 83.5% (45.2-110.9%), P=0.041] was noted. Moreover in male recipients, but not in women, it was shown a direct correlation with pre-LT SMI (rho 0.352, P=0.020) and inverse correlation with 1 month post-LT SMI variation (rho -0.301, P=0.049). A low GRR was identified as an independent prognostic factor for recipient overall survival (HR 6.045, P<0.001). Additionally to the hemodynamic factors of portal circulation and the quality of the graft, the metabolic status of the recipients has a significant role in the GR process. A pre-LT low SMM is associated with impaired GRR and this negative impact is more evident in male recipients.

Recovery of knee function associated with regeneration of semitendinosus and gracillis grafts used for reconstructive procedures

Recovery of knee function associated with regeneration of semitendinosus and gracillis grafts used for reconstructive procedures

Deceleration of Liver Regeneration by Knockdown of Heme Oxygenase-1 is Associated With Impairment of Liver Injury Recovery After Reduced-Size Liver Transplantation in Rats

AimIt has been reported that heme oxygenase-1 (HO-1) is upregulated during hepatocyte proliferation. Herein, we used a half-size liver transplantation (HSLT) model to study the impact of HO-1 on liver grafts proliferation. To the best of our knowledge, this is the first time that HO-1 has been characterized as a regulator of liver graft regeneration. Materials and MethodsSaline and tin protoporphyrin (SnPP, a HO-1 competitive inhibitor) were separately administered in vehicle and SnPP group before rats HSLT. Plasma samples were collected at 0, 1, 3, and 5 days after HSLT for liver function analysis. Liver tissues were obtained at 0, 1, 3, and 5 days after HSLT for analyses of histologic, apoptosis, and proliferation index by immunohistochemical, enzyme-linked immunosorbent assay, quantitative real-time polymerase chain reaction, and Western blotting. ResultsHO-1 level was upregulated by the treatment of HSLT along with accelerated liver proliferation, which was reversed by SnPP. The reduced regeneration by SnPP lead to higher Suzuki’s scores, alanine aminotransferase, and aspartate aminotransferase levels. The interleukin-6 levels, p-Stat3/t-Stat3, c-myc, and c-jun were decreased in the SnPP group than the vehicle group. ConclusionsOur findings suggest that inhibition of HO-1 mitigates liver regeneration in part by downregulation of an interleukin-6/Stat3 axis. Targeted specific pharmacologic induction of HO-1 may be applicable in clinical practice.

The Impact of Biliary Reconstruction Methods on Small Partial Liver Grafts.

Male Lewis rats underwent isogenic arterialized 30% partial liver transplantation with small partial grafts, either via choledocho-jejunostomy or choledocho-choledochostomy. The 7-day survival rates of the choledocho-choledochostomy and choledocho-jejunostomy groups were 100% and 50%, respectively (P = 0.011). Choledocho-jejunostomy provoked reflux cholangitis, as confirmed by neutrophil infiltration around the bile ducts; suppressed and delayed liver regeneration in grafts, as confirmed by significant increases in intrahepatic interleukin-1β level, significant decreases in the graft weight increase ratios, hepatocyte proliferation, and intrahepatic mRNA expression of vascular endothelial growth factor; and induced graft dysfunction, as confirmed by the presence of massive ascites, significantly decreased bile production, and prolonged elevation of total bilirubin, aspartate aminotransferase, and alanine aminotransferase. Choledocho-jejunostomy predisposed grafts to cholangitis, impaired liver regeneration, and aggravated animal survival, suggesting that choledocho-choledochostomy may be preferable over choledocho-jejunostomy in adult-to-adult living-donor liver transplantation.

Molecular Pathways Underlying Adaptive Repair of the Injured Kidney: Novel Donation After Cardiac Death and Acute Kidney Injury Platforms.

To test the hypothesis that gene expression profiling in peripheral blood from patients who have undergone kidney transplantation (KT) will provide mechanistic insights regarding graft repair and regeneration. Renal grafts obtained from living donors (LD) typically function immediately, whereas organs from donation after cardiac death (DCD) or acute kidney injury (AKI) donors may experience delayed function with eventual recovery. Thus, recipients of LD, DCD, and AKI kidneys were studied to provide a more complete understanding of the molecular basis for renal recovery. Peripheral blood was collected from LD and DCD/AKI recipients before transplant and throughout the first 30 days thereafter. Total RNA was isolated and assayed on whole genome microarrays. Comparison of longitudinal gene expression between LD and AKI/DCD revealed 2 clusters, representing 141 differentially expressed transcripts. A subset of 11 transcripts was found to be differentially expressed in AKI/DCD versus LD. In all recipients, the most robust gene expression changes were observed in the first day after transplantation. After day 1, gene expression profiles differed depending upon the source of the graft. In patients receiving LD grafts, the expression of most genes did not remain markedly elevated beyond the first day post-KT. In the AKI/DCD groups, elevations in gene expression were maintained for at least 5 days post-KT. In all recipients, the pattern of coordinate gene overexpression subsided by 28 to 30 days. Gene expression in peripheral blood of AKI/DCD recipients offers a novel platform to understand the potential mechanisms and timing of kidney repair and regeneration after transplantation.

The role of vascularization in nerve regeneration of nerve graft.

Vascularization is an important factor in nerve graft survival and function. The specific molecular regulations and patterns of angiogenesis following peripheral nerve injury are in a broad complex of pathways. This review aims to summarize current knowledge on the role of vascularization in nerve regeneration, including the key regulation molecules, and mechanisms and patterns of revascularization after nerve injury. Angiogenesis, the maturation of pre-existing vessels into new areas, is stimulated through angiogenic factors such as vascular endothelial growth factor and precedes the repair of damaged nerves. Vascular endothelial growth factor administration to nerves has demonstrated to increase revascularization after injury in basic science research. In the clinical setting, vascularized nerve grafts could be used in the reconstruction of large segmental peripheral nerve injuries. Vascularized nerve grafts are postulated to accelerate revascularization and enhance nerve regeneration by providing an optimal nutritional environment, especially in scarred beds, and decrease fibroblast infiltration. This could improve functional recovery after nerve grafting, however, conclusive evidence of the superiority of vascularized nerve grafts is lacking in human studies. A well-designed randomized controlled trial comparing vascularized nerve grafts to non-vascularized nerve grafts involving patients with similar injuries, nerve graft repair and follow-up times is necessary to demonstrate the efficacy of vascularized nerve grafts. Due to technical challenges, composite transfer of a nerve graft along with its adipose tissue has been proposed to provide a healthy tissue bed. Basic science research has shown that a vascularized fascial flap containing adipose tissue and a vascular bundle improves revascularization through excreted angiogenic factors, provided by the stem cells in the adipose tissue as well as by the blood supply and environmental support. While it was previously believed that revascularization occurred from both nerve ends, recent studies propose that revascularization occurs primarily from the proximal nerve coaptation. Fascial flaps or vascularized nerve grafts have limited applicability and future directions could lead towards off-the-shelf alternatives to autografting, such as biodegradable nerve scaffolds which include capillary-like networks to enable vascularization and avoid graft necrosis and ischemia.

Leveraging the zebrafish to model organ transplantation.

The availability of organs for transplant fails to meet the demand and this shortage is growing worse every year. As the cost of not getting a suitable donor organ can mean death for patients, new tools and approaches that allows us to make advances in transplantation faster and provide a different vantage point are required. To address this need, we introduce the concept of using the zebrafish (Danio rerio) as a new model system in organ transplantation. The zebrafish community offers decades of research experience in disease modeling and a rich toolbox of approaches for interrogating complex pathological states. We provide examples of how already existing zebrafish assays/tools from cancer, regenerative medicine, immunology, and others, could be leveraged to fuel new discoveries in pursuit of solving the organ shortage. Important innovations have enabled several types of transplants to be successfully performed in zebrafish, including stem cells, tumors, parenchymal cells, and even a partial heart transplant. These innovations have been performed against a backdrop of an expansive and impressive list of tools designed to uncover the biology of complex systems that include a wide array of fluorescent transgenic fish that label specific cell types and mutant lines that are transparent, immune-deficient. Allogeneic transplants can also be accomplished using immune suppressed and syngeneic fish. Each of these innovations within the zebrafish community would provide several helpful tools that could be applied to transplant research. We highlight some examples of existing tools and assays developed in the zebrafish community that could be leveraged to overcome barriers in organ transplantation, including ischemia-reperfusion, short preservation durations, regeneration of marginal grafts, and acute and chronic rejection.

Impact of the Reconstruction Material on the Patency of Middle Hepatic Vein in Living Donor Liver Transplantation Using the Right Liver

BackgroundA right liver graft with middle hepatic vein (MHV) reconstruction is the standard graft for adult-to-adult living donor liver transplantation (LDLT). The patency of reconstructed MHV affects the recovery and regeneration of graft. The aim of the study is to evaluate the patency rate of reconstructed MHV according to the reconstruction material in LDLT using the right liver. MethodsThe data was collected retrospectively on 521 patients who underwent LDLT with right liver graft form August 2003 to December 2012 at the Seoul St. Mary’s Hospital in Seoul. Two serial comparisons were performed. At first, patients were divided into 2 groups: biologic graft group (n = 252) and synthetic graft group (n = 177). Second, patients were divided into 6 groups: No MHV reconstruction (n = 92); MHV was reconstructed by greater saphenous vein (GSV) (n = 20); recipient’s portal vein (PV) (n = 219); cryopreserved iliac artery (CIA) (n = 2); cryopreserved iliac vein (CIV) (n = 11); polytetrafluoroethylene (PTFE) graft (n = 105); and polyethylene terephthalate (PETE) graft (n = 72). We compared the patency of reconstructed MHV among these groups by computed tomography angiography at 7 days, 20 days, 90 days, and 1 year. ResultsAt the first comparison, the patency rate of the biologic graft group on the seventh postoperative day was 61.9%, and the synthetic graft group was 72.4% (P = .029). At postoperative 1 year, the patency rate of the biologic graft group was 42.9%, and the synthetic graft group was 24.1% (P = .001). At the second comparison, the MHV patency of GSV, PV, CIA, CIV, PTFE, and PETE was 65.0%, 62.5%, 50%, 63.6%, 75%, 72% on the seventh postoperative days (P = .318); 60%, 57.1%, 50%, 54.5%, 69%, 55.6% on the 20th postoperative days (P = .444); 40%, 48.8%, 50%, 27.3%, 47%, 34.1% on the 90th postoperative days (P = .294); and 30%, 45.2%, 50%, 27.3%, 27%, 26.4% at 1 postoperative year (P = .008). ConclusionAlthough there was no statistical difference in comparison of each material, there were significant differences in MHV patency rates between the biologic and the synthetic group. Therefore, the synthetic graft could be considered in living donor liver transplantation with MHV reconstruction.

The cell source in tissue regeneration of vascular grafts

The development of small-diameter artificial vascular grafts has become a research hotspot in recent years. To achieve long-term patency, an ideal vascular graft should have the capacity to recruit host cells to participate in vascular tissue regeneration. Based on previous research, we provide detailed descriptions of the cell sources and cell types involved in vascular graft regeneration. Methodology to determine host cell infiltration and the limitations of current techniques are also discussed.

Factors associated with low graft regeneration in the early phase after living donor liver transplantation.

Appropriate graft regeneration after living donor liver transplantation (LDLT) is crucial to avoid small-for-size syndrome. We enrolled 44 recipients who underwent ABO-identical/compatible LDLT from December 2007 to August 2016 and determined possible factors associated with low graft regeneration after LDLT. Liver regeneration was calculated by the ratio of the graft size on postoperative day (POD) 7±1day (calculated by CT volumetry) to the size of the donated liver at implant. Postoperative outcomes were compared between the low and high regeneration groups. Median regeneration rate was 1.65-fold. Regeneration rate was negatively correlated with graft-to-recipient weight ratio. Postoperative morbidity rates on POD 14-90 were significantly higher in the low group compared with the high group (63% vs 18%, P=.03). Graft and patient survival in the low group were significantly worse than the high group (1-year graft survival 73% vs 100%, P=.002; patient survival 82% vs 100%, P=.01). Cold ischemia time (CIT; per 10minute; odds ratio [OR] =1.37) and platelet count <60000/μL on POD 5 (OR=14.32) were independently associated with low regeneration. In conclusion, longer CIT and postoperative thrombocytopenia were associated with low graft regeneration in the early phase after LDLT, which could consequently lead to poor graft and patient survival.

Auxiliary xenotransplantation as an in vivo bioreactor—Development of a transplantable liver graft from a tiny partial liver

We established a completely novel method of auxiliary xenogeneic partial liver transplantation and examined whether liver grafts procured from Syrian hamsters regenerated in nude rats, which were used as in vivo bioreactors. The hamsters and the rats were all males (n=10). Partial liver grafts from hamsters were transplanted into nude rats in an auxiliary manner. We evaluated liver graft injury, rejection, and regeneration during 7days after auxiliary xenogeneic partial liver transplantation. All rats survived until sacrifice on post-operative day (POD) 1, 3, and 7. HE-staining showed normal at POD1, mild periportal edema, and slight bile duct and venous endothelial inflammation at POD3, and moderate acute cellular rejection at POD7 without parenchymal necrosis. The liver regeneration rates at POD3 and 7 were 1.54±0.23 and 2.54±0.43, respectively. The Ki-67 labeling index was also elevated at POD3 (27.5±4.1%). Serum HGF and VEGF were elevated at POD1 and 3. ATP levels of liver grafts recovered at POD7. These results revealed that with appropriate immunosuppressive therapy, partial liver graft regeneration occurred in a xenogeneic animal, which suggests liver grafts regenerated in xenogeneic environments, such as an in vivo bioreactor, have potential to be transplantable liver grafts for humans.

IL-1β siRNA adenovirus benefits liver regeneration by improving mesenchymal stem cells survival after acute liver failure

Background: Uncontrolled hapatic inflammatory response is regarded as the primary pathological mechanism of acute liver failure and impairs the regeneration of hepatocytes and stem cell grafts. Interleukin-1 plays a key role for activating immune and inflammatory response. Recently, siRNA has made quite a few progresses in treating inflammatory response.Aim. To assess the effect of IL-1β siRNA adenovirus on MSC and the therapeutic effect of MSC combined with IL-1β siRNA adenovirus in ALF.Material and methods. We implanted MSC or/and IL-1β siRNA adenovirus via the tail vein, using CCl4-induced ALF in a mice model. Mice were sacrificed at different time points. Blood samples and liver tissues were collected. Hepatic injury, liver regeneration, cytokines (CXCL1, IL-1β, IL-10, IL-6, VEGF and HGF), animal survival and vital MSC were assessed after cell transplantation.Results. MSC combined with IL-1β siRNA reduced the inflammatory levels and prevented liver failure. These animals administrated with MSC and IL-1β siRNA also exhibited improved liver regeneration and increased survival rates. Immunohistochemistry and fluorescence microscopy revealed the number of vital MSC in ALF + MSC + IL-1β siRNA group were significantly more than that in ALF + MSC group.Conclusion. IL-1β siRNA adenovirus could enhance MSC ability of tissue regeneration through increasing its survival rate. Accordingly, combination of IL-1β siRNA adenovirus and MSC had a synergistic effect on acute liver failure.

The effect of hyperlipidemia on bone graft regeneration of peri-implantal created defects in rabbits

AimIt is reported that hyperlipidemia affects quality and density of bone and adversely affects wound healing. The effect of hyperlipidemia on implant osseointegration and peri-implant defect regeneration has not been fully explained. The purpose of this study was to examine the effects of hyperlipidemia on the healing potential of the materials used for peri-implant bone regeneration and implant stability.Materials and methodsTwelve male, New Zealand rabbits were used in this study. Half of the rabbits were fed a 2% cholesterol diet for 8 weeks to induce hypercholesterolemia. Peri-implant defects (7 mm diameter) were created in the tibias of rabbits and placed implants (3.3 mm in diameter). This study was conducted as a split-mouth design. Animals were randomly divided into two groups: (1) hypercholesterol+autogenous graft group and hypercholesterol+xenograft group (n = 6), and (2) autogenous graft and xenograft groups as controls (n = 6). At 8 weeks after surgery, the rabbits were euthanized. During implant surgery and at 8 weeks, implant stability was measured with resonance frequency analysis (RFA values). Bone-to-implant contact (BIC) was analyzed via histomorphometric analysis.ResultsHyperlipidemic groups showed significantly lower BIC values than those of the control groups at 8 weeks (p < 0.05). According to baseline RFA readings, there was no significant difference between control and hyperlipidemic groups (p ˃ 0.05). The hypercholesterol+autogenous graft group had significantly lower RFA readings and BIC values than the hypercholesterol+xenograft group at 8 weeks (p < 0.05).ConclusionWithin the limitations of this study, it was found that hyperlipidemia may negatively affect the implant stability especially in the autogenous group and also, may decrease peri-implant bone regeneration. However, further studies are necessary to confirm these results more.

Purpose of the measurement of intraoperative hepatic hemodynamics in liver transplant surgery

Liver graft function depends on different biological factors that are related to the donor, the recipient and the potential damage arising from the organ preservation technique. However, adequate hepatic artery flow and portal vein flow rates ensure a sufficient flow of oxygen and nutrients in order to ensure a suitable cellular graft function after the extreme metabolic decrease condition induced by hypothermia and the preservation solution. Liver inflow is a highly complex system due to its double irrigation system. These two systems are connected by the well-known “hepatic arterial buffer response” concept. This mechanism explains changes in hepatic arterial flow (HAF) as a compensation for changes in the portal vein flow (PVF), so that the hepatic artery adjusts total flow in relation to alterations in the portal blood flow. At the moment, the minimum HAF and PVF required for an adequate regeneration and functional recovery of the liver graft have not been yet established.

Polyimide Electrode-Based Electrical Stimulation Impedes Early Stage Muscle Graft Regeneration.

Given the increasing use of regenerative free muscle flaps for various reconstructive procedures and neuroprosthetic applications, there is great interest and value in their enhanced regeneration, revascularization, and reinnervation for improved functional recovery. Here, we implant polyimide-based mircroelectrodes on free flap grafts and perform electrical stimulation for 6 weeks in a murine model. Using electrophysiological and histological assessments, we compare outcomes of stimulated grafts with unstimulated control grafts. We find delayed reinnervation and abnormal electromyographic (EMG) signals, with significantly more polyphasia, lower compound muscle action potentials and higher fatigability in stimulated animals. These metrics are suggestive of myopathy in the free flap grafts stimulated with the electrode. Additionally, active inflammatory processes and partial necrosis are observed in grafts stimulated with the implanted electrode. The results suggest that under this treatment protocol, implanted epimysial electrodes and electrical stimulation to deinnervated, and devascularized flaps during the early recovery phase may be detrimental to regeneration. Future work should determine the optimal implantation and stimulation window for accelerating free muscle graft regeneration.