Single-Nuclei RNA-Sequencing of the Gastrocnemius Muscle in Peripheral Artery Disease.

BACKGROUND: Lower extremity peripheral artery disease (PAD) is a growing epidemic with limited effective treatment options. Here, we provide a single-nuclei atlas of PAD limb muscle to facilitate a better understanding of the composition of cells and transcriptional differences that comprise the diseased limb muscle. METHODS: We obtained gastrocnemius muscle specimens from 20 patients with PAD and 12 non-PAD controls. Nuclei were isolated and single-nuclei RNA-sequencing was performed. The composition of nuclei was characterized by iterative clustering via principal component analysis, differential expression analysis, and the use of known marker genes. Bioinformatics analysis was performed to determine differences in gene expression between PAD and non-PAD nuclei, as well as subsequent analysis of intercellular signaling networks. Additional histological analyses of muscle specimens accompany the single-nuclei RNA-sequencing atlas. RESULTS: Single-nuclei RNA-sequencing analysis indicated a fiber type shift with patients with PAD having fewer type I (slow/oxidative) and more type II (fast/glycolytic) myonuclei compared with non-PAD, which was confirmed using immunostaining of muscle specimens. Myonuclei from PAD displayed global upregulation of genes involved in stress response, autophagy, hypoxia, and atrophy. Subclustering of myonuclei also identified populations that were unique to PAD muscle characterized by metabolic dysregulation. PAD muscles also displayed unique transcriptional profiles and increased diversity of transcriptomes in muscle stem cells, regenerating myonuclei, and fibro-adipogenic progenitor cells. Analysis of intercellular communication networks revealed fibro-adipogenic progenitors as a major signaling hub in PAD muscle, as well as deficiencies in angiogenic and bone morphogenetic protein signaling which may contribute to poor limb function in PAD. CONCLUSIONS: This reference single-nuclei RNA-sequencing atlas provides a comprehensive analysis of the cell composition, transcriptional signature, and intercellular communication pathways that are altered in the PAD condition.

A patient-centered textbook outcome measure effectively discriminates contemporary elective open abdominal aortic aneurysm repair quality.

BACKGROUND: There is persistent controversy surrounding the merit of surgical volume benchmarks being used solely as a sufficient proxy for assessing the quality of open abdominal aortic aneurysm (AAA) repair. Importantly, operative volume quotas may fail to reflect a more nuanced and comprehensive depiction of surgical outcomes most relevant to patients. Accordingly, we herein propose a patient-centered textbook outcome (TO) for AAA repair that is analogous to other large magnitude extirpative operations performed in other surgical specialties, and test its feasibility to discriminate hospital performance using Society for Vascular Surgery (SVS) volume guidelines. METHODS: All elective open infrarenal AAA repairs (OAR) in the SVS-Vascular Quality Initiative were examined (2009-2022). The primary end point was a TO, defined as a composite of no in-hospital complication or reintervention/reoperation, length of stay of ≤10 days, home discharge, and 1-year survival rates. The discriminatory ability of the TO measure was assessed by comparing centers that did or did not meet the SVS annual OAR volume threshold recommendation (high volume ≥10 OARs/year; low volume <10 OARs/year). Logistic regression and multivariable models adjusted for patient and procedure-related differences. RESULTS: A total of 9657 OARs across 198 centers were analyzed (mean age, 69.5 ± 8.4 years; female, 26%; non-White, 12%). A TO was identified in 44% (n = 4293) of the overall cohort. The incidence of individual TO components included no in-hospital complication (61%), no in-hospital reintervention or reoperation (92%), length of stay of ≤10 days (78%), home discharge (76%), and 1-year survival (91%). Median annual center volume was 6 (interquartile range, 3-10) and a majority of centers did not meet the SVS volume suggested threshold (<10 OARs/year, n = 148 [74%]). However, most patients (6265 of 9657 [65%]) underwent OAR in high-volume hospitals. When comparing high- and low-volume centers, a TO was more likely to occur in high-volume institutions: ≥10 OARs/year (46%) vs <10 OARs/year (42%; P = .0006). The association of a protective effect for higher center volume remained after risk adjustment (odds ratio, 1.1; 95% confidence interval, 1.05-1.26; P = .003). CONCLUSIONS: TOs for elective OAR reflect a more nuanced and comprehensive patient centered proxy to measure care delivery, consistent with other surgical specialties. Surprisingly, a TO was achieved in <50% of elective AAA cases nationally. Although the likelihood of a TO seems to correlate with SVS center volume recommendations, it more importantly reflects elements which may be prioritized by patients and thus offers insights into further improving real-world AAA care.

N-acetylcysteine treatment attenuates hemodialysis access-related limb pathophysiology in mice with chronic kidney disease.

The objective of the present study was to determine if treatment with N-acetylcysteine (NAC) could reduce access-related limb dysfunction in mice. Male and female C57BL6J mice were fed an adenine-supplemented diet to induce chronic kidney disease (CKD) prior to the surgical creation of an arteriovenous fistula (AVF) in the iliac vascular bundle. AVF creation significantly increased peak aortic and infrarenal vena cava blood flow velocities, but NAC treatment had no significant impact, indicating that fistula maturation was not impacted by NAC treatment. Hindlimb muscle and paw perfusion recovery and muscle capillary density in the AVF limb were unaffected by NAC treatment. However, NAC treatment significantly increased the mass of the tibialis anterior (P = 0.0120) and soleus (P = 0.0452) muscles post-AVF. There was a significant main effect of NAC treatment on hindlimb grip strength at postoperative day 12 (POD 12) (P = 0.0003), driven by significantly higher grip strength in both male (P = 0.0273) and female (P = 0.0031) mice treated with NAC. There was also a significant main effect of NAC treatment on the walking speed at postoperative day 12 (P = 0.0447), and post hoc testing revealed an improvement in NAC-treated male mice (P = 0.0091). The area of postsynaptic acetylcholine receptors (P = 0.0263) and motor endplates (P = 0.0240) was also increased by NAC treatment. Interestingly, hindlimb skeletal muscle mitochondrial oxidative phosphorylation trended higher in NAC-treated female mice but was not statistically significant (P = 0.0973). Muscle glutathione levels and redox status were not significantly impacted by NAC treatment in either sex. In summary, NAC treatment attenuated some aspects of neuromotor pathology in mice with chronic kidney disease following AVF creation.NEW & NOTEWORTHY Hemodialysis via autogenous arteriovenous fistula (AVF) is the preferred first-line modality for renal replacement therapy in patients with end-stage kidney disease. However, patients undergoing AVF surgery frequently experience a spectrum of hand disability symptoms postsurgery including weakness and neuromotor dysfunction. Unfortunately, no treatment is currently available to prevent or mitigate these symptoms. Here, we provide evidence that daily N-acetylcysteine supplementation can attenuate some aspects of limb neuromotor function in a preclinical mouse model of AVF.

Outcomes of endovascular abdominal aortic aneurysm repair conversion in octogenarians treated at a high-volume aorta center.

BACKGROUND: Endovascular abdominal aortic aneurysm repair (EVAR) has become the dominant treatment strategy for infrarenal abdominal aortic aneurysms but has been especially preferred for octogenarian (age ≥80 years) patients because of concerns surrounding comorbidity severity and physiologic frailty. However, EVAR failure resulting in subsequent open conversion (EVAR-c) has been increasingly reported in older patients, although a paucity of literature focusing on the outcomes in this subgroup is available. The purpose of the present analysis was to evaluate our experience with EVAR-c for octogenarians (age ≥80 years) compared with that for younger patients (age <80 years). METHODS: A retrospective review of all nonmycotic EVAR-c procedures (2002-2020) at a single high-volume academic hospital with a dedicated aorta center (available at: https://www.uf-health-aortic-disease-center) was performed. A total of 162 patients were categorized into octogenarian (age ≥80 years; n = 43) and nonoctogenarian (age <80 years; n = 119) cohorts and compared. The primary end point was 30-day mortality. The secondary end points included complications, 90-day mortality, and overall survival. Cox regression was used to determine the effects of selected covariates on mortality risk. The Kaplan-Meier method was used to estimate survival. RESULTS: No differences in the preadmission EVAR reintervention rates were present (octogenarians, 42%; nonoctogenarians, 43%; P = 1.00) although the interval to the first reintervention was longer for the octogenarians (41 months) than for the nonoctogenarians (15 months; P = .01). In addition, the time to EVAR-c was significantly longer for the octogenarian patients (61 months) than for the nonoctogenarian patients (39 months; P < .01). No difference in rupture presentation was evident (14% vs 10%; P = .6). However, elective EVAR-c occurred less frequently for octogenarians (42%) than for nonoctogenarians (59%; P = .07). The abdominal aortic aneurysm diameter was significantly larger for elective octogenarian EVAR-c (7.8 ± 1.9 cm) than for nonoctogenarian EVAR-c (7.0 ± 1.5 cm; P = .02), and the presence of a type Ia endoleak was the most common indication overall (58%; n = 91). A trend toward greater 30-day mortality was evident for octogenarian patients (16%) compared with nonoctogenarian patients (7%; P = .06). Similarly, the 90-day mortality was greater for the octogenarian patients (26%) than for the nonoctogenarian patients (10%; P = .02). However, the incidence of any complication (56% vs 49%; P = .5), readmission rate (12% vs 6%; P = .3), unplanned reoperation rate (10% vs 5%; P = .5), and length of stay (11 days vs 9 days; P = .3) were not significantly different between the two groups. Age ≥80 years was predictive of short-term mortality after nonelective but not after elective surgery. However, increasing comorbidities, nonelective admission, and renal or mesenteric revascularization showed the strongest association with mortality risk. Survival at 1 and 3 years was not different between the two groups when comparing all patients after the first 90 days postoperatively. CONCLUSIONS: Although the unadjusted perioperative mortality was greater for octogenarian patients, the risk-adjusted elective outcomes were comparable to those for younger EVAR-c patients when treated at a high-volume aortic surgery center. This finding underscores the importance of appropriate patient selection and modulation of operative complexity when feasible to achieve optimal results. Providers caring for octogenarian patients with EVAR failure should consider timely elective referral to high-volume aorta centers to reduce resource usage and the frequency of nonelective presentations.

Factors associated with lack of clinical improvement after vein ablation in the vascular quality initiative.

BACKGROUND: Insurance companies have adopted variable and inconsistent approval criteria for chronic venous disease (CVD) treatment. Although vein ablation (VA) is accepted as the standard of care for venous ulcers, the treatment criteria for patients with milder forms of CVD remain controversial. This study aims to identify factors associated with a lack of clinical improvement (LCI) in patients with less severe CVD without ulceration undergoing VA to improve patient selection for treatment. METHODS: We performed a retrospective analysis of patients undergoing VA for CEAP C2 to C4 disease in the Vascular Quality Initiative varicose veins database from 2014 to 2023. Patients who required intervention in multiple veins, had undergone prior interventions, or presented with CEAP C5 to C6 disease were excluded. The difference (Δ) in venous clinical severity score (VCSS; VCSS before minus after the procedure) was used to categorize the patients. Patients with a ΔVCSS of ≤0 were defined as having LCI after VA, and patients with ≥1 point decrease in the VCSS after VA (ΔVCSS ≥1) as having some benefit from the procedure and, therefore, "clinical improvement." The characteristics of both groups were compared, and multivariable regression analysis was performed to identify factors independently associated with LCI. A second analysis was performed based on the VVSymQ instrument, which measures patient-reported outcomes using five specific symptoms (ie, heaviness, achiness, swelling, throbbing pain, and itching). Patients with LCI showed no improvement in any of the five symptoms, and those with clinical improvement had a decrease in severity of at least one symptom. RESULTS: A total of 3544 patients underwent initial treatment of CVD with a single VA. Of the 3544 patients, 2607 had VCSSs available before and after VA, and 420 (16.1%) had LCI based on the ΔVCSS. Patients with LCI were more likely to be significantly older and African American and have CEAP C2 disease compared with patients with clinical improvement. Patients with clinical improvement were more likely to have reported using compression stockings before treatment. The vein diameters were not different between the two groups. The incidence of complications was overall low, with minor differences between the two groups. However, the patients with LCI were significantly more likely to have symptoms after intervention than those with improvement. Patients with LCI were more likely to have technical failure, defined as vein recanalization. On multivariable regression, age (odds ratio [OR], 1.01; 95% confidence interval [CI], 1.00-1.02) and obesity (OR, 1.47; 95% CI, 1.09-2.00) were independently associated with LCI, as was treatment of less severe disease (CEAP C2; OR, 1.82; 95% CI, 1.30-2.56) compared with more advanced disease (C4). The lack of compression therapy before intervention was also associated with LCI (OR, 6.05; 95% CI, 4.30-8.56). The analysis based on the VVSymQ showed similar results. CONCLUSIONS: LCI after VA is associated with treating patients with a lower CEAP class (C2 vs C4) and a lack of compression therapy before intervention. Importantly, no significant association between vein size and clinical improvement was observed.

Soft robot-mediated autonomous adaptation to fibrotic capsule formation for improved drug delivery.

The foreign body response impedes the function and longevity of implantable drug delivery devices. As a dense fibrotic capsule forms, integration of the device with the host tissue becomes compromised, ultimately resulting in device seclusion and treatment failure. We present FibroSensing Dynamic Soft Reservoir (FSDSR), an implantable drug delivery device capable of monitoring fibrotic capsule formation and overcoming its effects via soft robotic actuations. Occlusion of the FSDSR porous membrane was monitored over 7 days in a rodent model using electrochemical impedance spectroscopy. The electrical resistance of the fibrotic capsule correlated to its increase in thickness and volume. Our FibroSensing membrane showed great sensitivity in detecting changes at the abiotic/biotic interface, such as collagen deposition and myofibroblast proliferation. The potential of the FSDSR to overcome fibrotic capsule formation and maintain constant drug dosing over time was demonstrated in silico and in vitro. Controlled closed loop release of methylene blue into agarose gels (with a comparable fold change in permeability relating to 7 and 28 days in vivo) was achieved by adjusting the magnitude and frequency of pneumatic actuations after impedance measurements by the FibroSensing membrane. By sensing fibrotic capsule formation in vivo, the FSDSR will be capable of probing and adapting to the foreign body response through dynamic actuation changes. Informed by real-time sensor signals, this device offers the potential for long-term efficacy and sustained drug dosing, even in the setting of fibrotic capsule formation.

Towards a Whole Sample Imaging Approach Using Diffusion Tensor Imaging to Examine the Foreign Body Response to Explanted Medical Devices.

Analysing the composition and organisation of the fibrous capsule formed as a result of the Foreign Body Response (FBR) to medical devices, is imperative for medical device improvement and biocompatibility. Typically, analysis is performed using histological techniques which often involve random sampling strategies. This method is excellent for acquiring representative values but can miss the unique spatial distribution of features in 3D, especially when analysing devices used in large animal studies. To overcome this limitation, we demonstrate a non-destructive method for high-resolution large sample imaging of the fibrous capsule surrounding human-sized implanted devices using diffusion tensor imaging (DTI). In this study we analyse the fibrous capsule surrounding two unique macroencapsulation devices that have been implanted in a porcine model for 21 days. DTI is used for 3D visualisation of the microstructural organisation and validated using the standard means of fibrous capsule investigation; histological analysis and qualitative micro computed tomography (microCT) and scanning electron microscopy (SEM) imaging. DTI demonstrated the ability to distinguish microstructural differences in the fibrous capsules surrounding two macroencapsulation devices made from different materials and with different surface topographies. DTI-derived metrics yielded insight into the microstructural organisation of both capsules which was corroborated by microCT, SEM and histology. The non-invasive characterisation of the integration of implants in the body has the potential to positively influence analysis methods in pre-clinical studies and accelerate the clinical translation of novel implantable devices.

Dynamic actuation enhances transport and extends therapeutic lifespan in an implantable drug delivery platform.

Fibrous capsule (FC) formation, secondary to the foreign body response (FBR), impedes molecular transport and is detrimental to the long-term efficacy of implantable drug delivery devices, especially when tunable, temporal control is necessary. We report the development of an implantable mechanotherapeutic drug delivery platform to mitigate and overcome this host immune response using two distinct, yet synergistic soft robotic strategies. Firstly, daily intermittent actuation (cycling at 1 Hz for 5 minutes every 12 hours) preserves long-term, rapid delivery of a model drug (insulin) over 8 weeks of implantation, by mediating local immunomodulation of the cellular FBR and inducing multiphasic temporal FC changes. Secondly, actuation-mediated rapid release of therapy can enhance mass transport and therapeutic effect with tunable, temporal control. In a step towards clinical translation, we utilise a minimally invasive percutaneous approach to implant a scaled-up device in a human cadaveric model. Our soft actuatable platform has potential clinical utility for a variety of indications where transport is affected by fibrosis, such as the management of type 1 diabetes.

Claviculectomy for exposure and redo repair of expanding, recurrent right subclavian aneurysm.

Subclavian artery aneurysms (SAAs) are rare, and their repair can be technically complex. We have reported the redo repair of a large, expanding, right SAA after primary repair consisting of total aortic arch replacement with bilateral subclavian artery ligation and bypass. The redo repair used claviculectomy to facilitate exposure, ligation of the right deep cervical and internal thoracic arteries from within the aneurysm sac, and revision of the previous axillary artery bypass that had thrombosed owing to the mass effect of the expanding SAA. Claviculectomy can facilitate repair of large SAAs that are poorly suited to more routine exposure approaches, with acceptable risk and functional outcomes.

A versatile technique for high-resolution three-dimensional imaging of human arterial segments using microcomputed tomography.

BACKGROUND: Quantitative methods for evaluating microstructure of arterial specimens typically rely on histologic techniques that involve random sampling, which cannot account for the unique spatial distribution of features in three dimensions. METHODS: To overcome this limitation, we demonstrate a nondestructive method for three-dimensional imaging of intact human blood vessels using microcomputed tomography (microCT). Human artery segments were dehydrated and stained in an iodine solution then imaged with a standard laboratory microCT scanner. Image visualization and segmentation was performed using commercially available and open source software. RESULTS: Staining of cadaveric vessels with iodine enabled clear visualization of the arterial wall with microCT, preserved tissue morphology, and generated high-resolution images with a voxel size of 5.4 µm. Various components of the arterial wall were segmented using a combination of manual and automatic thresholding algorithms. CONCLUSIONS: Our approach allows for spatial mapping of human artery tissue samples that can guide targeted histologic analysis of smaller tissue segments, provide geometric data to inform finite element models, quantify degree of atherosclerosis, and help to evaluate the foreign body response to intravascular medical implants. (JVS-Vascular Science 2020;2:13-19.). CLINICAL RELEVANCE: In this article, we describe a powerful technique for whole artery analysis of pathologic human tissue specimens that provides high-resolution spatial detail regarding composition of the blood vessel wall. The protocol described here is a valuable adjunct that can be used as a research tool to inform finite element modeling of arteries, quantify pathologic response (ie, neointimal hyperplasia and vascular calcification), and evaluate the tissue/device interface of implanted medical devices.

Additive Manufacturing of Multi-Scale Porous Soft Tissue Implants That Encourage Vascularization and Tissue Ingrowth.

Medical devices, such as silicone-based prostheses designed for soft tissue implantation, often induce a suboptimal foreign-body response which results in a hardened avascular fibrotic capsule around the device, often leading to patient discomfort or implant failure. Here, it is proposed that additive manufacturing techniques can be used to deposit durable coatings with multiscale porosity on soft tissue implant surfaces to promote optimal tissue integration. Specifically, the "liquid rope coil effect", is exploited via direct ink writing, to create a controlled macro open-pore architecture, including over highly curved surfaces, while adapting atomizing spray deposition of a silicone ink to create a microporous texture. The potential to tailor the degree of tissue integration and vascularization using these fabrication techniques is demonstrated through subdermal and submuscular implantation studies in rodent and porcine models respectively, illustrating the implant coating's potential applications in both traditional soft tissue prosthetics and active drug-eluting devices.

Assessing the Effects of VEGF Releasing Microspheres on the Angiogenic and Foreign Body Response to a 3D Printed Silicone-Based Macroencapsulation Device.

Macroencapsulation systems have been developed to improve islet cell transplantation but can induce a foreign body response (FBR). The development of neovascularization adjacent to the device is vital for the survival of encapsulated islets and is a limitation for long-term device success. Previously we developed additive manufactured multi-scale porosity implants, which demonstrated a 2.5-fold increase in tissue vascularity and integration surrounding the implant when compared to a non-textured implant. In parallel to this, we have developed poly(ε-caprolactone-PEG-ε-caprolactone)-b-poly(L-lactide) multiblock copolymer microspheres containing VEGF, which exhibited continued release of bioactive VEGF for 4-weeks in vitro. In the present study, we describe the next step towards clinical implementation of an islet macroencapsulation device by combining a multi-scale porosity device with VEGF releasing microspheres in a rodent model to assess prevascularization over a 4-week period. An in vivo estimation of vascular volume showed a significant increase in vascularity (* p = 0.0132) surrounding the +VEGF vs. -VEGF devices, however, histological assessment of blood vessels per area revealed no significant difference. Further histological analysis revealed significant increases in blood vessel stability and maturity (** p = 0.0040) and vessel diameter size (*** p = 0.0002) surrounding the +VEGF devices. We also demonstrate that the addition of VEGF microspheres did not cause a heightened FBR. In conclusion, we demonstrate that the combination of VEGF microspheres with our multi-scale porous macroencapsulation device, can encourage the formation of significantly larger, stable, and mature blood vessels without exacerbating the FBR.

Implantable Therapeutic Reservoir Systems for Diverse Clinical Applications in Large Animal Models.

Regenerative medicine approaches, specifically stem cell technologies, have demonstrated significant potential to treat a diverse array of pathologies. However, such approaches have resulted in a modest clinical benefit, which may be attributed to poor cell retention/survival at the disease site. A delivery system that facilitates regional and repeated delivery to target tissues can provide enhanced clinical efficacy of cell therapies when localized delivery of high doses of cells is required. In this study, a new regenerative reservoir platform (Regenervoir) is described for use in large animal models, with relevance to cardiac, abdominal, and soft tissue pathologies. Regenervoir incorporates multiple novel design features essential for clinical translation, with a focus on scalability, mechanism of delivery, fixation to target tissue, and filling/refilling with a therapeutic cargo, and is demonstrated in an array of clinical applications that are easily translated to human studies. Regenervoir consists of a porous reservoir fabricated from a single material, a flexible thermoplastic polymer, capable of delivering cargo via fill lines to target tissues. A radiopaque shear thinning hydrogel can be delivered to the therapy reservoir and multiple fixation methods (laparoscopic tacks and cyanoacrylate bioadhesive) can be used to secure Regenervoir to target tissues through a minimally invasive approach.

The role of osteopontin in recovery from hind limb ischemia.

OBJECTIVE: Osteopontin (OPN) is a highly phosphorylated extracellular matrix glycoprotein that is involved in a diversity of biological processes. In the vascular wall, OPN is produced by monocytes/macrophages, endothelial cells, and smooth muscle cells, and it is thought to mediate adhesion, migration, and survival of these cell types. In this study, we hypothesized that OPN plays a critical role in recovery from limb ischemia. METHODS AND RESULTS: We induced hind limb ischemia in wild-type and OPN-/- mice. OPN-/- mice exhibited significantly delayed recovery of ischemic foot perfusion as determined by LDPI, impaired collateral vessel formation as measured using micro-CT, and diminished functional capacity of the ischemic limb. In the aortic ring assay, normal endothelial cell sprouting was found in OPN-/- mice. However, OPN-/- peritoneal monocytes/macrophages were found to possess significantly reduced migration in response to chemoattraction. CONCLUSIONS: This study provides evidence that a definitive biological role exists for OPN during ischemic limb revascularization, and we have suggested that this may be driven by impaired monocyte/macrophage migration in OPN-/- mice. These findings provide the first in vivo evidence that OPN may be a key regulator in postnatal vascular growth.

A novel platelet lysate hydrogel for endothelial cell and mesenchymal stem cell-directed neovascularization.

UNLABELLED: Mesenchymal stem cells (MSC) hold promise in promoting vascular regeneration of ischemic tissue in conditions like critical limb ischemia of the leg. However, this approach has been limited in part by poor cell retention and survival after delivery. New biomaterials offer an opportunity to localize cells to the desired tissue after delivery, but also to improve cell survival after delivery. Here we characterize the mechanical and microstructural properties of a novel hydrogel composed of pooled human platelet lysate (PL) and test its ability to promote MSC angiogenic activity using clinically relevant in vitro and in vivo models. This PL hydrogel had comparable storage and loss modulus and behaved as a viscoelastic solid similar to fibrin hydrogels despite having 1/4-1/10th the fibrin content of standard fibrin gels. Additionally, PL hydrogels enabled sustained release of endogenous PDGF-BB for up to 20days and were resistant to protease degradation. PL hydrogel stimulated pro-angiogenic activity by promoting human MSC growth and invasion in a 3D environment, and enhancing endothelial cell sprouting alone and in co-culture with MSCs. When delivered in vivo, the combination of PL and human MSCs improved local tissue perfusion after 8days compared to controls when assessed with laser Doppler perfusion imaging in a murine model of hind limb ischemia. These results support the use of a PL hydrogel as a scaffold for MSC delivery to promote vascular regeneration. STATEMENT OF SIGNIFICANCE: Innovative strategies for improved retention and viability of mesenchymal stem cells (MSCs) are needed for cellular therapies. Human platelet lysate is a potent serum supplement that improves the expansion of MSCs. Here we characterize our novel PL hydrogel's desirable structural and biologic properties for human MSCs and endothelial cells. PL hydrogel can localize cells for retention in the desired tissue, improves cell viability, and augments MSCs' angiogenic activity. As a result of these unique traits, PL hydrogel is ideally suited to serve as a cell delivery vehicle for MSCs injected into ischemic tissues to promote vascular regeneration, as demonstrated here in a murine model of hindlimb ischemia.