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Papers by Co Co

Impaired skin healing and progression into chronic wounds is a prevalent and growing medical prob... more Impaired skin healing and progression into chronic wounds is a prevalent and growing medical problem. Porous, resorbable biomaterials can be used as temporary substrates placed into skin defects to support cell infiltration, neo-tissue formation, and remodeling of nonhealing wounds. Naturally-derived biomaterials have promising healing benefits, but their low mechanical properties and exuberant costs limit their performance and use. Synthetic materials can be affordably manufactured and tuned across a broader range of physiochemical properties, but opportunities remain for tailoring them for ideal host immune and regenerative responses. Polyesters are the most clinically-tested class of synthetic biomaterials, but their hydrolysis releases acidic degradation products that can cause autocatalytic degradation processes that are poorly controlled and are not tied to cellular or other biologic activities. Here, we systemically explored a series of ROS-degradable polythioketal (PTK) uret...

ACS Nano, Sep 23, 2013

A family of pH-responsive diblock polymers composed of poly[(ethylene glycol)-b-[(2-(dimethylamin... more A family of pH-responsive diblock polymers composed of poly[(ethylene glycol)-b-[(2-(dimethylamino)ethyl methacrylate)-co-(butyl methacrylate)] PEG-(DMAEMA-co-BMA) was reversible addition fragmentation chain transfer (RAFT) synthesized with 0-75 mole% BMA in the second polymer block. The relative mole% of DMAEMA and BMA was varied in order to identify a polymer that can be used to formulate PEGylated, siRNA-loaded polyplex nanoparticles (NPs) with an optimized balance of cationic and hydrophobic content in the NP core based on siRNA packaging, cytocompatibility, blood circulation half-life, endosomal escape, and in vivo bioactivity. The polymer with 50:50 mole% of DMAEMA:BMA (polymer "50B") in the RAFTpolymerized block efficiently condensed siRNA into 100-nm NPs that displayed pH-dependent membrane disruptive behavior finely tuned for endosomal escape. In vitro delivery of siRNA with polymer 50B produced up to 94% protein-level knockdown of the model gene luciferase. The PEG corona of the NPs blocked nonspecific interactions with constituents of human whole blood, and the relative hydrophobicity of polymer 50B increased NP stability in the presence of human serum or the polyanion heparin. When injected intravenously, 50B NPs enhanced blood circulation half-life 3-fold relative to more standard PEG-DMAEMA (0B) NPs (p<0.05), due to improved stability and a reduced rate of renal clearance. The 50B NPs enhanced siRNA biodistribution to the liver and other organs and significantly increased gene silencing in the liver, kidneys, and spleen relative to the benchmark polymer 0B (p<0.05). These collective findings validate the functional significance of tuning the balance of cationic and hydrophobic content of polyplex NPs utilized for systemic siRNA delivery in vivo.

Macrophages present a spectrum of phenotypes that mediate both the pathogenesis and resolution of... more Macrophages present a spectrum of phenotypes that mediate both the pathogenesis and resolution of atherosclerotic lesions. Inflammatory macrophage phenotypes are pro-atherogenic, but the natural factors that instigate this polarization are largely unknown. Here, we demonstrate that microbial small RNAs (msRNA) are enriched on LDL and drive pro-inflammatory macrophage polarization and cytokine secretion via activation of the ribonucleic acid sensor toll-like receptor 8 (TLR8). Removal of msRNA cargo during LDL re-constitution yields particles that readily promote sterol loading but fail to stimulate inflammatory activation. Competitive antagonism of TLR8 with non-targeting locked nucleic acids (nt-LNA) was found to prevent nLDL-induced macrophage polarization in vitro, and re-organize lesion macrophage phenotypes in vivo, as determined by single-cell RNA sequencing. Critically, this was associated with reduced disease burden in distinct mouse models of atherosclerosis. These results ...

Materials

Autograft (AG) is the gold standard for bone grafts, but limited quantities and patient morbidity... more Autograft (AG) is the gold standard for bone grafts, but limited quantities and patient morbidity are associated with its use. AG extenders have been proposed to minimize the volume of AG while maintaining the osteoinductive properties of the implant. In this study, poly(ester urethane) (PEUR) and poly(thioketal urethane) (PTKUR) AG extenders were implanted in a 20-mm rabbit radius defect model to evaluate new bone formation and graft remodeling. Outcomes including µCT and histomorphometry were measured at 12 weeks and compared to an AG (no polymer) control. AG control examples exhibited new bone formation, but inconsistent healing was observed. The implanted AG control was resorbed by 12 weeks, while AG extenders maintained implanted AG throughout the study. Bone growth from the defect interfaces was observed in both AG extenders, but residual polymer inhibited cellular infiltration and subsequent bone formation within the center of the implant. PEUR-AG extenders degraded more rapi...

Cellular and Molecular Bioengineering, 2022

Introduction Short interfering RNAs (siRNAs) are potent nucleic acid-based drugs designed to targ... more Introduction Short interfering RNAs (siRNAs) are potent nucleic acid-based drugs designed to target disease driving genes that may otherwise be undruggable with small molecules. However, therapeutic potential of siRNA in vivo is limited by poor pharmacokinetic properties, including rapid renal clearance and nuclease degradation. Backpacking on natural carriers such as albumin, which is present at high concentration and has a long half-life in serum, is an effective way to modify pharmacokinetics of biologic drugs that otherwise have poor bioavailability. In this work, we sought to develop albumin-binding aptamer-siRNA chimeras to improve the bioavailability of siRNA. Methods A Systematic Evolution of Ligands through Exponential Enrichment (SELEX) approach was used to obtain modified RNA-binding aptamers, which were then fused directly to siRNA via in vitro transcription. Molecular and pharmacokinetic properties of the aptamer-siRNA chimeras were subsequently measured in vitro and in vivo. Results In vitro assays show that albumin-binding aptamers are stable in serum while maintaining potent gene knockdown capabilities in the chimera format. In vivo, the absolute circulation half-life of the best-performing aptamer-siRNA chimera (Clone 1) was 1.6-fold higher than a scrambled aptamer chimera control. Conclusions Aptamer-siRNA chimeras exhibit improved bioavailability without compromising biological activity. Hence, this albumin-binding aptamer-siRNA chimera approach may be a promising strategy for drug delivery applications. Supplementary Information The online version contains supplementary material available at 10.1007/s12195-022-00718-y.

The Duvall Advanced Therapeutics Laboratory specializes in design and application of smart polyme... more The Duvall Advanced Therapeutics Laboratory specializes in design and application of smart polymerbased technologies for: (1) intracellular delivery of biological drugs such as peptides and nucleic acids, (2) proximity-activated targeting of drugs to sites of inflammation and matrix remodeling, and (3) long-term, "ondemand" drug release from localized depots. These delivery systems are designed to improve the therapeutic index of existing drugs and/or to serve as enabling technologies for manipulation of intracellular targets currently considered to be "undruggable". To achieve optimal, finely-tuned properties for these varied biomedical applications, polymers are utilized that respond to one or more environmental stimuli including pH, matrix metalloproteinases, reactive oxygen species, and temperature. This talk will focus on the latest nanoparticle and bioconjugate strategies from our group focused on development of new molecularly-targeted breast cancer therapies.

Fetal growth restriction (FGR) significantly contributes to neonatal and perinatal morbidity and ... more Fetal growth restriction (FGR) significantly contributes to neonatal and perinatal morbidity and mortality. Currently, there are no effective treatment options for FGR during pregnancy. We have developed a nanoparticle gene therapy targeting the placenta to increase expression of human insulin-like growth factor 1 (hIGF-1) to correct fetal growth trajectories. Using the maternal nutrient restriction (MNR) guinea pig model of FGR, an ultrasound-guided, intra-placental injection of non-viral, polymer-based nanoparticle gene therapy containing plasmid with the hIGF-1 gene and placenta-specific Cyp19a1 promotor was administered at mid-pregnancy. Sustained hIGF-1 expression was confirmed in the placenta five days after treatment. Whilst gene therapy treatment did not change fetal weight, circulating fetal glucose concentration were 33-67% higher. This was associated with increased expression of glucose and amino acid transporters in the placenta. Additionally, nanoparticle gene therapy t...

ACS Applied Materials & Interfaces, 2021

Osteoarthritis (OA) is treated with the intra-articular injection of steroids such as dexamethaso... more Osteoarthritis (OA) is treated with the intra-articular injection of steroids such as dexamethasone (DEX) to provide shortterm pain management. However, DEX treatment suffers from rapid joint clearance. Here, 20 × 10 μm, shape-defined poly(D,L-lactide-coglycolide)acid microPlates (μPLs) are created and intra-articularly deposited for the sustained release of DEX. Under confined conditions, DEX release is projected to persist for several months, with only ∼20% released in the first month. In a highly rigorous murine knee overload injury model (post-traumatic osteoarthritis), a single intra-articular injection of Cy5-μPLs is detected in the cartilage surface, infrapatellar fat pad/synovium, joint capsule, and posterior joint space up to 30 days. One intra-articular injection of DEX-μPL (1 mg kg −1) decreased the expression of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6, and matrix metalloproteinase (MMP)-13 by approximately half compared to free DEX at 4 weeks post-treatment. DEX-μPL also reduced loadinduced histological changes in the articular cartilage and synovial tissues relative to saline or free DEX. In sum, the μPLs provide sustained drug release along with the capability to precisely control particle geometry and mechanical properties, yielding longlasting benefits in overload-induced OA. This work motivates further study and development of particles that provide combined pharmacological and mechanical benefits.

Acta Biomaterialia, 2021

Most fractures heal by a combination of endochondral and intramembranous ossification dependent u... more Most fractures heal by a combination of endochondral and intramembranous ossification dependent upon strain and vascularity at the fracture site. Many biomaterials-based bone regeneration strategies rely on the use of calcium phosphates such as nano-crystalline hydroxyapatite (nHA) to create bone-like scaffolds. In this study, nHA was dispersed in reactive polymers to form composite scaffolds that were evaluated both in vitro and in vivo. Matrix assays, immunofluorescent staining, and Western blots demonstrated that nHA influenced mineralization and subsequent osteogenesis in a dose-dependent manner in vitro. Furthermore, nHA dispersed in polymeric composites promoted osteogenesis by a similar mechanism as particulated nHA. Scaffolds were implanted into a 2-mm defect in the femoral diaphysis or metaphysis of Sprague-Dawley rats to evaluate new bone formation at 4 and 8 weeks. Two formulations were tested: a poly(thioketal urethane) scaffold without nHA (PTKUR) and a PTKUR scaffold augmented with 22 wt% nHA (22nHA). The scaffolds supported new bone formation in both anatomic sites. In the metaphysis, augmentation of scaffolds with nHA promoted an intramembranous healing response. Within the diaphysis, nHA inhibited endochondral ossification. Immunohistochemistry was performed on cryo-sections of the bone/scaffold interface in which CD146, CD31, Endomucin, CD68, and Myeloperoxidase were evaluated. No significant differences in the infiltrating cell populations were observed. These findings suggest that nHA dispersed in polymeric composites induces osteogenic differentiation of adherent endogenous cells, which has skeletal site-specific effects on fracture healing. SIGNIFICANCE STATEMENT: Understanding the mechanism by which synthetic scaffolds promote new bone formation in preclinical models is crucial for bone regeneration applications in the clinic where complex fracture cases are seen. In this study, we found that dispersion of nHA in polymeric scaffolds promoted in vitro osteogenesis in a dose-dependent manner through activation of the PiT1 receptor and subsequent downstream Erk1/2 signaling. While augmentation of polymeric scaffolds with nHA enhanced intramembranous ossification in metaphyseal defects, it inhibited endochondral ossification in diaphyseal defects. Thus, our findings provide new insights into designing synthetic bone grafts that complement the skeletal site-specific fracture healing response.

In vivonanocarrier-associated toxicity is a significant and poorly understood hurdle to clinical ... more In vivonanocarrier-associated toxicity is a significant and poorly understood hurdle to clinical translation of siRNA nanomedicines. In this work, we demonstrate that platelet activating factor (PAF), an inflammatory lipid mediator, plays a key role in nanocarrier-associated toxicities, and that prophylactic inhibition of the PAF receptor (PAFR) completely prevents these toxicities. High-dose intravenous injection of siRNA-polymer nano-complexes (si-NPs) elicited acute, shock-like symptoms (vasodilation and vascular leak) in mice and caused a three-fold increase in blood PAF levels. PAFR inhibition completely prevented these toxicities, indicating PAF activity is a primary driver of systemic si-NP toxicity. Pre-treatment with clodronate liposomes fully abrogated si-NP-associated increases in blood PAF and consequent toxicities, suggesting that nanoparticle uptake by Kupffer macrophages is the source of PAF. Assessment of varied si-NP chemistries further confirmed that toxicity level...

ACS Nano, 2020

Breast cancer patients are at high risk for bone metastasis. Metastatic bone disease is a major c... more Breast cancer patients are at high risk for bone metastasis. Metastatic bone disease is a major clinical problem that leads to a reduction in mobility, increased risk of pathologic fracture, severe bone pain, and other skeletal-related events. The transcription factor Gli2 drives expression of parathyroid hormone-related protein (PTHrP), which activates osteoclastmediated bone destruction, and previous studies showed that Gli2 genetic repression in bone-metastatic tumor cells significantly reduces tumor-induced bone destruction. Small molecule inhibitors of Gli2 have been identified; however, the lipophilicity and poor pharmacokinetic profile of these compounds have precluded their success in vivo. In this study, we designed a bone-targeted nanoparticle (BTNP) comprising an amphiphilic diblock copolymer of poly-[(propylene sulfide)-block-(alendronate acrylamide-coN ,N-dimethylacrylamide)] [PPS-b-P(Aln-co-DMA)] to encapsulate and preferentially deliver a small molecule Gli2 inhibitor, GANT58, to boneassociated tumors. The mol % of the bisphosphonate Aln in the hydrophilic polymer block was varied in order to optimize BTNP targeting to tumor-associated bone by a combination of nonspecific tumor accumulation (presumably through the enhanced permeation and retention effect) and active bone binding. Although 100% functionalization with Aln created BTNPs with strong bone binding, these BTNPs had highly negative zeta-potential, resulting in shorter circulation time, greater liver uptake, and less distribution to metastatic tumors in bone. However, 10 mol % of Aln in the hydrophilic block generated a formulation with a favorable balance of systemic pharmacokinetics and bone binding, providing the highest bone/liver biodistribution ratio among formulations tested. In an intracardiac tumor cell injection model of breast cancer bone metastasis, treatment with the lead candidate GANT58-BTNP formulation decreased tumor-associated bone lesion area 3-fold and increased bone volume fraction in the tibiae of the mice 2.5-fold. Aln conferred bone targeting to the GANT58-BTNPs, which increased GANT58 concentration in the tumor-associated bone relative to untargeted NPs, and also provided benefit through the direct antiresorptive therapeutic function of Aln. The dual benefit of the Aln in the BTNPs was supported by the observations that drug-free Aln-containing BTNPs improved bone volume fraction in bone-tumor-bearing mice, while GANT58-BTNPs created better therapeutic outcomes than both unloaded BTNPs and GANT58-loaded untargeted NPs. These findings suggest GANT58-BTNPs have potential to potently inhibit tumor-driven osteoclast activation and resultant bone destruction in patients with bone-associated tumor metastases.

Endosomal escape is a critical step in intracellular delivery of biomacromolecular drugs, but qua... more Endosomal escape is a critical step in intracellular delivery of biomacromolecular drugs, but quantitative, high throughput study of endosomal vesicle disruption remains elusive. We designed two genetically encoded split luciferase “turn on” reporters that can be assayed rapidly in well plates on live cells using a luminometer. Both systems use non-luminescent N-terminal and C-terminal luciferase fragments which can reconstitute a functional luminescent enzyme when they are held in proximity by their fusion partners. The first system uses Gal8 and CALCOCO2 fused to these fragments, which interact following endosome disruption and facilitate complementation of the split luciferase fragments to produce significant luminescence when luciferin is added. The second system uses the N-terminal carbohydrate recognition domain of Gal8 (G8-NCRD) fused to both luciferase fragments. Following endosome disruption, G8-NCRD binds to exposed glycans inside endosomes, concentrating both fragments th...

Nature Communications, 2019

Peptides and biologics provide unique opportunities to modulate intracellular targets not druggab... more Peptides and biologics provide unique opportunities to modulate intracellular targets not druggable by conventional small molecules. Most peptides and biologics are fused with cationic uptake moieties or formulated into nanoparticles to facilitate delivery, but these systems typically lack potency due to low uptake and/or entrapment and degradation in endolysosomal compartments. Because most delivery reagents comprise cationic lipids or polymers, there is a lack of reagents specifically optimized to deliver cationic cargo. Herein, we demonstrate the utility of the cytocompatible polymer poly(propylacrylic acid) (PPAA) to potentiate intracellular delivery of cationic biomacromolecules and nano-formulations. This approach demonstrates superior efficacy over all marketed peptide delivery reagents and enhances delivery of nucleic acids and gene editing ribonucleoproteins (RNPs) formulated with both commercially-available and our own custom-synthesized cationic polymer delivery reagents....

Tissue Engineering Part B: Reviews, 2019

To this day, tissue reconstruction and replacement to address extensive tissue defects due to tra... more To this day, tissue reconstruction and replacement to address extensive tissue defects due to trauma, tumor resection, genetic and/or chronic diseases, or excessive debridement present a major clinical challenge. Traditional reconstructive techniques most commonly utilize autologous tissue. Undoubtedly, autologous composite tissue transfers or ''flaps,'' skin grafts, as well as the harvesting of bone and/or cartilage have substantially improved the health, functional, and aesthetic outcomes of millions of patients. Unfortunately, these procedures are not without their drawbacks. These include increased operative time, complexity, cost, limited availability of qualitative autologous tissue, wound healing complications, tissue flap failure, and substantial donor-site morbidity. Recently, collaborative research teams-consisting of surgeons, scientists, and engineers-have made substantial progress in their attempts to solve these problems. This article provides historical perspective, covers the major limitations of current standards of care, and reviews recent advances and future prospects in applied bioengineering in the context of tissue reconstruction, replacement, and regeneration.

Biomaterials, 2018

While polymeric nano-formulations for RNAi therapeutics hold great promise for molecularly-target... more While polymeric nano-formulations for RNAi therapeutics hold great promise for molecularly-targeted, personalized medicine, they possess significant systemic delivery challenges including rapid clearance from circulation and the potential for carrier-associated toxicity due to cationic polymer or lipid components. Herein, we evaluated the in vivo pharmacokinetic and safety impact of often-overlooked formulation parameters, including the ratio of carrier polymer to cargo siRNA and hydrophobic siRNA modification in combination with hydrophobic polymer components (dual hydrophobization). For these studies, we used nano-polyplexes (NPs) with well-shielded, zwitterionic coronas, resulting in various NP formulations of equivalent hydrodynamic size and neutral surface charge regardless of charge ratio. Doubling nano-polyplex charge ratio from 10 to 20 increased circulation half-life five-fold and pharmacokinetic area under the curve four-fold, but was also associated with increased liver enzymes, a marker of hepatic damage. Dual hydrophobization achieved by formulating NPs with palmitic acid-modified siRNA (siPA-NPs) both reduced the amount of carrier polymer required to achieve optimal pharmacokinetic profiles and abrogated liver toxicities. We also show that optimized zwitterionic siPA-NPs are well-tolerated upon long-term, repeated administration in mice and exhibit greater than twofold increased uptake in orthotopic MDA-MB-231 xenografts compared to commercial transfection reagent, in vivo-jetPEI ®. These data suggest that charge ratio optimization has important in vivo implications and that dual hydrophobization strategies can be used to maximize both NP circulation time and safety.

Tissue Engineering Part A, 2018

Iliac crest autograft (AG) is the gold standard for bone grafting. Due to the limited supply of a... more Iliac crest autograft (AG) is the gold standard for bone grafting. Due to the limited supply of autograft, synthetic materials such as ceramics and polymers have been proposed as AG extenders to minimize the volume of AG required for induction of new bone formation. However, the feasibility of reactive polymers for use as settable AG extenders has not been previously investigated. In this study, a reactive oxygen species-degradable poly(thioketal urethane) (PTKUR) was evaluated as a settable AG extender. AG was anticipated to enhance infiltration of cells into the defect and induce new bone formation. Histological analysis of a preliminary study in a rat femoral segmental defect model showed that cells infiltrated PTKUR/AG implants at 4 weeks. In a second experiment, implantation into an intertransverse process model of bone formation showed bone remodeling from the superior and inferior transverse processes. Histological analysis combining data from stains and fluorochrome injections showed lamellar bone formation ongoing near the base of the transverse processes after 8 weeks. Similar findings were observed for a second group, in which 35% of the AG was replaced with calcium phosphate granules. These observations highlight the potential of PTKUR for use as a settable AG extender.

Journal of controlled release : official journal of the Controlled Release Society, Jan 28, 2018

Herein, excipients are investigated to ameliorate the deleterious effects of lyophilization on pe... more Herein, excipients are investigated to ameliorate the deleterious effects of lyophilization on peptide-polymer nano-polyplex (NP) morphology, cellular uptake, and bioactivity. The NPs are a previously-described platform technology for intracellular peptide delivery and are formulated from a cationic therapeutic peptide and the anionic, pH-responsive, endosomolytic polymer poly(propylacrylic acid) (PPAA). These NPs are effective when formulated and immediately used for delivery into cells and tissue, but they are not amenable to reconstitution following storage as a lyophilized powder due to aggregation. To develop a lyophilized NP format that facilitates longer-term storage and ease of use, MAPKAP kinase 2 inhibitory peptide-based NPs (MK2i-NPs) were prepared in the presence of a range of concentrations of the excipients sucrose, trehalose, and lactosucrose prior to lyophilization and storage. All excipients improved particle morphology post-lyophilization and significantly improved...

Cell death & disease, Jan 17, 2018

Estrogen receptor-α positive (ERα+) breast cancer accounts for approximately 70-80% of the nearly... more Estrogen receptor-α positive (ERα+) breast cancer accounts for approximately 70-80% of the nearly 25,0000 new cases of breast cancer diagnosed in the US each year. Endocrine-targeted therapies (those that block ERα activity) serve as the first line of treatment in most cases. Despite the proven benefit of endocrine therapies, however, ERα+ breast tumors can develop resistance to endocrine therapy, causing disease progression or relapse, particularly in the metastatic setting. Anti-apoptotic Bcl-2 family proteins enhance breast tumor cell survival, often promoting resistance to targeted therapies, including endocrine therapies. Herein, we investigated whether blockade of anti-apoptotic Bcl-2 family proteins could sensitize luminal breast cancers to anti-estrogen treatment. We used long-term estrogen deprivation (LTED) of human ERα+ breast cancer cell lines, an established model of sustained treatment with and acquired resistance to aromatase inhibitors (AIs), in combination with Bcl-...

Journal of Controlled Release, 2017

A rationally-designed library of ternary siRNA polyplexes was developed and screened for gene sil... more A rationally-designed library of ternary siRNA polyplexes was developed and screened for gene silencing efficacy in vitro and in vivo with the goal of overcoming both cell-level and systemic delivery barriers. [2-(dimethylamino)ethyl methacrylate] (DMAEMA) was homopolymerized or colpolymerized (50 mol% each) with butyl methacrylate (BMA) from a reversible additionfragmentation chain transfer (RAFT) chain transfer agent, with and without pre-conjugation to polyethylene glycol (PEG). Both single block polymers were tested as core-forming units, and both PEGylated, diblock polymers were screened as corona-forming units. Ternary siRNA polyplexes were assembled with varied amounts and ratios of core-forming polymers to PEGylated corona-forming polymers. The impact of polymer composition/ratio, hydrophobe (BMA) placement, and surface PEGylation density was correlated to important outcomes such as polyplex size, stability, pH-dependent membrane disruptive activity, biocompatibility, and gene silencing efficiency. The lead formulation, DB4-PDB12, was optimally PEGylated not only to ensure colloidal stability (no change in size by DLS between 0 and 24 hr) and neutral surface charge (0.139 mV) but also to maintain higher cell uptake (>90% positive cells) than the most densely PEGylated particles. The DB4-PDB12 polyplexes also incorporated BMA in both the polyplex core-and corona-forming polymers, resulting in robust endosomolysis and in vitro siRNA silencing (~85% protein level knockdown) of the model gene luciferase across multiple cell types. Further, the DB4-PDB12 polyplexes exhibited greater stability, increased blood circulation time, reduced renal clearance, increased tumor biodistribution, and greater silencing of luciferase compared to our previously-optimized, binary parent formulation following intravenous (i.v.) delivery. This polyplex library approach enabled concomitant optimization of the composition and ratio of core-and corona-forming polymers (indirectly tuning PEGylation density) and identification of a ternary nanomedicine optimized to overcome important siRNA delivery barriers in vitro and in vivo.

Perfusion, 2017

Objectives: Unregulated intraoperative distension of human saphenous vein (SV) graft leads to sup... more Objectives: Unregulated intraoperative distension of human saphenous vein (SV) graft leads to supraphysiologic luminal pressures and causes acute physiologic and cellular injury to the conduit. The effect of distension on tissue viscoelasticity, a biophysical property critical to a successful graft, is not well described. In this investigation, we quantify the loss of viscoelasticity in SV deformed by distension and compare the results to tissue distended in a pressure-controlled fashion. Materials and Methods: Unmanipulated porcine SV was used as a control or distended without regulation and distended with an in-line pressure release valve (PRV). Rings were cut from these tissues and suspended on a muscle bath. Force versus time tracings of tissue constricted with KCl (110 mM) and relaxed with sodium nitroprusside (SNP) were fit to the Hill model of viscoelasticity, using mean absolute error (MAE) and r2-goodness of fit as measures of conformity. Results: One-way ANOVA analysis dem...