Publications by authors named "Naren Vyavahare"

39 Publications

Systemic delivery of targeted nanotherapeutic reverses angiotensin II-induced abdominal aortic aneurysms in mice.

Sci Rep 2021 Apr 21;11(1):8584. Epub 2021 Apr 21.

Department of Bioengineering, Clemson University, 501 Rhodes Engineering Research Center, Clemson, SC, 29634, USA.

Abdominal aortic aneurysm (AAA) disease causes dilation of the aorta, leading to aortic rupture and death if not treated early. It is the 14th leading cause of death in the U.S. and 10th leading cause of death in men over age 55, affecting thousands of patients. Despite the prevalence of AAA, no safe and efficient pharmacotherapies exist for patients. The deterioration of the elastic lamina in the aneurysmal wall is a consistent feature of AAAs, making it an ideal target for delivering drugs to the AAA site. In this research, we conjugated nanoparticles with an elastin antibody that only targets degraded elastin while sparing healthy elastin. After induction of aneurysm by 4-week infusion of angiotensin II (Ang II), two biweekly intravenous injections of pentagalloyl glucose (PGG)-loaded nanoparticles conjugated with elastin antibody delivered the drug to the aneurysm site. We show that targeted delivery of PGG could reverse the aortic dilation, ameliorate the inflammation, restore the elastic lamina, and improve the mechanical properties of the aorta at the AAA site. Therefore, simple iv therapy of PGG loaded nanoparticles can be an effective treatment option for early to middle stage aneurysms to reverse disease progression and return the aorta to normal homeostasis.
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http://dx.doi.org/10.1038/s41598-021-88017-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8060294PMC
April 2021

Advancing peptide siRNA-carrier designs through L/D-amino acid stereochemical modifications to enhance gene silencing.

Mol Ther Nucleic Acids 2021 Jun 19;24:462-476. Epub 2021 Mar 19.

Department of Oral Health Sciences, James B. Edwards College of Dental Medicine, Medical University of South Carolina (MUSC), Charleston, SC 29425, USA.

The 599 peptide has been previously shown to effectively deliver small interfering RNAs (siRNAs) to cancer cells, inducing targeted-oncogene silencing, with a consequent inhibition of tumor growth. Although effective, this study was undertaken to advance the 599 peptide siRNA-carrier design through L/D-amino acid stereochemical modifications. Consequently, 599 was modified to generate eight different peptide variants, incorporating either different stereochemical patterns of L/D-amino acids or a specific D-amino acid substitution. Upon analysis of the variants, it was observed that these modifications could, in some instances, increase/decrease the binding, nuclease/serum stability, and complex release of siRNAs, as well as influence the gene-silencing efficiencies of the complex. These modifications were also found to affect cellular uptake and intracellular localization patterns of siRNA cargo, with one particular variant capable of mediating binding of siRNAs to specific cellular projections, identified as filopodia. Interestingly, this variant also exhibited the most enhanced gene silencing in comparison to the parent 599 peptide, thus suggesting a possible connection between filopodia binding and enhanced gene silencing. Together, these data demonstrate the utility of peptide stereochemistry, as well as the importance of a key D-amino acid modification, in advancing the 599 carrier design for the enhancement of gene silencing in cancer cells.
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http://dx.doi.org/10.1016/j.omtn.2021.03.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8040110PMC
June 2021

Polyphenol treatments increase elastin and collagen deposition by human dermal fibroblasts; Implications to improve skin health.

J Dermatol Sci 2021 May 16;102(2):94-100. Epub 2021 Mar 16.

Department of Bioengineering, Clemson University, Clemson, SC, USA. Electronic address:

Background: Skin aging is marked by progressive loss in elastin and collagen that causes wrinkling and sagging of skin. Tropoelastin (TE) is the precursor monomer of elastin secreted by cells that cross-links extracellularly to create functional elastic fibers. Cells maintain the capacity to make TE during the aging process. However, the process of extracellular tropoelastin cross-linking diminishes with age. Others have shown that TE production by cells increases with UV exposure.

Objective: We hypothesize that polyphenols may help coacervate cell secreted TE due to its elastin binding property and increase insoluble elastin in human dermal fibroblasts (HDFs). Increase in TE production by short term UV exposure may further improve elastin deposition by polyphenols.

Methods: We treated HDFs with polyphenols viz epigallocatechin gallate (EGCG) and pentagalloyl glucose (PGG) either with or without intermittent (UVA, 12 min three times a week) exposure for 3, 7, and 14 days.

Results: Polyphenols increased insoluble elastin deposition several folds as compared to control untreated cells. Furthermore, short UVA light exposure led to several-fold increased TE production in HDFs. Still, UVA exposure alone was unable to increase insoluble elastic fibers. When polyphenols were introduced with UVA exposure, insoluble elastin deposition was further enhanced in HDFs (30-45-fold increase). Polyphenol treatments with UVA exposure also led to increased collagen deposition in cell cultures. Polyphenols also prevented cell oxidation during UVA exposure.

Conclusions: Polyphenols in combination with short exposure to UVA light increase extracellular matrix deposition of elastin and collagen and may improve skin properties.
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http://dx.doi.org/10.1016/j.jdermsci.2021.03.002DOI Listing
May 2021

Targeted Gold Nanoparticles as an Indicator of Mechanical Damage in an Elastase Model of Aortic Aneurysm.

Ann Biomed Eng 2020 Aug 2;48(8):2268-2278. Epub 2020 Apr 2.

Biomedical Engineering Program, University of South Carolina, Columbia, SC, 29208, USA.

Elastin is a key structural protein and its pathological degradation deterministic in aortic aneurysm (AA) outcomes. Unfortunately, using current diagnostic and clinical surveillance techniques the integrity of the elastic fiber network can only be assessed invasively. To address this, we employed fragmented elastin-targeting gold nanoparticles (EL-AuNPs) as a diagnostic tool for the evaluation of unruptured AAs. Electron dense EL-AuNPs were visualized within AAs using micro-computed tomography (micro-CT) and the corresponding Gold-to-Tissue volume ratios quantified. The Gold-to-Tissue volume ratios correlated strongly with the concentration (0, 0.5, or 10 U/mL) of infused porcine pancreatic elastase and therefore the degree of elastin damage. Hyperspectral mapping confirmed the spatial targeting of the EL-AuNPs to the sites of damaged elastin. Nonparametric Spearman's rank correlation indicated that the micro-CT-based Gold-to-Tissue volume ratios had a strong correlation with loaded (ρ = 0.867, p-val = 0.015) and unloaded (ρ = 0.830, p-val = 0.005) vessel diameter, percent dilation (ρ = 0.976, p-val = 0.015), circumferential stress (ρ = 0.673, p-val = 0.007), loaded (ρ = - 0.673, p-val = 0.017) and unloaded (ρ = - 0.697, p-val = 0.031) wall thicknesses, circumferential stretch (ρ = - 0.7234, p-val = 0.018), and lumen area compliance (ρ = - 0.831, p-val = 0.003). Likewise, in terms of axial force and axial stress vs. stretch, the post-elastase vessels were stiffer. Collectively, these findings suggest that, when combined with CT imaging, EL-AuNPs can be used as a powerful tool in the non-destructive estimation of mechanical and geometric features of AAs.
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http://dx.doi.org/10.1007/s10439-020-02500-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7564014PMC
August 2020

Nanoparticle-based targeted delivery of pentagalloyl glucose reverses elastase-induced abdominal aortic aneurysm and restores aorta to the healthy state in mice.

PLoS One 2020 27;15(3):e0227165. Epub 2020 Mar 27.

Department of Bioengineering, Clemson University, Clemson, SC, United States of America.

Aim: Abdominal aortic aneurysms (AAA) is a life-threatening weakening and expansion of the abdominal aorta due to inflammatory cell infiltration and gradual degeneration of extracellular matrix (ECM). There are no pharmacological therapies to treat AAA. We tested the hypothesis that nanoparticle (NP) therapy that targets degraded elastin and delivers anti-inflammatory, anti-oxidative, and ECM stabilizing agent, pentagalloyl glucose (PGG) will reverse advance stage aneurysm in an elastase-induced mouse model of AAA.

Method And Results: Porcine pancreatic elastase (PPE) was applied periadventitially to the infrarenal aorta in mice and AAA was allowed to develop for 14 days. Nanoparticles loaded with PGG (EL-PGG-NPs) were then delivered via IV route at 14-day and 21-day (10 mg/kg of body weight). A control group of mice received no therapy. The targeting of NPs to the AAA site was confirmed with fluorescent dye marked NPs and gold NPs. Animals were sacrificed at 28-d. We found that targeted PGG therapy reversed the AAA by decreasing matrix metalloproteinases MMP-9 and MMP-2, and the infiltration of macrophages in the medial layer. The increase in diameter of the aorta was reversed to healthy controls. Moreover, PGG treatment restored degraded elastic lamina and increased the circumferential strain of aneurysmal aorta to the healthy levels.

Conclusion: Our results support that site-specific delivery of PGG with targeted nanoparticles can be used to treat already developed AAA. Such therapy can reverse inflammatory markers and restore arterial homeostasis.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0227165PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7100957PMC
May 2020

Gold nanoparticles that target degraded elastin improve imaging and rupture prediction in an AngII mediated mouse model of abdominal aortic aneurysm.

Theranostics 2019 31;9(14):4156-4167. Epub 2019 May 31.

Department of Bioengineering, Clemson University.

: Abdominal aortic aneurysms (AAA) are characterized by a progressive disruption and weakening of the extracellular matrix (ECM) leading to dilation of the aorta which can be fatal if not treated. Current diagnostic imaging modalities provides little insight on the varying degree of ECM degeneration that precedes rupture in AAAs. Targeted delivery of contrast agents such as gold nanoparticles (GNPs) that bind to degraded matrix could prove useful when combined with computed tomography (CT) to provide a non-invasive surrogate marker of AAA rupture potential. : AAAs were induced by chronic infusion of angiotensin II (AngII) into low density-lipoprotein receptor-deficient (LDLr -/-) mice in combination with a high-fat diet. Abdominal ultrasound was used to monitor disease progression and to assess the circumferential strain throughout the cardiac cycle. At six weeks, GNPs conjugated with an elastin antibody (EL-GNP) were injected retro-orbitally. Mice were euthanized 24 hours after EL-GNP injection, and aortas were explanted and scanned with a micro-CT system. Histological assessment and 3D models of the aneurysms with micro-CT were used to determine the EL-GNPs distribution. Isolated vessel burst pressure testing was performed on each aneurysmal aorta to quantify rupture strength and to assess rupture location. : Aneurysms were found along the suprarenal aorta in AngII infused mice. Darkfield microscopy indicated EL-GNPs accumulation around the site of degraded elastin while avoiding the healthy and intact elastin fibers. Using nonlinear regression, the micro-CT signal intensity of EL-GNPs along the suprarenal aortas correlated strongly with burst pressures (R=0.9415) but not the dilation as assessed by ultrasound measurements. : Using an established mouse model of AAA, we successfully demonstrated targeting of EL-GNPs to damaged aortic elastin and correlated micro-CT-based signal intensities with burst pressures. Thus, we show that this novel targeting technique can be used as a diagnostic tool to predict the degree of elastin damage and therefore rupture potential in AAAs better than the extent of dilation.
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http://dx.doi.org/10.7150/thno.34441DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6592177PMC
July 2020

Site-specific chelation therapy with EDTA-loaded albumin nanoparticles reverses arterial calcification in a rat model of chronic kidney disease.

Sci Rep 2019 02 22;9(1):2629. Epub 2019 Feb 22.

Department of Bioengineering, Clemson University, Clemson, SC, USA.

Medial arterial calcification (MAC) is a common outcome in diabetes and chronic kidney disease (CKD). It occurs as linear mineral deposits along the degraded elastin lamellae and is responsible for increased aortic stiffness and subsequent cardiovascular events. Current treatments for calcification, particularly in CKD, are predominantly focused on regulating the mineral disturbance and other risk factors. Ethylene diamine tetraacetic acid (EDTA), a chelating agent, can resorb mineral deposits, but the systemic delivery of EDTA may cause side effects such as hypocalcemia and bone resorption. We have developed elastin antibody conjugated albumin nanoparticles that target only degraded elastin in vasculature while sparing healthy tissues. In this study, we tested a targeted nanoparticle-based EDTA chelation therapy to reverse CKD-associated MAC. Renal failure was induced in Sprague-Dawley rats by a high adenine diet supplemented by high P and Ca for 28 days that led to MAC. Intravenous delivery of DiR dye-loaded nanoparticles confirmed targeting to vascular degraded elastin and calcification sites within 24 hours. Next, EDTA-loaded albumin nanoparticles conjugated with an anti-elastin antibody were intravenously injected twice a week for two weeks. The targeted nanoparticles delivered EDTA at the site of vascular calcification and reversed mineral deposits without any untoward effects. Systemic EDTA injections or blank nanoparticles were ineffective in reversing MAC. Reversal of calcification seems to be stable as it did not return after the treatment was stopped for an additional four weeks. Targeted EDTA chelation therapy successfully reversed calcification in this adenine rat model of CKD. We consider that targeted NP therapy will provide an attractive option to reverse calcification and has a high potential for clinical translation.
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http://dx.doi.org/10.1038/s41598-019-39639-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6385348PMC
February 2019

Pentagalloyl glucose increases elastin deposition, decreases reactive oxygen species and matrix metalloproteinase activity in pulmonary fibroblasts under inflammatory conditions.

Biochem Biophys Res Commun 2018 04 19;499(1):24-29. Epub 2018 Mar 19.

Department of Bioengineering, Clemson University, SC, United States. Electronic address:

Emphysema is characterized by degradation of lung alveoli that leads to poor airflow in lungs. Irreversible elastic fiber degradation by matrix metalloproteinases (MMPs) and reactive oxygen species (ROS) activity leads to loss of elasticity and drives the progression of this disease. We investigated if a polyphenol, pentagalloyl glucose (PGG) can increase elastin production in pulmonary fibroblasts. We also studied the effect of PGG treatment in reducing MMP activity and ROS levels in cells. We exposed rat pulmonary fibroblasts to two different types of inflammatory environments i.e., tumor necrosis factor-α (TNF-α) and cigarette smoke extract (CSE) to mimic the disease. Parameters like lysyl oxidase (LOX) and elastin gene expression, MMP-9 activity in the medium, lysyl oxidase (LOX) activity and ROS levels were studied to assess the effect of PGG on pulmonary fibroblasts. CSE inhibited lysyl oxidase (LOX) enzyme activity that resulted in a decreased elastin formation. Similarly, TNF-α treated cells showed less elastin in the cell layers. Both these agents caused increase in MMP activity and ROS levels in cells. However, when supplemented with PGG treatment along with these two inflammatory agents, we saw a significant increase in elastin deposition, reduction in both MMP activity and ROS levels. Thus PGG, which has anti-inflammatory, anti-oxidant properties coupled with its ability to aid in elastic fiber formation, can be a multifunctional drug to potentially arrest the progression of emphysema.
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http://dx.doi.org/10.1016/j.bbrc.2018.03.100DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5894519PMC
April 2018

Systemic Delivery of Nanoparticles Loaded with Pentagalloyl Glucose Protects Elastic Lamina and Prevents Abdominal Aortic Aneurysm in Rats.

J Cardiovasc Transl Res 2016 12 19;9(5-6):445-455. Epub 2016 Aug 19.

Clemson University, Clemson, SC, USA.

Degeneration of elastin plays a vital role in the pathology and progression of abdominal aortic aneurysm (AAA). Our previous study showed that pentagalloyl glucose (PGG), a core derivative of tannic acid, hinders the development of AAAs in a clinically relevant animal model when applied locally. In this study, we tested whether targeted nanoparticles (NPs) can deliver PGG to the site of an aneurysm and prevent aneurysmal growth by protecting elastin. PGG-loaded albumin NPs with a surface-conjugated elastin-specific antibody were prepared. Aneurysms were induced by calcium chloride-mediated injury to the abdominal aorta in rats. NPs were injected into the tail vein after 10 days of CaCl injury. Rats were euthanized after 38 days. PGG delivery led to reduction in macrophage recruitment, matrix metalloproteinase (MMP) activity, elastin degradation, calcification, and development of aortic aneurysm. Such NP delivery offers the potential for the development of effective and safe therapies for AAA.
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http://dx.doi.org/10.1007/s12265-016-9709-xDOI Listing
December 2016

Targeted drug delivery to emphysematous lungs: Inhibition of MMPs by doxycycline loaded nanoparticles.

Pulm Pharmacol Ther 2016 08 25;39:64-73. Epub 2016 Jun 25.

Department of Bioengineering, Clemson University, SC, USA. Electronic address:

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http://dx.doi.org/10.1016/j.pupt.2016.06.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4988062PMC
August 2016

Prevention of abdominal aortic aneurysm progression by targeted inhibition of matrix metalloproteinase activity with batimastat-loaded nanoparticles.

Circ Res 2015 Nov 6;117(11):e80-9. Epub 2015 Oct 6.

From the Department of Bioengineering, Clemson University, SC (N.N., P.N.-G., A.S., A.C., P.G., N.R.V.); Department of Biomedical Engineering, Edwards Lifesciences Center for Advanced Cardiovascular Technology, University of California, Irvine (A.S.); and Division of Vascular Surgery, Greenville Health System, SC (C.G.C., B.H.G.).

Rationale: Matrix metalloproteinases (MMPs)-mediated extracellular matrix destruction is the major cause of development and progression of abdominal aortic aneurysms. Systemic treatments of MMP inhibitors have shown effectiveness in animal models, but it did not translate to clinical success either because of low doses used or systemic side effects of MMP inhibitors. We propose a targeted nanoparticle (NP)-based delivery of MMP inhibitor at low doses to the abdominal aortic aneurysms site. Such therapy will be an attractive option for preventing expansion of aneurysms in patients without systemic side effects.

Objective: Our previous study showed that poly(d,l-lactide) NPs conjugated with an antielastin antibody could be targeted to the site of an aneurysm in a rat model of abdominal aortic aneurysms. In the study reported here, we tested whether such targeted NPs could deliver the MMP inhibitor batimastat (BB-94) to the site of an aneurysm and prevent aneurysmal growth.

Methods And Results: Poly(d,l-lactide) NPs were loaded with BB-94 and conjugated with an elastin antibody. Intravenous injections of elastin antibody-conjugated BB-94-loaded NPs targeted the site of aneurysms and delivered BB-94 in a calcium chloride injury-induced abdominal aortic aneurysms in rats. Such targeted delivery inhibited MMP activity, elastin degradation, calcification, and aneurysmal development in the aorta (269% expansion in control versus 40% elastin antibody-conjugated BB-94-loaded NPs) at a low dose of BB-94. The systemic administration of BB-94 alone at the same dose was ineffective in producing MMP inhibition.

Conclusions: Targeted delivery of MMP inhibitors using NPs may be an attractive strategy to inhibit aneurysmal progression.
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http://dx.doi.org/10.1161/CIRCRESAHA.115.307207DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4636940PMC
November 2015

A novel crosslinking method for improved tear resistance and biocompatibility of tissue based biomaterials.

Biomaterials 2015 Oct 14;66:83-91. Epub 2015 Jul 14.

Cardiovascular Implant Research Laboratory, Department of Bioengineering, Clemson University, Clemson, SC, 29634, USA. Electronic address:

Over 300,000 heart valve replacements are performed annually to replace stenotic and regurgitant heart valves. Bioprosthetic heart valves (BHVs), derived from glutaraldehyde crosslinked (GLUT) porcine aortic valve leaflets or bovine pericardium are often used. However, valve failure can occur within 12-15 years due to calcification and/or progressive degeneration. In this study, we have developed a novel fabrication method that utilizes carbodiimide, neomycin trisulfate, and pentagalloyl glucose crosslinking chemistry (TRI) to better stabilize the extracellular matrix of porcine aortic valve leaflets. We demonstrate that TRI treated leaflets show similar biomechanics to GLUT crosslinked leaflets. TRI treated leaflets had better resistance to enzymatic degradation in vitro and demonstrated better tearing toughness after challenged with enzymatic degradation. When implanted subcutaneously in rats for up to 90 days, GLUT control leaflets calcified heavily while TRI treated leaflets resisted calcification, retained more ECM components, and showed better biocompatibility.
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http://dx.doi.org/10.1016/j.biomaterials.2015.07.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4522354PMC
October 2015

Rat aortic smooth muscle cells cultured on hydroxyapatite differentiate into osteoblast-like cells via BMP-2-SMAD-5 pathway.

Calcif Tissue Int 2015 Apr 1;96(4):359-69. Epub 2015 Mar 1.

Department of Bioengineering, Clemson University, 501 Rhodes Research Center, Clemson, SC, 29634, USA.

Vascular calcification is an important pathological condition associated with increased risk of cardiovascular mortality. Hydroxyapatite (HA) found in such deposits is the same polymorph of calcium (Ca) found in bone, indicating calcification may involve mechanisms akin to bone formation. Vascular smooth muscle cells (Vsmcs) have been shown to undergo phenotypic change to osteoblast-like cells. However, the mechanisms underlying this phenotypic change are unclear, and whether the stimulus to become osteogenic is a result of loss of mineralization inhibitors or early mineral deposits is not known. Our aim in this study is to identify mechanisms and signal transduction pathways that cause differentiation of Vsmcs into osteoblast-like cells in the presence of HA. We first characterized vascular origin of Vsmcs by studying the expression of smooth muscle cell markers: myosin heavy chain and smooth muscle actin along with SM22α at both mRNA and protein levels. Vsmcs grown on HA exhibited progressive change in cellular morphology at 3-, 7-, and 14-day time points. Culturing of Vsmcs on HA disc resulted in decrease in media Ca levels and increased expression of Ca-sensing receptor (CaSR) on Vsmcs resulting in upregulation of intracellular CaSR signaling leading to increased BMP-2 secretion. BMP-2 pathway mediated differentiation of Vsmcs to osteoblast-like cells shown by expression of osteogenic markers like runt-related transcription factor 2, osteocalcin, and alkaline phosphatase at mRNA and protein levels. Blocking CaSR by NPS-2143 reduced BMP-2 secretion and blocking the BMP-2 pathway by LDN-193189, a BMP inhibitor, modulated expression of osteogenic markers confirming their role in osteogenesis of Vsmcs.
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http://dx.doi.org/10.1007/s00223-015-9962-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4393885PMC
April 2015

Targeted chelation therapy with EDTA-loaded albumin nanoparticles regresses arterial calcification without causing systemic side effects.

J Control Release 2014 Dec 5;196:79-86. Epub 2014 Oct 5.

Department of Bioengineering, Clemson University, USA. Electronic address:

Background And Aims: Elastin-specific medial arterial calcification (MAC) is an arterial disease commonly referred as Monckeberg's sclerosis. It causes significant arterial stiffness, and as yet, no clinical therapy exists to prevent or reverse it. We developed albumin nanoparticles (NPs) loaded with disodium ethylene diaminetetraacetic acid (EDTA) that were designed to target calcified elastic lamina when administrated by intravenous injection.

Methods And Results: We optimized NP size, charge, and EDTA-loading efficiency (150-200 nm, zeta potential of -22.89--31.72 mV, loading efficiency for EDTA~20%) for in vivo targeting in rats. These NPs released EDTA slowly for up to 5 days. In both ex-vivo study and in vivo study with injury-induced local abdominal aortic calcification, we showed that elastin antibody-coated and EDTA-loaded albumin NPs targeted the damaged elastic lamina while sparing healthy artery. Intravenous NP injections reversed elastin-specific MAC in rats after four injections over a 2-week period. EDTA-loaded albumin NPs did not cause the side effects observed in EDTA injection alone, such as decrease in serum calcium (Ca), increase in urine Ca, or toxicity to kidney. There was no bone loss in any treated groups.

Conclusion: We demonstrate that elastin antibody-coated and EDTA-loaded albumin NPs might be a promising nanoparticle therapy to reverse elastin-specific MAC and circumvent side effects associated with systemic EDTA chelation therapy.
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http://dx.doi.org/10.1016/j.jconrel.2014.09.029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4268131PMC
December 2014

Nanoparticle targeting to diseased vasculature for imaging and therapy.

Nanomedicine 2014 Jul 22;10(5):1003-12. Epub 2014 Feb 22.

Department of Bioengineering, Clemson University, Clemson, SC, USA. Electronic address:

Unlabelled: Significant challenges remain in targeting drugs to diseased vasculature; most important being rapid blood flow with high shear, limited availability of stable targets, and heterogeneity and recycling of cellular markers. We developed nanoparticles (NPs) to target degraded elastic lamina, a consistent pathological feature in vascular diseases. In-vitro organ and cell culture experiments demonstrated that these NPs were not taken up by cells, but instead retained within the extracellular space; NP binding was proportional to the extent of elastic lamina damage. With three well-established rodent models of vascular diseases such as aortic aneurysm (calcium chloride mediated aortic injury in rats), atherosclerosis (fat-fed apoE-/- mice), and vascular calcification (warfarin + vitamin K injections in rats), we show precise NPs spatial targeting to degraded vascular elastic lamina while sparing healthy vasculature when NPs were delivered systemically. Nanoparticle targeting degraded elastic lamina is attractive to deliver therapeutic or imaging agents to the diseased vasculature.

From The Clinical Editor: This novel work focuses on nanoparticle targeting of degraded elastic lamina in a variety of diseases, including atherosclerosis, vascular calcification, and aneurysm formation, and demonstrates the feasibility to deliver therapeutic or imaging agents to the diseased vasculature.
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http://dx.doi.org/10.1016/j.nano.2014.02.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4077993PMC
July 2014

Hydroxyapatite and calcified elastin induce osteoblast-like differentiation in rat aortic smooth muscle cells.

Exp Cell Res 2014 Apr 18;323(1):198-208. Epub 2014 Jan 18.

Department of Bioengineering, Clemson University, USA. Electronic address:

Vascular calcification can be categorized into two different types. Intimal calcification related to atherosclerosis and elastin-specific medial arterial calcification (MAC). Osteoblast-like differentiation of vascular smooth muscle cells (VSMCs) has been shown in both types; however, how this relates to initiation of vascular calcification is unclear. We hypothesize that the initial deposition of hydroxyapatite-like mineral in MAC occurs on degraded elastin first and that causes osteogenic transformation of VSMCs. To test this, rat aortic smooth muscle cells (RASMCs) were cultured on hydroxyapatite crystals and calcified aortic elastin. Using RT-PCR and specific protein assays, we demonstrate that RASMCs lose their smooth muscle lineage markers like alpha smooth muscle actin (SMA) and myosin heavy chain (MHC) and undergo chondrogenic/osteogenic transformation. This is indicated by an increase in the expression of typical chondrogenic proteins such as aggrecan, collagen type II alpha 1(Col2a1) and bone proteins such as runt-related transcription factor 2 (RUNX2), alkaline phosphatase (ALP) and osteocalcin (OCN). Furthermore, when calcified conditions are removed, cells return to their original phenotype. Our data supports the hypothesis that elastin degradation and calcification precedes VSMCs' osteoblast-like differentiation.
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http://dx.doi.org/10.1016/j.yexcr.2014.01.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3969787PMC
April 2014

Elasto-regenerative properties of polyphenols.

Biochem Biophys Res Commun 2014 Feb 16;444(2):205-11. Epub 2014 Jan 16.

Department of Bioengineering, Clemson University, Clemson, SC, USA. Electronic address:

Abdominal aortic aneurysms (AAA) are progressive dilatations of infra-renal aorta causing structural weakening rendering the aorta prone to rupture. AAA can be potentially stabilized by inhibiting inflammatory enzymes such as matrix metalloproteinases (MMP); however, active regression of AAA is not possible without new elastic fiber regeneration. Here we report the elastogenic benefit of direct delivery of polyphenols such as pentagalloyl glucose (PGG), epigallocatechin gallate (EGCG), and catechin, to smooth muscle cells obtained either from healthy or from aneurysmal rat aorta. Addition of 10 μg/ml PGG and ECGC induce elastin synthesis, organization, and crosslinking while catechin does not. Our results indicate that polyphenols bind to monomeric tropoelastin and enhance coacervation, aid in crosslinking of elastin by increasing lysyl oxidase (LOX) synthesis, and by blocking MMP-2 activity. Thus, polyphenol treatments leads to increased mature elastin fibers synthesis without increasing the production of intracellular tropoelastin.
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http://dx.doi.org/10.1016/j.bbrc.2014.01.027DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3947410PMC
February 2014

Neomycin and pentagalloyl glucose enhanced cross-linking for elastin and glycosaminoglycans preservation in bioprosthetic heart valves.

J Biomater Appl 2014 Jan;28(5):757-66

Cardiovascular Implant Research Laboratory, Department of Bioengineering, Clemson University, Clemson, SC, USA.

Glutaraldehyde cross-linked bioprosthetic heart valves fail within 12-15 years of implantation due to limited durability. Glutaraldehyde does not adequately stabilize extracellular matrix components such as glycosaminoglycans and elastin, and loss of these components could be a major cause of degeneration of valve after implantation. We have shown earlier that neomycin-based cross-linking stabilizes glycosaminoglycans in the tissue but fails to stabilize elastin component. Here, we report a new treatment where neomycin and pentagalloyl glucose (PGG) were incorporated into glutaraldehyde cross-linking neomycin-PGG-Glutaraldehyde (NPG) to stabilize both glycosaminoglycans and elastin in porcine aortic valves. In vitro studies demonstrated a marked increase in extracellular matrix stability against enzymatic degradation after cross-linking and 10 month storage in NPG group when compared to glutaraldehyde controls. Tensile properties showed increased lower elastic modulus in both radial and circumferential directions in NPG group as compared to glutaraldehyde, probably due to increased elastin stabilization with no changes in upper elastic modulus and extensibility. The enhanced extracellular matrix stability was further maintained in NPG-treated tissues after rat subdermal implantation for three weeks. NPG group also showed reduced calcification when compared to glutaraldehyde controls. We conclude that NPG cross-linking would be an excellent alternative to glutaraldehyde cross-linking of bioprosthetic heart valves to improve its durability.
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http://dx.doi.org/10.1177/0885328213479047DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4594843PMC
January 2014

Efficacy of reversal of aortic calcification by chelating agents.

Calcif Tissue Int 2013 Nov;93(5):426-35

Department of Bioengineering, Clemson University, 501 Rhodes Engineering Research Center, Clemson, SC, 29634, USA.

Elastin-specific medial vascular calcification, termed "Monckeberg's sclerosis," has been recognized as a major risk factor for various cardiovascular events. We hypothesize that chelating agents, such as disodium ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and sodium thiosulfate (STS) might reverse elastin calcification by directly removing calcium from calcified tissues into soluble calcium complexes. We assessed the chelating ability of EDTA, DTPA, and STS on removal of calcium from hydroxyapatite (HA) powder, calcified porcine aortic elastin, and calcified human aorta in vitro. We show that both EDTA and DTPA could effectively remove calcium from HA and calcified tissues, while STS was not effective. The tissue architecture was not altered during chelation. In the animal model of aortic elastin-specific calcification, we further show that local periadventitial delivery of EDTA loaded in to poly(lactic-co-glycolic acid) nanoparticles regressed elastin-specific calcification in the aorta. Collectively, the data indicate that elastin-specific medial vascular calcification could be reversed by chelating agents.
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http://dx.doi.org/10.1007/s00223-013-9780-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3809012PMC
November 2013

High-glucose levels and elastin degradation products accelerate osteogenesis in vascular smooth muscle cells.

Diab Vasc Dis Res 2013 Sep 10;10(5):410-9. Epub 2013 Jun 10.

Department of Bioengineering, Clemson University, Clemson, SC 29634, USA.

Diabetes mellitus (DM) is a chronic disease in which the body either does not use or produce the glucose metabolising hormone insulin efficiently. Calcification of elastin in the arteries of diabetics is a major predictor of cardiovascular diseases. It has been previously shown that elastin degradation products work synergistically with transforming growth factor-beta 1 (TGF-β1) to induce osteogenesis in vascular smooth muscle cells. In this study, we tested the hypothesis that high concentration of glucose coupled with elastin degradation products and TGF-β1 (a cytokine commonly associated with diabetes) will cause a greater degree of osteogenesis compared to normal vascular cells. Thus, the goal of this study was to analyse the effects of high concentration of glucose, elastin peptides and TGF-β1 on bone-specific markers like alkaline phosphatase (ALP), osteocalcin (OCN) and runt-related transcription factor 2 (RUNX2). We demonstrated using relative gene expression and specific protein assays that elastin degradation products in the presence of high glucose cause the increase in expression of the specific elastin-laminin receptor-1 (ELR-1) and activin receptor-like kinase-5 (ALK-5) present on the surface of the vascular cells, in turn leading to overexpression of typical osteogenic markers like ALP, OCN and RUNX2. Conversely, blocking of ELR-1 and ALK-5 strongly suppressed the expression of the osteogenic proteins. In conclusion, our results indicate that glucose plays an important role in amplifying the osteogenesis induced by elastin peptides and TGF-β1, possibly by activating the ELR-1 and ALK-5 signalling pathways.
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http://dx.doi.org/10.1177/1479164113485101DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5403374PMC
September 2013

On the biomechanical role of glycosaminoglycans in the aortic heart valve leaflet.

Acta Biomater 2013 Jan 2;9(1):4653-60. Epub 2012 Oct 2.

Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA.

While the role of collagen and elastin fibrous components in heart valve valvular biomechanics has been extensively investigated, the biomechanical role of the glycosaminoglycan (GAG) gelatinous-like material phase remains unclear. In the present study, we investigated the biomechanical role of GAGs in porcine aortic valve (AV) leaflets under tension utilizing enzymatic removal. Tissue specimens were removed from the belly region of porcine AVs and subsequently treated with either an enzyme solution for GAG removal or a control (buffer with no enzyme) solution. A dual stress level test methodology was used to determine the effects at low and high (physiological) stress levels. In addition, planar biaxial tests were conducted both on-axis (i.e. aligned to the circumferential and radial axes) and at 45° off-axis to induce maximum shear, to explore the effects of augmented fiber rotations on the fiber-fiber interactions. Changes in hysteresis were used as the primary metric of GAG functional assessment. A simulation of the low-force experimental setup was also conducted to clarify the internal stress system and provide viscoelastic model parameters for this loading range. Results indicated that under planar tension the removal of GAGs had no measureable affect extensional mechanical properties (either on- or 45° off-axis), including peak stretch, hysteresis and creep. Interestingly, in the low-force range, hysteresis was markedly reduced, from 35.96±2.65% in control group to 25.00±1.64% (p<0.001) as a result of GAG removal. Collectively, these results suggest that GAGs do not play a direct role in modulating the time-dependent tensile properties of valvular tissues. Rather, they appear to be strongly connected with fiber-fiber and fiber-matrix interactions at low force levels. Thus, we speculate that GAGs may be important in providing a damping mechanism to reduce leaflet flutter when the leaflet is not under high tensile stress.
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http://dx.doi.org/10.1016/j.actbio.2012.09.031DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3508081PMC
January 2013

Neomycin and carbodiimide crosslinking as an alternative to glutaraldehyde for enhanced durability of bioprosthetic heart valves.

J Biomater Appl 2013 May 29;27(8):948-60. Epub 2011 Dec 29.

Department of Bioengineering, Clemson University, Clemson, SC 29634, USA.

Glutaraldehyde cross-linked porcine aortic valves, referred to as bioprosthetic heart valves (BHVs), are often used in heart valve replacements. Glutaraldehyde does not stabilize glycosaminoglycans (GAGs) and they are lost during preparation, in vivo implantation, cyclic fatigue, and storage. We report that binding of neomycin, a hyaluronidase inhibitor, to the tissues with carbodiimide cross-linking improves GAG retention without reducing collagen and elastin stability. It also led to improved biomechanical properties. Neomycin carbodiimide cross-linking did not significantly reduce calcification in a rat subdermal implantation model when they were stored in formaldehyde after cross-linking. Removal of formaldehyde storage significantly reduced calcification.
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http://dx.doi.org/10.1177/0885328211430542DOI Listing
May 2013

Porcine vena cava as an alternative to bovine pericardium in bioprosthetic percutaneous heart valves.

Biomaterials 2012 Jan 10;33(1):1-8. Epub 2011 Oct 10.

Department of Bioengineering, Clemson University, Clemson, SC 29634, USA.

Percutaneous heart valves are revolutionizing valve replacement surgery by offering a less invasive treatment option for high-risk patient populations who have previously been denied the traditional open chest procedure. Percutaneous valves need to be crimped to accommodate a small-diameter catheter during deployment, and they must then open to the size of heart valve. Thus the material used must be strong and possess elastic recoil for this application. Most percutaneous valves utilize bovine pericardium as a material of choice. One possible method to reduce the device delivery diameter is to utilize a thin, highly elastic tissue. Here we investigated porcine vena cava as an alternative to bovine pericardium for percutaneous valve application. We compared the structural, mechanical, and in vivo properties of porcine vena cava to those of bovine pericardium. While the extracellular matrix fibers of pericardium are randomly oriented, the vena cava contains highly aligned collagen and elastin fibers that impart strength to the vessel in the circumferential direction and elasticity in the longitudinal direction. Moreover, the vena cava contains a greater proportion of elastin, whereas the pericardium matrix is mainly composed of collagen. Due to its high elastin content, the vena cava is significantly less stiff than the pericardium, even after crosslinking with glutaraldehyde. Furthermore, the vena cava's mechanical compliance is preserved after compression under forces similar to those exerted by a stent, whereas pericardium is significantly stiffened by this process. Bovine pericardium also showed surface cracks observed by scanning electron microscopy after crimping that were not seen in vena cava tissue. Additionally, the vena cava exhibited reduced calcification (46.64 ± 8.15 μg Ca/mg tissue) as compared to the pericardium (86.79 ± 10.34 μg/mg). These results suggest that the vena cava may provide enhanced leaflet flexibility, tissue resilience, and tissue integrity in percutaneous heart valves, ultimately reducing the device profile while improving the durability of these valves.
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http://dx.doi.org/10.1016/j.biomaterials.2011.09.027DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3208764PMC
January 2012

Neomycin enhances extracellular matrix stability of glutaraldehyde crosslinked bioprosthetic heart valves.

J Biomed Mater Res B Appl Biomater 2011 Nov 28;99(2):217-29. Epub 2011 Jun 28.

Department of Bioengineering, Cardiovascular Implant Research Laboratory, Clemson University, 501 Rhodes Engineering Research Center, Clemson, South Carolina 29634, USA.

Glutaraldehyde (GLUT) crosslinked porcine aortic heart valves are continued to be extensively used in heart valve replacement surgeries. GLUT does not crosslink glycosaminoglycans in the tissue and we have demonstrated that GAG loss is associated with tissue degeneration. In this study, we examined the ability of neomycin to enhance GLUT crosslinking to stabilize GAGs, as well as provide evidence of improved functional integrity. Neomycin enhanced GLUT crosslinked (NG) leaflets exposed to collagenase and elastase enzymes exhibited an increased resistance to proteolytic degradation. Furthermore, NG leaflets exhibited small but significant increases in collagen denaturation temperatures when compared to that of standard GLUT crosslinked BHVs. NG leaflets subjected to storage, accelerated cyclic fatigue, and in vitro enzyme mediated GAG degradation revealed improved GAG stabilization versus standard GLUT crosslinked valves, which sustained substantial decreases in GAG content. Ultrastructural analysis using transmission electron microscopy qualitatively confirmed NG leaflets preserved GAGs after enzymatic degradation. Biomechanical analyses demonstrated that NG leaflets were functionally similar to GLUT tissues but were slightly stiffer under both planar biaxial tension and under flexure. Interestingly, after GAGase treatment, GLUT tissues showed increased areal compliance and reduced hysteresis, while NG leaflets were unchanged. Collectively, NG cross-linking functionally insulated the tissue from GAG digestion, and imparted modest additional matrix stiffness but maintained tissue hysteresis properties.
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http://dx.doi.org/10.1002/jbm.b.31889DOI Listing
November 2011

Neomycin fixation followed by ethanol pretreatment leads to reduced buckling and inhibition of calcification in bioprosthetic valves.

J Biomed Mater Res B Appl Biomater 2010 Jan;92(1):168-77

Department of Bioengineering, Cardiovascular Implant Research Laboratory (CIRL), Clemson University, Clemson, South Carolina 29634, USA.

Glutaraldehyde crosslinked bioprosthetic heart valves (BHVs) have two modalities of failure: degeneration (cuspal tear due to matrix failure) and calcification. They can occur independently as well as one can lead to the other causing co-existence. Calcific failure has been extensively studied before and several anti-calcification treatments have been developed; however, little research is directed to understand mechanisms of valvular degeneration. One of the shortcomings of glutaraldehyde fixation is its inability to stabilize all extracellular matrix components in the tissue. Previous studies from our lab have demonstrated that neomycin could be used as a fixative to stabilize glycosaminoglycans (GAGs) present in the valve to improve matrix properties. But neomycin fixation did not prevent cuspal calcification. In the present study, we wanted to enhance the anti-calcification potential of neomycin fixed valves by pre-treating with ethanol or removing the free aldehydes by sodium borohydride treatment. Ethanol treatment has been previously used and found to have excellent anti-calcification properties for valve cusps. Results demonstrated in this study suggest that neomycin followed by ethanol treatment effectively preserves GAGs both in vitro as well as in vivo after subdermal implantation in rats. In vivo calcification was inhibited in neomycin fixed cusps pretreated with ethanol compared to glutaraldehyde (GLUT) control. Sodium borohydride treatment by itself did not inhibit calcification nor stabilized GAGs against enzymatic degradation. Neomycin fixation followed by ethanol treatment of BHVs could prevent both modalities of failure, thereby increasing the effective durability and lifetime of these bioprostheses several fold.
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http://dx.doi.org/10.1002/jbm.b.31503DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2796079PMC
January 2010

In vivo vascular tissue engineering: influence of cytokine and implant location on tissue specific cellular recruitment.

J Tissue Eng Regen Med 2009 Jun;3(4):280-9

Department of Bioengineering, Clemson University, Clemson, SC 29634, USA.

In vivo tissue engineering has been explored as a means to create autologous vascular replacements. Elastin is necessary to sustain continual pulsatile flow and to prevent the dilatation of vascular tissues. Unfortunately, elastogenesis in tissue-engineered constructs has been very limited. To overcome this limitation, we have created tubular elastin scaffolds from porcine carotid arteries. Elastin would provide the necessary elasticity to the graft on implanting these scaffolds as vascular grafts. In this study, elastin tubes with agarose gel containing either stromal-derived factor-1 alpha [SDF; for homing of endothelial cells (ECs)] or basic fibroblast growth factor (bFGF; for homing of myofibroblasts) were implanted into adipose tissue, as it is a known source of stem/progenitor cells. We also implanted these tubes into subdermal pouches (as a control location). We observed a difference in the types of cells recruited-ECs were recruited in large numbers by SDF in the adipose tissue, whereas the adipose-FGF group had a vascularized (smooth muscle and EC-positive), collagenous capsule (adventitia) with many smooth muscle alpha-actin (SMA)-positive cells in the elastin scaffold layer (media). These results were in contrast to the subdermal group, which only recruited fibroblasts and some SMA-positive cells. Also, more cell infiltration and neo-collagen formation was seen in adipose implants. This study provides novel results by the use of specific cytokines and implant locations to recruit tissue-specific cells to create autologous vascular grafts.
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http://dx.doi.org/10.1002/term.164DOI Listing
June 2009

Neomycin binding preserves extracellular matrix in bioprosthetic heart valves during in vitro cyclic fatigue and storage.

Acta Biomater 2009 May 27;5(4):983-92. Epub 2008 Nov 27.

Cardiovascular Implant Research Laboratory (CIRL), Department of Bioengineering, Clemson University, 501 Rhodes Hall, Clemson, SC 29634, USA.

Bioprosthetic heart valve (BHV) cusps have a complex architecture consisting of an anisotropic arrangement of collagen, glycosaminoglycans (GAGs) and elastin. Glutaraldehyde (GLUT) is used as a fixative for all clinical BHV implants; however, it only stabilizes the collagen component of the tissue, and other components such as GAGs and elastin are lost from the tissue during processing, storage or after implantation. We have shown previously that the effectiveness of the chemical crosslinking can be increased by incorporating neomycin trisulfate, a hyaluronidase inhibitor, to prevent the enzyme-mediated GAG degradation. In the present study, we optimized carbodiimide-based GAG-targeted chemistry to incorporate neomycin into BHV cusps prior to conventional GLUT crosslinking. This crosslinking leads to enhanced preservation of GAGs during in vitro cyclic fatigue and storage. The neomycin group showed greater GAG retention after both 10 and 50 million accelerated fatigue cycles and after 1 year of storage in GLUT solution. Thus, additional binding of neomycin to the cusps prior to standard GLUT crosslinking could enhance tissue stability and thus heart valve durability.
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http://dx.doi.org/10.1016/j.actbio.2008.11.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2702722PMC
May 2009

A novel synthetic route for the preparation of hydrolytically degradable synthetic hydrogels.

J Biomed Mater Res A 2009 Sep;90(4):1073-82

Department of Bioengineering, Micro-Environmental Engineering Laboratory, Clemson University, 501 Rhodes Research Center, Clemson, South Carolina 29634, USA.

A variety of approaches have been described for the modification of synthetic, water soluble polymers with hydrolytically degradable bonds and terminal vinyl groups that can be crosslinked in situ by photo- or redox-initiated free radical polymerization. However, changes in macromer concentration, functionality, and molecular weight commonly used to achieve variable degradation rates simultaneously alter hydrogel mechanical properties. Herein, we describe a novel, two-step synthetic route for the preparation of hydrolytically degradable, crosslinkable PEG-based macromers based on chemical intermediaries that form ester linkages with variable alkyl chain length. Changes in the concentration of a single macromer were shown to provide effective variation of degradation, but with corresponding significant changes in tensile properties. Through variation in the alkyl chain length of the chemical intermediary, variable degradation times ranging from weeks to months are achieved, without significantly affecting initial gelation efficiency, swelling, or tensile properties. When modified with adhesive ligands, hydrogels supported viability of encapsulated and adherent cells. Controlled release of a model protein (Immunoglobulin G) was attained as a function of hydrogel degradation rate. Independent control of hydrogel degradation and mechanical properties will offer improved flexibility for studying the effect of these material characteristics on cellular function and may be useful in the design of matrices for tissue engineering and controlled release of bioactive molecules.
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http://dx.doi.org/10.1002/jbm.a.32172DOI Listing
September 2009

Synthesis and characterization of biodegradable elastomeric polyurethane scaffolds fabricated by the inkjet technique.

Biomaterials 2008 Oct 3;29(28):3781-91. Epub 2008 Jul 3.

Department of Bioengineering, Clemson University, 420 Rhodes Research Centre, Clemson, SC 29634, USA.

Biodegradable polyurethanes (PUs) were synthesized from methylene di-p-phenyl-diisocyanate (MDI), polycaprolactone diol (PCL-diol) and N,N-bis (2-hydorxyethyl)-2-aminoethane-sulfonic acid (BES), serving as a hard segment, soft segment and chain extender, respectively. MDI was chosen due to its reactivity and wide application in synthesis of biomedical polyurethanes due to its reactivity; PCL-diol was chosen because of its biodegradability; and BES was chosen because it allowed the introduction sulfonic acid groups onto the polymer chains. We evaluated the polyurethanes' degradation rate, mechanical properties, hydrophilicity, antithrombogenecity, and ability to support fibroblast cell attachment and growth by comparing with polymers having a 2,2-(methylimino)diethanol (MIDE) chain extender. Mechanical testing demonstrated that the PU containing BES has tensile strengths of about 17 MPa and elongations up to 400%, about three times the strength and four times the elongation than the MIDE based PUs. The polymers showed decreased in vitro degradation rates, lower glass transition temperature (T(g)) and hydrophilicity possibly due to enhanced microphase separation. Preliminary cytocompatibility studies showed that all the PUs are non-toxic, but PU containing BES exhibited much lower cell attachment and proliferation than the MIDE chain extended polymers. An in vitro platelet adhesion assay showed lower platelet attachment on BES containing PU. Additionally, due to the existence of sulfonic acid groups, the BES extended PU became water soluble in basic condition and insoluble in acidic condition, a phenomenon that is reversible at pH value of 8.7, making this a pH sensitive polymer attractive for bioprinting applications. By adding acetic acid into an inkjet cartridge and printing it onto a PU solution with pH above 8.7, precision fabricated scaffolds can be obtained, suggesting that BES based PUs are promising candidates as synthetic inks used for customizable fabrication of tissue engineering scaffolds.
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http://dx.doi.org/10.1016/j.biomaterials.2008.06.009DOI Listing
October 2008

The effect of glycosaminoglycan stabilization on tissue buckling in bioprosthetic heart valves.

Biomaterials 2008 Apr 15;29(11):1645-53. Epub 2008 Jan 15.

Cardiovascular Implant Research Laboratory, Department of Bioengineering, Clemson University, 401 Rhodes Engineering Research Center, Clemson, SC 29634, USA.

Bioprosthetic valves are used in thousands of heart valve replacement surgeries. Existing glutaraldehyde-crosslinked bioprosthetic valves fail due to either calcification or degeneration. Glutaraldehyde crosslinking does not stabilize valvular glycosaminoglycans (GAGs). GAGs, predominantly present in the medial spongiosa layer of native heart valve cusps, play an important role in regulating physico-mechanical behavior of the native cuspal tissue during dynamic motion. The primary objective of this study was to identify the role of cuspal GAGs in valve tissue buckling. Glutaraldehyde-crosslinked cusps showed extensive buckling compared to fresh, native cusps. Removal of GAGs by treatment with GAG-degrading enzymes led to a marked increase in buckling behavior in glutaraldehyde-crosslinked cusps. We demonstrate that the retention of valvular GAGs by carbodiimide crosslinking together with chemical attachment of neomycin trisulfate (a hyaluronidase inhibitor), prior to glutaraldehyde crosslinking, reduces the extent of buckling in bioprosthetic heart valves. Furthermore, following exposure to GAG-digestive enzymes, neomycin-trisulfate-bound cusps experienced no alterations in buckling behavior. Such moderate buckling patterns mimicked that of fresh, untreated cusps subjected to similar bending curvatures. Thus, GAG stabilization may subsequently improve the durability of these bioprostheses.
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http://dx.doi.org/10.1016/j.biomaterials.2007.12.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2268977PMC
April 2008