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Despite significant progress in the field of biomaterials for bone repair, the lack of attention to the vascular and nervous networks within bone implants could be one of the main reasons for the delayed or impaired recovery of bone defects. The design of innovative biomaterials should improve the host capacity of healing to restore a functional tissue, taking into account that the nerve systems closely interact with blood vessels in the bone tissue. The aim of this work is to develop a cell-free and growth factor-free hydrogel capable to promote angiogenesis and innervation. To this end, we have used elastin-like polypeptides (ELPs), poly(ethylene glycol) (PEG) and increasing concentrations of the adhesion peptide IKVAV (25% (w/w) representing 1.7 mM and 50% (w/w) representing 4.1 mM) to formulate and produce hydrogels. When characterized in vitro , hydrogels have fine-tunable rheological properties, microporous structure and are biocompatible. At the biological level, 50% IKVAV composition up-regulated Runx2 , Osx, Spp1 , Vegfa and Bmp2 in mesenchymal stromal cells and Tek in endothelial cells, and sustained the formation of long neurites in sensory neurons. When implanted subcutaneously in mice, hydrogels induced no signals of major inflammation and the 50% IKVAV composition induced higher vessel density and formation of nervous terminations in the peripheral tissue. This novel composite has important features for tissue engineering, showing higher osteogenic, angiogenic and innervation potential in vitro , being not inflammatory in vivo , and inducing angiogenesis and innervation subcutaneously. One of the main limitations in the field of tissue engineering remains the sufficient vascularization and innervation during tissue repair. In this scope, the development of advanced biomaterials that can support these processes is of crucial importance. Here, we formulated different compositions of Elastin-like polypeptide-based hydrogels bearing the IKVAV adhesion sequence. These compositions showed controlled mechanical properties, and were degradable in vitro. Additionally, we could identify in vitro a composition capable to promote neurite formation and to modulate endothelial and mesenchymal stromal cells gene expression, in view of angiogenesis and osteogenesis, respectively. When tested in vivo , it showed no signs of major inflammation and induced the formation of a highly vascularized and innervated neotissue. In this sense, our approach represents a potential advance in the development of new strategies to promote tissue regeneration, taking into account both angiogenesis and innervation. [ABSTRACT FROM AUTHOR]

Introduction: Fusion of therapeutic agents to Elastin-like Polypeptide (ELP) is a novel drug delivery strategy for prevention of placental drug transfer. Previous studies have used a 60 kDa ELP tag for this purpose. However, placental transfer of ELP may be size dependent. The goal of this study was to measure the effects of ELP polymer size on pharmacokinetics, biodistribution, and placental transfer of ELP.Methods: Three ELPs ranging from 25 to 86 kDa (4.1-6.8 nm hydrodynamic radius) were fluorescently labeled and administered by i.v. bolus to pregnant Sprague Dawley rats on gestational day 14. Plasma levels were monitored for 4 h, organ levels and placental transfer determined by ex vivo fluorescence imaging, and placental localization determined by confocal microscopy.Results: Increasing ELP size resulted in slower plasma clearance and increased deposition in all major maternal organs, except in the kidneys where an opposite effect was observed. Placental levels increased with an increase in size, while in the pups, little to no ELP was detected.Discussion: Pharmacokinetics and biodistribution of ELPs during pregnancy are size dependent, but all ELPs tested were too large to traverse the placental barrier. These studies verify that ELP fusion is a powerful method of modulating half-life and preventing placental transfer of cargo molecules. The tunable nature of the ELP sequence makes it ideal for drug delivery applications during pregnancy, where it can be used to target drugs to the mother while preventing fetal drug exposure. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Engineering of functional vascularized liver tissues holds great promise in addressing donor organ shortage for transplantation. Whole organ decellularization is a cell removal method that retains the native vascular structures of the organ such that it can be anastomosed with the recipient circulation after recellularization with healthy cells. However, a main hurdle to successful implantation of bioengineered organ is the inability to efficiently re-endothelialize the vasculature with a functional endothelium, resulting in blood clotting which is the primary cause of failure in early transplant studies. Here, we present an efficient approach for enhancing re-endothelialization of decellularized rat liver scaffolds by conjugating the REDV cell-binding domain to improve attachment of endothelial cells (EC) on vascular wall surfaces. In order to facilitate expression and purification of the peptide, REDV was fused with elastin-like peptide (ELP) that confers thermally triggered aggregation behavior to the fusion protein. After validating the adhesive properties of the REDV-ELP peptide, we covalently coupled REDV-ELP to the blood vasculature of decellularized rat livers and seeded EC using perfusion of the portal vein. We showed that REDV-ELP increased cell attachment, spreading and proliferation of EC within the construct resulting in uniform endothelial lining of the scaffold vasculature. We further observed that REDV-ELP conjugation dramatically reduced platelet adhesion and activation. Altogether, our results demonstrate that this method allowed functional re-endothelialization of liver scaffold and show great potential toward the generation of functional bioengineered liver for long-term transplantation. Statement of Significance There is a critical need for novel organ replacement therapies as the grafts for transplantation fall short of demand. Recent advances in tissue engineering, through the use of decellularized scaffolds, have opened the possibility that engineered grafts could be used as substitutes for donor livers. However, successful implantation has been challenged by the inability to create a functional vasculature. Our research study reports a new strategy to increase efficiency of endothelialization by increasing the affinity of the vascular matrix for endothelial cells. We functionalized decellularized liver scaffold using elastin-like peptides grafted with REDV cell binding domain. We showed that REDV-ELP conjugation improve endothelial cell attachment and proliferation within the scaffold, demonstrating the feasibility of re-endothelializing a whole liver vasculature using our technique. [ABSTRACT FROM AUTHOR]

Intracerebral hemorrhage (ICH) frequently results in severe disabilities and high mortality. RGD-containing elastin-like polypeptide (REP), a modified elastin-like polypeptide (ELP), is a thermally responsive biopolymer. REP has high affinity for cells and is known to show non-immunotoxicity, -cytotoxicity, and -inflammatory responses. Here we found that administration of REP in the acute phase of the ICH rat model reduced the hematoma volume, decreased the number of activated microglia, attenuated the expression of von Willebrand Factor (vWF), and prevented the leakage of immunoglobulin G (IgG) into the cerebral parenchyma without any occlusion of intact microvessels. Therefore, the present data suggest that REP treatment could be a novel therapeutic strategy for attenuating the acute phase of ICH. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: Hepatitis B virus (HBV) is a member of the hepadnavirus family. The HBV genome contains four genes designated as S, C, P, and X. The HBV X (HBx) gene encodes for a 16.5-kDa regulatory protein that enhances HBV replication and exerts multifunctional activities. The aim of this study is to describe the rapid and easy purification of HBx using ELP (elastin-like polypeptide) fusion protein. Methods: The ELP–HBx fusion protein was overexpressed in Escherichia coli. Environmental sensitivity was demonstrated via turbidity and dynamic light scattering as a function of temperature. HBx was purified as an ELP fusion protein. ELPs are biopolymers of the pentapeptide repeat Val-Pro-Gly-Xaa-Gly that undergo an inverse temperature phase transition. ELP follows in temperature and salt consistency, precipitation, and solution repetition (inverse transition cycling) with polypeptide, where it purifies the protein in a simple manner. Results: Fusion proteins underwent supramolecular aggregation at 40 °C in 1 M NaCl and slowly resolubilized at subphysiologic temperatures. ELP domain proteolysis liberated a peptide of comparable size and immunoreactivity to the commercial HBx. Conclusion: This study suggests that HBx can be purified rapidly and easily using inverse transition cycling, and that this method can be applied in determination of HBx 3D structures and HBx stability study. [Copyright &y& Elsevier]

Abstract: Recombinant elastin-like protein (ELP) polymers display several favorable characteristics for tissue repair and replacement as well as drug delivery applications. However, these materials are derived from peptide sequences that do not lend themselves to cell adhesion, migration, or proliferation. This report describes the chemoselective ligation of peptide linkers bearing the bioactive RGD sequence to the surface of ELP hydrogels. Initially, cystamine is conjugated to ELP, followed by the temperature-driven formation of elastomeric ELP hydrogels. Cystamine reduction produces reactive thiols that are coupled to the RGD peptide linker via a terminal maleimide group. Investigations into the behavior of endothelial cells and mesenchymal stem cells on the RGD-modified ELP hydrogel surface reveal significantly enhanced attachment, spreading, migration and proliferation. Attached endothelial cells display a quiescent phenotype. [Copyright &y& Elsevier]

Abstract: The integration of viral gene delivery with key features of biomaterial scaffolds that modulate viral delivery in a controlled manner offers a promising strategy for numerous tissue engineering applications. In this study adeno-associated virus (AAV), which is widely utilized in human gene therapy as a gene carrier due to its safety and efficient gene delivery capability, was encapsulated within electrospun nanofibrous scaffolds composed of blended mixtures of elastin-like polypeptides (ELP) and poly (ε-caprolactone) (PCL) and was employed to transduce fibroblasts adherent on the scaffolds. Combinatorial interactions between ELP and PCL chains upon physical blending significantly altered the mechanical properties (i.e. wettability, elastic modulus, strain, etc.) of the ELP/PCL composites, thus providing key tools to mediate controlled release of AAV vectors and robust cellular transduction on the fibrous scaffolds. The ability of ELP/PCL composites to manipulate the controlled release of AAV-mediated gene delivery for subsequent high-efficiency cellular transduction will provide tremendous opportunities for a variety of tissue engineering applications. [Copyright &y& Elsevier]

Abstract: Polypeptides based on the alternating hydrophobic and cross-linking domain structure of human elastin are capable of undergoing self-assembly to produce polymeric matrices with unique biological and mechanical properties. Here, we test the initial feasibility of using a genipin cross-linked elastin-based material as an acellular plug in the treatment of an osteochondral defect in the rabbit knee. Full-thickness defects in the weight-bearing surface of the medial femoral condyle in 18 New Zealand White rabbits were surgically produced and press fitted with cylindrical pads composed of genipin cross-linked elastin-like polypeptides, with identical wounds in the opposite knee left untreated as controls. The biocompatibility of the material, overall wound healing and regeneration of subchondral tissue was assessed at 2, 4 and 6weeks by histological evaluation, synovial fluid analysis and microcomputerized tomography scanning. Histological analysis revealed the regeneration of subchondral bone at the periphery of the material, with evidence of hyaline-like overgrowth across the apical surface in 11/16 cases. Pads developed tight contacts with host tissue and appeared completely biocompatible, with no evidence of localized immune response or increased inflammation compared to controls. The material was stable to 6weeks, with an aggregate elastic modulus calculated at ∼470kPa when tested under confined compression. Further studies are required to assess material degradation over time and long-term replacement with repair tissue. [Copyright &y& Elsevier]