Elastin-like recombinamer-covered stents: Towards a fully biocompatible and non-thrombogenic device for cardiovascular diseases

Biological properties of self-assembled nanofibers of elastin-like block polypeptides for tissue-engineered vascular grafts: platelet inhibition, endothelial cell activation and smooth muscle cell maintenance

Strategic materials design is essential for the development of small-diameter, tissue-engineered vascular grafts. Self-assembled nanofibers of elastin-like polypeptides represent promising vascular graft components as they replicate the organized elastin structure of native blood vessels. Further, the bioactivity of nanofibers can be modified by the addition of functional peptide motifs. In the present study, we describe the development of a novel nanofiber-forming elastin-like polypeptide (ELP) with an arginine-glutamic acid-aspartic acid-valine (REDV) sequence. The biological characteristics of the REDV-modified ELP nanofibers relevant to applications in vascular grafting were compared to ELP without ligands for integrin, ELP with arginine-glycine-aspartic acid (RGD) sequence, collagen and cell culture glass. Among them, REDV-modified ELP nanofibers met the preferred biological properties for vascular graft materials, i.e. (i) inhibition of platelet adhesion and activation, (ii) endothelial cell adhesion and proliferation and (iii) maintenance of smooth muscle cells in a contractile phenotype to prevent cell overgrowth. The results indicate that REDV-modified ELP nanofibers represent promising candidates for the further development of small-diameter vascular grafts.

Nanofibrous polytetrafluoroethylene/poly(ε-caprolactone) membrane with hierarchical structures for vascular patch

With the prevalence of cardiovascular diseases, developing cardiovascular supplements is becoming increasingly urgent. The ability of cells to rapidly adhere and proliferate to achieve endothelialization is extremely important for vascular grafts. In this work, we electrospun polytetrafluoroethylene (PTFE) nanofibrous membranes and used induced crystallization to manufacture poly(ε-caprolactone) (PCL) shish-kebab microstructures on PTFE nanofibers to overcome the inertness of PTFE, and promote cell adhesion and proliferation. PCL lamella periodically grew on the surface of PTFE nanofibers yielding a hierarchical structure, which improved the biocompatibility and mechanical properties of the PTFE nanofibrous membrane. The deposition of PCL lamella improved the hydrophilicity of electrospun PTFE nanofibers membrane, leading to good cell proliferation and adhesion. Also, due to the surface inertness of the substrate material PTFE, this PTFE/PCL composite film has good anti-platelet adhesion properties. Furthermore, cell proliferation could be regulated by controlling the integrity of the PCL crystal network. The vascular patch showed similar mechanical properties to natural blood vessels, providing a new strategy for vascular tissue engineering.

Biohybrid elastin-like venous valve with potential for in situ tissue engineering

Chronic venous insufficiency (CVI) is a leading vascular disease whose clinical manifestations include varicose veins, edemas, venous ulcers, and venous hypertension, among others. Therapies targeting this medical issue are scarce, and so far, no single venous valve prosthesis is clinically available. Herein, we have designed a bi-leaflet transcatheter venous valve that consists of (i) elastin-like recombinamers, (ii) a textile mesh reinforcement, and (iii) a bioabsorbable magnesium stent structure. Mechanical characterization of the resulting biohybrid elastin-like venous valves (EVV) showed an anisotropic behavior equivalent to the native bovine saphenous vein valves and mechanical strength suitable for vascular implantation. The EVV also featured minimal hemolysis and platelet adhesion, besides actively supporting endothelialization in vitro, thus setting the basis for its application as an in situ tissue engineering implant. In addition, the hydrodynamic testing in a pulsatile bioreactor demonstrated excellent hemodynamic valve performance, with minimal regurgitation (<10%) and pressure drop (<5 mmHg). No stagnation points were detected and an in vitro simulated transcatheter delivery showed the ability of the venous valve to withstand the implantation procedure. These results present a promising concept of a biohybrid transcatheter venous valve as an off-the-shelf implant, with great potential to provide clinical solutions for CVI treatment.

Application of bioengineered elastin-like polypeptide-based system for targeted gene delivery in tumor cells

Successful gene delivery depends on the entry of negatively charged DNAs and oligonucleotides across the various barriers of the tumor cells and localization into the nucleus for its transcription and protein translation. Here, we have reported a thermal responsive self-assemble and highly biocompatible, targeted ELP-based gene delivery system. These systems consist of cell-penetrating peptides, Tat and single or multiple repeats of IL-4 receptor targeting peptide AP-1 along the backbone of ELP. Cell-penetrating peptides were introduced for nuclear localization of genes of interest, AP-1 for targeting IL-4R highly expressed tumor cells and ELP for stable condensation favoring protection of nucleic acids. The designed multidomain fusion ELPs referred to as Tat-ELP, Tat-A₁E₂₈ and Tat-A₄V₄₈ were employed to generate formulation with pEGFP-N1. Profound formulation of stable complexes occurred at different molar ratios owing to electrostatic interactions of positively charged amino acids in polymers with negatively charged nucleic acids. Among the complexes, Tat-A₄V₄₈ containing four copies of AP-1 showed maximum complexation with pEGFP-N1 in lower molar ratio. The polymer-pEGFP complexes were further analyzed for its transfection efficiency in different cancer cell lines. Both the targeted polymers, Tat-A₄V₄₈ and Tat-A₁E₂₈ upon transfection displayed significant EGFP-expression with low toxicity in different cancer cells. Therefore, both Tat-A₄V₄₈ and Tat-A₁E₂₈ can be considered as novel transfection system for successful gene delivery with therapeutic applications.

Monitoring the Remodeling of Biohybrid Tissue-Engineered Vascular Grafts by Multimodal Molecular Imaging

Tissue-engineered vascular grafts (TEVGs) with the ability to grow and remodel open new perspectives for cardiovascular surgery. Equipping TEVGs with synthetic polymers and biological components provides a good compromise between high structural stability and biological adaptability. However, imaging approaches to control grafts' structural integrity, physiological function, and remodeling during the entire transition between late in vitro maturation and early in vivo engraftment are mandatory for clinical implementation. Thus, a comprehensive molecular imaging concept using magnetic resonance imaging (MRI) and ultrasound (US) to monitor textile scaffold resorption, extracellular matrix (ECM) remodeling, and endothelial integrity in TEVGs is presented here. Superparamagnetic iron-oxide nanoparticles (SPION) incorporated in biodegradable poly(lactic-co-glycolic acid) (PLGA) fibers of the TEVGs allow to quantitatively monitor scaffold resorption via MRI both in vitro and in vivo. Additionally, ECM formation can be depicted by molecular MRI using elastin- and collagen-targeted probes. Finally, molecular US of α_v β₃ integrins confirms the absence of endothelial dysfunction; the latter is provocable by TNF-α. In conclusion, the successful employment of noninvasive molecular imaging to longitudinally evaluate TEVGs remodeling is demonstrated. This approach may foster its translation from in vitro quality control assessment to in vivo applications to ensure proper prostheses engraftment.

Recombinant Proteins-Based Strategies in Bone Tissue Engineering

The increase in fracture rates and/or problems associated with missing bones due to accidents or various pathologies generates socio-health problems with a very high impact. Tissue engineering aims to offer some kind of strategy to promote the repair of damaged tissue or its restoration as close as possible to the original tissue. Among the alternatives proposed by this specialty, the development of scaffolds obtained from recombinant proteins is of special importance. Furthermore, science and technology have advanced to obtain recombinant chimera’s proteins. This review aims to offer a synthetic description of the latest and most outstanding advances made with these types of scaffolds, particularly emphasizing the main recombinant proteins that can be used to construct scaffolds in their own right, i.e., not only to impregnate them, but also to make scaffolds from their complex structure, with the purpose of being considered in bone regenerative medicine in the near future.

Self-assembling systems comprising intrinsically disordered protein polymers like elastin-like recombinamers

Despite lacking cooperatively folded structures under native conditions, numerous intrinsically disordered proteins (IDPs) nevertheless have great functional importance. These IDPs are hybrids containing both ordered and intrinsically disordered protein regions (IDPRs), the structure of which is highly flexible in this unfolded state. The conformational flexibility of these disordered systems favors transitions between disordered and ordered states triggered by intrinsic and extrinsic factors, folding into different dynamic molecular assemblies to enable proper protein functions. Indeed, prokaryotic enzymes present less disorder than eukaryotic enzymes, thus showing that this disorder is related to functional and structural complexity. Protein-based polymers that mimic these IDPs include the so-called elastin-like polypeptides (ELPs), which are inspired by the composition of natural elastin. Elastin-like recombinamers (ELRs) are ELPs produced using recombinant techniques and which can therefore be tailored for a specific application. One of the most widely used and studied characteristic structures in this field is the pentapeptide (VPGXG)_n . The structural disorder in ELRs probably arises due to the high content of proline and glycine in the ELR backbone, because both these amino acids help to keep the polypeptide structure of elastomers disordered and hydrated. Moreover, the recombinant nature of these systems means that different sequences can be designed, including bioactive domains, to obtain specific structures for each application. Some of these structures, along with their applications as IDPs that self-assemble into functional vesicles or micelles from diblock copolymer ELRs, will be studied in the following sections. The incorporation of additional order- and disorder-promoting peptide/protein domains, such as α-helical coils or β-strands, in the ELR sequence, and their influence on self-assembly, will also be reviewed. In addition, chemically cross-linked systems with controllable order-disorder balance, and their role in biomineralization, will be discussed. Finally, we will review different multivalent IDPs-based coatings and films for different biomedical applications, such as spatially controlled cell adhesion, osseointegration, or biomaterial-associated infection (BAI).

Development of In Vitro Endothelialised Stents - Review

Endovascular treatment is prevalent as a primary treatment for coronary and peripheral arterial diseases. Although the introduction of drug-eluting stents (DES) dramatically reduced the risk of in-stent restenosis, stent thrombosis persists as an issue. Notwithstanding improvements in newer generation DES, they are yet to address the urgent clinical need to abolish the late stent complications that result from in-stent restenosis and are associated with late thrombus formation. These often lead to acute coronary syndromes with high mortality in coronary artery disease and acute limb ischemia with a high risk of limb amputation in peripheral arterial disease. Recently, a significant amount of research has focused on alternative solutions to improve stent biocompatibility by using tissue engineering. There are two types of tissue engineering endothelialisation methods: in vitro and in vivo. To date, commercially available in vivo endothelialised stents have failed to demonstrate antithrombotic or anti-stenosis efficacy in clinical trials. In contrast, the in vitro endothelialisation methods exhibit the advantage of monitoring cell type and growth prior to implantation, enabling better quality control. The present review discusses tissue-engineered candidate stents constructed by distinct in vitro endothelialisation approaches, with a particular focus on fabrication processes, including cell source selection, stent material composition, stent surface modifications, efficacy and safety evidence from in vitro and in vivo studies, and future directions.

Elastin-Plasma Hybrid Hydrogels for Skin Tissue Engineering

Dermo-epidermal equivalents based on plasma-derived fibrin hydrogels have been extensively studied for skin engineering. However, they showed rapid degradation and contraction over time and low mechanical properties which limit their reproducibility and lifespan. In order to achieve better mechanical properties, elasticity and biological properties, we incorporated a elastin-like recombinamer (ELR) network, based on two types of ELR, one modified with azide (SKS-N₃) and other with cyclooctyne (SKS-Cyclo) chemical groups at molar ratio 1:1 at three different SKS (serine-lysine-serine sequence) concentrations (1, 3, and 5 wt.%), into plasma-derived fibrin hydrogels. Our results showed a decrease in gelation time and contraction, both in the absence and presence of the encapsulated human primary fibroblasts (hFBs), higher mechanical properties and increase in elasticity when SKSs content is equal or higher than 3%. However, hFBs proliferation showed an improvement when the lowest SKS content (1 wt.%) was used but started decreasing when increasing SKS concentration at day 14 with respect to the plasma control. Proliferation of human primary keratinocytes (hKCs) seeded on top of the hybrid-plasma hydrogels containing 1 and 3% of SKS showed no differences to plasma control and an increase in hKCs proliferation was observed for hybrid-plasma hydrogels containing 5 wt.% of SKS. These promising results showed the need to achieve a balance between the reduced contraction, the better mechanical properties and biological properties and indicate the potential of using this type of hydrogel as a testing platform for pharmaceutical products and cosmetics, and future work will elucidate their potential.

The Effects of Crosslinking on the Rheology and Cellular Behavior of Polymer-Based 3D-Multilayered Scaffolds for Restoring Articular Cartilage

Polymer-based tri-layered (bone, intermediate and top layers) scaffolds used for the restoration of articular cartilage were prepared and characterized in this study to emulate the concentration gradient of cartilage. The scaffolds were physically or chemically crosslinked. In order to obtain adequate scaffolds for the intended application, the impact of the type of calcium phosphate used in the bone layer, the polymer used in the intermediate layer and the interlayer crosslinking process were analyzed. The correlation among SEM micrographs, physical-chemical characterization, swelling behavior, rheological measurements and cell studies were examined. Storage moduli at 1 Hz were 0.3-1.7 kPa for physically crosslinked scaffolds, and 4-5 kPa (EDC/NHS system) and 15-20 kPa (glutaraldehyde) for chemically crosslinked scaffolds. Intrinsic viscoelasticity and poroelasticity were considered in discussing the physical mechanism dominating in different time/frequency scales. Cell evaluation showed that all samples are available as alternatives to repair and/or substitute cartilage in articular osteoarthritis.

Extracellular matrix biomimetic polymeric membranes enriched with silver nanoparticles for wound healing

Severe skin injuries, including burns, represent a real concern for the global health-care system and therefore, there is an increased interest in developing wound dressings, in order to stimulate and enhance skin tissue repair. The aim of this study was to design novel hybrid materials, biomimetic to skin extracellular matrix and enriched with silver nanoparticles (nAg), in order to provide both dermal tissue regeneration and antimicrobial activity. Two material variants (variant A and variant B) consisting of type I collagen (COL), chondroitin sulfate (CS) and k-elastin peptides (EL) enriched with positively-charged nAg, were conditioned as membranes. UV exposure ensured both sterilisation and cross-linking of the materials. Physico-chemical characterization of the hybrid biomaterials showed values of density and swelling degree higher than those of COL membrane, while the process of in vitro degradation followed a similar pattern. Infrared spectroscopy and X-ray diffraction indicated alterations of the characteristic structural features and crystallinity of COL after blending with CS and EL and nAg embedding. Scanning electron microscopy observations revealed different surface morphologies of the hybrid membranes, according to their composition. In vitro studies on L929 fibroblasts and HaCaT keratinocytes showed that both hybrid membranes exhibited good cytocompatibility and promoted higher cell proliferation compared to COL sample, as evaluated by MTT and Live/Dead assays. The presence of actin filaments highlighted by fluorescent labelling confirmed the fibroblast and keratinocyte adhesion onto the surface of hybrid membranes. Most importantly, both materials showed an increased wound healing ability in an in vitro scratch assay model, stimulating cell migration at 24 h post-seeding. In addition, good antimicrobial activity was recorded, especially against Gram-positive bacterial strain. Altogether, our findings recommend COL-CS-EL-nAg hybrid membranes as good candidates for wound healing acceleration and bioengineering of skin tissue.

Elastin-like recombinamer-based devices releasing Kv1.3 blockers for the prevention of intimal hyperplasia: An in vitro and in vivo study

Coronary artery disease (CAD) is the most common cardiovascular disorder. Vascular surgery strategies for coronary revascularization (either percutaneous or open) show a high rate of failure because of restenosis of the vessel, due to phenotypic switch of vascular smooth muscle cells (VSMCs) leading to proliferation and migration. We have previously reported that the inhibition of Kv1.3 channel function with selective blockers represents an effective strategy for the prevention of restenosis in human vessels used for coronary angioplasty procedures. However, delivery systems for controlled release of these drugs have not been investigated. Here we tested the efficacy of several formulations of elastin like recombinamers (ELRs) hydrogels to deliver the Kv1.3 blocker PAP-1 in various restenosis models. The dose and time course of PAP-1 release from ELRs click hydrogels was able to inhibit human VSMC proliferation in vitro as well as remodeling of human vessels in organ culture and restenosis in in vivo models. We conclude that this combination of active compound and advanced delivery method could improve the outcomes of vascular surgery in patients. STATEMENT OF SIGNIFICANCE: Vascular surgery strategies for coronary revascularization show a high rate of failure, because of occlusion (restenosis) of the vessel, due to vascular smooth muscle cells proliferation and migration. We have previously reported that blockers of Kv1.3 channels represent an effective anti-restenosis therapy, but delivery systems for their controlled release have not being explored. Here we tested the efficacy of several formulations of elastin like recombinamers (ELRs) hydrogels to deliver the Kv1.3 blocker PAP-1 in various restenosis models, both in vivo and in vitro, and also in human vessels. We demonstrated that combination of active compound and advanced delivery method could improve the outcomes of vascular surgery in patients.

Functional characterization of an enzymatically degradable multi-bioactive elastin-like recombinamer

One of the main goals in both tissue engineering and regenerative medicine is to design innovative synthetic scaffolds that can simulate and control the communication pathways between cells and the extracellular matrix (ECM). In this context, we describe herein the characterization of protein polymer, a recombinant elastin-like recombinamer (ELR) designed for developing tissue-engineered devices for use in vascular regeneration. This ELR is composed of an elastin-like backbone that contains a fibronectin domain, which provides specific, endothelial cell adhesion, and a protease target domain directed towards specific proteases involved in ECM remodeling. We also compare the specific response of endothelial and fibroblast cells to ELR scaffolds and show that cell adhesion and spreading on this ELR is significantly higher for endothelial cells than for fibroblasts. The reactivity of this polymer and its hydrogels to specific enzymatic degradation is demonstrated in vitro. As with natural elastin, enzymatic hydrolysis of the ELR produces elastin-derived peptides, or "matrikines", which, in turn, are potentially able to regulate important cell activities.

Late endothelial progenitor cell-capture stents with CD146 antibody and nanostructure reduce in-stent restenosis and thrombosis

The restoration of damaged endothelium is promising to reduce side effects, including restenosis and thrombosis, in the stent treatment for vascular diseases. Current technologies based on drug delivery for these complications still do not satisfy patients due to invariant recurrence rate. Recently, even if one approach was applied to clinical trial to develop the firstly commercialized stent employing circulating endothelial progenitor cells (EPCs) in blood vessels, it resulted in failure in clinical trial. Based on instruction of the failed case, we designed an advanced EPC-capture stent covered with anti-CD146 antibody (Ab) immobilized silicone nanofilament (SiNf) for the highly efficient and specific capture of not early but late stage of EPCs. In vitro cell capture test demonstrates enhanced capture efficiency and adhesion morphology of late EPCs on the modified substrate. The modified substrates could capture 8 times more late EPCs and even 3 times more mesenchymal stem cells (MSCs) as compared to unmodified one. A porcine model with high similarity to human reproduced in vivo results ideally translated from in vitro cell capture results. As restenosis indicators, lumen area, neointimal rate and stenosis area for modified stents were reduced at the range of 30-60% as compared to those for bare metal stent (BMS). Fibrin score indicating thrombosis was lowered less than half as comparing to that on BMS. These inspiring results are attributed to ~2-fold increased endothelial coverage, determined by immuno-histological staining. Taken together, the CD146 Ab-armed nanofilamentous stent could show great performance in the reduction of thrombosis and restenosis through re-endothelialization due to highly efficient specific cell capture. STATEMENT OF SIGNIFICANCE: Stents have been developed from simple metal stents to functionalized stents for past decades. However, they have still risks to relapse the occlusion in stented arteries. In this paper, we describe the fabrication and optimization of cell capturing stents to maximize the effective re-endothelialization through the serial coating of silicone nanofilaments and anti-CD146 antibody. The nanofilaments increase the amount of coated antibodies and provide the anchoring points of circulating angiogenic cells for strong focal adhesion. We demonstrate high immobilizing ability of circulating angiogenic cells (endotheliali progenitor cells and mesenchymal stem cells) in vitro under similar shear stress to coronary arteries (15 dyne/cm²). Also, we show accelerating re-endothelialization and the efficient prevention of restenosis in porcine coronary arteries in vivo.

Elastin-Based Materials: Promising Candidates for Cardiac Tissue Regeneration

Stroke and cardiovascular episodes are still some of the most common diseases worldwide, causing millions of deaths and costing billions of Euros to healthcare systems. The use of new biomaterials with enhanced biological and physical properties has opened the door to new approaches in cardiovascular applications. Elastin-based materials are biomaterials with some of the most promising properties. Indeed, these biomaterials have started to yield good results in cardiovascular and angiogenesis applications. In this review, we explore the latest trends in elastin-derived materials for cardiac regeneration and the different possibilities that are being explored by researchers to regenerate an infarcted muscle and restore its normal function. Elastin-based materials can be processed in different manners to create injectable systems or hydrogel scaffolds that can be applied by simple injection or as patches to cover the damaged area and regenerate it. Such materials have been applied to directly regenerate the damaged cardiac muscle and to create complex structures, such as heart valves or new bio-stents that could help to restore the normal function of the heart or to minimize damage after a stroke. We will discuss the possibilities that elastin-based materials offer in cardiac tissue engineering, either alone or in combination with other biomaterials, in order to illustrate the wide range of options that are being explored. Moreover, although tremendous advances have been achieved with such elastin-based materials, there is still room for new approaches that could trigger advances in cardiac tissue regeneration.

Genetically Engineered Elastin-based Biomaterials for Biomedical Applications

Protein-based polymers are some of the most promising candidates for a new generation of innovative biomaterials as recent advances in genetic-engineering and biotechnological techniques mean that protein-based biomaterials can be designed and constructed with a higher degree of complexity and accuracy. Moreover, their sequences, which are derived from structural protein-based modules, can easily be modified to include bioactive motifs that improve their functions and material-host interactions, thereby satisfying fundamental biological requirements. The accuracy with which these advanced polypeptides can be produced, and their versatility, self-assembly behavior, stimuli-responsiveness and biocompatibility, means that they have attracted increasing attention for use in biomedical applications such as cell culture, tissue engineering, protein purification, surface engineering and controlled drug delivery. The biopolymers discussed in this review are elastin-derived protein-based polymers which are biologically inspired and biomimetic materials. This review will also focus on the design, synthesis and characterization of these genetically encoded polymers and their potential utility for controlled drug and gene delivery, as well as in tissue engineering and regenerative medicine.

Combinatorial functionalization with bisurea-peptides and antifouling bisurea additives of a supramolecular elastomeric biomaterial

The bioactive additive toolbox to functionalize supramolecular elastomeric materials expands rapidly. Here we have set an explorative step toward screening of complex combinatorial functionalization with antifouling and three peptide-containing additives in a bisurea-based supramolecular system. Thorough investigation of surface properties of thin films with contact angle measurements, X-ray photoelectron spectroscopy and atomic force microscopy, was correlated to cell-adhesion of endothelial and smooth muscle cells to apprehend their respective predictive values for functional biomaterial development. Peptides were presented at the surface alone, and in combinatorial functionalization with the oligo(ethylene glycol)-based non-cell adhesive additive. The bisurea-RGD additive was cell-adhesive in all conditions, whereas the endothelial cell-specific bisurea-REDV showed limited bioactive properties in all chemical nano-environments. Also, aspecific functionality was observed for a bisurea-SDF1α peptide. These results emphasize that special care should be taken in changing the chemical nano-environment with peptide functionalization. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1725-1735.

A double safety lock tumor-specific device for suicide gene therapy in breast cancer

The complexity and continuous evolution of cancer make the design of novel strategies of treatment a constant challenge in biomedicine. Moreover, most of cancer treatments are still not tumor-specific and provoke high systemic toxicity. Herein we have developed a novel selective nanodevice to eliminate tumor cells while leaving healthy ones intact. To achieve this objective, a polyplex carrier, comprising an elastin like-recombinamer covalently conjugated to an aptamer and complexed with therapeutic DNA, was tested. This carrier forms a double-lock multifunctional device due to specific binding to a tumor cell marker and the selective expression of therapeutic DNA inside human breast-cancer cells. Due to the stability provided by ELRs, the homogeneous population of polyplexes obtained showed selective toxicity against cancer cells in in vitro and in vivo assay. Inhibition of tumor progression was detected early being very significant at the end point, with a dose-dependent reduction in tumor mass. Histological studies revealed a specific reduction in tumor parenchyma and in specific tumor cell markers. These results represent an important step toward the rational development of an efficient, safe and more specialized gene-delivery device for tumor therapy.

Small Caliber Compliant Vascular Grafts Based on Elastin-Like Recombinamers for in situ Tissue Engineering

Vascular disease is a leading cause of death worldwide, but surgical options are restricted by the limited availability of autologous vessels, and the suboptimal performance of prosthetic vascular grafts. This is especially evident for coronary artery by-pass grafts, whose small caliber is associated with a high occlusion propensity. Despite the potential of tissue-engineered grafts, compliance mismatch, dilatation, thrombus formation, and the lack of functional elastin are still major limitations leading to graft failure. This calls for advanced materials and fabrication schemes to achieve improved control on the grafts' properties and performance. Here, bioinspired materials and technical textile components are combined to create biohybrid cell-free implants for endogenous tissue regeneration. Clickable elastin-like recombinamers are processed to form an open macroporous 3D architecture to favor cell ingrowth, while being endowed with the non-thrombogenicity and the elastic behavior of the native elastin. The textile components (i.e., warp-knitted and electrospun meshes) are designed to confer suture retention, long-term structural stability, burst strength, and compliance. Notably, by controlling the electrospun layer's thickness, the compliance can be modulated over a wide range of values encompassing those of native vessels. The grafts support cell ingrowth, extracellular matrix deposition and endothelium development in vitro. Overall, the fabrication strategy results in promising off-the-shelf hemocompatible vascular implants for in situ tissue engineering by addressing the known limitations of bioartificial vessel substitutes.

Trends in the design and use of elastin-like recombinamers as biomaterials

Elastin-like recombinamers (ELRs), which derive from one of the repetitive domains found in natural elastin, have been intensively studied in the last few years from several points of view. In this mini review, we discuss all the recent works related to the investigation of ELRs, starting with those that define these polypeptides as model intrinsically disordered proteins or regions (IDPs or IDRs) and its relevance for some biomedical applications. Furthermore, we summarize the current knowledge on the development of drug, vaccine and gene delivery systems based on ELRs, while also emphasizing the use of ELR-based hydrogels in tissue engineering and regenerative medicine (TERM). Finally, we show different studies that explore applications in other fields, and several examples that describe biomaterial blends in which ELRs have a key role. This review aims to give an overview of the recent advances regarding ELRs and to encourage further investigation of their properties and applications.

An elastin-like recombinamer-based bioactive hydrogel embedded with mesenchymal stromal cells as an injectable scaffold for osteochondral repair

The aim of this study was to evaluate injectable, in situ cross-linkable elastin-like recombinamers (ELRs) for osteochondral repair. Both the ELR-based hydrogel alone and the ELR-based hydrogel embedded with rabbit mesenchymal stromal cells (rMSCs) were tested for the regeneration of critical subchondral defects in 10 New Zealand rabbits. Thus, cylindrical osteochondral defects were filled with an aqueous solution of ELRs and the animals sacrificed at 4 months for histological and gross evaluation of features of biomaterial performance, including integration, cellular infiltration, surrounding matrix quality and the new matrix in the defects. Although both approaches helped cartilage regeneration, the results suggest that the specific composition of the rMSC-containing hydrogel permitted adequate bone regeneration, whereas the ELR-based hydrogel alone led to an excellent regeneration of hyaline cartilage. In conclusion, the ELR cross-linker solution can be easily delivered and forms a stable well-integrated hydrogel that supports infiltration and de novo matrix synthesis.

Bicyclic RGD peptides with high integrin α v β 3 and α 5 β 1 affinity promote cell adhesion on elastin-like recombinamers

Biomaterial design in tissue engineering aims to identify appropriate cellular microenvironments in which cells can grow and guide new tissue formation. Despite the large diversity of synthetic polymers available for regenerative medicine, most of them fail to fully match the functional properties of their native counterparts. In contrast, the few biological alternatives employed as biomaterials lack the versatility that chemical synthesis can offer. Herein, we studied the HUVEC adhesion and proliferation properties of elastin-like recombinamers (ELRs) that were covalently functionalized with each three high-affinity and selectivity α _v β ₃- and α ₅ β ₁-binding bicyclic RGD peptides. Next to the bicycles, ELRs were also functionalized with various integrin-binding benchmark peptides, i.e. knottin-RGD, cyclo-[KRGDf] and GRGDS, allowing for better classification of the obtained results. Covalent functionalization with the RGD peptides, as validated by MALDI-TOF analysis, guarantees flexibility and minimal steric hindrance for interactions with cellular integrins. In addition to the covalently modified RGD-ELRs, we also synthesized another benchmark ELR comprising RGD as part of the backbone. HUVEC adhesion and proliferation analysis using the PicoGreen® assay revealed a higher short-term adhesion and proliferative capacity of cells on ELR surfaces functionalized with high affinity, integrin-binding bicyclic RGD-peptides compared with the ELRs containing RGD in the backbone.

Self-assembly in elastin-like recombinamers: a mechanism to mimic natural complexity

The topic of self-assembled structures based on elastin-like recombinamers (ELRs, i.e., elastin-like polymers recombinantly bio-produced) has released a noticeable amount of references in the last few years. Most of them are intended for biomedical applications. In this review, a complete revision of the bibliography is carried out. Initially, the self-assembly (SA) concept is considered from a general point of view, and then ELRs are described and characterized based on their intrinsic disorder. A classification of the different self-assembled ELR-based structures is proposed based on their morphologies, paying special attention to their tentative modeling. The impact of the mechanism of SA on these biomaterials is analyzed. Finally, the implications of ELR SA in biological systems are considered.

Combining Catalyst-Free Click Chemistry with Coaxial Electrospinning to Obtain Long-Term, Water-Stable, Bioactive Elastin-Like Fibers for Tissue Engineering Applications

Elastic fibers are a fundamental requirement for tissue-engineered equivalents of physiologically elastic native tissues. Here, a simple one-step electrospinning approach is developed, combining i) catalyst-free click chemistry, ii) coaxial electrospinning, and iii) recombinant elastin-like polymers as a relevant class of biomaterials. Water-stable elastin-like fibers are obtained without the use of cross-linking agents, catalysts, or harmful organic solvents. The fibers can be directly exposed to an aqueous environment at physiological temperature and their morphology maintained for at least 3 months. The bioactivity of the fibers is demonstrated with human vascular cells and the potential of the process for vascular tissue engineering is shown by fabricating small-diameter tubular fibrous scaffolds. Moreover, highly porous fluffy 3D constructs are obtained without the use of specially designed collectors or sacrificial materials, further supporting their applicability in the biomedical field. Ultimately, the strategy that is developed here may be applied to other click systems, contributing to expanding their potential in medical technology.

Random and oriented electrospun fibers based on a multicomponent, in situ clickable elastin-like recombinamer system for dermal tissue engineering

Herein we present a system to obtain fibers from clickable elastin-like recombinamers (ELRs) that crosslink in situ during the electrospinning process itself, with no need for any further treatment to stabilize them. These ELR-click fibers are completely stable under in vitro conditions. A wrinkled fiber morphology is obtained. In addition to a random fiber orientation, oriented fibers with a high degree of alignment and coherence can also be obtained by using a rotational electrode. The production of multicomponent fibers means that different functionalities, such as cell-adhesion domains (RGD peptides), can be incorporated into them. In a subsequent study, two main cell lines present in the dermis and epidermis, namely keratinocytes and fibroblasts, were cultured on top of the ELR-click fibers. Adhesion, proliferation, fluorescence, immunostaining and histology studies showed the cytocompatibility of these scaffolds, thus suggesting their possible use for wound dressings in skin tissue engineering applications.

STATEMENT OF SIGNIFICANCE

For the first time stable electrospun bioactive fibers are obtained by the in situ mixing of two "clickable" ELR components previously described by Gonzalez et al (Acta Biomaterialia 2014). This work describes an efficient system to prepare fibrous scaffolds based on peptidic polymers by electrospinning without the need of crosslinking agents that could be harmful for cells or living tissues. These bioactive fibers support cell growth due to the inclusion of RGD motifs (Staubli et al. Biomaterials 2017). Finally, the in vitro biocompatibility of the two main cell types found in the outer layers of skin, fibroblasts and keratinocytes, indicates that this system is of great interest to prepare elastic artificial skin substitutes for wound healing applications.

Hybrid elastin-like recombinamer-fibrin gels: physical characterization and in vitro evaluation for cardiovascular tissue engineering applications

In the field of tissue engineering, the properties of the scaffolds are of crucial importance for the success of the application. Hybrid materials combine the properties of the different components that constitute them. In this study hybrid gels of Elastin-Like Recombinamer (ELR) and fibrin were prepared with a range of polymer concentrations and ELR-to-fibrin ratios. The correlation between SEM micrographs, porosities, swelling ratios and rheological properties was discussed and a poroelastic mechanism was suggested to explain the mechanical behavior of the hybrid gels. Applicability as scaffold materials for cardiovascular tissue engineering was shown by the realization of cell-laden matrixes which supported the synthesis of collagens as revealed by immunohistochemical analysis. As a proof of concept, a tissue-engineered heart valve was fabricated by injection moulding and cultivated in a bioreactor for 3 weeks under dynamic conditions. Tissue analysis revealed the production of collagen I and III, fundamental proteins for cardiovascular constructs.

Bioactive scaffolds based on elastin-like materials for wound healing

Wound healing is a complex process that, in healthy tissues, starts immediately after the injury. Even though it is a natural well-orchestrated process, large trauma wounds, or injuries caused by acids or other chemicals, usually produce a non-elastic deformed tissue that not only have biological reduced properties but a clear aesthetic effect. One of the main drawbacks of the scaffolds used for wound dressing is the lack of elasticity, driving to non-elastic and contracted tissues. In the last decades, elastin based materials have gained in importance as biomaterials for tissue engineering applications due to their good cyto- and bio-compatibility, their ease handling and design, production and modification. Synthetic elastin or elastin like-peptides (ELPs) are the two main families of biomaterials that try to mimic the outstanding properties of natural elastin, elasticity amongst others; although there are no in vivo studies that clearly support that these two families of elastin based materials improve the elasticity of the artificial scaffolds and of the regenerated skin. Within the next pages a review of the different forms (coacervates, fibres, hydrogels and biofunctionalized surfaces) in which these two families of biomaterials can be processed to be applied in the wound healing field have been done. Here, we explore the mechanical and biological properties of these scaffolds as well as the different in vivo approaches in which these scaffolds have been used.

Macroporous click-elastin-like hydrogels for tissue engineering applications

Elastin is a key extracellular matrix (ECM) protein that imparts functional elasticity to tissues and therefore an attractive candidate for bioengineering materials. Genetically engineered elastin-like recombinamers (ELRs) maintain inherent properties of the natural elastin (e.g. elastic behavior, bioactivity, low thrombogenicity, inverse temperature transition) while featuring precisely controlled composition, the possibility for biofunctionalization and non-animal origin. Recently the chemical modification of ELRs to enable their crosslinking via a catalyst-free click chemistry reaction, has further widened their applicability for tissue engineering. Despite these outstanding properties, the generation of macroporous click-ELR scaffolds with controlled, interconnected porosity has remained elusive so far. This significantly limits the potential of these materials as the porosity has a crucial role on cell infiltration, proliferation and ECM formation. In this study we propose a strategy to overcome this issue by adapting the salt leaching/gas foaming technique to click-ELRs. As result, macroporous hydrogels with tuned pore size and mechanical properties in the range of many native tissues were reproducibly obtained as demonstrated by rheological measurements and quantitative analysis of fluorescence, scanning electron and two-photon microscopy images. Additionally, the appropriate size and interconnectivity of the pores enabled smooth muscle cells to migrate into the click-ELR scaffolds and deposit extracellular matrix. The macroporous structure together with the elastic performance and bioactive character of ELRs, the specificity and non-toxic character of the catalyst-free click-chemistry reaction, make these scaffolds promising candidates for applications in tissue regeneration. This work expands the potential use of ELRs and click chemistry systems in general in different biomedical fields.

Bioorthogonal Strategies for Engineering Extracellular Matrices

Hydrogels are commonly used as engineered extracellular matrix (ECM) mimics in applications ranging from tissue engineering to in vitro disease models. Ideal mechanisms used to crosslink ECM-mimicking hydrogels do not interfere with the biology of the system. However, most common hydrogel crosslinking chemistries exhibit some form of cross-reactivity. The field of bio-orthogonal chemistry has arisen to address the need for highly specific and robust reactions in biological contexts. Accordingly, bio-orthogonal crosslinking strategies have been incorporated into hydrogel design, allowing for gentle and efficient encapsulation of cells in various hydrogel materials. Furthermore, the selective nature of bio-orthogonal chemistries can permit dynamic modification of hydrogel materials in the presence of live cells and other biomolecules to alter matrix mechanical properties and biochemistry on demand. In this review, we provide an overview of bio-orthogonal strategies used to prepare cell-encapsulating hydrogels and highlight the potential applications of bio-orthogonal chemistries in the design of dynamic engineered ECMs.

Control of angiogenesis and host response by modulating the cell adhesion properties of an Elastin-Like Recombinamer-based hydrogel

The control of the in vivo vascularization of engineered tissue substitutes is essential in order to obtain either a rapid induction or a complete inhibition of the process (e.g. in muscles and hyaline-cartilage, respectively). Among the several polymers available, Elastin-Like Recombinamers (ELR)-based hydrogel stands out as a promising material for tissue engineering thanks to its viscoelastic properties, non-toxicity, and non-immunogenicity. In this study, we hypothesized that varying the cell adhesion properties of ELR-hydrogels could modulate the high angiogenic potential of adipose tissue-derived stromal vascular fraction (SVF) cells, predominantly composed of endothelial/mural and mesenchymal cells. Human SVF cells, embedded in RGD-REDV-bioactivated or unmodified ELR-hydrogels, were implanted in rat subcutaneous pockets either immediately or upon 5-day-culture in perfusion-bioreactors. Perfusion-based culture enhanced the endothelial cell cord-like-organization and the release of pro-angiogenic factors in functionalized constructs. While in vivo vascularization and host cell infiltration within the bioactivated gels were highly enhanced, the two processes were strongly inhibited in non-functionalized SVF-based hydrogels up to 28 days. ELR-based hydrogels showed a great potential to determine the successful integration of engineered substitutes thanks to their capacity to finely control the angiogenic/inflammation process at the recipient site, even in presence of SVF cells.

Adding Functions to Biomaterial Surfaces through Protein Incorporation

The concept of biomaterials has evolved from one of inert mechanical supports with a long-term, biologically inactive role in the body into complex matrices that exhibit selective cell binding, promote proliferation and matrix production, and may ultimately become replaced by newly generated tissues in vivo. Functionalization of material surfaces with biomolecules is critical to their ability to evade immunorecognition, interact productively with surrounding tissues and extracellular matrix, and avoid bacterial colonization. Antibody molecules and their derived fragments are commonly immobilized on materials to mediate coating with specific cell types in fields such as stent endothelialization and drug delivery. The incorporation of growth factors into biomaterials has found application in promoting and accelerating bone formation in osteogenerative and related applications. Peptides and extracellular matrix proteins can impart biomolecule- and cell-specificities to materials while antimicrobial peptides have found roles in preventing biofilm formation on devices and implants. In this progress report, we detail developments in the use of diverse proteins and peptides to modify the surfaces of hard biomaterials in vivo and in vitro. Chemical approaches to immobilizing active biomolecules are presented, as well as platform technologies for isolation or generation of natural or synthetic molecules suitable for biomaterial functionalization.

Biocompatible ELR-Based Polyplexes Coated with MUC1 Specific Aptamers and Targeted for Breast Cancer Gene Therapy

The search for new and biocompatible materials with high potential for improvement is a challenge in gene delivery applications. A cell type specific vector made of elastin-like recombinamer (ELR) and aptamers has been specifically designed for the intracellular delivery of therapeutic material for breast cancer therapy. A lysine-enriched ELR was constructed and complexed with plasmid DNA to give positively charged and stable polyplexes. Physical characterization of these polyplexes showed a particle size of around 140 nm and a zeta potential of approximately +40 mV. The incorporation of MUC1-specific aptamers into the polyplexes resulted in a slight decrease in zeta potential but increased cell transfection specificity for MCF-7 breast cancer cells with respect to a MUC1-negative tumor line. After showing the transfection ability of this aptamer-ELR vector which is facilitated mainly by macropinocytosis uptake, we demonstrated its application for suicide gene therapy using a plasmid containing the gene of the toxin PAP-S. The strategy developed in this work about using ELR as polymeric vector and aptamers as supplier of specificity to deliver therapeutic material into MUC1-positive breast cancer cells shows promising potential and continues paving the way for ELRs in the biomedical field.

Immobilization of Ophiopogonin D on stainless steel surfaces for improving surface endothelialization

Ophiopogonin D, a traditional Chinese medicine, was immobilized onto the surface of cardiovascular 316L SS material to improve surface endothelialization.

Advances in Functional Assemblies for Regenerative Medicine

The ability to synthesise bioresponsive systems and selectively active biochemistries using polymer-based materials with supramolecular features has led to a surge in research interest directed towards their development as next generation biomaterials for drug delivery, medical device design and tissue engineering.

Recombinant Technology in the Development of Materials and Systems for Soft-Tissue Repair

The field of biomedicine is constantly investing significant research efforts in order to gain a more in-depth understanding of the mechanisms that govern the function of body compartments and to develop creative solutions for the repair and regeneration of damaged tissues. The main overall goal is to develop relatively simple systems that are able to mimic naturally occurring constructs and can therefore be used in regenerative medicine. Recombinant technology, which is widely used to obtain new tailored synthetic genes that express polymeric protein-based structures, now offers a broad range of advantages for that purpose by permitting the tuning of biological and mechanical properties depending on the intended application while simultaneously ensuring adequate biocompatibility and biodegradability of the scaffold formed by the polymers. This Progress Report is focused on recombinant protein-based materials that resemble naturally occurring proteins of interest for use in soft tissue repair. An overview of recombinant biomaterials derived from elastin, silk, collagen and resilin is given, along with a description of their characteristics and suggested applications. Current endeavors in this field are continuously providing more-improved materials in comparison with conventional ones. As such, a great effort is being made to put these materials through clinical trials in order to favor their future use.

Study of novel coating strategy for coronary stents: simutaneous coating of VEGF and anti- CD34 antibody

Introduction

Intravascular coronary stenting has been used in the treatment of coronary artery disease (CAD), with a major limitation of in-stent restenosis (ISR). The 316 stainless steel has been widely used for coronary stents. In this study, we developed a novel coating method to reduce ISR by simultaneously coating vascular endothelial growth factor (VEGF) and anti-CD34 antibody on 316L stainless steel.

Methods

Round 316L stainless steel sheets in the D-H group were polymerized with compounds generated from condensation reaction of dopamine and heparin using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS). Sixteen sheets from the D-H group were further immersed into 1ug/ml VEGF₁₆₅ and 3mg/ml heparin sodium one after another for 10 times, and named as the D-(H-V)₁₀ group. Eight sheets from the D-(H-V)₁₀ group were coated with anti-CD34 antibody and termed as the D-(H-V)₁₀-A group. Immunofluorescence assay and ELISA were used to evaluate whether the 316L stainless steel disks were successfully coated with VEGF and anti-CD34 antibody.

Results

The results of immunofluorescence assay and ELISA showed that VEGF could be detected in the D-(H-V)₁₀ and D-(H-V)₁₀-A group, suggesting the steel sheets were successfully covered with VEGF. Anti-CD34 antibody could only be observed in the D-(H-V)₁₀-A group, which was the only group coated with CD34 antibody. Both results suggested that the 316L stainless steel sheets were successfully coated with VEGF and anti-CD34 antibody.

Conclusion

Our study developed a method to simultaneously coat VEGF and anti-CD34 antibody to stainless metal steel. This research serves as a fundamental role for a novel coating strategy.

Descriptors: Coronary Artery Disease. Drug-Eluting Stents. Coronary Restenosis. Vascular Endothelial Growth Factor. Antigens, CD34.