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Synthetic vascular grafts are commonly used in patients with severe occlusive arterial disease when autologous grafts are not an option. Commercially available synthetic grafts are confronted with challenging outcomes: they have a lower patency rate than autologous grafts and are currently unable to promote arterial regeneration. Polyglycerol sebacate (PGS), a non-toxic polymer with a tunable degradation profile, has shown promising results as a small-diameter vascular graft component that can support the formation of neoarteries. In this review, we first present an overview of the synthesis and modification of PGS followed by an examination of its mechanical properties. We then report on the performance, degradation, regeneration, and remodeling of PGS-based small-diameter vascular grafts, with a focus on efforts to reduce thrombosis, prevent dilation, and promote cellular residency and extracellular matrix regeneration that resembles the native artery in spatial distribution and organization. We also highlight recent advances in the incorporation of novel in situ cell sources for arterial regeneration and their potential application in PGS-based vascular grafts. Finally, we compare vascular grafts fabricated using PGS-based materials with other elastomeric alternatives., (© 2023 The Authors. Journal of Biomedical Materials Research Part A published by Wiley Periodicals LLC.)

Hollow-fiber capillary bundles are widely used in the production of medical devices for blood oxygenation and purification purposes such as in cardiopulmonary bypass, hemodialysis, and hemofiltration, but the blood interfacing inner surfaces of these capillaries provide poor hemocompatibility. Here, we present a novel method of packed-bed plasma ion implantation (PBPII) for the modification of the inner surfaces of polymeric hollow-fiber bundles enclosed in a cassette. The method is simple and can be performed on an intact hollow-fiber bundle cassette by the placement of a hollow cylindrical electrode, connected to a negative high-voltage pulse generator, around the cassette. The method does not require the insertion of electrodes inside the capillaries or the cassette. Nitrogen gas is fed into the capillaries inside the cassette by connecting the inlet of the cassette to a gas source. Upon the application of negative high-voltage bias pulses to the electrode, plasma is ignited inside the cassette, achieving the surface modification of both the internal and external surfaces of the capillaries. Fourier transform infrared-attenuated total reflectance spectroscopy of the PBPII-treated capillaries revealed the formation of aromatic C═C bonds, indicating the progressive carbonization of the capillary surfaces. The PBPII treatment was found to be uniform along the capillaries and independent of the radial position in the cassette. Atomic force microscopy of cross sections through the capillaries revealed that the increased stiffness associated with the carbonized layer on the inner surface of the PBPII-treated capillary has a depth (∼40 nm) consistent with that expected for ions accelerated by the applied bias voltage. The modified internal surfaces of the capillary bundle showed a greatly increased wettability and could be biofunctionalized by covalently immobilizing protein directly from the buffer solution. The direct, reagent-free protein immobilization was demonstrated using tropoelastin as an example protein. Covalent binding of the protein was confirmed by its resistance to removal by hot sodium dodecyl sulfate detergent washing, which is known to disrupt physical binding.

Polyurethanes are a diverse class of polymers, with independently tunable mechanical and biodegradation properties making them a versatile platform material for biomedical implants. Previous iterations have failed to adequately embody appropriate mechanical and biological properties, particularly for vascular medicine where strength, compliance and multifaceted biocompatibility are required. We have synthesized a new polyurethane formulation with finely tuned mechanical properties, combining high strength and extensibility with a low Young's modulus. Additional cross-linking during synthesis enhanced stability and limits leaching. Under cyclic testing, hysteresis was minimal following completion of the initial cycles, indicating the robustness of the material. Building on this platform, we used plasma immersion ion implantation to activate the polymer surface and functionalized it with recombinant human tropoelastin. With tropoelastin covalently bound to the surface, human coronary endothelial cells showed improved attachment and proliferation. In the presence of heparinized whole blood, tropoelastin-coated polyurethane showed very low thrombogenicity in both static and flow conditions. Using this formulation, we synthesized robust, elastic prototype conduits which easily retained multiple sutures and were successfully implanted in a pilot rat aortic interposition model. We have thus created an elastic, strong biomaterial platform, functionalized with an important regulator of vascular biology, with the potential for further evaluation as a new synthetic graft material.

Biomimetic materials which integrate with surrounding tissues and regulate new tissue formation are attractive for tissue engineering and regenerative medicine. Plasma immersion ion-implanted (PIII) polyethersulfone (PES) provides an excellent platform for the irreversible immobilization of bioactive proteins and peptides. PIII treatment significantly improves PES wettability and results in the formation of acidic groups on the PES surface, with the highest concentration observed at 40-80 s of PIII treatment. The elastomeric protein tropoelastin can be stably adhered to PIII-treated PES in a cell-interactive conformation by tailoring the pH and salt levels of the protein-surface association conditions. Tropoelastin-coated PIII-treated PES surfaces are resistant to molecular fouling, and actively promote high levels of fibroblast adhesion and proliferation while maintaining cell morphology. Tropoelastin, unlike other extracellular matrix proteins such as fibronectin, uniquely retains full bioactivity even after medical-grade ethylene oxide sterilization. This dual approach of PIII treatment and tropoelastin cloaking allows for the stable, robust functionalization of clinically used polymer materials for directed cellular interactions., (© 2017 The Author(s).)

The elastomeric proteins elastin and resilin have been used extensively in the fabrication of biomaterials for tissue engineering applications due to their unique mechanical and biological properties. Tropoelastin is the soluble monomer component of elastin. Tropoelastin and resilin are both highly elastic with high resilience, substantial extensibility, high durability and low energy loss, which makes them excellent candidates for the fabrication of elastic tissues that demand regular and repetitive movement like the skin, lung, blood vessels, muscles and vocal folds. Combinations of these proteins with silk fibroin further enhance their biomechanical and biological properties leading to a new class of protein alloy materials with versatile properties. In this review, the properties of tropoelastin-based and resilin-based biomaterials with and without silk are described in concert with examples of their applications in tissue engineering., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Blended polymers are used extensively in many critical medical conditions as components of permanently implanted devices. Hybrid protein polymers containing recombinant human tropoelastin and silk fibroin have favorable characteristics as implantable scaffolds in terms of mechanical and biological properties. A firefly luciferase transgenic mouse model was used to monitor real-time IL-1β production localized to the site of biomaterial implantation, to observe the acute immune response (up to 5 days) to these materials. Significantly reduced levels of IL-1β were observed in silk/tropoelastin implants compared to control silk only implants at 1, 2 and 3 days post-surgery. Subsequently, mice (n = 9) were euthanized at 10 days (10D) and 3 weeks (3W) post-surgery to assess inflammatory cell infiltration and collagen deposition, using histopathology and immunohistochemistry. Compared to control silk only implants, fewer total inflammatory cells were found in silk/tropoelastin (∼29% at 10D and ∼47% at 3W). Also fewer ingrowth cells (∼42% at 10D and ∼63% at 3W) were observed within the silk/tropoelastin implants compared to silk only. Lower IL-6 (∼52%) and MMP-2 (∼84%) (pro-inflammatory) were also detected for silk/tropoelastin at 10 days. After 3 weeks implantation, reduced neovascularization (vWF ∼43%), fewer proliferating cells (Ki67 ∼58% and PCNA ∼41%), macrophages (F4/80 ∼64%), lower IL-10 (∼47%) and MMP-9 (∼55%) were also observed in silk/tropoelastin materials compared to silk only. Together, these results suggest that incorporation of tropoelastin improves on the established biocompatibility of silk fibroin, uniquely measured here as a reduced foreign body inflammatory response., (Crown Copyright © 2014. Published by Elsevier Ltd. All rights reserved.)

The interaction of proteins and cells with polymers is critical to their use in scientific and medical applications. In this study, plasma immersion ion implantation (PIII) was used to modify the surface of the conducting polymer, polypyrrole, which possesses electrical properties. PIII treatment enabled persistent, covalent binding of the cell adhesive protein, tropoelastin, without employing chemical linking molecules. In contrast tropoelastin was readily eluted from the untreated surface. Through this differential persistence of binding, surface bound tropoelastin supported cell adhesion and spreading on the PIII treated but not the untreated polypyrrole surface. The application of a steel shadow mask during PIII treatment allowed for spatial definition of tropoelastin exclusively to PIII treated regions. The general applicability of this approach to other extracellular matrix proteins was illustrated using collagen I, which displayed similar results to tropoelastin but required extended washing conditions. This approach allowed fine patterning of cell adhesion and spreading to tropoelastin and collagen, specifically on PIII treated polypyrrole regions. We therefore present a methodology to alter the functionality of polypyrrole surfaces, generating surfaces that can spatially control cellular interactions through protein functionalization with the potential for electrical stimulation., (Copyright © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

The aim of this study was to demonstrate the effect of elastin on chondrocyte adhesion and proliferation within the structure of poly (ɛ-caprolactone) (PCL)/elastin composites. The homogenous 3D structure composites were constructed by using high pressure CO(2) in two stages. Porous PCL structures with average pore sizes of 540 ± 21 μm and a high degree of interconnectivity were produced using gas foaming/salt leaching. The PCL scaffolds were then impregnated with elastin and cross-linked with glutaraldehyde (GA) under high pressure CO(2). The effects of elastin and cross-linker concentrations on the characteristics of composites were investigated. Increasing the elastin concentration from 25mg/ml to 100mg/ml elevated the amount of cross-linked elastin inside the macropores of PCL. Fourier transform infrared (FTIR) analysis showed that elastin was homogeneously distributed throughout the 3D structure of all composites. The weight gain of composites increased 2-fold from 15.8 ± 0.3 to 38.3 ± 0.7 (w/w) % by increasing the elastin concentration from 25mg/ml to 50mg/ml and approached a plateau above this concentration. The presence of elastin within the pores of PCL improved the water uptake properties of PCL scaffolds; the water uptake ratio of PCL was enhanced 100-fold from 0.030 ± 0.005g liquid/g polymer to 11.80 ± 0.01g liquid/g polymer, when the elastin solution concentration was 50mg/ml. These composites exhibited lower compressive modulus and energy loss compared to pure PCL scaffolds due to their higher water content and elasticity. In vitro studies show that these composites can support primary articular cartilage chondrocyte adhesion and proliferation within the 3D structures. These results demonstrate the potential of using PCL/elastin composites for cartilage repair., (2010. Published by Elsevier Ltd. All rights reserved.)

Polymers are used for the fabrication of many prosthetic implants. It is desirable for these polymers to promote biological function by promoting the adhesion, differentiation and viability of cells. Here we have used plasma immersion ion implantation (PIII) treatment of polystyrene to modify the polymer surface, and so modulate the binding of the extracellular matrix protein tropoelastin. PIII treated, but not untreated polystyrene, bound tropoelastin in a sodium dodecyl sulfate (SDS)-resistant manner, consistent with previous enzyme-binding data that demonstrated the capability of these surfaces to covalently attach proteins without employing chemical linking molecules. Furthermore sulfo-NHS acetate (SNA) blocking of tropoelastin lysine side chains eliminated the SDS-resistant binding of tropoelastin to PIII-treated polystyrene. This implies tropoelastin is covalently attached to the PIII-treated surface via its lysine side chains. Cell spreading was only observed on tropoelastin coated, PIII-treated polystyrene surfaces, indicating that tropoelastin was more biologically active on the PIII-treated surface compared to the untreated surface. A contact mask was used to pattern the PIII treatment. Following tropoelastin attachment, cells spread preferentially on the PIII-treated sections of the polystyrene surface. This demonstrates that PIII treatment of polystyrene improves the polymer's tropoelastin binding properties, with advantages for tissue engineering and prosthetic design.

Tropoelastin, the polypeptide monomer precursor of elastin, is covalently cross-linked to give stable elastic structures. We show here that elastic biomaterials can be generated from tropoelastin in the absence of the classically accepted cross-linking pathway. Under alkaline conditions tropoelastin proceeds through a sol-gel transition leading to the formation of an irreversible hydrogel. This does not occur at neutral pH. The resulting biomaterial is stable, elastic and flexible. Scanning electron microscopy revealed that the hydrogel forms through the coalescence of approximately 1 microm quantized protein spheres. These spheres resemble the tropoelastin-rich globules that accumulate on cultured cell surfaces during elastin formation. In vitro cell culture studies demonstrate that the hydrogel can support human skin fibroblast proliferation. In vivo studies demonstrate that following injection, the tropoelastin solution undergoes rapid localized gelation to form a persistent mass. These subcutaneous rodent injection data establish the material's potential as a novel cell-compatible elastic scaffold that can be formed in situ.

The attachment of bioactive protein to surfaces underpins the development of biosensors and diagnostic microarrays. We present a surface treatment using plasma immersion ion implantation (PIII) to create stable covalent binding sites for the attachment of functional soya-bean peroxidase (SBP). Fourier transform infrared spectra of the surfaces show that protein is retained on the surface after boiling in sodium dodecyl sulphate and sodium hydroxide, which is indicative of covalent attachment. The activity of SBP on the treated surfaces remains high in comparison with SBP attached to control surfaces over the course of 11 days. Surface plasmon resonance was used to show that the surface coverage of the attached protein is close to a monolayer. We describe the potential of the PIII treatment method to be used as a one-step dry process to create surfaces for large-scale protein micro- or nanopatterning.

In this study for the first time the effect of high-pressure CO2 on the coacervation of alpha-elastin was investigated using analytical techniques including light spectroscopy and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging and circular dichroism (CD) spectroscopy. The coacervation behavior of alpha-elastin, a protein biopolymer, was determined at temperatures below 40 degrees C and pressures lower than 180 bar. At these conditions elevated pressures did not disrupt the ability of alpha-elastin to coacervate. It was feasible to monitor the presence of amide I, II, and III bands for alpha-elastin at high-pressure CO2 using ATR-FTIR imaging. At a constant temperature the peak absorption was substantially enhanced by increasing the pressure of the system. CD analysis demonstrated the preservation of secondary structure attributes of alpha-elastin exposed to dense gas CO2 at the pressure range investigated in this study. The lower critical solution temperature of alpha-elastin was dramatically decreased from 37 to 16 degrees C when the CO2 pressure increased from 1 to 50 bar, without a significant change after that. Carbon dioxide at high pressures also impeded the reversible coacervation of alpha-elastin solution. These effects were predominantly associated with the lowered pH of the aqueous solution and maybe the interaction between CO2 and hydrophobic domains of alpha-elastin.

Tunable protein composites are important for constructing extracellular matrix mimics of human nerve tissues with control of charge, structural, and mechanical properties. Molecular interaction mechanisms between silk fibroin protein and recombinant human tropoelastin, based on charge, are utilized to generate a new group of multifunctional protein alloys with different net charges. These new biomaterials are then utilized as a biomaterial platform to control neuron cell response. With a +38 net charge in water, tropoelastin molecules provide extraordinary elasticity and selective interactions with cell surface integrins. In contrast, negatively charged silk fibroin protein (net charge −36) provides remarkable toughness and stiffness with morphologic stability in material formats via autoclaving-induced beta-sheet crystal physical crosslinks. The combination of these properties in alloy format extends the versatility of both structural proteins, providing a new biocompatible, biodegradable, and charge-tunable biomaterial platform for neural repair. The data point to these protein alloys as an alternative to commonly used charged synthetic polymers, particularly with regard to the versatility of material formats (e.g., gels, sponges, films, fibers). The results also provide a practical example of physically designed protein materials with control of net charge to direct biological outcomes, in this case for neuronal tissue engineering. [ABSTRACT FROM AUTHOR]

New multifunctional, degradable, polymeric biomaterial systems would provide versatile platforms to address cell and tissue needs in both in vitro and in vivo environments. While protein-based composites or alloys are the building blocks of biological organisms, similar systems have not been largely exploited, to date, to generate ad hoc biomaterials able to control and direct biological functions by recapitulating their inherent structural and mechanical complexities. Therefore, we have recently proposed silktropoelastin material platforms that are able to conjugate a mechanically robust and durable protein, silk, to a highly flexible and biologically active protein, tropoelastin. This review focuses on the elucidation of the interactions between silk and tropoelastin to control the structure of the material its properties, and ultimately functions. In addition, an approach is provided for novel material designs to provide tools to control biological outcomes through surface roughness, elasticity, and net charge for neuronal and mesenchymal stem-cell-based tissue engineering. [ABSTRACT FROM AUTHOR]

Soluble elastin-like peptides (ELPs) can be engineered into a range of physical forms, from hydrogels and scaffolds to fibers and artificial tissues, finding numerous applications in medicine and engineering as “smart polymers”. Elastin-like peptides are attractive candidates as a platform for novel biomaterial design because they exhibit a highly tunable response spectrum, with reversible phase transition capabilities. Here, we report the design of the first virtual library of elastin-like protein models using methods for enhanced sampling to study the effect of peptide chemistry, chain length, and salt concentration on the structural transitions of ELPs, exposing associated molecular mechanisms. We describe the behavior of the local molecular structure under increasing temperatures and the effect of peptide interactions with nearest hydration shell water molecules on peptide mobility and propensity to exhibit structural transitions. Shifts in the magnitude of structural transitions at the single-molecule scale are explained from the perspective of peptide-ion-water interactions in a library of four unique elastin-like peptide systems. Predictions of structural transitions are subsequently validated in experiment. This library is a valuable resource for recombinant protein design and synthesis as it elucidates mechanisms at the single-molecule level, paving a feedback path between simulation and experiment for smart material designs, with applications in biomedicine and diagnostic devices. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to investigate the effect of high pressure CO2 on the crosslinking of elastin-based polymers and the characteristics of the fabricated hydrogels. A hydrogel was fabricated by chemically crosslinking α-elastin with glutaraldehyde at high pressure CO2. The effects of pressure, reaction time, and crosslinker concentration on the characteristics of the fabricated hydrogels were determined. The reaction time had negligible effect on either the swelling ratio or the pore size of the fabricated hydrogels. Increasing the processing pressure from 30bar to 150bar resulted in a 60% increase in the hydrogel swelling ratio. The crosslinked hydrogels displayed stimuli-responsive characteristics towards temperature and salt concentration. The dense gas process facilitated coacervation, expedited the crosslinking reaction, and dramatically affected the micro- and macrostructures of pores within the sample. The results of micro-CT scan and SEM images demonstrated that pore interconnectivity was substantially enhanced for α-elastin hydrogels fabricated using high pressure CO2. Dense gas CO2 reduced the wall thickness and size of the pores and importantly induced channels within the structure of the α-elastin hydrogels. In vitro cell culture studies demonstrated that the channels facilitated fibroblast penetration and proliferation within α-elastin structures. [Copyright &y& Elsevier]

Abstract: A structural protein blend system based on silkworm silk fibroin and recombinant human tropoelastin is described. Silk fibroin, a semicrystalline fibrous protein with beta-sheet crystals provides mechanical strength and controllable biodegradation, while tropoelastin, a noncrystallizable elastic protein provides elasticity. Differential scanning calorimetry (DSC) and temperature modulated DSC (TMDSC) indicated that silk becomes miscible with tropoelastin at different blend ratios, without macrophase separation. Fourier transform infrared spectroscopy (FTIR) revealed secondary structural changes of the blend system (beta-sheet content) before and after methanol treatment. Atomic Force Microscopy (AFM) nano-indentation demonstrated that blending silk and tropoelastin at different ratios resulted in modification of mechanical features, with resilience from ∼68%–∼97%, and elastic modulus between 2 and 9 Mpa, depending on the ratio of the two polymers. Some of these values are close to those of native aortic elastin or elastin-like polypeptides. Significantly, during blending and drying silk–tropoelastin form micro- and nano-scale porous morphologies which promote human mesenchymal stem cell attachment and proliferation. These blends offer a new protein biomaterial system for cell support and tailored biomaterial properties to match mechanical needs. [ABSTRACT FROM AUTHOR]