Hydrogen-bonded Multilayers of Silk Fibroin: From Coatings to Cell-mimicking Shaped Microcontainers

Innovative electrospun PCL/fibroin/l-dopa scaffolds scaffolds supporting bone tissue regeneration

Poly-caprolactone is one of the most promising biocompatible polymers on the market, in particular for temporary devices that are not subjected to high physiological loads. Even if completely resorbable in various biological environments, poly-caprolactione does not play any specific biological role in supporting tissue regeneration and for this reason has a limited range of possible applications. In this preliminary work, for the first time l-dopa and fibroin have been combined with electrospun poly-caprolactone fibers in order to induce bioactive effects and, in particular, stimulate the proliferation, adhesion and osteoconduction of the polymeric fibers. Results showed that addition of low-molecular weight fibroin reduces the mechanical strength of the fibers while promoting the formation of mineralized deposits, when tested in vitro with KUSA-A1 mesenchymal cells. l-dopa, on the other hand, improved the mechanical properties and stimulated the formation of agglomerates of mineralized deposits containing calcium and phosphorous with high specific volume. The combination of the two substances resulted in good mechanical properties and higher amounts of mineralized deposits formed in vitro.

Designing Natural Polymer-Based Capsules and Spheres for Biomedical Applications-A Review

Natural polymers, such as polysaccharides and polypeptides, are potential candidates to serve as carriers of biomedical cargo. Natural polymer-based carriers, having a core-shell structural configuration, offer ample scope for introducing multifunctional capabilities and enable the simultaneous encapsulation of cargo materials of different physical and chemical properties for their targeted delivery and sustained and stimuli-responsive release. On the other hand, carriers with a porous matrix structure offer larger surface area and lower density, in order to serve as potential platforms for cell culture and tissue regeneration. This review explores the designing of micro- and nano-metric core-shell capsules and porous spheres, based on various functions. Synthesis approaches, mechanisms of formation, general- and function-specific characteristics, challenges, and future perspectives are discussed. Recent advances in protein-based carriers with a porous matrix structure and different core-shell configurations are also presented in detail.

Anisotropic Particles through Multilayer Assembly

The anisotropy in the shape of polymeric particles has been demonstrated to have many advantages over spherical particulates, including bio-mimetic behavior, shaped-directed flow, deformation, surface adhesion, targeting, motion, and permeability. The layer-by-layer (LbL) assembly is uniquely suited for synthesizing anisotropic particles as this method allows for simple and versatile replication of diverse colloid geometries with precise control over their chemical and physical properties. This review highlights recent progress in anisotropic particles of micrometer and nanometer sizes produced by a templated multilayer assembly of synthetic and biological macromolecules. Synthetic approaches to produce capsules and hydrogels utilizing anisotropic templates such as biological, polymeric, bulk hydrogel, inorganic colloids, and metal-organic framework crystals as sacrificial templates are overviewed. Structure-property relationships controlled by the anisotropy in particle shape and surface are discussed and compared with their spherical counterparts. Advances and challenges in controlling particle properties through varying shape anisotropy and surface asymmetry are outlined. The perspective applications of anisotropic colloids in biomedicine, including programmed behavior in the blood and tissues as artificial cells, nano-motors/sensors, and intelligent drug carriers are also discussed.

Improving the Activity of DNA-Encoded Sensing Elements through Confinement in Silk Microcapsules

Assembling synthetic bioparts into simplified artificial cells holds tremendous promise for advancing studies into the synthesis, biosensing, and delivery of biomolecules. Currently, the most successful techniques for encapsulation of the transcription-translation machinery exploit compartmentalization in liposomal vesicles. However, improvements to these methods may increase permeability to polar molecules, functionalization of the membrane with biologically active elements, and encapsulation efficiency. Microcapsules prepared via templated layer-by-layer (LbL) assembly using natural polymers have the potential to resolve some of the hurdles associated with liposomes. Here, we introduce a design for immobilizing DNA templates encoding translationally activated riboswitches and RNA aptamers into microcapsules prepared from regenerated silk fibroin protein. Adjusting several key parameters such as the presence of a polymer primer, concentration of silk protein, and DNA loadings during LbL assembly resulted in biocompatible, semipermeable, DNA-laden microcapsules. To preserve bioactivity, DNA was immobilized inside of the capsule membrane, which not only promoted stability during long-term storage at ambient conditions but also improved output response from spatially confined DNA-encoded sensing elements (SEs). Multiple copies of mRNA and GFPa1 protein were synthesized upon activation with specific analytes during in vitro transcription/translation reactions, demonstrating that selective permeability of silk microcapsules was essential for the diffusion of components of the cell-free system inside of the capsules. Further functionalization of capsule shells with gold nanoparticles (AuNPs) and antibodies (IgG) demonstrated the applicability of microcompartmentalized colloidal objects carrying SEs for remote sensing and/or targeted delivery. In the future, multifunctional, biocompatible silk-based microcapsules loaded with different RNA sensors can help advance the design of multiplexed biosensors tracking multiple biomarkers in complex media.

Utilization of Waste Leather Powders for Highly Effective Removal of Dyes from Water

As a natural polymer, leather and its associated industries are known to be the leading economic sector in many countries. However, the huge amounts of leather waste generated from the leather industry causes severe environmental pollution. Herein, cow leather (CL) powders were prepared using a homemade machine and used as a low-cost adsorbent for the effective removal of reactive dyes from wastewater. The as-prepared CL powders exhibited dot-like, rod-like, and fiber-like morphologies. A Fourier transform infrared analysis and an x-ray diffraction analysis demonstrated that the CL powders retained the main structure of the protein contained in it. In addition, an improvement in thermal stability was also observed for the CL powders. Dye adsorption experiments indicate that the CL powders showed the highly effective removal of C.I. Reactive Red 120 (RR120), C.I. Reactive Yellow 127 (RY127), and C.I. Reactive Blue 222 (RB222) with the adsorption capacity of 167.0, 178.9, and 129.6 mg·g⁻¹, respectively. The Langmuir, pseudo-second order, and intraparticle diffusion models could well depict the adsorption equilibrium and kinetics of CL powders toward the investigated reactive dyes. The as-prepared CL powders can be used as a potential adsorbent in the treatment of dye contaminated wastewater. Future studies will mainly focus on the application of the adsorbed CL powders for the pigment printing of textile materials.

Shape-Dependent Biodistribution of Biocompatible Silk Microcapsules

Microcapsules are emerging as promising microsize drug carriers due to their remarkable deformability. Shape plays a dominant role in determining their vascular transportation. Herein, we explored the effect of the shape of the microcapsules on the in vivo biodistribution for rational design of microcapsules to achieve optimized targeting efficiency. Silk fibroin, a biocompatible, biodegradable, and abundant material, was utilized as a building block to construct biconcave discoidal and spherical microcapsules with diameter of 1.8 μm and wall thickness of 20 nm. We have compared the cytocompatibility, cellular uptake, and biodistribution of both microcapsules. Both biconcave and spherical microcapsules exhibited excellent cytocompatibility and internalization into cancer cells. During blood circulation in mice, both microcapsules showed retention in liver and kidney and most underwent renal clearance. However, we observed significantly higher accumulation of biconcave silk microcapsules in lung compared with spherical microcapsules, and the accumulation was found to be stable in lung even after 3 days. The higher concentration of biconcave discoidal microcapsules found in lung arises from pulmonary environment, margination dynamics, and enhanced deformation in bloodstream. Red blood cell (RBC)-mimicking silk microcapsules demonstrated here can potentially serve as a promising platform for delivering drugs for lung diseases.

Small Angle Scattering for Pharmaceutical Applications: From Drugs to Drug Delivery Systems

The sub-nanometer scale provided by small angle neutron and X-ray scattering is of special importance to pharmaceutical and biomedical investigators. As drug delivery devices become more functionalized and continue decreasing in size, the ability to elucidate details on size scales smaller than those available from optical techniques becomes extremely pertinent. Information gathered from small angle scattering therefore aids the endeavor of optimizing pharmaceutical efficacy at its most fundamental level. This chapter will provide some relevant examples of drug carrier technology and how small angle scattering (SAS) can be used to solve their mysteries. An emphasis on common first-step data treatments is provided which should help clarify the contents of scattering data to new researchers. Specific examples of pharmaceutically relevant research on novel systems and the role SAS plays in these studies will be discussed. This chapter provides an overview of the current applications of SAS in drug research and some practical considerations for selecting scattering techniques.

Advances in Protein-Based Materials: From Origin to Novel Biomaterials

Biomaterials play a very important role in biomedicine and tissue engineering where they directly affect the cellular activities and their microenvironment . Myriad of techniques have been employed to fabricate a vast number natural, artificial and recombinant polymer s in order to harness these biomaterials in tissue regene ration , drug delivery and various other applications. Despite of tremendous efforts made in this field during last few decades, advanced and new generation biomaterials are still lacking. Protein based biomaterials have emerged as an attractive alternatives due to their intrinsic properties like cell to cell interaction , structural support and cellular communications. Several protein based biomaterials like, collagen , keratin , elastin , silk protein and more recently recombinant protein s are being utilized in a number of biomedical and biotechnological processes. These protein-based biomaterials have enormous capabilities, which can completely revolutionize the biomaterial world. In this review, we address an up-to date review on the novel, protein-based biomaterials used for biomedical field including tissue engineering, medical science, regenerative medicine as well as drug delivery. Further, we have also emphasized the novel fabrication techniques associated with protein-based materials and implication of these biomaterials in the domain of biomedical engineering .

Shaped stimuli-responsive hydrogel particles: syntheses, properties and biological responses

This review summarizes a pool of current experimental approaches and discusses perspectives in the development of the synergistic combination of shape and stimuli-response in particulate hydrogels.

Engineering DN hydrogels from regenerated silk fibroin and poly(N-vinylcaprolactam)

The development of novel hydrogels that possess adequate elasticity and toughness to withstand mechanically active environments, along with being biocompatible, remains a significant challenge in the design of materials for tissue engineering applications. In this study, a family of regenerated silk fibroin (RSF) based double network (DN) hydrogels were fabricated for the first time using a rapid one-pot method. The DN hydrogels combine the rigid covalently crosslinked RSF with the softer poly(N-vinylcaprolactam) (PVCL) through strong physical interactions. The formation of these DN hydrogels resulted in an improvement of the water uptake capacity, elasticity and toughness compared to the individual RSF hydrogel. The elasticity of the RSF/PVCL DN hydrogels was closer to that of native cartilage, which makes them promising materials for cartilage regeneration applications. An in vitro study on adhesion, proliferation and differentiation of a mouse pre-chondrocyte cell line (ATDC5) conducted using microscopic analysis, a cell proliferation assay and RT-PCR confirmed the cells cultured on the less stiff hydrogels demonstrated the most favourable chondrogenic response. Thus, this study demonstrates the potential of RSF-based hybrid hydrogels for cartilage tissue engineering applications.

Non-affinity factors modulating vascular targeting of nano- and microcarriers

Particles capable of homing and adhering to specific vascular biomarkers have potential as fundamental tools in drug delivery for mediation of a wide variety of pathologies, including inflammation, thrombosis, and pulmonary disorders. The presentation of affinity ligands on the surface of a particle provides a means of targeting the particle to sites of therapeutic interest, but a host of other factors come into play in determining the targeting capacity of the particle. This review presents a summary of several key considerations in nano- and microparticle design that modulate targeted delivery without directly altering epitope-specific affinity. Namely, we describe the effect of factors in definition of the base carrier (including shape, size, and flexibility) on the capacity of carriers to access, adhere to, and integrate in target biological milieus. Furthermore, we present a summary of fundamental dynamics of carrier behavior in circulation, taking into account interactions with cells in circulation and the role of hemodynamics in mediating the direction of carriers to target sites. Finally, we note non-affinity aspects to uptake and intracellular trafficking of carriers in target cells. In total, recent findings presented here may offer an opportunity to capitalize on mitigating factors in the behavior of ligand-targeted carriers in order to optimize targeting.

Tuning assembly and enzymatic degradation of silk/poly(N-vinylcaprolactam) multilayers via molecular weight and hydrophobicity

We report on enzymatically degradable nanothin coatings obtained by layer-by-layer (LbL) assembly of silk fibroin with poly(N-vinylcaprolactam) (PVCL) via hydrogen bonding and hydrophobic interactions. We found that both silk β-sheet content, controlled through dipping and spin-assisted LbL, and PVCL molecular weight regulate film thickness, microstructure, pH-stability, and biodegradability with a nanoscale precision. Thickness of (silk/PVCL) films increased with increase in PVCL molecular weight and decrease in deposition pH. The impact of assembly pH on film growth was more dramatic for dipped films. These systems show a significant rise in thickness with increase in PVCL molecular weight at pH < 5 but become independent on polymer chain length at pH ≥ 5. We also found that spin-assisted films exhibited a greater stability at elevated pH and against enzymatic degradation as compared to their dipped counterparts. For both film types, the pH and enzymatic stability was improved with increasing PVCL length and β-sheet content, indicating enhanced hydrophobic and hydrogen-bonded interactions between PVCL and silk. Finally, we fabricated spherical and cubical (silk/PVCL) LbL capsules of regulated permeability and enzymatic degradation. Our approach gives a unique opportunity to tune thickness, morphology, structure, and biodegradability rate of silk films and capsules by varying silk secondary structure and PVCL length. Accounting for all-aqueous fabrication and the biocompatibility of both polymers these biodegradable materials provide novel platforms for delivery systems and medical devices.

Sugar-mediated disassembly of mucin/lectin multilayers and their use as pH-Tolerant, on-demand sacrificial layers

The layer-by-layer (LbL) assembly of thin films on surfaces has proven to be an extremely useful technology for uses ranging from optics to biomedical applications. Releasing these films from the substrate to generate so-called free-standing multilayer films opens a new set of applications. Current approaches to generating such materials are limited because they can be cytotoxic, difficult to scale up, or have undesirable side reactions on the material. In this work, a new sacrificial thin film system capable of chemically triggered dissolution at physiological pH of 7.4 is described. The film was created through LbL assembly of bovine submaxillary mucin (BSM) and the lectin jacalin (JAC) for a (BSM/JAC) multilayer system, which remains stable over a wide pH range (pH 3-9) and at high ionic strength (up to 5 M NaCl). This stability allows for subsequent LbL assembly of additional films in a variety of conditions, which could be released from the substrate by incubation in the presence of a competitive inhibitor sugar, melibiose, which selectively disassembles the (BSM/JAC) section of the film. This novel multilayer system was then applied to generate free-standing, 7 μm diameter, circular ultrathin films, which can be attached to a cell surface as a "backpack". A critical thickness of about 100 nm for the (BSM/JAC) film was required to release the backpacks from the glass substrate, after incubation in melibiose solution at 37 °C for 1 h. Upon their release, backpacks were subsequently attached to murine monocytes without cytotoxicity, thereby demonstrating the compatibility of this mucin-based release system with living cells.

Internalization of red blood cell-mimicking hydrogel capsules with pH-triggered shape responses

We report on naturally inspired hydrogel capsules with pH-induced transitions from discoids to oblate ellipsoids and their interactions with cells. We integrate characteristics of erythrocytes such as discoidal shape, hollow structure, and elasticity with reversible pH-responsiveness of poly(methacrylic acid) (PMAA) to design a new type of drug delivery carrier to be potentially triggered by chemical stimuli in the tumor lesion. The capsules are fabricated from cross-linked PMAA multilayers using sacrificial discoid silicon templates. The degree of capsule shape transition is controlled by the pH-tuned volume change, which in turn is regulated by the capsule wall composition. The (PMAA)15 capsules undergo a dramatic 24-fold volume change, while a moderate 2.3-fold volume variation is observed for more rigid PMAA-(poly(N-vinylpyrrolidone) (PMAA-PVPON)5 capsules when solution pH is varied between 7.4 and 4. Despite that both types of capsules exhibit discoid-to-oblate ellipsoid transitions, a 3-fold greater swelling in radial dimensions is found for one-component systems due to a greater degree of the circular face bulging. We also show that (PMAA-PVPON)5 discoidal capsules interact differently with J774A.1 macrophages, HMVEC endothelial cells, and 4T1 breast cancer cells. The discoidal capsules show 60% lower internalization as compared to spherical capsules. Finally, hydrogel capsules demonstrate a 2-fold decrease in size upon internalization. These capsules represent a unique example of elastic hydrogel discoids capable of pH-induced drastic and reversible variations in aspect ratios. Considering the RBC-mimicking shape, their dimensions, and their capability to undergo pH-triggered intracellular responses, the hydrogel capsules demonstrate considerable potential as novel carriers in shape-regulated transport and cellular uptake.

pH-responsive hydrogel cubes for release of doxorubicin in cancer cells

Doxorubicin (DOX)-loaded poly(methacrylic acid) hydrogel cubes release the drug at pH <5. These hydrogels are developed for shape-directed cellular uptake for drug delivery.

pH-Programmable Sequential Dissolution of Multilayer Stacks of Hydrogen-Bonded Polymers

We report that the interlayer diffusion of polymer chains within heterostructured hydrogen-bonded multilayer films depends on the stacking order: polymers diffuse more when high pH stability polymer pairs are assembled on top of low pH stability polymer pairs. By varying the stacking sequence, the fraction of the film that is released from the substrate can be tuned to achieve sequential pH-programmed release of the multilayer film. Also, we show that a multifunctional freestanding film with tunable film thickness can be generated by appropriate stacking and subsequent thermal cross-linking.

Thermosensitive multilayer hydrogels of poly(N-vinylcaprolactam) as nanothin films and shaped capsules

We report on nanothin multilayer hydrogels of cross-linked poly(N-vinylcaprolactam) (PVCL) that exhibit distinctive and reversible thermoresponsive behavior. The single-component PVCL hydrogels were produced by selective cross-linking of PVCL in layer-by-layer films of PVCL-NH(2) copolymers assembled with poly(methacrylic acid) (PMAA) via hydrogen bonding. The degree of the PVCL hydrogel film shrinkage, defined as the ratio of wet thicknesses at 25°C to 50°C, was demonstrated to be 1.9±0.1 and 1.3±0.1 for the films made from PVCL-NH(2)-7 and PVCL-NH(2)-14 copolymers, respectively. No temperature-responsive behavior was observed for non-cross-linked two-component films due to the presence of PMAA. We also demonstrated that temperature-sensitive PVCL capsules of cubical and spherical shapes could be fabricated as hollow hydrogel replicas of inorganic templates. The cubical (PVCL)(7) capsules retained their cubical shape when temperature was elevated from 25°C to 50°C exhibiting 21±1% decrease in the capsule size. Spherical hydrogel capsules demonstrated similar shrinkage of 23±1%. The temperature-triggered capsule size changes were completely reversible. Our work opens new prospects for developing biocompatible and nanothin hydrogel-based coatings and containers for temperate-regulating drug delivery, cellular uptake, sensing, and transport behavior in microfluidic devices.