Aerogel sponges of silk fibroin, hyaluronic acid and heparin for soft tissue engineering: Composition-properties relationship

Soft and flexible polyvinyl alcohol/pullulan aerogels with fast and high water absorption capacity for facial mask substrates

Facial mask substrates commonly used in skincare are often considered unhealthy and environmentally unfriendly due to their composition of premoistened nonwovens containing various preservatives. This study aims to address this issue by developing a preservative-free degradable aerogel made from polyvinyl alcohol (PVA)/pullulan (PUL) using a unidirectional freeze-drying method. The aerogels had ordered three-dimensional porous structures and exhibited desirable mechanical properties. They were soft and flexible in both dry and wet states, and their Young's moduli were comparable to that of human skin. The aerogels had high porosity, ranging from 93.0 % to 95.1 %, and exhibited a high water absorption rate and water absorption capacity (ranging from 7.5 g/g to 10.1 g/g). After 30 min of water evaporation, the aerogels showed excellent moisture retention, ranging from 88 % to 93 %. Additionally, the PVA/PUL aerogel efficiently loaded and released active ingredients, such as rapidly releasing ascorbic acid (> 90 % within 30 min). These findings suggest that the PVA/PUL aerogel has potential as a material for facial mask substrates.

Implantable SDF-1α-loaded silk fibroin hyaluronic acid aerogel sponges as an instructive component of the glioblastoma ecosystem: Between chemoattraction and tumor shaping into resection cavities

In view of inevitable recurrences despite resection, glioblastoma (GB) is still an unmet clinical need. Dealing with the stromal-cell derived factor 1-alpha (SDF-1α)/CXCR4 axis as a hallmark of infiltrative GB tumors and with the resection cavity situation, the present study described the effects and relevance of a new engineered micro-nanostructured SF-HA-Hep aerogel sponges, made of silk fibroin (SF), hyaluronic acid (HA) and heparin (Hep) and loaded with SDF-1α, to interfere with the GB ecosystem and residual GB cells, attracting and confining them in a controlled area before elimination. 70 µm-pore sponges were designed as an implantable scaffold to trap GB cells. They presented shape memory and fit brain cavities. Histological results after implantation in brain immunocompetent Fischer rats revealed that SF-HA-Hep sponges are well tolerated for more than 3 months while moderately and reversibly colonized by immuno-inflammatory cells. The use of human U87MG GB cells overexpressing the CXCR4 receptor (U87MG-CXCR4+) and responding to SDF-1α allowed demonstrating directional GB cell attraction and colonization of the device in vitro and in vivo in orthotopic resection cavities in Nude rats. Not modifying global survival, aerogel sponge implantation strongly shaped U87MG-CXCR4+ tumors in cavities in contrast to random infiltrative growth in controls. Overall, those results support the interest of SF-HA-Hep sponges as modifiers of the GB ecosystem dynamics acting as "cell meeting rooms" and biocompatible niches whose properties deserve to be considered toward the development of new clinical procedures. STATEMENT OF SIGNIFICANCE: Brain tumor glioblastoma (GB) is one of the worst unmet clinical needs. To prevent the relapse in the resection cavity situation, new implantable biopolymer aerogel sponges loaded with a chemoattractant molecule were designed and preclinically tested as a prototype targeting the interaction between the initial tumor location and its attraction by the peritumoral environment. While not modifying global survival, biocompatible SDF1-loaded hyaluronic acid and silk fibroin sponges induce directional GB cell attraction and colonization in vitro and in rats in vivo. Interestingly, they strongly shaped GB tumors in contrast to random infiltrative growth in controls. These results provide original findings on application of exogenous engineered niches that shape tumors and serve as cell meeting rooms for further clinical developments.

Production of Exopolysaccharide-Based Porous Structures for Biomedical Applications: A Review

Exopolysaccharides, obtained from microorganisms as fermentation products, are interesting candidates for biomedical applications as scaffolds: they are biocompatible, nontoxic, antimicrobial, antitumor materials. To produce exopolysaccharide-based scaffolds, sol-gel technology could be used, which ends with the removal of the liquid phase from the polymeric network (i.e., the drying step). The aim of this review is to point out the most relevant strengths and weaknesses of the different drying techniques, focusing attention on the production of exopolysaccharide-based porous structures. Among these drying processes, supercritical carbon dioxide-assisted drying is the most promising strategy to obtain dried gels to use in the biomedical field: it produces highly porous and lightweight devices with outstanding surface areas and regular microstructure and nanostructure (i.e., aerogels). As a result of the analysis carried out in the present work, it emerged that supercritical technologies should be further explored and applied to the production of exopolysaccharide-based nanostructured scaffolds. Moving research towards this direction, exopolysaccharide utilization could be intensified and extended to the production of high added-value devices.

Comprehensive review on biosynthesis of hyaluronic acid with different molecular weights and its biomedical applications

Hyaluronic acid (HA), an anionic and nonsulfated glycosaminoglycan, is the main structural component of various tissues and plays an important role in various biological processes. Given the promising properties of HA, such as high cellular compatibility, moisture retention, antiaging, proper interaction with cells, and CD44 targeting, HA can be widely used extensively in drug delivery, tissue engineering, wound healing, and cancer therapy. HA can obtain from animal tissues and microbial fermentation, but its applications depend on its molecular weight. Microbial fermentation is a common method for HA production on an industrial scale and S. zooepidemicus is the most frequently used strain in HA production. Culture conditions including pH, temperature, agitation rate, aeration speed, shear stress, dissolved oxygen, and bioreactor type significantly affect HA biosynthesis properties. In this review all the HA production methods and purification techniques to improve its physicochemical and biological properties for various biomedical applications are discussed in details. In addition, we showed that how HA molecular weight can significantly affect its properties and applications.

Regenerated silk fibroin loaded with natural additives: a sustainable approach towards health care

According to World Health Organization (WHO), on average, 0.5 Kg of hazardous waste is generated per bed every day in high-income countries. The adverse effects imposed by synthetic materials and chemicals on the environment and humankind have urged researchers to explore greener technologies and materials. Amidst of all the natural fibers, silk fibroin (SF), by virtue of its superior toughness (6 × 10⁴∼16 × 10⁴ J/kg), tensile strength (47.2-67.7 MPa), tunable biodegradability, excellent Young's modulus (1.9-3.9 GPa), presence of functional groups, ease of processing, and biocompatibility has garnered an enormous amount of scientific interests. The use of silk fibroin conjoint with purely natural materials can be an excellent solution for the adverse effects of chemical-based treatment techniques. Considering this noteworthiness, vigorous research is going on in silk-based biomaterials, and it is opening up new vistas of opportunities. This review enswathes the structural aspects of silk fibroin along with its potency to form composites with other natural materials, such as curcumin, keratin, alginate, hydroxyapatite, hyaluronic acid, and cellulose, that can replace the conventionally used synthetic materials, providing a sustainable pathway to biomedical engineering. It was observed that a large amount of polar functional moieties present on the silk fibroin surface enables them to compatibilize easily with the natural additives. The conjunction of silk with natural additives initiates synergistic interactions that mitigate the limitations offered by individual units as well as enhance the applicability of materials. Further the current status and challenges in the commercialization of silk-based biomedical devices are discussed.

Sericultural By-Products: The Potential for Alternative Therapy in Cancer Drug Design

Major progress has been made in cancer research; however, cancer remains one of the most important health-related burdens. Sericulture importance is no longer limited to the textile industry, but its by-products, such as silk fibroin or mulberry, exhibit great impact in the cancer research area. Fibroin, the pivotal compound that is found in silk, owns superior biocompatibility and biodegradability, representing one of the most important biomaterials. Numerous studies have reported its successful use as a drug delivery system, and it is currently used to develop three-dimensional tumor models that lead to a better understanding of cancer biology and play a great role in the development of novel antitumoral strategies. Moreover, sericin's cytotoxic effect on various tumoral cell lines has been reported, but also, it has been used as a nanocarrier for target therapeutic agents. On the other hand, mulberry compounds include various bioactive elements that are well known for their antitumoral activities, such as polyphenols or anthocyanins. In this review, the latest progress of using sericultural by-products in cancer therapy is discussed by highlighting their notable impact in developing novel effective drug strategies.

Highlights on Advancing Frontiers in Tissue Engineering

The field of tissue engineering continues to advance, sometimes in exponential leaps forward, but also sometimes at a rate that does not fulfill the promise that the field imagined a few decades ago. This review is in part a catalog of success in an effort to inform the process of innovation. Tissue engineering has recruited new technologies and developed new methods for engineering tissue constructs that can be used to mitigate or model disease states for study. Key to this antecedent statement is that the scientific effort must be anchored in the needs of a disease state and be working toward a functional product in regenerative medicine. It is this focus on the wildly important ideas coupled with partnered research efforts within both academia and industry that have shown most translational potential. The field continues to thrive and among the most important recent developments are the use of three-dimensional bioprinting, organ-on-a-chip, and induced pluripotent stem cell technologies that warrant special attention. Developments in the aforementioned areas as well as future directions are highlighted in this article. Although several early efforts have not come to fruition, there are good examples of commercial profitability that merit continued investment in tissue engineering. Impact statement Tissue engineering led to the development of new methods for regenerative medicine and disease models. Among the most important recent developments in tissue engineering are the use of three-dimensional bioprinting, organ-on-a-chip, and induced pluripotent stem cell technologies. These technologies and an understanding of them will have impact on the success of tissue engineering and its translation to regenerative medicine. Continued investment in tissue engineering will yield products and therapeutics, with both commercial importance and simultaneous disease mitigation.

Manufacturing of self-standing multi-layered 3D-bioprinted alginate-hyaluronate constructs by controlling the cross-linking mechanisms for tissue engineering applications

3D bioprinting of self-supporting stable tissue and organ structure is critically important in extrusion-based bioprinting system, especially for tissue engineering and regenerative medicine applications. However, the development of self-standing bioinks with desired crosslinking density, biocompatibility, tunable mechanical strength and other properties like self-healing, in situ gelation, drug or protein incorporation is still a challenge. In this study, we report a hydrogel bioink prepared from alginate (Alg) and hyaluronic acid (HA) crosslinked through multiple crosslinking mechanisms, i.e., acyl-hydrazone, hydrazide interactions and calcium ions. These Alg-HA gels were highly dynamic and shear-thinning with exceptional biocompatibility and tunable mechanical properties. The increased dynamic nature of the gels is mainly chemically attributed to the presence of acyl-hydrazone bonds formed between the amine groups of the acyl-hydrazide of alginate and the monoaldehyde of the hyaluronic acid. Among the different combinations of Alg-HA gel compositions prepared, the A5H5 (Alginate-acyl-hydrazide: HA-monoaldehyde, ratio 50:50) one showed a gelation time of ~60 s, viscosity of ~400 Pa.s (at zero shear rate), high stability in various pH solutions and increased degradation time (>50 days) than the other samples. The A5H5 gels showed high printability with increased post-printing stability as observed from the 3D printed structures (e.g., hollow tube (~100 layers), porous cube (~50 layers), star, heart-in, meniscus and lattice). The scanning electron microscopy analysis of the 3D constructs and hydrogels showed the interconnected pores (~181 µm) and crosslinked networks. Further, the gels showed sustained release of 5-amino salicylic acid and bovine serum albumin. Also, the mechanical properties were tuned by secondary crosslinking via different calcium concentrations. In vitro assays confirmed the cytocompatibility of these gels, where the 3D bioprinted lattice and tubular (~70 layers) constructs demonstrated high cell viability under fluorescence analysis. In in vivo studies, Alg-HA gel showed high biocompatibility (>90%) and increased angiogenesis (3 folds) and reduced macrophage infiltration (2-fold decrease), demonstrating the promising potential of these hydrogels in 3D bioprinting applications for tissue engineering and regenerative medicine with tunable properties.

Near-infrared analysis of nanofibrillated cellulose aerogel manufacturing

Biomaterial aerogel fabrication by freeze-drying must be further improved to reduce the costs of lengthy freeze-drying cycles and to avoid the formation of spongy cryogels and collapse of the aerogel structures. Residual water content is a critical quality attribute of the freeze-dried product, which can be monitored in-line with near-infrared (NIR) spectroscopy. Predictive models of NIR have not been previously applied for biomaterials and the models were mostly focused on the prediction of only one formulation at a time. We recorded NIR spectra of different nanofibrillated cellulose (NFC) hydrogel formulations during the secondary drying and set up a partial least square regression model to predict their residual water contents. The model can be generalized to measure residual water of formulations with different NFC concentrations and the excipients, and the NFC fiber concentrations and excipients can be separated with the principal component analysis. Our results provide valuable information about the freeze-drying of biomaterials and aerogel fabrication, and how NIR spectroscopy can be utilized in the optimization of residual water content.

Nanoparticle-containing electrospun nanofibrous scaffolds for sustained release of SDF-1α

Chemokines such as stromal cell-derived factor-1α (SDF-1α) regulate the migration of cancer cells that can spread from their primary tumor site by migrating up an SDF-1α concentration gradient, facilitating their local invasion and metastasis. Therefore, the implantation of SDF-1α-releasing scaffolds can be a useful strategy to trap cancer cells expressing the CXCR4 receptor. In this work, SDF-1α was encapsulated into poly(lactic-co-glycolic acid) (PLGA)-based nanoparticles and subsequently electrospun with chitosan to produce nanofibrous scaffolds of average fiber diameter of 261 ± 45 nm, intended for trapping glioblastoma (GBM) cells. The encapsulated SDF-1α maintained its biological activity after the electrospinning process as assessed by its capacity to induce the migration of cancer cells. The scaffolds could also provide sustained release of SDF-1α for at least 5 weeks. Using NIH3T3 mouse fibroblasts, human Thp-1 macrophages, and rat primary astrocytes we showed that the scaffolds possessed high cytocompatibility in vitro. Furthermore, a 7-day follow-up of Fischer rats bearing implanted scaffolds demonstrated the absence of adverse effects in vivo. In addition, the nanofibrous structure of the scaffolds provided excellent anchoring sites to support the adhesion of human GBM cells by extension of their pseudopodia. The scaffolds also demonstrated slow degradation kinetics, which may be useful in maximizing the time window for trapping GBM cells. As surgical resection does not permit a complete removal of GBM tumors, our results support the future implantation of these scaffolds into the walls of the resection cavity to evaluate their capacity to attract and trap the residual GBM cells in the brain.

Hyaluronan as a Prominent Biomolecule with Numerous Applications in Medicine

Hyaluronan (HA) is a natural glycosaminoglycan present in many tissues of all vertebrates. HA has various biological functions, which are dependent on its molar mass. High-molar-mass HA has anti-angiogenic, immunosuppressive and anti-inflammatory properties, while low-molar-mass HA has opposite effects. HA has also antioxidative properties, however on the other hand it can be readily degraded by reactive oxygen species. For many years it has been used in treatment of osteoarthritis, cosmetics and in ophthalmology. In the last years there has been a growing interest of HA to also be applied in other fields of medicine such as skin wound healing, tissue engineering, dentistry and gene delivery. In this review we summarize information on modes of HA administration, properties and effects of HA in various fields of medicine including recent progress in the investigation of HA.

Freeze-Dried Matrices Composed of Degradable Polymers with Surfactant-Loaded Microparticles Based on Pectin and Sodium Alginate

Gelatin/polyvinylpyrrolidone/hydroxyethyl cellulose/glycerol porous matrices with microspheres made of sodium alginate or pectin and sodium alginate were produced. A surfactant was loaded into these microparticles. The microspheres were characterized using optical microscopy, scanning electron microscopy SEM, and laser diffraction particle size analyzer. For the matrices, the density, porosity, swelling capacity, dissolution in phosphate saline buffer were determined and SEM, mechanical, and thermogravimetric studies were applied. The results showed that the size of the two-component microspheres was slightly larger than that of single-ingredient microparticles. The images confirmed the spherical shape of the microparticles. The prepared matrices had high water uptake ability and porosity due to the presence of hydrophilic polymers. The presence of microparticles in the matrices caused a decrease in these parameters. Degradation of the composites with the microspheres was significantly faster than the matrix without them. The addition of microparticles increased the stiffness and toughness of the prepared materials. The efficiency of the thermal decomposition main stage was reduced in the samples with microspheres, whereas a char residue increased in these composites.

Crosslinked Silk Fibroin/Gelatin/Hyaluronan Blends as Scaffolds for Cell-Based Tissue Engineering

3D porous scaffolds fabricated from binary and ternary blends of silk fibroin (SF), gelatin (G), and hyaluronan (HA) and crosslinked by the carbodiimide coupling reaction were developed. Water-stable scaffolds can be obtained after crosslinking, and the SFG and SFGHA samples were stable in cell culture medium up to 10 days. The presence of HA in the scaffolds with appropriate crosslinking conditions greatly enhanced the swellability. The microarchitecture of the freeze-dried scaffolds showed high porosity and interconnectivity. In particular, the pore size was significantly larger with an addition of HA. Biological activities of NIH/3T3 fibroblasts seeded on SFG and SFGHA scaffolds revealed that both scaffolds were able to support cell adhesion and proliferation of a 7-day culture. Furthermore, cell penetration into the scaffolds can be observed due to the interconnected porous structure of the scaffolds and the presence of bioactive materials which could attract the cells and support cell functions. The higher cell number was noticed in the SFGHA samples, possibly due to the HA component and the larger pore size which could improve the microenvironment for fibroblast adhesion, proliferation, and motility. The developed scaffolds from ternary blends showed potential in their application as 3D cell culture substrates in fibroblast-based tissue engineering.

Natural Silk Nanofibril Aerogels with Distinctive Filtration Capacity and Heat-Retention Performance

Nanofibrous aerogels have been extensively developed as multifunctional substrates in a wide range of fields. Natural silk nanofibrils (SNFs) are an appealing biopolymer due to their natural abundance, mechanical toughness, biodegradability, and excellent biocompatibility. However, fabricating 3D SNF materials with mechanical flexibility remains a challenge. Herein, SNF-based aerogels with controlled structures and well mechanical resilience were prepared. SNFs were extracted from silkworm silks by mechanical disintegration based on an all-aqueous system. The nanofibrils network and hierarchical cellular structure of the aerogels were tuned by the assembly of SNFs and foreign poly(vinyl alcohol) (PVA). The SNF aerogels exhibited an ultralow density (as low as 2.0 mg·cm^-3) and well mechanical properties with a structure allowing for large deformations. These SNF aerogels demonstrated a reversible compression and stress retention after 100 cycles of compression. Furthermore, the resulting aerogels were used for air filtration and showed efficient filtration performance with a high dust-holding capacity and low resistance. Moreover, an extremely low thermal conductivity of 0.028 W·(m·K)^-1 was achieved by the aerogel, showing its potential for use in heat-retention applications. This study provides a useful strategy for exploring the use of natural silks in 3D aerogels and offers options for developing filtration materials and ultralight heat-retention materials.

How to Improve Physico-Chemical Properties of Silk Fibroin Materials for Biomedical Applications?-Blending and Cross-Linking of Silk Fibroin-A Review

This review supplies a report on fresh advances in the field of silk fibroin (SF) biopolymer and its blends with biopolymers as new biomaterials. The review also includes a subsection about silk fibroin mixtures with synthetic polymers. Silk fibroin is commonly used to receive biomaterials. However, the materials based on pure polymer present low mechanical parameters, and high enzymatic degradation rate. These properties can be problematic for tissue engineering applications. An increased interest in two- and three-component mixtures and chemically cross-linked materials has been observed due to their improved physico-chemical properties. These materials can be attractive and desirable for both academic, and, industrial attention because they expose improvements in properties required in the biomedical field. The structure, forms, methods of preparation, and some physico-chemical properties of silk fibroin are discussed in this review. Detailed examples are also given from scientific reports and practical experiments. The most common biopolymers: collagen (Coll), chitosan (CTS), alginate (AL), and hyaluronic acid (HA) are discussed as components of silk fibroin-based mixtures. Examples of binary and ternary mixtures, composites with the addition of magnetic particles, hydroxyapatite or titanium dioxide are also included and given. Additionally, the advantages and disadvantages of chemical, physical, and enzymatic cross-linking were demonstrated.

Investigation of Aerogel Production Processes: Solvent Exchange under High Pressure Combined with Supercritical Drying in One Apparatus

This work aims to contribute to the theoretical and experimental research of supercritical processes for intensification and combination in one apparatus. Investigation is carried out to improve production technology of organic alginate aerogels. It is proposed within the investigation to carry out the solvent exchange stage, an important stage of organic aerogels production, under pressure in a carbon dioxide medium in the same apparatus used for supercritical drying. The phase behavior in the system "carbon dioxide-water-2-propanol", which arises during such a solvent exchange stage, is studied theoretically. An experimental study of the process of step-by-step solvent exchange under pressure was carried out through multiphase and homogeneous regions of the phase diagram of such a system. As a result, new highly efficient technology for the production of organic aerogels was proposed, which can be implemented by combining the two main stages of the process.

Hyaluronic Acid as a Component of Natural Polymer Blends for Biomedical Applications: A Review

In this review, we provide a report on recent studies in the field of research on the blends of hyaluronic acid with other natural polymers, namely collagen and chitosan. Hyaluronic acid has attracted significant interest in biomedical and cosmetic applications due to its interesting properties. In recent years, blends of hyaluronic acid with other polymers have been studied for new materials development. New materials may show improved properties that are important in the biomedical applications and in cosmetic preparations. In this review paper, the structure, preparation, and properties of hyaluronic acid blends with collagen and chitosan have been discussed and examples of new materials based on such blends have been presented. A comparison of the currently available information in the field has been shown. Future aspects in the field of hyaluronic acid blends and their applications in the biomedical and cosmetic industry have also been mentioned.