Production of self-assembling biomaterials for tissue engineering

Collagen-Based Wound Dressings: Innovations, Mechanisms, and Clinical Applications

Collagen-based wound dressings have developed as an essential component of contemporary wound care, utilizing collagen's inherent properties to promote healing. This review thoroughly analyzes collagen dressing advances, examining different formulations such as hydrogels, films, and foams that enhance wound care. The important processes by which collagen promotes healing (e.g., promoting angiogenesis, encouraging cell proliferation, and offering structural support) are discussed to clarify its function in tissue regeneration. The effectiveness and adaptability of collagen dressings are demonstrated via clinical applications investigated in acute and chronic wounds. Additionally, commercially accessible collagen-based skin healing treatments are discussed, demonstrating their practical use in healthcare settings. Despite the progress, the study discusses the obstacles and restrictions encountered in producing and adopting collagen-based dressings, such as the difficulties of manufacturing and financial concerns. Finally, the current landscape's insights indicate future research possibilities for collagen dressing optimization, bioactive agent integration, and overcoming existing constraints. This analysis highlights the potential of collagen-based innovations to improve wound treatment methods and patient care.

Altering the mechanical properties of self-assembled filaments through engineering of EspA bacterial protein

Protein-based biomaterials are in high demand due to their high biocompatibility, non-toxicity, and biodegradability. In this study, we explore the bacterial E. coli secreted protein A (EspA), which self-assembles into long extracellular filaments, as a potential building block for new protein-based biomaterials. We investigated the morphological and mechanical properties of EspA filaments and how protein engineering can modify them. Our study include three types of filaments: natural EspA filaments, full-length recombinant EspA filaments, and truncated recombinant EspA filaments lacking a third of the original codon region. The recombinant EspA proteins formed curly, thin filaments with higher longitudinal elasticity (shorter persistence length) compared to the natural, linear filaments. Additionally, the recombinant filaments had a radial elastic modulus about an order of magnitude lower than the natural filaments. The truncated recombinant filaments had a higher radial modulus than the full-length ones, and unlike the purely elastic natural filaments, recombinant filaments were less compliant with the applied force that penetrated them. These differences underscore the potential to modulate EspA filament properties through protein sequence mutations. Our findings suggest EspA as a fundamental element for developing a new biomaterial with a hierarchical structure, enabling the fabrication of macroscopic substances from self-assembled EspA-modulated filaments.

Preparation, design, identification and application of self-assembly peptides from seafood: A review

Hydrogels formed by self-assembling peptides with low toxicity and high biocompatibility have been widely used in food and biomedical fields. Seafood contains rich protein resources and is also one of the important sources of natural bioactive peptides. The self-assembled peptides in seafood have good functional activity and are very beneficial to human health. In this review, the sequence of seafood self-assembly peptide was introduced, and the preparation, screening, identification and characterization. The rule of self-assembled peptides was elucidated from amino acid sequence composition, amino acid properties (hydrophilic, hydrophobic and electric), secondary structure, interaction and peptide properties (hydrophilic and hydrophobic). It was introduced that the application of hydrogels formed by self-assembled peptides, which lays a theoretical foundation for the development of seafood self-assembled peptides in functional foods and the application of biological materials.

Evaluation puramatrix as a 3D microenvironment for neural differentiation of human breastmilk stem cells

The extracellular matrix is recognized as an efficient and determining component in the growth, proliferation, and differentiation of cells due to its ability to perceive and respond to environmental signals. Applying three-dimensional scaffolds can create conditions similar to the extracellular matrix and provide an opportunity to investigate cell fate. In this study, we employed the PuraMatrix hydrogel scaffold as an advanced cell culture platform for the neural differentiation of stem cells derived from human breastmilk to design an opportune model for tissue engineering. Isolated stem cells from breastmilk were cultured and differentiated into neural-like cells on PuraMatrix peptide hydrogel and in the two-dimensional system. The compatibility of breastmilk-derived stem cells with PuraMatrix and cell viability was evaluated by scanning electron microscopy and MTT assay, respectively. Induction of differentiation was achieved by exposing cells to the neurogenic medium. After 21 days of the initial differentiation process, the expression levels of glial fibrillary acidic protein (GFAP), microtubule-associated protein (MAP2), β-tubulin III, and neuronal nuclear antigen (NeuN) were analyzed using the immunostaining technique. The results illustrated a notable expression of MAP2, β-tubulin-III, and NeuN in the three-dimensional cell culture in comparison to the two-dimensional system, indicating the beneficial effect of PuraMatrix scaffolds in the process of differentiating breastmilk-derived stem cells into neural-like cells. In view of the obtained results, the combination of breastmilk-derived stem cells and PuraMatrix hydrogel scaffold could be an advisable preference for neural tissue regeneration and cell therapy.

Propelling Minimally Invasive Tissue Regeneration With Next-Era Injectable Pre-Formed Scaffolds

The growing aging population, with its associated chronic diseases, underscores the urgency for effective tissue regeneration strategies. Biomaterials play a pivotal role in the realm of tissue reconstruction and regeneration, with a distinct shift toward minimally invasive (MI) treatments. This transition, fueled by engineered biomaterials, steers away from invasive surgical procedures to embrace approaches offering reduced trauma, accelerated recovery, and cost-effectiveness. In the realm of MI tissue repair and cargo delivery, various techniques are explored. While in situ polymerization is prominent, it is not without its challenges. This narrative review explores diverse biomaterials, fabrication methods, and biofunctionalization for injectable pre-formed scaffolds, focusing on their unique advantages. The injectable pre-formed scaffolds, exhibiting compressibility, controlled injection, and maintained mechanical integrity, emerge as promising alternative solutions to in situ polymerization challenges. The conclusion of this review emphasizes the importance of interdisciplinary design facilitated by synergizing fields of materials science, advanced 3D biomanufacturing, mechanobiological studies, and innovative approaches for effective MI tissue regeneration.

Highly oriented hydrogels for tissue regeneration: design strategies, cellular mechanisms, and biomedical applications

Many human tissues exhibit a highly oriented architecture that confers them with distinct mechanical properties, enabling adaptation to diverse and challenging environments. Hydrogels, with their water-rich "soft and wet" structure, have emerged as promising biomimetic materials in tissue engineering for repairing and replacing damaged tissues and organs. Highly oriented hydrogels can especially emulate the structural orientation found in human tissue, exhibiting unique physiological functions and properties absent in traditional homogeneous isotropic hydrogels. The design and preparation of highly oriented hydrogels involve strategies like including hydrogels with highly oriented nanofillers, polymer-chain networks, void channels, and microfabricated structures. Understanding the specific mechanism of action of how these highly oriented hydrogels affect cell behavior and their biological applications for repairing highly oriented tissues such as the cornea, skin, skeletal muscle, tendon, ligament, cartilage, bone, blood vessels, heart, etc., requires further exploration and generalization. Therefore, this review aims to fill that gap by focusing on the design strategy of highly oriented hydrogels and their application in the field of tissue engineering. Furthermore, we provide a detailed discussion on the application of highly oriented hydrogels in various tissues and organs and the mechanisms through which highly oriented structures influence cell behavior.

Calming the Nerves via the Immune Instructive Physiochemical Properties of Self-Assembling Peptide Hydrogels

Current therapies for the devastating damage caused by traumatic brain injuries (TBI) are limited. This is in part due to poor drug efficacy to modulate neuroinflammation, angiogenesis and/or promoting neuroprotection and is the combined result of challenges in getting drugs across the blood brain barrier, in a targeted approach. The negative impact of the injured extracellular matrix (ECM) has been identified as a factor in restricting post-injury plasticity of residual neurons and is shown to reduce the functional integration of grafted cells. Therefore, new strategies are needed to manipulate the extracellular environment at the subacute phase to enhance brain regeneration. In this review, potential strategies are to be discussed for the treatment of TBI by using self-assembling peptide (SAP) hydrogels, fabricated via the rational design of supramolecular peptide scaffolds, as an artificial ECM which under the appropriate conditions yields a supramolecular hydrogel. Sequence selection of the peptides allows the tuning of these hydrogels' physical and biochemical properties such as charge, hydrophobicity, cell adhesiveness, stiffness, factor presentation, degradation profile and responsiveness to (external) stimuli. This review aims to facilitate the development of more intelligent biomaterials in the future to satisfy the parameters, requirements, and opportunities for the effective treatment of TBI.

Development of a New Collagen Gel Product for Leather Finishing

Leather finishing is a critical process in the leather industry, as it significantly influences the final appearance, durability, and quality of leather products. Traditional leather finishing techniques often involve the use of synthetic chemicals, which may lead to environmental concerns and potential health hazards. In this study, we investigate the feasibility and effectiveness of a new collagen-based product for leather finishing. Collagen, a natural protein found abundantly in animals, has shown promise as an environmentally friendly and sustainable alternative for leather finishing. The new collagen gel product obtained from bovine hide waste by using an alkaline extraction method with lime was functionalized through an enzymatic treatment that allows to achieve a finishing product suitable for coating formulations, and at the same time, a biodegradable finishing. The collagen gel product was optimized by varying parameters, such as temperature, pH, and enzyme quantity. The optimized collagen gel product exhibits a wide particle size range and retains the triple-helical structure of collagen. The leather samples treated with the collagen gel product show enhanced properties compared to those with conventional finishes. The results show that the collagen gel product enhances water vapor permeability, color stability, and touch in the finishes. However, a low resistance to wet rubbing is obtained; therefore, it is necessary to study how to improve this parameter.

Perspectives on Multiscale Colloid-Based Materials for Biomedical Applications

Colloid-based materials with tunable biophysical and chemical properties have demonstrated significant potential in a wide range of biomedical applications. The ability to manipulate these properties across various size scales, encompassing nano-, micro-, and macrodomains, is essential to enhancing current biomedical technologies and facilitating the development of novel applications. Focusing on material design, we explore various synthetic colloid-based materials at the nano- and microscales and investigate their correlation with biological systems. Furthermore, we examine the utilization of the self-assembly of colloids to construct monolithic and macroscopic materials suitable for biointerfaces. By probing the potential of spatial imaging and localized drug delivery, enhanced functionality, and colloidal manipulation, we highlight emerging opportunities that could significantly advance the field of colloid-based materials in biomedical applications.

Polymeric Materials, Advances and Applications in Tissue Engineering: A Review

Tissue Engineering (TE) is an interdisciplinary field that encompasses materials science in combination with biological and engineering sciences. In recent years, an increase in the demand for therapeutic strategies for improving quality of life has necessitated innovative approaches to designing intelligent biomaterials aimed at the regeneration of tissues and organs. Polymeric porous scaffolds play a critical role in TE strategies for providing a favorable environment for tissue restoration and establishing the interaction of the biomaterial with cells and inducing substances. This article reviewed the various polymeric scaffold materials and their production techniques, as well as the basic elements and principles of TE. Several interesting strategies in eight main TE application areas of epithelial, bone, uterine, vascular, nerve, cartilaginous, cardiac, and urinary tissue were included with the aim of learning about current approaches in TE. Different polymer-based medical devices approved for use in clinical trials and a wide variety of polymeric biomaterials are currently available as commercial products. However, there still are obstacles that limit the clinical translation of TE implants for use wide in humans, and much research work is still needed in the field of regenerative medicine.

Novel Trends in Hydrogel Development for Biomedical Applications: A Review

Nowadays, there are still numerous challenges for well-known biomedical applications, such as tissue engineering (TE), wound healing and controlled drug delivery, which must be faced and solved. Hydrogels have been proposed as excellent candidates for these applications, as they have promising properties for the mentioned applications, including biocompatibility, biodegradability, great absorption capacity and tunable mechanical properties. However, depending on the material or the manufacturing method, the resulting hydrogel may not be up to the specific task for which it is designed, thus there are different approaches proposed to enhance hydrogel performance for the requirements of the application in question. The main purpose of this review article was to summarize the most recent trends of hydrogel technology, going through the most used polymeric materials and the most popular hydrogel synthesis methods in recent years, including different strategies of enhancing hydrogels’ properties, such as cross-linking and the manufacture of composite hydrogels. In addition, the secondary objective of this review was to briefly discuss other novel applications of hydrogels that have been proposed in the past few years which have drawn a lot of attention.

Synthesis, Self-Assembly, and Cell Responses of Aromatic IKVAV Peptide Amphiphiles

Synthetic bioactive aromatic peptide amphiphiles have been recognized as key elements of emerging biomedical strategies due to their biocompatibility, design flexibility, and functionality. Inspired by natural proteins, we synthesized two supramolecular materials of phenyl-capped Ile-Lys-Val-Ala-Val (Ben-IKVAV) and perfluorophenyl-capped Ile-Lys-Val-Ala-Val (PFB-IKVAV). We employed UV-vis absorption, fluorescence, circular dichroism, and Fourier-transform infrared spectroscopy to examine the driving force in the self-assembly of the newly discovered materials. It was found that both compounds exhibited ordered π-π interactions and secondary structures, especially PFB-IKVAV. The cytotoxicity of human mesenchymal stem cells (hMSCs) and cell differentiation studies was also performed. In addition, the immunofluorescent staining for neuronal-specific markers of MAP2 was 4.6 times (neural induction medium in the presence of PFB-IKVAV) that of the neural induction medium (control) on day 7. From analyzing the expression of neuronal-specific markers in hMSCs, it can be concluded that PFB-IKVAV may be a potential supramolecular biomaterial for biomedical applications.

Bioinspired tunable hydrogels: An update on methods of preparation, classification, and biomedical and therapeutic applications

Hydrogels exhibit water-insoluble three-dimensional polymeric networks capable of absorbing large amounts of biological fluids. Both natural and synthetic polymers are used for the preparation of hydrogel networks. Such polymeric networks are fabricated through chemical or physical mechanisms of crosslinking. Chemical crosslinking is accomplished mainly through covalent bonding, while physical crosslinking involves self-healing secondary forces like H-bonding, host-guest interactions, and antigen-antibody interactions. The building blocks of the hydrogels play an important role in determining the mechanical, biological, and physicochemical properties. Hydrogels are used in a variety of biomedical applications like diagnostics (biodetection and bioimaging), delivery of therapeutics (drugs, immunotherapeutics, and vaccines), wound dressing and skin materials, cardiac complications, contact lenses, tissue engineering, and cell culture because of the inherent characteristics like enhanced water uptake and structural similarity with the extracellular matrix (ECM). This review highlights the recent trends and advances in the roles of hydrogels in biomedical and therapeutic applications. We also discuss the classification and methods of hydrogels preparation. A brief outlook on the future directions of hydrogels is also presented.

Anisotropic Responsive Microgels Based on the Cholesteric Phase of Chitin Nanocrystals

Anisotropic stimuli-responsive microgels based upon the cholesteric phase of chitin nanocrystals and N-isopropylacrylamide were designed and synthesized. The cholesteric structure was interrogated, and the texture was shown to directly influence the microgel shape and anisotropy. Changes in the microgel volume led to changes in the texture, where microgels comprising up to six bands exhibited a twisted bipolar texture, while those with greater volumes displayed a concentric-packing structure. As designed, the imprinted cholesteric phase induced an asymmetric response to temperature, leading to a change in shape and optical properties. Furthermore, the cholesteric structure is able to deform, facilitating transport into a small channel. Access to synthetic structures having a self-assembled twisted texture derived from cholesterics embedded within a polymer matrix will provide guidelines for designing biopolymer composites with programmable motion.

Natural Polymer-Based Micronanostructured Scaffolds for Bone Tissue Engineering

Although bone tissue allografts and autografts aremoften used as a regenerative tissue during the bone healing, their availability, donor site morbidity, and immune response to grafted tissue are limiting factors their more common usage. Tissue engineered implants, such as acellular or cellular polymeric structures, can be an alternative solution. A variety of scaffold fabrication techniques including electrospinning, particulate leaching, particle sintering, and more recently 3D printing have been used to create scaffolds with interconnected pores and mechanical properties for tissue regeneration. Simply combining particle sintering and molecular self-assembly to create porous microstructures with imbued nanofibers to produce micronanostructures for tissue regeneration applications. Natural polymers like polysaccharides, proteins and peptides of plant or animal origin have gained significant attention due to their assured biocompatibility in tissue regeneration. However, majority of these polymers are water soluble and structures derived from them are in the form of hydrogels and require additional stabilization via cross-linking. For bone healing applications scaffolds are required to be strong, and support attachment, proliferation and differentiation of osteoprogenitors into osteoblasts. Our ongoing work utilizes plant polysaccharide cellulose derivatives and collagen to create mechanically stable and bioactive micronanostructured scaffold for bone tissue engineering. Scaffold microstructure is essentially solvent sintered cellulose acetate (CA) microspheres in the form of a negative template for trabecular bone with defined pore and mechanical properties. Collagen nanostructures are imbued into the 3D environment of CA scaffolds using collagen molecular self-assembly principles. The resultant CA-collagen micronanostructures provide the benefits of combined polymers and serve as an alternative material platform to many FDA approved polyesters. Our ongoing studies and published work confirm improved osteoprogenitor adhesion, proliferation, migration, differentiation, extracellular matrix (ECM) secretion in promoting bone healing. In this chapter we will provide a detailed protocol on the creation of micronanostructured CA-collagen scaffolds and their characterization for bone tissue engineering using human mesenchymal stem cells.

Coaxial Electrospun PLLA Fibers Modified with Water-Soluble Materials for Oligodendrocyte Myelination

Myelin sheaths are essential in maintaining the integrity of axons. Development of the platform for in vitro myelination would be especially useful for demyelinating disease modeling and drug screening. In this study, a fiber scaffold with a core-shell structure was prepared in one step by the coaxial electrospinning method. A high-molecular-weight polymer poly-L-lactic acid (PLLA) was used as the core, while the shell was a natural polymer material such as hyaluronic acid (HA), sodium alginate (SA), or chitosan (CS). The morphology, differential scanning calorimetry (DSC), Fourier transform infrared spectra (FTIR), contact angle, viability assay, and in vitro myelination by oligodendrocytes were characterized. The results showed that such fibers are bead-free and continuous, with an average size from 294 ± 53 to 390 ± 54 nm. The DSC and FTIR curves indicated no changes in the phase state of coaxial brackets. Hyaluronic acid/PLLA coaxial fibers had the minimum contact angle (53.1° ± 0.24°). Myelin sheaths were wrapped around a coaxial electrospun scaffold modified with water-soluble materials after a 14-day incubation. All results suggest that such a scaffold prepared by coaxial electrospinning potentially provides a novel platform for oligodendrocyte myelination.

Palmitic acid sophorolipid biosurfactant: from self-assembled fibrillar network (SAFiN) to hydrogels with fast recovery

Nanofibres are an interesting phase into which amphiphilic molecules can self-assemble. Described for a large number of synthetic lipids, they were seldom reported for natural lipids like microbial amphiphiles, known as biosurfactants. In this work, we show that the palmitic acid congener of sophorolipids (SLC16:0), one of the most studied families of biosurfactants, spontaneously forms a self-assembled fibre network (SAFiN) at pH below 6 through a pH jump process. pH-resolved in situ small-angle X-ray scattering (SAXS) shows a continuous micelle-to-fibre transition, characterized by an enhanced core-shell contrast between pH 9 and pH 7 and micellar fusion into a flat membrane between pH 7 and pH 6, approximately. Below pH 6, homogeneous, infinitely long nanofibres form by peeling off the membranes. Eventually, the nanofibre network spontaneously forms a thixotropic hydrogel with fast recovery rates after applying an oscillatory strain amplitude out of the linear viscoelastic regime: after being submitted to strain amplitudes during 5 min, the hydrogel recovers about 80% and 100% of its initial elastic modulus after, respectively, 20 s and 10 min. Finally, the strength of the hydrogel depends on the medium's final pH, with an elastic modulus fivefold higher at pH 3 than at pH 6. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

A Close Look at Molecular Self-Assembly with the Transmission Electron Microscope

Molecular self-assembly is pervasive in the formation of living and synthetic materials. Knowledge gained from research into the principles of molecular self-assembly drives innovation in the biological, chemical, and materials sciences. Self-assembly processes span a wide range of temporal and spatial domains and are often unintuitive and complex. Studying such complex processes requires an arsenal of analytical and computational tools. Within this arsenal, the transmission electron microscope stands out for its unique ability to visualize and quantify self-assembly structures and processes. This review describes the contribution that the transmission electron microscope has made to the field of molecular self-assembly. An emphasis is placed on which TEM methods are applicable to different structures and processes and how TEM can be used in combination with other experimental or computational methods. Finally, we provide an outlook on the current challenges to, and opportunities for, increasing the impact that the transmission electron microscope can have on molecular self-assembly.

Hydrogel-Stiffening and Non-Cell Adhesive Properties of Amphiphilic Peptides with Central Alkylene Chains

Amphiphilic peptides bearing terminal alkyl tails form supramolecular nanofibers that are increasingly used as biomaterials with multiple functionalities. Insertion of alkylene chains in peptides can be designed as another type of amphiphilic peptide, yet the influence of the internal alkylene chains on self-assembly and biological properties remains poorly defined. Unlike the terminal alkyl tails, the internal alkylene chains can affect not only the hydrophobicity but also the flexibility and packing of the peptides. Herein, we demonstrate the supramolecular and biological effects of the central alkylene chain length inserted in a peptide. Insertion of the alkylene chain at the center of the peptide allowed for strengthened β-sheet hydrogen bonds and modulation of the packing order, and consequently the amphiphilic peptide bearing C2 alkylene chain formed a hydrogel with the highest stiffness. Interestingly, the amphiphilic peptides bearing internal alkylene chains longer than C2 showed a diminished cell-adhesive property. This study offers a novel molecular design to tune mechanical and biological properties of peptide materials.

(Macro)molecular self-assembly for hydrogel drug delivery

Hydrogels prepared via self-assembly offer scalable and tunable platforms for drug delivery applications. Molecular-scale self-assembly leverages an interplay of attractive and repulsive forces; drugs and other active molecules can be incorporated into such materials by partitioning in hydrophobic domains, affinity-mediated binding, or covalent integration. Peptides have been widely used as building blocks for self-assembly due to facile synthesis, ease of modification with bioactive molecules, and precise molecular-scale control over material properties through tunable interactions. Additional opportunities are manifest in stimuli-responsive self-assembly for more precise drug action. Hydrogels can likewise be fabricated from macromolecular self-assembly, with both synthetic polymers and biopolymers used to prepare materials with controlled mechanical properties and tunable drug release. These include clinical approaches for solubilization and delivery of hydrophobic drugs. To further enhance mechanical properties of hydrogels prepared through self-assembly, recent work has integrated self-assembly motifs with polymeric networks. For example, double-network hydrogels capture the beneficial properties of both self-assembled and covalent networks. The expanding ability to fabricate complex and precise materials, coupled with an improved understanding of biology, will lead to new classes of hydrogels specifically tailored for drug delivery applications.

Functionalized Peptide Fibrils as a Scaffold for Active Substances in Wound Healing

Technological developments in the field of biologically active peptide applications in medicine have increased the need for new methods for peptide delivery. The disadvantage of peptides as drugs is their low biological stability. Recently, great attention has been paid to self-assembling peptides that can form fibrils. Such a formulation makes bioactive peptides more resistant to enzymatic degradation and druggable. Peptide fibrils can be carriers for peptides with interesting biological activities. These features open up prospects for using the peptide fibrils as long-acting drugs and are a valid alternative to conventional peptidic therapies. In our study, we designed new peptide scaffolds that are a hybrid of three interconnected amino acid sequences and are: pro-regenerative, cleavable by neutrophilic elastase, and fibril-forming. We intended to obtain peptides that are stable in the wound environment and that, when applied, would release a biologically active sequence. Our studies showed that the designed hybrid peptides show a high tendency toward regular fibril formation and are able to release the pro-regenerative sequence. Cytotoxicity studies showed that all the designed peptides were safe, did not cause cytotoxic effects and revealed a pro-regenerative potential in human fibroblast and keratinocyte cell lines. In vivo experiments in a dorsal skin injury model in mice indicated that two tested peptides moderately promote tissue repair in their free form. Our research proves that peptide fibrils can be a druggable form and a scaffold for active peptides.

Elastin-inspired supramolecular hydrogels: a multifaceted extracellular matrix protein in biomedical engineering

The phenomenal advancement in regenerative medicines has led to the development of bioinspired materials to fabricate a biomimetic artificial extracellular matrix (ECM) to support cellular survival, proliferation, and differentiation. Researchers have diligently developed protein polymers consisting of functional sequences of amino acids evolved in nature. Nowadays, certain repetitive bioinspired polymers are treated as an alternative to synthetic polymers due to their unique properties like biodegradability, easy scale-up, biocompatibility, and non-covalent molecular associations which imparts tunable supramolecular architecture to these materials. In this direction, elastin has been identified as a potential scaffold that renders extensibility and elasticity to the tissues. Elastin-like polypeptides (ELPs) are artificial repetitive polymers that exhibit lower critical solution temperature (LCST) behavior in a particular environment than synthetic polymers and hence have gained extensive interest in the fabrication of stimuli-responsive biomaterials. This review discusses in detail the unique structural aspects of the elastin and its soluble precursor, tropoelastin. Furthermore, the versatility of elastin-like peptides is discussed through numerous examples that bolster the significance of elastin in the field of regenerative medicines such as wound care, cardiac tissue engineering, ocular disorders, bone tissue regeneration, etc. Finally, the review highlights the importance of exploring short elastin-mimetic peptides to recapitulate the structural and functional aspects of elastin for advanced healthcare applications.

Effectiveness of Self-assembling Peptide P11-4 Compared to Tricalcium Phosphate Fluoride Varnish in Remineralization of White Spot Lesions: A Clinical Randomized Trial

Background

Fluoride varnish with therapeutic tricalcium phosphate formulas such as Clinpro™ varnish has shown greater tendency in treating white spot lesions (WSLs) by inhibiting the progression of initial enamel lesions through the mineral exchange. The self-assembling peptide SAP₁₁-4 (Curodont Repair, CDR) works on a different scale in treating WSLs by mimicking the enamel matrix and aiming to guided enamel regeneration.

Aim

To quantitatively and qualitatively compare the effectiveness of the SAP₁₁-4 vs tricalcium posphate fluoride (TCPF) in remineralization of WSLs in young permanent teeth.

Materials and methods

Nine healthy patients were enrolled in this study. The trial was performed on 40 young permanent teeth in the initial demineralization stage. Teeth were randomly assigned to receive either TCPF (group I) or SAP₁₁-4 (group II). Lesions were assessed at pretreatment, 3, and 6 months posttreatment quantitatively per laser fluorescence DIAGNOdent pen and qualitatively through the International Caries Detection and Assessment System (ICDAS) II.

Results

The result of the current study revealed a significant quantitative and qualitative increase in remineralization of WSLs in both groups and over time intervals. However, the WSL recovery was significantly better in the self-assembling peptide group, reflecting an excellent remineralization potential of the WSLs by the SAP₁₁-4 compared to TCPF varnish.

Conclusion

Both TCPF and SAP₁₁-4 were effective in treating WSLs. However, the success of guided enamel regeneration by the SAP₁₁-4 through the biomineralization has proven superiority of this material compared to TCPF.

Clinical significance

Early detection of WSLs and minimal intervention through remineralizing agents can limit unnecessary tissue loss, further caries progression, and consequently prevent further harm to the patients.

How to cite this article

Kobeissi R, Badr SBY, Osman E. Effectiveness of Self-assembling Peptide P₁₁-4 Compared to Tricalcium Phosphate Fluoride Varnish in remineralization of White Spot Lesions: A Clinical Randomized Trial. Int J Clin Pediatr Dent 2020;13(5):451-456.

Review of Integrin-Targeting Biomaterials in Tissue Engineering

The ability to direct cell behavior has been central to the success of numerous therapeutics to regenerate tissue or facilitate device integration. Biomaterial scientists are challenged to understand and modulate the interactions of biomaterials with biological systems in order to achieve effective tissue repair. One key area of research investigates the use of extracellular matrix-derived ligands to target specific integrin interactions and induce cellular responses, such as increased cell migration, proliferation, and differentiation of mesenchymal stem cells. These integrin-targeting proteins and peptides have been implemented in a variety of different polymeric scaffolds and devices to enhance tissue regeneration and integration. This review first presents an overview of integrin-mediated cellular processes that have been identified in angiogenesis, wound healing, and bone regeneration. Then, research utilizing biomaterials are highlighted with integrin-targeting motifs as a means to direct these cellular processes to enhance tissue regeneration. In addition to providing improved materials for tissue repair and device integration, these innovative biomaterials provide new tools to probe the complex processes of tissue remodeling in order to enhance the rational design of biomaterial scaffolds and guide tissue regeneration strategies.

Designing peptide nanoparticles for efficient brain delivery

The targeted delivery of therapeutic compounds to the brain is arguably the most significant open problem in drug delivery today. Nanoparticles (NPs) based on peptides and designed using the emerging principles of molecular engineering show enormous promise in overcoming many of the barriers to brain delivery faced by NPs made of more traditional materials. However, shortcomings in our understanding of peptide self-assembly and blood-brain barrier (BBB) transport mechanisms pose significant obstacles to progress in this area. In this review, we discuss recent work in engineering peptide nanocarriers for the delivery of therapeutic compounds to the brain: from synthesis, to self-assembly, to in vivo studies, as well as discussing in detail the biological hurdles that a nanoparticle must overcome to reach the brain.

Self-assembling Peptides in Current Nanomedicine: Versatile Nanomaterials for Drug Delivery

BACKGROUND

The development of modern nanomedicine greatly depends on the involvement of novel materials as drug delivery system. In order to maximize the therapeutic effects of drugs and minimize their side effects, a number of natural or synthetic materials have been widely investigated for drug delivery. Among these materials, biomimetic self-assembling peptides (SAPs) have received more attention in recent years. Considering the rapidly growing number of SAPs designed for drug delivery, a summary of how SAPs-based drug delivery systems were designed, would be beneficial.

METHOD

We outlined research works on different SAPs that have been investigated as carriers for different drugs, focusing on the design of SAPs nanomaterials and how they were used for drug delivery in different strategies.

RESULTS

Based on the principle rules of chemical complementarity and structural compatibility, SAPs such as ionic self-complementary peptide, peptide amphiphile and surfactant-like peptide could be designed. Determined by the features of peptide materials and the drugs to be delivered, different strategies such as hydrogel embedding, hydrophobic interaction, electrostatic interaction, covalent conjugation or the combination of them could be employed to fabricate SAPs-drug complex, which could achieve slow release, targeted or environment-responsive delivery of drugs. Furthermore, some SAPs could also be combined with other types of materials for drug delivery, or even act as drug by themselves.

CONCLUSION

Various types of SAPs have been designed and used for drug delivery following various strategies, suggesting that SAPs as a category of versatile nanomaterials have promising potential in the field of nanomedicine.

An in-vivo Intraoral Defect Model for Assessing the Use of P11-4 Self-Assembling Peptide in Periodontal Regeneration

Periodontal disease is one of the most common diseases worldwide. It has a significant impact on oral health and subsequently the individual's quality of life. However, optimal regeneration of periodontal tissues, using current treatments, has yet to be achieved. Peptide self-assembly has provided a step-change in nanobiotechnology and regenerative medicine fields. Our aim was to investigate the effects of a self-assembling peptide (SAP; P11-4) on periodontal regeneration in a preclinical model. Twenty-six bilateral maxillary critical-sized periodontal defects were created surgically in 13 rats. Defects on one side of the mouth were filled with P11-4 hydrogel; the contra-lateral defect was untreated (control). Rats were sacrificed immediately post-surgery (time 0) and after 2 and 4 weeks. Retrieved maxillae were processed for histological, immunohistochemical, and histomorphometric assessments. The results of histological analysis showed greater organization of periodontal fibers in defects treated with P11-4, at both time points, when compared to untreated defects. Histomorphometry showed that treated defects had both a significant increase in functional periodontal ligament length and a reduction in epithelial down growth after 4 weeks. At 2 weeks, treated defects showed a significant increase in expression of osteocalcin and osteoprotegerin as judged by immunohistochemistry. Also, a significantly higher osteoprotegerin/RANKL ratio was shown in treated defects. In conclusion, the results demonstrated enhanced regeneration of periodontal tissues when SAP P11-4 was used to fill periodontal defects in rats. The findings of this study suggest that SAP P11-4 is a promising novel candidate for periodontal regenerative therapy. Further investigations are required for optimization before clinical use.

Biomimetic peptide enriched nonwoven scaffolds promote calcium phosphate mineralisation

Cell-free translational strategies are needed to accelerate the repair of mineralised tissues, particularly large bone defects, using minimally invasive approaches. Regenerative bone scaffolds should ideally mimic aspects of the tissue's ECM over multiple length scales and enable surgical handling and fixation during implantation in vivo. Leveraging the knowledge gained with bioactive self-assembling peptides (SAPs) and SAP-enriched electrospun fibres, we presented a cell free approach for promoting mineralisation via apatite deposition and crystal growth, in vitro, of SAP-enriched nonwoven scaffolds. The nonwoven scaffold was made by electrospinning poly(ε-caprolactone) (PCL) in the presence of either peptide P₁₁-4 (Ac-QQRFEWEFEQQ-Am) or P₁₁-8 (Ac QQRFOWOFEQQ-Am), in light of the polymer's fibre forming capability and its hydrolytic degradability as well as the well-known apatite nucleating capability of SAPs. The 11-residue family of peptides (P₁₁-X) has the ability to self-assemble into β-sheet ordered structures at the nano-scale and to generate hydrogels at the macroscopic scale, some of which are capable of promoting biomineralisation due to their apatite-nucleating capability. Both variants of SAP-enriched nonwoven used in this study were proven to be biocompatible with murine fibroblasts and supported nucleation and growth of apatite minerals in simulated body fluid (SBF) in vitro. The fibrous nonwoven provided a structurally robust scaffold, with the capability to control SAP release behaviour. Up to 75% of P₁₁-4 and 45% of P₁₁-8 were retained in the fibres after 7 day incubation in aqueous solution at pH 7.4. The encapsulation of SAP in a nonwoven system with apatite-forming as well as localised and long-term SAP delivery capabilities is appealing as a potential means of achieving cost-effective bone repair therapy for critical size defects.

A structurally robust electrospun peptide-enriched scaffold, with controlled peptide release behaviour, supports nucleation and growth of hydroxyapatite minerals in vitro.

Conjugates of Chitosan and Calcium Alginate with Oligoproline and Oligohydroxyproline Derivatives for Potential Use in Regenerative Medicine

New materials that are as similar as possible in terms of structure and biology to the extracellular matrix (external environment) of cells are of great interest for regenerative medicine. Oligoproline and oligohydroxyproline derivatives (peptides 2-5) are potential mimetics of collagen fragments. Peptides 2-5 have been shown to be similar to the model collagen fragment (H-Gly-Hyp-Pro-Ala-Hyp-Pro-OH, 1) in terms of both their spatial structure and biological activity. In this study, peptides 2-5 were covalently bound to nonwovens based on chitosan and calcium alginate. Incorporation of the peptides was confirmed by Fourier transform -infrared (FT-IR) and zeta potential measurements. Biological studies (cell metabolic activity by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test and Live/Dead assay) proved that the obtained peptide-polysaccharide conjugates were not toxic to the endothelial cell line EA.hy 926. In many cases, the conjugates had a highly affirmative influence on cell proliferation. The results of this study show that conjugates of chitosan and calcium alginate with oligoproline and oligohydroxyproline derivatives have potential for use in regenerative medicine.

A Bibliometric Review of Artificial Extracellular Matrices Based on Tissue Engineering Technology Literature: 1990 through 2019

Artificial extracellular matrices (aECMs) are an extension of biomaterials that were developed as in-vitro model environments for tissue cells that mimic the native in vivo target tissues’ structure. This bibliometric analysis evaluated the research productivity regarding aECM based on tissue engineering technology. The Web of Science citation index was examined for articles published from 1990 through 2019 using three distinct aECM-related topic sets. Data were also visualized using network analyses (VOSviewer). Terms related to in-vitro, scaffolds, collagen, hydrogels, and differentiation were reoccurring in the aECM-related literature over time. Publications with terms related to a clinical direction (wound healing, stem cells, artificial skin, in-vivo, and bone regeneration) have steadily increased, as have the number of countries and institutions involved in the artificial extracellular matrix. As progress with 3D scaffolds continues to advance, it will become the most promising technology to provide a therapeutic option to repair or replace damaged tissue.

Hierarchically structured hydrogels utilizing multifunctional assembling peptides for 3D cell culture

Approaches for the creation of soft materials, particularly hydrogels, with hierarchical structure are of interest in a variety of applications owing to their unique properties. In the context of tissue mimics, hydrogels with multiscale structures more accurately capture the complexities of tissues within the body (e.g., fibrous collagen-rich microenvironments). However, cytocompatible fabrication of such materials with hierarchical structures and independent control of mechanical and biochemical properties remains challenging and is needed for probing and directing cell-microenvironment interactions for three-dimensional (3D) cell encapsulation and culture applications. To address this, we have designed innovative multifunctional assembling peptides: these unique peptides contain a core block that mimics the structure of collagen for achieving relevant melting temperatures; 'sticky' ends to promote assembly of long fibrils; and a biocompatible reactive handle that is orthogonal to assembly to allow the formation of desired multiscale structures and their subsequent rapid, light-triggered integration within covalently crosslinked synthetic hydrogels. Nano- to micro-fibrils were observed to form in physiologically-relevant aqueous solutions, where both underlying peptide chemical structure and assembly conditions were observed to impact the resulting fibril sizes. These assembled structures were 'locked' into place and integrated as linkers within cell-degradable, bioactive hydrogels formed with photoinitiated thiol-ene 'click' chemistry. Hydrogel compositions were identified for achieving robust mechanical properties like those of soft tissues while also retaining higher ordered structures after photopolymerization. The utility of these innovative materials for 3D cell culture was demonstrated with human mesenchymal stem cells, where cell morphologies reminiscent of responses to assembled native collagen were observed now with a fully synthetic material. Using a bottom-up approach, a new materials platform has been established that combines the advantageous properties of covalent and assembling chemistries for the creation of synthetic hydrogels with controllable nanostructure, mechanical properties, and biochemical content.

Biofabrication for neural tissue engineering applications

Unlike other tissue types, the nervous tissue extends to a wide and complex environment that provides a plurality of different biochemical and topological stimuli, which in turn defines the advanced functions of that tissue. As a consequence of such complexity, the traditional transplantation therapeutic methods are quite ineffective; therefore, the restoration of peripheral and central nervous system injuries has been a continuous scientific challenge. Tissue engineering and regenerative medicine in the nervous system have provided new alternative medical approaches. These methods use external biomaterial supports, known as scaffolds, to create platforms for the cells to migrate to the injury site and repair the tissue. The challenge in neural tissue engineering (NTE) remains the fabrication of scaffolds with precisely controlled, tunable topography, biochemical cues, and surface energy, capable of directing and controlling the function of neuronal cells toward the recovery from neurological disorders and injuries. At the same time, it has been shown that NTE provides the potential to model neurological diseases in vitro, mainly via lab-on-a-chip systems, especially in cases for which it is difficult to obtain suitable animal models. As a consequence of the intense research activity in the field, a variety of synthetic approaches and 3D fabrication methods have been developed for the fabrication of NTE scaffolds, including soft lithography and self-assembly, as well as subtractive (top-down) and additive (bottom-up) manufacturing. This article aims at reviewing the existing research effort in the rapidly growing field related to the development of biomaterial scaffolds and lab-on-a-chip systems for NTE applications. Besides presenting recent advances achieved by NTE strategies, this work also delineates existing limitations and highlights emerging possibilities and future prospects in this field.

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.

Probing mechanical properties and failure mechanisms of fibrils of self-assembling peptides

Self-assembling peptides (SAPs) are a promising class of biomaterials amenable to easy molecular design and functionalization. Despite their increasing usage in regenerative medicine, a detailed analysis of their biomechanics at the nanoscale level is still missing. In this work, we propose and validate, in all-atom dynamics, a coarse-grained model to elucidate strain distribution, failure mechanisms and biomechanical effects of functionalization of two SAPs when subjected to both axial stretching and bending forces. We highlight different failure mechanisms for fibril seeds and fibrils, as well as the negligible contribution of the chosen functional motif to the overall system rupture. This approach could lay the basis for the development of "more" coarse-grained models in the long pathway connecting SAP sequences and hydrogel mechanical properties.

Advances in immunotherapy delivery from implantable and injectable biomaterials

Macroscale biomaterials, such as preformed implantable scaffolds and injectable soft materials, possess powerful synergies with anti-cancer immunotherapies. Immunotherapies on their own typically have poor delivery properties, and often require repeated high-dose injections that result in serious off-tumor effects and/or limited efficacy. Rationally designed biomaterials allow for discrete localization and controlled release of immunotherapeutic agents, and have been shown in a large number of applications to improve outcomes in the treatment of cancers via immunotherapy. Among various strategies, macroscale biomaterial delivery systems can take the form of robust tablet-like scaffolds that are surgically implanted into a tumor resection site, releasing programmed immune cells or immunoregulatory agents. Alternatively they can be developed as soft gel-like materials that are injected into solid tumors or sites of resection to stimulate a potent anti-tumor immune response. Biomaterials synthesized from diverse components such as polymers and peptides can be combined with any immunotherapy in the modern toolbox, from checkpoint inhibitors and stimulatory adjuvants, to cancer antigens and adoptive T cells, resulting in unique synergies and improved therapeutic efficacy. The field is growing rapidly in size as publications continue to appear in the literature, and biomaterial-based immunotherapies are entering clinical trials and human patients. It is unarguably an exciting time for cancer immunotherapy and biomaterial researchers, and further work seeks to understand the most critical design considerations in the development of the next-generation of immunotherapeutic biomaterials. This review will discuss recent advances in the delivery of immunotherapies from localized biomaterials, focusing on macroscale implantable and injectable systems. STATEMENT OF SIGNIFICANCE: Anti-cancer immunotherapies have shown exciting clinical results in the past few decades, yet they suffer from a few distinct limitations, such as poor delivery kinetics, narrow patient response profiles, and systemic side effects. Biomaterial systems are now being developed that can overcome many of these problems, allowing for localized adjuvant delivery, focused dose concentrations, and extended therapy presentation. The field of biocompatible carrier materials is uniquely suited to be combined with immunotherapy, promising to yield significant improvements in treatment outcomes and clinical care. In this review, the first pioneering efforts and most recent advances in biomaterials for immunotherapeutic applications are explored, with a specific focus on implantable and injectable biomaterials such as porous scaffolds, cryogels, and hydrogels.

Evaluation of enamel remineralizing potential of self-assembling peptide P11-4 on artificially induced enamel lesions in vitro

PURPOSE

The purpose of this study was to evaluate the remineralizing efficacy of self-assembling peptide (SAP) P₁₁-4 qualitatively and quantitatively using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX), respectively.

METHODOLOGY

Enamel samples (n = 24) were prepared by sectioning extracted premolars and subjected for demineralization to create artificial enamel lesions. The structural and elemental concentrations (calcium and phosphate weight %) were assessed to obtain baseline data using SEM and EDX spectroscopy, respectively. The samples were randomly allocated into two groups and were treated with SAP P₁₁-4 (test group) and casein phosphopeptides-amorphous calcium phosphate (CPP-ACP) (control group) followed by storage in artificial saliva to evaluate the remineralizing efficacy at 1-week, 1-month, and 3-month intervals.

RESULTS

Data were analyzed using the ANOVA and unpaired t-test. From the observed results, CPP-ACP showed a significant increase in Ca: P ratio (2.04 ± 0.2) with irregular surface calcific deposition at 1-week interval and this reduced with time (1.87 ± 0.11 at 3-month interval). Whereas P₁₁-4 showed a significant increase in Ca: P ratio (1.95 ± 0.10) with uniform ion deposition suggestive of hydroxyapatite nucleation over a 3-month period.

CONCLUSION

SAP P₁₁-4 exhibited superior remineralization with uniform mineral deposition compared to CPP-ACP at 3-month interval.

Multicomponent peptide assemblies

Self-assembled peptide nanostructures have been increasingly exploited as functional materials for applications in biomedicine and energy. The emergent properties of these nanomaterials determine the applications for which they can be exploited. It has recently been appreciated that nanomaterials composed of multicomponent coassembled peptides often display unique emergent properties that have the potential to dramatically expand the functional utility of peptide-based materials. This review presents recent efforts in the development of multicomponent peptide assemblies. The discussion includes multicomponent assemblies derived from short low molecular weight peptides, peptide amphiphiles, coiled coil peptides, collagen, and β-sheet peptides. The design, structure, emergent properties, and applications for these multicomponent assemblies are presented in order to illustrate the potential of these formulations as sophisticated next-generation bio-inspired materials.