Biological designer self-assembling peptide nanofiber scaffolds significantly enhance osteoblast proliferation, differentiation and 3-D migration

Enhanced osteogenesis of human mesenchymal stem cells by self-assembled peptide hydrogel functionalized with glutamic acid templated peptides

Self-assembling peptide (SAP) hydrogel has been shown to be an excellent biological material for three-dimensional cell culture and stimulatie cell migration and differentiation into the scaffold, as well as for repairing bone tissue defects. Herein, we designed one of the SAP scaffolds KLD (KLDLKLDLKLDL) through direct coupling to short bioactive motif O1 (EEGGC) and O2 (EEEEE) of which bioactivity on osteogenic differentiation was previously demonstrated and self-assembled in different concentrations (0.5%, 1%, and 2%). Our aim was to enhance osteogenesis and biomineralization of injectable SAP hydrogels with controlled mechanical properties so that the peptide hydrogel also becomes capable of being injected to bone defects. The molecular integration of the nanofibrous peptide scaffolds was observed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The rheological properties and degradation profile of SAP hydrogels were evaluated to ensure stability of SAPs. Compared with pure KLD scaffold, we found that these designed bioactive peptide scaffolds significantly promoted hMSCs proliferation depicted by biochemical analysis of alkaline phosphatase (ALP) activity, total calcium deposition. Moreover, key osteogenic markers of ALP activity, collagen type I (COL-1), osteopontin (OP), and osteocalcin (OCN) expression levels determined by real-time polymerase chain reaction (PCR) and immunofluorescence analysis were also significantly increased with the addition of glutamic acid residues to KLD. We demonstrated that the designed SAP scaffolds promoted the proliferation and osteogenic differentiation of hMSCs. Our results suggest that these designed bioactive peptide scaffolds may be useful for promoting bone tissue regeneration.

A Customized Self-Assembling Peptide Hydrogel-Wrapped Stem Cell Factor Targeting Pulp Regeneration Rich in Vascular-Like Structures

Pulp regeneration is to replace the inflamed/necrotic pulp tissue with regenerated pulp-like tissue to rejuvenate the teeth. Self-assembling peptide hydrogels RADA16-I (Ac-(RADA16-I)₄-CONH₂) can provide a three-dimensional environment for cells. The stem cell factor (SCF) plays a crucial role in homing stem cells. Combining these advantages, our study investigated the effects of SCF-RADA16-I on adhesion, proliferation, and migration of human dental pulp stem cells (DPSCs) and the angiogenesis of human umbilical vein endothelial cells (HUVECs). The β-sheet and grid structure were observed by circular dichroism (CD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Cytoskeleton staining, living cell staining, cell viability, cell migration, angiogenesis, and western blot assays were performed, and the results indicated that all the SCF groups were superior to the corresponding non-SCF groups in cell adhesion, proliferation, migration, and angiogenesis. RADA16-I provided a three-dimensional environment for DPSCs. Besides, the SCF promoted HUVECs to form more vascular-like structures and release more vascular endothelial growth factor A. In summary, the SCF-loaded RADA16-I scaffold improved adhesion, proliferation, and migration of DPSCs and the formation of more vascular-like structures of HUVECs. SCF-RADA16-I holds promise for guided pulp regeneration, and it can potentially be applied widely in tissue engineering and translational medicine in the future.

Self-assembling peptide hydrogels functionalized with LN- and BDNF- mimicking epitopes synergistically enhance peripheral nerve regeneration

The regenerative capacity of the peripheral nervous system is closely related to the role that Schwann cells (SCs) play in construction of the basement membrane containing multiple extracellular matrix proteins and secretion of neurotrophic factors, including laminin (LN) and brain-derived neurotrophic factor (BDNF). Here, we developed a self-assembling peptide (SAP) nanofiber hydrogel based on self-assembling backbone Ac-(RADA)4-NH2 (RAD) dual-functionalized with laminin-derived motif IKVAV (IKV) and a BDNF-mimetic peptide epitope RGIDKRHWNSQ (RGI) for peripheral nerve regeneration, with the hydrogel providing a three-dimensional (3D) microenvironment for SCs and neurites. Methods: Circular dichroism (CD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the secondary structures, microscopic structures, and morphologies of self-assembling nanofiber hydrogels. Then the SC adhesion, myelination and neurotrophin secretion were evaluated on the hydrogels. Finally, the SAP hydrogels were injected into hollow chitosan tubes to bridge a 10-mm-long sciatic nerve defect in rats, and in vivo gene expression at 1 week, axonal regeneration, target muscular re-innervation, and functional recovery at 12 weeks were assessed. Results: The bioactive peptide motifs were covalently linked to the C-terminal of the self-assembling peptide and the functionalized peptides could form well-defined nanofibrous hydrogels capable of providing a 3D microenvironment similar to native extracellular matrix. SCs displayed improved cell adhesion on hydrogels with both IKV and RGI, accompanied by increased cell spreading and elongation relative to other groups. RSCs cultured on hydrogels with IKV and RGI showed enhanced gene expression of NGF, BDNF, CNTF, PMP22 and NRP2, and decreased gene expression of NCAM compared with those cultured on other three groups after a 7-day incubation. Additionally, the secretion of NGF, BDNF, and CNTF of RSCs was significantly improved on dual-functionalized peptide hydrogels after 3 days. At 1 week after implantation, the expressions of neurotrophin and myelin-related genes in the nerve grafts in SAP and Autograft groups were higher than that in Hollow group, and the expression of S100 in groups containing both IKV and RGI was significantly higher than that in groups containing either IKV or RGI hydrogels, suggesting enhanced SC proliferation. The morphometric parameters of the regenerated nerves, their electrophysiological performance, the innervated muscle weight and remodeling of muscle fibers, and motor function showed that RAD/IKV/RGI and RAD/IKV-GG-RGI hydrogels could markedly improve axonal regeneration with enhanced re-myelination and motor functional recovery through the synergetic effect of IKV and RGI functional motifs. Conclusions: We found that the dual-functionalized SAP hydrogels promoted RSC adhesion, myelination, and neurotrophin secretion in vitro and successfully bridged a 10-mm gap representing a sciatic nerve defect in rats in vivo. The results demonstrated the synergistic effect of IKVAV and RGI on axonal regrowth and function recovery after peripheral nerve injury.

Sequence-Dependent Bioactivity and Self-Assembling Properties of RGD-Containing Amphiphilic Peptides as Extracellular Scaffolds

Cell adhesion is a fundamental biological process involved in a wide range of cellular and biological activity. Integrin-ligand binding is largely responsible for cell adhesion with an extracellular matrix, and the RGD sequence is an epitope in ligand proteins such as fibronectin. The extracellular matrix consists of fibrous proteins with embedded ligands for integrins. Such a biological architecture has been reconstructed for biochemical, pharmaceutical, and biomaterial studies using artificial supramolecular systems to reproduce cell adhesion functionality, and fiber-forming self-assembling peptides containing RGD are one such promising material for this purpose. In this study, using RADA16 as a model fiber-forming peptide, a series of RGD-containing variants have been synthesized by the replacement of one alanine with glycine at different positions, in which all the variants consist of identical amino acid components. The position of the RGD unit influenced the supramolecular self-assembly of the amphiphilic peptide to inhibit β-sheet formation (A6G) or twist the molecular alignment in β-sheet-type assemblies (A10G and A14G). Furthermore, A10G and A14G formed assembled nanofibers, which afforded hydrogels with higher viscoelasticities than other RGD-containing variants. In contrast to A10G and A14G, which exhibit substantial cell adhesion functionality, the cell adhesion efficiencies of the other RGD-containing variants were significantly reduced. This suggests that the higher order structure could strongly influence the cell adhesion functionality of RGD-containing supramolecular nanofibers.

Cross-Linked Self-Assembling Peptides and Their Post-Assembly Functionalization via One-Pot and In Situ Gelation System

Supramolecular nanostructures formed through peptide self-assembly can have a wide range of applications in the biomedical landscape. However, they often lose biomechanical properties at low mechanical stress due to the non-covalent interactions working in the self-assembling process. Herein, we report the design of cross-linked self-assembling peptide hydrogels using a one-pot in situ gelation system, based on 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide/N-hydroxysulfosuccinimide (EDC/sulfo–NHS) coupling, to tune its biomechanics. EDC/sulfo–NHS coupling led to limited changes in storage modulus (from 0.9 to 2 kPa), but it significantly increased both the strain (from 6% to 60%) and failure stress (from 19 to 35 Pa) of peptide hydrogel without impairing the spontaneous formation of β-sheet-containing nano-filaments. Furthermore, EDC/sulfo–NHS cross-linking bestowed self-healing and thixotropic properties to the peptide hydrogel. Lastly, we demonstrated that this strategy can be used to incorporate bioactive functional motifs after self-assembly on pre-formed nanostructures by functionalizing an Ac-LDLKLDLKLDLK-CONH₂ (LDLK12) self-assembling peptide with the phage display-derived KLPGWSG peptide involved in the modulation of neural stem cell proliferation and differentiation. The incorporation of a functional motif did not alter the peptide’s secondary structure and its mechanical properties. The work reported here offers new tools to both fine tune the mechanical properties of and tailor the biomimetic properties of self-assembling peptide hydrogels while retaining their nanostructures, which is useful for tissue engineering and regenerative medicine applications.

Controlled Dynamics of Neural Tumor Cells by Templated Liquid Crystalline Polymer Networks

The ability to control the alignment and organization of cell populations has great potential for tissue engineering and regenerative medicine. A variety of approaches such as nano/microtopographical patterning, mechanical loading, and nanocomposite synthesis have been developed to engineer scaffolds able to control cellular properties and behaviors. In this work, a patterned liquid crystal polymer network (LCN) film is synthesized by using a nematic liquid crystal template in which the molecular orientations are predesigned by photopatterning technique. Various configurations of polymer networks such as linear and circular patterns are created. When neural tumor cells are plated onto the templated LCN films, the cell alignment, migration, and proliferation are directed in both linear and curvilinear fashions following the pattern of the aligned polymer chains. A complex LCN pattern with zigzag geometry is also fabricated and found to be capable of controlling cell alignment and collective cellular organization. The demonstrated control of cell dynamics and organization by LCN films with various molecular alignments opens new opportunities to design scaffolds to control cultured cell organization in a manner resembling that found in tissues and to develop novel advanced materials for nerve repair, tissue engineering, and regenerative medicine applications.

A controlled nucleation and formation rate of self-assembled peptide nanofibers

Self-assembling peptide matrixes are powerful platforms for encouraging tissue regeneration, but are usually formed within seconds and remain relatively static in both structure and function throughout their application. For the first time, we have shown that it is possible to extend the time it takes for peptide self-assembly so as to allow for the dynamic building of a self-assembled system over days, in the presence of an enzyme. Specifically, K₅ and K₁₀ sequences were conjugated, via a thrombin-specific cleavage domain NleTPR/SFL, to prevent the nanofiber formation and form stable nanoparticles composed of (RADA)₄-GG-NleTPR/SFL-K₅ and (RADA)₄-GG-NleTPR/SFL-K₁₀ that act as nucleation sites for reassembling. Upon introduction of thrombin, a model enzyme, this system showed an extremely slow rate of nanofiber formation in a parallel direction that is in sharp contrast to the well-known rapid assembly of (RADA)₄ systems with random networks. These bioresponsive materials may provide a novel platform for utilizing long-term enzymatic profiles to form new nanofibers within an existing matrix over long therapeutic timeframes.

Proteins, peptides and peptidomimetics as active agents in implant surface functionalization

The recent impact of implants on improving the human life quality has been enormous. During the past two decades we witnessed major advancements in both material and structural development of implants. They were driven mainly by the increasing patients' demand and the need to address the major issues that come along with the initially underestimated complexity of the bone-implant interface. While both, the materials and design of implants reached a certain, balanced state, recent years brought a shift in focus towards the bone-implant interface as the weakest link in the increasing implant long-term usability. As a result, several approaches were developed. They aimed at influencing and enhancing the implant osseointegration and its proper behavior when under load and stress. With this review, we would like to discuss the recent advancements in the field of implant surface modifications, emphasizing the importance of chemical methods, focusing on proteins, peptides and peptidomimetics as promising agents for titanium surface coatings.

Temperature-Responsive Multifunctional Protein Hydrogels with Elastin-like Polypeptides for 3-D Angiogenesis

Supramolecular protein hydrogels with tunable properties represent promising candidates for advanced designer extracellular matrices (ECMs). To control cellular functions, ECMs should be able to spatiotemporally regulate synergistic signaling between transmembrane receptors and growth factor (GF) receptors. In this study, we developed genetically engineered temperature-responsive multifunctional protein hydrogels. The designed hydrogel was fabricated by combining the following four peptide blocks: thermosensitive elastin-like polypeptides (ELPs), a polyaspartic acid (polyD) chain to control aggregation and delivery of GFs, a de novo-designed helix peptide that forms antiparallel homotetrameric coiled-coils, and a biofunctional peptide. The resultant coiled-coil unit bound ELPs (CUBEs) exhibit a controllable sol-gel transition with tunable mechanical properties. CUBEs were functionalized with bone sialoprotein-derived RGD (bRGD), and human umbilical vein endothelial cells (HUVECs) were three-dimensionally cultured in bRGD-modified CUBE (bRGD-CUBE) hydrogels. Proangiogenic activity of HUVECs was promoted by bRGD. Moreover, heparin-binding angiogenic GFs were immobilized to bRGD-CUBEs via electrostatic interactions. HUVECs cultured in GF-tethered bRGD-CUBE hydrogels formed three-dimensional (3-D) tubulelike structures. The designed CUBE hydrogels may demonstrate utility as advanced smart biomaterials for biomedical applications. Further, the protein hydrogel design strategy may provide a novel platform for constructing designer 3-D microenvironments for specific cell types.

Protamine-induced condensation of peptide nanofilaments into twisted bundles with controlled helical geometry

Chiral self-assembly of peptides is of fundamental interest in the field of biology and material science. Protamine, an alkaline biomacromolecule which is ubiquitous in fish and mammalian, plays crucial roles in directing the helical twisting of DNA. Inspired by this, we reported a bioinspired pathway to direct the hierarchical chiral self-assembly of a short synthetic dipeptide. The peptide could self-assemble into negatively charged chiral micelles in water that spontaneously formed a nematic liquid crystalline phase. By incorporation with protamine, the micelles condensed with the protamine into large helical bundles with precisely controlled diameter. Furthermore, to simulate the intracellular environments, we investigated macromolecular crowding on the coassembly of peptide and protamine, which leads to the formation of much thinner helical structures. The results highlight the roles of highly charged biomacromolecules and macromolecular crowding on peptide self-assembly, which are beneficial for the practical applications of self-assembling peptides in biomedicine and sensing.

Dipeptide Self-Assembled Hydrogels with Tunable Mechanical Properties and Degradability for 3D Bioprinting

Supramolecular hydrogels self-assembled from short peptides have shown great potential as biomimetic extracellular matrices with controllable properties designed at the molecular level. However, their weak mechanical strength still remains a big challenge for 3D bioprinting. Herein, two oppositely charged dipeptides are designed and used as bioinks in a ″layer-by-layer″ alternative bioprinting strategy. During printing, in situ gelation is achieved by electrostatic interactions between two dipeptides without additional cross-linking procedures. The binary hydrogels have tunable mechanical properties with elastic moduli ranging from 4 to 62 kPa and controllable biodegradability from days to weeks, which can ideally mimic the natural environment of a variety of cell types. It is demonstrated that the hydrogel scaffold enables the formation, growth, and natural release of HepaRG spheroids with sizes up to millimeters. This strategy may be suitable to develop a series of new bioink materials based on peptides and other supramolecular polymers for 3D bioprinting.

Conductive biomaterials for muscle tissue engineering

Muscle tissues are soft tissues that are of great importance in force generation, body movements, postural support and internal organ function. Muscle tissue injuries would not only result in the physical and psychological pain and disability to the patient, but also become a severe social problem due to the heavy financial burden they laid on the governments. Current treatments for muscle tissue injuries all have their own severe limitations and muscle tissue engineering has been proposed as a promising therapeutic strategy to treat with this problem. Conductive biomaterials are good candidates as scaffolds in muscle tissue engineering due to their proper conductivity and their promotion on muscle tissue formation. However, a review of conductive biomaterials function in muscle tissue engineering, including the skeletal muscle tissue, cardiac muscle tissue and smooth muscle tissue regeneration is still lacking. Here we reviewed the recent progress of conductive biomaterials for muscle regeneration. The recent synthesis and fabrication methods of conductive scaffolds containing conductive polymers (mainly polyaniline, polypyrrole and poly(3,4-ethylenedioxythiophene), carbon-based nanomaterials (mainly graphene and carbon nanotube), and metal-based biomaterials were systematically discussed, and their application in a variety of forms (such as hydrogels, films, nanofibers, and porous scaffolds) for different kinds of muscle tissues formation (skeletal muscle, cardiac muscle and smooth muscle) were summarized. Furthermore, the mechanism of how the conductive biomaterials affect the muscle tissue formation was discussed and the future development directions were included.

A biomimetic self-assembling peptide promotes bone regeneration in vivo: A rat cranial defect study

Rationally designed, pH sensitive self-assembling β-peptides (SAPs) which are capable of reversibly switching between fluid and gel phases in response to environmental triggers are potentially useful injectable scaffolds for skeletal tissue engineering applications. SAP P₁₁-4 (CH₃COQQRFEWEFEQQNH₂) has been shown to nucleate hydroxyapatite mineral de novo and has been used in dental enamel regeneration. We hypothesised that addition of mesenchymal stromal cells (MSCs) would enhance the in vivo effects of P₁₁-4 in promoting skeletal tissue repair. Cranial defects were created in athymic rats and filled with either Bio-Oss® (anorganic bone chips) or P₁₁-4 ± human dental pulp stromal cells (HDPSCs). Unfilled defects served as controls. After 4 weeks, only those defects filled with P₁₁-4 alone showed significantly increased bone regeneration (almost complete healing), compared to unfilled control defects, as judged using quantitative micro-CT, histology and immunohistochemistry. In silico modelling indicated that fibril formation may be essential for any mineral nucleation activity. Taken together, these data suggest that self-assembling peptides are a suitable scaffold for regeneration of bone tissue in a one step, cell-free therapeutic approach.

Effect of Biomaterial Electrical Charge on Bone Morphogenetic Protein-2-Induced In Vivo Bone Formation

IMPACT STATEMENT

Biomaterials can play a dual role in bone regeneration: they enable local sustained delivery of growth factors, such as bone morphogenetic protein-2 (BMP-2), while they provide structural support as scaffold. By better imitating the properties of native bone tissue, scaffolds may be both osteoconductive and osteoinductive. The latter can be achieved by modifying the electrical charge of the surface. The present work uses tunable oligo[(polyethylene glycol) fumarate] hydrogel and demonstrates that negative charge enhances BMP-2-induced bone formation compared with neutral or positive charge. Altogether, this indicates that tissue-specific surface charge modifications of biomaterials hold great promise in the field of tissue regeneration.

Sustained Release of Dexamethasone from Sulfobutyl Ether β-cyclodextrin Modified Self-Assembling Peptide Nanoscaffolds in a Perinatal Rat Model of Hypoxia-Ischemia

Inflammation plays a critical role in the development of hypoxia-ischemia (HI) induced newborn brain damage. A localized, sustained delivery of dexamethasone (Dex) through an intracerebral injection could reduce the inflammatory response in the injured perinatal brain while avoiding unnecessary side effects. Herein, investigated using anionic sulfobutyl ether β-cyclodextrin (SBE-β-CD) to load Dex in the (RADA)₄ nanofiber networks as a means of reducing the inflammatory response to HI injury is investigated. The ionic interaction between SBE-β-CD and (RADA)₄ dramatically affects nanofiber formation and the stability of the nanoscaffold is highly dependent on the SBE-β-CD/(RADA)₄ ratio. It is observed that the Dex release rate is affected by the concentration of SBE-β-CD and (RADA)₄ peptide. A higher concentration of SBE-β-CD or (RADA)₄ results in a higher drug encapsulation efficiency and slower release rate of Dex. This phenomenon may be related to the structure of fiber bundles. Animal studies show that nanoscaffold loaded with Dex inhibits both microglia activation and glial scar formation compared to controls (Dex alone or nanoscaffold alone) within 2 days of injury. It is thought that this is a step toward building a multifaceted nanoscaffold that can be used to treat HI events in perinates.

Using Self-Assembling Peptides to Integrate Biomolecules into Functional Supramolecular Biomaterials

Throughout nature, self-assembly gives rise to functional supramolecular biomaterials that can perform complex tasks with extraordinary efficiency and specificity. Inspired by these examples, self-assembly is increasingly used to fabricate synthetic supramolecular biomaterials for diverse applications in biomedicine and biotechnology. Peptides are particularly attractive as building blocks for these materials because they are based on naturally derived amino acids that are biocompatible and biodegradable; they can be synthesized using scalable and cost-effective methods, and their sequence can be tailored to encode formation of diverse architectures. To endow synthetic supramolecular biomaterials with functional capabilities, it is now commonplace to conjugate self-assembling building blocks to molecules having a desired functional property, such as selective recognition of a cell surface receptor or soluble protein, antigenicity, or enzymatic activity. This review surveys recent advances in using self-assembling peptides as handles to incorporate biologically active molecules into supramolecular biomaterials. Particular emphasis is placed on examples of functional nanofibers, nanovesicles, and other nano-scale structures that are fabricated by linking self-assembling peptides to proteins and carbohydrates. Collectively, this review highlights the enormous potential of these approaches to create supramolecular biomaterials with sophisticated functional capabilities that can be finely tuned to meet the needs of downstream applications.

Self-assembling peptides cross-linked with genipin: resilient hydrogels and self-standing electrospun scaffolds for tissue engineering applications

Self-assembling peptides (SAPs) are synthetic bioinspired biomaterials that can be feasibly multi-functionalized for applications in surgery, drug delivery, optics and tissue engineering (TE). Despite their promising biocompatibility and biomimetic properties, they have never been considered real competitors of polymers and/or cross-linked extracellular matrix (ECM) natural proteins. Indeed, synthetic SAP-made hydrogels usually feature modest mechanical properties, limiting their potential applications, due to the transient non-covalent interactions involved in the self-assembling phenomenon. Cross-linked SAP-hydrogels have been recently introduced to bridge this gap, but several questions remain open. New strategies leading to stiffer gels of SAPs may allow for a full exploitation of the SAP technology in TE and beyond. We have developed and characterized a genipin cross-linking strategy significantly increasing the stiffness and resiliency of FAQ(LDLK)3, a functionalized SAP already used for nervous cell cultures. We characterized different protocols of cross-linking, analyzing their dose and time-dependent efficiency, influencing stiffness, bioabsorption time and molecular arrangements. We choose the best developed protocol to electrospin into nanofibers, for the first time, self-standing, water-stable and flexible fibrous mats and micro-channels entirely made of SAPs. This work may open the door to the development and tailoring of bioprostheses entirely made of SAPs for different TE applications.

Multifunctionalized hydrogels foster hNSC maturation in 3D cultures and neural regeneration in spinal cord injuries

Cells reside in 3D microenvironments in living tissues; consequently, 3D cultures gained great interest because they better mimic the natural conditions of cells. Self-assembling peptides (SAPs) are synthetic bioabsorbable biomaterials that can provide customized 3D microenvironments regulating cell functionalities and tissue repair. Here we introduce a SAP-hydrogel designed to support human neural stem cell (hNSC) differentiation in 3D serum-free conditions, generating mature and active human neurons in vitro. We also demonstrate its functional neurorigenerative potential in rat spinal cord injuries, peaking when seeded with hNSCs progeny predifferentiated in vitro for 6 weeks. Despite these promising results, this approach should be confirmed in the future with medium-size animal models and with additional and refined behavioral tests before entering a clinical trial.

Three-dimensional cell cultures are leading the way to the fabrication of tissue-like constructs useful to developmental biology and pharmaceutical screenings. However, their reproducibility and translational potential have been limited by biomaterial and culture media compositions, as well as cellular sources. We developed a construct comprising synthetic multifunctionalized hydrogels, serum-free media, and densely seeded good manufacturing practice protocol-grade human neural stem cells (hNSC). We tracked hNSC proliferation, differentiation, and maturation into GABAergic, glutamatergic, and cholinergic neurons, showing entangled electrically active neural networks. The neuroregenerative potential of the “engineered tissue” was assessed in spinal cord injuries, where hNSC-derived progenitors and predifferentiated hNSC progeny, embedded in multifunctionalized hydrogels, were implanted. All implants decreased astrogliosis and lowered the immune response, but scaffolds with predifferentiated hNSCs showed higher percentages of neuronal markers, better hNSC engraftment, and improved behavioral recovery. Our hNSC-construct enables the formation of 3D functional neuronal networks in vitro, allowing novel strategies for hNSC therapies in vivo.

Self-Assembling Peptides as Extracellular Matrix Mimics to Influence Stem Cell's Fate

Interest in biologically active materials that can be used as cell culture substrates for medicinal applications has increased dramatically over the last decade. The design and development of biomaterials mimicking the natural environment of different cell types, the so-called extracellular matrix (ECM), is the focus of research in this field. The ECM exists as an ensemble of several adhesion proteins with different functionalities that can be presented to the embedded cells. These functionalities regulate numerous cellular processes. Therefore, different approaches and strategies using peptide- and protein-based biopolymers have been investigated to support the proliferation, differentiation, and self-renewal of stem cells, in the context of regenerative medicine. This minireview summarizes recent developments in this area, with a focus on peptide-based biomaterials used as stem cell culture substrates.

Peptide Self-Assembly into Hydrogels for Biomedical Applications Related to Hydroxyapatite

Amphiphilic peptides can be self-assembled by establishing physical cross-links involving hydrogen bonds and electrostatic interactions with divalent ions. The derived hydrogels have promising properties due to their biocompatibility, reversibility, trigger capability, and tunability. Peptide hydrogels can mimic the extracellular matrix and favor the growth of hydroxyapatite (HAp) as well as its encapsulation. Newly designed materials offer great perspectives for applications in the regeneration of hard tissues such as bones, teeth, and cartilage. Furthermore, development of drug delivery systems based on HAp and peptide self-assembly is attracting attention.

Self-assembled GFFYK peptide hydrogel enhances the therapeutic efficacy of mesenchymal stem cells in a mouse hindlimb ischemia model

Mesenchymal stem cell (MSC) transplantation has emerged as a very promising strategy for the treatments of peripheral artery disease (PAD). However, MSC-based therapies are limited by low cell retention and survival rate in the ischemic zone. Small molecular (SM) hydrogels have shown attractive abilities to enhance the therapeutic effects of human MSCs via promoting their proliferation or maintaining their differentiation potential. Here, we designed and synthesized a new bioactive and biocompatible hydrogel, Nap-GFFYK-Thiol, using disulfide bonds as cleavable linkers to control the molecular self-assembly and we hypothesized this hydrogel could enhance the retention and engraftment of human placenta-derived MSCs (hP-MSCs) in a mouse ischemic hindlimb model. In vitro results demonstrated that the Nap-GFFYK-Thiol hydrogel increased cell viability through paracrine effects. Moreover, it enhanced the proangiogenic and anti-apoptotic effects of hP-MSCs. In vivo, Nap-GFFYK-Thiol hydrogel improved the hP-MSC retention in the murine ischemic hindlimb model as visualized by bioluminescence imaging. Furthermore, cotransplantation of hP-MSCs with hydrogel improved blood perfusion, leading to superior limb salvage. These therapeutic effects may attribute to reduced inflammatory cell infiltration, enhanced angiogenesis as well as suppressed collagen deposition. In conclusion, the Nap-GFFYK-Thiol hydrogel fabricated using disulfide bonds as cleavable linkers serves as an artificial niche for promoting hP-MSC survival and proangiogenic factor secretion in PAD therapy and thereby provide an alternative strategy for PAD therapy. STATEMENT OF SIGNIFICANCE: Although several phase I/II clinical trials of MSC-based treatments for critical limb ischemia (CLI) are ongoing, MSC-based therapies are still challenged by the low quality and quantity of cells in the ischemic zone, especially in cases of extensive or irreversible damage. Hydrogels have favorable biocompatibility and safety records in the medical field. In the current study, we engineered a new bioactive and biocompatible hydrogel, Nap-GFFYK-Thiol, using disulfide bonds as cleavable linkers to enhance the therapeutic efficacy of human placenta-derived MSCs (hP-MSCs) in mouse limb ischemia model. Notably, Nap-GFFYK-Thiol hydrogel acts as an artificial niche for promoting hP-MSC survival and proangiogenic factor secretion in PAD therapy, which further promoted the restoration of blood perfusion and regeneration of muscle cells. Considering the proangiogenic effect of Nap-GFFYK-Thiol on hP-MSCs, our results may provide a new strategy for the treatment of PAD.

Recent advances in the design of injectable hydrogels for stem cell-based therapy

The recent advances in the design of injectable hydrogels for stem cell delivery, especially for in vivo applications, are overviewed in this review.

Stem cell therapy in Alzheimer's disease: possible benefits and limiting drawbacks

Alzheimer's disease (AD) is the sixth leading cause of death globally and the main reason for dementia in elderly people. AD is a long-term and progressive neurodegenerative disorder that steadily worsens memory and communicating skills eventually leads to a disabled person of performing simple daily tasks. Unfortunately, numerous clinical trials exploring new therapeutic drugs have encountered disappointing outcomes in terms of improved cognitive performance since they are not capable of halting or stimulating the regeneration of already-damaged neural cells, and merely provide symptomatic relief. Therefore, a deeper understanding of the mechanism of action of stem cell may contribute to the development of novel and effective therapies. The revolutionary discovery of stem cells has cast a new hope for the development of disease-modifying treatments for AD, in terms of their potency in the replenishment of lost cells via differentiating towards specific lineages, stimulating in situ neurogenesis, and delivering the therapeutic agents to the brain. Herein, firstly, we explore the pathophysiology of AD. Next, we summarize the most recent preclinical stem cell reports designed for AD treatment, their benefits and outcomes according to cell type. We briefly review relevant clinical trials and their potential clinical applications in order to find a unique solution to effectively relieve the patients' pain.

C-Terminal Residue of Ultrashort Peptides Impacts on Molecular Self-Assembly, Hydrogelation, and Interaction with Small-Molecule Drugs

Single molecular changes on a tripeptide can have dramatic effects on their self-assembly and hydrogelation. Herein, we explore C-terminal residue variation on two consistent ultrashort peptide backbones, i.e. acetylated-Leu-Ile-Val-Ala-Gly-Xaa and acetylated-Ile-Val-Xaa (Xaa = His, Arg, Asn). The objective of this study is to identify candidates that can form hydrogels for small-molecule drug (SMD) delivery. Haemolysis and cytotoxicity (with human adipose-derived mesenchymal stem cells) assays showed that the new soluble peptides (Xaa = His, Arg) are cytocompatible. Gelation studies showed that all but acetylated-Ile-Val-Arg could gel under physiological conditions. Longer peptidic backbones drive self-assembly more effectively as reflected in field emission scanning electron microscopy (FESEM) and circular dichroism spectroscopy studies. Rheological studies revealed that the resultant hydrogels have varying stiffness and yield stress, depending on the backbone and C-terminal residue. Visible spectroscopy-based elution studies with SMDs (naltrexone, methotrexate, doxorubicin) showed that besides the C-terminal residue, the shape of the SMD also determines the rate and extent of SMD elution. Based on the elution assays, infrared spectroscopy, and FESEM, we propose models for the peptide fibril-SMD interaction. Our findings highlight the importance of matching the molecular properties of the self-assembling peptide and SMD in order to achieve the desired SMD release profile.

Self-Assembling Peptide Gels for 3D Prostate Cancer Spheroid Culture

Progress in prostate cancer research is presently limited by a shortage of reliable in vitro model systems. The authors describe a novel self-assembling peptide, bQ13, which forms nanofibers and gels useful for the 3D culture of prostate cancer spheroids, with improved cytocompatibility compared to related fibrillizing peptides. The mechanical properties of bQ13 gels can be controlled by adjusting peptide concentration, with storage moduli ranging between 1 and 10 kPa. bQ13's ability to remain soluble at mildly basic pH considerably improved the viability of encapsulated cells compared to other self-assembling nanofiber-forming peptides. LNCaP cells formed spheroids in bQ13 gels with similar morphologies and sizes to those formed in Matrigel or RADA16-I. Moreover, prostate-specific antigen (PSA) is produced by LNCaP cells in all matrices, and PSA production is more responsive to enzalutamide treatment in bQ13 gels than in other fibrillized peptide gels. bQ13 represents an attractive platform for further tailoring within 3D cell culture systems.

All-trans retinoic acid can antagonize osteoblastogenesis induced by different BMPs irrespective of their dimerization types and dose-efficiencies

Introduction

Alcoholism can lead to low mineral density, compromised regenerative bone capacity and delayed osteointegration of dental implants. This may be partially attributed to the inhibitive effect of all-trans retinoic acid (ATRA), a metabolite of alcohol, on osteoblastogenesis. Our previous studies demonstrated that heterodimeric bone morphogenetic protein 2/7 (BMP2/7) was a more potent BMP than homodimeric BMP2 or BMP7, and could antagonize the inhibitive effect of ATRA to rescue osteoblastogenesis.

Materials and methods

In this study, we compared the effectiveness of BMP2/7, BMP2 and BMP7 in restoring osteoblastogenesis of murine preosteoblasts upon inhibition with 1 µM ATRA, and we further analyzed the potential mechanisms. We measured the following parameters: cell viability, ALP, OCN, mineralization, the expression of osteogenic differentiation marker genes (Collagen I, ALP and OCN) and the expression of BMP signaling key genes (Dlx5, Runx2, Osterix and Smad1).

Results

BMP2/7 treatment alone induced significantly higher osteoblastogenesis compared to BMP2 and BMP7. When cells were treated by ATRA, BMP2/7 was superior only in rescuing cell viability and ALP activity, compared to BMP2 or BMP7. However, BMP2/7 was not superior to BMP2 or BMP7 in restoring OCN expression and extracellular mineralized nodules, or in rescuing expression of two key osteogenic genes, Dlx5 and Runx2. Irrespective of their dimeric types or potency, the selected BMPs could antagonize the inhibitory effect of ATRA on osteoblastogenesis.

Conclusion

The presence of ATRA, BMP2/7 still induced significantly higher cell viability and early differentiation than the homodimers. However, ATRA significantly attenuated the advantages of BMP2/7 in inducing late and final osteoblastogenic differentiation over the homodimers.

Sustained Release of Antimicrobial Peptide from Self-Assembling Hydrogel Enhanced Osteogenesis

Biomaterials have been widely used in bone infection and osteomyelitis resulting from their versatile functionalities. As far as we know, the appearance of osteomyelitis was mainly caused by bacteria. Therefore, a biomaterial that can cure bone infection and promote osteogenesis may become an ideal candidate for the treatment of osteomyelitis. Cationic antimicrobial peptides (AMPs) have been proved to have an excellent ability to kill bacteria, fungi, viruses, and parasites. However, the application of AMPs in bone infection and osteomyelitis is quite limited. Here, we designed a new hydrogel that has an inhibitory effect on the proliferation of S. aureus and enhances osteogenesis. RADA16 self-assembling peptide has been applied for AMPs delivery. In this study, we demonstrated that RADA16 could form a stable structure and afford the sustained release of AMPs. The interwoven nanofiber morphology was detected by field emission scanning electron microscopy. The sustained release study revealed that the release of AMPs could be obtained until 28 days. In vitro research showed this new self-assembling hydrogel could promote the proliferation of bone mesenchymal stem cells (BMSCs) and inhibited the growth of S. aureus. More importantly, the results in vivo also proved that RADA16-AMP self-assembling peptide had an excellent effect on bone formation. Our findings implied that we successfully combined RADA16 and AMPs together and laid the foundation for the application of this new hydrogel and open new avenues for biomaterials.

Biomaterials Enabled Cell-Free Strategies for Endogenous Bone Regeneration

Repairing bone defects poses a major orthopedic challenge because current treatments are constrained by the limited regenerative capacity of human bone tissue. Novel therapeutic strategies, such as stem cell therapy and tissue engineering, have the potential to enhance bone healing and regeneration, and hence may improve quality of life for millions of people. However, the ex vivo expansion of stem cells and their in vivo delivery pose technical difficulties that hamper clinical translation and commercial development. A promising alternative to cell delivery-based strategies is to stimulate or augment the inherent self-repair mechanisms of the patient to promote endogenous restoration of the lost/damaged bone. There is growing evidence indicating that increasing the endogenous regenerative potency of bone tissues for therapeutics will require the design and development of new generations of biomedical devices that provide key signaling molecules to instruct cell recruitment and manipulate cell fate for in situ tissue regeneration. Currently, a broad range of biomaterial-based deployment technologies are becoming available, which allow for controlled spatial presentation of biological cues required for endogenous bone regeneration. This article aims to explore the proposed concepts and biomaterial-enabled strategies involved in the design of cell-free endogenous techniques in bone regenerative medicine.

Amphiphilic peptides as novel nanomaterials: design, self-assembly and application

Designer self-assembling peptides are a category of emerging nanobiomaterials which have been widely investigated in the past decades. In this field, amphiphilic peptides have received special attention for their simplicity in design and versatility in application. This review focuses on recent progress in designer amphiphilic peptides, trying to give a comprehensive overview about this special type of self-assembling peptides. By exploring published studies on several typical types of amphiphilic peptides in recent years, herein we discuss in detail the basic design, self-assembling behaviors and the mechanism of amphiphilic peptides, as well as how their nanostructures are affected by the peptide characteristics or environmental parameters. The applications of these peptides as potential nanomaterials for nanomedicine and nanotechnology are also summarized.

In Vitro Repair of Meniscal Radial Tear With Hydrogels Seeded With Adipose Stem Cells and TGF-β3

BACKGROUND

Radial tears of the meniscus are a common knee injury, frequently resulting in osteoarthritis. To date, there are no established, effective treatments for radial tears. Adipose-derived stem cells (ASCs) may be an attractive cell source for meniscal regeneration because they can be quickly isolated in large number and are capable of undergoing induced fibrochondrogenic differentiation mediated by transforming growth factor β3 (TGF-β3). However, the use of ASCs for meniscal repair is largely unexplored.

HYPOTHESIS

ASC-seeded hydrogels with preloaded TGF-β3 will improve meniscal healing of radial tears, as modeled in an explant model.

STUDY DESIGN

Controlled laboratory study.

METHODS

With an institutional review board-exempted protocol, human ASCs were isolated from the infrapatellar fat pads of 3 donors, obtained after total knee replacement, and characterized. ASCs were encapsulated in photocrosslinkable methacrylated gelatin hydrogels to form 3-dimensional constructs, which were placed into tissue culture. The effect of TGF-β3-whether preloaded into the hydrogel or added as a soluble medium supplement-on matrix-sulfated proteoglycan deposition in the constructs was evaluated. A meniscal explant culture model was used to simulate meniscal repair. Cylindrical-shaped explants were excised from the inner avascular region of adult bovine menisci, and a radial tear was modeled by cutting perpendicular to the meniscal main fibers to the length of the radius. Six combinations of hydrogels-namely, acellular and ASC-seeded hydrogels supplemented with preloaded TGF-β3 (2 µg/mL) or soluble TGF-β3 (10 ng/mL) and without supplement-were injected into the radial tear and stabilized by photocrosslinking with visible light. At 4 and 8 weeks of culture, healing was assessed through histology, immunofluorescence staining, and mechanical testing.

RESULTS

ASCs isolated from the 3 donors exhibited colony-forming and multilineage differentiation potential. Hydrogels preloaded with TGF-β3 and those cultured in soluble TGF-β3 showed robust matrix-sulfated proteoglycan deposition. ASC-seeded hydrogels promoted superior healing as compared with acellular hydrogels, with preloaded or soluble TGF-β3 further improving histological scores and mechanical properties.

CONCLUSION

These findings demonstrated that ASC-seeded hydrogels preloaded with TGF-β3 enhanced healing of radial meniscal tears in an in vitro meniscal repair model.

CLINICAL RELEVANCE

Injection delivery of ASCs in a TGF-β3-preloaded photocrosslinkable hydrogel represents a novel candidate strategy to repair meniscal radial tears and minimize further osteoarthritic joint degeneration.

Assembly of Gold Nanorods on HSA Amyloid Fibrils to Develop a Conductive Nanoscaffold for Potential Biomedical and Biosensing Applications

Today, Gold Nanorods have promised variety of applications in conjugation with biomolecules of interest. Discovery of functional amyloids has also been highlighted with possible use in designing high performance materials. To exploit dual properties of both Nano and Bio counterparts in new functional materials, this effort has focused on synthesis of a potential hybrid system of Gold nanorods (GNRs) and HSA amyloid fibrils to develop a conductive nanoscaffold. UV-Vis spectroscopy, Thioflavin T (ThT) assay, Far-UV Circular Dichroism (CD) spectropolarimetry, fluorescence and Transmission Electron microscopy were used to characterize formation of the nanostructures and amyloid fibrils. Surface plasmon resonance of GNRs was also monitored upon interaction with HSA amyloid fibrils, showing that the plasmonic component of the hybrid system has maintained its characteristic rod morphology without any perturbations. Analysis of Nyquist plots for the hybrid nanoscaffold showed that the electronic behavior of the hybrid system has been enhanced due to the presence of the assembled GNRs. Results of this investigation highlight the possibility of fabricating hybrid nano-bioscaffolds as promising candidates in versatile biomedical and biosensing applications.

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.

Beyond Covalent Crosslinks: Applications of Supramolecular Gels

Traditionally, gels have been defined by their covalently cross-linked polymer networks. Supramolecular gels challenge this framework by relying on non-covalent interactions for self-organization into hierarchical structures. This class of materials offers a variety of novel and exciting potential applications. This review draws together recent advances in supramolecular gels with an emphasis on their proposed uses as optoelectronic, energy, biomedical, and biological materials. Additional special topics reviewed include environmental remediation, participation in synthesis procedures, and other industrial uses. The examples presented here demonstrate unique benefits of supramolecular gels, including tunability, processability, and self-healing capability, enabling a new approach to solve engineering challenges.

Biofunctionalized peptide nanofiber-based composite scaffolds for bone regeneration

Bone tissue had moderate self-healing capabilities, but biomaterial scaffolds were required for the repair of some defects such as large bone defects. Peptide nanofiber scaffolds demonstrated important potential in regenerative medicine. Functional modification and controlled release of signal molecules were two significant approaches to increase the bioactivity of biofunctionalized peptide nanofiber scaffolds, but peptide scaffolds were limited by insufficient mechanical strength. Thus, it was necessary to combine peptide scaffolds with other materials including polymers, hydroxyapatite, demineralized bone matrix (DBM) and metal materials based on the requirement of different bone defects. As the development of peptide-based composite scaffolds continued to evolve, ultimate translation to the clinical environment may allow for improved therapeutic outcomes for bone repair.

From supramolecular polymers to multi-component biomaterials

The most striking and general property of the biological fibrous architectures in the extracellular matrix (ECM) is the strong and directional interaction between biologically active protein subunits. These fibers display rich dynamic behavior without losing their architectural integrity. The complexity of the ECM taking care of many essential properties has inspired synthetic chemists to mimic these properties in artificial one-dimensional fibrous structures with the aim to arrive at multi-component biomaterials. Due to the dynamic character required for interaction with natural tissue, supramolecular biomaterials are promising candidates for regenerative medicine. Depending on the application area, and thereby the design criteria of these multi-component fibrous biomaterials, they are used as elastomeric materials or hydrogel systems. Elastomeric materials are designed to have load bearing properties whereas hydrogels are proposed to support in vitro cell culture. Although the chemical structures and systems designed and studied today are rather simple compared to the complexity of the ECM, the first examples of these functional supramolecular biomaterials reaching the clinic have been reported. The basic concept of many of these supramolecular biomaterials is based on their ability to adapt to cell behavior as a result of dynamic non-covalent interactions. In this review, we show the translation of one-dimensional supramolecular polymers into multi-component functional biomaterials for regenerative medicine applications.

The effects of motif net charge and amphiphilicity on the self-assembly of functionally designer RADA16-I peptides

RADA16-I (Ac-(RADA)₄-CONH₂) is a widely investigated self-assembling peptide (SAP) in the biomedical field. It can undergo ordered self-assembly to form stable secondary structures, thereby further forming a nanofiber hydrogel. The modification of RADA16-I with functional peptide motifs has become a popular research topic. Researchers aim to exhibit particular biomedical signaling, and subsequently, further expand its applications. However, only a few fundamental reports are available on the influences of the peptide motifs on self-assembly mechanisms of designer functional RADA16-I SAPs. In this study, we designed RGD-modified RADA16-I SAPs with a series of net charges and amphiphilicities. The assembly/reassembly of these functionally designer SAPs was thoroughly studied using Raman spectroscopy, CD spectroscopy, and AFM. The nanofiber morphology and the secondary structure largely depended on the balance between the hydrophobic effects versus like-charge repulsions of the motifs, which should be to the focus in order to achieve a tailored nanostructure. Our study would contribute insight into considerations for sophisticated design of SAPs for biomedical applications.

Mechanical characteristics of beta sheet-forming peptide hydrogels are dependent on peptide sequence, concentration and buffer composition

Self-assembling peptide hydrogels can be modified regarding their biodegradability, their chemical and mechanical properties and their nanofibrillar structure. Thus, self-assembling peptide hydrogels might be suitable scaffolds for regenerative therapies and tissue engineering. Owing to the use of various peptide concentrations and buffer compositions, the self-assembling peptide hydrogels might be influenced regarding their mechanical characteristics. Therefore, the mechanical properties and stability of a set of self-assembling peptide hydrogels, consisting of 11 amino acids, made from four beta sheet self-assembling peptides in various peptide concentrations and buffer compositions were studied. The formed self-assembling peptide hydrogels exhibited stiffnesses ranging from 0.6 to 205 kPa. The hydrogel stiffness was mostly affected by peptide sequence followed by peptide concentration and buffer composition. All self-assembling peptide hydrogels examined provided a nanofibrillar network formation. A maximum self-assembling peptide hydrogel dissolution of 20% was observed for different buffer solutions after 7 days. The stability regarding enzymatic and bacterial digestion showed less degradation in comparison to the self-assembling peptide hydrogel dissolution rate in buffer. The tested set of self-assembling peptide hydrogels were able to form stable scaffolds and provided a broad spectrum of tissue-specific stiffnesses that are suitable for a regenerative therapy.

Branched peptides integrate into self-assembled nanostructures and enhance biomechanics of peptidic hydrogels

Self-assembling peptides (SAP) have drawn an increasing interest in the tissue engineering community. They display unquestionable biomimetic properties, tailorability and promising biocompatibility. However their use has been hampered by poor mechanical properties making them fragile soft scaffolds. To increase SAP hydrogel stiffness we introduced a novel strategy based on multiple ramifications of (LDLK)₃, a well-known linear SAP, connected with one or multiple "lysine knots". Differently branched SAPs were tested by increasing the number of (LDLK)₃-like branches and by adding the neuro-regenerative functional motif BMHP1 as a single branch. While pure branched peptides did not have appealing self-assembling propensity, when mixed with the corresponding linear SAP they increased the stiffness of the overall hydrogel of multiple times. Notably, optimal results (or peak) were obtained 1) at similar molar ratio (between linear and branched peptides) for all tested sequences and 2) for the branched SAPs featuring the highest number of branches made of (LDLK)₃. The functional motif BMHP1, as expected, seemed not to contribute to the increase of the storage modulus as efficiently as (LDLK)₃. Interestingly, branched SAPs improved the β-sheet self-arrangement of (LDLK)₃ and allowed for the formation of assembled nanofibers. Indeed in coarse-grained molecular dynamics we showed they readily integrate in the assembled aggregates providing "molecular connections" among otherwise weakly paired β-structures. Lastly, branched SAPs did not affect the usual response of human neural stem cells cultured on (LDLK)₃-like scaffolds in vitro. Hence, branched SAPs may be a valuable new tool to enhance mechanical properties of self-assembling peptide biomaterials harmlessly; as neither chemical nor enzymatic cross-linking reactions are involved. As a consequence, branched SAPs may enlarge the field of application of SAPs in tissue engineering and beyond.

STATEMENT OF SIGNIFICANCE

Self-assembling peptides stand at the forefront of regenerative medicine because they feature biomimetic nano-architectures that mimic the complexity of natural peptide-based extracellular matrices of living tissues. Their superior biocompatibility and ease of scale-up production are hampered by weak mechanical properties due to transient non-covalent interactions among and within the self-assembled peptide chains, thus limiting their potential applications. We introduced new branched self-assembling peptides to be used as "molecular connectors" among self-assembled nanostructures made of linear SAPs. Branched SAPs could be mixed with linear SAPs before self-assembling in order to have them intermingled with different β-sheets of linear SAPs after gelation. This strategy caused a manifold increase of the stiffness of the assembled hydrogels (proportional to the number of self-assembling branches), did not affect SAP propensity to form β-sheet but, instead, further stimulated their secondary structure rearrangements. It is now possible to modularly improve SAP scaffold mechanical properties without using harmful chemical reactions. Therefore, branched SAPs represent an additional tool to be adopted for efficient and harmless SAP scaffold customization in tissue engineering.

A new embolic liquid agent comprised of amino acid

Transcatheter arterial or venous embolization has been widely used to address solid tumors by occluding the tumor-feeding vessels. It is also performed to treat portosystemic shunts and to stop bleeding by repair of the site of trauma. Commonly used embolic materials are gelatin sponges, coils, beads, and liquid agents such as absolute ethanol, histoacyryl, and onyx. In the field of interventional radiology, embolotherapy is performed routinely. Liquid embolization agents have different characteristics. Their coagulation time, the inflammatory reaction of the vascular wall or surrounding tissue, and their adhesion to the vascular wall vary. PuraMatrix, a liquid embolic agent not yet available for clinical use, is comprised of amino acid. We introduce and discuss preliminary experimental studies to examine its potential for use in humans.

Discovery and design of self-assembling peptides

Peptides are ubiquitous in nature and useful in many fields, from agriculture as pesticides, in medicine as antibacterial and antifungal drugs founded in the innate immune systems, to medicinal chemistry as hormones. However, the concept of peptides as materials was not recognized until 1990 when a self-assembling peptide as a repeating segment in a yeast protein was serendipitously discovered. Peptide materials are so called because they have bona fide materials property and are made from simple amino acids with well-ordered nanostructures under physiological conditions. These structures include well-ordered nanofibres, nanotubes and nanovesicles. These peptide materials have been used for: (i) three-dimensional tissue cell cultures of primary cells and stem cells, (ii) three-dimensional tissue printing, (iii) sustained releases of small molecules, growth factors, monoclonal antibody and siRNA, (iv) accelerated wound healing in reparative and regenerative medicine as well as tissue engineering, (v) used to stabilize membrane proteins including difficult G-protein coupled receptors and photosystem I for designing nanobiodevices, (vi) a few self-assembling peptides have been used in human clinical trials for accelerated wound healings in surgical uses and (vii) in human clinical trials for siRNA delivery for treatment of cancers. It is likely that these self-assembling peptides will open doors for more and more diverse uses. The field of self-assembling peptides is growing in a number of directions in areas of materials, synthetic biology, and clinical medicine and beyond.