Peptide Gel Research Articles

Peptide-Based Low Molecular Weight Photosensitive Supramolecular Gelators.

Over the last couple of decades, stimuli-responsive supramolecular gels comprising synthetic short peptides as building blocks have been explored for various biological and material applications. Though a wide range of stimuli has been tested depending on the structure of the peptides, light as a stimulus has attracted extensive attention due to its non-invasive, non-contaminant, and remotely controllable nature, precise spatial and temporal resolution, and wavelength tunability. The integration of molecular photo-switch and low-molecular-weight synthetic peptides may thus provide access to supramolecular self-assembled systems, notably supramolecular gels, which may be used to create dynamic, light-responsive “smart” materials with a variety of structures and functions. This short review summarizes the recent advancement in the area of light-sensitive peptide gelation. At first, a glimpse of commonly used molecular photo-switches is given, followed by a detailed description of their incorporation into peptide sequences to design light-responsive peptide gels and the mechanism of their action. Finally, the challenges and future perspectives for developing next-generation photo-responsive gels and materials are outlined.

The effect of antimicrobial peptide gel RISE-AP12 on decreasing neutrophil and enhancing macrophage in nicotine-periodontitis Wistar rat model

Background: Periodontitis, an inflammation that causes alveolar bone destruction, is caused by bacteria and aggravated by nicotine exposure and is therefore a disease that many smokers have. Antibacterial agents are essential for the rejuvenation process in periodontitis treatment; antimicrobial peptide (AMP) gel is a broad-spectrum antibacterial agent that is hardly cause bacteria resistance. Purpose: The objective of this study is to determine the effect of AMP gel administration on neutrophil and macrophage counts on periodontitis regeneration in nicotine-exposed rats. Methods: 24 Wistar rats were separated into four groups: nicotineexposed, non-nicotine-exposed, treatment and control. Rats with periodontitis were given AMP in the gingival line on days 1, 3 and 7 after having their mandibular central incisors ligated for 14 days to induce periodontitis. After AMP treatment, two groups of rats were collected randomly. Each group were decapitated, followed by treatment and histological examination with hematoxylin-eosin staining in the pathology laboratory to view neutrophils and macrophages. The asymmetric Kruskal Wallis test was used to analyse the data. Results: In mice treated with AMP, neutrophil counts on day 3 were lower than in distilled water (Aquadest) controls. The number of macrophages on day 3 was higher than that of the Aquadest control. Kruskal Wallis test results for neutrophils were p = 0.017 and for macrophages p = 0.01, where both test results had p < 0.05, there were significant differences between the neutrophil and macrophage groups. Conclusion: The administration of AMP effects on decreasing the number of neutrophils and enhancing macrophages in the periodontitis regeneration. in nicotine-exposed rats.

Mediating Oxidation of Thioethers with Iodine-A Mild and Versatile Pathway to Trigger the Formation of Peptide Hydrogels.

The development of redox‐triggerable peptide hydrogels poses fundamental challenges, since the highly specific peptide architectures required inevitably limit the versatility of such materials. A powerful, yet rarely applied approach to bypass those barriers is the application of a mediating redox reaction to gradually decrease the pH during hydrogel formation. We report a versatile strategy to trigger the formation of peptide hydrogels from readily accessible acid‐triggerable gelators by generating protons by oxidation of thioethers with triiodide. Adding thiodiglycol as a readily available thioether auxiliary to the basic precursor solution of a peptide gelator efficiently yielded hydrogels after mixing with triiodide, as studied in detail for Nap‐FF and demonstrated for other peptides. Furthermore, incorporation of the thioether moiety in the gelator backbone via the amino acid methionine, as shown for the tailormade Nap‐FMDM peptide, reduces the number of required additives.

Cooperative Metal Ion Coordination to the Short Self-Assembling Peptide Promotes Hydrogelation and Cellular Proliferation.

Noncovalent interactions among short peptides and proteins lead to their molecular self-assembly into supramolecular packaging, which provides the fundamental basis of life. These biomolecular assemblies are highly susceptible to the environmental conditions, including temperature, light, pH, and ionic concentration, and thus inspiring the fabrication of a new class of stimuli-responsive biomaterials. Here, for the first time the cooperative effect of the divalent metal ions to promote hydrogelation in the short collagen inspired self-assembling peptide for developing advanced biomaterials is reported. Introduction of the biologically relevant metal ions (Ca2+ /Mg2+ ) to the peptide surpasses its limitation to self-assemble into a multiscale structure at physiological pH. In particular, in presence of metal ions, the negatively charged peptide shows a distinct shift in its equilibrium point of gelation and demonstrates conversion from sol to gel and thus enabling the scope of fabricating an advanced biomaterial for controlling cellular behavior. Interestingly, tunable mechanical strength and improved cellular response are observed within ion-coordinated peptide hydrogels compared to the peptide gelator. Microscopic analyses, rheological assessment, and biological studies establish the importance of utilizing a novel strategy by simply using metal ions to modulate the physical and biological attributes of collagen inspired peptide (CIPs) to construct next-generation biomaterials.

NGIWY-Amide: A Bioinspired Ultrashort Self-Assembled Peptide Gelator for Local Drug Delivery Applications.

Fibrillar structures derived from plant or animal origin have long been a source of inspiration for the design of new biomaterials. The Asn-Gly-Ile-Trp-Tyr-NH2 (NGIWY-amide) pentapeptide, isolated from the sea cucumber Apostichopus japonicus, which spontaneously self-assembles in water to form hydrogel, pertains to this category. In this study, we evaluated this ultra-short cosmetic bioinspired peptide as vector for local drug delivery applications. Combining nuclear magnetic resonance, circular dichroism, infrared spectroscopy, X-ray diffraction, and rheological studies, the synthesized pentapeptide formed a stiff hydrogel with a high β-sheet content. Molecular dynamic simulations aligned well with scanning electron and atomic-force microscopy studies, revealing a highly filamentous structure with the fibers adopting a helical-twisted morphology. Model dye localization within the supramolecular hydrogel provided insights on the preferential distribution of hydrophobic and hydrophilic compounds in the hydrogel network. That was further depicted in the diffusion kinetics of drugs differing in their aqueous solubility and molecular weight, namely, doxorubicin hydrochloride, curcumin, and octreotide acetate, highlighting its versatility as a delivery vector of both hydrophobic and hydrophilic compounds of different molecular weight. Along with the observed cytocompatibility of the hydrogel, the NGIWY-amide pentapeptide may offer new approaches for cell growth, drug delivery, and 3D bioprinting tissue-engineering applications.

Self-assembled di- and tripeptide gels for the passive entrapment and pH-responsive, sustained release of an antidiabetic drug, glimepiride.

Diabetes is a global epidemic that poses a severe challenge to public health. The characteristic features of this disease are hyperglycemia and deterioration of the function of pancreatic β-cells, which leads to oxidative stress and organ damage. Glimepiride is used to treat type II diabetes but is associated with side effects, like lower half-life, faster elimination, and hypoglycemia. Self-assembled peptide gels have drawn attention as a drug delivery depot because of their biocompatibility, diverse design, tunable functionality, and dynamic self-assembly properties. In order to overcome the challenge of oxidative stress and side effects associated with the use of glimepiride, we have developed glimepiride-loaded, self-assembled peptide gels from di- and tripeptides employing amino acids with inherent antioxidant properties. Dipeptides, Fmoc-Tyr-Tyr-NH2 (YY) and Fmoc-Trp-Trp-NH2 (WW), and a tripeptide, Fmoc-Trp-Trp-His-NH2 (WWH), were developed and self-assembled into gels. The gels exhibited excellent viscoelastic properties and self-healing abilities, and the presence of β-sheet secondary structures. The dipeptide gels provided a sustained drug release but more drug was released at physiological pH (7.4) than acidic pH (5 and 6), whereas the tripeptide gel released more drug at acidic pH. The gels showed free radical scavenging activities of more than 90% and were able to decrease the amount of oxidative stress caused by the ROS in HepG2 cells. They were non-toxic to the cell line tested and HepG2 cells treated with the releasate of tripeptide gels showed enhanced glucose uptake. This work for the first time reports the development of glimepiride-loaded self-assembled peptide gels, which can serve as a dynamic, multidimensional biomaterial to reduce oxidative stress, hypoglycemia, and repetitive dosing of drugs in diabetic patients by controlling glimepiride release.

Self-assembling peptide gels promote angiogenesis and functional recovery after spinal cord injury in rats

Spinal cord injury (SCI) leads to disruption of the blood–spinal cord barrier, hemorrhage, and tissue edema, which impair blood circulation and induce ischemia. Angiogenesis after SCI is an important step in the repair of damaged tissues, and the extent of angiogenesis strongly correlates with the neural regeneration. Various biomaterials have been developed to promote angiogenesis signaling pathways, and angiogenic self-assembling peptides are useful for producing diverse supramolecular structures with tunable functionality. RADA16 (Ac-RARADADARARADADA-NH2), which forms nanofiber networks under physiological conditions, is a self-assembling peptide that can provide mechanical support for tissue regeneration and reportedly has diverse roles in wound healing. In this study, we applied an injectable form of RADA16 with or without the neuropeptide substance P to the contused spinal cords of rats and examined angiogenesis within the damaged spinal cord and subsequent functional improvement. Histological and immunohistochemical analyses revealed that the inflammatory cell population in the lesion cavity was decreased, the vessel number and density around the damaged spinal cord were increased, and the levels of neurofilaments within the lesion cavity were increased in SCI rats that received RADA16 and RADA16 with substance P (rats in the RADA16/SP group). Moreover, real-time PCR analysis of damaged spinal cord tissues showed that IL-10 expression was increased and that locomotor function (as assessed by the Basso, Beattie, and Bresnahan (BBB) scale and the horizontal ladder test) was significantly improved in the RADA16/SP group compared to the control group. Our findings indicate that RADA16 modified with substance P effectively stimulates angiogenesis within the damaged spinal cord and is a candidate agent for promoting functional recovery post-SCI.

Antimicrobial and Bioactive Silk Peptide Hybrid Hydrogel with a Heterogeneous Double Network Formed by Orthogonal Assembly.

Hydrogels mimic the natural extracellular matrix in terms of their nanofibrous structure and large water content. However, the lack of a combination of properties including sufficient heterogeneity in the gel structure, intrinsic antimicrobial activity, and bioactivity limits the efficiency of hydrogels for tissue engineering applications. In this work, a hydrogel with a combination of these properties was fabricated by hybridizing silk fibroin with a low-molecular-weight peptide gelator. It was observed that silk fibroin and the peptide gelator assembled orthogonally in sequence. While the morphology of silk fibroin nanofibrils was not affected by the peptide gelator, silk fibroin promoted the formation of wider nanoribbons of the peptide gelator by modulating its nucleation and growth. Orthogonal assembly maintained the antimicrobial activity of the peptide gelator and the excellent biocompatibility of silk fibroin in the hybrid gel. The hybrid gel also demonstrated improved interactions with cells, an indicator of a higher bioactivity, possibly due to the heterogeneous double network structure.

Biostimulation of Bacteria in Liquid Culture for Identification of New Antimicrobial Compounds.

We hypothesized that environmental microbiomes contain a wide range of bacteria that produce yet uncharacterized antimicrobial compounds (AMCs) that can potentially be used to control pathogens. Over 600 bacterial strains were isolated from soil and food compost samples, and 68 biocontrol bacteria with antimicrobial activity were chosen for further studies based on inhibition assays against a wide range of food and plant pathogens. For further characterization of the bioactive compounds, a new method was established that used living pathogens in a liquid culture to stimulate bacteria to produce high amounts of AMCs in bacterial supernatants. A peptide gel electrophoresis microbial inhibition assay was used to concurrently achieve size separation of the antimicrobial peptides. Fifteen potential bioactive peptides were then further characterized by tandem MS, revealing cold-shock proteins and 50S ribosomal proteins. To identify non-peptidic AMCs, bacterial supernatants were analyzed by HPLC followed by GC/MS. Among the 14 identified bioactive compounds, 3-isobutylhexahydropyrrolo[1,2-a]pyrazine-1,4-dione and 2-acetyl-3-methyl-octahydropyrrolo[1,2-a]piperazine-1,4-dione were identified as new AMCs. Our work suggests that antimicrobial compound production in microbes is enhanced when faced with a threat from other microorganisms, and that this approach can rapidly lead to the development of new antimicrobials with the potential for upscaling.

Topical Application of Temperature-Sensitive Gel Containing Caerin 1.1 and 1.9 Peptides on TC-1 Tumour-Bearing Mice Induced High-Level Immune Response in the Tumour Microenvironment

The development of topical cream drugs that increase the immune activation of tumour-infiltrating lymphocytes against tumour and chronic viral infection-associated lesions is of great immunotherapeutic significance. This study demonstrates that the topical application of a temperature-sensitive gel containing caerin 1.1 and 1.9 peptides reduces nearly 50% of the tumour weight of HPV16 E6/E7-transformed TC-1 tumour-bearing mice via improving the tumour microenvironment. Confocal microscopy confirms the time-dependent penetration of caerin 1.9 through the epidermal layer of the ear skin structure of mice. Single-cell transcriptomic analysis shows that the caerin 1.1/1.9 gel expands the populations with high immune activation level and largely stimulates the pro-inflammatory activity of NK and dendritic cells. Closely associated with INFα response, Cebpb seems to play a key role in altering the function of all Arg1hi macrophages in the caerin group. In addition, the caerin gel treatment recruits almost two-fold more activated CD8+ T cells to the TME, relative to the untreated tumour, which shows a synergistic effect derived from the regulation of S1pr1, Ccr7, Ms4a4b and Gimap family expression. The TMT10plex-labelling proteomic quantification further demonstrates the activation of interferon-alpha/beta secretion and response to cytokine stimulus by the caerin gel, while the protein contents of several key regulators were elevated by more than 30%, such as Cd5l, Gzma, Ifit1, Irf9 and Stat1. Computational integration of the proteome with the single-cell transcriptome consistently suggested greater activation of NK and T cells with the topical application of caerin peptide gel.

Peptide hydrogels for affinity-controlled release of therapeutic cargo: Current and potential strategies.

The development of devices for the precise and controlled delivery of therapeutics has grown rapidly over the last few decades. Drug delivery materials must provide a depot with delivery profiles that satisfy pharmacodynamic and pharmacokinetic requirements resulting in clinical benefit. Therapeutic efficacy can be limited due to short half-life and poor stability. Thus, to compensate for this, frequent administration and high doses are often required to achieve therapeutic effect, which in turn increases potential side effects and systemic toxicity. This can potentially be mitigated by using materials that can deliver drugs at controlled rates, and material design principles that allow this are continuously evolving. Affinity-based release strategies incorporate a myriad of reversible interactions into a gel network, which have affinities for the therapeutic of interest. Reversible binding to the gel network impacts the release profile of the drug. Such affinity-based interactions can be modulated to control the release profile to meet pharmacokinetic benchmarks. Much work has been done developing affinity-based control in the context of polymer-based materials. However, this strategy has not been widely implemented in peptide-based hydrogels. Herein, we present recent advances in the use of affinity-controlled peptide gel release systems and their associated mechanisms for applications in drug delivery.

Novel self-assembling peptide hydrogel with pH-tunable assembly microstructure, gel mechanics and the entrapment of curcumin

Insight is provided into the mechanism of peptide gelation, a self-assembled process of particular interest, due to its wide existence in natural events and broad applications in food and biomaterials field, but hard to control as minor alterations in the peptide sequence. Here, we design a family of pentapeptides and control their self-assembly behaviors, from micro- and nanoparticles to nanofibers and hydrogels. Furthermore, based on the thermodynamics, the gelation kinetics and the ionization status of terminal groups, the peptide assembly goes through five stages as varying the pH value and the assembly structures are highly dependent on the charging status of the terminal groups. The gelation rules of these peptides are further investigated. Besides, we also load hydrophobic functional molecule (curcumin) into different self-assembly nanostructures with high encapsulation efficiency and remarkable thermal and light protection on curcumin. These peptides assemblies with tunable structures, encapsulation ability and photothermal stabilization could become promising candidates for hydrophobic function factor delivery in food industry.

Self-Assembling Peptide Gels Promote Angiogenesis and Functional Recovery after Spinal Cord Injury in Rats

Spinal cord injury (SCI) leads to disruption of the blood-spinal cord barrier, hemorrhage and tissue edema, which impair blood circulation and induce ischemia. Angiogenesis after SCI is an important step in the repair of damaged tissues, and its extent strongly correlates with neural regeneration. Various biomaterials have been developed to promote angiogenesis signaling pathways, and angiogenic self-assembling peptides are useful for producing diverse supramolecular structures with tunable functionality. RADA16 (Ac-RARADADARARADADA-NH2), which forms nanofiber networks under physiological conditions, is a self-assembling peptide that can provide mechanical support for tissue regeneration and reportedly has diverse roles in wound healing. In this study, we applied an injectable form of RADA16 with or without a neuropeptide, substance P, to the contused spinal cord in rats and examined angiogenesis within the damaged spinal cord and subsequent functional improvement. Histological and immunohistochemical analyses revealed that the inflammatory cell population in the lesion cavity was decreased, whereas the vessel number and density around the damaged spinal cord were increased, and neurofilaments within the lesion cavity were increased in SCI rats that received RADA16 and RADA16 with substance P (RADA16/SP group). Moreover, real-time PCR of the damaged spinal cord showed that IL-10 expression was increased, and locomotor function (assessed by the Basso, Beattie, and Bresnahan (BBB) scale and the horizontal ladder test) was significantly improved in the RADA16/SP group compared to the control. Our findings indicate that RADA16 with substance P effectively stimulates angiogenesis within the damaged spinal cord and is a possible candidate for post-SCI functional recovery. Funding: This work was supported by the National Research Foundation (NRF) and the Ministry of Science and ICT (MSIT) (2019R1A6A1A11034536, 2020R1A2C2004764); the Korea Medical Device Development Fund grant funded by the Korean government (the Ministry of Science and ICT; the Ministry of Trade, Industry and Energy; the Ministry of Health & Welfare; the Ministry of Food and Drug Safety) (202017D01); the Ministry of Trade, Industry and Energy (MOTIE) (20008686); and the KU-KIST Graduate School of Converging Science and Technology Program, Republic of Korea. Declaration of Interests: The authors declare no conflicts of interest. Ethics Approval Statement: All animal experiments were approved by the Institutional Animal Care and Use Committee of Dankook University (Approval No. 19-010).

Stimuli-responsive biphenyl-tripeptide supramolecular hydrogels as biomimetic extracellular matrix scaffolds for cartilage tissue engineering

Supramolecular hydrogel composed of aromatic short peptide gelator was an attractive biomaterial owing to its simple and convenient synthetic route, nano-fibrillar microstructure resembling natural collagen fibers and intelligent response to external stimulus. Herein, stimuli-responsive biphenyl-tripeptide supramolecular hydrogels was prepared to simulate extracellular matrix scaffolds by temperature switch, ion induction and pH switch. The amino acid arrangement substantially affected gelation behavior, only BPAA-βAFF and BPAA-FFβA could form nanostructured supramolecular hydrogels with 8-10 nm nanotubes or nanofibers by potential intermolecular hydrogen bond interactions and π-π stacking. The minimum gelation concentration (MGC) and maximum storage modulus were 0.4 mM (0.023 wt%) and around 8.2 KPa. The two supramolecular hydrogels could support adhesion and proliferation of L929 cells. Moreover, the BPAA-βAFF hydrogel promoted proliferation and ECM secretion of chondrocytes in vitro, and facilitate the phenotype maintenance of hyaline cartilage. All the results demonstrated that BPAA-βAFF hydrogel hold great potential application prospects in cartilage tissue engineering. Statement of SignificanceDiphenylalanine was served as a core segment conjugating with 4-biphenylacetic acid (BPAA) to produce biphenyl-tripeptide compounds with transforming amino sequence, and multiple external stimuli was applied to study the gelation properties of the aromatic short peptide gelators. “FF” brick (phenylalanine-phenylalanine) was crucial for formation of fibrous supramolecular hydrogels. Meanwhile, the sequence of amino acids arrangement also had an essential effect on the gelation behavior. Optimal BPAA-βAFF with ultra-low minimum gelation concentration (0.4 mM, about 0.023 wt%) and similar microstructure to extracellular matrix (ECM) of nature cartilage tissue could promote the proliferation and ECM secretion of chondrocytes in vitro, and facilitate the formation of hyaline cartilage.

Construction of self-assembled nanogel as mulitenzyme mimics for bioresponsive tandem-catalysis imaging

The self-assembled phospholipid- or cytosol-associated multienzyme complexes constitute necessary components of the foundation of life. As a proof of concept, metal-coordinated supramolecular nanogels (MCSGs) have been designed, with the self-assembly of di-lysine coordinated iron (Fe(Lys)2)-functionalized peptide gelators on the interface by an in situ amidation-induced protonation process. The monoatomic and highly dispersed active centers of Fe(Lys)2 offered the nanogel mimics with excellent reaction rates due to the high density and nano compartmental structure similar to the natural matrix-associated multienzyme complex. SiO2@MCSGs show both superoxide dismutase (SOD) activity and peroxidase (POD) activity, and the higher activities compared with the activity of free Fe(Lys)2 molecules can be detected. After loading the substrate 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS), SiO2@MCSGsABTS can responsively convert O2− · in the tumor microenvironment into H2O2 intermediates and then tandem catalyzed the oxidization of ABTS for contrast photoacoustic (PA) imaging of tumor by the SOD-POD mimic activity, showing their great potential as the efficient enzymatic agents for pathological theranostics.

Short Peptides as Tunable, Switchable, and Strong Gelators.

This Perspective outlines our current understanding of molecular gels composed of short and ultrashort peptides over the past 20 years. We discuss in detail the state of the art regarding self-assembly mechanisms, structure, thermal stability, and kinetics of fibril and/or network formation. Emphasis is put on the importance of the combined use of spectroscopy and rheology for characterizing and validating self-assembly models. While a range of peptide chemistries are reviewed, we focus our discussion on a unique new class of ultrashort peptide gelators, denoted GxG peptides (x: guest residue), which are capable of forming self-assembled fibril networks. The storage moduli of GxG gels are tunable up to 100 kPa depending on concentration, pH, and/or cosolvent. The sheet structures of the fibrils differ from canonical β-sheets. When appropriate, each section highlights opportunities for additional research and technologies that would further our understanding.

PuraStat in gastrointestinal bleeding: results of a prospective multicentre observational pilot study

BackgroundA recently developed haemostatic peptide gel for endoscopic application has been introduced to improve the management of gastrointestinal bleeding. The aim of this pilot study was to evaluate the feasibility, safety, efficacy and indication profiles of PuraStat in a clinical setting.MethodsIn this prospective observational multicentre pilot study, patients with acute non-variceal gastrointestinal bleeding (upper and lower) were included. Primary and secondary application of PuraStat was evaluated. Haemoglobin, prothrombin time, platelets and transfusion behaviour were documented before and after haemostasis. The efficacy of PuraStat was assessed during the procedure, at 3 days and 1 week after application.Results111 patients with acute gastrointestinal bleeding were recruited into the study. 70 percent (78/111) of the patients had upper gastrointestinal bleeding and 30% (33/111) had lower gastrointestinal bleeding. After primary application of PuraStat, initial haemostatic success was achieved in 94% of patients (74/79, 95% CI 88–99%), and in 75% of the patients when used as a secondary haemostatic product, following failure of established techniques (24/32, 95% CI 59–91%). The therapeutic success rates (absence of rebleeding) after 3 and 7 days were 91% and 87% after primary use, and 87% and 81% in all study patients. Overall rebleeding rate at 30 day follow-up was 16% (18/111). In the 5 patients who finally required surgery (4.5%), PuraStat allowed temporary haemostasis and stabilisation.ConclusionsPuraStat expanded the therapeutic toolbox available for an effective treatment of gastrointestinal bleeding sources. It could be safely applied and administered without complications as a primary or secondary therapy. PuraStat may additionally serve as a bridge to surgery in order to achieve temporary haemostasis in case of refractory severe bleeding, possibly playing a role in preventing immediate emergency surgery.

Occurrence of Peptide-Peptide Interactions during the Purification of Self-Assembling Peptide f1-8 from a β-Lactoglobulin Tryptic Hydrolysate.

Self-assembling peptides have gained attention because of their nanotechnological applications. Previous work demonstrated that the self-assembling peptide f1-8 (Pf1-8) that is generated from the tryptic hydrolysis of β-lactoglobulin can form a hydrogel after several purification steps, including membrane filtration and consecutive washes. This study evaluates the impact of each processing step on peptide profile, purity, and gelation capacity of each fraction to understand the purification process of Pf1-8 and the peptide-peptide interactions involved. We showed that peptide-peptide interactions mainly occurred through electrostatic and hydrophobic interactions, influencing the fraction compositions. Indeed, the purity of Pf1-8 did not correlate with the number of wash steps. In addition to Pf1-8, two other hydrophobic peptides were identified, peptide f15-20, and peptide f41-60. The gelation observed could be induced either through peptide-peptide interactions or through self-assembling, both being driven by non-covalent bond and more specifically hydrophobic interactions.

Dopamine Self-Polymerization as a Simple and Powerful Tool to Modulate the Viscoelastic Mechanical Properties of Peptide-Based Gels.

Dopamine is a small versatile molecule used for various biotechnological and biomedical applications. This neurotransmitter, in addition to its biological role, can undergo oxidative self-polymerization to yield polydopamine, a robust universal coating material. Herein, we harness dopamine self-polymerization to modulate the viscoelastic mechanical properties of peptide-based gels, expanding their ever-growing application potential. By combining rapid peptide assembly with slower dopamine auto-polymerization, a double network gel is formed, where the fibrillar peptide gel network serves as a scaffold for polydopamine deposition, allowing polydopamine to interpenetrate the gel network as well as establishing crosslinks within the matrix. We have shown that triggering the assembly of a lysine-rich peptide gelator in the presence of dopamine can increase the mechanical rigidity of the resultant gel by a factor of 90 in some cases, while retaining the gel’s shear thin-recovery behavior. We further investigate how factors such as polymerization time, dopamine concentration and peptide concentration alter the mechanical properties of the resultant gel. The hybrid peptide–dopamine gel systems were characterized using rheological measurements, circular dichroism spectroscopy and transmission electron microscopy. Overall, triggering peptide gelation in the presence of dopamine represents a simple yet powerful approach to modulate the viscoelastic mechanical properties of peptide-based gels.

Serum Protein Adsorption Modulates the Toxicity of Highly Positively Charged Hydrogel Surfaces.

Hydrogels formed from peptide self-assembly are a class of materials that are being explored for their utility in tissue engineering, drug and cell delivery, two- and three-dimensional cell culture, and as adjuvants in surgical procedures. Most self-assembled peptide gels can be syringe-injected in vivo to facilitate the local delivery of payloads, including cells, directly to the targeted tissue. Herein, we report that highly positively charged peptide gels are inherently toxic to cells, which would seem to limit their utility. However, adding media containing fetal bovine serum, a common culture supplement, directly transforms these toxic gels into cytocompatible materials capable of sustaining cell viability even in the absence of added nutrients. Multistage mass spectrometry showed that at least 40 serum proteins can absorb to a gel's surface through electrostatic attraction ameliorating its toxicity. Further, cell-based studies employing model gels having only bovine serum albumin, fetuin-A, or vitronectin absorbed to the gel surface showed that single protein additives can also be effective depending on the identity of the cell line. Separate studies employing these model gels showed that the mechanism(s) responsible for mitigating apoptosis involve both the pacification of gel surface charge and adsorbed protein-mediated cell signaling events that activate both the PI3/Akt and MAPK/ERK pathways which are known to facilitate resistance to stress-induced apoptosis and overall cell survival.