pH as a trigger of peptide beta-sheet self-assembly and reversible switching between nematic and isotropic phases

Localized self-assembly of macroscopically structured supramolecular hydrogels through reaction-diffusion

Localized molecular self-assembly has been developed as an effective approach for the fabrication of spatially resolved supramolecular hydrogels, showing great potential for many high-tech applications. However, the fabrication of macroscopically structured supramolecular hydrogels through molecular self-assembly remains a challenge. Herein, we report on localized self-assembly of low molecular weight hydrogelators through a simple reaction-diffusion approach, giving rise to various macroscopically patterned supramolecular hydrogels. This is achieved on the basis of an acid-catalyzed hydrazone supramolecular hydrogelator system. The acid was pre-loaded in a polydimethylsiloxane (PDMS) substrate, generating a proton gradient in the vicinity of the PDMS surface after immersing the PDMS in the aqueous solution of the hydrogelator precursors. The acid dramatically accelerates the in situ formation and self-assembly of the hydrazone hydrogelators, leading to localized formation of supramolecular hydrogels. The growth rate of the supramolecular hydrogels can be easily tuned through controlling the concentrations of the hydrogelator precursors and HCl. Importantly, differently shaped supramolecular hydrogel objects can be obtained by simply changing the shapes of PDMS. This work suggests that reaction-diffusion-mediated localized hydrogelation can serve as an approach towards macroscopically structuralized supramolecular hydrogels, which may find potential applications ranging from tissue engineering to biosensors.

Biomimetic Remineralization of Artificial Caries Lesions with a Calcium Coacervate, Its Components and Self-Assembling Peptide P11-4 In Vitro

The application of calcium coacervates (CCs) may hold promise for dental hard tissue remineralization. The aim of this study was to evaluate the effect of the infiltration of artificial enamel lesions with a CC and its single components including polyacrylic acid (PAA) compared to that of the self-assembling peptide P11-4 in a pH-cycling (pHC) model. Enamel specimens were prepared from bovine incisors, partly varnished, and stored in demineralizing solution (DS; pH 4.95; 17 d) to create two enamel lesions per sample. The specimens were randomly allocated to six groups (n = 15). While one lesion per specimen served as the no-treatment control (NTC), another lesion (treatment, T) was etched (H3PO4, 5 s), air-dried and subsequently infiltrated for 10 min with either a CC (10 mg/mL PAA, 50 mM CaCl2 (Ca) and 1 M K2HPO4 (PO4)) (groups CC and CC + DS) or its components PAA, Ca or PO4. As a commercial control, the self-assembling peptide P11-4 (CurodontTM Repair, Credentis, Switzerland) was tested. The specimens were cut perpendicularly to the lesions, with half serving as the baseline (BL) while the other half was exposed to either a demineralization solution for 20 d (pH 4.95; group CC + DS) or pHC for 28 d (pH 4.95, 3 h; pH 7, 21 h; all five of the other groups). The difference in integrated mineral loss between the lesions at BL and after the DS or pHC, respectively, was analyzed using transversal microradiography (ΔΔZ = ΔZpHC - ΔZbaseline). Compared to the NTC, the mineral gain in the T group was significantly higher in the CC + DS, CC and PAA (p < 0.05, Wilcoxon). In all of the other groups, no significant differences between treated and untreated lesions were detected (p > 0.05). Infiltration with the CC and PAA resulted in a consistent mineral gain throughout the lesion body. The CC as well as its component PAA alone promoted the remineralization of artificial caries lesions in the tested pHC model. Infiltration with PAA further resulted in mineral gain in deeper areas of the lesion body.

DRGD-linked charged EKKE dimeric dodecapeptide: pH-based amyloid nanostructures and their application in lead and uranium binding

Peptides have been reported to undergo self-assembly into diverse nanostructures, influenced by several parameters, including their amino acid sequence, pH, charge, solvent, and temperature. Inspired by natural systems, researchers have developed biomimetic peptides capable of self-assembling into supramolecular functional structures. The present study explored a newly designed peptide sequence, EKKEDRGDEKKE, where E = glutamic acid, K = lysine, D = aspartic acid, G = glycine, and R = arginine, with a metal binding DRGD sequence incorporated between the exclusively charged EKKE peptide. We investigated the formation and the potential of the EKKEDRGDEKKE peptide in retaining the structure and morphology adopted by the individual EKKE peptide. According to a combination of experimental techniques such as thioflavin T fluorescence, field emission-scanning electron microscopy, atomic force microscopy, and circular dichroism, it was evident that the EKKEDRGDEKKE peptide displayed a pH-dependent propensity to adopt amyloid-like structures. Furthermore, the self-assembled entities formed under acidic, basic, and neutral conditions exhibited morphological variations, which resembled that observed for the exclusively charged EKKE peptide. Furthermore, the incorporation of the functional DRGD motif resulted in promising binding to two toxic metal ions, lead (Pb) and uranium (U), as evidenced by a range of spectroscopic techniques, including UV-visible spectroscopy, atomic absorption spectroscopy, fluorescence spectroscopy, and X-ray photoelectron spectroscopy. The use of the amyloid-forming EKKEDRGDEKKE scaffold can also be extended to potential biomedical applications.

Coiled-coil scallops (Chlamys farreri) peptide hydrogel with metal ionic and temperature tunable assembly

Self-assembly of peptides is a powerful method of preparing nanostructured materials. Peptides frequently utilize charged groups as a convenient switch for controlling assembly state by pH, ionic strength or temperature. In this study, the molecular properties and gel-forming ability of Chlamys farreri protein hydrolysates were studied. According to self-assembled theory, the presence of isoleucine at position 'a' and leucine at 'd' causes a switch between coiled-coil structures. Compared to P-2-CG, the components of α-helix (23.60 ± 0.56%) were changed into β-sheet (4.83 ± 2.86%) in the secondary structure of the hydrogel induced by ZnCl2. NMR siginals appeared at high field,which indicated hydrogen bonds were formed between P-2-CG and solvent environments at 20 °C. With temperature going up, the hydrogen bonds were broken and nanofibrils were changed into dense aggregates. We expected that P-2-CG could provide a new candidate for preparing metal-induced nanofibers or hydrogels with further applications in food industry.

Thermo-reversible self-assembled novel gellan gum hydrogels containing amino acid biogelators with antibacterial activity

In recent years, hydrogels derived from natural polymers have gained considerable attention. However, lack of mechanical strength and poor stability has become major lacuna of such systems. Scientists have attempted to resolve this problem by introducing chemical cross-linkers or synthetic modifications of natural polymers. In contrast, biological cross-linkers may be more beneficial due to their cytocompatibility and non-immunogenicity. As a biogelator, amino acids (AA) may be lucrative, yet they remain untapped till date. Present study, for the first time, reports exploitation of ʟ-Lysine, ʟ-Arginine, ʟ-Aspartic acid, and ʟ-Glutamic acid as biogelator to fabricate novel gellan gum (GG) hydrogels through green chemistry. Furthermore, as a first instance, molecular docking was applied to gain insight into the interaction between GG and AA. As predicted through docking, physical cross-linking of these hydrogels accounted for their thermo-reversibility. Moreover, to assess the suitability of prepared hydrogel for its intended use, systematic characterization studies were performed via FTIR, Raman spectroscopy, XRD, FE-SEM, and TGA. Additionally, rheological behavior of hydrogels was investigated using variety of parameters. Interestingly, GG-AA hydrogels exhibited around 99 % antibacterial activity against multidrug-resistant bacteria. According to the findings of this study, these novel hydrogels may have immense potential in the food and biomedical sectors.

Side-Chain Chemistry Governs Hierarchical Order of Charge-Complementary β-sheet Peptide Coassemblies

Self-assembly of proteinaceous biomolecules into functional materials with ordered structures that span length scales is common in nature yet remains a challenge with designer peptides under ambient conditions. This report demonstrates how charged side-chain chemistry affects the hierarchical co-assembly of a family of charge-complementary β-sheet-forming peptide pairs known as CATCH(X+/Y-) at physiologic pH and ionic strength in water. In a concentration-dependent manner, the CATCH(6K+) (Ac-KQKFKFKFKQK-Am) and CATCH(6D-) (Ac-DQDFDFDFDQD-Am) pair formed either β-sheet-rich microspheres or β-sheet-rich gels with a micron-scale plate-like morphology, which were not observed with other CATCH(X+/Y-) pairs. This hierarchical order was disrupted by replacing D with E, which increased fibril twisting. Replacing K with R, or mutating the N- and C-terminal amino acids in CATCH(6K+) and CATCH(6D-) to Qs, increased observed co-assembly kinetics, which also disrupted hierarchical order. Due to the ambient assembly conditions, active CATCH(6K+)-green fluorescent protein fusions could be incorporated into the β-sheet plates and microspheres formed by the CATCH(6K+/6D-) pair, demonstrating the potential to endow functionality.

Research progress of biomimetic materials in oral medicine

Biomimetic materials are able to mimic the structure and functional properties of native tissues especially natural oral tissues. They have attracted growing attention for their potential to achieve configurable and functional reconstruction in oral medicine. Though tremendous progress has been made regarding biomimetic materials, significant challenges still remain in terms of controversy on the mechanism of tooth tissue regeneration, lack of options for manufacturing such materials and insufficiency of in vivo experimental tests in related fields. In this review, the biomimetic materials used in oral medicine are summarized systematically, including tooth defect, tooth loss, periodontal diseases and maxillofacial bone defect. Various theoretical foundations of biomimetic materials research are reviewed, introducing the current and pertinent results. The benefits and limitations of these materials are summed up at the same time. Finally, challenges and potential of this field are discussed. This review provides the framework and support for further research in addition to giving a generally novel and fundamental basis for the utilization of biomimetic materials in the future.

Hierarchical assembly of tryptophan zipper peptides into stress-relaxing bioactive hydrogels

Soft materials in nature are formed through reversible supramolecular assembly of biological polymers into dynamic hierarchical networks. Rational design has led to self-assembling peptides with structural similarities to natural materials. However, recreating the dynamic functional properties inherent to natural systems remains challenging. Here we report the discovery of a short peptide based on the tryptophan zipper (trpzip) motif, that shows multiscale hierarchical ordering that leads to emergent dynamic properties. Trpzip hydrogels are antimicrobial and self-healing, with tunable viscoelasticity and unique yield-stress properties that allow immediate harvest of embedded cells through a flick of the wrist. This characteristic makes Trpzip hydrogels amenable to syringe extrusion, which we demonstrate with examples of cell delivery and bioprinting. Trpzip hydrogels display innate bioactivity, allowing propagation of human intestinal organoids with apical-basal polarization. Considering these extensive attributes, we anticipate the Trpzip motif will prove a versatile building block for supramolecular assembly of soft materials for biotechnology and medicine.

Self-assembling peptides for managing white spot lesions: a systematic review and meta-analysis

PURPOSE

The primary objective of the review was to assess the effectiveness of self-assembling P11-4 peptide (SAP) with or without any fluoride agents (FA) in remineralization of the White spot lesions (WSLs)/incipient carious lesions (ICLs) compared to other enamel remineralizing agents/non-intervention/placebo.

METHODS

Human RCTs published during the period from 1st January 2000-30th June 2021 were searched in the electronic bibliographic databases and scanning reference lists of articles from PubMed, Google Scholar, and The Cochrane Central Register of Controlled Trials. The Risk-of-Bias was assessed using version 2 of the Cochrane risk-of-bias tool for randomized trials (RoB 2) tool for all included studies. The statistical heterogeneity between studies was assessed by the Cochrane Q test and I2 test. A random-effects model was used considering the variations in true effects size between the included studies. The quality of the evidence for remineralizing effectiveness of SAP/SAP + FA was done using the GRADEpro GDT software which employs GRADE.

RESULTS

Four out of eight included trials were assessed to have "high risk" of bias. Mean difference for Laser fluorescence outcome assessment method (SAP v/s FA) was - 4.89 (95% CI: - 17.35 to 7.57; p = 0. 44; I2 = 89%). The combined risk ratio observed through Nyvad criteria (SAP v/s FA) was 0.12 (95% CI: 0.01-1.59; p = 0.11; I2 = 71%). Mean difference for Laser fluorescence outcome assessment method (SAP + FA v/s FA) was - 11.52 (95% CI: - 14.43 to - 8.61; p =  < 0.001;I2 = 0%). The combined risk ratio for ICDAS outcome assessment method (SAP + FA v/s FA) was 0.27 (95% CI: 0.03-2.84; p = 0.15; I2 = 53%).

CONCLUSION

Considering the results observed from the included trials we are uncertain whether SAP/SAP + FA increases/decreases the remineralizing/regeneration of WSLs/ICLs.

Self-assembling peptide and nano-silver fluoride in remineralizing early enamel carious lesions: randomized controlled clinical trial

BACKGROUND

Nanoparticles and regenerative biomineralization are new caries prevention technologies. This study assessed the remineralizing effect of self-assembling peptide (P11-4), Nanosilver Fluoride (NSF) and sodium fluoride (NaF) on white spot lesions (WSLs) in permanent teeth.

METHODS

Sixty six young adults with WSLs on buccal surfaces in permanent teeth and ICDAS code 1 or 2, were randomly assigned to one of three groups; P11-4, NSF or NaF. Assessment of ICDAS scores, lesion activity (Nyvad scores) and diagnodent readings of lesions were done at baseline and after 1, 3, 6 and 12 months of agents' application. Comparisons between groups were made using chi squared test and comparison within groups were made using McNemar test. Multilevel binary logistic regression was used to assess the effect of agents on change of ICDAS scores after 3, 6 and 12 months (reduction versus no reduction).

RESULTS

There were 147 teeth in 66 patients; mean ± SD age = 13.46 ± 4.31 years. There were significant differences in the change of ICDAS scores among the three groups after 3 and 6 months (p = 0.005). The reduction in ICDAS score increased steadily in all groups across time with the greatest increase in the P11-4 group: 54.5% after 12 months. Lesion activity (Nyvad scores) showed significant differences among the three groups with the greatest percentage of inactive cases in the P11-4 group. Multilevel binary logistic regression showed non-significant reduction of ICDAS in P11-4 and NSF varnishes compared to NaF varnish (AOR = 2.56, 95% CI: 0.58, 8.77 and AOR = 2.12, 95% CI: 0.59, 7.64 respectively).

CONCLUSION

P11-4 and NSF varnish reduced the ICDAS scores, caries activity and diagnodent readings of WSLs in permanent teeth. However, the change in ICDAS scores was not significantly different from NaF.

TRIAL REGISTRATION

This trial was prospectively registered on the clinicaltrials.gov registry with ID: NCT04929509 on 18/6/2021.

Self-assembled peptide P11-4 interacts with the type I collagen C-terminal telopeptide domain and calcium ions

OBJECTIVES

Evaluate molecularly the role of P11-4 self-assembly peptide in dentin remineralization and its interaction with collagen I.

METHODS

The calcium-responsive P11-4 peptide was analyzed by intrinsic fluorescence emission spectrum, circular dichroism spectrum (CD), and atomic force microscope (AFM). Differential light scattering was used to monitor the nucleation growth rate of calcium phosphate nanocrystals in the absence or in the presence of P11-4. AFM was used to analyze the radial size (nm) of calcium phosphate nanocrystals formed in the absence or in the presence of P11-4, as well as to verify the spatial structure of P11-4 in the absence or in the presence of Ca2+.

RESULTS

The interaction of Ca2+ with the P11-4 (KD = 0.58 ± 0.06 mM) promotes the formation of β-sheet antiparallel structure, leads to its precipitation in saturated solutions of Ca/P = 1.67 and induces the formation of parallel large fibrils (0.6 - 1.5 µm). P11-4 organized the HAP nucleation by reducing both the growth rate and size variability of nanocrystals, analyzed by the F test (p < 0.0001, N = 30). P11-4 interacts (KD = 0.75 ± 0.06 μM) with the KGHRGFSGL motif present at the C-terminal collagen telopeptide domain. P11-4 also increased the amount of HAP and collagen in the MDPC-23 cells.

SIGNIFICANCE

The presented data propose a mechanism that will help future clinical and/or basic research to better understand a molecule able to inhibit structural collagen loss and help the impaired tissue to remineralize.

The Self Assembling peptide P11-4 influences viability and osteogenic differentiation of stem cells of the apical papilla (SCAP)

OBJECTIVE

to analyze the effect of P₁₁-4 self-assembly peptide on cell viability and osteogenic capacity of SCAPs through mineral deposition and gene expression of osteogenic markers. .

METHODS

SCAPs were seeded in contact with P₁₁-4 (10 µg/ml, 100 µg/ml and 1 mg/ml) solution. Cell viability was evaluated using a colorimetric assay MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) in an experimental time of 24, 48 and 72 h (n=7). Mineral deposition and quantification provided by the cells was tested using the Alizarin Red staining and Cetylpyridinium Chloride (CPC), respectively, after 30 days (n=4). Gene expression of Runt-related transcription factor 2 (RUNX2), Alkaline phosphatase (ALP) and Osteocalcin (OCN) was quantified using quantitative polymerase chain reaction (RT-qPCR), at 3 and 7 days with Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as the housekeeping gene, and relative gene expression was measured using the ΔΔCq method. Data were analyzed using Kruskall-Wallis followed by multiple comparisons, and T-test for gene expression with α=0.05.

RESULTS

All tested concentrations (10 µg/ml, 100 µg/ml and 1 mg/ml) were not cytotoxic at time 24 and 48 h. After 72 h, a slight decrease in cell viability was observed for the lowest concentration (10 µg/ml). The concentration of 100 µg/ml P11-4 showed the highest mineral deposition. However, qPCR analysis of P11-4 (10 µg/ml) showed upregulation of RUNX2 and OCN at 3 days, with downregulation of ALP at 3 and 7d.

CONCLUSION

P11-4 did not affect cell viability, induced mineral deposition in SCAPs, and upregulated the expression of RUNX2 and OCN genes at 3 days, while downregulating ALP expression at 3 and 7 days.

CLINICAL SIGNIFICANCE

Based on the results obtained in this study it can be stated that self-assembling peptide P11-4 is a potential candidate to induce mineralization on dental stem cells for regenerative purposes and also for a clinical use as a capping agent without compromising the cells health.

Molecularly Stimuli-Responsive Self-Assembled Peptide Nanoparticles for Targeted Imaging and Therapy

Self-assembly has emerged as an extensively used method for constructing biomaterials with sizes ranging from nanometers to micrometers. Peptides have been extensively investigated for self-assembly. They are widely applied owing to their desirable biocompatibility, biodegradability, and tunable architecture. The development of peptide-based nanoparticles often requires complex synthetic processes involving chemical modification and supramolecular self-assembly. Stimuli-responsive peptide nanoparticles, also termed "smart" nanoparticles, capable of conformational and chemical changes in response to stimuli, have emerged as a class of promising materials. These smart nanoparticles find a diverse range of biomedical applications, including drug delivery, diagnostics, and biosensors. Stimuli-responsive systems include external stimuli (such as light, temperature, ultrasound, and magnetic fields) and internal stimuli (such as pH, redox environment, salt concentration, and biomarkers), facilitating the generation of a library of self-assembled biomaterials for biomedical imaging and therapy. Thus, in this review, we mainly focus on peptide-based nanoparticles built by self-assembly strategy and systematically discuss their mechanisms in response to various stimuli. Furthermore, we summarize the diverse range of biomedical applications of peptide-based nanomaterials, including diagnosis and therapy, to demonstrate their potential for medical translation.

A Facile and Versatile Approach to Construct Photoactivated Peptide Hydrogels by Regulating Electrostatic Repulsion

Short peptides that can respond to external stimuli have been considered as the preferred building blocks to construct hydrogels for biomedical applications. In particular, photoresponsive peptides that are capable of triggering the formation of hydrogels upon light irradiation allow the properties of hydrogels to be changed remotely by precise and localized actuation. Here, we used the photochemical reaction of the 2-nitrobenzyl ester group (NB) to develop a facile and versatile strategy for constructing photoactivated peptide hydrogels. The peptides with high aggregation propensity were designed as hydrogelators, which were photocaged by a positively charged dipeptide (KK) to provide strong charge repulsion and prevent self-assembly in water. Light irradiation led to the removal of KK and triggered the self-assembly of peptides and the formation of hydrogel. Light stimulation endows spatial and temporal control, which enables the formation of hydrogel with precisely tunable structure and mechanical properties. Cell culture and behavior study indicated that the optimized photoactivated hydrogel was suitable for 2D and 3D cell culture, and its photocontrollable mechanical strength could regulate the spreading of stem cells on its surface. Therefore, our strategy provides an alternative way to construct photoactivated peptide hydrogels with wide applications in biomedical areas.

Insight into the development of versatile dentin bonding agents to increase the durability of the bonding interface

Despite the huge improvements made in adhesive technology over the past 50 years, there are still some unresolved issues regarding the durability of the adhesive interface. A complete sealing of the interface between the resin and the dentin substrate remains difficult to achieve, and it is doubtful whether an optimal interdiffusion of the adhesive system within the demineralized collagen framework can be produced in a complete and homogeneous way. In fact, it is suggested that hydrolytic degradation, combined with the action of dentin matrix enzymes, destabilizes the tooth-adhesive bond and disrupts the unprotected collagen fibrils. While a sufficient resin–dentin adhesion is usually achieved immediately, bonding efficiency declines over time. Thus, here, a review will be carried out through a bibliographic survey of scientific articles published in the last few years to present strategies that have been proposed to improve and/or develop new adhesive systems that can help prevent degradation at the adhesive interface. It will specially focus on new clinical techniques or new materials with characteristics that contribute to increasing the durability of adhesive restorations and avoiding the recurrent replacement restorative cycle and the consequent increase in damage to the tooth.

pH-feedback systems to program autonomous self-assembly and material lifecycles

pH-responsive systems have gained importance for the development of smart materials and for biomedical applications because they can switch between different states by simple acid/base triggers. However, such equilibrium systems lack the autonomous behaviour that is so ubiquitous in living systems that self-regulate out of equilibrium. As a contribution to the emerging field of autonomous chemical systems, we have developed pH-feedback systems (pH-FS) based on the coupling of acid- and base-producing steps in chemical reaction networks. The resulting autonomous nonlinear pH curves can be coupled with a variety of pH-sensitive building blocks to program the lifecycles of the associated transient state at the level of self-assemblies and material systems. In this article, we discuss the different generations of such pH-feedback systems, the principles of their coupling to self-assemblies with lifecycles and highlight emerging concepts for the design of autonomous functional materials. The specificity, robustness, and flexible operation of such pH-FS can also be used to realize chemo-structural and chemo-mechanical feedbacks that extend the behaviour of such materials systems toward complex and functional life-like systems.

Fabrication of silk sericin-anthocyanin nanocoating for chelating and saturation-visualization detection of metal ions

Silk sericin (SS) is a natural water-soluble protein with the potential to chelate metal ions via its polar groups. However, the difficulty of identifying the saturation of SS limits its application as filter films. One solution is to construct SS filter films with an indicator to reflect the degree of saturation of silk sericin. Hence, the nanocoating consisting of co-assembled SS protein and anthocyanin (C3G) nanoparticles is designed, constructed, and characterized to chelate metal ions with a saturation-visualization detection behavior. Here, metal ions Zn²⁺ and Al³⁺ are chosen as models to explore the chelating ability of SS and indicator behaviors of C3G, which could indicate the saturation degree of SS. Interestingly, after the saturation of SS in the solution and filter film situations, the visible color progressively shifts from pink to blue (Zn²⁺) or violet (Al³⁺), with the corresponding redshift of UV-Vis absorbance of C3G. Remarkable removal effectiveness of Zn²⁺ and Al³⁺, namely 93.16% and 53.97%, as well as an evident saturation-visualization detection, were identified by filter paper films with the nanocoating. Our research provides a fresh viewpoint for designing SS filter films that could effectively remove metal ions while enabling real-time viewing.

Self-assembling peptide-laden electrospun scaffolds for guided mineralized tissue regeneration

OBJECTIVES

Electrospun scaffolds are a versatile biomaterial platform to mimic fibrillar structure of native tissues extracellular matrix, and facilitate the incorporation of biomolecules for regenerative therapies. Self-assembling peptide P11-4 has emerged as a promising strategy to induce mineralization; however, P11-4 application has been mostly addressed for early caries lesions repair on dental enamel. Here, to investigate P11-4's efficacy on bone regeneration, polymeric electrospun scaffolds were developed, and then distinct concentrations of P11-4 were physically adsorbed on the scaffolds.

METHODS

P11-4-laden and pristine (P11-4-free) electrospun scaffolds were immersed in simulated body fluid and mineral precipitation identified by SEM. Functional groups and crystalline phases were analyzed by FTIR and XRD, respectively. Cytocompatibility, mineralization, and gene expression assays were conducted using stem cells from human exfoliated deciduous teeth. To investigate P11-4-laden scaffolds potential to induce in vivo mineralization, an established rat calvaria critical-size defect model was used.

RESULTS

We successfully synthesized nanofibrous (∼ 500 nm fiber diameter) scaffolds and observed that functionalization with P11-4 did not affect the fibers' diameter. SEM images indicated mineral precipitation, while FTIR and XRD confirmed apatite-like formation and crystallization for P11-4-laden scaffolds. In addition, P11-4-laden scaffolds were cytocompatible, highly stimulated cell-mediated mineral deposition, and upregulated the expression of mineralization-related genes compared to pristine scaffolds. P11-4-laden scaffolds led to enhanced in vivo bone regeneration after 8 weeks compared to pristine PCL.

SIGNIFICANCE

Electrospun scaffolds functionalized with P11-4 are a promising strategy for inducing mineralized tissues regeneration in the craniomaxillofacial complex.

The influence of component structural arrangement on peptide vaccine immunogenicity

Peptide-based subunit vaccines utilise minimal immunogenic components (i.e. peptides) to generate highly specific immune responses, without triggering adverse reactions. However, strong adjuvants and/or effective delivery systems must be incorporated into such vaccines, as peptide antigens cannot induce substantial immune responses on their own. Unfortunately, many adjuvants are too weak or too toxic to be used in combination with peptide antigens. These shortcomings have been addressed by the conjugation of peptide antigens with lipidic/ hydrophobic adjuvanting moieties. The conjugates have shown promising safety profiles and improved immunogenicity without the help of traditional adjuvants and have been efficient in inducing desired immune responses following various routes of administration, including subcutaneous, oral and intranasal. However, not only conjugation per se, but also component arrangement influences vaccine efficacy. This review highlights the importance of influence of the vaccine chemical structure modification on the immune responses generated. It discusses a variety of factors that affect the immunogenicity of peptide conjugates, including: i) self-adjuvanting moiety length and number; ii) the orientation of epitopes and self-adjuvanting moieties in the conjugate; iii) the presence of spacers between conjugated components; iv) multiepitopic arrangement; and v) the effect of chirality on vaccine efficacy.

Effect of a Self-Assembly Peptide on Surface Roughness and Hardness of Bleached Enamel

After bleaching, enamel surfaces are damaged, contributing to erosion and tooth sensitivity. Although fluoride is used after bleaching to try and revert alterations, it is not capable of repairing tooth structure. This study compared the effect of a self-assembly peptide (P11-4), with and without fluoride, and sodium fluoride (NaF 2%) on the Knoop microhardness (KHN) and surface roughness (Ra (μm)) of bleached enamel with an in-office bleaching regimen. Enamel blocks of bovine teeth (5 × 5 × 2 mm) with standardized surface hardness were bleached with 35% carbamide peroxide, following the manufacturer’s instructions. The teeth were randomly divided into the following groups (n = 7) according to post-bleaching treatment: no treatment (negative control) (C-); 2% NaF (NaF); Curodont™ Repair (Repair); and Curodont™ Protect (Protect). Specimens were stored in artificial saliva at 37 °C. To evaluate the effect of the post-bleaching treatments, KHN and Ra were measured before bleaching (baseline) and 24 h and 7 days after bleaching. Data were submitted to repeated measures ANOVA and Bonferroni tests (α = 0.05). There were significant interactions between the study factors (p = 0.001). After 7 days, Repair (572.50 ± 79.04) and Protect (583.00 ± 74.76) specimens showed increased surface KHN, with values higher than the NaF (465.50 ± 41.50) and C- (475.22 ± 58.95) baseline values. There was no significant difference in KHN at 24 h among groups (p = 0.587). At 24 h after bleaching, Repair was significantly different from all groups (p < 0.05). Repair showed the lowest Ra (μm) values (0.133 ± 0.035). After seven days, there was no significant difference in Ra values among groups when compared to the baseline. The use of P11-4-based materials after bleaching resulted in the fastest recovery to baseline enamel properties.

pH- and concentration-dependent supramolecular assembly of a fungal defensin plectasin variant into helical non-amyloid fibrils

Self-assembly and fibril formation play important roles in protein behaviour. Amyloid fibril formation is well-studied due to its role in neurodegenerative diseases and characterized by refolding of the protein into predominantly β-sheet form. However, much less is known about the assembly of proteins into other types of supramolecular structures. Using cryo-electron microscopy at a resolution of 1.97 Å, we show that a triple-mutant of the anti-microbial peptide plectasin, PPI42, assembles into helical non-amyloid fibrils. The in vitro anti-microbial activity was determined and shown to be enhanced compared to the wildtype. Plectasin contains a cysteine-stabilised α-helix-β-sheet structure, which remains intact upon fibril formation. Two protofilaments form a right-handed protein fibril. The fibril formation is reversible and follows sigmoidal kinetics with a pH- and concentration dependent equilibrium between soluble monomer and protein fibril. This high-resolution structure reveals that α/β proteins can natively assemble into fibrils.

Here the authors report the cryo-EM structure of a triple-mutant of the anti-microbial peptide plectasin, PPI42, assembling in a pH- and concentration dependent manner into helical non-amyloid fibrils. The fibrils formation is reversible, and follows a sigmoidal kinetics. The fibrils adopt a right-handed helical superstructure composed by two protofilaments, stabilized by an outer hydrophobic ring and an inner hydrophobic centre. These findings reveal that α/β proteins can natively assemble into fibrils.

Self-assembly peptide P11-4 induces mineralization and cell-migration of odontoblast-like cells

OBJECTIVES

Self-assembling peptide P11-4 is amphiphilic and pH-triggered, effective on repairing early enamel carious lesions and dentin remineralization. However, P11-4 effects on dentin biomineralization and repair ability remain unexplored. Thus, cytocompatibility and effectiveness of P11-4 on inducing mineralization and migration of odontoblast-like cells (MDPC-23) were investigated.

METHODS

MDPC-23 were seeded in contact with P11-4 (0.5 and 1 µg/ml), Dentin Matrix Protein 1 (DMP1 0.5 and 1 µg/ml) or Calcium hydroxide (Ca(OH)2 100 µg/ml) solutions. Cell viability was verified using MTT (n = 6/group). Mineral deposition was tested using Alizarin Red (n = 4/group). Cell migration was assessed by light microscopy (n = 2/group). MTT and Alizarin Red data were compared using Kruskal-Wallis and Mann-Whitney (α=0.01).

RESULTS

P11-4 (0.5 and 1 µg/ml) and DMP1 (0.5 and 1 µg/ml) resulted the highest cell viability; Ca(OH)2 presented the lowest. 1 µg/ml DMP1 and 1 µg/ml P11-4 promoted the highest mineral deposition. Ca(OH)2 presented lower values of mineral deposits than DMP1 1 µg/ml (p < 0.01), but similar to P11-4 1 µg/ml. P11-4 and DMP1 at 0.5 µg/ml induced lesser mineral precipitation than P11-4 and DMP1 at 1 µg/ml (p < 0.01), with no difference to Ca(OH)2. All materials stimulated cell migration, however, lower concentrations of DMP1 and P11-4 demonstrated a higher migration potential.

CONCLUSION

P11-4 did not affect cell viability, induces mineral deposition and MDPC-23 migration like DMP1.

CLINICAL SIGNIFICANCE

Self-assembling peptide P11-4 does not affect the cell viability and induces mineral deposition comparable to native protein involved in biomineralization. Combined with its ability to bind type I collagen, P11-4 is a promising bioinspired molecule that provides native-tissue conditions and foster further studies on its ability to form dentin bridges in pulp-capping strategies.

Acidic and basic self-assembling peptide and peptide-graphene oxide hydrogels: characterisation and effect on encapsulated nucleus pulposus cells

Extracellular pH can have a profound effect on cell metabolism, gene and protein expression. Nucleus pulposus (NP) cells, for example, under acidic conditions accelerate the production of degradative enzymes and pro-inflammatory cytokines, leading ultimately to intervertebral disc degeneration, a major cause of back pain. Self-assembling peptide hydrogels constitute a well-established class of biomaterials that could be exploited as pH-tunable platform to investigate cell behaviour under normal and non-physiological pH. In this paper we formulated acidic (pH = 4) and basic (pH = 9) hydrogels, from the same octapeptide FEFKFEFK (F8) (F = phenyalanine, E = glutamic acid, K = lysine), to test the effect of non-physiological pH on encapsulated NP cells. Similarly, graphene oxide-containing F8 hydrogels (GO-F8) were formulated as stiffer analogues. Acidic and basic hydrogels showed peculiar morphologies and rheological properties, with all systems able to buffer within 30 minutes of exposure to cell culture media. NP cells seeded in acidic F8 hydrogels showed a more catabolic phenotype compared to basic hydrogels, with increased gene expression of degradative enzymes (MMP-3, ADAMTS-4), neurotrophic factors (NGF and BDNF) and NF-κB p65 phosphorylation. Acidic GO-F8 hydrogels also induced a catabolic response, although milder than basic counterparts and with the highest gene expression of characteristic NP-matrix components, aggrecan and collagen II. In all systems, the cellular response had a peak within 3 days of encapsulation, thereafter decreasing over 7 days, suggesting a 'transitory' effect of hydrogel pH on encapsulated cells. This work gives an insight on the effect of pH (and pH buffering) on encapsulated NP cells and offers new designs of low and high pH peptide hydrogels for 3D cell culture studies. STATEMENT OF SIGNIFICANCE: We have recently shown the potential of graphene oxide - self-assembling peptide hybrid hydrogels for NP cell culture and regeneration. Alongside cell carrier, self-assembling peptide hydrogels actually provide a versatile pH-tunable platform for biological studies. In this work we decided to explore the effect of non-physiological pH (and pH buffering) on encapsulated NP cells. Our approach allows the formulation of both acidic and basic hydrogels, starting from the same peptide sequence. We showed that the initial pH of the scaffold does not affect significantly cell response to encapsulation, but the presence of GO results in lower inflammatory levels and higher NP matrix protein production. This platform could be exploited to study the effect of pH on different cell types whose behaviour can be pH-dependent.

Adhesion and whitening efficacy of P11-4 self-assembling peptide and HAP suspension after using NaOCl as a pre-treatment agent

Background

This study evaluated the adhesion and whitening efficacy of a mixture of hydroxyapatite and P11-4 self-assembling peptide (HAP-peptide) on bovine enamel after pre-treatment with low-concentrated sodium hypochlorite (NaOCl).

Methods

Fifty-two caries-free bovine incisors were selected. 50 teeth were randomly allocated to five groups (n = 10). The first group was treated with a mixture of 6.25 wt% HAP and 5 ml P11-4 peptide, using NaOCl 3% as pre-treatment. Second, third and fourth groups were treated with 6.25 wt% HAP, 5 ml P11-4 peptide, and NaOCl 3%, respectively. In the fifth group, only water was applied (control group). The color of samples was measured using a spectrophotometer (USB4000-VIS-NIR-ES, Ostfildern, Germany). To evaluate color changes, ΔE values were statistically analyzed. Finally, adherence of HAP particles on two enamel surfaces with and without pre-treatment with NaOCl was analyzed with SEM.

Results

It was observed that the ΔE of the HAP-peptide suspension after pre-treatment with NaOCl was significantly stronger than the control group. In contrast, the overall color changes of separate applications of HAP, peptide, and NaOCl did not differ notably from the control group. SEM observations confirmed that pre-treatment with NaOCl resulted in a more pronounced coverage of HAP on the enamel surface.

Conclusions

Pre-treatment with a low-concentrated NaOCl enhanced the adherence of the HAP layer on the enamel surface, resulting in a stronger whitening effect.

Trial registration

The peptide-HAP suspension is effective in improving tooth whiteness.

Effectiveness of Self-Assembling Peptide (P11-4) in Dental Hard Tissue Conditions: A Comprehensive Review

The limitations on the use of fluoride therapy in dental caries prevention has necessitated the development of newer preventive agents. This review focusses on the recent and significant studies on P11-4 peptide with an emphasis on different applications in dental hard tissue conditions. The self-assembling peptide P11-4 diffuses into the subsurface lesion assembles into aggregates throughout the lesion, supporting the nucleation of de novo hydroxyapatite nanocrystals, resulting in increased mineral density. P11-4 treated teeth shows more remarkable changes in the lesion area between the first and second weeks. The biomimetic remineralisation facilitated in conjunction with fluoride application is an effective and non-invasive treatment for early carious lesions. Despite, some studies have reported that the P11-4 group had the least amount of remineralised enamel microhardness and a significantly lower mean calcium/phosphate weight percentage ratio than the others. In addition, when compared to a low-viscosity resin, self-assembling peptides could neither inhibit nor mask the lesions significantly. Moreover, when it is combined with other agents, better results can be achieved, allowing more effective biomimetic remineralisation. Other applications discussed include treatment of dental erosion, tooth whitening and dentinal caries. However, the evidence on its true clinical potential in varied dental diseases still remains under-explored, which calls for future cohort studies on its in vivo efficacy.

Efficacy and safety of P11-4 for the treatment of periodontal defects in dogs

Objectives

This study’s aim was to investigate the safety and performance of a self-assembling peptide matrix (SAPM) P₁₁-4 for the treatment of periodontal disease in a controlled pre-clinical study.

Materials and methods

Acute buccal bony dehiscence defects (LxW: 5 × 3 mm) were surgically created on the distal root of four teeth on one mandible side of 7 beagle dogs followed by another identical surgery 8 weeks later on the contralateral side. SAPM P₁₁-4 (with and without root conditioning with 24% EDTA (T1, T2)), Emdogain® (C) and a sham intervention (S) were randomly applied on the four defects at each time point. Four weeks after the second surgery and treatment, the animals were sacrificed, the mandibles measured by micro-computed tomography (µ-CT) and sections of the tissue were stained and evaluated histologically.

Results

Clinically and histologically, no safety concerns or pathological issues due to the treatments were observed in any of the study groups at any time point. All groups showed overall similar results after 4 and 12 weeks of healing regarding new cementum, functionality of newly formed periodontal ligament and recovery of height and volume of the new alveolar bone and mineral density.

Conclusion

A controlled clinical study in humans should be performed in a next step as no adverse effects or safety issues, which might affect clinical usage of the product, were observed.

Clinical relevance

The synthetic SAPM P₁₁-4 may offer an alternative to the animal-derived product Emdogain® in the future.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00784-021-04297-6.

S-Benzyl Cysteine Based Cyclic Dipeptide Super Hydrogelator: Enhancing Efficacy of an Anticancer Drug via Sustainable Release

Peptide based low molecular weight supramolecular hydrogels hold promising aspects in various fields of application especially in biomaterial and biomedical sciences such as drug delivery, wound healing, tissue engineering, cell proliferation, etc due to their extreme biocompatibility. Unlike linear peptides, cyclic peptides have more structural rigidity and tolerance to enzymatic degradation and high environmental stability which make them even better candidates for the above said applications. Herein, a new small cyclic dipeptide (CDP) cyclo-(Leu-S-Bzl-Cys) (P1) consisting of L-leucine and S-benzyl protected L-cysteine was reported which formed hydrogel at physiological conditions (at 37^o C and pH=7.46). The hydrogel formed from the cyclic dipeptide P1 showed very good tolerance towards environmental parameters such as pH, temperature and was seen to be stable for more than a year without any deformation. The hydrogel was thermoreversible and stable in the pH range 6-12. Mechanical strength of P1 hydrogel was measured by rheology experiment. AFM and FE-SEM images revealed that in aqueous solvents P1 self-assembled into a highly cross-linked nanofibrillar network which immobilized water molecules inside the cages and formed the hydrogel. The self-assembled cyclic dipeptide acquired antiparallel β-sheet secondary structure which was evident from CD and FT-IR studies. The β-sheet arrangement and formation of amyloid fibrils were further established by ThT binding assay. Furthermore, P1 was able to form hydrogel in presence of anticancer drug 5-fluorouracil (5FU) and sustainable release of the drug from the hydrogel was measured in-vitro. The hydrogelator P1 showed almost no cytotoxicity towards human colorectal cancer cell line HCT116 up to a considerable high concentration and showed potential application in sustainable drug delivery. The co-assembly of 5FU and P1 hydrogel exhibited much better anticancer activity towards HCT116 cancer cell line than 5-fluorouracil alone and decreased the IC₅₀ dose of 5-fluorouracil to a much lower value.

Engineering β-Sheet Peptide Coassemblies for Biomaterial Applications

Peptide coassembly, wherein at least two different peptides interact to form multicomponent nanostructures, is an attractive approach for generating functional biomaterials. Current efforts seek to design pairs of peptides, A and B, that form nanostructures (e.g., β-sheets with ABABA-type β-strand patterning) while resisting self-assembly (e.g., AAAAA-type or BBBBB-type β-sheets). To confer coassembly behavior, most existing designs have been based on highly charged variants of known self-assembling peptides; like-charge repulsion limits self-assembly while opposite-charge attraction promotes coassembly. Recent analyses using solid-state NMR and coarse-grained simulations reveal that preconceived notions of structure and molecular organization are not always correct. This perspective highlights recent advances and key challenges to understanding and controlling peptide coassembly.

Advances in biomineralization-inspired materials for hard tissue repair

Biomineralization is the process by which organisms form mineralized tissues with hierarchical structures and excellent properties, including the bones and teeth in vertebrates. The underlying mechanisms and pathways of biomineralization provide inspiration for designing and constructing materials to repair hard tissues. In particular, the formation processes of minerals can be partly replicated by utilizing bioinspired artificial materials to mimic the functions of biomolecules or stabilize intermediate mineral phases involved in biomineralization. Here, we review recent advances in biomineralization-inspired materials developed for hard tissue repair. Biomineralization-inspired materials are categorized into different types based on their specific applications, which include bone repair, dentin remineralization, and enamel remineralization. Finally, the advantages and limitations of these materials are summarized, and several perspectives on future directions are discussed.

Factors Affecting Secondary and Supramolecular Structures of Self-Assembling Peptide Nanocarriers

Self-assembling peptides are a popular vector for therapeutic cargo delivery due to their versatility, tunability, and biocompatibility. Accurately predicting secondary and supramolecular structures of self-assembling peptides is essential for de novo peptide design. However, computational modeling of such assemblies is not yet able to accurately predict structure formation for many peptide sequences. This review identifies patterns in literature between secondary and supramolecular structures, primary sequences, and applications to provide a guide for informed peptide design. An overview of peptide structures, their applications as nanocarriers, and analytical methods for characterizing secondary and supramolecular structure is examined. A top-down approach is then used to identify trends between peptide sequence and assembly structure from the current literature, including an analysis of the drivers at work, such as local and nonlocal sequence effects and solution conditions.

Mechanism of Amyloid Gel Formation by Several Short Amyloidogenic Peptides

Under certain conditions, many proteins/peptides are capable of self-assembly into various supramolecular formations: fibrils, films, amyloid gels. Such formations can be associated with pathological phenomena, for example, with various neurodegenerative diseases in humans (Alzheimer’s, Parkinson’s and others), or perform various functions in the body, both in humans and in representatives of other domains of life. Recently, more and more data have appeared confirming the ability of many known and, probably, not yet studied proteins/peptides, to self-assemble into quaternary structures. Fibrils, biofilms and amyloid gels are promising objects for the developing field of research of nanobiotechnology. To develop methods for obtaining nanobiomaterials with desired properties, it is necessary to study the mechanism of such structure formation, as well as the influence of various factors on this process. In this work, we present the results of a study of the structure of biogels formed by four 10-membered amyloidogenic peptides: the VDSWNVLVAG peptide (AspNB) and its analogue VESWNVLVAG (GluNB), which are amyloidogenic fragments of the glucantransferase Bgl2p protein from a yeast cell wall, and amyloidogenic peptides Aβ(31–40), Aβ(33–42) from the Aβ(1–42) peptide. Based on the analysis of the data, we propose a possible mechanism for the formation of amyloid gels with these peptides.

Concentration effects on the self-assembly of tyrosine molecules

Molecular self-assembly is a ubiquitous phenomenon in which individual atoms or molecules set up an ordered structure. It is of high interest for understanding the biology and a variety of diseases at the molecular level. In this work, we studied the self-assembly of tyrosine molecules via extensive molecular dynamics simulations. The formation of structures by self-assembly was systematically studied at various concentrations, from very low to very high. The temperature was kept constant, at which, in our former studies, we have already observed well-formed self-assembled structures. Depending on the concentration, the system displays a wide range of different structures, ranging from freely scattered monomers to very well formed four-fold structures. Different regimes of concentration dependence are observed. The results are proved by calculating the moments of inertia of the structures and the number of hydrogen bonds formed. Free energy landscapes calculated for the number of hydrogen bonds versus the number of contacts within a criterion provide insights into the structures observed.

Amelogenin Peptide-Chitosan Hydrogel for Biomimetic Enamel Regrowth

We designed synthetic peptides that have demonstrated an effective remineralization potential to restore incipient enamel decay. In order to develop a clinically viable approach we incorporated the amelogenin-derived peptides P26 and P32 into chitosan hydrogel and examined their efficacy in the remineralization of enamel. Peptides in chitosan exhibited increased stability in vitro as compared to peptides in solution at room temperature and at 37°C. Tooth models for enamel erosion (sections) and white spot lesions (blocks) were subject to periods of demineralization. Treatment groups were subjected to remineralization in artificial saliva in the presence of P26 and P32 in solution and in chitosan hydrogel (P26-CS and P32-CS). Quantitative light-induced fluorescence (QLF) was employed to analyze mineral density following demineralization and remineralization across all the treatment groups. Scanning electron microscopy and nanoindentation were used to characterize the surface structure and mechanical strength of regrown enamel. Control enamel sections treated in artificial saliva demonstrated randomly distributed, tiny, needle-shaped crystals with a low packing density and porosities displaying mineralization defects. In samples treated with P26-CS or P32-CS a denser coating of organized hydroxyapatite (HAP) crystals was formed covering the entire surfaces of demineralized enamel window. The hardness and modulus of enamel surfaces were increased after treatment with P26-CS and P32-CS with no significant difference in the mechanical properties between the two peptide hydrogels. Analysis of mineral density by QLF showed that in enamel sections P26 peptide alone or P26-CS significantly enhanced the remineralization. In enamel blocks P26 in solution had a better efficacy than P26-CS.

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.

Intracellular artificial supramolecules based on de novo designed Y15 peptides

De novo designed self-assembling peptides (SAPs) are promising building blocks of supramolecular biomaterials, which can fulfill a wide range of applications, such as scaffolds for tissue culture, three-dimensional cell culture, and vaccine adjuvants. Nevertheless, the use of SAPs in intracellular spaces has mostly been unexplored. Here, we report a self-assembling peptide, Y15 (YEYKYEYKYEYKYEY), which readily forms β-sheet structures to facilitate bottom-up synthesis of functional protein assemblies in living cells. Superfolder green fluorescent protein (sfGFP) fused to Y15 assembles into fibrils and is observed as fluorescent puncta in mammalian cells. Y15 self-assembly is validated by fluorescence anisotropy and pull-down assays. By using the Y15 platform, we demonstrate intracellular reconstitution of Nck assembly, a Src-homology 2 and 3 domain-containing adaptor protein. The artificial clusters of Nck induce N-WASP (neural Wiskott-Aldrich syndrome protein)-mediated actin polymerization, and the functional importance of Nck domain valency and density is evaluated.

Self-assembled peptide and protein nanostructures for anti-cancer therapy: Targeted delivery, stimuli-responsive devices and immunotherapy

Self-assembled peptides and proteins possess tremendous potential as targeted drug delivery systems and key applications of these well-defined nanostructures reside in anti-cancer therapy. Peptides and proteins can self-assemble into nanostructures of diverse sizes and shapes in response to changing environmental conditions such as pH, temperature, ionic strength, as well as host and guest molecular interactions; their countless benefits include good biocompatibility and high loading capacity for hydrophobic and hydrophilic drugs. These self-assembled nanomaterials can be adorned with functional moieties to specifically target tumor cells. Stimuli-responsive features can also be incorporated with respect to the tumor microenvironment. This review sheds light on the growing interest in self-assembled peptides and proteins and their burgeoning applications in cancer treatment and immunotherapy.

Adhesion and whitening effects of P11-4 self-assembling peptide and HAP suspension on bovine enamel

OBJECTIVES

This study evaluated the adhesion and whitening effects of a combination of P11-4 self-assembling peptide and hydroxyapatite (peptide-HAP) on bovine enamel.

METHODS

Forty-six caries-free bovine teeth were selected, and 40 teeth were randomly allocated to one of five groups (n = 8). First, the effects of application frequency, exposure time, and storage in saliva on the whitening effects of an experimental low-concentrated peptide-HAP suspension (0.5 wt% HAP; Curodont, Credentis) were evaluated and compared with a commercial bleaching agent (VivaStyle Paint on Plus, VS, Ivoclar Vivadent). Tooth color was measured using a spectrophotometer (Gretag MacBeth), and color changes ΔE were statistically analyzed. Second, the effects of peptide-HAP concentration (low versus high: 6.25% HAP; Curodont Protect), and its interactions with saliva and postapplication restaining, were investigated. Third, enamel surfaces (n = 2) were treated with low concentration peptide-HAP and high-concentration peptide-HAP in polymeric and monomeric forms (Curodont Protect & Curodont Repair, Credentis) and analyzed by SEM.

RESULTS

The ΔE of the low-concentration peptide-HAP suspension did not differ from that of VS. Application frequency, exposure time, and storage in saliva did not have any significant impact on whitening efficacy of the peptide-HAP suspension. Increasing the concentration of the suspension did not promote overall ΔE. SEM observations confirmed the presence of the newly generated peptide and HAP on the enamel surface.

CONCLUSIONS

The peptide-HAP suspension is a mild tooth whitener, and the adhesion of peptide-HAP to enamel is concentration dependent.

CLINICAL RELEVANCE

This peptide-HAP suspension is effective in offsetting discoloration caused by restaining after treatment.

Self-assembling peptide P11-4 in remineralization of enamel caries - a systematic review of in-vitro studies

OBJECTIVE

The present systematic review was conducted to investigate the effect of the self-assembling peptide (SAP) - P₁₁-4 in the remineralization of enamel caries.

MATERIAL AND METHODS

The systematic search for studies was conducted through CINAHL, EMBASE, MEDLINE, Scopus, PsychINFO, and various key journals. This review was conducted in adherence to PRISMA standards and was registered in PROSPERO with registration number CRD42019110156. The methodological quality of the studies was graded through Cochrane's tool of risk of bias in non-randomized studies - of interventions (ROBINS-I).

RESULTS

In total, 91 studies were identified for screening, and 12 studies were eligible. Ten studies showed effective enamel remineralization with P₁₁-4 compared to controls. One study showed a combination of P₁₁-4 with fluoride varnish or Casein Phosphopeptide-Amorphous Calcium Phosphate Fluoride (CPP-ACPF) leads to significantly higher remineralization compared to P₁₁-4 alone. Quality assessment of study showed 6 (50%) studies as medium risk of bias and 6 (50%) studies as low risk of bias.

CONCLUSION

To conclude, the present study results showed SAP- P₁₁-4 is effective in the remineralization of enamel caries.

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

Background

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

Aim

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

Materials and methods

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

Results

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

Conclusion

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

Clinical significance

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

How to cite this article

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

Impact of biomineralization on resin/biomineralized dentin bond longevity in a minimally invasive approach: An "in vitro" 18-month follow-up

OBJECTIVES

To determine the impact of treating caries-affected dentin (CAD) with: 0.2% sodium fluoride (NaF), casein phosphopeptide-amorphous calcium phosphate (CPP-ACP/MI Paste™) or peptide P₁₁-4 (Curodont™ Repair) on the longevity of resin/CAD interface at storage times of 24 -h, 6- and 18-month.

METHODS

255 caries-free third molars were used, and CAD was produced by a biological method. The teeth were randomly distributed into: G1- Sound dentin (SD); G2- CAD; G3- CAD + 0.2% NaF (CAD/NaF); G4- CAD + CPP-ACP (CAD/ACP); G5- CAD + Curodont™ Repair (CAD/P₁₁-4). The Filtek Z350 composite resin block was bonded to dentin using Adper™ Single 2 (4 mm/height). Resin/dentin blocks were stored in a solution of Simulated Body Fluid at 37 °C, pressures were modified to simulate natural pulpal pressures. Specimens were investigated by microtensile bond strength (μTBS) (n = 8), Scanning Electron Microscopy (to assess the failure mode) (n = 8), nanoinfiltration (to assess the interface sealing) (n = 3), in situ zymography (to assess the gelatinolytic activity) (n = 3) and micro-computed microtomography (μ-CT) (to assess the mineralization) (n = 3). Data from μTBS, μ-CT and, nanoinfiltration and hybrid layer formation/degradation were submitted to two-way ANOVA and Tukey tests, and failure patterns and in situ zymography to Kruskal-Wallis and Dunn tests (α = 5%).

RESULTS

The highest mineral density change by μ-CT, smallest silver nitrate infiltration and proteolytic activity in the adhesive layer were obtained significantly for the groups SD, CAD/ACP and CAD/P₁₁-4, with most mixed fractures at 18-month (p < 0.001). CAD/NaF showed significantly similar values to CAD, CAD and CAD/NaF which presented a high percentage of adhesive fracture (p < 0.001) at all time periods.

SIGNIFICANCE

Treating caries-affected dentin with remineralizing agents CPP-ACP and Curodont™ Repair, has the potential to be a clinically relevant treatment protocol to increase the longevity of adhesive restorations.

Peptide Nanomaterials for Drug Delivery Applications

Self-assembled peptides have been shown to form well-defined nanostructures which display outstanding characteristics for many biomedical applications and especially in controlled drug delivery. Such biomaterials are becoming increasingly popular due to routine, standardized methods of synthesis, high biocompatibility, biodegradability and ease of upscale. Moreover, one can modify the structure at the molecular level to form various nanostructures with a wide range of applications in the field of medicine. Through environmental modifications such as changes in pH and ionic strength and the introduction of enzymes or light, it is possible to trigger self-assembly and design a host of different self-assembled nanostructures. The resulting nanostructures include nanotubes, nanofibers, hydrogels and nanovesicles which all display a diverse range of physico-chemical and mechanical properties. Depending on their design, peptide self-assembling nanostructures can be manufactured with improved biocompatibility and in vivo stability and the ability to encapsulate drugs with the capacity for sustained drug delivery. These molecules can act as carriers for drug molecules to ferry cargo intracellularly and respond to stimuli changes for both hydrophilic and hydrophobic drugs. This review explores the types of self-assembling nanostructures, the effects of external stimuli on and the mechanisms behind the assembly process, and applications for such technology in drug delivery.

Self-Assembling Peptides as an Emerging Platform for the Treatment of Metabolic Syndrome

Metabolic syndrome comprises a cluster of comorbidities that represent a major risk of developing chronic diseases, such as type II diabetes, cardiovascular diseases, and stroke. Alarmingly, metabolic syndrome reaches epidemic proportions worldwide. Today, lifestyle changes and multiple drug-based therapies represent the gold standard to address metabolic syndrome. However, such approaches face two major limitations: complicated drug therapeutic regimes, which in most cases could lead to patient incompliance, and limited drug efficacy. This has encouraged scientists to search for novel routes to deal with metabolic syndrome and related diseases. Within such approaches, self-assembled peptide formulations have emerged as a promising alternative for treating metabolic syndrome. In particular, self-assembled peptide hydrogels, either as acellular or cell-load three-dimensional scaffoldings have reached significant relevance in the biomedical field to prevent and restore euglycemia, as well as for controlling cardiovascular diseases and obesity. This has been possible thanks to the physicochemical tunability of peptides, which are developed from a chemical toolbox of versatile amino acids enabling flexibility of designing a wide range of self-assembled/co-assembled nanostructures forming biocompatible viscoelastic hydrogels. Peptide hydrogels can be combined with several biological entities, such as extracellular matrix proteins, drugs or cells, forming functional biologics with therapeutic ability for treatment of metabolic syndrome-comorbidities. Additionally, self-assembly peptides combine safety, tolerability, and effectivity attributes; by this presenting a promising platform for the development of novel pharmaceuticals capable of addressing unmet therapeutic needs for diabetes, cardiovascular disorders and obesity. In this review, recent advances in developing self-assembly peptide nanostructures tailored for improving treatment of metabolic syndrome and related diseases will be discussed from basic research to preclinical research studies. Challenges facing the development of approved medicinal products based on self-assembling peptide nanomaterials will be discussed in light of regulatory requirement for clinical authorization.

Amyloid-Like Peptide Aggregates

Self-assembly of proteins and peptides into the amyloid fold is a widespread phenomenon in the natural world. The structural hallmark of self-assembly into amyloid fibrillar assemblies is the cross-beta motif, which conveys distinct morphological and mechanical properties. The amyloid fibril formation has contrasting results depending on the organism, in the sense that it can bestow an organism with the advantages of mechanical strength and improved functionality or, on the contrary, could give rise to pathological states. In this chapter we review the existing information on amyloid-like peptide aggregates, which could either be derived from protein sequences, but also could be rationally or de novo designed in order to self-assemble into amyloid fibrils under physiological conditions. Moreover, the development of self-assembled fibrillar biomaterials that are tailored for the desired properties towards applications in biomedical or environmental areas is extensively analyzed. We also review computational studies predicting the amyloid propensity of the natural amino acid sequences and the structure of amyloids, as well as designing novel functional amyloid materials.

Recent advances in the fabrication, functionalization, and bioapplications of peptide hydrogels

Self-assembled peptide-based nanomaterials have exhibited wide application potential in the fields of materials science, nanodevices, biomedicine, tissue engineering, biosensors, energy storage, environmental science, and others. Due to their porous structure, strong mechanical stability, high biocompatibility, and easy functionalization, three-dimensional self-assembled peptide hydrogels revealed promising potential in bio-related applications. To present the advances in this interesting topic, we present a review on the synthesis and functionalization of peptide hydrogels, as well as their applications in drug delivery, antibacterial materials, cell culture, biomineralization, bone tissue engineering, and biosensors. Specifically, we focus on the fabrication methods of peptide hydrogels through physical, chemical, and biological stimulations. In addition, the functional design of peptide hydrogels by incorporation with polymers, DNA, protein, nanoparticles, and carbon materials is introduced and discussed in detail. It is expected that this work will be helpful not only for the design and synthesis of various peptide-based nanostructures and nanomaterials, but also for the structural and functional tailoring of peptide-based nanomaterials to meet specific demands.

Charge guides pathway selection in β-sheet fibrillizing peptide co-assembly

Peptide co-assembly is attractive for creating biomaterials with new forms and functions. Emergence of these properties depends on the peptide content of the final assembled structure, which is difficult to predict in multicomponent systems. Here using experiments and simulations we show that charge governs content by affecting propensity for self- and co-association in binary CATCH(+/-) peptide systems. Equimolar mixtures of CATCH(2+/2-), CATCH(4+/4-), and CATCH(6+/6-) formed two-component β-sheets. Solid-state NMR suggested the cationic peptide predominated in the final assemblies. The cationic-to-anionic peptide ratio decreased with increasing charge. CATCH(2+) formed β-sheets when alone, whereas the other peptides remained unassembled. Fibrillization rate increased with peptide charge. The zwitterionic CATCH parent peptide, "Q11", assembled slowly and only at decreased simulation temperature. These results demonstrate that increasing charge draws complementary peptides together faster, favoring co-assembly, while like-charged molecules repel. We foresee these insights enabling development of co-assembled peptide biomaterials with defined content and predictable properties.

On the Mechanism of Self-Assembly by a Hydrogel-Forming Peptide

Self-assembling peptide-based hydrogels are a class of tunable soft materials that have been shown to be highly useful for a number of biomedical applications. The dynamic formation of the supramolecular fibrils that compose these materials has heretofore remained poorly characterized. A better understanding of this process would provide important insights into the behavior of these systems and could aid in the rational design of new peptide hydrogels. Here, we report the determination of the microscopic steps that underpin the self-assembly of a hydrogel-forming peptide, SgI_37-49. Using theoretical models of linear polymerization to analyze the kinetic self-assembly data, we show that SgI_37-49 fibril formation is driven by fibril-catalyzed secondary nucleation and that all the microscopic processes involved in SgI_37-49 self-assembly display an enzyme-like saturation behavior. Moreover, this analysis allows us to quantify the rates of the underlying processes at different peptide concentrations and to calculate the time evolution of these reaction rates over the time course of self-assembly. We demonstrate here a new mechanistic approach for the study of self-assembling hydrogel-forming peptides, which is complementary to commonly used materials science characterization techniques.