Biomimetic self-assembling peptides as scaffolds for soft tissue engineering

Spectroscopic Study of Micro-/Nano-Hydroxyapatite Polymer Composites Modified with Carbon Nanofibers

Nowadays, novel biomaterials are under intense research because they are part of promising therapies for the treatment of age-related diseases such as osteoporosis and bone defects. In the presented study, composites of poly(ε-caprolactone) (PCL), micro and nano hydroxyapatite (µ-HAp and n-HAp) and carbon nanofibers (CNFs) were prepared. The influence of additives on polymeric matrix was analyzed using scanning electron microscopy (SEM), Raman micro-spectroscopy, Raman mapping, and two-dimensional correlation spectroscopy (2D-COS). The bioactivity in vitro was evaluated by a 21-day incubation of prepared membranes in simulated body fluid (SBF). It was concluded that additives can behave as crystallization nuclei of PCL, but they are also located across the entire surface of PCL spherulites, not only in the center. With an increasing content of HAp additives, polymeric spherulites become smaller. The type of HAp (µ-HAp or n-HAp) influences the PCL matrix differently, as confirmed by 2D-COS. The component whose addition leads to most significant changes in the polymer is CNFs; polymeric spherulites are small to the extent that they are not distinguishable, and the overall amorphousness of the polymer is the highest among all tested materials, as is its hydrophobicity. The bioactivity test indicated that the membrane with the greatest potential for use as a biomaterial in bone tissue engineering is one consisting of n-HAp (15 wt%) and CNFs, as very uniform coverage of the produced apatite was observed on the surface of this membrane after incubation in SBF.

Divalent metal ion modulation of a simple peptide-based hydrogel: self-assembly and viscoelastic properties

Peptide self-assembly has been highly studied to understand the pathways in forming higher order structures along with the development and application of resulting hydrogel materials. Driven by noncovalent interactions, peptide hydrogels are stimuli-responsive to any addition to its gelling conditions. Here, a Phe-His based peptide, C14-FH(Trt)-OH, was synthesized and characterized with 1H NMR, FT-IR, MS, UV-vis spectroscopies and elemental analysis. Based on SEM imaging, the dipeptide conjugate was capable of forming a nanofibrous, interconnected network encapsulating buffer to produce a supramolecular hydrogel. Through the addition of Zn2+ and Cu2+, there is a clear change in the self-assembled nanostructures characterized through SEM. With this effect on self-assembly follows a change in the viscoelastic properties of the material, as determined through rheological frequency sweeps, with 2 and 3 orders of magnitude decreases in the elastic modulus G' in the presence of Zn2+ and Cu2+ respectively. This highlights the tunability of soft material properties with peptide design and self-assembly, through metal ions and Nδ-directed coordination.

Biomaterials and Cell Therapy Combination in Central Nervous System Treatments

Current pharmacological and surgical therapies for the central nervous system (CNS) show a limited capacity to reduce the damage progression; that together with the intrinsic limited capability of the CNS to regenerate greatly reduces the hopes of recovery. Among all the therapies proposed, the tissue engineering strategies supplemented with therapeutic stem cells remain the most promising. Neural tissue engineering strategies are based on the development of devices presenting optimal physical, chemical, and mechanical properties which, once inserted in the injured site, can support therapeutic cells, limiting the effect of a hostile environment and supporting regenerative processes. Thus, this review focuses on the employment of hydrogel and nanofibrous scaffolds supplemented with stem cells as promising therapeutic tools for the central and peripheral nervous systems in preclinical and clinical applications.

Effect of three different remineralising agents on prevention against acidic erosion of primary teeth: an in vitro study

PURPOSE

This study aimed to evaluate and compare the protective effect of fluoride varnish (Enamelast™, Ultradent Inc., Cologne, Germany), casein phosphopeptide-amorphous calcium phosphate fluoride/CPP-ACPF (MI Paste Plus, GC Corp., Tokyo, Japan) and self-assembling P11-4 peptide (Curodont™ Protect, Credentis AG, Windisch, Switzerland), against acidic erosion of primary teeth.

METHODS

Forty primary anterior teeth were randomly assigned to four groups (n = 10): group 1: control, group 2: fluoride varnish, group 3: CPP-ACPF and group 4: self-assembling P11-4 peptide. After applying remineralising agents, except for the control group, all specimens underwent an erosive challenge of carbonated soft drink and artificial saliva for 15 cycles of 6 s each at 6-h intervals for a day. Groups were compared in terms of surface microhardness, roughness readings, and surface scanning with an extra-oral scanner (D800; 3Shape A/S) before and after the erosive process.

RESULTS

All experimental groups showed superior results than the control group regarding microhardness, surface roughness, and substance loss. The fluoride varnish group showed significantly favourable results in microhardness change. There was no significant difference between the experimental groups regarding surface roughness and enamel loss measurements.

CONCLUSION

5% NaF fluoride varnish, CPP-ACPF and self-assembling P11-4 peptide protect the enamel of primary teeth against erosion compared to artificial saliva alone.

Controlling the Self-Assembly and Material Properties of β-Sheet Peptide Hydrogels by Modulating Intermolecular Interactions

Self-assembling peptides are a promising biomaterial with potential applications in medical devices and drug delivery. In the right combination of conditions, self-assembling peptides can form self-supporting hydrogels. Here, we describe how balancing attractive and repulsive intermolecular forces is critical for successful hydrogel formation. Electrostatic repulsion is tuned by altering the peptide's net charge, and intermolecular attractions are controlled through the degree of hydrogen bonding between specific amino acid residues. We find that an overall net peptide charge of +/-2 is optimal to facilitate the assembly of self-supporting hydrogels. If the net peptide charge is too low then dense aggregates form, while a high molecular charge inhibits the formation of larger structures. At a constant charge, altering the terminal amino acids from glutamine to serine decreases the degree of hydrogen bonding within the assembling network. This tunes the viscoelastic properties of the gel, reducing the elastic modulus by two to three orders of magnitude. Finally, hydrogels could be formed from glutamine-rich, highly charged peptides by mixing the peptides in combinations with a resultant net charge of +/-2. These results illustrate how understanding and controlling self-assembly mechanisms through modulating intermolecular interactions can be exploited to derive a range of structures with tuneable properties.

Technological and structural aspects of scaffold manufacturing for cultured meat: recent advances, challenges, and opportunities

In vitro cultured meat is an emerging area of research focus with an innovative approach through tissue engineering (i.e., cellular engineering) to meet the global food demand. The manufacturing of lab-cultivated meat is an innovative business that alleviates life-threatening environmental issues concerning public health and animal well-being on the global platform. There has been a noteworthy advancement in cultivating artificial meat, but still, there are numerous challenges that impede the swift headway of lab-grown meat production at a commercially large scale. In this review, we focus on the manufacturing of edible scaffolds for cultured meat production. In brief, first an introduction to cultivating artificial meat and its current scenario in the market is provided. Further, a discussion on the understanding of composition, cellular, and molecular communications in muscle tissue is presented, which are vital to scaling up the production of lab-grown meat. In continuation, the major components (e.g., cells, biomaterial scaffolds, and their manufacturing technologies, media, and potential bioreactors) for cultured meat production are conferred followed by a comprehensive discussion on the most recent advances in lab-cultured meat. Finally, existing challenges and opportunities including future research perspectives for scaling-up cultured meat production are discussed with conclusive interpretations.

Advances in microfabrication technologies in tissue engineering and regenerative medicine

BACKGROUND

Tissue engineering provides various strategies to fabricate an appropriate microenvironment to support the repair and regeneration of lost or damaged tissues. In this matter, several technologies have been implemented to construct close-to-native three-dimensional structures at numerous physiological scales, which are essential to confer the functional characteristics of living tissues.

METHODS

In this article, we review a variety of microfabrication technologies that are currently utilized for several tissue engineering applications, such as soft lithography, microneedles, templated and self-assembly of microstructures, microfluidics, fiber spinning, and bioprinting.

RESULTS

These technologies have considerably helped us to precisely manipulate cells or cellular constructs for the fabrication of biomimetic tissues and organs. Although currently available tissues still lack some crucial functionalities, including vascular networks, innervation, and lymphatic system, microfabrication strategies are being proposed to overcome these issues. Moreover, the microfabrication techniques that have progressed to the preclinical stage are also discussed.

CONCLUSIONS

This article aims to highlight the advantages and drawbacks of each technique and areas of further research for a more comprehensive and evolving understanding of microfabrication techniques in terms of tissue engineering and regenerative medicine applications.

FEK self-assembled peptide hydrogels facilitate primary hepatocytes culture and pharmacokinetics screening

A FEFEFKFK (FEK, F, phenylalaninyl; E, glutamyl; K, lysinyl)-based self-assembling peptide hydrogel (FEK-SAPH) was developed to replace sandwich culture (SC) for improved culture of primary hepatocytes in vitro. Under neutral conditions, FEK self-assembles to form β-sheet nanofibers, which in turn form FEK-SAPH. For the culture of rat primary hepatocytes (RPH), the use of FEK-SAPH simplified operation steps and promoted excellent cell-cell interactions while maintaining the SC-related RPH polarity trend. Compared with SC, FEK-SAPH cultured RPH for 14 days, the bile duct network was formed, the secretion of albumin and urea was improved, and the metabolic clearance rate based on cytochrome P450 (CYPs) was comparable. In FEK-SAPH culture, the expression level of the biliary efflux transporter bile salt export pump increased by 230.7%, while the biliary excretion index value of deuterium-labeled sodium taurocholate (d8-TCA) differed slightly from the SC value (72% and 77%, respectively, p = .0195). The inhibitory effect of cholestasis drugs on FEK-SAPH was significantly higher than that of SC. In FEK-SAPH, hepatoprotective drugs were more effective in antagonizing hepatotoxicity induced by lithocholic acid (LCA). FEK-SAPH cultured RPH with hepatoprotective drugs can better recover from LCA-induced damage. In summary, FEK-SAPH can be used as a substitute for SC for pharmacokinetic screening to evaluate the drug absorption, disposition, metabolism, excretion, and toxicity (ADMET) in hepatocytes.

Sa12b-Modified Functional Self-Assembling Peptide Hydrogel Enhances the Biological Activity of Nucleus Pulposus Mesenchymal Stem Cells by Inhibiting Acid-Sensing Ion Channels

Various hydrogels have been studied for nucleus pulposus regeneration. However, they failed to overcome the changes in the acidic environment during intervertebral disc degeneration. Therefore, a new functionalized peptide RAD/SA1 was designed by conjugating Sa12b, an inhibitor of acid-sensing ion channels, onto the C-terminus of RADA16-I. Then, the material characteristics and biocompatibility of RAD/SA1, and the bioactivities and mechanisms of degenerated human nucleus pulposus mesenchymal stem cells (hNPMSCs) were evaluated. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) confirmed that RAD/SA1 self-assembling into three-dimensional (3D) nanofiber hydrogel scaffolds under acidic conditions. Analysis of the hNPMSCs cultured in the 3D scaffolds revealed that both RADA16-I and RAD/SA1 exhibited reliable attachment and extremely low cytotoxicity, which were verified by SEM and cytotoxicity assays, respectively. The results also showed that RAD/SA1 increased the proliferation of hNPMSCs compared to that in culture plates and pure RADA16-I. Quantitative reverse transcription polymerase chain reaction, enzyme-linked immunosorbent assay, and western blotting demonstrated that the expression of collagen I was downregulated, while collagen II, aggrecan, and SOX-9 were upregulated. Furthermore, Ca²⁺ concentration measurement and western blotting showed that RAD/SA1 inhibited the expression of p-ERK through Ca²⁺-dependent p-ERK signaling pathways. Therefore, the functional self-assembling peptide nanofiber hydrogel designed with the short motif of Sa12b could be used as an excellent scaffold for nucleus pulposus tissue engineering. Moreover, RAD/SA1 exhibits great potential applications in the regeneration of mildly degenerated nucleus pulposus.

Self-Assembling Hydrogel Structures for Neural Tissue Repair

Hydrogel materials have been employed as biological scaffolds for tissue regeneration across a wide range of applications. Their versatility and biomimetic properties make them an optimal choice for treating the complex and delicate milieu of neural tissue damage. Aside from finely tailored hydrogel properties, which aim to mimic healthy physiological tissue, a minimally invasive delivery method is essential to prevent off-target and surgery-related complications. The specific class of injectable hydrogels termed self-assembling peptides (SAPs), provide an ideal combination of in situ polymerization combined with versatility for biofunctionlization, tunable physicochemical properties, and high cytocompatibility. This review identifies design criteria for neural scaffolds based upon key cellular interactions with the neural extracellular matrix (ECM), with emphasis on aspects that are reproducible in a biomaterial environment. Examples of the most recent SAPs and modification methods are presented, with a focus on biological, mechanical, and topographical cues. Furthermore, SAP electrical properties and methods to provide appropriate electrical and electrochemical cues are widely discussed, in light of the endogenous electrical activity of neural tissue as well as the clinical effectiveness of stimulation treatments. Recent applications of SAP materials in neural repair and electrical stimulation therapies are highlighted, identifying research gaps in the field of hydrogels for neural regeneration.

Self-assembly of bio-inspired heterochiral peptides

Peptide hydrogels, deriving from natural protein fragments, present unique advantages as compatibility and low cost of production that allow their wide application in different fields as wound healing, cell delivery and tissue regeneration. To engineer new biomaterials, the change of the chirality of single amino acids demonstrated a powerful approach to modulate the self-assembly mechanism. Recently we unveiled that a small stretch spanning residues 268-273 in the C-terminal domain (CTD) of Nucleophosmin 1 (NPM1) is an amyloid sequence. Herein, we performed a systematic D-scan of this sequence and analyzed the structural properties of obtained peptides. The conformational and kinetic features of self-aggregates and the morphologies of derived microstructures were investigated by means of different biophysical techniques, as well as the compatibility of hydrogels was evaluated in HeLa cells. All the investigated hexapeptides formed hydrogels even if they exhibited different conformational intermediates during aggregation, and they structural featured are finely tuned by introduced chiralities.

Advances in the Fabrication of Scaffold and 3D Printing of Biomimetic Bone Graft

The need for bone grafts is tremendous, and that leads to the use of autograft, allograft, and bone graft substitutes. The biology of the bone is quite complex regarding cellular composition and architecture, hence developing a mineralized connective tissue graft is challenging. Traditionally used bone graft substitutes including metals, biomaterial coated metals and biodegradable scaffolds, suffer from persistent limitations. With the advent and rise of additive manufacturing technologies, the future of repairing bone trauma and defects seems to be optimistic. 3D printing has significant advantages, the foremost of all being faster manipulation of various biocompatible materials and live cells or tissues into the complex natural geometries necessary to mimic and stimulate cellular bone growth. The advent of new-generation bioprinters working with high-precision, micro-dispensing and direct digital manufacturing is aiding in ground-breaking organ and tissue printing, including the bone. The future bone replacement for patients holds excellent promise as scientists are moving closer to the generation of better 3D printed bio-bone grafts that will be safer and more effective. This review aims to summarize the advances in scaffold fabrication techniques, emphasizing 3D printing of biomimetic bone grafts.

Self-assembling peptide scaffolds in the clinic

Well-defined scaffold hydrogels made of self-assembling peptides have found their way into clinical products. By examining the properties and applications of two self-assembling peptides-EAK16 and RADA16-we highlight the potential for translating designer biological scaffolds into commercial products.

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.

Treatment with functionalized designer self-assembling peptide hydrogels promotes healing of experimental periodontal defects

BACKGROUND/OBJECTIVES

It has been reported that self-assembling peptide (SAP) hydrogels with functionalized motifs enhance proliferation and migration of host cells. How these designer SAP hydrogels perform in the treatment of periodontal defects remains unknown. This study aimed to test the potential of local application of designer SAP hydrogels with two different functionalized motifs in the treatment of experimental periodontal defects.

MATERIAL AND METHODS

In vitro, viability/proliferation of rat periodontal ligament-derived cells (PDLCs) cultured on an SAP hydrogel RADA16 and RADA16 with functionalized motifs, PRG (integrin binding sequence) and PDS (laminin cell adhesion motif), was assessed. Cell morphology was analyzed by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). In vivo, standardized periodontal defects were made mesially in the maxillary first molars of Wistar rats. Defects received RADA16, PRG, PDS or left unfilled. At 2 or 4 weeks postoperatively, healing was assessed by microcomputed tomography, histological and immunohistochemical methods.

RESULTS

Viability/proliferation of PDLCs was significantly greater on PRG than on RADA16 or PDS at 72 hours. rPDLCs in the PRG group showed enhanced elongations and cell protrusions. In vivo, at 4 weeks, bone volume fractions in the PRG and PDS groups were significantly greater than the RADA16 group. Histologically, bone formation was more clearly observed in the PRG and PDS groups compared with the RADA16 group. At 4 weeks, epithelial downgrowth in the hydrogel groups was significantly reduced compared to the Unfilled group. In Azan-Mallory staining, PDL-like bundles ran in oblique direction in the hydrogel groups. At 2 weeks, in the area near the root, proliferating cell nuclear antigen (PCNA)-positive cells were detected significantly more in the PRG group than other groups. At 4 weeks, in the middle part of the defect, a significantly greater level of vascular endothelial growth factor (VEGF)-positive cells and α-smooth muscle actin (SMA)-positive blood vessels were observed in the PRG group than in other groups.

CONCLUSION

The results indicate that local application of the functionalized designer SAP hydrogels, especially PRG, promotes periodontal healing by increasing cell proliferation and angiogenesis.

Biomimetic peptide enriched nonwoven scaffolds promote calcium phosphate mineralisation

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

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

Ultrashort Peptide Self-Assembly: Front-Runners to Transport Drug and Gene Cargos

The translational therapies to promote interaction between cell and signal come with stringent eligibility criteria. The chemically defined, hierarchically organized, and simpler yet blessed with robust intermolecular association, the peptides, are privileged to make the cut-off for sensing the cell-signal for biologics delivery and tissue engineering. The signature service and insoluble network formation of the peptide self-assemblies as hydrogels have drawn a spell of research activity among the scientists all around the globe in the past decades. The therapeutic peptide market players are anticipating promising growth opportunities due to the ample technological advancements in this field. The presence of the other organic moieties, enzyme substrates and well-established protecting groups like Fmoc and Boc etc., bring the best of both worlds. Since the large sequences of peptides severely limit the purification and their isolation, this article reviews the account of last 5 years' efforts on novel approaches for formulation and development of single molecule amino acids, ultra-short peptide self-assemblies (di- and tri- peptides only) and their derivatives as drug/gene carriers and tissue-engineering systems.

Directive Effect of Chain Length in Modulating Peptide Nano-assemblies

BACKGROUND

RADA-4 (Ac-RADARADARADARADA-NH2) is the most extensively studied and marketed self-assembling peptide, forming hydrogel, used to create defined threedimensional microenvironments for cell culture applications.

OBJECTIVES

In this work, we use various biophysical techniques to investigate the length dependency of RADA aggregation and assembly.

METHODS

We synthesized a series of RADA-N peptides, N ranging from 1 to 4, resulting in four peptides having 4, 8, 12, and 16 amino acids in their sequence. Through a combination of various biophysical methods including thioflavin T fluorescence assay, static right angle light scattering assay, Dynamic Light Scattering (DLS), electron microscopy, CD, and IR spectroscopy, we have examined the role of chain-length on the self-assembly of RADA peptide.

RESULTS

Our observations show that the aggregation of ionic, charge-complementary RADA motifcontaining peptides is length-dependent, with N less than 3 are not forming spontaneous selfassemblies.

CONCLUSION

The six biophysical experiments discussed in this paper validate the significance of chain-length on the epitaxial growth of RADA peptide self-assembly.

Glutathione-adaptive peptide amphiphile vesicles rationally designed using positionable disulfide-bridges for effective drug transport

The drug loading/releasing capability of GSH-responsive nanovesicles self-assembled from peptide amphiphiles was controlled by varying the location and number of disulfide-linkages in the peptide for the selective drug-release into tumor cells.

Short to ultrashort peptide-based hydrogels as a platform for biomedical applications

Short peptides have attracted significant attention from researchers in the past few years due to their easy design, synthesis and characterization, diverse functionalisation possibilities, low cost, possibility to make a large range of hierarchical nanostructures and most importantly their high biocompatibility and biodegradability. Generally, short peptides are also relatively more stable than their longer variants, non-immunogenic in nature and many of them self-assemble to provide an exciting range of nanostructures, including hydrogels. Thus, the development of short peptide-based hydrogels has become an area of intense investigation. Although these hydrogels have a water content of greater than 90%, they are surprisingly highly stable structures, and thus have been used for various biomedical applications, including cell therapeutics, drug delivery, tissue engineering and regeneration, contact lenses, biosensors, and wound healing, by different researchers. Herein, we review the progress of research in the rapidly expanding field of short to ultrashort peptide-based hydrogels and their possible applications. Special attention is paid to address and review this field with regard to the stability of peptide-based hydrogels, particularly to enzymatic degradation.

Injectable Hydrogels for Cancer Therapy over the Last Decade

The interest in injectable hydrogels for cancer treatment has been significantly growing over the last decade, due to the availability of a wide range of starting polymer structures with tailored features and high chemical versatility. Many research groups are working on the development of highly engineered injectable delivery vehicle systems suitable for combined chemo-and radio-therapy, as well as thermal and photo-thermal ablation, with the aim of finding out effective solutions to overcome the current obstacles of conventional therapeutic protocols. Within this work, we have reviewed and discussed the most recent injectable hydrogel systems, focusing on the structure and properties of the starting polymers, which are mainly classified into natural or synthetic sources. Moreover, mapping the research landscape of the fabrication strategies, the main outcome of each system is discussed in light of possible clinical applications.

Enhanced Nanoassembly-Incorporated Antibacterial Composite Materials

The rapid advancement of peptide- and amino-acid-based nanotechnology offers new approaches for the development of biomedical materials. The utilization of fluorenylmethyloxycarbonyl (Fmoc)-decorated self-assembling building blocks for antibacterial and anti-inflammatory purposes represents promising advancements in this field. Here, we present the antibacterial capabilities of the nanoassemblies formed by Fmoc-pentafluoro-l-phenylalanine-OH, their substantial effect on bacterial morphology, as well as new methods developed for the functional incorporation of these nanoassemblies within resin-based composites. These amalgamated materials inhibit and hinder bacterial growth and viability and are not cytotoxic toward mammalian cell lines. Importantly, due to the low dosage required to confer antibacterial activity, the integration of the nanoassemblies does not affect their mechanical and optical properties. This approach expands on the growing number of accounts on the intrinsic antibacterial capabilities of self-assembling building blocks and serves as a basis for further design and development of enhanced composite materials for biomedical applications.

Coupling synthetic biology and programmable materials to construct complex tissue ecosystems

Synthetic biology combines engineering and biology to produce artificial systems with programmable features. Specifically, engineered microenvironments have advanced immensely over the past few decades, owing in part to the merging of materials with biological mimetic structures. In this review, we adapt a traditional definition of community ecology to describe "cellular ecology", or the study of the distribution of cell populations and interactions within their microenvironment. We discuss two exemplar hydrogel platforms: (1) self-assembling peptide (SAP) hydrogels and (2) Poly(ethylene) glycol (PEG) hydrogels and describe future opportunities for merging smart material design and synthetic biology within the scope of multicellular platforms.

Bone Tissue Engineering in a Perfusion Bioreactor Using Dexamethasone-Loaded Peptide Hydrogel

The main goal of this study was the formation of bone tissue using dexamethasone (DEX)-loaded [COCH₃]-RADARADARADARADA-[CONH₂] (RADA 16-I) scaffold that has the ability to release optimal DEX concentration under perfusion force. Bone-marrow samples were collected from three patients during a hip arthroplasty. Human mesenchymal stem cells (hMSCs) were isolated and propagated in vitro in order to be seeded on scaffolds made of DEX-loaded RADA 16-I hydrogel in a perfusion bioreactor. DEX concentrations were as follows: 4 × 10^-3, 4 × 10^-4 and 4 × 10^-5 M. After 21 days in a perfusion bioreactor, tissue was analyzed by scanning electron microscopy (SEM) and histology. Markers of osteogenic differentiation were quantified by real-time polymerase chain reaction (RT-PCR) and immunocytochemistry. Minerals were quantified and detected by the von Kossa method. In addition, DEX release from the scaffold in a perfusion bioreactor was assessed. The osteoblast differentiation was confirmed by the expression analysis of osteoblast-related genes (alkaline phosphatase (ALP), collagen I (COL1A1) and osteocalcin (OC). The hematoxylin/eosin staining confirmed the presence of cells and connective tissue, while SEM revealed morphological characteristics of cells, extracellular matrix and minerals-three main components of mature bone tissue. Immunocytochemical detection of collagen I is in concordance with given results, supporting the conclusion that scaffold with DEX concentration of 4 × 10^-4 M has the optimal engineered tissue morphology. The best-engineered bone tissue is produced on scaffold loaded with 4 × 10^-4 M DEX with a perfusion rate of 0.1 mL/min for 21 days. Differentiation of hMSCs on DEX-loaded RADA 16-I scaffold under perfusion force has a high potential for application in regenerative orthopedics.

Amino acid composition of nanofibrillar self-assembling peptide hydrogels affects responses of periodontal tissue cells in vitro

Background

The regeneration of tissue defects at the interface between soft and hard tissue, eg, in the periodontium, poses a challenge due to the divergent tissue requirements. A class of biomaterials that may support the regeneration at the soft-to-hard tissue interface are self-assembling peptides (SAPs), as their physicochemical and mechanical properties can be rationally designed to meet tissue requirements.

Materials and methods

In this work, we investigated the effect of two single-component and two complementary β-sheet forming SAP systems on their hydrogel properties such as nanofibrillar architecture, surface charge, and protein adsorption as well as their influence on cell adhesion, morphology, growth, and differentiation.

Results

We showed that these four 11-amino acid SAP (P11-SAP) hydrogels possessed physico-chemical characteristics dependent on their amino acid composition that allowed variabilities in nanofibrillar network architecture, surface charge, and protein adsorption (eg, the single-component systems demonstrated an ~30% higher porosity and an almost 2-fold higher protein adsorption compared with the complementary systems). Cytocompatibility studies revealed similar results for cells cultured on the four P11-SAP hydrogels compared with cells on standard cell culture surfaces. The single-component P11-SAP systems showed a 1.7-fold increase in cell adhesion and cellular growth compared with the complementary P11-SAP systems. Moreover, significantly enhanced osteogenic differentiation of human calvarial osteoblasts was detected for the single-component P11-SAP system hydrogels compared with standard cell cultures.

Conclusion

Thus, single-component system P11-SAP hydrogels can be assessed as suitable scaffolds for periodontal regeneration therapy, as they provide adjustable, extracellular matrix-mimetic nanofibrillar architecture and favorable cellular interaction with periodontal cells.

Multicomponent peptide assemblies

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

Macromolecule-Network Electrostatics Controlling Delivery of the Biotherapeutic Cell Modulator TIMP-2

Tissue inhibitor of metalloproteinase 2 (TIMP-2) is an endogenous 22 kDa proteinase inhibitor, demonstrating antitumorigenic, antimetastatic and antiangiogenic activities in vitro and in vivo. Recombinant TIMP-2 is currently undergoing preclinical testing in multiple, murine tumor models. Here we report the development of an inert, injectable peptide hydrogel matrix enabling encapsulation and sustained release of TIMP-2. We studied the TIMP-2 release profile from four β-hairpin peptide gels of varying net electrostatic charge. A negatively charged peptide gel (designated AcVES3) enabling encapsulation of 4 mg/mL of TIMP-2, without effects on rheological properties, facilitated the slow sustained release (0.9%/d) of TIMP-2 over 28 d. Released TIMP-2 is structurally intact and maintains the ability to inhibit MMP activity, as well as suppress lung cancer cell proliferation in vitro. These findings suggest that the AcVES3 hydrogel will be useful as an injectable vehicle for systemic delivery of TIMP-2 in vivo for ongoing preclinical development.

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

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

Balancing hydrophobicity and sequence pattern to influence self-assembly of amphipathic peptides

Amphipathic peptides with alternating polar and nonpolar amino acid sequences efficiently self-assemble into functional β-sheet fibrils as long as the nonpolar residues have sufficient hydrophobicity. For example, the Ac-(FKFE)2 -NH2 peptide rapidly self-assembles into β-sheet bilayer nanoribbons, while Ac-(AKAE)2 -NH2 fails to self-assemble under similar conditions due to the significantly reduced hydrophobicity and β-sheet propensity of Ala relative to Phe. Herein, we systematically explore the effect of substituting only two of the four Ala residues at various positions in the Ac-(AKAE)2 -NH2 peptide with amino acids of increasing hydrophobicity, β-sheet potential, and surface area (including Phe, 1-naphthylalanine (1-Nal), 2-naphthylalanine (2-Nal), cyclohexylalanine (Cha), and pentafluorophenylalanine (F5 -Phe)) on the self-assembly propensity of the resulting sequences. It was found that double Phe variants, regardless of the position of substitution, failed to self-assemble under the conditions used in this study. In contrast, all double 1-Nal and 2-Nal variants readily self-assembled, albeit at differing rates depending on the substitution patterns. To determine whether this was due to hydrophobicity or side chain surface area, we also prepared double Cha and F5 -Phe variant peptides (both side chain groups are more hydrophobic than Phe). Each of these variants also underwent effective self-assembly, with the aromatic F5 -Phe peptides doing so with greater efficiency. These findings provide insight into the role of amino acid hydrophobicity and sequence pattern on self-assembly proclivity of amphipathic peptides and on how targeted substitutions of nonpolar residues in these sequences can be exploited to tune the characteristics of the resulting self-assembled materials.

Bio-inspired synthesis of a hierarchical self-assembled zinc phosphate nanostructure in the presence of cowpea mosaic virus: in vitro cell cycle, proliferation and prospects for tissue regeneration

Self-assembly is an important auto-organization process used in designing structural biomaterials which have the potential capability to heal tissues after traumatic injury. Although various materials having the ability to heal after injury are available, there is still a substantial need to develop new improved materials. To address this issue, we have developed hierarchical three-dimensional (3D) self-assembled zinc phosphate (Zn₃(PO₄)₂) in the presence of cowpea mosaic virus (CPMV). Zn₃(PO₄)₂ nanoparticles are self-assembled into nanosheets with a high degree of isotropy and then self-organized into a 3D structure that can enhance surface interactions with biological entities. The self-assembled structure is formed through the auto-organization of nanoparticles of size ∼50 nm under the influence of CPMV. The cellular response of self-assembled Zn₃(PO₄)₂ and cell-particle adhesion behavior have been investigated through in vitro studies using modeled osteoblast-like MG63 cells. Self-assembled Zn₃(PO₄)₂ resulted in proliferation of MG63 cells of up to 310% within 7 days of incubation. A 15% higher proliferation was obtained than with commercially available hydroxyapatite (HAp). Immunofluorescent analysis of MG63 cells after co-culturing with self-assembled Zn₃(PO₄)₂ confirmed the healthy cytoskeletal organization and dense proliferation of MG63 cells. Further, Zn₃(PO₄)₂ exhibited ∼28% cell-cycle progression in S phase, which is higher than obtained with commercially available HAp. Overall, these results demonstrate the multiple functions of hierarchical self-assembled Zn₃(PO₄)₂ in the regeneration of bone tissue without defects and increasing the formation of cellular networks, and suggest its use in bone tissue engineering.

Carbon Monoxide and Its Controlled Release: Therapeutic Application, Detection, and Development of Carbon Monoxide Releasing Molecules (CORMs)

Carbon monoxide (CO) is attracting increasing attention because of its role as a gasotransmitter with cytoprotective and homeostatic properties. Carbon monoxide releasing molecules (CORMs) are spatially and temporally controlled CO releasers that exhibit superior and more effective pharmaceutical traits than gaseous CO because of their chemistry and structure. Experimental and preclinical research in animal models has shown the therapeutic potential of inhaled CO and CORMs, and the biological effects of CO and CORMs have also been observed in preclinical trials via the genetic modulation of heme oxygenase-1 (HO-1). In this review, we describe the pharmaceutical use of CO and CORMs, methods of detecting CO release, and developments in CORM design and synthesis. Many valuable clinical CORMs formulated using macromolecules and nanomaterials are also described.

Molecular, Local, and Network-Level Basis for the Enhanced Stiffness of Hydrogel Networks Formed from Coassembled Racemic Peptides: Predictions from Pauling and Corey

Hydrogels prepared from self-assembling peptides are promising materials for medical applications, and using both l- and d-peptide isomers in a gel's formulation provides an intuitive way to control the proteolytic degradation of an implanted material. In the course of developing gels for delivery applications, we discovered that a racemic mixture of the mirror-image β-hairpin peptides, named MAX1 and DMAX1, provides a fibrillar hydrogel that is four times more rigid than gels formed by either peptide alone-a puzzling observation. Herein, we use transmission electron microscopy, small angle neutron scattering, solid state NMR, diffusing wave, infrared, and fluorescence spectroscopies, and modeling to determine the molecular basis for the increased mechanical rigidity of the racemic gel. We find that enantiomeric peptides coassemble in an alternating fashion along the fibril long axis, forming an extended heterochiral pleat-like β-sheet, a structure predicted by Pauling and Corey in 1953. Hydrogen bonding between enantiomers within the sheet dictates the placement of hydrophobic valine side chains in the fibrils' dry interior in a manner that allows the formation of nested hydrophobic interactions between enantiomers, interactions not accessible within enantiomerically pure fibrils. Importantly, this unique molecular arrangement of valine side chains maximizes inter-residue contacts within the core of the fibrils resulting in their local stiffening, which in turn, gives rise to the significant increase in bulk mechanical rigidity observed for the racemic hydrogel.

Multifunctional, biocompatible and pH-responsive carbon nanotube- and graphene oxide/tectomer hybrid composites and coatings

Here we present a route for non-covalent functionalization of carboxylated multi-walled carbon nanotubes and graphene oxide with novel two-dimensional peptide assemblies. We show that self-assembled amino-terminated biantennary and tetraantennary oligoglycine peptides (referred to as tectomers) effectively coat carboxylated multi-walled carbon nanotubes and also strongly interact with graphene oxide due to electrostatic interactions and hydrogen bonding as the driving force, respectively. The resulting hybrids can be made into free-standing conducting composites or applied in the form of thin, pH-switchable bioadhesive coatings onto graphene oxide fibers. Monitoring of cell viability of pancreatic cell lines, seeded on those CNT hybrids, show that they can be used as two- and three-dimensional scaffolds to tissue engineer tumour models for studying ex vivo the tumour development and response to treatment. This highly versatile method in producing pH-responsive hybrids and coatings offers an attractive platform for a variety of biomedical applications and for the development of functional materials such as smart textiles, sensors and bioelectronic devices.

Femtosecond laser micro-machined polyimide films for cell scaffold applications

Engineering of sophisticated synthetic 3D scaffolds that allow controlling behaviour and location of the cells requires advanced micro/nano-fabrication techniques. Ultrafast laser micro-machining employing a 1030-nm wavelength Yb:KGW femtosecond laser and a micro-fabrication workstation for micro-machining of commercially available 12.7 and 25.4 μm thickness polyimide (PI) film was applied. Mechanical properties of the fabricated scaffolds, i.e. arrays of differently spaced holes, were examined via custom-built uniaxial micro-tensile testing and finite element method simulations. We demonstrate that experimental micro-tensile testing results could be numerically simulated and explained by two-material model, assuming that 2-6 μm width rings around the holes possessed up to five times higher Young's modulus and yield stress compared with the rest of the laser intacted PI film areas of 'dog-bone'-shaped specimens. That was attributed to material modification around the micro-machined holes in the vicinity of the position of the focused laser beam track during trepanning drilling. We demonstrate that virgin PI films provide a suitable environment for the mobility, proliferation and intercellular communication of human bone marrow mesenchymal stem cells, and discuss how cell behaviour varies on the micro-machined PI films with holes of different diameters (3.1, 8.4 and 16.7 μm) and hole spacing (30, 35, 40 and 45 μm). We conclude that the holes of 3.1 μm diameter were sufficient for metabolic and genetic communication through membranous tunneling tubes between cells residing on the opposite sides of PI film, but prevented the trans-migration of cells through the holes. Copyright © 2016 John Wiley & Sons, Ltd.

Role of Hydrophobic/Aromatic Residues on the Stability of Double-Wall β-Sheet Structures Formed by a Triblock Peptide

Bioinspired self-assembling peptides serve as powerful building blocks in the manufacturing of nanomaterials with tailored features. Because of their ease of synthesis, biocompatibility, and tunable activity, this emerging branch of biomolecules has become very popular. The triblock peptide architecture designed by the Hartgerink group is a versatile system that allows control over its assembly and has been shown to demonstrate tunable bioactivity. Three main forces, Coulomb repulsion, hydrogen bonding and hydrophobicity act together to guide the triblock peptides' assembly into one-dimensional objects and hydrogels. It was shown previously that both the nanofiber morphology (e.g., intersheet spacing, formation of antiparallel/parallel β-sheets) and hydrogel rheology strictly depend on the choice of the core residue where the triblock peptide fibers with aromatic cores in general form shorter fibers and yield poor hydrogels with respect to the ones with aliphatic cores. However, an elaborate understanding of the molecular reasons behind these changes remained unclear. In this study, by using carefully designed computer based free energy calculations, we analyzed the influence of the core residue on the formation of double-wall fibers and single-wall β-sheets. Our results demonstrate that the aromatic substitution impairs the fiber cores and this impairment is mainly associated with a reduced hydrophobic character of the aromatic side chains. Such weakening is most obvious in tryptophan containing peptides where the fiber core absorbs a significant amount of water. We also show that the ability of tyrosine to form side chain hydrogen bonds plays an indispensable role in the fiber stability. As opposed to the impairment of the fiber cores, single-wall β-sheets with aromatic faces become more stable compared to the ones with aliphatic faces suggesting that the choice of the core residue can also affect the underlying assembly mechanism. We also provide an in-depth comparison of competing structures (zero-dimensional aggregates, short and long fibers) in the triblock peptides' assembly and show that by adjusting the length of the terminal blocks, the fiber growth can be turned on or off while keeping the nanofiber morphology intact.

Self-Assembling Multidomain Peptide Nanofibers for Delivery of Bioactive Molecules and Tissue Regeneration

Multidomain peptides (MDPs) are a class of self-assembling peptides that are organized in a β-sheet motif, resulting in a nanofibrous architecture. This structure is stabilized by hydrophobic packing in the fiber core and a hydrogen-bonding network down the fiber long axis. Under easily controllable conditions, regulated by electrostatic interactions between the peptides and the pH and salt composition of the solvent, the nanofiber length can be dramatically extended, resulting in fiber entanglement and hydrogel formation. One of the chief strengths of this supramolecular material is that the design criteria governing its structure and assembly are robust and permit a wide range of modifications without disruption. This allows the MDPs to be tailored to suit a wide range of applications, particularly in biomedical engineering. For example, delivery of small molecules, proteins, and cells is easily achievable. These materials can be trapped within the matrices of the hydrogel or trapped within the hydrophobic core of the nanofiber, depending on the cargo and the design of the MDP. Interactions between the nanofibers and their cargo can be tailored to alter the release profile, and in the most sophisticated cases, different cargos can be released in a cascading time-dependent fashion. The MDP hydrogel and its cargo can be targeted to specific locations, as the thixotropic nature of the hydrogel allows it to be easily aspirated into a syringe and then delivered from a narrow-bore needle. The sequence of amino acids making up the MDP can also be modified to permit cross-linking or enzymatic degradation. Selection of sequences with or without these modifications allows one to control the rate of degradation in vivo from as rapidly as 1 week to well over 6 weeks as the MDP nanofibers are degraded to their amino acid components. MDP sequences can also be modified to add biomimetic sequences derived from growth factors and other signaling proteins. These chemical signals are displayed at a very high density on the fibers’ surface, where they contribute to the modification of cellular behavior. We have used this approach to drive blood vessel formation, which is critical for tissue regeneration generally and more specifically for the treatment of diseases related to poor blood flow. MDPs represent an ideal case of bottom-up design where control of chemical structure leads to control of self-assembly and nanostructure and thereby control of material properties that collectively can control biological function.

Biomimetic Remineralization of Carious Lesions by Self-Assembling Peptide

Caries is the most common disease in the world. Great efforts have been undertaken for prevention and to identify a regenerative treatment solution for dental caries. Self-assembling β-sheet forming peptides have previously shown to form 3-dimensional fiber networks supporting tissue regeneration. In particular, the self-assembling peptide P₁₁-4 has shown potential in the treatment and prevention of dental caries. It has previously been shown that application of monomeric P₁₁-4 solution to early carious lesions can increase net mineral gain by forming de novo hydroxyapatite crystals. The hypothesis for the mode of action was that monomeric self-assembling peptide P₁₁-4 diffuses into the subsurface lesion body and assembles therein into higher order fibrils, facilitating mineralization of the subsurface volume by mimicking the natural biomineralization of the tooth enamel, and it remains within the lesion body as a scaffold built-in by the newly formed hydroxyapatite. The aim of the present study was to investigate the mechanism of action of the self-assembling peptide P₁₁-4 supporting mineralization of carious enamel. By various analytical methods, it could be shown that the self-assembling peptide P₁₁-4 diffuses into the subsurface lesion, assembles into higher formed aggregates throughout the whole volume of the lesion, and supports nucleation of de novo hydroxyapatite nanocrystals and consequently results in increased mineral density within the subsurface carious lesion. The results showed that the application of self-assembling peptide P₁₁-4 can facilitate the subsurface regeneration of the enamel lesion by supporting de novo mineralization in a similar mode of action as has been shown for the natural formation of dental enamel.