Ultrashort Peptide Bioinks Support Automated Printing of Large-Scale Constructs Assuring Long-Term Survival of Printed Tissue Constructs

3D Bioprinting Using Universal Fugitive Network Bioinks

Three-dimensional (3D) bioprinting has emerged with potential for creating functional 3D tissues with customized geometries. However, the limited availability of bioinks capable of printing 3D structures with both high-shape fidelity and desired biological environments for encapsulated cells remains a key challenge. Here, we present a 3D bioprinting approach that uses universal fugitive network bioinks prepared by loading cells and hydrogel precursors (bioink base materials) into a 3D printable fugitive carrier. This approach constructs 3D structures of cell-encapsulated hydrogels by printing 3D structures using fugitive network bioinks, followed by cross-linking printed structures and removing the carrier from them. The use of the fugitive carrier decouples the 3D printability of bioinks from the material properties of bioink base materials, making this approach readily applicable to a range of hydrogel systems. The decoupling also enables the design of bioinks for the biological functionality of the final printed constructs without compromising the 3D printability. We demonstrate the generalizable 3D printability by printing self-supporting 3D structures of various hydrogels, including conventionally non-3D printable hydrogels and those with a low polymer content. We conduct preprinting screening of bioink base materials through 3D cell culture to select bioinks with high cell compatibility. The selected bioinks produce 3D constructs of cell-encapsulated hydrogels with both high-shape fidelity and high cell viability and proliferation. The universal fugitive network bioink platform could significantly expand 3D printable bioinks with customizable biological functionalities and the adoption of 3D bioprinting in diverse research and applied settings.

Fundamentals and Applications of Raman-Based Techniques for the Design and Development of Active Biomedical Materials

Raman spectroscopy is an analytical method based on light-matter interactions that can interrogate the vibrational modes of matter and provide representative molecular fingerprints. Mediated by its label-free, non-invasive nature, and high molecular specificity, Raman-based techniques have become ubiquitous tools for in situ characterization of materials. This review comprehensively describes the theoretical and practical background of Raman spectroscopy and its advanced variants. The numerous facets of material characterization that Raman scattering can reveal, including biomolecular identification, solid-to-solid phase transitions, and spatial mapping of biomolecular species in bioactive materials, are highlighted. The review illustrates the potential of these techniques in the context of active biomedical material design and development by highlighting representative studies from the literature. These studies cover the use of Raman spectroscopy for the characterization of both natural and synthetic biomaterials, including engineered tissue constructs, biopolymer systems, ceramics, and nanoparticle formulations, among others. To increase the accessibility and adoption of these techniques, the present review also provides the reader with practical recommendations on the integration of Raman techniques into the experimental laboratory toolbox. Finally, perspectives on how recent developments in plasmon- and coherently-enhanced Raman spectroscopy can propel Raman from underutilized to critical for biomaterial development are provided.

3D-Printing Multi-Component Multi-Domain Supramolecular Gels with Differential Conductivity

We report the use of wet-spinning to 3D-print gels from low-molecular-weight gelators (LMWGs) based on the 1,3 : 2,4-dibenzylidenesorbitol (DBS) scaffold. Gel stripes assembled from DBS-CONHNH2 and DBS-COOH are printed, and their conductivities assessed. Printed gels based on DBS-CONHNH2 can be loaded with Au(III), which is reduced in situ to form embedded gold nanoparticles (AuNPs). The conductivity of these gels increases because of electron transport mediated by the AuNPs, whereas the conductivity of DBS-COOH, which does not promote AuNP formation, remains lower. We then fabricate multi-component gel patterns comprised of spatially well-defined domains of printed DBS-CONHNH2/AuNP (higher conductivity) and DBS-COOH (lower conductivity) resulting in soft multi-domain materials with differential conductivity. Such materials have future prospects in applications such as soft nanoelectronics or tissue engineering.

Salt-induced Fmoc-tripeptide supramolecular hydrogels: a combined experimental and computational study of the self-assembly

Delving into the mechanism behind the molecular interactions at the atomic level of short-sequence peptides plays a key role in the development of nanomaterials with specific structure-property-function relationships from a bottom-up perspective. Due to their poor water solubility, the self-assembly of Fmoc-bearing peptides is usually induced by dissolution in an organic solvent, followed by a dilution step in water, pH changes, and/or a heating-cooling process. Herein, we report a straightforward methodology for the gelation of Fmoc-FFpY (F: phenylalanine; Y: tyrosine; and p: PO42-), a negatively charged tripeptide, in NaCl solution. The electrostatic interactions between Fmoc-FFpY and Na+ ions give rise to different nanofibrillar hydrogels with rheological properties and nanofiber sizes modulated by the NaCl concentration in pure aqueous media. Initiated by the electrostatic interactions between the peptide phosphate groups and the Na+ ions, the peptide self-assembly is stabilized thanks to hydrogen bonds between the peptide backbones and the π-π stacking of aromatic Fmoc and phenyl units. The hydrogels showed self-healing and thermo-responsive properties for potential biomedical applications. Molecular dynamics simulations from systems devoid of prior training not only confirm the aggregation of peptides at a critical salt concentration and the different interactions involved, but also corroborate the secondary structure of the hydrogels at the microsecond timescale. It is worth highlighting the remarkable achievement of reproducing the morphological behavior of the hydrogels using atomistic simulations. To our knowledge, this study is the first to report such a correspondence.

Peptide Gel Electrolytes for Stabilized Zn Metal Anodes

The rechargeable aqueous Zn ion battery (AZIB) is considered a promising candidate for future energy storage applications due to its intrinsic safety features and low cost. However, Zn dendrites and side reactions (e.g., corrosion, hydrogen evolution reaction, and inactive side product (Zn hydroxide sulfate) formation) at the Zn metal anode have been serious obstacles to realizing a satisfactory AZIB performance. The application of gel electrolytes is a common strategy for suppressing these problems, but the normally used highly cross-linked polymer matrix (e.g., polyacrylamide (PAM)) brings additional difficulties for battery assembly and recycling. Herein, we have developed a gel electrolyte for Zn metal anode stabilization, where a peptide matrix, a highly biocompatible material, is used for gel construction. Various experiments and simulations elucidate the sulfate anion-assisted self-assembly gel formation and its effect in stabilizing Zn metal anodes. Unlike polymer gel electrolytes, the peptide gel electrolyte can reversibly transform between gel and liquid states, thus facilitating the gel-involved battery assembly and recycling. Furthermore, the peptide gel electrolyte provides fast Zn ion diffusion (comparable to conventional liquid electrolyte) while suppressing side reactions and dendrite growth, thus achieving highly stable Zn metal anodes as validated in various cell configurations. We believe that our concept of gel electrolyte design will inspire more future directions for Zn metal anode protection based on gel electrolyte design.

Marine polysaccharides, proteins, lipids, and silica for drug delivery systems: A review

Marine environments represent an incredible source of biopolymers with potential biomedical applications. Recently, drug delivery studies have received great attention for the increasing need to improve site specificity, therapeutic value, and bioavailability, reducing off-target effects. Marine polymers, such as alginate, carrageenan, collagen, chitosan, and silica, have reported unique biochemical features, allowing an efficient binding with drugs, and a controlled release to the target tissue, also obtainable through "green processes". In the present review, we i) analysed the last ten years of scientific peer-reviewed literature; ii) divided the articles based on the achieved experimental phases, tagged as chemistry, drug release, and drug delivery, and iii) compared the best performances among marine polymers extracted from micro- and macro-organisms. Many reviews describe drug carriers from marine organisms, focusing on a single biopolymer or a chemical class. Our study is a groundbreaking literature collection, representing the first thorough investigation of all marine biopolymers described. Most articles report experimental results on the chemical characterisation of marine biopolymers and their in vitro behaviour as drug carriers, although development processes and commercial applications are still in the early stages. Hence, the next efforts should be focused on the sustainable production of marine polymers and final product development.

Selectively Positioned Catechol Moiety Supports Ultrashort Self-Assembling Peptide Hydrogel Adhesion for Coral Restoration

Coral reef survival is threatened globally. One way to restore this delicate ecosystem is to enhance coral growth by the controlled propagation of coral fragments. To be sustainable, this technique requires the use of biocompatible underwater adhesives. Hydrogels based on rationally designed ultrashort self-assembling peptides (USP) are of great interest for various biological and environmental applications, due to their biocompatibility and tunable mechanical properties. Implementing superior adhesion properties to the USP hydrogel compounds is crucial in both water and high ionic strength solutions and is relevant in medical and marine environmental applications such as coral regeneration. Some marine animals secrete large quantities of the aminoacids dopa and lysine to enhance their adhesion to wet surfaces. Therefore, the addition of catechol moieties to the USP sequence containing lysine (IIZK) should improve the adhesive properties of USP hydrogels. However, it is challenging to place the catechol moiety (Do) within the USP sequence at an optimal position without compromising the hydrogel self-assembly process and mechanical properties. Here, we demonstrate that, among three USP hydrogels, DoIIZK is the least adhesive and that the adhesiveness of the IIZDoK hydrogel is compromised by its poor mechanical properties. The best adhesion outcome was achieved using the IIZKDo hydrogel, the only one to show equally sound adhesive and mechanical properties. A mechanistic understanding of this outcome is presented here. This property was confirmed by the successful gluing of coral fragments by means of IIZKDo hydrogel that are still thriving after more than three years since the deployment. The validated biocompatibility of this underwater hydrogel glue suggests that it could be advantageously implemented for other applications, such as surgical interventions.

Fabrication of a three-dimensional bone marrow niche-like acute myeloid Leukemia disease model by an automated and controlled process using a robotic multicellular bioprinting system

BACKGROUND

Acute myeloid leukemia (AML) is a hematological malignancy that remains a therapeutic challenge due to the high incidence of disease relapse. To better understand resistance mechanisms and identify novel therapies, robust preclinical models mimicking the bone marrow (BM) microenvironment are needed. This study aimed to achieve an automated fabrication process of a three-dimensional (3D) AML disease model that recapitulates the 3D spatial structure of the BM microenvironment and applies to drug screening and investigational studies.

METHODS

To build this model, we investigated a unique class of tetramer peptides with an innate ability to self-assemble into stable hydrogel. An automated robotic bioprinting process was established to fabricate a 3D BM (niche-like) multicellular AML disease model comprised of leukemia cells and the BM's stromal and endothelial cellular fractions. In addition, monoculture and dual-culture models were also fabricated. Leukemia cell compatibility, functionalities (in vitro and in vivo), and drug assessment studies using our model were performed. In addition, RNAseq and gene expression analysis using TaqMan arrays were also performed on 3D cultured stromal cells and primary leukemia cells.

RESULTS

The selected peptide hydrogel formed a highly porous network of nanofibers with mechanical properties similar to the BM extracellular matrix. The robotic bioprinter and the novel quadruple coaxial nozzle enabled the automated fabrication of a 3D BM niche-like AML disease model with controlled deposition of multiple cell types into the model. This model supported the viability and growth of primary leukemic, endothelial, and stromal cells and recapitulated cell-cell and cell-ECM interactions. In addition, AML cells in our model possessed quiescent characteristics with improved chemoresistance attributes, resembling more the native conditions as indicated by our in vivo results. Moreover, the whole transcriptome data demonstrated the effect of 3D culture on enhancing BM niche cell characteristics. We identified molecular pathways upregulated in AML cells in our 3D model that might contribute to AML drug resistance and disease relapse.

CONCLUSIONS

Our results demonstrate the importance of developing 3D biomimicry models that closely recapitulate the in vivo conditions to gain deeper insights into drug resistance mechanisms and novel therapy development. These models can also improve personalized medicine by testing patient-specific treatments.

Intelligent Vascularized 3D/4D/5D/6D-Printed Tissue Scaffolds

Blood vessels are essential for nutrient and oxygen delivery and waste removal. Scaffold-repairing materials with functional vascular networks are widely used in bone tissue engineering. Additive manufacturing is a manufacturing technology that creates three-dimensional solids by stacking substances layer by layer, mainly including but not limited to 3D printing, but also 4D printing, 5D printing and 6D printing. It can be effectively combined with vascularization to meet the needs of vascularized tissue scaffolds by precisely tuning the mechanical structure and biological properties of smart vascular scaffolds. Herein, the development of neovascularization to vascularization to bone tissue engineering is systematically discussed in terms of the importance of vascularization to the tissue. Additionally, the research progress and future prospects of vascularized 3D printed scaffold materials are highlighted and presented in four categories: functional vascularized 3D printed scaffolds, cell-based vascularized 3D printed scaffolds, vascularized 3D printed scaffolds loaded with specific carriers and bionic vascularized 3D printed scaffolds. Finally, a brief review of vascularized additive manufacturing-tissue scaffolds in related tissues such as the vascular tissue engineering, cardiovascular system, skeletal muscle, soft tissue and a discussion of the challenges and development efforts leading to significant advances in intelligent vascularized tissue regeneration is presented.

In Situ Covalent Reinforcement of a Benzene-1,3,5-Tricarboxamide Supramolecular Polymer Enables Biomimetic, Tough, and Fibrous Hydrogels and Bioinks

Synthetic hydrogels often lack the load-bearing capacity and mechanical properties of native biopolymers found in tissue, such as cartilage. In natural tissues, toughness is often imparted via the combination of fibrous noncovalent self-assembly with key covalent bond formation. This controlled combination of supramolecular and covalent interactions remains difficult to engineer, yet can provide a clear strategy for advanced biomaterials. Here, a synthetic supramolecular/covalent strategy is investigated for creating a tough hydrogel that embodies the hierarchical fibrous architecture of the extracellular matrix (ECM). A benzene-1,3,5-tricarboxamide (BTA) hydrogelator is developed with synthetically addressable norbornene handles that self-assembles to form a and viscoelastic hydrogel. Inspired by collagen's covalent cross-linking of fibrils, the mechanical properties are reinforced by covalent intra- and interfiber cross-links. At over 90% water, the hydrogels withstand up to 550% tensile strain, 90% compressive strain, and dissipated energy with recoverable hysteresis. The hydrogels are shear-thinning, can be 3D bioprinted with good shape fidelity, and can be toughened via covalent cross-linking. These materials enable the bioprinting of human mesenchymal stromal cell (hMSC) spheroids and subsequent differentiation into chondrogenic tissue. Collectively, these findings highlight the power of covalent reinforcement of supramolecular fibers, offering a strategy for the bottom-up design of dynamic, yet tough, hydrogels and bioinks.

The Impact of Mechanical Cues on the Metabolomic and Transcriptomic Profiles of Human Dermal Fibroblasts Cultured in Ultrashort Self-Assembling Peptide 3D Scaffolds

Cells' interactions with their microenvironment influence their morphological features and regulate crucial cellular functions including proliferation, differentiation, metabolism, and gene expression. Most biological data available are based on in vitro two-dimensional (2D) cellular models, which fail to recapitulate the three-dimensional (3D) in vivo systems. This can be attributed to the lack of cell-matrix interaction and the limitless access to nutrients and oxygen, in contrast to in vivo systems. Despite the emergence of a plethora of 3D matrices to address this challenge, there are few reports offering a proper characterization of these matrices or studying how the cell-matrix interaction influences cellular metabolism in correlation with gene expression. In this study, two tetrameric ultrashort self-assembling peptide sequences, FFIK and FIIK, were used to create in vitro 3D models using well-described human dermal fibroblast cells. The peptide sequences are derived from naturally occurring amino acids that are capable of self-assembling into stable hydrogels without UV or chemical cross-linking. Our results showed that 2D cultured fibroblasts exhibited distinct metabolic and transcriptomic profiles compared to 3D cultured cells. The observed changes in the metabolomic and transcriptomic profiles were closely interconnected and influenced several important metabolic pathways including the TCA cycle, glycolysis, MAPK signaling cascades, and hemostasis. Data provided here may lead to clearer insights into the influence of the surrounding microenvironment on human dermal fibroblast metabolic patterns and molecular mechanisms, underscoring the importance of utilizing efficient 3D in vitro models to study such complex mechanisms.

Molecular Tuning of a Benzene-1,3,5-Tricarboxamide Supramolecular Fibrous Hydrogel Enables Control over Viscoelasticity and Creates Tunable ECM-Mimetic Hydrogels and Bioinks

Traditional synthetic covalent hydrogels lack the native tissue dynamics and hierarchical fibrous structure found in the extracellular matrix (ECM). These dynamics and fibrous nanostructures are imperative in obtaining the correct cell/material interactions. Consequently, the challenge to engineer functional dynamics in a fibrous hydrogel and recapitulate native ECM properties remains a bottle-neck to biomimetic hydrogel environments. Here, the molecular tuning of a supramolecular benzene-1,3,5-tricarboxamide (BTA) hydrogelator via simple modulation of hydrophobic substituents is reported. This tuning results in fibrous hydrogels with accessible viscoelasticity over 5 orders of magnitude, while maintaining a constant equilibrium storage modulus. BTA hydrogelators are created with systematic variations in the number of hydrophobic carbon atoms, and this is observed to control the viscoelasticity and stress-relaxation timescales in a logarithmic fashion. Some of these BTA hydrogels are shear-thinning, self-healing, extrudable, and injectable, and can be 3D printed into multiple layers. These hydrogels show high cell viability for chondrocytes and human mesenchymal stem cells, establishing their use in tissue engineering applications. This simple molecular tuning by changing hydrophobicity (with just a few carbon atoms) provides precise control over the viscoelasticity and 3D printability in fibrillar hydrogels and can be ported onto other 1D self-assembling structures. The molecular control and design of hydrogel network dynamics can push the field of supramolecular chemistry toward the design of new ECM-mimicking hydrogelators for numerous cell-culture and tissue-engineering applications and give access toward highly biomimetic bioinks for bioprinting.

The Influence of Prenatal Exposure to Methamphetamine on the Development of Dopaminergic Neurons in the Ventral Midbrain

Methamphetamine, a highly addictive central nervous system (CNS) stimulant, is used worldwide as an anorexiant and attention enhancer. Methamphetamine use during pregnancy, even at therapeutic doses, may harm fetal development. Here, we examined whether exposure to methamphetamine affects the morphogenesis and diversity of ventral midbrain dopaminergic neurons (VMDNs). The effects of methamphetamine on morphogenesis, viability, the release of mediator chemicals (such as ATP), and the expression of genes involved in neurogenesis were evaluated using VMDNs isolated from the embryos of timed-mated mice on embryonic day 12.5. We demonstrated that methamphetamine (10 µM; equivalent to its therapeutic dose) did not affect the viability and morphogenesis of VMDNs, but it reduced the ATP release negligibly. It significantly downregulated Lmx1a, En1, Pitx3, Th, Chl1, Dat, and Drd1 but did not affect Nurr1 or Bdnf expression. Our results illustrate that methamphetamine could impair VMDN differentiation by altering the expression of important neurogenesis-related genes. Overall, this study suggests that methamphetamine use may impair VMDNs in the fetus if taken during pregnancy. Therefore, it is essential to exercise strict caution for its use in expectant mothers.

3D Printing of Self-Assembling Nanofibrous Multidomain Peptide Hydrogels

3D printing has become one of the primary fabrication strategies used in biomedical research. Recent efforts have focused on the 3D printing of hydrogels to create structures that better replicate the mechanical properties of biological tissues. These pose a unique challenge, as soft materials are difficult to pattern in three dimensions with high fidelity. Currently, a small number of biologically derived polymers that form hydrogels are frequently reused for 3D printing applications. Thus, there exists a need for novel hydrogels with desirable biological properties that can be used as 3D printable inks. In this work, the printability of multidomain peptides (MDPs), a class of self-assembling peptides that form a nanofibrous hydrogel at low concentrations, is established. MDPs with different charge functionalities are optimized as distinct inks and are used to create complex 3D structures, including multi-MDP prints. Additionally, printed MDP constructs are used to demonstrate charge-dependent differences in cellular behavior in vitro. This work presents the first time that self-assembling peptides have been used to print layered structures with overhangs and internal porosity. Overall, MDPs are a promising new class of 3D printable inks that are uniquely peptide-based and rely solely on supramolecular mechanisms for assembly.

The Influence of Prenatal Exposure to Quetiapine Fumarate on the Development of Dopaminergic Neurons in the Ventral Midbrain of Mouse Embryos

The effects of second-generation antipsychotics on prenatal neurodevelopment, apoptotic neurodegeneration, and postnatal developmental delays have been poorly investigated. Even at standard doses, the use of quetiapine fumarate (QEPF) in pregnant women might be detrimental to fetal development. We used primary mouse embryonic neurons to evaluate the disruption of morphogenesis and differentiation of ventral midbrain (VM) neurons after exposure to QEPF. The dopaminergic VM neurons were deliberately targeted due to their roles in cognition, motor activity, and behavior. The results revealed that exposure to QEPF during early brain development decreased the effects of the dopaminergic lineage-related genes Tyrosine hydroxylase(Th), Dopamine receptor D1 (Drd1), Dopamine transporter (Dat), LIM homeobox transcription factor 1 alfa (Lmx1a), and Cell adhesion molecule L1 (Chl1), and the senescent dopaminergic gene Pituitary homeobox 3 (Pitx3). In contrast, Brain derived neurotrophic factor (Bdnf) and Nuclear receptor-related 1 (Nurr1) expressions were significantly upregulated. Interestingly, QEPF had variable effects on the development of non-dopaminergic neurons in VM. An optimal dose of QEPF (10 µM) was found to insignificantly affect the viability of neurons isolated from the VM. It also instigated a non-significant reduction in adenosine triphosphate formation in these neuronal populations. Exposure to QEPF during the early stages of brain development could also hinder the formation of VM and their structural phenotypes. These findings could aid therapeutic decision-making when prescribing 2nd generation antipsychotics in pregnant populations.

Wet-spinning multi-component low-molecular-weight gelators to print synergistic soft materials

Two different low-molecular-weight gelators (LMWGs) have been 3D-printed as filaments by wet-spininng. When the two LMWGs are simultaneously wet-spun, the co-assembled hybrid gel filaments combine the individual properties of the two gelators (dynamic pH response and in-situ metal nanoparticle formation) in synergistic ways, creating gel objects with new properties.

Modular mixing of benzene-1,3,5-tricarboxamide supramolecular hydrogelators allows tunable biomimetic hydrogels for control of cell aggregation in 3D

Few synthetic hydrogels can mimic both the viscoelasticity and supramolecular fibrous structure found in the naturally occurring extracellular matrix (ECM). Furthermore, the ability to control the viscoelasticity of fibrous supramolecular hydrogel networks to influence cell culture remains a challenge. Here, we show that modular mixing of supramolecular architectures with slow and fast exchange dynamics can provide a suitable environment for multiple cell types and influence cellular aggregation. We employed modular mixing of two synthetic benzene-1,3,5-tricarboxamide (BTA) architectures: a small molecule water-soluble BTA with slow exchange dynamics and a telechelic polymeric BTA-PEG-BTA with fast exchange dynamics. Copolymerisation of these two supramolecular architectures was observed, and all tested formulations formed stable hydrogels in water and cell culture media. We found that rational tuning of mechanical and viscoelastic properties is possible by mixing BTA with BTA-PEG-BTA. These hydrogels showed high viability for both chondrocyte (ATDC5) and human dermal fibroblast (HDF) encapsulation (>80%) and supported neuronal outgrowth (PC12 and dorsal root ganglion, DRG). Furthermore, ATDC5s and human mesenchymal stem cells (hMSCs) were able to form spheroids within these viscoelastic hydrogels, with control over cell aggregation modulated by the dynamic properties of the material. Overall, this study shows that modular mixing of supramolecular architectures enables tunable fibrous hydrogels, creating a biomimetic environment for cell encapsulation. These materials are suitable for the formation and culture of spheroids in 3D, critical for upscaling tissue engineering approaches towards cell densities relevant for physiological tissues.

An Overview of the Supramolecular Systems for Gene and Drug Delivery in Tissue Regeneration

Tissue regeneration is a prominent area of research, developing biomaterials aimed to be tunable, mechanistic scaffolds that mimic the physiological environment of the tissue. These biomaterials are projected to effectively possess similar chemical and biological properties, while at the same time are required to be safely and quickly degradable in the body once the desired restoration is achieved. Supramolecular systems composed of reversible, non-covalently connected, self-assembly units that respond to biological stimuli and signal cells have efficiently been developed as preferred biomaterials. Their biocompatibility and the ability to engineer the functionality have led to promising results in regenerative therapy. This review was intended to illuminate those who wish to envisage the niche translational research in regenerative therapy by summarizing the various explored types, chemistry, mechanisms, stimuli receptivity, and other advancements of supramolecular systems.

Multi-layer 3D printed dipeptide-based low molecular weight gels

We describe the direct 3D printing of dipeptide hydrogels, forming layers from gels prepared from different dipeptides. The dipeptides self-assemble into fibres that lead to very different microstructures letting us differentiate between the gels. We show how the mechanical properties of the overall 3D printed structures are affected by the composition of each of the layers, allowing us to build up structures with different microstructure and stiffness. We also discuss the interface between layers formed from different gelators, showing that the gels remain independent from neighbouring printed material, even when prepared in very close proximity.

Controlled-Alignment Patterns of Dipeptide Micro- and Nanofibers

Ordered assemblies of the peptide diphenylalanine (FF) are produced and deposited on planar substrates. The FF aggregate growth is achieved through precipitation from aqueous ammonia solutions induced by solvent evaporation. The applied dip-coating technique confines the FF assembly growth to a narrow zone near the three-phase contact. The growth was observed online by optical microscopy and was investigated systematically as a function of the process parameters. Depending on the external gas flow (to influence solvent evaporation), the withdrawal speed, the initial FF, and the initial ammonia concentrations, FF forms long, straight, and rigid microfibers and/or shorter, curved nanofibers. Under certain process conditions, the FF fibers can also aggregate into stripes. These can be deposited as large arrays of uniform stripes with regular widths and spacings. Scenarios leading to the various types of fibers and the stripe formation are presented and discussed in view of the experimental findings.

A Parkinson's disease model composed of 3D bioprinted dopaminergic neurons within a biomimetic peptide scaffold

Parkinson's disease (PD) is a progressive neurological disorder that affects movement. It is associated with lost dopaminergic (DA) neurons in thesubstantia nigra, a process that is not yet fully understood. To understand this deleterious disorder, there is an immense need to develop efficientin vitrothree-dimensional (3D) models that can recapitulate complex organs such as the brain. However, due to the complexity of neurons, selecting suitable biomaterials to accommodate them is challenging. Here, we report on the fabrication of functional DA neuronal 3D models using ultrashort self-assembling tetrapeptide scaffolds. Our peptide-based models demonstrate biocompatibility both for primary mouse embryonic DA neurons and for human DA neurons derived from human embryonic stem cells. DA neurons encapsulated in these scaffolds responded to 6-hydroxydopamine, a neurotoxin that selectively induces loss of DA neurons. Using multi-electrode arrays, we recorded spontaneous activity in DA neurons encapsulated within these 3D peptide scaffolds for more than 1 month without decrease of signal intensity. Additionally, vascularization of our 3D models in a co-culture with endothelial cells greatly promoted neurite outgrowth, leading to denser network formation. This increase of neuronal networks through vascularization was observed for both primary mouse DA and cortical neurons. Furthermore, we present a 3D bioprinted model of DA neurons inspired by the mouse brain and created with an extrusion-based 3D robotic bioprinting system that was developed during previous studies and is optimized with time-dependent pulsing by microfluidic pumps. We employed a hybrid fabrication strategy that relies on an external mold of the mouse brain construct that complements the shape and size of the desired bioprinted model to offer better support during printing. We hope that our 3D model provides a platform for studies of the pathogenesis of PD and other neurodegenerative disorders that may lead to better understanding and more efficient treatment strategies.

3D printing of biocompatible low molecular weight gels: Imbricated structures with sacrificial and persistent N-alkyl-d-galactonamides

HYPOTHESIS

We have shown earlier that low molecular weight gels based on N-heptyl-d-galactonamide hydrogels can be 3D printed by solvent exchange, but they tend to dissolve in the printing bath. We wanted to explore the printing of less soluble N-alkyl-d-galactonamides with longer alkyl chains. Less soluble hydrogels could be good candidates as cell culture scaffolds.

EXPERIMENTS

N-hexyl, N-octyl and N-nonyl-d-galactonamide solutions in dimethylsulfoxide are injected in a bath of water following patterns driven by a 2D drawing robot coupled to a z-platform. Solubilization of the gels with time has been determined and solubility of the gelators has been measured by NMR. Imbricated structures have been built with N-nonyl-d-galactonamide as a persistent ink and N-hexyl or N-heptyl-d-galactonamide as sacrificial inks. Human mesenchymal stem cells have been cultured on N-nonyl-d-galactonamide hydrogels prepared by cooling or by 3D printing.

FINDINGS

The conditions for printing well-resolved 3D patterns have been determined for the three gelators. In imbricated structures, the solubilization of N-hexyl or N-heptyl-d-galactonamide occurred after a few hours or days and gave channels. Human mesenchymal stem cells grown on N-nonyl-d-galactonamide hydrogels prepared by heating-cooling, which are stable and have a fibrillar microstructure, developed properly. 3D printed hydrogels, which microstructure is made of micrometric flakes, appeared too fragile to withstand cell growth.

Synthesis and Organization of Gold-Peptide Nanoparticles for Catalytic Activities

A significant development in the synthesis strategies of metal-peptide composites and their applications in biomedical and bio-catalysis has been reported. However, the random aggregation of gold nanoparticles provides the opportunity to find alternative fabrication strategies of gold-peptide composite nanomaterials. In this study, we used a facile strategy to synthesize the gold nanoparticles via a green and simple approach where they show self-alignment on the assembled nanofibers of ultrashort oligopeptides as a composite material. A photochemical reduction method is used, which does not require any external chemical reagents for the reduction of gold ions, and resultantly makes the gold nanoparticles of size ca. 5 nm under mild UV light exposure. The specific arrangement of gold nanoparticles on the peptide nanofibers may indicate the electrostatic interactions of two components and the interactions with the amino group of the peptide building block. Furthermore, the gold-peptide nanoparticle composites show the ability as a catalyst to degradation of environmental pollutant p-nitrophenol to p-aminophenol, and the reaction rate constant for catalysis is calculated as 0.057 min-1 at a 50-fold dilute sample of 2 mg/mL and 0.72 mM gold concentration in the composites. This colloidal strategy would help researchers to fabricate the metalized bioorganic composites for various biomedical and bio-catalysis applications.

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

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

Peptide nanogels as a scaffold for fabricating dermal grafts and 3D vascularized skin models

Millions of people worldwide suffer from skin injuries, which create significant problems in their lives and are costly to cure. Tissue engineering is a promising approach that aims to fabricate functional organs using biocompatible scaffolds. We designed ultrashort tetrameric peptides with promising properties required for skin tissue engineering. Our work aimed to test the efficacy of these scaffolds for the fabrication of dermal grafts and 3D vascularized skin tissue models. We found that the direct contact of keratinocytes and fibroblasts enhanced the proliferation of the keratinocytes. Moreover, the expression levels of TGF-β1, b-FGF, IL-6, and IL-1α is correlated with the growth of the fibroblasts and keratinocytes in the co-culture. Furthermore, we successfully produced a 3D vascularized skin co-culture model using these peptide scaffolds. We believe that the described results represent an advancement in the fabrication of skin tissue equivalent, thereby providing the opportunity to rebuild missing, failing, or damaged parts.

Graphical abstract

Ecologically Friendly Biofunctional Ink for Reconstruction of Rigid Living Systems Under Wet Conditions

The development of three-dimensional (3D)-printable inks is essential for several applications, from industrial manufacturing to novel applications for biomedical engineering. Remarkably, biomaterials for tissue engineering applications can be expanded to other new horizons; for instance, restoration of rigid living systems as coral reefs is an emergent need derived from recent issues from climate change. The coral reefs have been endangered, which can be observed in the increasing bleaching around the world. Very few studies report eco-friendly inks for matter since most conventional approaches require synthetic polymer, which at some point could be a pollutant depending on the material. Therefore, there is an unmet need for cost-effective formulations from eco-friendly materials for 3D manufacturing to develop carbonate-based inks for coral reef restoration. Our value proposition derives from technologies developed for regenerative medicine, commonly applied for human tissues like bone and cartilage. In our case, we created a novel biomaterial formulation from biopolymers such as gelatin methacrylate, poly (ethylene glycol diacrylate), alginate, and gelatin as scaffold and binder for the calcium carbonate and hydroxyapatite bioceramics needed to mimic the structure of rigid structures. This project presents evidence from 2D/3D manufacturing, chemical, mechanical, and biological characterization, which supports the hypothesis of its utility to aid in the fight to counteract the coral bleaching that affects all the marine ecosystem, primarily when this is supported by solid research in biomaterials science used for living systems, it can extend tissue engineering into new approaches in different domains such as environmental or marine sciences.

Exploiting the fundamentals of biological organization for the advancement of biofabrication

The field of biofabrication continues to progress, offering higher levels of spatial control, reproducibility, and functionality. However, we remain far from recapitulating what nature has achieved. Biological systems such as tissues and organs are assembled from the bottom-up through coordinated supramolecular and cellular processes that result in their remarkable structures and functionalities. In this perspective, we propose that incorporating such biological assembling mechanisms within fabrication techniques, offers an opportunity to push the boundaries of biofabrication. We dissect these mechanisms into distinct biological organization principles (BOPs) including self-assembly, compartmentalization, diffusion-reaction, disorder-to-order transitions, and out-of-equilibrium processes. We highlight recent work demonstrating the viability and potential of these approaches to enhance scalability, reproducibility, vascularization, and biomimicry; as well as current challenges to overcome.

Enhancing Peptide Biomaterials for Biofabrication

Biofabrication using well-matched cell/materials systems provides unprecedented opportunities for dealing with human health issues where disease or injury overtake the body’s native regenerative abilities. Such opportunities can be enhanced through the development of biomaterials with cues that appropriately influence embedded cells into forming functional tissues and organs. In this context, biomaterials’ reliance on rigid biofabrication techniques needs to support the incorporation of a hierarchical mimicry of local and bulk biological cues that mimic the key functional components of native extracellular matrix. Advances in synthetic self-assembling peptide biomaterials promise to produce reproducible mimics of tissue-specific structures and may go some way in overcoming batch inconsistency issues of naturally sourced materials. Recent work in this area has demonstrated biofabrication with self-assembling peptide biomaterials with unique biofabrication technologies to support structural fidelity upon 3D patterning. The use of synthetic self-assembling peptide biomaterials is a growing field that has demonstrated applicability in dermal, intestinal, muscle, cancer and stem cell tissue engineering.

Delivery of Endothelial Cell-Laden Microgel Elicits Angiogenesis in Self-Assembling Ultrashort Peptide Hydrogels In Vitro

Blood vessel generation is an essential process for tissue formation, regeneration, and repair. Notwithstanding, vascularized tissue fabrication in vitro remains a challenge, as current fabrication techniques and biomaterials lack translational potential in medicine. Naturally derived biomaterials harbor the risk of immunogenicity and pathogen transmission, while synthetic materials need functionalization or blending to improve their biocompatibility. In addition, the traditional top-down fabrication techniques do not recreate the native tissue microarchitecture. Self-assembling ultrashort peptides (SUPs) are promising chemically synthesized natural materials that self-assemble into three-dimensional nanofibrous hydrogels resembling the extracellular matrix (ECM). Here, we use a modular tissue-engineering approach, embedding SUP microgels loaded with human umbilical vein endothelial cells (HUVECs) into a 3D SUP hydrogel containing human dermal fibroblast neonatal (HDFn) cells to trigger angiogenesis. The SUPs IVFK and IVZK were used to fabricate microgels that gel in a water-in-oil emulsion using a microfluidic droplet generator chip. The fabricated SUP microgels are round structures that are 300-350 μm diameter in size and have ECM-like topography. In addition, they are stable enough to keep their original size and shape under cell culture conditions and long-term storage. When the SUP microgels were used as microcarriers for growing HUVECs and HDFn cells on the microgel surface, cell attachment, stretching, and proliferation could be demonstrated. Finally, we performed an angiogenesis assay in both SUP hydrogels using all SUP combinations between micro- and bulky hydrogels. Endothelial cells were able to migrate from the microgel to the surrounding area, showing angiogenesis features such as sprouting, branching, coalescence, and lumen formation. Although both SUP hydrogels support vascular network formation, IVFK outperformed IVZK in terms of vessel network extension and branching. Overall, these results demonstrated that cell-laden SUP microgels have great potential to be used as a microcarrier cell delivery system, encouraging us to study the angiogenesis process and to develop vascularized tissue-engineering therapies.

Wet spinning of a library of carbohydrate low molecular weight gels

HYPOTHESIS

Recently, a low molecular weight hydrogel based on a carbohydrate alkyl amide has been successfully used as biomaterial for neuron cell culture and for 3D printing. Varying the molecular structure should make it possible to extend the library of carbohydrate low molecular weight hydrogels available for these applications and to improve their performances.

EXPERIMENTS

Thirteen molecules easy to synthetize and designed to be potentially biocompatible were prepared. They are based on gluconamide, glucoheptonamide, galactonamide, glucamide, aliphatic chains and glycine. Their gelation in water was investigated in thermal conditions and wet spinning conditions, namely by dimethylsulfoxide-water exchange under injection.

FINDINGS

Nine molecules give hydrogels in thermal conditions. By wet spinning, six molecules self-assemble fast enough, within few seconds, to form continous hydrogel filaments. Therefore, the method enables to shape by injection these mechanically fragile hydrogels, notably in the perspective of 3D printing. Depending on the molecular structure, persistent or soluble gel filaments are obtained. The microstructures are varied, featuring entangled ribbons, platelets or particles. In thermal gelation, molecules with a symmetrical polar head (galacto, glucoheptono) give flat ribbons and molecules with an asymmetrical polar head (gluco) give helical ribbons. The introduction of an extra glycine linker disturbs this trend.

Scaffolds from Self-Assembling Tetrapeptides Support 3D Spreading, Osteogenic Differentiation, and Angiogenesis of Mesenchymal Stem Cells

The apparent rise of bone disorders demands advanced treatment protocols involving tissue engineering. Here, we describe self-assembling tetrapeptide scaffolds for the growth and osteogenic differentiation of human mesenchymal stem cells (hMSCs). The rationally designed peptides are synthetic amphiphilic self-assembling peptides composed of four amino acids that are nontoxic. These tetrapeptides can quickly solidify to nanofibrous hydrogels that resemble the extracellular matrix and provide a three-dimensional (3D) environment for cells with suitable mechanical properties. Furthermore, we can easily tune the stiffness of these peptide hydrogels by just increasing the peptide concentration, thus providing a wide range of peptide hydrogels with different stiffnesses for 3D cell culture applications. Since successful bone regeneration requires both osteogenesis and vascularization, our scaffold was found to be able to promote angiogenesis of human umbilical vein endothelial cells (HUVECs) in vitro. The results presented suggest that ultrashort peptide hydrogels are promising candidates for applications in bone tissue engineering.