The study highlights developments in hydrogel materials with biological responsiveness built in. These ‘smart’ biomaterials change properties in response to selective biological recognition events. When exposed to a biological target (nutrient, growth factor, receptor, antibody, enzyme, or whole cell), molecular recognition events trigger changes in molecular interactions that translate into macroscopic responses, such as swelling/collapse or solution-to-gel transitions. The hydrogel transitions may be used directly as optical readouts for biosensing, linked to the release of actives for drug delivery, or instigate biochemical signaling events that control or direct cellular behavior. Accordingly, bioresponsive hydrogels have gained significant interest for application in diagnostics, drug delivery, and tissue regeneration/wound healing.
Controlling cancer cell fate using localized biocatalytic self-assembly of an aromatic carbohydrate amphiphile
We report on a simple carbohydrate amphiphile able to self-assemble into nanofibers upon enzymatic dephosphorylation. The self-assembly can be triggered by alkaline phosphatase (ALP) in solution or in situ by the ALP produced by osteosarcoma cell line, SaOs2. In the latter case, assembly and localized gelation occurs mainly on the cell surface. The gelation of the pericellular environment induces a reduction of the SaOs2 metabolic activity at an initial stage (≤7 h) that results in cell death at longer exposure periods (≥24 h). We show that this effect depends on the phosphatase concentration and thus, it is cell-selective with prechondrocytes ATDC5 (that express ~15-20 times lower ALP activity compared to SaOs2) not being affected at concentrations ≤ 1 mM. These results demonstrate that simple carbohydrate derivatives can be used in an anti-osteosarcoma strategy with limited impact on the surrounding healthy cells/tissues.
Probing the Metabolomics of Stem Cell Differentiation with Biomaterials
In this issue of Chem, Ulijn, Dalby, and co-workers have developed a novel biomaterials platform as a screening tool for identifying metabolites that can bias differentiation of mesenchymal stem cells.
Stem Cell Fate Is a Touchy Subject
Uncoupling synergistic interactions between physio-chemical cues that guide stem cell fate may improve efforts to direct their differentiation in culture. Using supramolecular hydrogels,Alakpa et al. (2016)demon-strate that mesenchymal stem cell differentiation is paired to depletion of bioactive metabolites, which can be utilized to chemically induce osteoblast and chondrocyte fate.
Self-assembled peptide-based hydrogels as scaffolds for anchorage- dependent cells
We report here the design of a biomimetic nanofibrous hydrogel as a 3D-scaffold for anchorage-dependent cells. The peptide-based bioactive hydrogel is formed through molecular self-assembly andthe building blocks are a mixture of two aromatic short peptide derivatives: Fmoc-FF (Fluo-renylmethoxycarbonyl-diphenylalanine) and Fmoc-RGD (arginine-glycine-aspartate) as the simplestself-assembling moieties reported so far for the construction of small-molecule-based bioactive hydro-gels. This hydrogel provides a highly hydrated, stiff and nanofibrous hydrogel network that uniquelypresents bioactive ligands at the fibre surface; therefore it mimics certain essential features of the extracellular matrix. The RGD sequence as part of the Fmoc-RGD building block plays a dual role ofa structural component and a biological ligand. Spectroscopic and imaging analysis using CD, FTIR,fluorescence, TEM and AFM confirmed that FF and RGD peptide sequences self-assemble intob-sheetsinterlocked byp–pstacking of the Fmoc groups. This generates the cylindrical nanofibres interwovenwithin the hydrogel with the presence of RGDs in tunable densities on the fibre surfaces. This rapidgelling material was observed to promote adhesion of encapsulated dermal fibroblasts through specificRGD–integrin binding, with subsequent cell spreading and proliferation; therefore it may offer aneconomical model scaffold to 3D-culture other anchorage-dependent cells forin-vitrotissueregeneration.
Three-dimensional cell culture of chondrocytes on modified di-phenylalanine scaffolds
The design of self-assembled peptide-based structures for three-dimensional cell culture and tissue repairhas been a key objective in biomaterials science for decades. In search of the simplest possible peptidesystem that can self-assemble, we discovered that combinations of di-peptides that are modified witharomatic stacking ligands could form nanometre-sized fibres when exposed to physiological conditions. Forexample, we demonstrated that a number of Fmoc (fluoren-9-ylmethyloxycarbonyl) modified di- and tri-peptides form highly ordered hydrogels via hydrogen-bonding andπ–πinteractions from the fluorenyl rings.These highly hydrated gels allowed for cell proliferation of chondrocytes in three dimensions [Jayawarna,Ali, Jowitt, Miller, Saiani, Gough and Ulijn (2006) Adv. Mater.18, 611–614]. We demonstrated that fibrousarchitecture and physical properties of the resulting materials were dictated by the nature of the aminoacid building blocks. Here, we report the self-assembly process of three di-phenylalanine analogues, Fmoc-Phe-Phe-OH, Nap (naphthalene)-Phe-Phe-OH and Cbz (benzyloxycarbonyl)-Phe-Phe-OH, to compare andcontrast the self-assembly properties and cell culture conditions attributable to their protecting groupdifference. Fibre morphology analysis of the three structures using cryo-SEM (scanning electron microscopy)and TEM (transmission electron microscopy) suggested fibrous structures with dramatically varying fibrildimensions, depending on the aromatic ligand used. CD and FTIR (Fourier-transform IR) data confirmedβ-sheet arrangements in all three samples in the gel state. The ability of these three new hydrogels tosupport cell proliferation of chondrocytes was confirmed for all three materials.
Fmoc-Diphenylalanine Self Assembles to a Hydrogel via a Novel Architecture Based on p–p Interlocked b-Sheets
A number of strategies exist to design molecular materialsbased on self-assembled peptides and their derivatives.These include soft materials based on a variety of structuralmotifs including coiled-coils,[2,3]b-sheets,[4,5]b-hairpins,andpeptide amphiphiles.[7–9]In these systems, the peptide chainsusually contain at least ten amino acids. It has been known forsome time that using aromatic components in conjunctionwith peptides allows the use of much smaller peptides by tak-ing advantage ofp-stacking interactions.[10–15]One system thathas been illustrated is that ofN-fluorenylmethoxycarbonyl di-phenylalanine (Fmoc-FF) which forms a hydrogel under phys-iological conditions.
Nanostructured Hydrogels for Three-Dimensional Cell Culture Through Self-Assembly of Fluorenylmethoxycarbonyl– Dipeptides
Materials that form spontaneously by self-assembly fromnatural or synthetic building blocks are promising for a varietyof applications. In biomedicine, there is significant interest inexploiting self-assembly to construct mimics of the extracellularmatrix (ECM) for cell-culture applications. Zhang and co-workers described the use of octapeptides and hexadecapep-tides with alternating charged and hydrophobic amino acids togenerate highly hydrated gels for cultures of nerve cells, en-dothelial cells, and chondrocytes. Stupp and co-workers dem-onstrated that bioactive pentapeptides modified with octapep-tide spacers and aliphatic tails spontaneously form nanofibrousscaffolds that support selective differentiation of neural pro-genitor cells. These successful results clearly illustrate thatman-made hydrogels hold promise as scaffold materials forthree-dimensional (3D) cell cultures and tissue engineering.This Communication details the spontaneous assembly, underphysiological conditions, of much smaller amphiphilic buildingblocks consisting of (mixtures of) dipeptides linked to fluore-nylmethoxycarbonyl, and their use as scaffoldmaterials in 3D cell culture.
2018-CHIMIA- TEDD Annual Meeting with 3D Bioprinting Workshop
Bioprinting is the technology of choice for realizing functional tissues such as vascular system, muscle, cartilage and bone. In the future, bioprinting will influence the way we engineer tissues and bring it to a new level of physiological relevance. That was the topic of the 2017 TEDD Annual Meeting at ZHAW Waedenswil on 8th and 9th November. In an exciting workshop, the two companies regenHU Ltd. and CELLINK gave us an insight into highly topical applications and collaborations in this domain.
Improving cartilage phenotype from differentiated pericytes in tunable peptide hydrogels
Differentiation of stem cells to chondrocytes in vitro usually results in a heterogeneous phenotype. This is evident in the often detected over expression of type X collagen which, in hyaline cartilage structure is not characteristic of the mid-zone but of the deep-zone ossifying tissue. Methods to better match cartilage developed in vitro to characteristic in vivo features are therefore highly desirable in regenerative medicine. This study compares phenotype characteristics between pericytes, obtained from human adipose tissue, differentiated using diphenylalanine/serine (F2/S) peptide hydrogels with the more widely used chemical induced method for chondrogenesis. Significantly higher levels of type II collagen were noted when pericytes undergo chondrogenesis in the hydrogel in the absence of induction media. There is also a balanced expression of collagen relative to aggrecan production, a feature which was biased toward collagen production when cells were cultured with induction media. Lastly, metabolic profiles of each system show considerable overlap between both differentiation methods but subtle differences which potentially give rise to their resultant phenotype can be ascertained. The study highlights how material and chemical alterations in the cellular microenvironment have wide ranging effects on resultant tissue type.
Introducing chemical functionality in Fmoc-peptide gels for cell culture
Aromatic short peptide derivatives, i.e. peptides modified with aromatic groups such as 9-fluorenylmethoxycarbonyl (Fmoc), can self-assemble into self-supporting hydrogels. These hydrogels have some similarities to extracellular matrices due to their high hydration, relative stiffness and nanofibrous architecture. We previously demonstrated that Fmoc-diphenylalanine (Fmoc-F2) provides a suitable matrix for two-dimensional (2D) or three-dimensional (3D) culture of primary bovine chondrocytes. In this paper we investigate whether the introduction of chemical functionality, such as NH2, COOH or OH, enhances compatibility with different cell types. A series of hydrogel compositions consisting of combinations of Fmoc-F2 and n-protected Fmoc amino acids, lysine (K, with side chain R = (CH2)4NH2), glutamic acid (D, with side chain R = CH2COOH), and serine (S, with side chain R = CH2OH) were studied. All compositions produced fibrous scaffolds with fibre diameters in the range of 32–65 nm as assessed by cryo-scanning electron microscopy and atomic force microscopy. Fourier transform infrared spectroscopy analysis suggested that peptide segments adopt a predominantly antiparallel β-sheet conformation. Oscillatory rheology results show that all four hydrogels have mechanical profiles of soft viscoelastic materials with elastic moduli dependent on the chemical composition, ranging from 502 Pa (Fmoc-F2/D) to 21.2 KPa (Fmoc-F2). All gels supported the viability of bovine chondrocytes as assessed by a live–dead staining assay. Fmoc-F2/S and Fmoc-F2/D hydrogels in addition supported viability for human dermal fibroblasts (HDF) while Fmoc-F2/S hydrogel was the only gel type that supported viability for all three cell types tested. Fmoc-F2/S was therefore investigated further by studying cell proliferation, cytoskeletal organization and histological analysis in 2D culture. In addition, the Fmoc-F2/S gel was shown to support retention of cell morphology in 3D culture of bovine chondrocytes. These results demonstrate that introduction of chemical functionality into Fmoc-peptide scaffolds may provide gels with tunable chemical and mechanical properties for in vitro cell culture.
Tunable Supramolecular Hydrogels for Selection of Lineage-Guiding Metabolites in Stem Cell Cultures
Stem cells are known to differentiate in response to the chemical and mechanical properties of the substrates on which they are cultured. Thus, supramolecular biomaterials with tunable properties are well suited for the study of stem cell differentiation. In this report, we exploited this phenomenon by combining stem cell differentiation in hydrogels with variable stiffness and metabolomics analysis to identify specific bioactive lipids that are uniquely used up during differentiation. To achieve this, we cultured perivascular stem cells on supramolecular peptide gels of different stiffness, and metabolite depletion followed. On soft (1 kPa), stiff (13 kPa), and rigid (32 kPa) gels, we observed neuronal, chondrogenic, and osteogenic differentiation, respectively, showing that these stem cells undergo stiffness-directed fate selection. By analyzing concentration variances of >600 metabolites during differentiation on the stiff and rigid gels (and focusing on chondrogenesis and osteogenesis as regenerative targets, respectively), we identified that specific lipids (lysophosphatidic acid and cholesterol sulfate, respectively), were significantly depleted. We propose that these metabolites are therefore involved in the differentiation process. In order to unequivocally demonstrate that the lipid metabolites that we identified play key roles in driving differentiation, we subsequently demonstrated that these individual lipids can, when fed to standard stem cell cultures, induce differentiation toward chondrocyte and osteoblast phenotypes. Our concept exploits the design of supramolecular biomaterials as a strategy for discovering cell-directing bioactive metabolites of therapeutic relevance.