Progress and limitations in engineering cellular adhesion for research and therapeutics

Intercellular interactions form the cornerstone of multicellular biology. Despite advances in protein engineering, researchers artificially directing physical cell interactions still rely on endogenous cell adhesion molecules (CAMs) alongside off-target interactions and unintended signaling. Recently, methods for directing cellular interactions have been developed utilizing programmable domains such as coiled coils (CCs), nanobody-antigen, and single-stranded DNA (ssDNA). We first discuss desirable molecular- and systems-level properties in engineered CAMs, using the helixCAM platform as a benchmark. Next, we propose applications for engineered CAMs in immunology, developmental biology, tissue engineering, and neuroscience. Biologists in various fields can readily adapt current engineered CAMs to establish control over cell interactions, and their utilization in basic and translational research will incentivize further expansion in engineered CAM capabilities.

Photoinduced Amyloid Fibril Degradation for Controlled Cell Patterning

Amyloid-like fibrils are a special class of self-assembling peptides that emerge as a promising nanomaterial with rich bioactivity for applications such as cell adhesion and growth. Unlike the extracellular matrix, the intrinsically stable amyloid-like fibrils do not respond nor adapt to stimuli of their natural environment. Here, a self-assembling motif (CKFKFQF), in which a photosensitive o-nitrobenzyl linker (PCL) is inserted, is designed. This peptide (CKFK-PCL-FQF) assembles into amyloid-like fibrils comparable to the unsubstituted CKFKFQF and reveals a strong response to UV-light. After UV irradiation, the secondary structure of the fibrils, fibril morphology, and bioactivity are lost. Thus, coating surfaces with the pre-formed fibrils and exposing them to UV-light through a photomask generate well-defined areas with patterns of intact and destroyed fibrillar morphology. The unexposed, fibril-coated surface areas retain their ability to support cell adhesion in culture, in contrast to the light-exposed regions, where the cell-supportive fibril morphology is destroyed. Consequently, the photoresponsive peptide nanofibrils provide a facile and efficient way of cell patterning, exemplarily demonstrated for A549, Chinese Hamster Ovary, and Raw Dual type cells. This study introduces photoresponsive amyloid-like fibrils as adaptive functional materials to precisely arrange cells on surfaces.

A review on recent advances in polymer and peptide hydrogels

In this review, we focus on the very recent developments on the use of the stimuli responsive properties of polymer hydrogels for targeted drug delivery, tissue engineering, and biosensing utilizing their different optoelectronic properties. Besides, the stimuli-responsive hydrogels, the conducting polymer hydrogels are discussed, with specific attention to the energy generation and storage behavior of the xerogel derived from the hydrogel. The electronic and ionic conducting gels have been discussed that have applications in various electronic devices, e.g., organic field effect transistors, soft robotics, ionic skins, and sensors. The properties of polymer hybrid gels containing carbon nanomaterials have been exemplified here giving attention to applications in supercapacitors, dye sensitized solar cells, photocurrent switching, etc. Recent trends in the properties and applications of some natural polymer gels to produce thermal and acoustic insulating materials, drug delivery vehicles, self-healing material, tissue engineering, etc., are discussed. Besides the polymer gels, peptide gels of different dipeptides, tripeptides, oligopeptides, polypeptides, cyclic peptides, etc., are discussed, giving attention mainly to biosensing, bioimaging, and drug delivery applications. The properties of peptide-based hybrid hydrogels with polymers, nanoparticles, nucleotides, fullerene, etc., are discussed, giving specific attention to drug delivery, cell culture, bio-sensing, and bioimaging properties. Thus, the present review delineates, in short, the preparation, properties, and applications of different polymer and peptide hydrogels prepared in the past few years.

Parallel multiphoton excited fabrication of tissue engineering scaffolds using a diffractive optical element

Multiphoton excited photochemistry is a powerful technique for freeform nano/microfabrication. However, the construction of large and complex structures using single point scanning is slow, where this is a significant limitation for biological investigations. We demonstrate increased throughput via parallel fabrication using a diffractive optical element. To implement an approach with large field of view and near-theoretical resolution, a scan lens was designed that is optimized for using low-magnification high NA objective lenses. We demonstrate that with this approach it is possible to synthesize large scaffolds at speeds several times faster than by single point scanning.

Recent advances in nanotherapeutic strategies for spinal cord injury repair

Spinal cord injury (SCI) is a devastating and complicated condition with no cure available. The initial mechanical trauma is followed by a secondary injury characterized by inflammatory cell infiltration and inhibitory glial scar formation. Due to the limitations posed by the blood-spinal cord barrier, systemic delivery of therapeutics is challenging. Recent development of various nanoscale strategies provides exciting and promising new means of treating SCI by crossing the blood-spinal cord barrier and delivering therapeutics. As such, we discuss different nanomaterial fabrication methods and provide an overview of recent studies where nanomaterials were developed to modulate inflammatory signals, target inhibitory factors in the lesion, and promote axonal regeneration after SCI. We also review emerging areas of research such as optogenetics, immunotherapy and CRISPR-mediated genome editing where nanomaterials can provide synergistic effects in developing novel SCI therapy regimens, as well as current efforts and barriers to clinical translation of nanomaterials.

Biomaterial-based microstructures fabricated by two-photon polymerization microfabrication technology

Two-photon polymerization (TPP) microfabrication technology can freely prepare micro/nano structures with different morphologies and high accuracy for micro/nanophotonics, micro-electromechanical systems, microfluidics, tissue engineering and drug delivery.

In Situ Imprinting of Topographic Landscapes at the Cell-Substrate Interface

In their native environments, adherent cells encounter dynamic topographical cues involved in promoting differentiation, orientation, and migration. Ideally, such processes would be amenable to study in cell culture using tools capable of imposing dynamic, arbitrary, and reversible topographic features without perturbing environmental conditions or causing chemical and/or structural disruptions to the substrate surface. To address this need, we report here development of an in vitro strategy for challenging cells with dynamic topographical experiences in which protein-based hydrogel substrate surfaces are modified in real time by positioning a pulsed, near-infrared laser focus within the hydrogel, promoting chemical cross-linking which results in local contraction of the protein matrix. Scanning the laser focus through arbitrary patterns directed by a dynamic reflective mask creates an internal contraction pattern that is projected onto the hydrogel surface as features such as rings, pegs, and grooves. By subjecting substrates to a sequence of scan patterns, we show that topographic features can be created, then eliminated or even reversed. Because laser-induced shrinkage can be confined to 3D voxels isolated from the cell-substrate interface, hydrogel modifications are made without damaging cells or disrupting the chemical or structural integrity of the surface.

Bioinspired Load-Bearing Hydrogel Based on Engineered Sea Anemone Skin-Derived Collagen-Like Protein

With the help of recombinant DNA technology, many protein candidates have been investigated and engineered for biomaterial applications. Particularly, several repeat sequences with unique secondary structures have been selected as minimal building blocks for biosynthesis to improve the mechanical properties of biomaterials. However, most of these structural proteins have been limited to silk, elastin, collagen, and resilin for decades. In the present work, new repeat sequence found in sea anemone are characterized and biosynthesized into a recombinant protein (named anegen) for potential use as a load-bearing biomaterial. Because its repeat sequence unit has a unique polyproline II structure, which is prevalently found in the triple-helix of collagen, it is assumed to be a promising structural protein candidate that can provide conformational flexibility and elasticity. Because anegen has ≈10% tyrosine residues, inspiration is taken from di-tyrosine crosslinking in the hinge structures of insects, which can be initiated by light activation. It is found that the anegen hydrogel shows higher mechanical properties than a gelatin hydrogel and endures a compression series without deformation. Moreover, the mechanical properties of the anegen hydrogel are controllable through different crosslinking conditions in a wide range of material applications. Importantly, the anegen hydrogel exhibited suitable cell retainability and cell morphology as an implantable biomaterial. Thus, based on its mechanical properties and biocompatibility, the anegen hydrogel can be used as a potential load-bearing and cell-loading scaffolding biomaterial in the tissue and biomedical engineering fields.

Orthogonal click reactions enable the synthesis of ECM-mimetic PEG hydrogels without multi-arm precursors

Click chemistry reactions have become an important tool for synthesizing user-defined hydrogels consisting of poly(ethylene glycol) (PEG) and bioactive peptides for tissue engineering. However, because click crosslinking proceeds via a step-growth mechanism, multi-arm telechelic precursors are required, which has some disadvantages. Here, we report for the first time that this requirement can be circumvented to create PEG-peptide hydrogels solely from linear precursors through the use of two orthogonal click reactions, the thiol-maleimide Michael addition and thiol-norbornene click reaction. The rapid kinetics of both click reactions allowed for quick formation of norbornene-functionalized PEG-peptide block copolymers via Michael addition, which were subsequently photocrosslinked into hydrogels with a dithiol linker. Characterization and in vitro testing demonstrated that the hydrogels have highly tunable physicochemical properties and excellent cytocompatiiblity. In addition, stoichiometric control over the crosslinking reaction can be leveraged to leave unreacted norbornene groups in the hydrogel for subsequent hydrogel functionalization via bioorthogonal inverse-electron demand Diels-Alder click reactions with s-tetrazines. After selectively capping norbornene groups in a user-defined region with cysteine, this feature was leveraged for protein patterning. Collectively, these results demonstrate that our novel chemical strategy is a simple and versatile approach to the development of hydrogels for tissue engineering that could be useful for a variety of applications.

3D bioprinted rat Schwann cell-laden structures with shape flexibility and enhanced nerve growth factor expression

Three-dimensional (3D) bioprinting composite alginate-gelatin hydrogel has encouraged the fabrication of cell-laden functional structures with cells from various tissues. However, reports focusing on printing this hydrogel for nerve tissue research are limited. This study aims at building in vitro Schwann cell 3D microenvironment with customized shapes through 3D bioprinting technology. Rat Schwann cell RSC96s encapsulated in composite alginate-gelatin hydrogel were printed with an extrusion-based bioprinter. Cells maintained high viability of 85.35 ± 6.19% immediately after printing and the printed hydrogel supported long-term Schwann cell proliferation for 2 weeks. Furthermore, after 14 days of culturing, Schwann cells cultured in printed structures maintained viability of 92.34 ± 2.19% and showed enhanced capability of nerve growth factor (NGF) release (142.41 ± 8.99 pg/ml) compared with cells from two-dimensional culture (92.27 ± 9.30 pg/ml). Specific Schwann cell marker S100β was also expressed by cells in printed structures. These printed structures may have the potential to be used as in vitro neurotrophic factor carriers and could be integrated into complex biomimetic artificial structures with the assistance of 3D bioprinting technology.

Enhanced adhesion and differentiation of human mesenchymal stem cell inside apatite-mineralized/poly(dopamine)-coated poly(ε-caprolactone) scaffolds by stereolithography

The purpose of this study is to develop PCL scaffolds using stereolithography technology and induced modifications using a poly dopamine (PDA)-coated/HA precipitate to stimulate human mesenchymal stem cells (hMSCs).