Polyurethane acrylates as effective substrates for sustained in vitro culture of human myotubes

Tissue engineering modalities in skeletal muscles: focus on angiogenesis and immunomodulation properties

Muscular diseases and injuries are challenging issues in human medicine, resulting in physical disability. The advent of tissue engineering approaches has paved the way for the restoration and regeneration of injured muscle tissues along with available conventional therapies. Despite recent advances in the fabrication, synthesis, and application of hydrogels in terms of muscle tissue, there is a long way to find appropriate hydrogel types in patients with congenital and/or acquired musculoskeletal injuries. Regarding specific muscular tissue microenvironments, the applied hydrogels should provide a suitable platform for the activation of endogenous reparative mechanisms and concurrently deliver transplanting cells and therapeutics into the injured sites. Here, we aimed to highlight recent advances in muscle tissue engineering with a focus on recent strategies related to the regulation of vascularization and immune system response at the site of injury.

Rational design of biodegradable thermoplastic polyurethanes for tissue repair

As a type of elastomeric polymers, non-degradable polyurethanes (PUs) have a long history of being used in clinics, whereas biodegradable PUs have been developed in recent decades, primarily for tissue repair and regeneration. Biodegradable thermoplastic (linear) PUs are soft and elastic polymeric biomaterials with high mechanical strength, which mimics the mechanical properties of soft and elastic tissues. Therefore, biodegradable thermoplastic polyurethanes are promising scaffolding materials for soft and elastic tissue repair and regeneration. Generally, PUs are synthesized by linking three types of changeable blocks: diisocyanates, diols, and chain extenders. Alternating the combination of these three blocks can finely tailor the physio-chemical properties and generate new functional PUs. These PUs have excellent processing flexibilities and can be fabricated into three-dimensional (3D) constructs using conventional and/or advanced technologies, which is a great advantage compared with cross-linked thermoset elastomers. Additionally, they can be combined with biomolecules to incorporate desired bioactivities to broaden their biomedical applications. In this review, we comprehensively summarized the synthesis, structures, and properties of biodegradable thermoplastic PUs, and introduced their multiple applications in tissue repair and regeneration. A whole picture of their design and applications along with discussions and perspectives of future directions would provide theoretical and technical supports to inspire new PU development and novel applications.

Machine learning-based phenotypic screening for postmitotic growth inducers uncover vitamin D3 metabolites as small molecule ribosome agonists

Objectives

To restore tissue growth without increasing the risk for cancer during aging, there is a need to identify small molecule drugs that can increase cell growth without increasing cell proliferation. While there have been numerous high‐throughput drug screens for cell proliferation, there have been few screens for post‐mitotic anabolic growth.

Materials and Methods

A machine learning (ML)‐based phenotypic screening strategy was used to discover metabolites that boost muscle growth. Western blot, qRT‐PCR and immunofluorescence staining were used to evaluate myotube hypertrophy/maturation or protein synthesis. Mass spectrometry (MS)‐based thermal proteome profiling‐temperature range (TPP‐TR) technology was used to identify the protein targets that bind the metabolites. Ribo‐MEGA size exclusion chromatography (SEC) analysis was used to verify whether the ribosome proteins bound to calcitriol.

Results

We discovered both the inactive cholecalciferol and the bioactive calcitriol are amongst the top hits that boost post‐mitotic growth. A large number of ribosomal proteins' melting curves were affected by calcitriol treatment, suggesting that calcitriol binds to the ribosome complex directly. Purified ribosomes directly bound to pure calcitriol. Moreover, we found that calcitriol could increase myosin heavy chain (MHC) protein translation and overall nascent protein synthesis in a cycloheximide‐sensitive manner, indicating that calcitriol can directly bind and enhance ribosomal activity to boost muscle growth.

Conclusion

Through the combined strategy of ML‐based phenotypic screening and MS‐based omics, we have fortuitously discovered a new class of metabolite small molecules that can directly activate ribosomes to promote post‐mitotic growth.

Stiffness Sensing by Cells

Physical stimuli are essential for the function of eukaryotic cells, and changes in physical signals are important elements in normal tissue development as well as in disease initiation and progression. The complexity of physical stimuli and the cellular signals they initiate are as complex as those triggered by chemical signals. One of the most important, and the focus of this review, is the effect of substrate mechanical properties on cell structure and function. The past decade has produced a nearly exponentially increasing number of mechanobiological studies to define how substrate stiffness alters cell biology using both purified systems and intact tissues. Here we attempt to identify common features of mechanosensing in different systems while also highlighting the numerous informative exceptions to what in early studies appeared to be simple rules by which cells respond to mechanical stresses.

A novel polyurethane-based biodegradable elastomer as a promising material for skeletal muscle tissue engineering

A key challenge in skeletal muscle tissue engineering is the choice of a proper scaffolding material as it should demonstrate elastic behavior to withstand and support the dynamic loading of the tissue microenvironment while being biodegradable and biocompatible. In this study, we tested the applicability of a novel biodegradable polyurethane (PU) elastomer chain extended with fibrinogen (Fib) to fulfill these requirements. Biodegradable polyurethane-fibrinogen (PU-Fib) elastomers were synthesized by step-wise condensation polymerization. Firstly, PU prepolymer was synthesized and then Fib was integrated into PU prepolymer during the second step of polymerization. The chemical, thermal, viscoelastic, mechanical and biodegradation properties of PU-Fib were characterized. FTIR-ATR spectrum showed amide bands specific to PU and Fib, DSC thermograms showed the suitable integration between the components. Dynamic mechanical analysis revealed Tg and Tα* transitions at 64.5 °C and 38.4 °C, respectively. PU and Fib had shown chemically compatible interactions and when compared to PCL, PU-Fib possessed viscoelastic properties more suitable to the native tissue. PU-Fib films were produced and seeded with C2C12 mouse myoblasts. Uniaxial cyclic stretch was applied to the cell seeded films for 21 d to mimic the native dynamic tissue microenvironment. Cell proliferation, viability and the expression of muscle-specific markers (immunofluorescent staining for myogenin and myosin heavy chain) were assessed. Myoblasts proliferated well on PU-Fib films; aligned parallel along their long edge, and express myogenic markers under biomimetic dynamic culture. It was possible to culture myoblasts with high viability on PU-Fib elastomeric films mimicking native muscle microenvironment.

Synthesis and Characterization of Dual Stimuli-Sensitive Biodegradable Polyurethane Soft Hydrogels for 3D Cell-Laden Bioprinting

Three-dimensional bioprinting serves as an attractive platform to fabricate customized tissue-engineered substitutes from biomaterials and cells for the repair or replacement of injured tissues and organs. A common challenge for 3D bioprinting materials is that the structures printed from the biodegradable polymer hydrogels tend to collapse because of the poor mechanical stability. In this study, dual stimuli-responsive biodegradable polyurethane (PU) dispersions (PUA2 and PUA3) were synthesized from an eco-friendly waterborne process. Acrylate group was introduced in the PU chain end to serve as a photosensitive moiety for UV-induced cross-linking and improvement of the printability, while mixed oligodiols in the soft segment remained to be the thermosensitive moiety. The photo/thermal-induced morphological changes of PU nanoparticles were verified by dynamic light scattering, small-angle X-ray scattering, and rheological measurement of the dispersions. It was observed that these PU nanoparticles became more rod-like in shape after UV treatment and formed compact packing structures upon further heating. With the thermosensitive properties, these UV-cured PU dispersions underwent rapid thermal gelation with gel moduli in the range 0.5-2 kPa near body temperature. The rheological properties of the PU hydrogels including dynamic viscoelasticity, creep recovery, and shear thinning behavior at 37 °C were favorable for processing by microextrusion-based 3D printing and could be easily mixed with cells before printing to produce cell-laden constructs. The dual-responsive hydrogel constructs demonstrated higher resolution and shape fidelity as well as better cell viability and proliferation than the thermoresponsive control. Moreover, the softer hydrogel (PUA3) with a low modulus (<1 kPa) could offer neural stem cells a tofu-like, stable, and inductive 3D microenvironment to proliferate and differentiate. We expect that the photo/thermoresponsive biodegradable polyurethane ink may offer unique rheological properties to contribute toward the custom-made bioprinting of soft tissues.