3D Printed Biodegradable Polyurethaneurea Elastomer Recapitulates Skeletal Muscle Structure and Function

Abstract

Effective skeletal muscle tissue engineering relies on control over the scaffold architecture for providing muscle cells with the required directionality, together with a mechanical property match with the surrounding tissue. Although recent advances in 3D printing fulfill the first requirement, the available synthetic polymers either are too rigid or show unfavorable surface and degradation profiles for the latter. In addition, natural polymers that are generally used as hydrogels lack the required mechanical stability to withstand the forces exerted during muscle contraction. Therefore, one of the most important challenges in the 3D printing of soft and elastic tissues such as skeletal muscle is the limitation of the availability of elastic, durable, and biodegradable biomaterials. Herein, we have synthesized novel, biocompatible and biodegradable, elastomeric, segmented polyurethane and polyurethaneurea (TPU) copolymers which are amenable for 3D printing and show high elasticity, low modulus, controlled biodegradability, and improved wettability, compared to conventional polycaprolactone (PCL) and PCL-based TPUs. The degradation profile of the 3D printed TPU scaffold was in line with the potential tissue integration and scaffold replacement process. Even though TPU attracts macrophages in 2D configuration, its 3D printed form showed limited activated macrophage adhesion and induced muscle-like structure formation by C2C12 mouse myoblasts in vitro, while resulting in a significant increase in muscle regeneration in vivo in a tibialis anterior defect in a rat model. Effective muscle regeneration was confirmed with immunohistochemical assessment as well as evaluation of electrical activity produced by regenerated muscle by EMG analysis and its force generation via a custom-made force transducer. Micro-CT evaluation also revealed production of more muscle-like structures in the case of implantation of cell-laden 3D printed scaffolds. These results demonstrate that matching the tissue properties for a given application via use of tailor-made polymers can substantially contribute to the regenerative outcomes of 3D printed tissue engineering scaffolds.

Anisotropic dense collagen hydrogels possessing two ranges of porosity to create the adequate microenvironment for muscle bundles: a step towards skeletal muscle modeling

“…Hence, the scaffold was suitable to sustain the development of fused myoblasts into myotubes in 3D after 4 days. Previous works investigated the C2C12 behavior on different porous collagen structures [26,31]. Unfortunately, the 3D organization of cells in these materials was questionable because cells only adhered to the pore surface and did not fill up the entire volume to acquire an organotypic organization.…”

“…Additionally, pore geometry is barely controllable [24,25]. 3D printing can create an intrinsic porosity by stacking round filaments [26–28]. However, the 90° switch between layers disturbs anisotropy and the channel shape, limiting its utilization.…”

“…Other techniques, such as needle or suture thread molding, generate large and elongated channels suitable for cell colonization and differentiation into myotubes (>500 µm) [26,29–31]. This kind of porosity is challenging to obtain by 3D printing due to the channel collapsing.…”

Biobased Elastomer Nanofibers Guide Light‐Controlled Human‐iPSC‐Derived Skeletal Myofibers

“…Polyurethane (PU) elastomers are widely used in implantable biomedical applications [ 20 ] because of their excellent hyperelasticity, biocompatibility and fatigue resistance in vivo. [ 21 , 22 ] Thermoplastic PU (TPU) and polyurethane‐urea (PUU) copolymers consist of both soft and hard segments, linked by covalent bonds along a linear macromolecular backbone, [ 23 ] and can be made from a diverse range of raw molecular components. This, and their ease of modification, enables the specification of tissue‐specific properties when used as scaffolds for tissue engineering.…”

“…This includes highly tunable and responsive mechanical properties, controlled biotic degradation, and low toxic residue formation. TPUs can be easily processed using 3D printing [ 23 ] and fiber‐spinning technologies such as electrospinning, [ 24 , 25 ] enabling the generation of spatially organized scaffolds with ECM‐like microstructure.…”