In Vivo Printing of Nanoenabled Scaffolds for the Treatment of Skeletal Muscle Injuries.

Extremity skeletal muscle injuries result in substantial disability. Current treatments fail to recoup muscle function, but properly designed and implemented tissue engineering and regenerative medicine techniques can overcome this challenge. In this study, a nanoengineered, growth factor-eluting bioink that utilizes Laponite nanoclay for the controlled release of vascular endothelial growth factor (VEGF) and a GelMA hydrogel for a supportive and adhesive scaffold that can be crosslinked in vivo is presented. The bioink is delivered with a partially automated handheld printer for the in vivo formation of an adhesive and 3D scaffold. The effect of the controlled delivery of VEGF alone or paired with adhesive, supportive, and fibrilar architecture has not been studied in volumetric muscle loss (VML) injuries. Upon direct in vivo printing, the constructs are adherent to skeletal muscle and sustained release of VEGF. The in vivo printing of muscle ink in a murine model of VML injury promotes functional muscle recovery, reduced fibrosis, and increased anabolic response compared to untreated mice. The in vivo construction of a therapeutic-eluting 3D scaffold paves the way for the immediate treatment of a variety of soft tissue traumas.

In situ printing of scaffolds for reconstruction of bone defects.

Bone defects are commonly caused by traumatic injuries and tumor removal and critically sized defects overwhelm the regenerative capacity of the native tissue. Reparative strategies such as auto, xeno, and allografts have proven to be insufficient to reconstruct and regenerate these defects. For the first time, we introduce the use of handheld melt spun three dimensional printers that can deposit materials directly within the defect site to properly fill the cavity and form free-standing scaffolds. Engineered composite filaments were generated from poly(caprolactone) (PCL) doped with zinc oxide nanoparticles and hydroxyapatite microparticles. The use of PCL-based materials allowed low-temperature printing to avoid overheating of the surrounding tissues. The in situ printed scaffolds showed moderate adhesion to wet bone tissue, which can prevent scaffold dislocation. The printed scaffolds showed to be osteoconductive and supported the osteodifferentiation of mesenchymal stem cells. Biocompatibility of the scaffolds upon in vivo printing subcutaneously in mice showed promising results. STATEMENT OF SIGNIFICANCE.

In Situ Printing of Adhesive Hydrogel Scaffolds for the Treatment of Skeletal Muscle Injuries.

Reconstructive surgery remains inadequate for the treatment of volumetric muscle loss (VML). The geometry of skeletal muscle defects in VML injuries varies on a case-by-case basis. Three-dimensional (3D) printing has emerged as one strategy that enables the fabrication of scaffolds that match the geometry of the defect site. However, the time and facilities needed for imaging the defect site, processing to render computer models, and printing a suitable scaffold prevent immediate reconstructive interventions post-traumatic injuries. In addition, the proper implantation of hydrogel-based scaffolds, which have generated promising results in vitro, is a major challenge. To overcome these challenges, a paradigm is proposed in which gelatin-based hydrogels are printed directly into the defect area and cross-linked in situ. The adhesiveness of the bioink hydrogel to the skeletal muscles was assessed ex vivo. The suitability of the in situ printed bioink for the delivery of cells is successfully assessed in vitro. Acellular scaffolds are directly printed into the defect site of mice with VML injury, exhibiting proper adhesion to the surrounding tissue and promoting remnant skeletal muscle hypertrophy. The developed handheld printer capable of 3D in situ printing of adhesive scaffolds is a paradigm shift in the rapid yet precise filling of complex skeletal muscle tissue defects.

Soft-Nanoparticle Functionalization of Natural Hydrogels for Tissue Engineering Applications.

Tissue engineering has emerged as an important research area that provides numerous research tools for the fabrication of biologically functional constructs that can be used in drug discovery, disease modeling, and the treatment of diseased or injured organs. From a materials point of view, scaffolds have become an important part of tissue engineering activities and are usually used to form an environment supporting cellular growth, differentiation, and maturation. Among various materials used as scaffolds, hydrogels based on natural polymers are considered one of the most suitable groups of materials for creating tissue engineering scaffolds. Natural hydrogels, however, do not always provide the physicochemical and biological characteristics and properties required for optimal cell growth. This review discusses the properties and tissue engineering applications of widely used natural hydrogels. In addition, methods of modulation of their physicochemical and biological properties using soft nanoparticles as fillers or reinforcing agents are presented.