Aerobic exercise and scaffolds with hierarchical porosity synergistically promote functional recovery post volumetric muscle loss.

Volumetric muscle loss (VML), which refers to a composite skeletal muscle defect, most commonly heals by scarring and minimal muscle regeneration but substantial fibrosis. Current surgical interventions and physical therapy techniques are limited in restoring muscle function following VML. Novel tissue engineering strategies may offer an option to promote functional muscle recovery. The present study evaluates a colloidal scaffold with hierarchical porosity and controlled mechanical properties for the treatment of VML. In addition, as VML results in an acute decrease in insulin-like growth factor 1 (IGF-1), a myogenic factor, the scaffold was designed to slowly release IGF-1 following implantation. The foam-like scaffold is directly crosslinked onto remnant muscle without the need for suturing. In situ 3D printing of IGF-1-releasing porous muscle scaffold onto VML injuries resulted in robust tissue ingrowth, improved muscle repair, and increased muscle strength in a murine VML model. Histological analysis confirmed regeneration of new muscle in the engineered scaffolds. In addition, the scaffolds significantly reduced fibrosis and increased the expression of neuromuscular junctions in the newly regenerated tissue. Exercise training, when combined with the engineered scaffolds, augmented the treatment outcome in a synergistic fashion. These data suggest highly porous scaffolds and exercise therapy, in combination, may be a treatment option following VML.

Development and optimization of an ocular hydrogel adhesive patch using definitive screening design (DSD).

Adhesive hydrogels based on chemically modified photocrosslinkable polymers with specific physicochemical properties are frequently utilized for sealing wounds or incisions. These adhesive hydrogels offer tunable characteristics such as tailorable tissue adhesion, mechanical properties, swelling ratios, and enzymatic degradability. In this study, we developed and optimized a photocrosslinkable adhesive patch, GelPatch, with high burst pressure, minimal swelling, and specific mechanical properties for application as an ocular (sclera and subconjunctival) tissue adhesive. To achieve this, we formulated a series of hydrogel patches composed of different polymers with various levels of methacrylation, molecular weights, and hydrophobic/hydrophilic properties. A computerized multifactorial definitive screening design (DSD) analysis was performed to identify the most prominent components impacting critical response parameters such as adhesion, swelling ratio, elastic modulus, and second order interactions between applied components. These parameters were mathematically processed to generate a predictive model that identifies the linear and non-linear correlations between these factors. In conclusion, an optimized formulation of GelPatch was selected based on two modified polymers: gelatin methacryloyl (GelMA) and glycidyl methacrylated hyaluronic acid (HAGM). The ex vivo results confirmed adhesion and retention of the optimized hydrogel subconjunctivally and on the sclera for up to 4 days. The developed formulation has potential to be used as an ocular sealant for quick repair of laceration type ocular injuries.

Engineering a drug eluting ocular patch for delivery and sustained release of anti-inflammatory therapeutics.

Ocular inflammation is commonly associated with eye disease or injury. Effective and sustained ocular delivery of therapeutics remains a challenge due to the eye physiology and structural barriers. Herein, we engineered a photocrosslinkable adhesive patch (GelPatch) incorporated with micelles (MCs) loaded with Loteprednol etabonate (LE) for delivery and sustained release of drug. The engineered drug loaded adhesive hydrogel, with controlled physical properties, provided a matrix with high adhesion to the ocular surfaces. The incorporation of MCs within the GelPatch enabled solubilization of LE and its sustained release within 15 days. In vitro studies showed that MC loaded GelPatch supported cell viability and growth. In addition, subcutaneous implantation of the MC loaded GelPatch in rats confirmed its in vivo biocompatibility and stability within 28 days. This non-invasive, adhesive, and biocompatible drug eluting patch can be used as a matrix for the delivery and sustained release of hydrophobic drugs.

In situ bioprinting: intraoperative implementation of regenerative medicine.

Bioprinting has emerged as a strong tool for devising regenerative therapies to address unmet medical needs. However, the translation of conventional in vitro bioprinting approaches is partially hindered due to challenges associated with the fabrication and implantation of irregularly shaped scaffolds and their limited accessibility for immediate treatment by healthcare providers. An alternative strategy that has recently drawn significant attention is to directly print the bioink into the patient's body, so-called 'in situ bioprinting'. The bioprinting strategy and the associated bioink need to be specifically designed for in situ bioprinting to meet the particular requirements of direct deposition in vivo. In this review, we discuss the developed in situ bioprinting strategies, their advantages, challenges, and possible future improvements.

Nanoengineered myogenic scaffolds for skeletal muscle tissue engineering.

Extreme loss of skeletal muscle overwhelms the natural regenerative capability of the body, results in permanent disability and substantial economic burden. Current surgical techniques result in poor healing, secondary injury to the autograft donor site, and incomplete recuperation of muscle function. Most current tissue engineering and regenerative strategies fail to create an adequate mechanical and biological environment that enables cell infiltration, proliferation, and myogenic differentiation. In this study, we present a nanoengineered skeletal muscle scaffold based on functionalized gelatin methacrylate (GelMA) hydrogel, optimized for muscle progenitors' proliferation and differentiation. The scaffold was capable of controlling the release of insulin-like growth factor 1 (IGF-1), an important myogenic growth factor, by utilizing the electrostatic interactions with LAPONITE® nanoclays (NCs). Physiologically relevant levels of IGF-1 were maintained during a controlled release over two weeks. The NC was able to retain 50% of the released IGF-1 within the hydrogel niche, significantly improving cellular proliferation and differentiation compared to control hydrogels. IGF-1 supplemented medium controls required 44% more IGF-1 than the comparable NC hydrogel composites. The nanofunctionalized scaffold is a viable option for the treatment of extreme muscle injuries and offers scalable benefits for translational interventions and the growing field of clean meat production.

Colloidal multiscale porous adhesive (bio)inks facilitate scaffold integration.

Poor cellular spreading, proliferation, and infiltration, due to the dense biomaterial networks, have limited the success of most thick hydrogel-based scaffolds for tissue regeneration. Here, inspired by whipped cream production widely used in pastries, hydrogel-based foam bioinks are developed for bioprinting of scaffolds. Upon cross-linking, a multiscale and interconnected porous structure, with pores ranging from few to several hundreds of micrometers, is formed within the printed constructs. The effect of the process parameters on the pore size distribution and mechanical and rheological properties of the bioinks is determined. The developed foam bioinks can be easily printed using both conventional and custom-built handheld bioprinters. In addition, the foam inks are adhesive upon in situ cross-linking and are biocompatible. The subcutaneous implantation of scaffolds formed from the engineered foam bioinks showed their rapid integration and vascularization in comparison with their non-porous hydrogel counterparts. In addition, in vivo application of the foam bioink into the non-healing muscle defect of a murine model of volumetric muscle loss resulted in a significant functional recovery and higher muscle forces at 8 weeks post injury compared with non-treated controls.

Extrusion-based 3D (Bio)Printed Tissue Engineering Scaffolds: Process-Structure-Quality Relationships.

Biological additive manufacturing (Bio-AM) has emerged as a promising approach for the fabrication of biological scaffolds with nano- to microscale resolutions and biomimetic architectures beneficial to tissue engineering applications. However, Bio-AM processes tend to introduce flaws in the construct during fabrication. These flaws can be traced to material nonhomogeneity, suboptimal processing parameters, changes in the (bio)printing environment (such as nozzle clogs), and poor construct design, all with significant contributions to the alteration of a scaffold's mechanical properties. In addition, the biological response of endogenous and exogenous cells interacting with the defective scaffolds could become unpredictable. In this review, we first described extrusion-based Bio-AM. We highlighted the salient architectural and mechanotransduction parameters affecting the response of cells interfaced with the scaffolds. The process phenomena leading to defect formation and some of the tools for defect detection are reviewed. The limitations of the existing developments and the directions that the field should grow in order to overcome said limitations are discussed.

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.

Highly tough and ultrafast self-healable dual physically crosslinked sulfated alginate-based polyurethane elastomers for vascular tissue engineering.

Since vascular diseases are regarded as a major cause of death worldwide, developing engineered biomimetic elastomers with physicochemical and biological properties resembling those of the natural vascular tissues, is vital for vascular tissue engineering (VTE). This study reports synthesis of highly tough supramolecular biologically active alginate-based supramolecular polyurethane (BASPU) elastomers that benefit from the presence of two physical networks with different strength of soft tertiary ammonium-soft sulfate pairs, as strong ionic bonds, and soft tertiary ammonium-hard carboxylate groups, as the weak bonds. The presence of sulfate groups resulted in low Young's modulus, high toughness and stretchability, proper energy dissipation, ultrafast self-healing and complete healing efficiency of BASPU. In vitro studies showed higher endothelial cells attachment, higher anticoagulation ability and significantly less platelet adhesion for BASPUs compared to the commercial vascular prosthesis. The histological studies of subcutaneously implanted scaffolds confirmed their low fibrosis and gradual biodegradation during 2 months of following.

Sustainable drug release from polycaprolactone coated chitin-lignin gel fibrous scaffolds.

Non-healing wounds have placed an enormous stress on both patients and healthcare systems worldwide. Severe complications induced by these wounds can lead to limb amputation or even death and urgently require more effective treatments. Electrospun scaffolds have great potential for improving wound healing treatments by providing controlled drug delivery. Previously, we developed fibrous scaffolds from complex carbohydrate polymers [i.e. chitin-lignin (CL) gels]. However, their application was limited by solubility and undesirable burst drug release. Here, a coaxial electrospinning is applied to encapsulate the CL gels with polycaprolactone (PCL). Presence of a PCL shell layer thus provides longer shelf-life for the CL gels in a wet environment and sustainable drug release. Antibiotics loaded into core-shell fibrous platform effectively inhibit both gram-positive and -negative bacteria without inducting observable cytotoxicity. Therefore, PCL coated CL fibrous gel platforms appear to be good candidates for controlled drug release based wound dressing applications.

Process-Structure-Quality Relationships of Three-Dimensional Printed Poly(Caprolactone)-Hydroxyapatite Scaffolds.

Bone defects are common and, in many cases, challenging to treat. Tissue engineering is an interdisciplinary approach with promising potential for treating bone defects. Within tissue engineering, three-dimensional (3D) printing strategies have emerged as potent tools for scaffold fabrication. However, reproducibility and quality control are critical aspects limiting the translation of 3D printed scaffolds to clinical use, which remain to be addressed. To elucidate the factors that yield to the generation of defects in bioprinting and to achieve reproducible biomaterial printing, the objective of this article is to frame a systematic approach for optimizing and validating 3D printing of poly(caprolactone) (PCL)-hydroxyapatite (HAp) composite scaffolds. We delineate the effect of PCL-to-HAp ratio, print velocity, print temperature, and extrusion pressure on the architectural and mechanical properties of the 3D printed scaffold. Furthermore, we present an in situ image-based monitoring approach to quantify key quality-related aspects of constructs, such as the ability to deposit material consistently and print elementary shapes with fewer flaws. Our results show that small defects generated during the printing process have a significant role in lowering the mechanical properties of 3D printed polymeric scaffolds. In addition, the in vitro osteoinductivity of the fabricated scaffolds is demonstrated. Impact statement Identifying quality control measures is essential in the translation of three-dimensional (3D) printed scaffolds into clinical practice. In this article, we highlighted the importance of selected printing parameters on the quality of the 3D printed scaffolds. We also demonstrated that flaws, such as voids, significantly lower the mechanical properties (compressive modulus) of 3D printed polymeric scaffolds.

A Wirelessly Controlled Smart Bandage with 3D-Printed Miniaturized Needle Arrays.

Chronic wounds are one of the most devastating complications of diabetes and are the leading cause of nontraumatic limb amputation. Despite the progress in identifying factors and promising in vitro results for the treatment of chronic wounds, their clinical translation is limited. Given the range of disruptive processes necessary for wound healing, different pharmacological agents are needed at different stages of tissue regeneration. This requires the development of wearable devices that can deliver agents to critical layers of the wound bed in a minimally invasive fashion. Here, for the first time, a programmable platform is engineered that is capable of actively delivering a variety of drugs with independent temporal profiles through miniaturized needles into deeper layers of the wound bed. The delivery of vascular endothelial growth factor (VEGF) through the miniaturized needle arrays demonstrates that, in addition to the selection of suitable therapeutics, the delivery method and their spatial distribution within the wound bed is equally important. Administration of VEGF to chronic dermal wounds of diabetic mice using the programmable platform shows a significant increase in wound closure, re-epithelialization, angiogenesis, and hair growth when compared to standard topical delivery of therapeutics.

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.

3D-Printed Sugar-Based Stents Facilitating Vascular Anastomosis.

Microvascular anastomosis is a common part of many reconstructive and transplant surgical procedures. While venous anastomosis can be achieved using microvascular anastomotic coupling devices, surgical suturing is the main method for arterial anastomosis. Suture-based microanastomosis is time-consuming and challenging. Here, dissolvable sugar-based stents are fabricated as an assistive tool for facilitating surgical anastomosis. The nonbrittle sugar-based stent holds the vessels together during the procedure and are dissolved upon the restoration of the blood flow. The incorporation of sodium citrate minimizes the chance of thrombosis. The dissolution rate and the mechanical properties of the sugar-based stent can be tailored between 4 and 8 min. To enable the fabrication of stents with desirable geometries and dimensions, 3D printing is utilized to fabricate the stents. The effectiveness of the printed sugar-based stent is assessed ex vivo. The fabrication procedure is fast and can be performed in the operating room.