Engineering muscle tissue for the fetus: getting ready for a strong life

Synthetic materials in craniofacial regenerative medicine: A comprehensive overview

The state-of-the-art approach to regenerating different tissues and organs is tissue engineering which includes the three parts of stem cells (SCs), scaffolds, and growth factors. Cellular behaviors such as propagation, differentiation, and assembling the extracellular matrix (ECM) are influenced by the cell's microenvironment. Imitating the cell's natural environment, such as scaffolds, is vital to create appropriate tissue. Craniofacial tissue engineering refers to regenerating tissues found in the brain and the face parts such as bone, muscle, and artery. More biocompatible and biodegradable scaffolds are more commensurate with tissue remodeling and more appropriate for cell culture, signaling, and adhesion. Synthetic materials play significant roles and have become more prevalent in medical applications. They have also been used in different forms for producing a microenvironment as ECM for cells. Synthetic scaffolds may be comprised of polymers, bioceramics, or hybrids of natural/synthetic materials. Synthetic scaffolds have produced ECM-like materials that can properly mimic and regulate the tissue microenvironment's physical, mechanical, chemical, and biological properties, manage adherence of biomolecules and adjust the material's degradability. The present review article is focused on synthetic materials used in craniofacial tissue engineering in recent decades.

Bioprinting on sheet-based scaffolds applied to the creation of implantable tissue-engineered constructs with potentially diverse clinical applications: Tissue-Engineered Muscle Repair (TEMR) as a representative testbed

Purpose: This report explores the overlooked potential of bioprinting to automate biomanufacturing of simple tissue structures, such as the uniform deposition of (mono)layers of progenitor cells on sheetlike decellularized extracellular matrices (dECM). In this scenario, dECM serves as a biodegradable celldelivery matrix to provide enhanced regenerative microenvironments for tissue repair. The Tissue-Engineered Muscle Repair (TEMR) technology-where muscle progenitor cells are seeded onto a porcine bladder acellular matrix (BAM), serves as a representative testbed for bioprinting applications. Previous work demonstrated that TEMR implantation improved functional outcomes following VML injury in biologically relevant rodent models.Materials and Methods: In the described bioprinting system, a cell-laden hydrogel bioink is used to deposit high cell densities (1.4 × 105-3.5 × 105 cells/cm²), onto both sides of the bladder acellular matrix as proof-of-concept.Results: These bioprinting methods achieve a reproducible and homogeneous distribution of cells, on both sides of the BAM scaffold, after just 24hrs, with cell viability as high as 98%. These preliminary results suggest bioprinting allows for improved dual-sided cell coverage compared to manual-seeding.Conclusions: Bioprinting can enable automated fabrication of TEMR constructs with high fidelity and scalability, while reducing biomanufacturing costs and timelines. Such bioprinting applications are underappreciated, yet critical, to expand the overall biomanufacturing paradigm for tissue engineered medical products. In addition, biofabrication of sheet-like implantable constructs, with cells deposited on both sides, is a process that is both scaffold and cell-type agnostic, and furthermore, is amenable to many geometries, and thus, additional tissue engineering applications beyond skeletal muscle.

Analysis and Modeling of Rat Gait Biomechanical Deficits in Response to Volumetric Muscle Loss Injury

There is currently a substantial volume of research underway to develop more effective approaches for the regeneration of functional muscle tissue as treatment for volumetric muscle loss (VML) injury, but few studies have evaluated the relationship between injury and the biomechanics required for normal function. To address this knowledge gap, the goal of this study was to develop a novel method to quantify the changes in gait of rats with tibialis anterior (TA) VML injuries. This method should be sensitive enough to identify biomechanical and kinematic changes in response to injury as well as during recovery. Control rats and rats with surgically-created VML injuries were affixed with motion capture markers on the bony landmarks of the back and hindlimb and were recorded walking on a treadmill both prior to and post-surgery. Data collected from the motion capture system was exported for post-hoc analysis in OpenSim and Matlab. In vivo force testing indicated that the VML injury was associated with a significant deficit in force generation ability. Analysis of joint kinematics showed significant differences at all three post-surgical timepoints and gait cycle phase shifting, indicating augmented gait biomechanics in response to VML injury. In conclusion, this method identifies and quantifies key differences in the gait biomechanics and joint kinematics of rats with VML injuries and allows for analysis of the response to injury and recovery. The comprehensive nature of this method opens the door for future studies into dynamics and musculoskeletal control of injured gait that can inform the development of regenerative technologies focused on the functional metrics that are most relevant to recovery from VML injury.

A coupled framework of in situ and in silico analysis reveals the role of lateral force transmission in force production in volumetric muscle loss injuries

Volumetric muscle loss injuries (VML) are challenging to treat because of the variability in wound location. Regenerative medicine offers promising alternative treatments, but there is little understanding of the correlation between magnitude of VML injuries and corresponding functional deficits that must be addressed. There is a need for a tool that can elucidate the relationship between VML injury and force loss, as well as the impact on specific mechanisms responsible for force production. The purpose of this study was to develop a novel coupled framework of in situ and in silico methods to more precisely understand the relationship between injury location and force production deficits. We created a three-dimensional finite-element model of the pennate latissimus dorsi (LD) muscle in the rat and validated the model experimentally. We found that the model's prediction (2.6 N/g Model I, 2.1 N/g Model V) compared favorably to in situ testing of isometric force generation of the injured rat LD muscle (2.8 ± 0.3 N/g Experimental I, 2.0 ± 0.2 N/g Experimental V). Further model analysis revealed that the contribution from lateral and longitudinal force transmission to the total force varied with injury location and led to a greater understanding of the mechanisms responsible for VML-related force deficits. In the future, the coupled computational and experimental framework can be used to inform development of preclinical VML injury models that better recapitulate the spectrum of VML injuries observed in affected patients, and the mechanistic insight can accelerate the creation of improved regenerative therapeutics for VML injuries.

Smooth muscle cell differentiation from rabbit amniotic cells

Amniotic fluid (AF) is the liquid layer that provides mechanical support and allows movement of the fetus during embryogenesis. Mesenchymal stem cells (MSCs), which have differentiation capacity, are also found in AF-derived cells at a low ratio. Smooth muscle cells (SMCs) play an important role in organ function and are frequently used in tissue engineering. We examined the differentiation of AF-derived MSCs (AMSCs) into SMCs. AMSCs were sorted from cultured amniotic cells and differentiated into SMCs using differentiation agents, including platelet-derived growth factor BB (PDGF-BB) and tumor growth factor β (TGF-β). Characterization of differentiated SMCs was confirmed morphologically, molecularly (via quantitative polymerase chain reaction [qPCR] and immunocytochemistry [ICC]), and functionally (using a contractile assay and fluo-4 calcium signaling assay). Poly(lactide-co-glycolide) (PLGA) scaffolds were fabricated, and the attachment capacity of AMSCs was assessed via scanning electron microscopy. AMSCs were successfully differentiated into SMCs. Our results indicate that AMSCs change their morphology and exhibit increased expression of ACTA2 and MYH11, which was confirmed via qPCR and ICC. Furthermore, functional experiments revealed that differentiated SMCs had both contraction ability and increased Ca² concentration in the cytoplasm. Finally, PLGA scaffolds were prepared and AMSCs were successfully planted onto the scaffolds. The AMSCs fully differentiated into functional SMCs, and the PLGA polymer is a suitable scaffold material for AMSCs. With further clinical trials, AF-derived MSC-based SMC engineering may become a highly efficient treatment option.

Characterization of a Murine Model of Bioequivalent Bladder Wound Healing and Repair Following Subtotal Cystectomy

Previous work demonstrated restoration of a bioequivalent bladder within 8 weeks of removing the majority of the bladder (subtotal cystectomy or STC) in rats. The goal of the present study was to extend our investigations of bladder repair to the murine model, to harness the power of mouse genetics to delineate the cellular and molecular mechanisms responsible for the observed robust bladder regrowth. Female C57 black mice underwent STC, and at 4, 8, and 12 weeks post-STC, bladder repair and function were assessed via cystometry, ex vivo pharmacologic organ bath studies, and T₂-weighted magnetic resonance imaging (MRI). Histology was also performed to measure bladder wall thickness. We observed a time-dependent increase in bladder capacity (BC) following STC, such that 8 and 12 weeks post-STC, BC and micturition volumes were indistinguishable from those of age-matched non-STC controls and significantly higher than observed at 4 weeks. MRI studies confirmed that bladder volume was indistinguishable within 3 months (11 weeks) post-STC. Additionally, bladders emptied completely at all time points studied (i.e., no increases in residual volume), consistent with functional bladder repair. At 8 and 12 weeks post-STC, there were no significant differences in bladder wall thickness or in the different components (urothelium, lamina propria, or smooth muscle layers) of the bladder wall compared with age-matched control animals. The maximal contractile response to pharmacological activation and electrical field stimulation increased over time in isolated tissue strips from repaired bladders but remained lower at all time points compared with controls. We have established and validated a murine model for the study of de novo organ repair that will allow for further mechanistic studies of this phenomenon after, for example, genetic manipulation.

Keratin Hydrogel Enhances In Vivo Skeletal Muscle Function in a Rat Model of Volumetric Muscle Loss

Volumetric muscle loss (VML) injuries exceed the considerable intrinsic regenerative capacity of skeletal muscle, resulting in permanent functional and cosmetic deficits. VML and VML-like injuries occur in military and civilian populations, due to trauma and surgery as well as due to a host of congenital and acquired diseases/syndromes. Current therapeutic options are limited, and new approaches are needed for a more complete functional regeneration of muscle. A potential solution is human hair-derived keratin (KN) biomaterials that may have significant potential for regenerative therapy. The goal of these studies was to evaluate the utility of keratin hydrogel formulations as a cell and/or growth factor delivery vehicle for functional muscle regeneration in a surgically created VML injury in the rat tibialis anterior (TA) muscle. VML injuries were treated with KN hydrogels in the absence and presence of skeletal muscle progenitor cells (MPCs), and/or insulin-like growth factor 1 (IGF-1), and/or basic fibroblast growth factor (bFGF). Controls included VML injuries with no repair (NR), and implantation of bladder acellular matrix (BAM, without cells). Initial studies conducted 8 weeks post-VML injury indicated that application of keratin hydrogels with growth factors (KN, KN+IGF-1, KN+bFGF, and KN+IGF-1+bFGF, n = 8 each) enabled a significantly greater functional recovery than NR (n = 7), BAM (n = 8), or the addition of MPCs to the keratin hydrogel (KN+MPC, KN+MPC+IGF-1, KN+MPC+bFGF, and KN+MPC+IGF-1+bFGF, n = 8 each) (p < 0.05). A second series of studies examined functional recovery for as many as 12 weeks post-VML injury after application of keratin hydrogels in the absence of cells. A significant time-dependent increase in functional recovery of the KN, KN+bFGF, and KN+IGF+bFGF groups was observed, relative to NR and BAM implantation, achieving as much as 90% of the maximum possible functional recovery. Histological findings from harvested tissue at 12 weeks post-VML injury documented significant increases in neo-muscle tissue formation in all keratin treatment groups as well as diminished fibrosis, in comparison to both BAM and NR. In conclusion, keratin hydrogel implantation promoted statistically significant and physiologically relevant improvements in functional outcomes post-VML injury to the rodent TA muscle.

The Potential of Combination Therapeutics for More Complete Repair of Volumetric Muscle Loss Injuries: The Role of Exogenous Growth Factors and/or Progenitor Cells in Implantable Skeletal Muscle Tissue Engineering Technologies

Despite the robust regenerative capacity of skeletal muscle, there are a variety of congenital and acquired conditions in which the volume of skeletal muscle loss results in major permanent functional and cosmetic deficits. These latter injuries are referred to as volumetric muscle loss (VML) injuries or VML-like conditions, and they are characterized by the simultaneous absence of multiple tissue components (i.e., nerves, vessels, muscles, satellite cells, and matrix). There are currently no effective treatment options. Regenerative medicine/tissue engineering technologies hold great potential for repair of these otherwise irrecoverable VML injuries. In this regard, three-dimensional scaffolds have been used to deliver sustained amounts of growth factors into a variety of injury models, to modulate host cell recruitment and extracellular matrix remodeling. However, this is a nascent field of research, and more complete functional improvements require more precise control of the spatiotemporal distribution of critical growth factors over a physiologically relevant range. This is especially true for VML injuries where incorporation of a cellular component into the scaffolds might provide not only a source of new tissue formation but also additional signals for host cell migration, recruitment, and survival. To this end, we review the major features of muscle repair and regeneration for largely recoverable injuries, and then discuss recent cell- and/or growth factor-based approaches to repair the more profound and irreversible VML and VML-like injuries. The underlying supposition is that more rationale incorporation of exogenous growth factors and/or cellular components will be required to optimize the regenerative capacity of implantable therapeutics for VML repair.

Application potential of bone marrow mesenchymal stem cell (BMSCs) based tissue-engineering for spinal cord defect repair in rat fetuses with spina bifida aperta

Spina bifida aperta are complex congenital malformations resulting from failure of fusion in the spinal neural tube during embryogenesis. Despite surgical repair of the defect, most patients who survive with spina bifida aperta have a multiple system handicap due to neuron deficiency of the defective spinal cord. Tissue engineering has emerged as a novel treatment for replacement of lost tissue. This study evaluated the prenatal surgical approach of transplanting a chitosan-gelatin scaffold seeded with bone marrow mesenchymal stem cells (BMSCs) in the healing the defective spinal cord of rat fetuses with retinoic acid induced spina bifida aperta. Scaffold characterisation revealed the porous structure, organic and amorphous content. This biomaterial promoted the adhesion, spreading and in vitro viability of the BMSCs. After transplantation of the scaffold combined with BMSCs, the defective region of spinal cord in rat fetuses with spina bifida aperta at E20 decreased obviously under stereomicroscopy, and the skin defect almost closed in many fetuses. The transplanted BMSCs in chitosan-gelatin scaffold survived, grew and expressed markers of neural stem cells and neurons in the defective spinal cord. In addition, the biomaterial presented high biocompatibility and slow biodegradation in vivo. In conclusion, prenatal transplantation of the scaffold combined with BMSCs could treat spinal cord defect in fetuses with spina bifida aperta by the regeneration of neurons and repairmen of defective region.