Collagen Modified Anisotropic PLA Scaffold as a base for Peripheral Nerve Regeneration

Poly(Propylene Carbonate)-Based Biodegradable and Environment-Friendly Materials for Biomedical Applications

Poly(propylene carbonate) (PPC) is an emerging "carbon fixation" polymer that holds the potential to become a "biomaterial of choice" in healthcare owing to its good biocompatibility, tunable biodegradability and safe degradation products. However, the commercialization and wide application of PPC as a biomedical material are still hindered by its narrow processing temperature range, poor mechanical properties and hydrophobic nature. Over recent decades, several physical, chemical and biological modifications of PPC have been achieved by introducing biocompatible polymers, inorganic ions or small molecules, which can endow PPC with better cytocompatibility and desirable biodegradability, and thus enable various applications. Indeed, a variety of PPC-based degradable materials have been used in medical applications including medical masks, surgical gowns, drug carriers, wound dressings, implants and scaffolds. In this review, the molecular structure, catalysts for synthesis, properties and modifications of PPC are discussed. Recent biomedical applications of PPC-based biomaterials are highlighted and summarized.

Neuro-bone tissue engineering: emerging mechanisms, potential strategies, and current challenges

The skeleton is a highly innervated organ in which nerve fibers interact with various skeletal cells. Peripheral nerve endings release neurogenic factors and sense skeletal signals, which mediate bone metabolism and skeletal pain. In recent years, bone tissue engineering has increasingly focused on the effects of the nervous system on bone regeneration. Simultaneous regeneration of bone and nerves through the use of materials or by the enhancement of endogenous neurogenic repair signals has been proven to promote functional bone regeneration. Additionally, emerging information on the mechanisms of skeletal interoception and the central nervous system regulation of bone homeostasis provide an opportunity for advancing biomaterials. However, comprehensive reviews of this topic are lacking. Therefore, this review provides an overview of the relationship between nerves and bone regeneration, focusing on tissue engineering applications. We discuss novel regulatory mechanisms and explore innovative approaches based on nerve-bone interactions for bone regeneration. Finally, the challenges and future prospects of this field are briefly discussed.

Neuro-regenerative behavior of adipose-derived stem cells in aligned collagen I hydrogels

Peripheral nerve injuries persist as a major clinical issue facing the US population and can be caused by stretch, laceration, or crush injuries. Small nerve gaps are simple to treat, and the nerve stumps can be reattached with sutures. In longer nerve gaps, traditional treatment options consist of autografts, hollow nerve guidance conduits, and, more recently, manufactured fibrous scaffolds. These manufactured scaffolds often incorporate stem cells, growth factors, and/or extracellular matrix (ECM) proteins to better mimic the native environment but can have issues with homogenous cell distribution or uniformly oriented neurite outgrowth in scaffolds without fibrous alignment. Here, we utilize a custom device to fabricate collagen I hydrogels with aligned fibers and encapsulated adipose-derived mesenchymal stem cells (ASCs) for potential use as a peripheral nerve repair graft. Initial results of our scaffold system revealed significantly less cell viability in higher collagen gel concentrations; 3 mg/mL gels showed 84.8 ± 7.3% viable cells, compared to 6 mg/mL gels viability of 76.7 ± 9.5%. Mechanical testing of the 3 mg/mL gels showed a Young's modulus of 6.5 ± 0.8 kPa nearly matching 7.45 kPa known to support Schwann cell migration. Further analysis of scaffolds coupled with stretching in vitro revealed heightened angiogenic and factor secretion, ECM deposition, fiber alignment, and dorsal root ganglia (DRG) neurite outgrowth along the axis of fiber alignment. Our platform serves as an in vitro testbed to assess neuro-regenerative potential of ASCs in aligned collagen fiber scaffolds and may provide guidance on next-generation nerve repair scaffold design.

Topographic Cues of a PLGA Scaffold Promote Odontogenic Differentiation of Dental Pulp Stem Cells through the YAP/β-Catenin Signaling Axis

PURPOSE

The underlying mechanism of how topographic cues of artificial scaffolds regulate cell function remains poorly understood. Yes-associated protein (YAP) and β-catenin signaling have both been reported to play important roles in mechano-transduction and dental pulp stem cells (DPSCs) differentiation. We investigated the effects of YAP and β-catenin in spontaneous odontogenic differentiation of DPSCs induced by topographic cues of a poly(lactic-co-glycolic acid) (PLGA) membrane.

METHODS

The topographic cues and function of a fabricated PLGA scaffold were explored via scanning electron microscopy (SEM), alizarin red staining (ARS), reverse transcription-polymerase chain reaction (RT-PCR), and pulp capping. Immunohistochemistry (IF), RT-PCR, and western blotting (WB) were used to observe the activation of YAP and β-catenin when DPSCs were cultured on the scaffolds. Further, YAP was inhibited or overexpressed on either side of the PLGA membrane, and YAP, β-catenin, and odontogenic marker expression were analyzed using IF, ARS, and WB.

RESULTS

The closed side of the PLGA scaffold promoted spontaneous odontogenic differentiation and nuclear translocation of YAP and β-catenin in vitro and in vivo compared to the open side. The YAP antagonist verteporfin inhibited β-catenin expression, nuclear translocation, and odontogenic differentiation on the closed side, but the effects were rescued by LiCl. YAP overexpressing DPSCs on the open side activated β-catenin signaling and promoted odontogenic differentiation.

CONCLUSION

The topographic cue of our PLGA scaffold promotes odontogenic differentiation of DPSCs and pulp tissue through the YAP/β-catenin signaling axis.

GDNF-Loaded Polydopamine Nanoparticles-Based Anisotropic Scaffolds Promote Spinal Cord Repair by Modulating Inhibitory Microenvironment

Spinal cord injury (SCI) is a devastating injury that causes permanent loss of sensation and motor function. SCI repair is a significant challenge due to the limited regenerating ability of adult neurons and the complex inflammatory microenvironment. After SCI, the oxidative stress induced by excessive reactive oxygen species (ROS) often leads to prolonged neuroinflammation that results in sustained damage to the spinal cord tissue. Polydopamine (PDA) shows remarkable capability in scavenging ROS to treat numerous inflammatory diseases. In this study, glial cell-derived neurotrophic factor (GDNF)-loaded PDA nanoparticle-based anisotropic scaffolds for spinal cord repair are developed. It is found that mesoporous PDA nanoparticles (mPDA NPs) in the scaffolds efficiently scavenge ROS and promote microglia M2 polarization, thereby inhibiting inflammatory response at the injury site and providing a favorable microenvironment for nerve cell survival. Furthermore, the GDNF encapsulated in mPDA NPs promotes corticospinal tract motor axon regeneration and its locomotor functional recovery. Together, findings from this study reveal that the GDNF-loaded PDA/Gelatin scaffolds hold potential as an effective artificial transplantation material for SCI treatment.

Recent advances in 3D-printed polylactide and polycaprolactone-based biomaterials for tissue engineering applications

The three-dimensional printing (3DP) also known as the additive manufacturing (AM), a novel and futuristic technology that facilitates the printing of multiscale, biomimetic, intricate cytoarchitecture, function-structure hierarchy, multi-cellular tissues in the complicated micro-environment, patient-specific scaffolds, and medical devices. There is an increasing demand for developing 3D-printed products that can be utilized for organ transplantations due to the organ shortage. Nowadays, the 3DP has gained considerable interest in the tissue engineering (TE) field. Polylactide (PLA) and polycaprolactone (PCL) are exemplary biomaterials with excellent physicochemical properties and biocompatibility, which have drawn notable attraction in tissue regeneration. Herein, the recent advancements in the PLA and PCL biodegradable polymer-based composites as well as their reinforcement with hydrogels and bio-ceramics scaffolds manufactured through 3DP are systematically summarized and the applications of bone, cardiac, neural, vascularized and skin tissue regeneration are thoroughly elucidated. The interaction between implanted biodegradable polymers, in-vivo and in-vitro testing models for possible evaluation of degradation and biological properties are also illustrated. The final section of this review incorporates the current challenges and future opportunities in the 3DP of PCL- and PLA-based composites that will prove helpful for biomedical engineers to fulfill the demands of the clinical field.