Combinatorial biomatrix/cell-based therapies for restoration of host tissue architecture and function

Enhanced hyaline cartilage formation and continuous osteochondral regeneration via 3D-Printed heterogeneous hydrogel with multi-crosslinking inks

The unique gradient structure and complex composition of osteochondral tissue pose significant challenges in defect regeneration. Restoration of tissue heterogeneity while maintaining hyaline cartilage components has been a difficulty of an osteochondral tissue graft. A novel class of multi-crosslinked polysaccharide-based three-dimensional (3D) printing inks, including decellularized natural cartilage (dNC) and nano-hydroxyapatite, was designed to create a gradient scaffold with a robust interface-binding force. Herein, we report combining a dual-nozzle cross-printing technology and a gradient crosslinking method to create the scaffolds, demonstrating stable mechanical properties and heterogeneous bilayer structures. Biofunctional assessments revealed the remarkable regenerative effects of the scaffold, manifesting three orders of magnitude of mRNA upregulation during chondrogenesis and the formation of pure hyaline cartilage. Transcriptomics of the regeneration site in vivo and scaffold cell interaction tests in vitro showed that printed porous multilayer scaffolds could form the correct tissue structure for cell migration. More importantly, polysaccharides with dNC provided a hydrophilic microenvironment. The microenvironment is crucial in osteochondral regeneration because it could guide the regenerated cartilage to ensure the hyaline phenotype.

In vitro and in vivo efficacy of naturally derived scaffolds for cartilage repair and regeneration

Intrinsically present bioactive cues allow naturally derived materials to mimic important characteristics of cartilage while also facilitating cellular recruitment, infiltration, and differentiation. Such traits are often what tissue engineers desire when they fabricate scaffolds, and yet, literature from the past decade is replete with examples of how most natural constructs with native biomolecules have only offered sub-optimal results in the treatment of cartilage defects. This paper provides an in-depth investigation of the performance of such scaffolds through a review of a collection of natural materials that have been used so far in repairing/regenerating articular cartilage. Although in vivo and clinical studies are the best indicators of scaffold efficacy, it was, however, observed that a large number of natural constructs had very promising scaffold characteristics to begin with, and would often show good in vitro/in vivo results. Finally, an examination of the biochemistry and biomechanics of repair tissues in studies that reported positive outcomes showed that these attributes often approached target cartilage values. The paper concludes with an outline of current trends as well as future directions for the field. STATEMENT OF SIGNIFICANCE: This review offers an exclusive focus on natural scaffold materials for cartilage repair and regeneration and provides a quantitative and qualitative analysis of their performance under a variety of in vitro and in vivo conditions. Readers can learn about environments where natural scaffolds have had the most success and tailor strategies to optimize their own work. Furthermore, given how the glycosaminoglycan (GAG) to hydroxyproline (HYP) ratio and moduli are fundamental attributes of hyaline cartilage, this paper adds to the body of knowledge by exploring how these characteristics reflect in preclinical outcomes. Such perspectives can greatly aid researchers better utilize natural materials for Cartilage Tissue Engineering (CTE).

Receptor for hyaluronan mediated motility (RHAMM/HMMR) is a novel target for promoting subcutaneous adipogenesis

Hyaluronan, CD44 and the Receptor for Hyaluronan-Mediated Motility (RHAMM, gene name HMMR) regulate stem cell differentiation including mesenchymal progenitor differentiation. Here, we show that CD44 expression is required for subcutaneous adipogenesis, whereas RHAMM expression suppresses this process. We designed RHAMM function blocking peptides to promote subcutaneous adipogenesis as a clinical and tissue engineering tool. Adipogenic RHAMM peptides were identified by screening for their ability to promote adipogenesis in culture assays using rat bone marrow mesenchymal stem cells, mouse pre-adipocyte cell lines and primary human subcutaneous pre-adipocytes. Oil red O uptake into fat droplets and adiponectin production were used as biomarkers of adipogenesis. Positive peptides were formulated in either collagen I or hyaluronan (Orthovisc) gels then assessed for their adipogenic potential in vivo following injection into dorsal rat skin and mammary fat pads. Fat content was quantified and characterized using micro CT imaging, morphometry, histology, RT-PCR and ELISA analyses of adipogenic gene expression. Injection of screened peptides increased dorsal back subcutaneous fat pad area (208.3 ± 10.4 mm²versus control 84.11 ± 4.2 mm²; p < 0.05) and mammary fat pad size (45 ± 11 mg above control background, p = 0.002) in female rats. This effect lasted >5 weeks as detected by micro CT imaging and perilipin 1 mRNA expression. RHAMM expression suppresses while blocking peptides promote expression of PPARγ, C/EBP and their target genes. Blocking RHAMM function by peptide injection or topical application is a novel and minimally invasive method for potentially promoting subcutaneous adipogenesis in lipodystrophic diseases and a complementary tool to subcutaneous fat augmentation techniques.

pH-Modulating Poly(ethylene glycol)/Alginate Hydrogel Dressings for the Treatment of Chronic Wounds

The development of chronic wounds has been frequently associated with alkaline pH values. The application of pH-modulating wound dressings can, therefore, be a promising treatment option to promote normal wound healing. This study reports on the development and characterization of acidic hydrogel dressings based on interpenetrating poly(ethylene glycol) diacrylate/acrylic acid/alginate networks. The incorporation of ionizable carboxylic acid groups results in high liquid uptake up to 500%. The combination of two separate polymer networks significantly improves the tensile and compressive stability. In a 2D cell migration assay, the application of hydrogels (0% to 1.5% acrylic acid) results in complete "wound" closure; hydrogels with 0.25% acrylic acid significantly increase the cell migration velocity to 19.8 ± 1.9 µm h^-1 . The most promising formulation (hydrogels with 0.25% acrylic acid) is tested on 3D human skin constructs, increasing keratinocyte ingrowth into the wound by 164%.

Antibacterial nanofibrous scaffolds with lowered cytotoxicity using keratin extracted from quail feathers

This study aims to extract keratin from quail feather wastes and incorporate it with silver nanoparticles into a synthetic biodegradable polymer in order to fabricate a nanofibrous scaffold with improved biomedical properties. Polyvinyl alcohol was used as the host polymer and spinning dopes with different amounts (0, 0.15, and 0.75 wt %) of extracted keratin and the same amount of silver nanoparticles prepared in order to fabricate scaffolds. According to the results, the scaffolds with a higher amount of extracted keratin (i.e. 0.75 wt %) provided less bead formation and more uniformity; also, they gave 99.9% and 98% of the antibacterial activity against gram negative ( Escherichia coli) and gram positive ( Staphylococcus aureus) bacteria, respectively. The analysis of the biological response of fibroblast cells cultured on the synthetic scaffolds exhibited remarkable improvement in comparison to the pristine (polyvinyl alcohol-Ag) scaffolds. This article concludes that the addition of extracted keratin into a polymeric matrix (polyvinyl alcohol) can improve both antibacterial properties and cell viability for the resultant scaffolds, and this qualifies them as potent candidates for biomedical applications.

Systematic evaluation of natural scaffolds in cutaneous wound healing

Current strategies to improve wound healing are often created from multiple components that may include a scaffold, cells, and bioactive cues. Acellular natural hydrogels are an attractive approach since the material's intrinsic biological activity can be paired with mechanical properties similar to soft tissue to induce a host's response toward healing. In this report, a systematic evaluation was conducted to study the effect of hydrogel scaffold implantation in skin healing using a human-relevant murine wound healing model. Fibrin, micro porous hyaluronic acid, and composite hydrogels were utilized to study the effect of conductive scaffolds on the wound healing process. Composite hydrogels were paired with plasmin-degradable VEGF nanocapsules to investigate its impact as an inductive composite hydrogel on tissue repair. By 7 days, wound healing and vessel maturation within the newly formed tissue was significantly improved by the inclusion of porous scaffold architecture and VEGF nanocapsules.

Electrical and Mechanical Strategies to Enable Cardiac Repair and Regeneration

Inadequate replacement of lost ventricular myocardium from myocardial infarction leads to heart failure. Investigating the regenerative capacity of mammalian hearts represents an emerging direction for tissue engineering and cell-based therapy. Recent advances in stem cells hold promise to restore cardiac functions. However, embryonic or induced pluripotent stem cell-derived cardiomyocytes lack functional phenotypes of the native myocardium, and transplanted tissues are not fully integrated for synchronized electrical and mechanical coupling with the host. In this context, this review highlights the mechanical and electrical strategies to promote cardiomyocyte maturation and integration, and to assess the functional phenotypes of regenerating myocardium. Simultaneous microelectrocardiogram and high-frequency ultrasound techniques will also be introduced to assess electrical and mechanical coupling for small animal models of heart regeneration.

Stem cells in the management of advanced heart failure

PURPOSE OF REVIEW

Outcomes of stem cell trials in patients with advanced heart failure have been divergent, which has raised some scepticism about this therapy and led to recommending slowing clinical trials until basic issues have been more thoroughly addressed. It is therefore timely and relevant to examine the current data and discuss how recent findings may change the perspectives of stem cell therapy.

RECENT FINDINGS

The most important recent change has been a shift in the mechanistic paradigm. Although the initial objective of stem cells was to physically replace dead cardiomyocytes and build a new electromechanically integrated myocardial tissue, it is now recognized that the unavoidable death of most of the transplanted cells makes this objective unrealistic. Indeed, the primary mechanism of action of the cells seems to be paracrine through the release of factors activating the endogenous signalling pathways, leading to cardioprotection. This hypothesis has several implications. First, it leads to focus on the efficiency of early retention, rather than on sustained survival, which, in turn, implies improving delivery approaches, largely through an increased reliance on adjunctive biomaterials; second, it may rationalize the use of allogeneic cells as long as their rejection is delayed to give them enough time for releasing the signalling biomolecules; and, finally, it raises the possibility that transplantation of cells could be replaced by the delivery of their sole secretome, possibly under the form of microvesicles.

SUMMARY

Put together, these approaches could streamline the translational process and enhance large-scale clinical applications.