With the significant financial burden of chronic cutaneous wounds on the healthcare system, not to the personal burden mention on those individuals afflicted, it has become increasingly essential to improve our clinical treatments. This requires the translation of the most recent benchtop approaches to clinical wound repair as our current treatment modalities have proven insufficient. The most promising potential treatment options rely on stem cell-based therapies. Stem cell proliferation and signaling play crucial roles in every phase of the wound healing process and chronic wounds are often associated with impaired stem cell function. Clinical approaches involving stem cells could thus be utilized in some cases to improve a body's inhibited healing capacity. We aim to present the laboratory research behind the mechanisms and effects of this technology as well as current clinical trials which showcase their therapeutic potential. Given the current problems and complications presented by chronic wounds, we hope to show that developing the clinical applications of stem cell therapies is the rational next step in improving wound care.

Cartilage, especially articular cartilage, is a unique connective tissue consisting of chondrocytes and cartilage matrix that covers the surface of joints. It plays a critical role in maintaining joint durability and mobility by providing nearly frictionless articulation for mechanical load transmission between joints. Damage to the articular cartilage frequently results from sport-related injuries, systemic diseases, degeneration, trauma, or tumors. Failure to treat impaired cartilage may lead to osteoarthritis, affecting more than 25% of the adult population globally. Articular cartilage has a very low intrinsic self-repair capacity due to the limited proliferative ability of adult chondrocytes, lack of vascularization and innervation, slow matrix turnover, and low supply of progenitor cells. Furthermore, articular chondrocytes are encapsulated in low-nutrient, low-oxygen environment. While cartilage restoration techniques such as osteochondral transplantation, autologous chondrocyte implantation (ACI), and microfracture have been used to repair certain cartilage defects, the clinical outcomes are often mixed and undesirable. Cartilage tissue engineering (CTE) may hold promise to facilitate cartilage repair. Ideally, the prerequisites for successful CTE should include the use of effective chondrogenic factors, an ample supply of chondrogenic progenitors, and the employment of cell-friendly, biocompatible scaffold materials. Significant progress has been made on the above three fronts in past decade, which has been further facilitated by the advent of 3D bio-printing. In this review, we briefly discuss potential sources of chondrogenic progenitors. We then primarily focus on currently available chondrocyte-friendly scaffold materials, along with 3D bioprinting techniques, for their potential roles in effective CTE. It is hoped that this review will serve as a primer to bring cartilage biologists, synthetic chemists, biomechanical engineers, and 3D-bioprinting technologists together to expedite CTE process for eventual clinical applications.

As an important post-transcriptional regulatory machinery mediated by ∼21nt short-interfering double-stranded RNA (siRNA), RNA interference (RNAi) is a powerful tool to delineate gene functions and develop therapeutics. However, effective RNAi-mediated silencing requires multiple siRNAs for given genes, a time-consuming process to accomplish. Here, we developed a user-friendly system for single-vector-based multiplex siRNA expression by exploiting the unique feature of restriction endonuclease BstXI. Specifically, we engineered a BstXI-based shotgun cloning (BSG) system, which consists of three entry vectors with siRNA expression units (SiEUs) flanked with distinct BstXI sites, and a retroviral destination vector for shotgun SiEU assembly. For proof-of-principle studies, we constructed multiplex siRNA vectors silencing β-catenin and/or Smad4 and assessed their functionalities in mesenchymal stem cells (MSCs). Pooled siRNA cassettes were effectively inserted into respective entry vectors in one-step, and shotgun seamless assembly of pooled BstXI-digested SiEU fragments into a retroviral destination vector followed. We found these multiplex siRNAs effectively silenced β-catenin and/or Smad4, and inhibited Wnt3A- or BMP9-specific reporters and downstream target expression in MSCs. Furthermore, multiplex silencing of β-catenin and/or Smad4 diminished Wnt3A and/or BMP9-induced osteogenic differentiation. Collectively, the BSG system is a user-friendly technology for single-vector-based multiplex siRNA expression to study gene functions and develop experimental therapeutics.