Leo L. Wang

Engineered Hydrogels for Local and Sustained Delivery of RNA-Interference Therapies

It has been nearly two decades since RNA-interference (RNAi) was first reported. While there are no approved clinical uses, several phase II and III clinical trials suggest the great promise of RNAi therapeutics. One challenge for RNAi therapies is the controlled localization and sustained presentation to target tissues, to both overcome systemic toxicity concerns and to enhance in vivo efficacy. One approach that is emerging to address these limitations is the entrapment of RNAi molecules within hydrogels for local and sustained release. In these systems, nucleic acids are either delivered as siRNA conjugates or within nanoparticles. A plethora of hydrogels has been implemented using these approaches, including both traditional hydrogels that have already been developed for other applications and new hydrogels developed specifically for RNAi delivery. These hydrogels have been applied to various applications in vivo, including cancer, bone regeneration, inflammation and cardiac repair. This review will examine the design and implementation of such hydrogel RNAi systems and will cover the most recent applications of these systems.

Injectable, Guest–Host Assembled Polyethylenimine Hydrogel for siRNA Delivery

While siRNA has tremendous potential for therapeutic applications, advancement is limited by poor delivery systems. Systemically, siRNAs are rapidly degraded, may have off-target silencing, and necessitate high working concentrations. To overcome this, we developed an injectable, guest-host assembled hydrogel between polyethylenimine (PEI) and polyethylene glycol (PEG) for local siRNA delivery. Guest-host modified polymers assembled with siRNAs to form polyplexes that had improved transfection and viability compared to PEI. At higher concentrations, these polymers assembled into shear-thinning hydrogels that rapidly self-healed. With siRNA encapsulation, the assemblies eroded as polyplexes which were active and transfected cells, observed by Cy3-siRNA uptake or GFP silencing in vitro. When injected into rat myocardium, the hydrogels localized polyplex release, observed by uptake of Cy5.5-siRNA and silencing of GFP for 1 week in a GFP-expressing rat. These results illustrate the potential for this system to be applied for therapeutic siRNA delivery, such as in cardiac pathologies.

Three-dimensional extrusion bioprinting of single- and double-network hydrogels containing dynamic covalent crosslinks: 3D EXTRUSION BIOPRINTING

The fabrication of three-dimensional (3D) scaffolds is indispensable to tissue engineering and 3D printing is emerging as an important approach towards this. Hydrogels are often used as inks in extrusion-based 3D printing, including with encapsulated cells; however, numerous challenging requirements exist, including appropriate viscosity, the ability to stabilize after extrusion, and cytocompatibility. Here, we present a shear-thinning and self-healing hydrogel crosslinked through dynamic covalent chemistry for 3D bioprinting. Specifically, hyaluronic acid was modified with either hydrazide or aldehyde groups and mixed to form hydrogels containing a dynamic hydrazone bond. Due to their shear-thinning and self-healing properties, the hydrogels could be extruded for 3D printing of structures with high shape fidelity, stability to relaxation, and cytocompatibility with encapsulated fibroblasts (>80% viability). Forces for extrusion and filament sizes were dependent on parameters such as material concentration and needle gauge. To increase scaffold functionality, a second photocrosslinkable interpenetrating network was included that was used for orthogonal photostiffening and photopatterning through a thiol-ene reaction. Photostiffening increased the scaffolds modulus (∼300%) while significantly decreasing erosion (∼70%), whereas photopatterning allowed for spatial modification of scaffolds with dyes. Overall, this work introduces a simple approach to both fabricate and modify 3D printed scaffolds.

Sustained release of endothelial progenitor cell-derived extracellular vesicles from shear-thinning hydrogels improves angiogenesis and promotes function after myocardial infarction

Aims Previous studies have demonstrated improved cardiac function following myocardial infarction (MI) after administration of endothelial progenitor cells (EPCs) into ischaemic myocardium. A growing body of literature supports paracrine effectors, including extracellular vesicles (EVs), as the main mediators of the therapeutic benefits of EPCs. The direct use of paracrine factors is an attractive strategy that harnesses the effects of cell therapy without concerns of cell engraftment or viability. We aim to reproduce the beneficial effects of EPC treatment through delivery of EPC-derived EVs within a shear-thinning gel (STG) for precise localization and sustained delivery. Methods and results EVs were harvested from EPCs isolated from adult male Rattus norvegicus (Wistar) rats and characterized by electron microscopy, nanoparticle tracking analysis (NTA), and mass spectrometry. EVs were incorporated into the STG and injected at the border zone in rat models of MI. Haemodynamic function, angiogenesis, and myocardial remodelling were analyzed in five groups: phosphate buffered saline (PBS) control, STG control, EVs in PBS, EVs in STG, and EPCs in STG. Electron microscopy and NTA of EVs showed uniform particles of 50-200 nm. EV content analysis revealed several key angiogenic mediators. EV uptake by endothelial cells was confirmed and followed by robust therapeutic angiogenesis. In vivo animal experiments demonstrated that delivery of EVs within the STG resulted in increased peri-infarct vascular proliferation, preservation of ventricular geometry, and improved haemodynamic function post-MI. Conclusions EPC-derived EVs delivered into ischaemic myocardium via an injectable hydrogel enhanced peri-infarct angiogenesis and myocardial haemodynamics in a rat model of MI. The STG greatly increased therapeutic efficiency and efficacy of EV-mediated myocardial preservation.

Update on injectables in the nose

Purpose of review The use of injectable fillers for nonsurgical rhinoplasty has increased tremendously over the past decade. This review describes the most commonly used fillers and their indications in the context of recent reports of both their successes and failures. Recent findings Hyaluronic acid and calcium hydroxylapatite are the two most commonly used fillers for injection. Recent studies have found that most injectable fillers are met with success and patient satisfaction, but vascular complications are still a serious problem of which physicians should be wary. Summary Injectable fillers should continue to be considered for patients on a case-by-case basis, but physicians should be knowledgeable of the various filler types, their indications, and injection technique to prevent serious complications.

Methods To Assess Shear-Thinning Hydrogels for Application As Injectable Biomaterials

Injectable hydrogels have gained popularity as a vehicle for the delivery of cells, growth factors, and other molecules to localize and improve their retention at the injection site, as well as for the mechanical bulking of tissues. However, there are many factors, such as viscosity, storage and loss moduli, and injection force, to consider when evaluating hydrogels for such applications. There are now numerous tools that can be used to quantitatively assess these factors, including for shear-thinning hydrogels because their properties change under mechanical load. Here, we describe relevant rheological tests and ways to measure injection force using a force sensor or a mechanical testing machine toward the evaluation of injectable hydrogels. Injectable, shear-thinning hydrogels can be used in a variety of clinical applications, and as an example we focus on methods for injection into the heart, where an understanding of injection properties and mechanical forces is imperative for consistent hydrogel delivery and retention. We discuss methods for delivery of hydrogels to mouse, rat, and pig hearts in models of myocardial infarction, and compare methods of tissue postprocessing for hydrogel preservation. Our intent is that the methods described herein can be helpful in the design and assessment of shear-thinning hydrogels for widespread biomedical applications.

Injectable and protease-degradable hydrogel for siRNA sequestration and triggered delivery to the heart

ABSTRACT Injectable hydrogels have significant therapeutic potential for treatment of myocardial infarction (MI) through tissue bulking and local drug delivery, including the delivery of small interfering RNAs (siRNAs). As siRNA targets are identified as potential treatments for MI, hydrogels may bolster efficacy through local and sustained release. Here, we designed an injectable hydrogel to respond to local upregulation in proteolytic activity after MI to erode and release siRNA against MMP2 (siMMP2), a target implicated in deleterious remodeling. Specifically, hyaluronic acid (HA) was modified with hydrazides or aldehydes and mixed to form shear‐thinning and self‐healing hydrogels through dynamic hydrazone bonds and with peptide crosslinkers that degrade in response to protease activity. HA was further modified with &bgr;‐cyclodextrin to sequester cholesterol‐modified siRNA, limiting passive diffusion. Hydrogels eroded in response to proteases and released active siRNA that knocked down MMP2 in primary cardiac fibroblasts. In a rat model of MI, hydrogels delivering siMMP2 attenuated hydrogel erosion by ˜46% at 4weeks when compared to hydrogels delivering control siRNA, ultimately improving myocardial thickness in the infarct. Delivery of the siMMP2 hydrogel led to significant functional improvements, including increased ejection fraction (27%, 66%), stroke volume (32%, 120%), and cardiac output (20%, 128%) when compared to controls (% increase versus hydrogels with control siRNA, % increase versus saline injection alone). This report demonstrates the utility of biomaterial‐based RNA delivery systems for cardiac applications.

Timing of Onset of Adverse Cutaneous Reactions Associated With Programmed Cell Death Protein 1 Inhibitor Therapy

Importance An increasing number of cutaneous adverse reactions resulting from use of programmed cell death protein 1 (PD-1) inhibitors have been described, but with relatively little focus to date on the timing of these reactions. Objective To determine the timing of cutaneous drug reactions after initiation of PD-1 inhibitor therapy. Design, Setting, and Participants This retrospective observational study included patients referred to an academic dermatology clinic by an oncologist from January 1, 2014, through February 28, 2018, with at least 1 skin biopsy specimen of a skin reaction associated with PD-1 inhibitor use. Participants were included if they had a biopsy-proven cutaneous reaction in response to a PD-1 inhibitor used alone or in combination with ipilimumab. Exposures All patients included in this study received pembrolizumab, nivolumab, or nivolumab with ipilimumab as immunotherapy for cancer. Main Outcomes and Measures The main outcome measure was time to onset of biopsy-proven cutaneous reactions that occurred during or after use of pembrolizumab or nivolumab. Results A total of 17 patients (12 men, 5 women; mean [SD] age, 68.6 [11.1] years) were identified who presented with cutaneous adverse reactions associated with PD-1 inhibitor therapy; these reactions included lichenoid dermatitis, bullous pemphigoid, erythema multiforme, eczema, lupus, and sarcoidosis. Twelve patients presented with reactions at least 3 months after beginning pembrolizumab or nivolumab therapy. The skin reactions presented a median (range) of 4.2 months (0.5-38.0 months) after drug initiation. In 5 cases, the cutaneous adverse reactions attributed to the PD-1 inhibitor therapy developed after the drug therapy was terminated. Conclusions and Relevance Diverse cutaneous adverse reactions secondary to PD-1 inhibitor use may present with delayed onsets and even after discontinuation of therapy. Dermatologists should be aware of the potential for delayed presentations of cutaneous adverse reactions.

Complications of Polydioxanone Foil Use in Nasal Surgery: A Case Series

Polydioxanone (PDS) foil is widely recognized as a septal cartilage replacement during rhinoplasties and is thought to be completely resorbable and biodegradable. Since its United States Food and Drug Administration approval in 2010, PDS foil has drawn significant enthusiasm and many surgeons consider it an ideal implantable biomaterial as reflected in numerous studies highlighting its benefits. However, scant literature exists highlighting relevant complications of PDS plates that may potentially lead to cavalier overuse. This descriptive case series assesses the outcomes of PDS foil usage in three patients seen for septoplasty at two independent institutions over the past 5 years. Our results demonstrate that PDS plate usage can lead to septal cartilage loss and resultant saddle nose deformıty associated with prolonged postoperative edema and inflammation. To our knowledge, this is the largest case series of this reported phenomenon.

Functional Compromise in the Middle Vault in the Management of Revision Rhinoplasty

Abstract As rhinoplasty procedures become more common, the need for revision surgeries increases as well. Unlike primary rhinoplasties, revision rhinoplasties can be more challenging because of anatomic differences from initial surgery, a lack of available cartilage, tissue remodeling responses, and other complications. As such, surgeons should be prepared to address revision rhinoplasty patients differently from primary rhinoplasty patients. Here, the authors describe a generalizable approach to revision functional rhinoplasty patients and detail some of the surgical techniques that can be employed to achieve optimal outcomes, with particular attention paid to procedures that can be used in the middle vault.