Hyaluronic acid (HA) is a major component of cartilage extracellular matrix and is an attractive material for use as 3D injectable matrices for cartilage regeneration. While previous studies have shown the promise of HA-based hydrogels to support cell-based cartilage formation, varying HA concentration generally led to simultaneous changes in both biochemical cues and stiffness. How cells respond to the change of biochemical content of HA remains largely unknown. Here we report an adaptable elastin-like protein-hyaluronic acid (ELP-HA) hydrogel platform using dynamic covalent chemistry, which allows varyiation of HA concentration without affecting matrix stiffness. ELP-HA hydrogels were created through dynamic hydrazone bonds via the reaction between hydrazine-modified ELP (ELP-HYD) and aldehyde-modified HA (HA-ALD). By tuning the stoichiometric ratio of aldehyde groups to hydrazine groups while maintaining ELP-HYD concentration constant, hydrogels with variable HA concentration (1.5%, 3%, or 5%) (w/v) were fabricated with comparable stiffness. To evaluate the effects of HA concentration on cell-based cartilage regeneration, chondrocytes were encapsulated within ELP-HA hydrogels with varying HA concentration. Increasing HA concentration led to a dose-dependent increase in cartilage-marker gene expression and enhanced sGAG deposition while minimizing undesirable fibrocartilage phenotype. The use of adaptable protein hydrogels formed via dynamic covalent chemistry may be broadly applicable as 3D scaffolds with decoupled niche properties to guide other desirable cell fates and tissue repair.

Zonal organization plays an important role in cartilage structure and function, whereas most tissue-engineering strategies developed to date have only allowed the regeneration of cartilage with homogeneous biochemical and mechanical cues. To better restore tissue structure and function, there is a strong need to engineer materials with biomimetic gradient niche cues that recapitulate native tissue organization. To address this critical unmet need, in this study, we report a method for rapid formation of tissue-scale gradient hydrogels as a three-dimensional (3D) cell niche with tunable biochemical and physical properties. When encapsulated in stiffness gradient hydrogels, both chondrocytes and mesenchymal stem cells demonstrated zone-specific response and extracellular deposition that mimics zonal organization of articular cartilage. Blocking cell mechanosensing using blebbistatin abolished the zonal response of chondrocytes in 3D hydrogels with a stiffness gradient. Such tissue-scale gradient hydrogels can provide a 3D artificial cell niche to enable tissue engineering of various tissue types with zonal organizations or tissue interfaces.

Articular cartilage is characterized by zonal organizations containing dual gradients of biochemical cues and mechanical cues. However, how biochemical gradient interacts with the mechanical gradient to drive the cartilage zonal development remains largely unknown. Here, we report the development of a dual-gradient hydrogel platform as a 3D niche to elucidate the relative contributions of biochemical and mechanical niche gradients in modulating zonal-specific chondrocyte responses and cartilage zonal organization. Chondroitin sulfate (CS), a major constituent of cartilage extracellular matrix, was chosen as the biochemical cue. Poly(ethylene glycol), a bioinert polymer, was used to create the stiffness gradient. Dual-gradient hydrogels upregulated cartilage marker expressions and increased chondrocyte proliferation and collagen deposition in a zonal-dependent manner. Hydrogels with CS gradient alone exhibited poor mechanical strength and degraded prematurely after 1 week of culture. While CS gradient alone did not support long-term culture, adding CS gradient to mechanical-gradient hydrogels substantially enhanced cell proliferation, glycosaminoglycan production, and collagen deposition compared to mechanicalgradient hydrogels alone. These results suggest that biochemical and mechanical gradient cues synergize to enhance cartilage zonal organization by chondrocytes in 3D. Together, our results validate the potential of dual-gradient hydrogels as a 3D cell niche for cartilage regeneration with zonal organization and may be used to recreate other tissue interfaces.

Brain cancer is a devastating disease given its extreme invasiveness and intricate location. Glioblastoma multiforme (GBM) is one of the most common forms of brain cancer, and cancer progression is often correlated with significantly altered tissue stiffness. To elucidate the effect of matrix stiffness on GBM cell fates, previous research is largely limited to 2D studies using immortalized cell lines, which has limited physiological relevance. The objective of the study is to develop gradient hydrogels with brain‐mimicking stiffness range as a 3Din vitro GBM model for screening of the effects of matrix stiffness on GBM. To increase the physiological relevance, patient‐derived tumor xenograft (PDTX) GBM cells were used. Our gradient platform allows formation of cell‐containing hydrogels with stiffness ranging from 40 Pa to 1,300 Pa within a few minutes. By focusing on a brain‐mimicking stiffness range, this gradient hydrogel platform is designed for investigating brain cancer. Increasing stiffness led to decreased GBM proliferation and less spreading, which is accompanied by downregulation of matrix‐metalloproteinases (MMPs). Using temozolomide (TMZ) as a model drug, we demonstrate that increasing stiffness led to higher drug resistance by PDTX GBM cells in 3D, suggesting matrix stiffness can directly modulate how GBM cells respond to drug treatment. While the current study focuses on stiffness gradient, the setup may also be adapted for screening other cancer niche cues such as how biochemical ligand gradient modulates brain cancer progression and drug responses using reduced materials and time.

Background Elderly patients in senior communities faced high barriers to care during the COVID‐19 pandemic, including increased vulnerability to COVID‐19, long quarantines for clinic visits, and difficulties with telemedicine adoption. Objective To pilot a new model of dermatologic care to overcome barriers for senior living communities during the COVID‐19 pandemic and assess patient satisfaction. Methods From 16 November 2020 to 9 July 2021, this quality improvement programme combined in‐residence full body imaging with real‐time outlier lesion identification and virtual teledermatology. Residents from the Sequoias Portola Valley Senior Living Retirement Community (Portola Valley, California) voluntarily enroled in the Stanford Skin Scan Programme. Non‐physician clinical staff with a recent negative COVID‐19 test travelled on‐site to obtain in‐residence full body photographs using a mobile app‐based system on an iPad called SkinIO that leverages deep learning to analyse patient images and suggest suspicious, outlier lesions for dermoscopic photos. A single dermatologist reviewed photographs with the patient and provided recommendations via a video visit. Objective measures included follow‐up course and number of skin cancers detected. Subjective findings were obtained through patient experience surveys. Results Twenty‐seven individuals participated, three skin cancers were identified, with 11 individuals scheduled for a follow up in‐person visit and four individuals starting home treatment. Overall, 88% of patients were satisfied with the Skin Scan programme, with 77% likely to recommend the programme to others. 92% of patients agreed that the Skin Scan photographs were representative of their skin. In the context of the COVID‐19 pandemic, 100% of patients felt the process was safer or comparable to an in‐person visit. Despite overall appreciation for the programme, 31% of patients reported that they would prefer to see dermatologist in‐person after the pandemic. Conclusions This programme offers a framework for how a hybrid skin scan programme may provide high utility for individuals with barriers to accessing in‐person clinics.