Winner of the Young Investigator Award of the Society for Biomaterials (USA) for 2016, 10th World Biomaterials Congress, May 17-22, 2016, Montreal QC, Canada: Aligned microribbon-like hydrogels for guiding three-dimensional smooth muscle tissue regeneration

Injectable and Microporous Microgel-Fiber Granular Hydrogel Loaded with Bioglass and siRNA for Promoting Diabetic Wound Healing

Injectable hydrogels find extensive application in the treatment of diabetic wound healing. However, traditional bulk hydrogels are significantly limited due to their nano-porous structure, which obstructs cell migration and tissue infiltration. Moreover, regulating inflammation and matrix metalloproteinase -9 (MMP-9) expression in diabetic wounds is crucial for enhancing wound healing. This study marks the first instance of introducing an efficient, scalable, and simple method for producing microfiber-gel granules encapsulating bioceramics powders. Utilizing this method, an injectable microporous granular microgel-fiber hydrogel (MFgel) is successfully developed by assembling microgel-fibers made from hyaluronic acid (HA) and sodium alginate (SA) loaded with small interfering RNA (siRNA) and bioglass (BG) particles. Compared to traditional hydrogels (Tgel), MFgel possesses a highly interconnected network with micron-sized pores, demonstrating favorable properties for cell adhesion and penetration in in vitro experiments. Additionally, MFgel exhibits a higher compressive modulus and superior mechanical stability. When implanted subcutaneously in mice, MFgel promotes cellular and tissue infiltration, facilitating cell proliferation. Furthermore, when applied to skin defects in diabetic rats, MFgel not only effectively regulates inflammation and suppresses MMP-9 expression but also enhances angiogenesis and collagen deposition, thereby significantly accelerating diabetic wound healing. Taken together, this hydrogel possesses great potential in diabetic wound healing applications.

Macroporous Granular Hydrogels Functionalized with Aligned Architecture and Small Extracellular Vesicles Stimulate Osteoporotic Tendon-To-Bone Healing

Osteoporotic tendon-to-bone healing (TBH) after rotator cuff repair (RCR) is a significant orthopedic challenge. Considering the aligned architecture of the tendon, inflammatory microenvironment at the injury site, and the need for endogenous cell/tissue infiltration, there is an imminent need for an ideal scaffold to promote TBH that has aligned architecture, ability to modulate inflammation, and macroporous structure. Herein, a novel macroporous hydrogel comprising sodium alginate/hyaluronic acid/small extracellular vesicles from adipose-derived stem cells (sEVs) (MHA-sEVs) with aligned architecture and immunomodulatory ability is fabricated. When implanted subcutaneously, MHA-sEVs significantly improve cell infiltration and tissue integration through its macroporous structure. When applied to the osteoporotic RCR model, MHA-sEVs promote TBH by improving tendon repair through macroporous aligned architecture while enhancing bone regeneration by modulating inflammation. Notably, the biomechanical strength of MHA-sEVs is approximately two times higher than the control group, indicating great potential in reducing postoperative retear rates. Further cell-hydrogel interaction studies reveal that the alignment of microfiber gels in MHA-sEVs induces tenogenic differentiation of tendon-derived stem cells, while sEVs improve mitochondrial dysfunction in M1 macrophages (Mφ) and inhibit Mφ polarization toward M1 via nuclear factor-kappaB (NF-κb) signaling pathway. Taken together, MHA-sEVs provide a promising strategy for future clinical application in promoting osteoporotic TBH.

Recent Advances in Macroporous Hydrogels for Cell Behavior and Tissue Engineering

Hydrogels have been extensively used as scaffolds in tissue engineering for cell adhesion, proliferation, migration, and differentiation because of their high-water content and biocompatibility similarity to the extracellular matrix. However, submicron or nanosized pore networks within hydrogels severely limit cell survival and tissue regeneration. In recent years, the application of macroporous hydrogels in tissue engineering has received considerable attention. The macroporous structure not only facilitates nutrient transportation and metabolite discharge but also provides more space for cell behavior and tissue formation. Several strategies for creating and functionalizing macroporous hydrogels have been reported. This review began with an overview of the advantages and challenges of macroporous hydrogels in the regulation of cellular behavior. In addition, advanced methods for the preparation of macroporous hydrogels to modulate cellular behavior were discussed. Finally, future research in related fields was discussed.

Aligned microribbon scaffolds with hydroxyapatite gradient for engineering bone-tendon interface

Injuries of the bone-to-tendon interface, such as rotator cuff and anterior cruciate ligament tears, are prevalent yet effective methods for repair remain elusive. Tissue engineering approaches that use cells and biomaterials offer a promising potential solution for engineering the bone-tendon interface, but previous strategies require seeding multiple cell types and use of multiphasic scaffolds to achieve zonal-specific tissue phenotype. Furthermore, mimicking the aligned tissue morphology present in native bone-tendon interface in 3D remains challenging. To facilitate clinical translation, engineering bone-tendon interface using a single cell source and one continuous scaffold with alignment cues would be more attractive, but has not been achieved before. To address these unmet needs, here we develop an aligned gelatin-microribbon (μRB) hydrogel scaffold with hydroxyapatite nanoparticle (HA-np) gradient for guiding zonal-specific differentiation of human mesenchymal stem cell (hMSC) to mimic the bone-tendon interface. We demonstrate aligned μRBs led to cell alignment in 3D, and HA gradient induced zonal-specific differentiation of MSCs that resembles the transition at the bone-tendon interface. Short chrondrogenic priming prior to exposure to osteogenic factors further enhanced the mimicry of bone-cartilage-tendon transition with significantly improved tensile moduli of the resulting tissues. In summary, aligned gelatin μRBs with HA gradient coupled with optimized soluble factors may offer a promising strategy for engineering bone-tendon interface using a single cell source.

Matrix Stiffness Modulates Patient-Derived Glioblastoma Cell Fates in Three-Dimensional Hydrogels

Cancer progression is known to be accompanied by changes in tissue stiffness. Previous studies have primarily employed immortalized cell lines and 2D hydrogel substrates, which do not recapitulate the 3D tumor niche. How matrix stiffness affects patient-derived cancer cell fate in 3D remains unclear. In this study, we report a matrix metalloproteinase-degradable poly(ethylene-glycol)-based hydrogel platform with brain-mimicking biochemical cues and tunable stiffness (40-26,600 Pa) for 3D culture of patient-derived glioblastoma xenograft (PDTX GBM) cells. Our results demonstrate that decreasing hydrogel stiffness enhanced PDTX GBM cell proliferation, and hydrogels with stiffness 240 Pa and below supported robust PDTX GBM cell spreading in 3D. PDTX GBM cells encapsulated in hydrogels demonstrated higher drug resistance than 2D control, and increasing hydrogel stiffness further enhanced drug resistance. Such 3D hydrogel platforms may provide a valuable tool for mechanistic studies of the role of niche cues in modulating cancer progression for different cancer types.

Nanoparticle-Mediated TGF-β Release from Microribbon-Based Hydrogels Accelerates Stem Cell-Based Cartilage Formation In Vivo

Conventional nanoporous hydrogels often lead to slow cartilage deposition by MSCs in 3D due to physical constraints and requirement for degradation. Our group has recently reported macroporous gelatin microribbon (μRB) hydrogels, which substantially accelerate MSC-based cartilage formation in vitro compared to conventional gelatin hydrogels. To facilitate translating the use of μRB-based scaffolds for supporting stem cell-based cartilage regeneration in vivo, there remains a need to develop a customize-designed drug delivery system that can be incorporated into μRB-based scaffolds. Towards this goal, here we report polydopamine-coated mesoporous silica nanoparticles (MSNs) that can be stably incorporated within the macroporous μRB scaffolds, and allow tunable release of transforming growth factor (TGF)-β3. We hypothesize that increasing concentration of polydopamine coating on MSNs will slow down TGF- β3 release, and TGF-β3 release from polydopamine-coated MSNs can enhance MSC-based cartilage formation in vitro and in vivo. We demonstrate that TGF-β3 released from MSNs enhance MSC-based cartilage regeneration in vitro to levels comparable to freshly added TGF-β3 in the medium, as shown by biochemical assays, mechanical testing, and histology. Furthermore, when implanted in vivo in a mouse subcutaneous model, only the group containing MSN-mediated TGF-β3 release supported continuous cartilage formation, whereas control group without MSN showed loss of cartilage matrix and undesirable endochondral ossification. The modular design of MSN-mediated drug delivery can be customized for delivering multiple drugs with individually optimized release kinetics, and may be applicable to enhance regeneration of other tissue types.

Spatially patterned microribbon-based hydrogels induce zonally-organized cartilage regeneration by stem cells in 3D

Regenerating cartilage with biomimetic zonal organization, which is critical for tissue function, remains a great challenge. The objective of this study was to evaluate the potential of spatially-patterned, multi-compositional, macroporous, extracellular matrix-based microribbon (µRB) µRB scaffolds to regenerate cartilage with biochemical, mechanical, and morphological zonal organization by mesenchymal stem cells (MSCs) compared to conventional multi-layer nanoporous hydrogels. MSCs were seeded in either trilayer microribbon (µRB) or hydrogel (HG) scaffolds that were composed of layered biomaterial compositions that had been chosen for their ability to differentiate MSCs into chondrocytes with zonal properties. To mimic the aligned collagen morphology in the superficial layer of native cartilage, an additional experimental group added MSC-laden aligned µRBs to the surface of the superficial layer of a µRB trilayer. Tuning µRB alignment and compositions in different zones led to zonal-specific responses of MSCs to create neocartilage with zonal biochemical, morphological, and mechanical properties, while trilayer HGs led to minimal cartilaginous deposition overall. Trilayer µRBs created neocartilage exhibiting significant increases in compressive modulus (up to 456 kPa) and > 4-fold increase in sGAG production from superficial to deep zones. Aligned gelatin µRBs in the superficial zone further enhanced biomimetic mimicry of the produced neocartilage by leading to robust collagen deposition and superficial zone protein production. STATEMENT OF SIGNIFICANCE: Regenerating cartilage with zonal organization using mesenchymal stem cells (MSCs) remains a great challenge. We developed a spatially-patterned, gradient, macroporous, trilayer microribbon (µRB) scaffold that we used to engineer MSC-based neocartilage with zonal trends that match native cartilage in many aspects, including collagen, sGAG, superficial zone protein, and compressive moduli. This is in direct contrast to conventional trilayer nanoporous hydrogels which led to minimal cartilage deposition and weak mechanical properties. It took only 21 days for MSC-seeded trilayer µRB scaffolds to reach cartilage-mimicking compressive moduli without requiring high cell seeding density, which has never been reported before. While this paper focuses on cartilage zonal organization, gradient µRB scaffolds can be used to repair other tissue interfaces such as osteochondral defects.

Structured Macroporous Hydrogels: Progress, Challenges, and Opportunities

Structured macroporous hydrogels that have controllable porosities on both the nanoscale and the microscale offer both the swelling and interfacial properties of bulk hydrogels as well as the transport properties of "hard" macroporous materials. While a variety of techniques such as solvent casting, freeze drying, gas foaming, and phase separation have been developed to fabricate structured macroporous hydrogels, the typically weak mechanics and isotropic pore structures achieved as well as the required use of solvent/additives in the preparation process all limit the potential applications of these materials, particularly in biomedical contexts. This review highlights recent developments in the field of structured macroporous hydrogels aiming to increase network strength, create anisotropy and directionality within the networks, and utilize solvent-free or additive-free fabrication methods. Such functional materials are well suited for not only biomedical applications like tissue engineering and drug delivery but also selective filtration, environmental sorption, and the physical templating of secondary networks.

Multifibrillar bundles of a self-assembling hyaluronic acid derivative obtained through a microfluidic technique for aortic smooth muscle cell orientation and differentiation

A hyaluronic acid derivative able to physically crosslink in a saline aqueous medium was employed for the production of fibers with a mean diameter of 50 μm using a microfluidic technique.