Optimizing an Injectable Composite Oxygen-Generating System for Relieving Tissue Hypoxia

Injectable Glucose-Releasing Microgels Enhance the Survival and Therapeutic Potential of Transplanted MSCs Under Ischemic Conditions

Mesenchymal stem cell (MSC)-based therapies show potential to treat ischemic diseases owing to their versatile functions. However, sustaining MSC viability and therapeutic efficacy in ischemic tissues postengraftment remains a significant challenge. This is because, although MSCs are metabolically flexible, they fail to adapt to hypoxic conditions in the absence of glucose, leading to cell death. To overcome these issues, it is aimed to establish an injectable glucose delivery system using starch and amyloglucosidase embedded in alginate microgels. Here, starch/amyloglucosidase (S/A) microgels are engineered to continuously release glucose for seven days via enzymatic hydrolysis, thereby supporting MSC functions under ischemic conditions. In vitro tests under oxygen/glucose-deprived conditions revealed that the S/A microgels not only maintained the viability and intracellular energy but also enhanced the pro-angiogenic and immunomodulatory functions of MSCs. In vivo data further confirmed the pro-survival and pro-angiogenic effects of S/A microgels on MSCs following subcutaneous engraftment in mice. Overall, the developed S/A microgel significantly enhanced the survival and therapeutic potential of MSCs via sustained glucose delivery, highlighting its potential use in advancing MSC-based therapies for ischemic conditions.

Functional β-TCP/MnO2 /PCL artificial periosteum promoting osteogenic differentiation of BMSCs by reducing locally reactive oxygen species level

Segmental bone defects caused by trauma, tumor resection or congenital malformations are often reconstructed with autologous, allogeneic bone grafts or artificial bone materials, of which, about 5% ~ 10% will have delayed healing or even nonunion of fractures. The loss of periosteum and excessive accumulation of ROS in fracture site leads to the aging of osteoblasts and the decline of their proliferation and differentiation, thus affecting the fracture healing process. In this study, we prepared a functional modified artificial periosteum β-TCP/MnO2 /PCL(β-TMP) by electrospinning with a function of catalyzing decomposition of H2 O2 . We examined the surface morphology of β-TMP, the concentration of Ca, P and Mn of β-TMP, as well as the diameter distribution range of nanofibers on β-TMP. Through X-ray diffraction patterns and Fourier transform infrared spectra, β-TMP was characterized and its hydrophilicity was tested. The release of Mn2+ and Ca2+ of 0.1 and 0.05% β-TMP in different pH values (7.4 and 5.5) determined by ICP. We also identified that β-TMP could reduce the level of ROS in cells by lowering the level of H2 O2 . 0%, 0.05% and 0.1% β-TMP displayed good cell compatibility, cell adhesion and cellular morphology in the condition with or without H2 O2 . 0.5% β-TMP showed compromised cell compatibility in normal condition, however, the compromised phenotypes could be partially rescued in the present of H2 O2 . Compared with 0%, 0.05% and 0.1% β-TMP displayed higher osteoblastic differentiation with or without H2 O2 in BMSCs as well as in MG-63. In sum, β-TMP helped osteogenesis and promoted repair of bone defects.

A pH-responsive polymer-coated CaO2as oxygen-generating nanoparticlein situfor enhanced chemo-photodynamic synergistic therapy against tumors

Photodynamic therapy (PDT) has emerged as an efficient strategy for tumor treatment. However, Insufficient amounts of inherent hypoxia and intrinsic hydrogen peroxide (H2O2) in the tumor microenvironment severely constrained PDT, as oxygen is the critical substrate for photosensitivity reaction. Here, a pH-responsive H2O2and O2self-supplying hybrid nanoparticle was designed. Through, the calcium peroxide (CaO2) as carriers loading a chemotherapeutic drug a photosensitizer 5,10,15,20-tetrakis(4-aminophenyl) porphyrin (TAPP) and doxorubicin (DOX), was covered with polyacrylic acid (PAA) to build up a feature material DOX-TAPP-CaO2@OA@PAA (denoted as DTCOP) through the reverse microemulsion method. In the acidic tumor microenvironment conditions exposing the water-sensitive CaO2nanocore to generate hydrogen peroxide (H2O2) and O2, the self-supplied O2alleviates hypoxia to enhance the PDT, and releasing DOX and TAPP. Synthetic characterization shows that the succeeded synthesized Nanocarriers could effectively carry DOX and TAPP to the tumor site and release O2at the low pH of TME. And the experimental results demonstrated that this interpose exogenous oxygen strategy is efficient at inhibition of tumor growth bothin vitroandin vivo. The nanocomposite exhibits excellent biocompatibility and the ability to inhibit tumor growth and has significant potential for the treatment of hypoxic tumors.

Oxygen-generating microparticles downregulate HIF-1α expression, increase cardiac contractility, and mitigate ischemic injury

Myocardial hypoxia is the low oxygen tension in the heart tissue implicated in many diseases, including ischemia, cardiac dysfunction, or after heart procurement for transplantation. Oxygen-generating microparticles have recently emerged as a potential strategy for supplying oxygen to sustain cell survival, growth, and tissue functionality in hypoxia. Here, we prepared oxygen-generating microparticles with poly D,L-lactic-co-glycolic acid, and calcium peroxide (CPO), which yielded a continuous morphology capable of sustained oxygen release for up to 24 h. We demonstrated that CPO microparticles increased primary rat cardiomyocyte metabolic activity while not affecting cell viability during hypoxia. Moreover, hypoxia-inducible factor (HIF)-1α, which is upregulated during hypoxia, can be downregulated by delivering oxygen using CPO microparticles. Single-cell traction force microscopy data demonstrated that the reduced energy generated by hypoxic cells could be restored using CPO microparticles. We engineered cardiac tissues that showed higher contractility in the presence of CPO microparticles compared to hypoxic cells. Finally, we observed reduced myocardial injuries in ex vivo rabbit hearts treated with CPO microparticles. In contrast, an acute early myocardial injury was observed for the hearts treated with control saline solution in hypoxia. In conclusion, CPO microparticles improved cell and tissue contractility and gene expression while reducing hypoxia-induced myocardial injuries in the heart. STATEMENT OF SIGNIFICANCE: Oxygen-releasing microparticles can reduce myocardial ischemia, allograft rejection, or irregular heartbeats after heart transplantation. Here we present biodegradable oxygen-releasing microparticles that are capable of sustained oxygen release for more than 24 hrs. We then studied the impact of sustained oxygen release from microparticles on gene expresseion and cardiac cell and tissue function. Previous studies have not measured cardiac tissue or cell mechanics during hypoxia, which is important for understanding proper cardiac function and beating. Using traction force microscopy and an engineered tissue-on-a-chip, we demonstrated that our oxygen-releasing microparticles improve cell and tissue contractility during hypoxia while downregulating the HIF-1α expression level. Finally, using the microparticles, we showed reduced myocardial injuries in rabbit heart tissue, confirming the potential of the particles to be used for organ transplantation or tissue engineering.

Oxygen-Generating Scaffolds: One Step Closer to the Clinical Translation of Tissue Engineered Products

The lack of oxygen supply in engineered constructs has been an ongoing challenge for tissue engineering and regenerative medicine. Upon implantation of an engineered tissue, spontaneous blood vessel formation does not happen rapidly, therefore, there is typically a limited availability of oxygen in engineered biomaterials. Providing oxygen in large tissue-engineered constructs is a major challenge that hinders the development of clinically relevant engineered tissues. Similarly, maintaining adequate oxygen levels in cell-laden tissue engineered products during transportation and storage is another hurdle. There is an unmet demand for functional scaffolds that could actively produce and deliver oxygen, attainable by incorporating oxygen-generating materials. Recent approaches include encapsulation of oxygen-generating agents such as solid peroxides, liquid peroxides, and fluorinated substances in the scaffolds. Recent approaches to mitigate the adverse effects, as well as achieving a sustained and controlled release of oxygen, are discussed. Importance of oxygen-generating materials in various tissue engineering approaches such as ex vivo tissue engineering, in situ tissue engineering, and bioprinting are highlighted in detail. In addition, the existing challenges, possible solutions, and future strategies that aim to design clinically relevant multifunctional oxygen-generating biomaterials are provided in this review paper.

Oxygen generating scaffolds regenerate critical size bone defects

Recent innovations in bone tissue engineering have introduced biomaterials that generate oxygen to substitute vasculature. This strategy provides the immediate oxygen required for tissue viability and graft maturation. Here we demonstrate a novel oxygen-generating tissue scaffold with predictable oxygen release kinetics and modular material properties. These hydrogel scaffolds were reinforced with microparticles comprised of emulsified calcium peroxide (CaO2) within polycaprolactone (PCL). The alterations of the assembled materials produced constructs within 5 ± 0.81 kPa to 34 ± 0.9 kPa in mechanical strength. The mass swelling ratios varied between 11% and 25%. Our in vitro and in vivo results revealed consistent tissue viability, metabolic activity, and osteogenic differentiation over two weeks. The optimized in vitro cell culture system remained stable at pH 8-9. The in vivo rodent models demonstrated that these scaffolds support a 70 mm3 bone volume that was comparable to the native bone and yielded over 90% regeneration in critical size cranial defects. Furthermore, the in vivo bone remodeling and vascularization results were validated by tartrate-resistant acid phosphatase (TRAP) and vascular endothelial growth factor (VEGF) staining. The promising results of this work are translatable to a repertoire of regenerative medicine applications including advancement and expansion of bone substitutes and disease models.

Strontium Peroxide-Loaded Composite Scaffolds Capable of Generating Oxygen and Modulating Behaviors of Osteoblasts and Osteoclasts

The reconstruction of bone defects remains challenging. The utilization of bone autografts, although quite promising, is limited by several drawbacks, especially substantial donor site complications. Recently, strontium (Sr), a bioactive trace element with excellent osteoinductive, osteoconductive, and pro-angiogenic properties, has emerged as a potential therapeutic agent for bone repair. Herein, a strontium peroxide (SrO₂)-loaded poly(lactic-co-glycolic acid) (PLGA)-gelatin scaffold system was developed as an implantable bone substitute. Gelatin sponges serve as porous osteoconductive scaffolds, while PLGA not only reinforces the mechanical strength of the gelatin but also controls the rate of water infiltration. The encapsulated SrO₂ can release Sr²⁺ in a sustained manner upon exposure to water, thus effectively stimulating the proliferation of osteoblasts and suppressing the formation of osteoclasts. Moreover, SrO₂ can generate hydrogen peroxide and subsequent oxygen molecules to increase local oxygen tension, an essential niche factor for osteogenesis. Collectively, the developed SrO₂-loaded composite scaffold shows promise as a multifunctional bioactive bone graft for bone tissue engineering.

Magnetic Responsive Release of Nitric Oxide from an MOF-Derived Fe3O4@PLGA Microsphere for the Treatment of Bacteria-Infected Cutaneous Wound

Nitric oxide (NO) is an essential endogenous signaling molecule regulating multifaceted physiological functions in the (cardio)vascular, neuronal, and immune systems. Due to the short half-life and location-/concentration-dependent physiological function of NO, translational application of NO as a novel therapeutic approach, however, awaits a strategy for spatiotemporal control on the delivery of NO. Inspired by the magnetic hyperthermia and magneto-triggered drug release featured by Fe₃O₄ conjugates, in this study, we aim to develop a magnetic responsive NO-release material (MagNORM) featuring dual NO-release phases, namely, burst and steady release, for the selective activation of NO-related physiology and treatment of bacteria-infected cutaneous wound. After conjugation of NO-delivery [Fe(μ-S-thioglycerol)(NO)₂]₂ with a metal-organic framework (MOF)-derived porous Fe₃O₄@C, encapsulation of obtained conjugates within the thermo-responsive poly(lactic-co-glycolic acid) (PLGA) microsphere completes the assembly of MagNORM. Through continuous/pulsatile/no application of the alternating magnetic field (AMF) to MagNORM, moreover, burst/intermittent/slow release of NO from MagNORM demonstrates the AMF as an ON/OFF switch for temporal control on the delivery of NO. Under continuous application of the AMF, in particular, burst release of NO from MagNORM triggers an effective anti-bacterial activity against both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). In addition to the magneto-triggered bactericidal effect of MagNORM against E. coli-infected cutaneous wound in mice, of importance, steady release of NO from MagNORM without the AMF promotes the subsequent collagen formation and wound healing in mice.

3D-printed oxygen-releasing scaffolds improve bone regeneration in mice

Low oxygen (O₂) diffusion into large tissue engineered scaffolds hinders the therapeutic efficacy of transplanted cells. To overcome this, we previously studied hollow, hyperbarically-loaded microtanks (μtanks) to serve as O₂ reservoirs. To adapt these for bone regeneration, we fabricated biodegradable μtanks from polyvinyl alcohol and poly (lactic-co-glycolic acid) and embedded them to form 3D-printed, porous poly-ε-caprolactone (PCL)-μtank scaffolds. PCL-μtank scaffolds were loaded with pure O₂ at 300-500 psi. When placed at atmospheric pressures, the scaffolds released O₂ over a period of up to 8 h. We confirmed the inhibitory effects of hypoxia on the osteogenic differentiation of human adipose-derived stem cells (hASCs and we validated that μtank-mediated transient hyperoxia had no toxic impacts on hASCs, possibly due to upregulation of endogenous antioxidant regulator genes. We assessed bone regeneration in vivo by implanting O₂-loaded, hASC-seeded, PCL-μtank scaffolds into murine calvarial defects (4 mm diameters × 0.6 mm height) and subcutaneously (4 mm diameter × 8 mm height). In both cases we observed increased deposition of extracellular matrix in the O₂ delivery group along with greater osteopontin coverages and higher mineral deposition. This study provides evidence that even short-term O₂ delivery from PCL-μtank scaffolds may enhance hASC-mediated bone tissue regeneration.

Modulation of Inherent Niches in 3D Multicellular MSC Spheroids Reconfigures Metabolism and Enhances Therapeutic Potential

Multicellular spheroids show three-dimensional (3D) organization with extensive cell–cell and cell–extracellular matrix interactions. Owing to their native tissue-mimicking characteristics, mesenchymal stem cell (MSC) spheroids are considered promising as implantable therapeutics for stem cell therapy. Herein, we aim to further enhance their therapeutic potential by tuning the cultivation parameters and thus the inherent niche of 3D MSC spheroids. Significantly increased expression of multiple pro-regenerative paracrine signaling molecules and immunomodulatory factors by MSCs was observed after optimizing the conditions for spheroid culture. Moreover, these alterations in cellular behaviors may be associated with not only the hypoxic niche developed in the spheroid core but also with the metabolic reconfiguration of MSCs. The present study provides efficient methods for manipulating the therapeutic capacity of 3D MSC spheroids, thus laying solid foundations for future development and clinical application of spheroid-based MSC therapy for regenerative medicine.

Hypoxia in Bone and Oxygen Releasing Biomaterials in Fracture Treatments Using Mesenchymal Stem Cell Therapy: A Review

Bone fractures have a high degree of severity. This is usually a result of the physical trauma of diseases that affect bone tissues, such as osteoporosis. Due to its highly vascular nature, the bone is in a constant state of remodeling. Although those of younger ages possess bones with high regenerative potential, the impact of a disrupted vasculature can severely affect the recovery process and cause osteonecrosis. This is commonly seen in the neck of femur, scaphoid, and talus bone. In recent years, mesenchymal stem cell (MSC) therapy has been used to aid in the regeneration of afflicted bone. However, the cut-off in blood supply due to bone fractures can lead to hypoxia-induced changes in engrafted MSCs. Researchers have designed several oxygen-generating biomaterials and yielded varying degrees of success in enhancing tissue salvage and preserving cellular metabolism under ischemia. These can be utilized to further improve stem cell therapy for bone repair. In this review, we touch on the pathophysiology of these bone fractures and review the application of oxygen-generating biomaterials to further enhance MSC-mediated repair of fractures in the three aforementioned parts of the bone.