Polysaccharide-Based Composite Hydrogel with Hierarchical Microstructure for Enhanced Vascularization and Skull Regeneration.

Critical-size skull defects caused by trauma, infection, and tumor resection raise great demands for efficient bone substitutes. Herein, a hybrid cross-linked hierarchical microporous hydrogel scaffold (PHCLS) was successfully assembled by a multistep procedure, which involved (i) the preparation of poly(lactic-co-glycolic)/nanohydroxyapatite (PLGA-HAP) porous microspheres, (ii) embedding the spheres in a solution of dopamine-modified hyaluronic acid and collagen I (Col I) and cross-linking via dopamine polyphenols binding to (i) Col I amino groups (via Michael addition) and (ii) PLGA-HAP (via calcium ion chelation). The introduction of PLGA-HAP not only improved the diversity of pore size and pore communication inside the matrix but also greatly enhanced the compressive strength (5.24-fold, 77.5 kPa) and degradation properties to construct a more stable mechanical structure. In particular, the PHCLS (200 mg, nHAP) promoted the proliferation, infiltration, and angiogenic differentiation of bone marrow mesenchymal stem cells in vitro, as well as significant ectopic angiogenesis and mineralization with a storage modulus enhancement of 2.5-fold after 30 days. Meanwhile, the appropriate matrix microenvironment initiated angiogenesis and early osteogenesis by accelerating endogenous stem cell recruitment in situ. Together, the PHCLS allowed substantial skull reconstruction in the rabbit cranial defect model, achieving 85.2% breaking load strength and 84.5% bone volume fractions in comparison to the natural cranium, 12 weeks after implantation. Overall, this study reveals that the hierarchical microporous hydrogel scaffold provides a promising strategy for skull defect treatment.

Nanostructured 3D-Printed Hybrid Scaffold Accelerates Bone Regeneration by Photointegrating Nanohydroxyapatite.

Nanostructured biomaterials that replicate natural bone architecture are expected to facilitate bone regeneration. Here, nanohydroxyapatite (nHAp) with vinyl surface modification is acquired by silicon-based coupling agent and photointegrated with methacrylic anhydride-modified gelatin to manufacture a chemically integrated 3D-printed hybrid bone scaffold (75.6 wt% solid content). This nanostructured procedure significantly increases its storage modulus by 19.43-fold (79.2 kPa) to construct a more stable mechanical structure. Furthermore, biofunctional hydrogel with biomimetic extracellular matrix is anchored onto the filament of 3D-printed hybrid scaffold (HGel-g-nHAp) by polyphenol-mediated multiple chemical reactions, which contributes to initiate early osteogenesis and angiogenesis by recruiting endogenous stem cells in situ. Significant ectopic mineral deposition is also observed in subcutaneously implanted nude mice with storage modulus enhancement of 25.3-fold after 30 days. Meanwhile, HGel-g-nHAp realizes substantial bone reconstruction in the rabbit cranial defect model, achieving 61.3% breaking load strength and 73.1% bone volume fractions in comparison to natural cranium 15 weeks after implantation. This optical integration strategy of vinyl modified nHAp provides a prospective structural design for regenerative 3D-printed bone scaffold.

Covalently Grafted Biomimetic Matrix Reconstructs the Regenerative Microenvironment of the Porous Gradient Polycaprolactone Scaffold to Accelerate Bone Remodeling.

Integrating a biomimetic extracellular matrix to improve the microenvironment of 3D printing scaffolds is an emerging strategy for bone substitute design. Here, a "soft-hard" bone implant (BM-g-DPCL) consisting of a bioactive matrix chemically integrated on a polydopamine (PDA)-coated porous gradient scaffold by polyphenol groups is constructed. The PDA-coated "hard" scaffolds promoted Ca2+ chelation and mineral deposition; the "soft" bioactive matrix is beneficial to the migration, proliferation, and osteogenic differentiation of stem cells in vitro, accelerated endogenous stem cell recruitment, and initiated rapid angiogenesis in vivo. The results of the rabbit cranial defect model (Φ = 10 mm) confirmed that BM-g-DPCL promoted the integration between bone tissue and implant and induced the deposition of bone matrix. Proteomics confirmed that cytokine adhesion, biomineralization, rapid vascularization, and extracellular matrix formation are major factors that accelerate bone defect healing. This strategy of highly chemically bonded soft-hard components guided the construction of the bioactive regenerative scaffold.

An instantly fixable and self-adaptive scaffold for skull regeneration by autologous stem cell recruitment and angiogenesis.

Limited stem cells, poor stretchability and mismatched interface fusion have plagued the reconstruction of cranial defects by cell-free scaffolds. Here, we designed an instantly fixable and self-adaptive scaffold by dopamine-modified hyaluronic acid chelating Ca2+ of the microhydroxyapatite surface and bonding type I collagen to highly simulate the natural bony matrix. It presents a good mechanical match and interface integration by appropriate calcium chelation, and responds to external stress by flexible deformation. Meanwhile, the appropriate matrix microenvironment regulates macrophage M2 polarization and recruits endogenous stem cells. This scaffold promotes the proliferation and osteogenic differentiation of BMSCs in vitro, as well as significant ectopic mineralization and angiogenesis. Transcriptome analysis confirmed the upregulation of relevant genes and signalling pathways was associated with M2 macrophage activation, endogenous stem cell recruitment, angiogenesis and osteogenesis. Together, the scaffold realized 97 and 72% bone cover areas after 12 weeks in cranial defect models of rabbit (Φ = 9 mm) and beagle dog (Φ = 15 mm), respectively.

Bioinspired Hydrogel Anchoring 3DP GelMA/HAp Scaffolds Accelerates Bone Reconstruction.

Seeking high biological activity and osteoinductive ability has always been an urgent problem for three-dimensional-printed (3DP) bony implants. Here, a 3DP methacrylic anhydride-modified gelatin (GelMA)/hydroxyapatite (HAp) scaffold with a high solid content of 82.5% was prepared and anchored by a functionalized polyphenol hydrogel. The scaffold and hydrogel were organically integrated into a bioinspired bony implant (HGH) by phenolic hydroxyl of hyaluronan derivatives conjugating amino groups of collagen I and GelMA and further chelating calcium ions of HAp. Compared with a simplex 3DP scaffold, this freeze-dried HGH presented better water retention, delayed degradation, and mechanical stability. It could promote migration, proliferation, and osteogenic differentiation of bone marrow stem cells in vitro. One week of implantation showed that it promoted directional migration of endogenous stem cells and early osteogenesis and angiogenesis. After 15 week surgery of rabbit skull defects, the BV/TV value of HGH returned to 73% of the normal group level. This strategy provided a new research idea for bone regeneration.

Redox and pH dual-responsive injectable hyaluronan hydrogels with shape-recovery and self-healing properties for protein and cell delivery.

In this work, 3, 3'-dithiobis (propanoic dihydrazide) modified and aldehyde-modified hyaluronic acid were respectively synthesized as precursor solutions to form redox and pH dual-responsive injectable hydrogels through dynamic acylhydrazone and disulfide linkages without exogenous stimulus conditions. The reversible sol-gel transition behavior of hydrogels could be repeated multiple times by adjusting DTT/H2O2 or HCl/TEA. Interestingly, the hydrogels shrank gradually when pH decreased, which improved significantly the storage modulus up to 8.4 times at pH 2. Furthermore, the hydrogel presented acid-switchable shape-recovery characteristics of self-healing by a dynamic recombination of acylhydrazone bonds. Moreover, the osmotic driving force derived from inner and outer concentration difference also affected the characteristic. The controlled release of bovine serum albumin (BSA) encapsulated in this hydrogel could be achieved in vitro under simulated pH/redox intracellular and intercellular microenvironment. This hydrogel could also promote chondrocytes proliferation.

A di-self-crosslinking hyaluronan-based hydrogel combined with type I collagen to construct a biomimetic injectable cartilage-filling scaffold.

Injectable hydrogels have attracted increasing attention because of convenient clinical operation, non-invasive surgical procedure and seamless filling of irregular defects. Here, injectable di-self-crosslinking HSMSSA hydrogel was formed via fast thiol/maleimide click chemistry reaction and thiol oxidation reaction as primary and secondary self-crosslinking network, respectively. Molecular weight and precursor concentration significantly affected physichemical properties and biological functions of hydrogels. Although single HSMSSA gel (0.1 M Da, 10 mg/mL) had moderate injectability, preferable mechanical properties and good proliferative ability of chondrocytes in vitro, and could greatly promote cartilaginous tissue formation in vivo, the lack of adhesion sites resulted in an untenable situation in maintaining effective connections among newborn cell clusters. However, the biomimetic injectable di-self-crosslinking blend hydrogel by combing injectable HSMSSA and bioactive Col I had improved resistance to degradation, chondrocytes adhesion and proliferation, especially for multiples ascending genes expression level associated with hyaline cartilage formation and polyproteoglycan secretion, which might be a potential clinical treatment strategy for constructing injectable cartilage repair filler by combining expanded autologous chondrocytes. STATEMENT OF SIGNIFICANCE: An injectable di-self-crosslinking Hyaluronan-Based hydrogel was formed via fast thiol/maleimide click chemistry reaction and thiol oxidation reaction as primary/secondary self-crosslinking network, respectively. Molecular weight and precursor concentration significantly affected physichemical properties and biological functions of the hydrogels. Although this HSMSSA gel (0.1 M Da, 10 mg/mL) had moderate injectability, preferable mechanical properties, and good proliferative ability of chondrocytes in vitro, and could greatly promote cartilaginous tissue formation in vivo, the lack of adhesion sites resulted in ineffective connections among newborn cell clusters. The biomimetic injectable di-self-crosslinking blend hydrogel improved chondrocyte adhesion and proliferation by combined injectable HSMSSA and bioactive Col I, especially for multiple ascending gene expression levels associated with hyaline cartilage formation and polyproteoglycan secretion.

Bionic cartilage acellular matrix microspheres as a scaffold for engineering cartilage.

Extracellular matrix (ECM) scaffolds made from decellularized natural cartilage have been successfully used in cartilage lesion repair, but allogeneic cartilage donors are always in shortage and xenogeneic cartilage tissues may have the risk of unknown disease transfer. In this study, we constructed artificial bionic cartilage microspheres by encapsulating MSCs in collagen microspheres and cultured in a chondrogenic-inducing medium. Then, acellular matrix microsphere (BCAMM) scaffolds were fabricated from the cultured microspheres at three different developmental stages. A novel technique was introduced to fabricate BCAMM scaffolds, which enabled the production and utilization of the scaffolds in a short time. Due to the differences in surface morphologies and biological compositions, the three BCAMM scaffolds showed different chondrogenic effects. The 10-day BCAMM (10-BCAMM) scaffold showed the best overall results, successfully inducing MSC chondrogenesis without any additional fetal bovine serum or induction components (TGF-ß or dexamethasone). In comparison, the 5-day BCAMM (5-BCAMM) scaffold showed potential osteogenic effects. The advantages of micron-sized BCAMMs are outlined, specifically in the easier decellularization process without grinding, homogeneous cell seeding and infiltration, chondrogenic induction and better fitting to the irregular lesion shape.

Repair of osteochondral defects in a rabbit model with artificial cartilage particulates derived from cultured collagen-chondrocyte microspheres.

Tissue engineered cartilage has become a promising candidate for restoration of defective cartilage, but is normally associated with problems including limited tissue size, inferior mechanical properties, poor tissue homogeneity and integrative properties compared to the native cartilage. In this study, we utilised our recently developed microsphere culture technique to fabricate artificial cartilage particulates (ACPs) using collagen hydrogel microspheres with allogenic chondrocytes. These ACPs were used to repair rabbit osteochondral defects in vivo. The results demonstrated that the optimised ACPs showed better cartilage repair and integration into the host tissue. Moreover, the mechanical integrity of ACPs protected the tissue underneath and enhanced the subchondral bone formation. After 3 months of surgery, the subchondral bone volume had recovered to a similar level to the natural tissue. Together, these results suggested that the ACPs prepared using our microsphere culture technique show great potential for osteochondral repair in future clinical applications.

Synthesis and photoluminescence characteristics of Sm3+ -doped Bi4 Si3 O12 red-emitting phosphor.

A series of novel red-emitting Sm3+ -doped bismuth silicate phosphors, Bi4 Si3 O12 :xSm3+ (0.01 ≤ x ≤ 0.06), were prepared via the sol-gel route. The phase of the synthesized samples calcinated at 800 °C is isostructural with Bi4 Si3 O12 according to X-ray diffraction results. Under excitation with 405 nm light, some typical peaks of Sm3+ ions centered at 566, 609, 655 and 715 nm are found in the emission spectra of the Sm3+ -doped Bi4 Si3 O12 phosphors. The strongest peak located at 609 nm is due to 4 G5/2 -6 H7/2 transition of Sm3+ . The luminescence intensity reaches its maximum value when the Sm3+ ion content is 4 mol%. The results suggest that Bi4 Si3 O12 :Sm3+ may be a potential red phosphor for white light-emitting diodes. Copyright © 2016 John Wiley & Sons, Ltd.