A miniaturized tunable optical attenuator with ultrawide bandwidth based on evanescent-field coupling between nanofibers.

We propose a novel miniaturized optical attenuator based on the evanescent-field coupling between two nanofibers. Benefiting from a wavelength-dependent waveguiding property of the coupled structure, a tunable attenuation with maximum extinction ratio of ~ 20 dB is demonstrated with an ultrawide optical bandwidth up to 0.7 µm in experiment. The wavelength-depended waveguiding properties of both one single nanofiber and coupled nanofibers are investigated in both theory and simulation. Using an adiabatic coupling structure, an attenuation range from - 0.16 dB to - 18.46 dB is obtained within a spectrum from 1.2 µm to 1.7 µm experimentally. Moreover, the simulated results indicate that, the attenuation only shows a slight change of ~ 0.1 dB with a lateral misalignment of 0.5 µm between the two nanofibers, indicating a high tolerance of this attenuator to the lateral misalignment. Considering the wide bandwidth as well as the ultracompact structure, this attenuator shows high potential in applications such as all-fiber optical sensing and communicating.

Combined Displacement and Angle Sensor with Ultra-High Compactness Based on Self-Imaging Effect of Optical Microgratings.

In this paper, an ultracompact combined sensor for displacement and angle-synchronous measurement is proposed based on the self-imaging effect of optical microgratings. Using a two-grating structure, linear and angular displacement can be measured by detecting the change of phase and amplitude of the optical transmission, respectively, within one single structure in the meantime. The optically transmitted properties of the two-grating structure are investigated in both theory and simulation. Simulated results indicate that optical transmission changes in a sinusoidal relationship to the input linear displacement. Meanwhile, the amplitude of the curve decreases with an input pitch angle, indicating the ability for synchronous measurement within one single compact structure. The synchronous measurement of the linear displacement and the angle is also demonstrated experimentally. The results show a resolution down to 4 nm for linear displacement measurement and a maximum sensitivity of 0.26 mV/arcsec within a range of ±1° for angle measurement. Benefiting from a simple common-path structure without using optical components, including reflectors and polarizers, the sensor shows ultra-high compactness for multiple-degrees-of-freedom measuring, indicating the great potential for this sensor in fields such as integrated mechanical positioning and semiconductor fabrication.

Chemical labeling achieves 8-oxo-7,8-dihydroguanine mapping in the microRNA transcriptome.

A labeling chemistry-based methodology, APSC-8-oxoGua-seq, is developed to sequence 8-oxoGua in the microRNA transcriptome. N-(3-Azidopropyl)-spermine-5-carboxamide (APSC) is designed for the selective labeling of 8-oxoGua, where its azide facilitates the conjugation of a cleavable linker via the click reaction, achieving 8-oxoGua pull-down and sequencing. Using APSC-8-oxoGua-seq, 8-oxoGua can be identified at single-base resolution.

Genome-wide analysis for nanofiber induced global gene expression profile: A study in MC3T3-E1 cells by RNA-Seq.

Nanofibers are one of the attractive biomaterials that can provide unique environments to direct cell behaviors. However, how nanofiber structure affects the global gene expression of laden cells remains unclear. Herein, high-throughput mRNA sequencing (RNA-seq) is applied to analyze the transcriptome of the MC3T3-E1 cells (a model osteoblast cell line) cultured on electrospun nanofibers. The cell-adhesive poly(L-lactide) nanofibers and membranes are developed by the mussel-inspired coating of gelatin-dopamine conjugate under H2O2-mediated oxidation. The MC3T3-E1 cells cultured on nanofibers exhibit elongated morphology and increased proliferation compared with those on membranes. The differences in global gene expression profiles are determined by RNA-seq, in which 905 differentially expressed genes (DEGs) are identified. Significantly, the DEGs related to cytoskeleton, promotion of cell cycle progression, cell adhesion, and cell proliferation, are higher expressed in the cells on nanofibers, while the DEGs involved in cell-cycle arrest and osteoblast mineralization are up-regulated in the cells on membranes. This study elucidates the roles of nanofiber structure in affecting gene expression of laden cells at the whole transcriptome level, and it will lay the foundation for understanding nanofiber-guided cell behaviors.

Development of artificial bone graft via in vitro endochondral ossification (ECO) strategy for bone repair.

Endochondral ossification (ECO) is a form of bone formation whereby the newly deposited bone replaces the cartilage template. A decellularized artificial cartilage graft (dLhCG), which is composed of hyaline cartilage matrixes, has been developed in our previous study. Herein, the osteogenesis of bone marrow-derived MSCs in the dLhCG through chondrogenic differentiation, chondrocyte hypertrophy, and subsequent transdifferentiation induction has been investigated by simulating the physiological processes of ECO for repairing critical-sized bone defects. The MSCs were recellularized into dLhCGs and subsequently allowed to undergo a 14-day proliferation period (mrLhCG). Following this, the mrLhCG constructs were subjected to two distinct differentiation induction protocols to achieve osteogenic differentiation: chondrogenic medium followed by chondrocytes culture medium with a high concentration of fetal bovine serum (CGCC group) and canonical osteogenesis inducing medium (OI group). The formation of a newly developed artificial bone graft, ossified dLhCG (OsLhCG), as well as its capability of aiding bone defect reconstruction were characterized by in vitro and in vivo trials, such as mRNA sequencing, quantitative real-time PCR (qPCR), immunohistochemistry, the greater omentum implantation in nude mice, and repair for the critical-sized femoral defects in rats. The results reveal that the differentiation induction of MSCs in the CGCC group can realize in vitro ECO through chondrogenic differentiation, hypertrophy, and transdifferentiation, while the MSCs in the OI group, as expected, realize ossification through direct osteogenic differentiation. The angiogenesis and osteogenesis of OsLhCG were proved by being implanted into the greater omentum of nude mice. Besides, the OsLhCG exhibits the capability to achieve the repair of critical-size femoral defects.

Ultracompact single-layer optical MEMS accelerometer based on evanescent coupling through silicon nanowaveguides.

In this paper, a novel optical MEMS accelerometer is proposed based on evanescent coupling between parallel silicon nanowaveguides. The coupling length between nanowaveguides changes due to the input acceleration, leading to a great change of coupling efficiency. As a result, the applied acceleration can be obtained by measuring the transmission of waveguiding light. Simulation results with optical displacement sensing sensitivity of 32.83%/[Formula: see text]m within measurement range of 1.68 g is obtained. This design shows high compactness with no need of assembly, suggesting great potential in applications such as integrated photonic circuits.

A catechol bioadhesive for rapid hemostasis and healing of traumatic internal organs and major arteries.

Uncontrolled hemorrhage caused by trauma to internal organs or major arteries poses critical threats to lives. However, rapid hemostasis followed by tissue repair remains an intractable challenge in surgery owing to the lack of ideal internal-use adhesives that can achieve fast and robust wet adhesion and accelerate wound healing. Herein, we develop a robust hemostatic bioadhesive (CAGA) from novel highly-branched aminoethyl gelatin with end-grafted abundant catechol (Gel-AE-Ca). The unique chemical structure of Gel-AE-Ca makes CAGA capable of gelling on wet tissues via synergetic cross-linking of catechol-Fe3+ chelation and horseradish peroxidase (HRP)/H2O2-triggered covalent bonds using a dual-channel needle, meeting the key demands of internal medical applications (e.g., instant and strong wet adhesion, injectability, biocompatibility, self-healing, stretching flexibility, infection resistance, and proper biodegradability). It exhibits rapid gelation within 10 s and robust wet tissue adhesion up to 115.0 ± 13.1 kPa of shear strength and 245.0 ± 33.8 mm Hg of sealing strength. In vivo trials demonstrate that CAGA can not only effectively seal anastomosis of the carotid artery, but achieve rapid hemostasis on the sites of liver incisions and penetrating cardiac wounds within 10 s. The wound closure by CAGA and its timely biodegradation promote wound healing of the vital organs.

Ultra-compact displacement and vibration sensor with a sub-nanometric resolution based on Talbot effect of optical microgratings.

Based on Talbot effect of optical microgratings, we report an ultra-compact sensor for displacement and vibration measurement with resolution down to sub-nanometer level. With no need of optical components such as reflectors, splitters, polarizers, and wave plates, the proposed sensor based on a common-path structure shows a high compactness. Using gratings with period of 3 µm, displacement measurement within a range of 1 mm is demonstrated experimentally. Associated with an interpolation circuit with subdividing factor of 4096, a resolution of 0.73 nm is obtained. The experimental results also show the ability for the sensor to detect in-plane vibration with frequency below 900 Hz. With a sub-nanometer resolution and an ultra-compact structure, the miniature sensor shows potential in applications such as high-precision machinery manufacturing and semiconductor processing.

Porous gelatin microsphere-based scaffolds containing MC3T3-E1 cells and calcitriol for the repair of skull defect.

There is an increasing demand for biomaterials with skull regeneration for clinical application. However, most of the current skull repair materials still have limitations, such as inadequate sources, poor cell adherence, differentiation, tissue infiltration, and foreign body sensation. Therefore, this study developed porous microsphere-based scaffolds containing mouse embryonic osteoblast precursor cells (MC3T3-E1 cells) and calcitriol (Cal) using gelatin and gelatin/hydroxyapatite through green freeze-crosslinking and freeze-drying. Gelatin was employed to prepare porous microspheres with a particle size of 100-300 µm, containing open pores of 2-70 µm and interconnected paths. Furthermore, the addition of Cal to porous gelatin microsphere-based scaffolds containing MC3T3-E1 cells (PGMSs-MC) and porous gelatin/hydroxyapatite composite microspheres containing MC3T3-E1 cells (HPGMSs-MC) improved their osteoinductivity and cell proliferation and promoted the formation of mature and well-organized bone. The developed Cal-HPGMSs-MC and Cal-PGMSs-MC displayed a good porous structure and cytocompatibility, histocompatibility, osteoconductivity, and osteoinduction. Thus, the designed scaffolds provide a promising prospect for tissue-engineered constructs with skull growth and integration, laying a foundation for further research on the reconstruction of skull defects.

A transcriptome sequencing study on the effect of macro-pores in hydrogel scaffolds on global gene expression of laden human cartilage chondrocytes.

The macro-porous hydrogel scaffolds can not only enhance the proliferation of laden chondrocytes but also favor the deposition of hyaline cartilaginous extracellular matrix, however, the underlying molecular mechanism is still unclear. Herein, the global gene expression of human cartilage chondrocytes (HCCs) encapsulated in traditional hydrogel (Gel) constructs and micro-cavitary gel (MCG) constructs are investigated by using high-throughput RNA sequencing (RNA-seq). The differentially expressed genes (DEGs) between the HCCs cultured in Gel and MCG constructs have been identified via bioinformatics analysis. Significantly, the DEGs that promote cell proliferation (e.g. POSTN, MKI67, KIF20A) or neo-cartilage formation (e.g. COL2, ASPN, COMP, FMOD, FN1), are more highly expressed in MCG constructs than in Gel constructs, while the expressions of the DEGs associated with chondrocyte hypertrophy (e.g. EGR1, IBSP) are upregulated in Gel constructs. The expression of representative DEGs is verified at both mRNA and protein levels. Besides, cellular viability and morphology as well as the enriched signaling pathway of DEGs are studied in detail. These results of this work may provide data for functional tissue engineering of cartilage.

Biomaterial Scaffolds Made of Chemically Cross-Linked Gelatin Microsphere Aggregates (C-GMSs) Promote Vascularized Bone Regeneration.

Various scaffolding systems have been attempted to facilitate vascularization in tissue engineering by optimizing biophysical properties (e.g., vascular-like structures, porous architectures, surface topographies) or loading biochemical factors (e.g., growth factors, hormones). However, vascularization during ossification remains an unmet challenge that hampers the repair of large bone defects. In this study, reconstructing vascularized bones in situ against critical-sized bone defects is endeavored using newly developed scaffolds made of chemically cross-linked gelatin microsphere aggregates (C-GMSs). The rationale of this design lies in the creation and optimization of cell-material interfaces to enhance focal adhesion, proliferation, and function of anchorage-dependent functional cells. In vitro trials are carried out by coculturing human aortic endothelial cells (HAECs) and murine osteoblast precursor cells (MC3T3-E1) within C-GMS scaffolds, in which endothelialized bone-like constructs are yielded. Angiogenesis and osteogenesis induced by C-GMSs scaffold are further confirmed via subcutaneous-embedding trials in nude mice. In situ trials for the repair of critical-sized femoral defects are subsequently performed in rats. The acellular C-GMSs with interconnected macropores, exhibit the capability to recruit the endogenous cells (e.g., bone-forming cells, vascular forming cells, immunocytes) and then promote vascularized bone regeneration as well as integration with host bone.

Three-dimensional (3D) hydrogel serves as a platform to identify potential markers of chondrocyte dedifferentiation by combining RNA sequencing.

Dedifferentiation of chondrocyte greatly restricts its function and application, however, it is poorly understood except a small number of canonical markers. The non-cell-adhesive property endows polysaccharide hydrogel with the ability to maintain chondrocyte phenotype, which can serve as a platform to identify new molecular markers and therapeutic targets of chondrocyte dedifferentiation. In this study, the high-throughput RNA sequencing (RNA-seq) was first performed on articular chondrocytes at primary (P0) and passage 1 (P1) stages to explore the global alteration of gene expression along with chondrocyte dedifferentiation. Significantly, several potential marker genes, such as PFKFB3, KDM6B, had been identified via comparatively analyzing their expression in P0 and P1 chondrocytes as well as in 3D constructs (i.e. chondrocyte-laden alginate hydrogel and HA-MA hydrogel) at both mRNA and protein level. Besides, the changes in cellular morphology and enriched pathway of differentially expressed genes during chondrocyte dedifferentiation was studied in detail. This study developed the use of hydrogel as a platform to investigate chondrocyte dedifferentiation; the results provided new molecular markers and potential therapeutic targets of chondrocyte dedifferentiation.

Progress of gelatin-based microspheres (GMSs) as delivery vehicles of drug and cell.

Gelatin has various attractive features as biomedical materials, for instance, biocompatibility, low immunogenicity, biodegradability, and ease of manipulation. In recent years, various gelatin-based microspheres (GMSs) have been fabricated with innovative technologies to serve as sustained delivery vehicles of drugs and genetic materials as well as beneficial bacteria. Moreover, GMSs have exhibited promising potentials to act as both cell carriers and 3D scaffold components in tissue engineering and regenerative medicine, which not only exhibit excellent injectability but also could be integrated into a macroscale construct with the laden cells. Herein, we aim to thoroughly summarize the recent progress in the preparations and biomedical applications of GMSs and then to point out the research direction in future. First, various methods for the fabrication of GMSs will be described. Second, the recent use of GMSs in tumor embolization and in the delivery of cells, drugs, and genetic material as well as bacteria will be presented. Finally, several key factors that may enhance the improvement of GMSs were suggested as delivery vehicles.

A Transcriptome Sequencing Study on Genome-Wide Gene Expression Differences of 3D Cultured Chondrocytes in Hydrogel Scaffolds with Different Gel Density.

Hydrogel is considered as a promising cell delivery vehicle in cartilage tissue engineering, whose tunable microenvironments may influence the function and fate of encapsulated chondrocytes. Here, the transcriptomes of chondrocytes that are encapsulated and cultured in hydrogel constructs respectively made of 0.8% and 4% alginate solution are investigated. Differences in chondrocyte transcriptome are detected via RNA-sequencing from these two cultural conditions. The differentially expressed genes (DEGs) are reflected in extracellular matrix (ECM) secretion, cell cycle, proliferation, cartilage development, and so on. Significantly, the expression of DEGs associated with cartilage ECM and cell proliferation are upregulated in 0.8% constructs; whilst the expressions of DEGs involved in cell cycle and matrix degradation are upregulated in 4% constructs. Moreover, interestingly, the expressions of chondrocyte hypertrophy markers are upregulated in 0.8% constructs; while 4% constructs seemingly favor the long-term maintenance of chondrocyte phenotype. Taken together, this study confirms on transcriptomic level that gel density affects gene expression and phenotype of the encapsulated chondrocytes; therefore, it may provide guidance for future design and fabrication of cartilage tissue engineering scaffolds.

Cross-linked gelatin microsphere-based scaffolds as a delivery vehicle of MC3T3-E1 cells: in vitro and in vivo evaluation.

Scaffolding plays a crucial role in bone tissue engineering by not only providing interfaces for cell adhesion, proliferation, and differentiation but also guiding neotissue formation. For this purpose, microspheres (MSs) are being increasingly used alone or in combination with other scaffolds. However, few researchers have used MSs to prepare 3D scaffolds by culture with delivered cells. In this study, we have developed covalent cross-linked gelatin MSs (ccG-MSs) (average diameter = 100-300 µm) to load mouse osteoblast MC3T3-E1 cells, which exhibit attachment and spreading on surfaces of ccG-MSs after co-culture. Significantly, the ccG-MSs can be integrated into a macroscopic construct with MC3T3-E1 cells after 5 days of cultivation. The MC3T3-E1 cells within ccG-MSs constructs show a higher viability and proliferation activity than those in the micro-cavitary gelatin gel (MCG) constructs. Calcium deposition, alkaline phosphatase activity as well as osteocalcin secretion within both ccG-MSs and MCG constructs have been evaluated in vitro and in vivo, respectively. Compared to MCG scaffolds, ccG-MS-based scaffolds can provide better cellular microenvironments for cell proliferation and osteogenic differentiation. Our findings will lay the foundation for understanding cellular behaviors in MS-based 3D constructs and help in designing MS-based bone tissue engineering scaffolds.

Progress in Articular Cartilage Tissue Engineering: A Review on Therapeutic Cells and Macromolecular Scaffolds.

Repair and regeneration of articular cartilage lesions have always been a major challenge in the medical field due to its peculiar structure (e.g., sparsely distributed chondrocytes, no blood supply, no nerves). Articular cartilage tissue engineering is considered as one promising strategy to achieve reconstruction of cartilage. With this perspective, the articular cartilage tissue engineering has been widely studied. Here, the recent progress of articular cartilage tissue engineering is reviewed. The ad hoc therapeutic cells and growth factors for cartilage regeneration are summarized and discussed. Various types of bio/macromolecular scaffolds together with their pros and cons are also reviewed and elaborated.

A novel cell encapsulatable cryogel (CECG) with macro-porous structures and high permeability: a three-dimensional cell culture scaffold for enhanced cell adhesion and proliferation.

Hydrogel scaffold is a popular cell delivery vehicle in tissue engineering and regenerative medicine due to its capability to encapsulate cells as well as its modifiable properties. However, the inherent submicron- or nano-sized polymer networks of conventional hydrogel will produce spatial constraints on cellular activities of encapsulated cells. In this study, we endeavor to develop an innovative cell encapsulatable cryogel (CECG) platform with interconnected macro-pores, by combining cell cryopreservation technique with cryogel preparation process. The hyaluronan (HA) CECG constructs are fabricated under the freezing conditions via UV photo-crosslinking of the HA methacrylate (HA-MA) that are dissolved in the 'freezing solvent', namely the phosphate buffered saline supplemented with dimethyl sulphoxide and fetal bovine serum. Two model cell types, chondrocytes and human mesenchymal stem cells (hMSCs), can be uniformly three-dimensionally encapsulated into HA CECG constructs with high cell viability, respectively. The macro-porous structures, generated from phase separation under freezing, endow HA CECG constructs with higher permeability and more living space for cell growth. The chondrocytes encapsulated in HA CECG possess enhanced proliferation and extracellular matrix secretion than those in conventional HA hydrogels. In addition, the HA-Gel CECG constructs, fabricated with HA-MA and gelatin methacrylate precursors, provide cell-adhesive interfaces to facilitate hMSCs attachment and proliferation. The results of this work may lay the foundation for us to explore the applications of the CECG-based scaffolds in the field of tissue engineering and regenerative medicine.

A mussel-inspired double-crosslinked tissue adhesive on rat mastectomy model: seroma prevention and in vivo biocompatibility.

BACKGROUND: Seroma formation is a common postsurgical complication of breast cancer surgery. It delays wound healing and may lead to other more serious complications. Conventional methods of reducing seroma formation through suturing or placement of surgical drainage produce inconsistent clinical outcomes. Tissue adhesives are viable alternatives but most of them are unsuitable for internal use and for large-area applications because of weak tissue adhesion strength or biocompatibility issues. The aim of this study was to evaluate the efficacy and biocompatibility of a mussel-inspired double-crosslinked tissue adhesive (DCTA) in reducing seroma formation after mastectomy. MATERIALS AND METHODS: Thirty-six female Sprague-Dawley rats were randomly assigned to either the saline control group (n = 12), the TISSEEL sealant (Baxter) group (n = 12), or the DCTA group (n = 12). After performing a mastectomy and applying the corresponding treatment, the efficacy of DCTA was evaluated by measurement of seroma volume while its biocompatibility was assessed via micronuclei test and histopathologic examination. RESULTS: During the 1-wk postsurgical period, the average total seroma volume of DCTA was significantly lower than the saline control group. Importantly, the mean seroma volume in DCTA showed a decreasing trend, whereas those in TISSEEL and saline control groups showed otherwise. The application of DCTA showed no genotoxic effect on the host and no severe inflammation. CONCLUSIONS: This study demonstrates that the good tissue adhesion strength and stability of DCTA were successful in reducing seroma formation over a period of 1 wk. Furthermore, the results also showed that it is biocompatible, which makes it suitable for large-area, internal use.

Macroporous Hydrogel Scaffolds for Three-Dimensional Cell Culture and Tissue Engineering.

Hydrogels have been promising candidate scaffolds for cell delivery and tissue engineering due to their tissue-like physical properties and capability for homogeneous cell loading. However, the encapsulated cells are generally entrapped and constrained in the submicron- or nanosized gel networks, seriously limiting cell growth and tissue formation. Meanwhile, the spatially confined settlement inhibits attachment and spreading of anchorage-dependent cells, leading to their apoptosis. In recent years, macroporous hydrogels have attracted increasing attention in use as cell delivery vehicles and tissue engineering scaffolds. The introduction of macropores within gel scaffolds not only improves their permeability for better nutrient transport but also creates space/interface for cell adhesion, proliferation, and extracellular matrix deposition. Herein, we will first review the development of macroporous gel scaffolds and outline the impact of macropores on cell behaviors. In the first part, the advantages and challenges of hydrogels as three-dimensional (3D) cell culture scaffolds will be described. In the second part, the fabrication of various macroporous hydrogels will be presented. Third, the enhancement of cell activities within macroporous gel scaffolds will be discussed. Finally, several crucial factors that are envisaged to propel the improvement of macroporous gel scaffolds are proposed for 3D cell culture and tissue engineering.

Enhancing vascularization of a gelatin-based micro-cavitary hydrogel by increasing the density of the micro-cavities.

The transport of nutrients and oxygen by vascular networks into engineered tissue constructs is critical to their successful integration into host tissues. Hydrogel has achieved some promising results as scaffolds for vascularization. However, the vascularization of hydrogel is still constrained by its inherent submicron- or nano-sized pores. In this study, two gelatin-based micro-cavitary gel (Gel-MCG) constructs with varying densities of micro-cavities were developed with a photocrosslinkable gelatin methacrylate (Gel-MA) precursor and porogenic gelatin microspheres (MS), and their functions in supporting vascularization within hydrogels were evaluated with endothelial progenitor outgrowth cells (EPOCs). The increase of cavitary density could enhance the vascularization of Gel-MCG constructs. After 14 d of culture in vitro, the vascularization of Gel-MCG constructs with higher cavitary density was significantly superior to that of gelatin spongy control and the fusion of vascularized cavities in the constructs could be observed. Further subcutaneous implantation of the Gel-MCG constructs with higher cavitary density into nude mice also showed obvious vascular invasion from host tissues. Taken together, these results indicate that the increase in cavitary density can efficiently facilitate the vascularization of Gel-MCG constructs both in vitro and in vivo and that such highly-porous Gel-MCG constructs have great potential to be a promising scaffold for the development of vascularized tissue constructs.