Role of corneal collagen fibrils in corneal disorders and related pathological conditions

The cornea is a soft tissue located at the front of the eye with the principal function of transmitting and refracting light rays to precisely sense visual information. Corneal shape, refraction, and stromal stiffness are to a large part determined by corneal fibrils, the arrangements of which define the corneal cells and their functional behaviour. However, the modality and alignment of native corneal collagen lamellae are altered in various corneal pathological states such as infection, injury, keratoconus, corneal scar formation, and keratoprosthesis. Furthermore, corneal recuperation after corneal pathological change is dependent on the balance of corneal collagen degradation and contraction. A thorough understanding of the characteristics of corneal collagen is thus necessary to develop viable therapies using the outcome of strategies using engineered corneas. In this review, we discuss the composition and distribution of corneal collagens as well as their degradation and contraction, and address the current status of corneal tissue engineering and the progress of corneal cross-linking.

Infrared nanoimaging of nanoscale sliding dislocation of collagen fibrils

Collagen,one of the major components in the mammalian connective tissues,plays an essential role in many vital physiological processes.Many common diseases,such as fibrosis,overuse injuries,and bone fracture,are associated with collagen arrangement defects.However,the underlying mechanism of collagen arrangement defects remains elusive.In this study,we applied infrared scattering-type scanning near-field optical microscopy to study collagen fibrils’structural properties.Experimentally,we observed two types of collagen fibrils’arrangement with different periodic characteristics.A crystal sliding model was employed to explain this observation qualitatively.Our results suggest that the collagen dislocation propagates in collagen fibrils,which may shed light on many collagen diseases’pathogenesis.These findings help to understand the regulation mechanism of hierarchical biological structure.

In vivo bone regeneration with injectable chitosan/hydroxyapatite/collagen composites and mesenchymal stem cells

For reconstruction of irregular bone defects, injectable biomaterials are more appropriate than the preformed biomaterials. We herein develop a biomimetic in situ-forming composite consisting of chitosan （CS） and mineralized collagen fibrils （nHAC）, which has a complex hierarchical structure similar to natural bone. The CSInHAC composites with or without mesenchymal stem cells （MSCs） are injected into cancellous bone defects at the distal end of rabbit femurs. Defects are assessed by radiographic, histological diagnosis and Raman microscopy until 12 weeks. The results show that MSCs improve the biocompatibility of CS/nHAC composites and enhance new bone formation in vivo at 12 weeks. It can be concluded that the injectable CSInHAC composites combined with MSCs may be a novel method for reconstruction of irregular bone defects.

Endometrial Collagen Fibril Hyperplasia is Associated with Implantation Failure in Women Undergoing IVF-ET

Objective To analyse the effects of controlled ovarian hyperstimulation （ COH） on the endometrial expression of collagen fibril （CF） during the peri-implantation period in patients undergoing IVF, and its relation to endometrial receptivity （ER） in repeated implantation failure（RIF）. Methods Peripheral blood and endometrial biopsies were obtained from 45 infertile women on days 5, 7 or 9 after oocytes retrieval or ovulation in a stimulated cycle （SC） and natural cycle （NC） respectively. CF was assayed by transmission electron microscope and quantified by modified Masson dyeing. The outcome of subsequent embryo transfer（ET） was observed. Results Levels of both E2 and progesterone were higher in the peripheral blood in SC than in NC. Also the expression of CF in the stroma in each secretory phase was increased significantly in SC （P 〈O.05）. After embryo transferring, expression levels of CF in the pregnancy group dropped between the mid- and late-secretory phase, but no change in the non-pregnancy group. In the same term, all patients undergone endometrial curettage had higher pregnancy rate than those without. Conclusion Imbalance of production and degradation of endometrial CF in the secretory phase resulting from COH may be the cause of defective ER and implantation failure in some RIF patients. Endometrial curettage may improve implantation rate by inducing appropriate CF hyperplasia and degradation.

Age-related differences in the biological parameters of vertebral cancellous bone from Chinese women

Background With aging, the human fracture risk gradually increase. This is mainly due to the corresponding changes of the biomechanical parameters of human bone presents with aging. We measured the microstructural parameters of lumbar bone from women in several age groups by micro-computed tomography and scanning electron microscopy. We observed changes in lumbar cancellous bone mineral density and in biomechanical parameters with aging to elucidate the relationship between age and risk of fracture. We provide theoretical support for human pathology, fracture risk increased with age and the individualized of each age group.

Nanostructural origins of irreversible deformation in bone revealed by an in situ atomic force microscopy study

The structural origins of bone toughness at the nanoscale are not completely understood.Therefore,we performed in situ scanning using atomic force microscopy during macroscopic mechanical testing of antler and bovine bone,to reveal the origins of the irreversible plastic deformation at the mineralized collagen fibril(MCF)array and MCF levels.We found that the plastic deformation behavior at the nanoscale level could be divided into two stages.The first stage of plastic deformation at the nanoscale level was characterized by slippage between the MCF arrays,which contained mineral aggregate grains with regular shapes under load.In the second stage of nanoscale plastic deformation,the MCFs broke through the bonds of the extrafibrillar mineral aggregate grains and exhibited interfibrillar slippage.These nanoscale plastic deformation behaviors may thus be the origins of stress whitening and irreversible plastic deformation.Thus,the findings in this study not only shed light on the plastic deformation mechanisms of MCF arrays and MCFs,but also provide structural and mechanistic insights into bioinspired materials design and mechanisms of relevant bone diseases.