Hyaluronic acid oligosaccharides modified mineralized collagen and chitosan with enhanced osteoinductive properties for bone tissue engineering.

In this study, we prepared a biomimetic hyaluronic acid oligosaccharides (oHAs)-based composite scaffold to develop a bone tissue-engineered scaffold for stimulating osteogenesis and endothelialization. The functional oHAs products were firstly synthesized, namely collagen/hyaluronic acid oligosaccharides/hydroxyapatite (Col/oHAs/HAP), chitosan/hyaluronic acid oligosaccharides (CTS/oHAs), and then uniformly distributed in poly (lactic-co-glycolic acid) (PLGA) solution followed by freeze-drying to obtain three-dimensional interconnected scaffolds as temporary templates for bone regeneration. The morphology, physicochemical properties, compressive strength, and degradation behavior of the fabricated scaffolds, as well as in vitro cell responses seeded on these scaffolds and in vivo biocompatibility, were investigated to evaluate the potential for bone tissue engineering. The results indicated that the oHAs-based scaffolds can promote the attachment of endothelial cells, facilitate the osteogenic differentiation of MC3T3-E1 and BMSCs, and have ideal biocompatibility and tissue regenerative capacity, suggesting their potential to serve as alternative candidates for bone tissue engineering applications.

Fabrication and assessment of chondroitin sulfate-modified collagen nanofibers for small-diameter vascular tissue engineering applications.

Chondroitin sulfate (ChS) has shown promising results in promoting cell proliferation and antithrombogenic activity. To engineered develop a dual-function vascular scaffold with antithrombosis and endothelialization, ChS was tethered to collagen to accelerate the growth of endothelial cells and prevent platelet activation. First, ChS was used to conjugate with collagen to generate glycosylated products (ChS-COL) via reductive amination. Then, the fabricated ChS-COL conjugates were electrospun into nanofibers and their morphologies and physicochemical characteristics, cell-scaffold responses and platelet behaviors upon ChS-COL nanofibers were comprehensively characterized to evaluate their potential use for small-diameter vascular tissue-engineered scaffolds. The experimental results demonstrated that the ChS modified collagen electrospun nanofibers were stimulatory of endothelial cell behavior, alleviated thrombocyte activation and maintained an antithrombotic effect in vivo in 10-day post-transplantation. The ChS-COL scaffolds encouraged rapid endothelialization, thus probably ensuring the antithrombotic function in long-term implantation, suggesting their promise for small-diameter vascular tissue engineering applications.

Design and comprehensive assessment of a biomimetic tri-layer tubular scaffold via biodegradable polymers for vascular tissue engineering applications.

Considering the structural complexity of the native artery wall and the limitations of current treatment strategies, developing a biomimetic tri-layer tissue-engineered vascular graft is a major developmental direction of vascular tissue regeneration. Biodegradable polymers exhibit adequate mechanical characteristics and feasible operability, showing potential prospects in the construction of tissue engineering scaffold. Herein, we present a bio-inspired tri-layer tubular graft using biodegradable polymers to simulate natural vascular architecture. The inner layer made of polycaprolactone (PCL) nanofiber possesses high tensile strength and contributed to endothelial cell adhesion and proliferation. The middle layer consisted of poly(lactic-co-glycolide) (PLGA) with a three-dimensional porous structure is appropriate for vascular smooth muscle cells (SMCs) penetration. The polyurethane (PU) was selected to be the outer layer, aiming to hold the entire tubular structure, suggesting superior mechanical properties and ideal biocompatibility. Adhesion between independent layers is achieved by thermal crosslinking. The compliance, burst pressure and suture retention force of the tubular scaffold were 2.50 ± 1.60%, 2737.73 ± 583.41 mmHg and 13.06 ± 1.89 N, respectively. The in vivo study of subcutaneous implantation for 8 weeks demonstrated the biomimetic tri-layer vascular graft could maintain intimal integrity, cell infiltration, collagen deposition and scaffold biodegradation. Overall, the biomimetic tri-layer vascular graft promises to be a potential candidate for vascular replacement and regeneration.

Improving in vitro biocompatibility on biomimetic mineralized collagen bone materials modified with hyaluronic acid oligosaccharide.

Hyaluronic acid (HA) has great potential in bone tissue engineering due to its favorable bioactivity and biocompatibility, especially hyaluronic acid oligosaccharides (oHAs) shows a promising result in endothelialization of blood vessel. To improve endothelialized effect and osteogenic performance of bone scaffold, we have created a biomimetic nanofiber network based on collagen modified with hyaluronic acid oligosaccharides (Col/oHAs) and its mineralized product. Biomimetically mineralized Col/oHAs based composite (Col/oHAs/HAP) was prepared via self-assembly at room temperature. The resultant composites were characterized by fourier transform infrared spectroscopy (FT-IR), X-Ray diffractometry (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and transmission electron microscopy (TEM). They show some characteristics of natural bone both in composition and microstructure. The nanofiber was fabricated as a hybrid network which bionics extracellular matrix (ECM) and was prepared to culture artery endothelial cell (PIEC) and the mouse parietal bone cell (MC3T3-E1). Cells attached tightly to the nanofibers and infiltrated into the materials, forming an interconnected cell community. Moreover, the as-prepared nanofiber was found to noticeably enhance cells adhesion and proliferation and upregulate alkaline phosphatase activity (ALP) and osteocalcin (OCN) expression suggesting positive cellular responses. These results indicated that the Col/oHAs/HAP composite has a promising capacity to direct the osteogenic differentiation by providing an adaptable environment and can be expected as an excellent candidate for bone tissue engineering approaches with improved performance of promoting PIEC proliferation.

Mechanical enhancement and in vitro biocompatibility of nanofibrous collagen-chitosan scaffolds for tissue engineering.

The collagen-chitosan complex with a three-dimensional nanofiber structure was fabricated to mimic native ECM for tissue repair and biomedical applications. Though the three-dimensional hierarchical fibrous structures of collagen-chitosan composites could provide more adequate stimulus to facilitate cell adhesion, migrate and proliferation, and thus have the potential as tissue engineering scaffolding, there are still limitations in their applications due to the insufficient mechanical properties of natural materials. Because poly (vinyl alcohol) (PVA) and thermoplastic polyurethane (TPU) as biocompatible synthetic polymers can offer excellent mechanical properties, they were introduced into the collagen-chitosan composites to fabricate the mixed collagen/chitosan/PVA fibers and a sandwich structure (collagen/chitosan-TPU-collagen/chitosan) of nanofiber in order to enhance the mechanical properties of the nanofibrous collagen-chitosan scaffold. The results showed that the tensile behavior of materials was enhanced to different degrees with the difference of collagen content in the fibers. Besides the Young's modulus had no obvious changes, both the break strength and the break elongation of materials were heightened after reinforced by PVA. For the collagen-chitosan nanofiber reinforced by TPU, both the break strength and the Young's modulus of materials were heightened in different degrees with the variety of collagen content in the fibers despite the decrease of the break elongation of materials to some extent. In vitro cell test demonstrated that the materials could provide adequate environment for cell adhesion and proliferation. All these indicated that the reinforced collagen-chitosan nanofiber could be as potential scaffold for tissue engineering according to the different mechanical requirements in clinic.

Degradability of injectable calcium sulfate/mineralized collagen-based bone repair material and its effect on bone tissue regeneration.

The nHAC/CSH composite is an injectable bone repair material with controllable injectability and self-setting properties prepared by introducing calcium sulfate hemihydrate (CSH) into mineralized collagen (nHAC). When mixed with water, the nHAC/CSH composites can be transformed into mineralized collagen/calcium sulfate dihydrate (nHAC/CSD) composites. The nHAC/CSD composites have good biocompatibility and osteogenic capability. Considering that the degradation behavior of bone repair material is another important factor for its clinical applications, the degradability of nHAC/CSD composites was studied. The results showed that the degradation ratio of the nHAC/CSD composites with lower nHAC content increased with the L/S ratio increase of injectable materials, but the variety of L/S ratio had no significant effect on the degradation ratio of the nHAC/CSD composites with higher nHAC content. Increasing nHAC content in the composites could slow down the degradation of nHAC/CSD composite. Setting accelerator had no significant effect on the degradability of nHAC/CSD composites. In vivo histological analysis suggests that the degradation rate of materials can match the growth rate of new mandibular bone tissues in the implanted site of rabbit. The regulable degradability of materials resulting from the special prescriptions of injectable nHAC/CSH composites will further improve the workability of nHAC/CSD composites.

Improved workability of injectable calcium sulfate bone cement by regulation of self-setting properties.

Calcium sulfate hemihydrate (CSH) powder as an injectable bone cement was prepared by hydrothermal synthesis of calcium sulfate dihydrate (CSD). The prepared materials showed X-ray diffraction peaks corresponding to the CSH structure without any secondary phases, implying complete conversion from CSD phase to CSH phase. Thermogravimetric (TG) analyses showed the crystal water content of CSH was about 6.0% (wt.), which is near to the theoretic crystal water value of CSH. From scanning electron microscopy (SEM) micrographs, sheet crystal structure of CSD was observed to transform into rod-like crystal structure of CSH. Most interesting and important of all, CSD as setting accelerator was also introduced into CSH powder to regulate self-setting properties of injectable CSH paste, and thus the self-setting time of CSH paste can be regulated from near 30 min to less than 5 min by adding various amounts of setting accelerator. Because CSD is not only the reactant of preparing CSH but also the final solidified product of CSH, the setting accelerator has no significant effect on the other properties of materials, such as mechanical properties. In vitro biocompatibility and in vivo histology studies have demonstrated that the materials have good biocompatibility and good efficacy in bone regeneration. All these will further improve the workability of CSH in clinic applications.

Mechanical properties and in vitro bioactivity of injectable and self-setting calcium sulfate/nano-HA/collagen bone graft substitute.

Calcium sulfate hemihydrate (CSH) was introduced into the mineralized collagen (nHAC) to prepare an injectable and self-setting in situ bone graft substitute. The mechanical properties of materials, which are dependant on the L/S ratio, the content of nHAC and setting accelerator, were discussed based on the satisfying injectability and setting properties. It was found that the compressive strength and modulus of materials increased with the decrease of nHAC content and L/S ratio. CSD as setting accelerator hardly had an effect on the compressive properties of materials because it is not only the reactant of preparing CSH but also the final solidified product of CSH instead of a foreign body. Though the compressive properties of nHAC/CSD composites changed with the variety of nHAC content and L/S ratio, the compressive strength and modulus of the materials ranged from 2.0 to nearly 20.0 MPa and 100.0 to 800.0 MPa, respectively, which are similar to that of cancellous bone. In vitro cell behavior demonstrated that the composites could provide adequate environment for cell adhesion and proliferation. All these indicated that the nHAC/CSH composites were a potential scaffold for bone tissue engineering.

Injectable calcium sulfate/mineralized collagen-based bone repair materials with regulable self-setting properties.

An injectable and self-setting bone repair materials (nano-hydroxyapatite/collagen/calcium sulfate hemihydrate, nHAC/CSH) was developed in this study. The nano-hydroxyapatite/collagen (nHAC) composite, which is the mineralized fibril by self-assembly of nano-hydrocyapatite and collagen, has the same features as natural bone in both main hierarchical microstructure and composition. It is a bioactive osteoconductor due to its high level of biocompatibility and appropriate degradation rate. However, this material lacks handling characteristics because of its particle or solid-preformed block shape. Herein, calcium sulfate hemihydrate (CSH) was introduced into nHAC to prepare an injectable and self-setting in situ bone repair materials. The morphology of materials was observed using SEM. Most important and interesting of all, calcium sulfate dihydrate (CSD), which is not only the reactant of preparing CSH but also the final solidified product of CSH, was introduced into nHAC as setting accelerator to regulate self-setting properties of injectable nHAC/CSH composite, and thus the self-setting time of nHAC/CSH composite can be regulated from more than 100 min to about 30 min and even less than 20 min by adding various amount of setting accelerator. The compressive properties of bone graft substitute after final setting are similar to those of cancellous bone. CSD as an excellent setting accelerator has no significant effect on the mechanical property and degradability of bone repair materials. In vitro biocompatibility and in vivo histology studies demonstrated that the nHAC/CSH composite could provide more adequate stimulus for cell adhesion and proliferation, embodying favorable cell biocompatibility and a strong ability to accelerate bone formation. It can offer a satisfactory biological environment for growing new bone in the implants and for stimulating bone formation.

Injectable bone cement based on mineralized collagen.

A novel injectable bone cement based on mineralized collagen was reported in this paper. The cement was fabricated by introducing calcium sulfate hemihydrate (CaSO(4).1/2H(2)O, CSH) into nano-hydroxyapatite/collagen (nHAC). The workability, in vitro degradation, in vitro and in vivo biocompatibility of the cement (nHAC/CSH) were studied. The comparative tests via in vitro and in vivo showed that the nHAC/CSH composite cement processed better biocompatibiltiy than that of pure CSH cement. The results implied that this new injectable cement should be very promising for bone repair.