Stimuli-sensitive drug delivery system (SSDDS) is an novel drug delivery carrier.It is sensitive to either the internal physiopathologic changes (pH,temperature) of the body or external stimulus signal (ultrasound,magnetic signal) and controls the release of the drugs that it carries according to the variation of physicochemical property which stimulated by the signals.SSDDS can be prepared from hydrogels,liposomes and magnetic nanoparticles.In contrast to non-stimuli-responsive drug delivery system,SSDDS has remarkable advantages including feedback regulation,stronger controllability and targeting therapy.This paper will review the advancement in stimuli-responsive drug delivery system in recent years.

Nano-hydroxyapatite biomimetic bone materials have become a hotspot in the field of tissue engineering research due to the similarity of the structure and composition to natural bone. This article describes a variety of preparation of nano-hydroxyapatite and synthesis of nano-hydroxyapatite composite, as well as the properties of nano-hydroxyapatite composite materials. Through surface-modification nanohydroxyapatite composite materials will have a potential application foreground including bone defects repair,drug carrier for cancer treatment. In this paper, research progress of nano-hydroxyapatite biomimetic bone materials in recent years were reviewed.

Xenogeneic/Allogeneic bone materials are among the hot research interests of biological scaffolds.These materials are ideal materials for repairing bone defects because they have the structure and morphology of the natural bones,are able to be degraded and absorbed in the body,and are less immunogenic through appropriato treatment.Through further modification with biological molecules such as growth factors,they could provide a better microenvironment for the bone cells to grow into and fully differentiate.This article summarizes the factors affecting the immunogenicity of xenogeneic/allogeneic bone and the methods of removing immunogenicity.Advances in sintered bone materials,defatted bone materials,deproteinated bone materials,decalcifying bone materials,and composite materials are reviewed in greater details.

Cartilage injury has a very limited capacity of recovery by itself due to the lack of blood vessel in cartilage tissues. Current studies indicate that many kinds of cytokines have the function of promoting cartilage formation or repairing the injured cartilage with cartilage-like tissues. Cell-mediated transfer of the respective genes may ideally combine the supply of a chondrogenic cell population with the production of certain factors se-creted from the lesion and to promote the repairing of the lesion, which is considered the best treatment. Gene therapy based on this technology has developed rapidly in recent years. This review aims to summarize some of the development of the research in the field.

Rapid prototyping technology, a kind of novel digital prototyping technology developed in mid-1980s based on a principle of discrete and accumulation, which fabricates a prototype by accurate accumulation of material according to the CAD models or CT data under the control of the computer without any other device. In recent years, it has shown a great application prospect in the field of orthopedics combined with three-dimensional image reconstruction of spiral CT and MRL In this article, review is given on the application development of rapid prototyping technology in orthopedics, such as organ model preparation and surgical planning, customized implant and bone tissue engineering porosity scaffold fabrication.

Spinal cord injury(SCI) is a serious nervous system trauma,which may consequently lead to various degrees of paralysis and toilet obstacles,and its disability and the high cost heavily burdened the families and community.Therefore,the research on spinal cord tissue regeneration and the repair after injury has important practical significance.A large number of experimental studies have shown that neurotrophic factor plays an important role in the nerve tissue repair process.This article reviews new research progress about the effects of neurotrophic factor in this field.

Owing to the profound impact of spinal cord injury, extensive studies have been carried out aimed at facilitating axonal regeneration following injury. Tissue engineering, as an emerging and rapidly growing field, has received extensive attention for nervous system axonal guidance. Numerous engineered substrates including biomaterial scaffolds, cells, biomolecules, have showed potential of supporting axonal regeneration and functional recovery. This article reviews current progresses on biomaterial scaffolds, cells, biomolecules for nerve repair, as well as therapeutic approaches that are being explored for spinal cord repairing.

Implant drug delivery system(IDDS) is helpful to the therapy of infection、tuberculosis and tumor of bone. With the development of tissue engineering, various materials has been used as the carriers for the IDDS. Research of the carrier materials used in implant drug delivery system is reviewed in this article.

The nerve tissue engineering (NTE) has been applied in the treatment of central nerve system injury or disease to restore its anatomic structure and function, in which the nervous scaffolds played important roles in supporting and nourishing the nerve tissues. Development, challenge confronted and foreground of research on scaffolds material in the nerve tissue engineering are reviewed in this article.

As an essential element of tissue engineering,the shape,pore size,and porosity of the porous scaffolds have direct influence on the attachment,proliferation,and differentiation of seeding cell as well as their properties.So it is important to be able to prepare an ideal porous scaffold which is able to provide the cells with an excellent micrcenvirenment in order to support their growth and differentiation.In this article,we reviewed some kinds of the preparation technologies of the porous scaffolds for tissue engineering,including fiber bonding,emulsion freeze drying,solvent casting/particulate leaching,high-pressuro processing,gas foaming/particulate leaching,thermally induced phase separation,and electro-spinning,with focus on rapid prototyping.It is our belief that the combination of the basic technologies and the rapid prototyping technology which is able to control the properties of the scaffolds and could be applied for individualized scaffold construction would be the major focus of research in the future.