中枢神经系统损伤修复生物材料研究进展

中枢神经系统损伤导致神经细胞死亡、组织破坏,造成神经功能永久性缺失,是长期困扰生物医学界的一大难题,目前尚无有效疗法。组织工程技术不仅能通过纳米生物材料为神经细胞和神经纤维生长提供结构支持,还能同时递送各种有利于神经再生修复的活性信号分子,有望在促进中枢神经损伤组织修复的同时,实现神经功能的重建,为中枢神经损伤再生修复带来希望。结合国内外有关中枢神经系统组织工程研究的最新进展,对中枢神经修复生物材料设计的主要策略、以及包括天然生物大分子和合成高分子在内的多种中枢神经修复生物材料的应用进行了详细综述。     

Investigation of nerve injury through microfluidic devices

Traumatic injuries, both in the central nervous system (CNS) and peripheral nervous system (PNS), can potentially lead to irreversible damage resulting in permanent loss of function. Investigating the complex dynamics involved in these processes may elucidate the biological mechanisms of both nerve degeneration and regeneration, and may potentially lead to the development of new therapies for recovery. A scientific overview on the biological foundations of nerve injury is presented. Differences between nerve regeneration in the central and PNS are discussed. Advances in microtechnology over the past several years have led to the development of invaluable tools that now facilitate investigation of neurobiology at the cellular scale. Microfluidic devices are explored as a means to study nerve injury at the necessary simplification of the cellular level, including those devices aimed at both chemical and physical injury, as well as those that recreate the post-injury environment.     

The effects of proteoglycan surface patterning on neuronal pathfinding

Protein micropatterning techniques are increasingly applied in cell choice assays to investigate fundamental biological phenomena that contribute to the host response to implanted biomaterials, and to explore the effects of protein stability and biological activity on cell behavior for in vitro cell studies. In the area of neuronal regeneration the protein micropatterning and cell choice assays are used to improve our understanding of the mechanisms directing nervous system during development and regenerative failure in the central nervous system (CNS) wound healing environment. In these cell assays, protein micropatterns need to be characterized for protein stability, bioactivity, and spatial distribution and then correlated with observed mammalian cell behavior using appropriate model system for CNS development and repair. This review provides the background on protein micropatterning for cell choice assays and describes some novel patterns that were developed to interrogate neuronal adaptation to inhibitory signals encountered in CNS injuries.     

Peripheral mineralization of a 3D biodegradable tubular construct as a way to enhance guidance stabilization in spinal cord injury regeneration

Spinal cord injuries (SCI) present a major challenge to therapeutic development due to its complexity. Combinatorial approaches using biodegradable polymers that can simultaneously provide a tissue scaffold, a cell vehicle, and a reservoir for sustained drug delivery have shown very promising results. In our previous studies we have developed a novel hybrid system consisting of starch/poly-e-caprolactone (SPCL) semi-rigid tubular porous structure, based on a rapid prototyping technology, filled by a gellan gum hydrogel concentric core for the regeneration within spinal-cord injury sites. In the present work we intend to promote enhanced osteointegration on these systems by pre-mineralizing specifically the external surfaces of the SPCL tubular structures, though a biomimetic strategy, using a sodium silicate gel as nucleating agent. The idea is to create two different cell environments to promote axonal regeneration in the interior of the constructs while inducing osteogenic activity on its external surface. By using a Teflon cylinder to isolate the interior of the scaffold, it was possible to observe the formation of a bone-like poorly crystalline carbonated apatite layer continuously formed only in the external side of the tubular structure. This biomimetic layer was able to support the adhesion of Bone Marrow Mesenchymal Stem Cells, which have gone under cytoskeleton reorganization in the first hours of culture when compared to cells cultured on uncoated scaffolds. This strategy can be a useful route for locally stimulate bone tissue regeneration and facilitating early bone ingrowth.     

Effective Modulation of CNS Inhibitory Microenvironment using Bioinspired Hybrid-Nanoscaffold-Based Therapeutic Interventions

Central nervous system (CNS) injuries are often debilitating, and most currently have no cure. This is due to the formation of a neuroinhibitory microenvironment at injury sites, which includes neuroinflammatory signaling and non-permissive extracellular matrix (ECM) components. To address this challenge, a viscous interfacial self-assembly approach, to generate a bioinspired hybrid 3D porous nanoscaffold platform for delivering anti-inflammatory molecules and establish a favorable 3D-ECM environment for the effective suppression of the neuroinhibitory microenvironment, is developed. By tailoring the structural and biochemical properties of the 3D porous nanoscaffold, enhanced axonal growth from the dual-targeting therapeutic strategy in a human induced pluripotent stem cell (hiPSC)-based in vitro model of neuroinflammation is demonstrated. Moreover, nanoscaffold-based approaches promote significant axonal growth and functional recovery in vivo in a spinal cord injury model through a unique mechanism of anti-inflammation-based fibrotic scar reduction. Given the critical role of neuroinflammation and ECM microenvironments in neuroinhibitory signaling, the developed nanobiomaterial-based therapeutic intervention may pave a new road for treating CNS injuries.     

Evaluation of 3D nano–macro porous bioactive glass scaffold for hard tissue engineering

Recently, nano–macro dual-porous, three-dimensional (3D) glass structures were developed for use as bioscaffolds for hard tissue regeneration, but there have been concerns regarding the interconnectivity and homogeneity of nanopores in the scaffolds, as well as the cytotoxicity of the environment deep inside due to limited fluid access. Therefore, mercury porosimetry, nitrogen absorption, and TEM have been used to characterize nanopore network of the scaffolds. In parallel, viability of MG 63 human osteosarcoma cells seeded on scaffold surface was investigated by fluorescence, confocal and electron microscopy methods. The results show that cells attach, migrate and penetrate inside the glass scaffold with high proliferation and viability rate. Additionally, scaffolds were implanted under the skin of a male New Zealand rabbit for in vivo animal test. Initial observations show the formation of new tissue with blood vessels and collagen fibers deep inside the implanted scaffolds with no obvious inflammatory reaction. Thus, the new nano–macro dual-porous glass structure could be a promising bioscaffold for use in regenerative medicine and tissue engineering for bone regeneration.     

Production of new 3D scaffolds for bone tissue regeneration by rapid prototyping

The incidence of bone disorders, whether due to trauma or pathology, has been trending upward with the aging of the worldwide population. The currently available treatments for bone injuries are rather limited, involving mainly bone grafts and implants. A particularly promising approach for bone regeneration uses rapid prototyping (RP) technologies to produce 3D scaffolds with highly controlled structure and orientation, based on computer-aided design models or medical data. Herein, tricalcium phosphate (TCP)/alginate scaffolds were produced using RP and subsequently their physicochemical, mechanical and biological properties were characterized. The results showed that 60/40 of TCP and alginate formulation was able to match the compression and present a similar Young modulus to that of trabecular bone while presenting an adequate biocompatibility. Moreover, the biomineralization ability, roughness and macro and microporosity of scaffolds allowed cell anchoring and proliferation at their surface, as well as cell migration to its interior, processes that are fundamental for osteointegration and bone regeneration.     

Self-assembling peptide nanofiber hydrogels for central nervous system regeneration

Central nervous system (CNS) presents a complex regeneration problem due to the inability of central neurons to regenerate correct axonal and dendritic connections. However, recent advances in developmental neurobiology, cell signaling, cell--matrix interaction, and biomaterials technologies have forced a reconsideration of CNS regeneration potentials from the viewpoint of tissue engineering and regenerative medicine. The applications of a novel tissue regeneration-inducing biomaterial and stem cells are thought to be critical for the mission. The use of peptide nanofiber hydrogels in cell therapy and tissue engineering offers promising perspectives for CNS regeneration. Self-assembling peptide undergo a rapid transformation from liquid to gel upon addition of counterions or pH adjustment, directly integrating with the host tissue. The peptide nanofiber hydrogels have mechanical properties that closely match the native central nervous extracellular matrix, which could enhance axonal growth. Such materials can provide an optimal three dimensional microenvironment for encapsulated cells. These materials can also be tailored with bioactive motifs to modulate the wound environment and enhance regeneration. This review intends to detail the recent status of self-assembling peptide nanofiber hydrogels for CNS regeneration.     

Systematic studies of a self-assembling peptide nanofiber scaffold with other scaffolds

A designer self-assembling peptide nanofiber scaffold has been systematically studied with 10 commonly used scaffolds in a several week study using neural stem cells (NSC), a potential therapeutic source for cellular transplantations in nervous system injuries. These cells not only provide a good in vitro model for the development and regeneration of the nervous system, but may also be helpful in testing for cytotoxicity, cellular adhesion, and differentiation properties of biological and synthetic scaffolds used in medical practices. We tested the self-assembling peptide nanofiber scaffold with the most commonly used scaffolds for tissue engineering and regenerative medicine including PLLA, PLGA, PCLA, collagen I, collagen IV, and Matrigel. Additionally, each scaffold was coated with laminin in order to evaluate the utility of this surface treatment. Each scaffold was evaluated by measuring cell viability, differentiation and maturation of the differentiated stem cell progeny (i.e. progenitor cells, astrocytes, oligodendrocytes, and neurons) over 4 weeks. The optimal scaffold should show high numbers of living and differentiated cells. In addition, it was demonstrated that the laminin surface treatment is capable of improving the overall scaffold performance. The designer self-assembling peptide RADA16 nanofiber scaffold represents a new class of biologically inspired material. The well-defined molecular structure with considerable potential for further functionalization and slow drug delivery makes the designer peptide scaffolds a very attractive class of biological material for a number of applications. The peptide nanofiber scaffold is comparable with the clinically approved synthetic scaffolds. The peptide scaffolds are not only pure, but also have the potential to be further designed at the molecular level, thus they promise to be useful for cell adhesion and differentiation studies as well as for future biomedical and clinical studies.     

Functional nanomaterials in peripheral nerve regeneration: Scaffold design,chemical principles and microenvironmental remodeling

Neuronal microenvironment imbalance is associated with successive and irreversible pathophysiological changes and insufficient functional restoration after peripheral nerve injury. Conventional neural-supporting scaffolds result in unsatisfactory curative effects due to lack of biomimetic nanotechnology designs and biochemical or physicochemical modifications. Consequently, they fail in rational and facile remodeling of the imbalanced growth microenvironment, and cannot recover neural structure and function. In recent years, with the increasing knowledge in neuronal injury-associated microenvironment, a number of novel strategies are applied in enhancing the biochemical and physicochemical natures of biomimetic nanomaterial-based scaffolds for nerve tissue engineering. These nanoscale scaffolds can trigger growth factor secretion and aggregation through surface modification, regulate ATP synthesis and hydrolysis, switch between oxidation and reduction states, and activate ion channels and stimulate electrical signals under certain biophysical cues. Consequently, they can determine neuronal cell fate by modulating their viability, development and cell cycles during the regeneration process. In this review, we systematically summarize the studies on the biomimetic scaffold design of functional nanomaterials, their basic topological, biochemical and physical properties, and nanotechnology-based restoration of a balanced nutritional microenvironment regarding four key neural regeneration factors, including immune response, intraneural vascularization, bioenergetic metabolism and bioelectrical conduction in order to provide ideas and inspiration for the nanomedicine-based neuronal regeneration therapy.     

Chitosan/silk fibroin-based tissue-engineered graft seeded with adipose-derived stem cells enhances nerve regeneration in a rat model

Sciatic nerve injury presents an ongoing challenge in reconstructive surgery. Local stem cell application has recently been suggested as a possible novel therapy. In the present study we evaluated the potential of a chitosan/silk fibroin scaffold serving as a delivery vehicle for adipose-derived stem cells and as a structural framework for the injured nerve regeneration. The cell-loaded scaffolds were used to regenerate rat sciatic nerve across a 10 mm surgically-induced sciatic nerve injury. The functional nerve recovery was assessed by both walking track and histology analysis. Results showed that the reconstruction of the injured sciatic nerve had been significantly enhanced with restoration of nerve continuity and function recovery in the cell-loaded scaffold groups, and their target skeletal muscle had been extensively reinnervated. This study raises a potential possibility of using the newly developed nerve grafts as a promising alternative for nerve regeneration.     

Pedestrian injuries in eight European countries: An analysis of hospital discharge data

Out of the 50,000 yearly road traffic deaths in the European Union (formed by 27 European countries and commonly designated as EU-27), some 8500 are pedestrians. While some studies focus on the increased risk for pedestrian mortality compared to other road users, there is a dearth of information on injury patterns that could be used to prioritize injury prevention measures. Hospital discharge data from eight European countries have been used in this study. Injury information from 10,341 pedestrians sustaining 19,424 injuries has been analyzed. Data have been augmented with Abbreviated Injury Scale, Functional Capacity Index and Injury Severity Score codes, and have been categorized into the Barell Matrix. Fractures (51.1%, 50.3-51.8) and internal injuries (21.3%, 20.7-21.9) are the most frequently found in the data; however, blood vessel injuries and internal injuries are the ones associated with the highest risk of death. Head and lower extremities account for 26% of the injuries each, being spinal and thoracic injuries those showing the highest threat to life risk. Hip and lower extremities injuries are the most frequent cause of functional limitation 1 year after discharge. Due to its intrinsic importance, different injury causation mechanisms for head injuries have been analyzed. Though current standards and regulations consider Head Injury Criterion (HIC) as the only tool to assess the risk of injuries to the head, real world injury data show that only 12.1% (11.0-13.2) of these injuries can be attributed to a pure translational mechanism and therefore susceptible to be predicted by HIC. Design of prevention strategies, particularly from the engineering point of view, should benefit from this information.     

Using a 3-D multicellular simulation of spinal cord injury with live cell imaging to study the neural immune barrier to nanoparticle uptake

Development of nanoparticle (NP) based therapies to promote regeneration in sites of central nervous system (CNS;i.e.brain and spinal cord) pathology relies critically on the availability of experimental models that offer biologically valid predictions of NP fate in vivo.However,there is a major lack of biological models that mimic the pathological complexity of target neural sites in vivo,particularly the responses of resident neural immune cells to NPs.Here,we have utilised a previously developed in vitro model of traumatic spinal cord injury (based on 3-D organotypic slice arrays) with dynamic time lapse imaging to reveal in real-time the acute cellular fate of NPs within injury foci.We demonstrate the utility of our model in revealing the well documented phenomenon of avid NP sequestration by the intrinsic immune cells of the CNS (the microglia).Such immune sequestration is a known translational barrier to the use of NP-based therapeutics for neurological injury.Accordingly,we suggest that the utility of our model in mimicking microglial sequestration behaviours offers a valuable investigative tool to evaluate strategies to overcome this cellular response within a simple and biologically relevant experimental system,whilst reducing the use of live animal neurological injury models for such studies.     

Efficient Delivery of Nerve Growth Factors to the Central Nervous System for Neural Regeneration

The central nervous system (CNS) plays a central role in the control of sensory and motor functions, and the disruption of its barriers can result in severe and debilitating neurological disorders. Neurotrophins are promising therapeutic agents for neural regeneration in the damaged CNS. However, their penetration across the blood–brain barrier remains a formidable challenge, representing a bottleneck for brain and spinal cord therapy. Herein, a nanocapsule‐based delivery system is reported that enables intravenously injected nerve growth factor (NGF) to enter the CNS in healthy mice and nonhuman primates. Under pathological conditions, the delivery of NGF enables neural regeneration, tissue remodeling, and functional recovery in mice with spinal cord injury. This technology can be utilized to deliver other neurotrophins and growth factors to the CNS, opening a new avenue for tissue engineering and the treatment of CNS disorders and neurodegenerative diseases.     

Spatiotemporally controlled and multifactor involved assay of neuronal compartment regeneration after chemical injury in an integrated microfluidics

Studies on the degeneration and regeneration of neurons as individual compartments of axons or somata can provide critical information for the clinical therapy of nervous system diseases. A controllable in vitro platform for multiple purposes is key to such studies. In the present study, we describe an integrated microfluidic device designed for achieving localized stimulation to neuronal axons or somata. We observed neuronal compartment degeneration after localized chemical stimulation and regeneration under the accessorial function of an interesting compound treatment or coculture with desired cells in controllable chambers. In a spatiotemporally controlled manner, this device was used to investigate hippocampal neuronal soma and axon degeneration after acrylamide stimulation, as well as subsequent regeneration after treatment with the monosialoganglioside GM1 or with cocultured glial cells (astrocytes or Schwann cells). To gain insight into the molecular mechanisms that mediate neuronal injury and regeneration, as well as to investigate whether acrylamide stimulation to neurons induces changes in Ca(2+) concentrations, the related neuronal genes and real-time Ca(2+) signal in neurons were also analyzed. The results showed that neuronal axons were more resistant to acrylamide injury than neuronal somata. Under localized stimulation, axons had self-destruct programs different from somata, and somatic injury caused the secondary response of axon collapse. This study provides a foundation for future in-depth analyses of spatiotemporally controlled and multifactor neuronal compartment regeneration after various injuries. The microfluidic device is also useful in evaluating potential therapeutic strategies to treat chemical injuries involving the central nervous system.     

Electrospun nanofibers: Work for medicine?

Attempts have been made to fabricate nanofibrous scaffolds to mimic the chemical composition and structural properties of the extracellular matrix (ECM) for tissue/organ replacement. Nanofiber scaffolds with various patterns have been successfully produced from synthetic and natural polymers through a relatively simple technique of electrospinning. The resulting patterns can mimic some of the diverse tissue-specific orientation and three-dimensional (3D) fibrous structures. Studies on cell-nanofiber interactions, including studies on stem cells, have revealed the importance of nanotopography on cell adhesion, proliferation and differentiation. Furthermore, clinical application of electrospun nanofibers including wound healing, tissue regeneration, drug delivery and stem cell therapy are highly feasible due to the ease and flexibility of fabrication of making nanofiber with this cost-effective method using electrospinning. In this review, we have highlighted the current state of the art and provided future perspectives on electrospun nanofiber in medical applications.     

The Risk Line: a special telephone line to provide means of reporting potential dangers and to increase public participation

Injuries constitute a significant public health problem. There is a risk of injury in any environment in which persons are present. The purpose of this paper is to describe the development and experiences from the Risk Line. The Risk Line is a special telephone number to provide means of reporting potential risks for injuries and dangerous products and to increase public participation in injury reporting. Various strategies have been used to make the Risk Line well known in the population. Weekly reports on the risk of playground, traffic, recreational, and residential injuries and dangerous products have been distributed to those who are responsible for eliminating these hazards. The major risk environments reported were traffic, recreational, residential environments, and playgrounds. Seventy-seven percent of the reported hazards had been eliminated. A majority of the public (72%) who had phoned the Risk Line stated that they had become more observant and aware of risks for injuries. In conjunction with injury statistics and safety inspections, information from the Risk Line can contribute to give an improved overall picture of where priorities are needed in safety promotion and injury prevention work.     

Progress of key strategies in development of electrospun scaffolds: bone tissue

There has been unprecedented development in tissue engineering (TE) over the last few years owing to its potential applications, particularly in bone reconstruction or regeneration. In this article, we illustrate several advantages and disadvantages of different approaches to the design of electrospun TE scaffolds. We also review the major benefits of electrospun fibers for three-dimensional scaffolds in hard connective TE applications and identify the key strategies that can improve the mechanical properties of scaffolds for bone TE applications. A few interesting results of recent investigations have been explained for future trends in TE scaffold research.     

The epidemiology and prevention of child pedestrian injury

Of pedestrian injuries that occur every year, approximately 50,000, including 1300 fatalities, are experienced by children between the ages of 1 and 14 years. Despite the importance of the problem, the pedestrian safety issue is often neglected in reports on vehicular injuries. Children between the ages of five and nine years, boys, and children in lower socioeconomic class are at higher risk of pedestrian injury than other children. Childhood pedestrian injuries take place predominantly in residential locations close to home and frequently occur while the child is at play. The risk of pedestrian injury to children is higher than that of other age groups when adjusted for traffic exposure, and a variety of developmental limitations may account for this fact. In spite of these limitations, children undertake collision avoidance maneuvers far more often than drivers do. Accident analyses have identified 15 different accident types, each reflecting a unique combination of human and environmental factors. Among children, the most frequently observed accident type is the midblock dart-out. Programs to modify pedestrian behavior, driver behavior, and vehicle design have met with modest success. In the United States, the cultural and political environments have not been favorable to the injury prevention effort. Urban designers and traffic engineers in Europe have undertaken a variety of modifications of the physical environment, and some of these have been successful in preventing pedestrian injuries to children.     

Nanostructured materials for cardiovascular tissue engineering

Substantial progress has been made in the field of cardiovascular tissue engineering with an ever increasing number of clinically viable implants being reported. However, poor cellular integration of constructs remains a major problem. Limitations in our knowledge of cell/substrate interactions and their impact upon cell proliferation, survival and phenotype are proving to be a major hindrance. Advances in nanotechnology have allowed researchers to fabricate scaffolds which mimic the natural cell environment to a greater extent; allowing the elucidation of appropriate physical cues which influence cell behaviour. The ability to manipulate cell/substrate interactions at the micro/nano scale may help to create a viable cellular environment which can integrate effectively with the host tissue. This review summarises the influence of nanotopographical features on cell behaviour and provides details of some popular fabricating techniques to manufacture 3D scaffolds for tissue engineering. Recent examples of the translation of this research into fabricating clinically viable implants for the regeneration of cardiovascular tissues are also provided.