Time-resolved study of the mechanical response of tissue phantoms to nanosecond laser pulses

We present a time-resolved study of the interaction of nanosecond laser pulses with tissue phantoms. When a laser pulse interacts with a material, optical energy is absorbed by a combination of linear (heat generation and thermoelastic expansion) and nonlinear absorption (expanding plasma), according to both the laser light irradiance and material properties. The objective is to elucidate the contribution of linear and nonlinear optical absorption to bubble formation. Depending on the local temperatures and pressures reached, both interactions may lead to the formation of bubbles. We discuss three experimental approaches: piezoelectric sensors, time-resolved shadowgraphy, and time-resolved interferometry, to follow the formation of bubbles and measure the pressure originated by 6 ns laser pulses interacting with tissue phantoms. We studied the bubble formation and pressure transients for varying linear optical absorption and for radiant exposures above and below threshold for bubble formation. We report a rapid decay (of 2 orders of magnitude) of the laser-induced mechanical pressure measured (by time-resolved shadowgraphy) very close to the irradiation spot and beyond 1 mm from the irradiation site (by the piezoelectric sensor). Through time-resolved interferometry measurements, we determined that bubble formation can occur at marginal temperature increments as low as 3°C.     

Electromagnetic-wave induced vibrations in the ocular region of the eye

The ocular region of the eye from the surface of the cornea to the retina is subjected to thermal stresses when radiating energy from a laser beam is incident on it. The absorbed energy represents a volume heat source which depends upon space and time. Acoustic waves are generated by the thermoelastic expansion of the biological material as well as by the electrostriction, caused by higher values of the fields. Assuming the eyeball to be a perfect sphere, the equation of inhomogeneous thermoelastic motion is solved to obtain the parameters of the acoustic wave generated under constrained surface conditions. The results indicate that the acoustic signal is a function of the eye and the acoustic properties of eye tissues only.     

Toward tissue engineering of the knee meniscus

This review details current efforts to tissue engineer the knee meniscus successfully. The meniscus is a fibrocartilaginous tissue found within the knee joint that is responsible for shock absorption, load transmission, and stability within the knee joint. If this tissue is damaged, either through tears or degenerative processes, then deterioration of the articular cartilage can occur. Unfortunately, there is a dearth in the amount of work done to tissue engineer the meniscus when compared to other musculoskeletal tissues, such as bone. This review gives a brief overview of meniscal anatomy, biochemical properties, biomechanical properties, and wound repair techniques. The discussion centers primarily on the different components of attempting to tissue engineer the meniscus, such as scaffold materials, growth factors, animal models, and culturing conditions. Our approach for tissue engineering the meniscus is also discussed.     

The effect of nanofiber alignment on the maturation of engineered meniscus constructs

The fibrocartilaginous menisci are load-bearing tissues vital to the normal functioning of the knee. Removal of damaged regions of the meniscus subsequent to injury impairs knee function and predisposes patients to osteoarthritis. In this study, we employed biodegradable nanofibrous scaffolds for the tissue engineering of the meniscus. Non-aligned (NA) or fiber-aligned (AL) nanofibrous scaffolds were seeded with meniscal fibrochondrocytes (MFCs) or mesenchymal stem cells (MSCs) to test the hypothesis that fiber-alignment would augment matrix content and organization, resulting in improved mechanical properties. Additionally, we proposed that MSCs could serve as an alternative to MFCs. With time in culture, MSC- and MFC-seeded NA and AL constructs increased in cellularity and extracellular matrix (ECM) content. Counter our initial hypothesis, NA and AL constructs contained comparable amounts of ECM, although a significantly larger increase in mechanical properties was observed for AL compared to NA constructs seeded with either cell type. Cell-seeded NA constructs increased in modulus by approximately 1MPa over 10 weeks while cell-seeded AL construct increased by >7MPa. Additionally, MSC-constructs yielded greater amounts of ECM and demonstrated comparable increases in mechanical properties, thereby confirming the utility of MSCs for meniscus tissue engineering. These results demonstrate that cell-seeded fiber-aligned nanofibrous scaffolds may serve as an instructive micro-pattern for directed tissue growth, reconstituting both the form and function of the native tissue.     

Design Characteristics for the Tissue Engineering of Cartilaginous Tissues

Tissues like the temporomandibular joint (TMJ) disc and the knee meniscus are often mistakenly viewed as a tantamount to hyaline cartilage, largely due to the absence of a comprehensive understanding of the distinguishing properties of cartilaginous tissues. Because of this confusion, fibrocartilaginous tissue engineering attempts may not be based on suitable experimental designs. Fibrocartilaginous tissues are markedly different than hyaline cartilage; however, the dearth of knowledge related to their cellular and biochemical composition, as well as their biomechanical characteristics, is stunning. Hyaline articular cartilage is exclusively composed of chondrocytes that produce primarily type II collagen, whereas the TMJ disc and the knee meniscus have a mixed cell population of fibroblasts and cells similar to chondrocytes, which predominantly secrete type I collagen. Additionally, fibrocartilaginous tissues have a low glycosaminoglycan content, a low compressive modulus, and a high tensile modulus when compared to hyaline cartilage. Therefore, it is crucial for fibrocartilaginous tissue engineering attempts to be tissue-specific, utilizing the knowledge of the distinct and unique properties of these tissues. At the same time, advances and insights related to the science and engineering aspect of hyaline cartilage regeneration must be carefully considered for the in vitro engineering of fibrocartilaginous tissues.     

运动性半月板损伤及组织工程半月板的应用

背景：半月板损伤是常见的膝关节运动损伤之一,常伴有关节软骨的损伤,其原因是膝关节内环境的紊乱。 目的：评价组织工程半月板在半月板构建中的生物支架材料的性能,以寻求合理的半月板替代物。 方法：以“组织工程;半月板修复;生物材料支架;运动性半月板损伤”为中文关键词,以“tissue engineering, the meniscus repair,biological material scaffold; athletic meniscal injury”为英文关键词,应用计算机检索维普数据库(1994-01/2009-12)和Pubmed数据库(1994-01/2009-12),纳入30篇运动性半月板损伤和组织工程半月板相关的文献。对半月板组织的特征、半月板组织工程种子细胞的来源、组织工程半月板支架材料生物相容性和可降解性以及细胞因子在组织工程半月板构建过程中的作用进行综合评价。 结果与结论：与传统半月板修复相比,组织工程化半月板具有无抗原性,来源不受限制,可按预先设计塑型,具有生命力等许多优点。但是组织工程化半月板仍有许多问题有待研究和解决,如何模拟体内环境,在体外成功构建半月板组织,如何提高支架材料的应用性,研制具有与正常人体半月板组织相接近的力学性能的支架材料是一个半月板修复的关键性问题。     

Mechanical Stimulation Toward Tissue Engineering of the Knee Meniscus

Current clinical practices do not adequately regenerate the meniscus of the knee secondary to a tear. Complete or partial meniscus removal leads to degenerative changes within the joint. Tissue engineering of the meniscus promises a potent solution. Before embarking on tissue engineering of the meniscus, it is crucial to have a thorough comprehension of the biomechanical role that this tissue fulfills and how the structure of meniscus is uniquely suited to that purpose. To better understand this, we have examined the meniscus, as well as associated tissues, within the body. For the first time, the knee meniscus is rigorously compared to ligament, tendon, and cartilage, and inferences are drawn on how mechanical stimulation may be used to channel growth in the meniscus. We have examined in detail the loading conditions that these tissues experience in vivo and how each is uniquely adapted to its loading environment. These tissues are capable of achieving some degree of remodeling because of mechanical stimuli. By understanding the mechanisms that can stimulate and promote regeneration in related tissues, we hope to harness that knowledge to achieve the goal of meniscal regeneration.     

Tissue engineering of the meniscus

Meniscus lesions are among the most frequent injuries in orthopaedic practice and they will inevitably lead to degeneration of the knee articular cartilage. The fibro-cartilage-like tissue of the meniscus is notorious for its limited regenerative capacity. Tissue engineering could offer new treatment modalities for repair of meniscus tears and eventually will enable the replacement of a whole meniscus by a tissue-engineered construct.Many questions remain to be answered before the final goal, a tissue-engineered meniscus is available for clinical implementation. These questions are related to the selection of an optimal cell type, the source of the cells, the need to use growth factor(s) and the type of scaffold that can be used for stimulation of differentiation of cells into tissues with optimal phenotypes. Particularly in a loaded, highly complex environment of the knee, optimal mechanical properties of such a scaffold seem to be of utmost importance.With respect to cells, autologous meniscus cells seems the optimal cell source for tissue engineering of meniscus tissue, but their availability is limited. Therefore research should be stimulated to investigate the suitability of other cell sources for the creation of meniscus tissue. Bone marrow stroma cells could be useful since it is well known that they can differentiate into bone and cartilage cells. With respect to growth factors, TGF-beta could be a suitable growth factor to stimulate cells into a fibroblastic phenotype but the problems of TGF-beta introduced into a joint environment should then be solved. Polyurethane scaffolds with optimal mechanical properties and with optimal interconnective macro-porosity have been shown to facilitate ingrowth and differentiation of tissue into fibro-cartilage. However, even these materials cannot prevent cartilage degeneration in animal models. Surface modification and/or seeding of cells into the scaffolds before implantation may offer a solution for this problem in the future.This review focuses on a number of specific questions; what is the status of the development of procedures for lesion healing and how far are we from replacing the entire meniscus by a (tissue-engineered) prosthesis. Subquestions related to the type of scaffold used are: is the degree of tissue ingrowth and differentiation related to the initial mechanical properties and if so, what is the influence of those properties on the subsequent remodelling of the tissue into fibro-cartilage; what is the ideal pore geometry and what is the optimal degradation period to allow biological remodelling of the tissue in the scaffold. Finally, we will finish with our latest results of the effect of tear reconstruction and the insertion of prostheses on articular cartilage degradation.     

Multilayered silk scaffolds for meniscus tissue engineering

Removal of injured/damaged meniscus, a vital fibrocartilaginous load-bearing tissue, impairs normal knee function and predisposes patients to osteoarthritis. Meniscus tissue engineering solution is one option to improve outcomes and relieve pain. In an attempt to fabricate knee meniscus grafts three layered wedge shaped silk meniscal scaffold system was engineered to mimic native meniscus architecture. The scaffolds were seeded with human fibroblasts (outside) and chondrocytes (inside) in a spatial separated mode similar to native tissue, in order to generate meniscus-like tissue in vitro. In chondrogenic culture in the presence of TGF-b3, cell-seeded constructs increased in cellularity and extracellular matrix (ECM) content. Histology and Immunohistochemistry confirmed maintenance of chondrocytic phenotype with higher levels of sulfated glycosaminoglycans (sGAG) and collagen types I and II. Improved scaffold mechanical properties along with ECM alignment with time in culture suggest this multiporous silk construct as a useful micro-patterned template for directed tissue growth with respect to form and function of meniscus-like tissue.     

Optoacoustic imaging based on the interferometric measurement of surface displacement

We present images of tissue phantoms and chicken chorio-allantoic membrane vasculature using a novel optoacoustic tomography technique based on the time-resolved interferometric measurement of laser-induced thermoelastic expansion. Our imaging system is based on a modified Mach-Zehnder interferometer that provides surface displacement measurements with a temporal resolution of 4 ns and a displacement sensitivity of 0.3 nm. The images are reconstructed from surface displacement measurements made at several locations following irradiation of the sample with Q-switched Nd:YAG (lambda=532, 1064 nm) laser pulses using a delay and sum beam-forming algorithm. The images shown demonstrate the ability of our method to provide better than 200-microm lateral and 30-microm axial resolution at depths exceeding ten transport mean free paths in highly scattering in-vitro and in-vivo model systems.     

Development of an artificial meniscus using polyvinyl alcohol-hydrogel for early return to,and continuance of,athletic life in sportspersons with severe meniscus injury. II: animal experiments

Due to the prognosis and sporting needs of young athletes who have severe meniscus injury, we have developed an artificial meniscus using polyvinyl alcohol-hydrogel (PVA-H). Biomechanical studies have shown that the human meniscus has various mechanical functions; in our mechanical tests, specimens of human meniscus (part I of this study) demonstrated unique viscoelastic properties. Those tests also showed that a high water-content PVA-H has very similar mechanical properties to those of human meniscus and potential as a substitutive meniscus implant. To assess further the use of PVA-H as an artificial meniscus, we have now performed animal experiments using a PVA-H with 90% water content. In rabbits, the lateral meniscus was replaced with an artificial meniscus in one knee of each animal and lateral meniscectomy was performed on the other side as a control. In the knees of meniscectomy group, degenerative changes in articular cartilage progressed with time and osteoarthritis was observed after 1 year. In the knees of the artificial meniscus group, regressive changes were initially observed, but did not progress, and knee joint function was good even after 1 year. Neither wear nor breakage were observed in artificial menisci. These results suggest that an artificial meniscus using a high water-content PVA-H might be clinically applicable.     

Optoacoustic real-time dosimetry for selective retina treatment

The selective retina treatment (SRT) targets retinal diseases associated with disorders in the retinal pigment epithelium (RPE). Due to the ophthalmoscopic invisibility of the laser-induced RPE effects, we investigate a noninvasive optoacoustic real-time dosimetry system. In vitro porcine RPE is irradiated with a Nd:YLF laser (527 nm, 1.7-micros pulse duration, 5 to 40 microJ, 30 pulses, 100-Hz repetition rate). Generated acoustic transients are measured with a piezoelectric transducer. During 27 patient treatments, the acoustic transients are measured with a transducer embedded in an ophthalmic contact lens. After treatment, RPE damage is visualized by fluorescein angiographic leakage. Below the RPE damage threshold, the optoacoustic transients show no pulse-to-pulse fluctuations within a laser pulse train. Above threshold, fluctuations of the individual transients among each other are observed. If optoacoustic pulse-to-pulse fluctuations are present, RPE leakage is observed in fluorescein angiography. In 96% of the irradiated areas, RPE leakage correlated with the optoacoustic defined threshold value. A noninvasive optoacoustic real-time dosimetry for SRT is developed and proved in vitro and during patient treatment. It detects the ophthalmoscopically invisible laser-induced damage of RPE cells and overcomes practical limitations of SRT for use in private practice.     

Scanning microwave-induced thermoacoustic tomography: signal, resolution, and contrast

Scanning thermoacoustic tomography was explored in the microwave region of the electromagnetic spectrum. Short microwave pulses were used to induce acoustic waves by thermoelastic expansion in biological tissues. Cross sections of tissue samples were imaged by a linear scan of the samples while a focused ultrasonic transducer detected the time-resolved thermoacoustic signals. Based on the microwave-absorption properties of normal and cancerous breast tissues, the piezoelectric signals in response to the thermoacoustic contrast were investigated over a wide range of electromagnetic frequencies and depths of tumor locations. The axial resolution is related to the temporal profile of the microwave pulses and to the impulse response of the ultrasonic transducer. The lateral resolution is related to the numerical aperture of the ultrasonic transducer as well as to the frequency spectra of the piezoelectric signals in the time window corresponding to the axial resolution. Gain compensation, counteracting the microwave attenuation, was applied to enhance the image contrast.     

Post-traumatic Osteoarthritis in Rabbits Following Traumatic Injury and Surgical Reconstruction of the Knee

Post-traumatic osteoarthritis (PTOA) of the knee is often attributed to anterior cruciate ligament (ACL) and meniscus injury. The development of PTOA, however, does not seem to depend on whether or not the damaged ACL is reconstructed. There has been a need to develop animal models to study the mechanisms of PTOA following reconstruction of a traumatized knee. Eighteen rabbits underwent closed-joint trauma to produce ACL rupture and meniscus damage. Then, for the first time, the traumatized knee was surgically repaired in this animal model. Upon euthanasia at 1-, 3- or 6-month post-trauma, joint stability, cartilage morphology and mechanical properties, as well as histology of the cartilage and subchondral bone were evaluated. Trauma-induced knee injury involved 72% mid-substance ACL rupture, 28% partial ACL tear and 56% concurrent medial meniscal damage. ACL reconstruction effectively restored joint stability by reducing joint laxity to a level similar to that in the contralateral intact knee. Compared to their contralateral controls, reconstructed limbs showed osteoarthritic changes to the cartilage and subchondral bone as early as 1-month post-trauma. The degeneration progressed over time up to 6-month. Overall, the medial compartments had more tissue damage than their corresponding lateral counterparts. Damage patterns to the ACL, the frequency of observed concurrent meniscal injury, and reductions in cartilage integrity and health were consistent with clinical observations of human patients who undergo ACL injury and reconstruction. Thus, we believe the combined closed-joint injury and surgical repair lapine model of PTOA, being first-ever and clinically relevant, shows promise to evaluate well-targeted therapeutics and other interventions for this chronic disease.

     

Microwave-induced thermoacoustic tomography using multi-sector scanning

A study of microwave-induced thermoacoustic tomography of inhomogeneous tissues using multi-sector scanning is presented. A short-pulsed microwave beam is used to irradiate the tissue samples. The microwave absorption excites time-resolved acoustic waves by thermoelastic expansion. The amplitudes of the acoustic waves are strongly related to locally absorbed microwave-energy density. The acoustic waves may propagate in all spatial directions. A focused ultrasonic transducer is employed to acquire temporal acoustic signals from multiple directions. Each detected signal is converted into a one-dimensional (1D) image along the acoustic axis of the transducer. The cross-sectional images of the tissue samples are calculated by combining all of the 1D images acquired in the same planes.     

A study of polyvinyl alcohol-hydrogel (PVA-H) artificial meniscus in vivo

The importance of knee meniscus function is now recognized, and the treatment of meniscus injury has been changing from resection to repair. However, depending on the type of injury, meniscectomy sometimes cannot be avoided. In such case, it is important to anticipate the future problem of degenerative change or osteoarthrosis in knee joint. In future, auto-graph using regenerative meniscus will be developed by tissue engineering. However, even if it will be possible, considering the healing period, the young athlete with severe meniscus injury may select meniscectomy in order to return to sports life as early as possible avoiding the long immobilization or declining sports skill. In consideration of the prognosis and circumstances in such patients, we need a artificial meniscus for salvage. To assess further the use of polyvinyl alcohol-hydrogel (PVA-H) artificial meniscus, we performed some mechanical tests about PVA-H and animal experiment. In mechanical tests, we found that a high water content PVA-H showed viscoelastic behaviour similar to that of human meniscus. Moreover, the frictional coefficient of PVA-H against natural articular cartilage was also effective. In the animal experiment using rabbits, the lateral meniscus was replaced with an artificial meniscus in one knee side and lateral meniscectomy was performed in another knee side of each rabbit. We have already reported the results up to 1 year after operation, present study investigated the results in postoperative 1.5 years.In the results, the articular cartilage state of knee joint implanted PVA-H meniscus was good even after 1.5 years, while OA change progressed in meniscectomy knee joint. In addition, neither wear nor breakage of PVA-H was observed. These results proved that an artificial meniscus using a high water content PVA-H can compensate for meniscal function and might be clinically applicable.     

The application of electrospinning used in meniscus tissue engineering

Meniscus is a fibrocartilaginous organ to redistribute stress and enhance the stability of knee joint. Meniscus injury is common and still a formidable challenge to orthopedic surgeons. Surgical techniques and allograft transplantation were primary approaches to meniscus repair, but with intrinsic limitations in clinical practice. Tissue engineering is the most promising method to repair meniscus at present. Electrospinning is a method to fabricate fibers in small scale. With different materials and parameters, electrospinning materials could have different mechanical properties, porosity, and orientation, which could mimic architectural features and mechanical properties of native meniscus. Therefore, electrospinning materials could be used in meniscus regeneration and curing. This review gave a brief introduction of meniscus structure, injury, treatment and the application of electrospinning fibers in meniscus tissue engineering and curing. Besides that, we summarized materials commonly used in electrospinning to fabricate meniscus scaffolds, and discussed the form of electrospinning fibers used such as scaffold, substitute and patch. Finally, the function of electrospinning fibers, for example, carrying drugs, providing mechanical properties were described. The potential applications of electrospinning fibers in meniscus therapy were proposed.     

Relationship between ultrastructure and biomechanical properties of the knee meniscus

The purpose of this study was to determine the biomechanical properties of the knee meniscus and to relate them to its ultrastructure. The knee joint menisci are semicircular, fibrocartilaginous structures interposed between the femoral and tibial condyles. For a long time, they were considered to be embryologic vestiges. This study describes the response of the knee joint meniscus to circumferential, radial and axial compressive forces. The results show an anisotropic response of the knee joint meniscus to unconfined compression. The Young’s modulus increased approximately twofold between vertical and circumferential or radial directions with a 10 mm/min-compression rate. This response is probably a direct consequence of the orientation of collagen fibres.     

激光诱发听觉系统神经冲动的研究进展

近年来利用激光诱发神经冲动逐渐成为研究的热点。本文归纳整理了近7年来激光在刺激听神经方面的主要研究进展,包括激光诱发耳蜗内听神经冲动的研究、激光参数和神经组织特性对激光诱发耳蜗听神经冲动的影响,并对激光诱发听神经冲动的安全性、多通道激光刺激、扩大激光刺激参数的范围等方面进行了展望。     

Stem cell-based meniscus tissue engineering

Knee meniscus, a fibrocartilaginous tissue, is characterized by heterogeneity in extracellular matrix (ECM) and biomechanical properties, and critical for orthopedic stability, load transmission, shock absorption, and stress distribution within the knee joint. Most damage to the meniscus cannot be effectively healed by the body due to its partial avascular nature; thus, damage caused by injury or age impairs normal knee function, predisposing patients to osteoarthritis. Meniscus tissue engineering offers a possible solution to this problem by generating replacement tissue that may be implanted into the defect site to mimic the function of natural meniscal tissue. To address this need, a multiporous, multilamellar meniscus was formed using silk protein scaffolds and stem cells. The silk scaffolds were seeded with human bone marrow stem cells and differentiated over time in chondrogenic culture in the presence of transforming growth factor-beta 3 to generate meniscus-like tissue in vitro. High cellularity along with abundant ECM leading to enhanced biomechanics similar to native tissue was found. Higher levels of collagen type I and II, sulfated glycosaminoglycans along with enhanced collagen 1-α1, aggrecan, and SOX9 gene expression further confirmed differentiation and matured cell phenotype. The results of this study are a step forward toward biomechanically competent meniscus engineering, reconstituting both form and function of the native meniscus.