Collagen orientation in periosteum and perichondrium is aligned with preferential directions of tissue growth

Artificial Periosteum with Oriented Surface Nanotopography and High Tissue Adherent Property

Massive periosteal defects often significantly impair bone regeneration and repair, which have become a major clinical challenge. Unfortunately, current engineered periosteal materials can hardly currently focus on achieving high tissue adhesion property, being suitable for cell growth, and inducing cell orientation concurrently to meet the properties of nature periosteum. Additionally, the preparation of oriented surface nanotopography often relies on professional equipment. In this study, inspired by the oriented collagen structure of nature periosteum, we present a composite artificial periosteum with a layer of oriented nanotopography surface containing carbon nanotubes (CNTs), cross-linked with adhesive polydopamine (PDA) hydrogel on both terminals. An oriented surface structure that can simulate the oriented alignment of periosteal collagen fibers can be quickly and conveniently obtained via a simple stretching of the membrane in a water bath. With the help of CNTs, our artificial periosteum exhibits sufficient mechanical strength and desired oriented nanotopological structure surface, which further induces the directional arrangement of human bone marrow mesenchymal stem cells (hBMSCs) on the membrane. These oriented hBMSCs express significantly higher levels of osteogenic genes and proteins, while the resultant composite periosteum can be stably immobilized in vivo in the rat model of massive calvarial defect through the PDA hydrogel, which finally shows promising bone regeneration ability. We anticipate that the developed functional artificial periosteum has great potential in biomedical applications for the treatment of composite defects of the bone and periosteum.

Surgical anatomy for Asian rhinoplasty: Part III

This article, which comprises the third part of a series on surgical anatomy for Asian rhinoplasty, addresses the lower one-third of the nose, including the alar cartilage and tip-supporting structures, known as distal mobile framework. As discussed in earlier parts of this series, diversity in surgical anatomy results in different surgical techniques in Asian rhinoplasty compared to rhinoplasty in Caucasian patients. Nasal tip structures are especially important due to their crucial importance for changing the nasal shape in Asians. This article, along with the previous ones, will provide both basic and advanced knowledge of practical surgical anatomy for Asian rhinoplasty.

The cellular basis of cartilage growth and shape change in larval and metamorphosing Xenopus frogs

As the first and sometimes only skeletal tissue to appear, cartilage plays a fundamental role in the development and evolution of vertebrate body shapes. This is especially true for amphibians whose largely cartilaginous feeding skeleton exhibits unparalleled ontogenetic and phylogenetic diversification as a consequence of metamorphosis. Fully understanding the evolutionary history, evolvability and regenerative potential of cartilage requires in-depth analysis of how chondrocytes drive growth and shape change. This study is a cell-level description of the larval growth and postembryonic shape change of major cartilages of the feeding skeleton of a metamorphosing amphibian. Histology and immunohistochemistry are used to describe and quantify patterns and trends in chondrocyte size, shape, division, death, and arrangement, and in percent matrix from hatchling to froglet for the lower jaw, hyoid and branchial arch cartilages of Xenopus laevis. The results are interpreted and integrated into programs of cell behaviors that account for the larval growth and histology, and metamorphic remodeling of each element. These programs provide a baseline for investigating hormone-mediated remodeling, cartilage regeneration, and intrinsic shape regulating mechanisms. These programs also contain four features not previously described in vertebrates: hypertrophied chondrocytes being rejuvenated by rapid cell cycling to a prechondrogenic size and shape; chondrocytes dividing and rearranging to reshape a cartilage; cartilage that lacks a perichondrium and grows at single-cell dimensions; and an adult cartilage forming de novo in the center of a resorbing larval one. Also, the unexpected superimposition of cell behaviors for shape change onto ones for larval growth and the unprecedented exploitation of very large and small cell sizes provide new directions for investigating the development and evolution of skeletal shape and metamorphic ontogenies.

Periosteal topology creates an osteo-friendly microenvironment for progenitor cells

The periosteum on the skeletal surface creates a unique micro-environment for cortical bone homeostasis, but how this micro-environment is formed remains a mystery. In our study, we observed the cells in the periosteum presented elongated spindle-like morphology within the aligned collagen fibers, which is in accordance with the differentiated osteoblasts lining on the cortical surface. We planted the bone marrow stromal cells(BMSCs), the regular shaped progenitor cells, on collagen-coated aligned fibers, presenting similar cell morphology as observed in the natural periosteum. The aligned collagen topology induced the elongation of BMSCs, whichfacilitated the osteogenic process. Transcriptome analysis suggested the aligned collagen induced the regular shaped cells to present part of the periosteum derived stromal cells(PDSCs) characteristics by showing close correlation of the two cell populations. In addition, the elevated expression of PDSCs markers in the cells grown on the aligned collagen-coated fibers further indicated the function of periosteal topology in manipulating cells' behavior. Enrichment analysis revealed cell-extracellular matrix interaction was the major pathway initiating this process, which created an osteo-friendly micro-environment as well. At last, we found the aligned topology of collagen induced mechano-growth factor expression as the result of Igf1 alternative splicing, guiding the progenitor cells behavior and osteogenic process in the periosteum. This study uncovers the key role of the aligned topology of collagen in the periosteum and explains the mechanism in creating the periosteal micro-environment, which gives the inspiration for artificial periosteum design.

Strategies to Convert Cells into Hyaline Cartilage: Magic Spells for Adult Stem Cells

Damaged hyaline cartilage gradually decreases joint function and growing pain significantly reduces the quality of a patient’s life. The clinically approved procedure of autologous chondrocyte implantation (ACI) for treating knee cartilage lesions has several limits, including the absence of healthy articular cartilage tissues for cell isolation and difficulties related to the chondrocyte expansion in vitro. Today, various ACI modifications are being developed using autologous chondrocytes from alternative sources, such as the auricles, nose and ribs. Adult stem cells from different tissues are also of great interest due to their less traumatic material extraction and their innate abilities of active proliferation and chondrogenic differentiation. According to the different adult stem cell types and their origin, various strategies have been proposed for stem cell expansion and initiation of their chondrogenic differentiation. The current review presents the diversity in developing applied techniques based on autologous adult stem cell differentiation to hyaline cartilage tissue and targeted to articular cartilage damage therapy.

Myocyte Culture with Decellularized Skeletal Muscle Sheet with Observable Interaction with the Extracellular Matrix

In skeletal muscles, muscle fibers are highly organized and bundled within the basement membrane. Several microfabricated substrate models have failed to mimic the macrostructure of native muscle, including various extracellular matrix (ECM) proteins. Therefore, we developed and evaluated a system using decellularized muscle tissue and mouse myoblasts C2C12 to analyze the interaction between native ECM and myocytes. Chicken skeletal muscle was sliced into sheets and decellularized to prepare decellularized skeletal muscle sheets (DSMS). C2C12 was then seeded and differentiated on DSMS. Immunostaining for ECM molecules was performed to examine the relationship between myoblast adhesion status, myotube orientation, and collagen IV orientation. Myotube survival in long-term culture was confirmed by calcein staining. C2C12 myoblasts adhered to scaffolds in DSMS and developed adhesion plaques and filopodia. Furthermore, C2C12 myotubes showed orientation along the ECM orientation within DSMS. Compared to plastic dishes, detachment was less likely to occur on DSMS, and long-term incubation was possible. This culture technique reproduces a cell culture environment reflecting the properties of living skeletal muscle, thereby allowing studies on the interaction between the ECM and myocytes.

The periosteum: a simple tissue with many faces, with special reference to the antler-lineage periostea

Periosteum is a thin membrane covering bone surfaces and consists of two layers: outer fibrous layer and inner cambium layer. Simple appearance of periosteum has belied its own complexity as a composite structure for physical bone protection, mechano-sensor for sensing mechanical loading, reservoir of biochemical molecules for initiating cascade signaling, niche of osteogenic cells for bone formation and repair, and "umbilical cord" for nourishing bone tissue. Periosteum-derived cells (PDCs) have stem cell attributes: self-renewal (no signs of senescence until 80 population doublings) and multipotency (differentiate into fibroblasts, osteoblasts, chondrocytes, adipocytes and skeletal myocytes). In this review, we summarized the currently available knowledge about periosteum and with special references to antler-lineage periostea, and demonstrated that although periosteum is a type of simple tissue in appearance, with multiple faces in functions; antler-lineage periostea add another dimension to the properties of somatic periostea: capable of initiation of ectopic organ formation upon transplantation and full mammalian organ regeneration when interacted with the covering skin. Very recently, we have translated this finding into other mammals, i.e. successfully induced partial regeneration of the amputated rat legs. We believe further refinement along this line would greatly benefit human health.

The spatial form periosteal-bone complex promotes bone regeneration by coordinating macrophage polarization and osteogenic-angiogenic events

Bone defects associated with soft tissue injuries are an important cause of deformity that threatens people’s health and quality of life. Although bone substitutes have been extensively explored, effective biomaterials that can coordinate early inflammation regulation and subsequent repair events are still lacking. We prepared a spatial form periosteal bone extracellular matrix (ECM) scaffold, which has advantages in terms of low immunogenicity, good retention of bioactive ingredients, and a natural spatial structure. The periosteal bone ECM scaffold with the relatively low-stiffness periosteum (41.6 ± 3.7 kPa) could inhibit iNOS and IL-1β expression, which might be related to actin-mediated YAP translocation. It also helped to promote CD206 expression with the potential influence of proteins related to immune regulation. Moreover, the scaffold combined the excellent properties of decalcified bone and periosteum, promoted the formation of blood vessels, and good osteogenic differentiation (RUNX2, Col 1α1, ALP, OPN, and OCN), and achieved good repair of a cranial defect in rats. This scaffold, with its natural structural and biological advantages, provides a new idea for bone healing treatment that is aligned with bone physiology.

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We provided a spatial form periosteal-bone complex.

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The scaffold preserved major biological components and spatial structure.

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The periosteum part of the scaffold acted as a physical barrier.

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The scaffold participated in the transformation of the macrophage phenotype.

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The scaffold promoted osteogenesis and angiogenesis.

Periosteal Tissue Engineering: Current Developments and Perspectives

Periosteum, a highly vascularized bilayer connective tissue membrane plays an indispensable role in the repair and regeneration of bone defects. It is involved in blood supply and delivery of progenitor cells and bioactive molecules in the defect area. However, sources of natural periosteum are limited, therefore, there is a need to develop tissue-engineered periosteum (TEP) mimicking the composition, structure, and function of natural periosteum. This review explores TEP construction strategies from the following perspectives: i) different materials for constructing TEP scaffolds; ii) mechanical properties and surface topography in TEP; iii) cell-based strategies for TEP construction; and iv) TEP combined with growth factors. In addition, current challenges and future perspectives for development of TEP are discussed.

An enhanced periosteum structure/function dual mimicking membrane forin-siturestorations of periosteum and bone

Periosteum plays a pivotal role in bone formation and reconstruction. The ideal repair process for critical-size bone defects with periosteum damage is to induce regeneration of periosteum tissue and the subsequent bone regeneration derived by the periosteum. Inspired by the bilayer structure of the natural periosteum, we develop a periosteum structure/function dual mimicking membrane for thein-siturestoration of periosteum and bone tissue. Among them, the macroporous fluffy guiding layer (TPF) simulates the fibrous layer of the natural periosteum, which is conducive to infiltration and oriented growth of fibroblasts. And the extracellular matrix-like bioactive layer (TN) simulates the cambium layer of the natural periosteum, which significantly enhances the proliferation and osteogenic differentiation of rat bone marrow mesenchymal stem cells. A middle dense layer (PC) connects the above two layers and has the function of preventing the invasion of soft tissues while enhancing the biomimetic periosteum.In vivorestoration results show that the tri-layer biomimetic periosteum (TPF/PC/TN) has an outstanding effect in promoting the regeneration of both vascularized periosteum and bone at the same time. Therefore, the enhanced biomimetic periosteum developed in this research has a great clinical value in the efficient and high-quality reconstruction of critical-size bone defects with periosteum damage.

Induced Periosteum-Mimicking Membrane with Cell Barrier and Multipotential Stromal Cell (MSC) Homing Functionalities

The current management of critical size bone defects (CSBDs) remains challenging and requires multiple surgeries. To reduce the number of surgeries, wrapping a biodegradable fibrous membrane around the defect to contain the graft and carry biological stimulants for repair is highly desirable. Poly(ε-caprolactone) (PCL) can be utilised to realise nonwoven fibrous barrier-like structures through free surface electrospinning (FSE). Human periosteum and induced membrane (IM) samples informed the development of an FSE membrane to support platelet lysate (PL) absorption, multipotential stromal cells (MSC) growth, and the prevention of cell migration. Although thinner than IM, periosteum presented a more mature vascular system with a significantly larger blood vessel diameter. The electrospun membrane (PCL3%-E) exhibited randomly configured nanoscale fibres that were successfully customised to introduce pores of increased diameter, without compromising tensile properties. Additional to the PL absorption and release capabilities needed for MSC attraction and growth, PCL3%-E also provided a favourable surface for the proliferation and alignment of periosteum- and bone marrow derived-MSCs, whilst possessing a barrier function to cell migration. These results demonstrate the development of a promising biodegradable barrier membrane enabling PL release and MSC colonisation, two key functionalities needed for the in situ formation of a transitional periosteum-like structure, enabling movement towards single-surgery CSBD reconstruction.

Thermally-triggered fabrication of cell sheets for tissue engineering and regenerative medicine

Cell transplantation is a promising approach for promoting tissue regeneration in the treatment of damaged tissues or organs. Although cells have conventionally been delivered by direct injection to damaged tissues, cell injection has limited efficiency to deliver therapeutic cells to the target sites. Progress in tissue engineering has moved scaffold-based cell/tissue delivery into the mainstream of tissue regeneration. A variety of scaffolds can be fabricated from natural or synthetic polymers to provide the appropriate culture conditions for cell growth and achieve in-vitro tissue formation. Tissue engineering has now become the primary approach for cell-based therapies. However, there are still serious limitations, particularly for engineering of cell-dense tissues. "Cell sheet engineering" is a scaffold-free tissue technology that holds even greater promise in the field of tissue engineering and regenerative medicine. Thermoresponsive poly(N-isopropylacrylamide)-grafted surfaces allow the fabrication of a tissue-like cell monolayer, a "cell sheet", and efficiently delivers this cell-dense tissue to damaged sites without the use of scaffolds. At present, this unique approach has been applied to human clinical studies in regenerative medicine. Furthermore, this thermally triggered cell manipulation system allows us to produce various types of 3D tissue models not only for regenerative medicine but also for tissue modeling, which can be used for drug discovery. Here, new cell sheet-based technologies are described including vascularization for scaled-up 3D tissue constructs, induced pluripotent stem (iPS) cell technology for human cell sheet fabrication and microfabrication for arranging tissue microstructures, all of which are expected to produce more complex tissues based on cell sheet tissue engineering.

Topographically Defined, Biodegradable Nanopatterned Patches to Regulate Cell Fate and Acceleration of Bone Regeneration

If only allowed to proceed naturally, the bone-healing process can take several weeks, months, or even years depending on the injury size. In terms of bone-healing speed, many studies have been conducted investigating the deliverance of various growth factors of implantable biomaterials to shorten the time for bone regeneration. However, there may be side effects such as nerve pain, infection, or ectopic bone formation. As an alternative method, we focused on biophysical guidance, which provided similar topographical cues to the cellular environment to recruit host cells for bone defect healing. In this study, we hypothesized that aligned nanotopographical features have enhanced osteoblast recruitment, migration, and differentiation without external stimuli. We designed and fabricated a biodegradable poly(lactic- co-glycolic acid) nanopatterned patch using simple solvent casting and capillary force lithography. We confirmed that a biodegradable nanopatterned patch (BNP) accelerated the migration of osteoblasts according to the orientation of the patterned direction. These highly aligned osteoblasts may contribute to in vitro osteogenic differentiation, such as alkaline phosphate activity, mineralization, and calcium deposition, compared to the biodegradable flat patch (BFP). To demonstrate bone defect healing by BNP guidance in vivo, we implanted either whole or bridge BNP on the critical size defect of mouse calvarial ( ø 4 mm) or tibia bone (3 × 7 mm²). Only the BNP-treated group showed faster new bone formation and compact bone regeneration at the calvarial or tibia bone defect area compared to BFP at 4 or 8 weeks. Bridge BNP guided, in particular, the regeneration of new bone formation along the parallel direction of nanopatterned substrates. Here, we show that a BNP with biophysical guidance should be suitable for use in bone tissue regeneration through accelerated migration of the intact host cell.

Mediating human stem cell behaviour via defined fibrous architectures by melt electrospinning writing

The architecture within which cells reside is key to mediating their specific functions within the body. In this study, we use melt electrospinning writing (MEW) to fabricate cell micro-environments with various fibrous architectures to study their effect on human stem cell behaviour. We designed, built and optimised a MEW apparatus and used it to fabricate four different platform designs of 10.4 ± 2 μm fibre diameter, with angles between fibres on adjacent layers of 90°, 45°, 10° and R (random). Mechanical characterisation was conducted via tensile testing, and human skeletal stem cells (hSSCs) were seeded to scaffolds to study the effect of architecture on cell morphology and mechanosensing (nuclear YAP). Cell morphology was significantly altered between groups, with cells on 90° scaffolds having a lower aspect ratio, greater spreading, greater cytoskeletal tension and nuclear YAP expression. Long term cell culture studies were then conducted to determine the differentiation potential of scaffolds in terms of alkaline phosphatase activity, collagen and mineral production. Across these studies, an increased cell spreading in 3-dimensions is seen with decreasing alignment of architecture correlated with enhanced osteogenesis. This study therefore highlights the critical role of fibrous architecture in regulating stem cell behaviour with implications for tissue engineering and disease progression.

STATEMENT OF SIGNIFICANCE

This is the first study which has investigated the effect of controlled fibrous architectures fabricated via melt electrospinning writing on stem cell behaviour and differentiation. After optimising the fabrication process and characterising scaffolds via SEM and mechanical testing, skeletal stem cells were seeded onto fibrous scaffolds with various micro-architectures. These architectures drove cell shape changes resulting in architecture dependent nuclear YAP localisation, suggesting altered mechanosensing at early time points. In agreement with these early markers, long term cell culture studies revealed for the first time that a 90° fibrous architecture is optimal for the osteogenic differentiation of skeletal stem cells.

Ischaemia, healing and outcomes in proximal humeral fractures

Interfragmental ischaemia is a prerequisite for the initiation of the inflammatory and immunological response to fracturing of bone.Intrafragmental ischaemia is inevitable: the extent of the initial ischaemic insult does not, however, directly relate to the outcome for healing of the fracture zones and avascular necrosis of the humeral head. The survival of distal regions of fragments with critical perfusion may be the result of a type of inosculation (blood vessel contact), which establishes reperfusion before either revascularization or neo-angiogenesis has occurred.Periosteum has a poorly defined role in fracture healing in the proximal humerus. The metaphyseal periosteal perfusion may have a profound effect, as yet undefined, on the healing of most metaphyseal fractures of the proximal humerus, and may be disturbed further by inadvertent surgical manipulation.The metaphysis can be considered as a 'torus' or ring of bone, its surface covered by periosteum antero- and posterolaterally, through which the tuberosity segments gain perfusion and capsular reflections antero- and posteromedially, through which the humeral head (articular) fragment gains perfusion.The torus is broken in relatively simple primary patterns: a fracture line at the upper surface of the torus is an anatomical 'neck' fracture; a fracture line at the lower surface of the torus is the surgical 'neck' fracture. Secondary fragmentation (through compression and/or distraction) of the torus itself creates complexity for analysis (classification), alters the capacity and outcome for healing (by variable interruption of the fragmental blood supply) and influences interfragmental stability. Cite this article: EFORT Open Rev 2018;3 DOI: 10.1302/2058-5241.3.180005.

Periosteum tissue engineering-a review

As always, the clinical therapy of critical size bone defects caused by trauma, tumor removal surgery or congenital malformation is facing great challenges. Currently, various approaches including autograft, allograft and cell-biomaterial composite based tissue-engineering strategies have been implemented to reconstruct injured bone. However, due to damage during the transplantation processes or design negligence of the bionic scaffolds, these methods expose vulnerabilities without the assistance of periosteum, a bilayer membrane on the outer surface of the bone. Periosteum plays a significant role in bone formation and regeneration as a store for progenitor cells, a source of local growth factors and a scaffold to recruit cells and growth factors, and more and more researchers have recognized its great value in tissue engineering application. Besides direct transplantation, periosteum-derived cells can be cultured on various scaffolds for osteogenesis or chondrogenesis application due to their availability. Research studies also provide a biomimetic methodology to synthesize artificial periosteum which mimic native periosteum in structure or function. According to the studies, these tissue-engineered periostea did obviously enhance the therapeutic effects of bone graft and scaffold engineering while they could be directly used as substitutes of native periosteum. Periosteum tissue engineering, whose related research studies have provided new opportunities for the development of bone tissue engineering and therapy, has gradually become a hot spot and there are still lots to consummate. In this review, tissue-engineered periostea were classified into four kinds and discussed, which might help subsequent researchers get a more systematic view of pseudo-periosteum.

Cyclic Tensile Strain Can Play a Role in Directing both Intramembranous and Endochondral Ossification of Mesenchymal Stem Cells

Successfully regenerating damaged or diseased bone and other joint tissues will require a detailed understanding of how joint specific environmental cues regulate the fate of progenitor cells that are recruited or delivered to the site of injury. The goal of this study was to explore the role of cyclic tensile strain (CTS) in regulating the initiation of mesenchymal stem cell/multipotent stromal cell (MSC) differentiation, and specifically their progression along the endochondral pathway. To this end, we first explored the influence of CTS on the differentiation of MSCs in the absence of any specific growth factor, and secondly, we examined the influence of the long-term application of this mechanical stimulus on markers of endochondral ossification in MSCs maintained in chondrogenic culture conditions. A custom bioreactor was developed to apply uniaxial tensile deformation to bone marrow-derived MSCs encapsulated within physiological relevant 3D fibrin hydrogels. Mechanical loading, applied in the absence of soluble differentiation factors, was found to enhance the expression of both tenogenic (COL1A1) and osteogenic markers (BMP2, RUNX2, and ALPL), while suppressing markers of adipogenesis. No evidence of chondrogenesis was observed, suggesting that CTS can play a role in initiating direct intramembranous ossification. During long-term culture in the presence of a chondrogenic growth factor, CTS was shown to induce MSC re-organization and alignment, increase proteoglycan and collagen production, and to enhance the expression of markers associated with endochondral ossification (BMP2, RUNX2, ALPL, OPN, and COL10A1) in a strain magnitude-dependent manner. Taken together, these findings indicate that tensile loading may play a key role in promoting both intramembranous and endochondral ossification of MSCs in a context-dependent manner. In both cases, this loading-induced promotion of osteogenesis was correlated with an increase in the expression of the osteogenic growth factor BMP2. The results of this study demonstrate the potent role that extrinsic mechanical loading plays in guiding stem cell fate, which must be carefully considered when designing cell and tissue-engineering therapies if they are to realize their clinical potential.

Three-dimensional morphometry of collagen fibrils in membranous bone

The collagen network acts as a scaffold for calcification and its three-dimensional structure influences bone strength. It is therefore important to observe the collagen network in detail and three-dimensionally. In this study, we observed the collagen network of chick embryonic calvariae in membranous bone three-dimensionally using orthogonally arranged FIB-SEM. A 25 × 25 μm area of chick embryonic calvaria was observed at a high resolution (25 nm per pixel). The inside of the bone (i.e. the primary calcified tissue), the bone cells (i.e. the osteoblasts and the osteocytes), the organelles, and the collagen fibrils were observed in detail. These structures were observed three-dimensionally using the Amira software program. In addition, the collagen fibrils of the bone were automatically extracted using the XTracing extension software program, and three-dimensional morphometry was performed. Almost all of the collagen fibrils ran along the longitudinal axis of the trabecular bone. We found that the regularity of the collagen fibril orientation was less remarkable in the osteoblast layer, which contained numerous osteoblasts. The collagen fibril orientation started to show regularity toward the central bone layer, which contained few bone cells.

Morphogenetically-Active Barrier Membrane for Guided Bone Regeneration, Based on Amorphous Polyphosphate

We describe a novel regeneratively-active barrier membrane which consists of a durable electrospun poly(ε-caprolactone) (PCL) net covered with a morphogenetically-active biohybrid material composed of collagen and inorganic polyphosphate (polyP). The patch-like fibrous collagen structures are decorated with small amorphous polyP nanoparticles (50 nm) formed by precipitation of this energy-rich and enzyme-degradable (alkaline phosphatase) polymer in the presence of calcium ions. The fabricated PCL-polyP/collagen hybrid mats are characterized by advantageous biomechanical properties, such as enhanced flexibility and stretchability with almost unaltered tensile strength of the PCL net. The polyP/collagen material promotes the attachment and increases the viability/metabolic activity of human mesenchymal stem cells compared to cells grown on non-coated mats. The gene expression studies revealed that cells, growing onto polyP/collagen coated mats show a significantly (two-fold) higher upregulation of the steady-state-expression of the angiopoietin-2 gene used as an early marker for wound healing than cells cultivated onto non-coated mats. Based on our results we propose that amorphous polyP, stabilized onto a collagen matrix, might be a promising component of functionally-active barrier membranes for guided tissue regeneration in medicine and dentistry.

Periosteum mechanobiology and mechanistic insights for regenerative medicine

Periosteum is a smart mechanobiological material that serves as a habitat and delivery vehicle for stem cells as well as biological factors that modulate tissue genesis and healing. Periosteum's remarkable regenerative capacity has been harnessed clinically for over two hundred years. Scientific studies over the past decade have begun to decipher the mechanobiology of periosteum, which has a significant role in its regenerative capacity. This integrative review outlines recent mechanobiological insights that are key to modulating and translating periosteum and its resident stem cells in a regenerative medicine context.

Visualisation of Collagen in fixed skeletal muscle tissue using fluorescently tagged Collagen binding protein CNA35

Detection and visualisation of Collagen structure are important to understand the relationship between mechanical behaviour and microstructure in skeletal muscle since Collagen is the main structural protein in animal connective tissues, and is primarily responsible for their passive load-bearing properties. In the current study, the direct detection and visualization of Collagen using fluorescently tagged CNA35 binding protein (fused to EGFP or tdTomato) is reported for the first time on fixed skeletal muscle tissue. This Technical Note also establishes a working protocol by examining tissue preparation, dilution factor, exposure time etc. for sensitivity and specificity. Penetration of the binding protein into intact mature skeletal muscle was found to be very limited, but detection works well on tissue sections with higher sensitivity on wax embedded sections compared to frozen sections. CNA35 fused to tdTomato has a higher sensitivity than CNA35 fused to EGFP but both show specific detection. Best results were obtained with 15μm wax embedded sections, with blocking of non-specific binding in 1% BSA and antigen retrieval in Sodium Citrate. There was a play-off between dilution of the binding protein and time of incubation but both CNA35-tdTomato and CNA35-EGFP worked well with approximately 100μg/ml of purified protein with overnight incubation, while CNA35-tdTomato could be utilized at 5 fold less concentration. This approach can be applied to study the relationship between skeletal muscle micro-structure and to observe mechanical response to applied deformation. It can be used more broadly to detect Collagen in a variety of fixed tissues, useful for structure-functions studies, constitutive modelling, tissue engineering and assessment of muscle tissue pathologies.

Advanced quantitative imaging and biomechanical analyses of periosteal fibers in accelerated bone growth

PURPOSE

The accepted mechanism explaining the accelerated growth following periosteal resection is that the periosteum serves as a mechanical restraint to restrict physeal growth. To test the veracity of this mechanism we first utilized Second Harmonic Generation (SHG) imaging to measure differences of periosteal fiber alignment at various strains. Additionally, we measured changes in periosteal growth factor transcription. Next we utilized SHG imaging to assess the alignment of the periosteal fibers on the bone both before and after periosteal resection. Based on the currently accepted mechanism, we hypothesized that the periosteal fibers adjacent to the physis should be more aligned (under tension) during growth and become less aligned (more relaxed) following metaphyseal periosteal resection. In addition, we measured the changes in periosteal micro- and macro-scale mechanics.

METHODS

30 seven-week old New Zealand White rabbits were sacrificed. The periosteum was imaged on the bone at five regions using SHG imaging. One centimeter periosteal resections were then performed at the proximal tibial metaphyses. The resected periosteal strips were stretched to different strains in a materials testing system (MTS), fixed, and imaged using SHG microscopy. Collagen fiber alignment at each strain was then determined computationally using CurveAlign. In addition, periosteal strips underwent biomechanical testing in both circumferential and axial directions to determine modulus, failure stress, and failure strain. Relative mRNA expression of growth factors: TGFβ-1, -2, -3, Ihh, PTHrP, Gli, and Patched were measured following loading of the periosteal strips at physiological strains in a bioreactor. The periosteum adjacent to the physis of six tibiae was imaged on the bone, before and after, metaphyseal periosteal resection, and fiber alignment was computed. One-way ANOVA statistics were performed on all data.

RESULTS

Imaging of the periosteum at different regions of the bone demonstrated complex regional differences in fiber orientation. Increasing periosteal strain on the resected strips increased periosteal fiber alignment (p<0.0001). The only exception to this pattern was the 10% strain on the tibial periosteum, which may indicate fiber rupture at this non-physiologic strain. Periosteal fiber alignment adjacent to the resection became less aligned while those adjacent to the physes remained relatively unchanged before and after periosteal resection. Increasing periosteal strain on the resected strips increased periosteal fiber alignment (p<0.0001). The only exception to this pattern was the 10% strain on the tibial periosteum, which may indicate fiber rupture (and consequent retraction) at this non-physiologic strain. Increasing periosteal strain revealed a significant increase in relative mRNA expression for Ihh, PTHrP, Gli, and Patched, respectively.

CONCLUSION

Periosteal fibers adjacent to the growth plate do not appear under tension in the growing limb, and the alignments of these fibers remain unchanged following periosteal resection.

SIGNIFICANCE

The results of this study call into question the long-accepted role of the periosteum acting as a simple mechanical tether restricting growth at the physis.

Collagen production of osteoblasts revealed by ultra-high voltage electron microscopy

In the bone, collagen fibrils form a lamellar structure called the "twisted plywood-like model." Because of this unique structure, bone can withstand various mechanical stresses. However, the formation of this structure has not been elucidated because of the difficulty of observing the collagen fibril production of the osteoblasts via currently available methods. This is because the formation occurs in the very limited space between the osteoblast layer and bone matrix. In this study, we used ultra-high-voltage electron microscopy (UHVEM) to observe collagen fibril production three-dimensionally. UHVEM has 3-MV acceleration voltage and enables us to use thicker sections. We observed collagen fibrils that were beneath the cell membrane of osteoblasts elongated to the outside of the cell. We also observed that osteoblasts produced collagen fibrils with polarity. By using AVIZO software, we observed collagen fibrils produced by osteoblasts along the contour of the osteoblasts toward the bone matrix area. Immediately after being released from the cell, the fibrils run randomly and sparsely. But as they recede from the osteoblast, the fibrils began to run parallel to the definite direction and became thick, and we observed a periodical stripe at that area. Furthermore, we also observed membrane structures wrapped around filamentous structures inside the osteoblasts. The filamentous structures had densities similar to the collagen fibrils and a columnar form and diameter. Our results suggested that collagen fibrils run parallel and thickly, which may be related to the lateral movement of the osteoblasts. UHVEM is a powerful tool for observing collagen fibril production.

Translating Periosteum's Regenerative Power: Insights From Quantitative Analysis of Tissue Genesis With a Periosteum Substitute Implant

: An abundance of surgical studies during the past 2 centuries provide empirical evidence of periosteum's regenerative power for reconstructing tissues as diverse as trachea and bone. This study aimed to develop quantitative, efficacy-based measures, thereby providing translational guidelines for the use of periosteum to harness the body's own healing potential and generate target tissues. The current study quantitatively and qualitatively demonstrated tissue generation modulated by a periosteum substitute membrane that replicates the structural constituents of native periosteum (elastin, collagen, progenitor cells) and its barrier, extracellular, and cellular properties. It shows the potentiation of the periosteum's regenerative capacity through the progenitor cells that inhabit the tissue, biological factors intrinsic to the extracellular matrix of periosteum, and mechanobiological factors related to implant design and implementation. In contrast to the direct intramembranous bone generated in defects surrounded by patent periosteum in situ, tissue generation in bone defects bounded by the periosteum substitute implant occurred primarily via endochondral mechanisms whereby cartilage was first generated and then converted to bone. In addition, in defects treated with the periosteum substitute, tissue generation was highest along the major centroidal axis, which is most resistant to prevailing bending loads. Taken together, these data indicate the possibility of designing modular periosteum substitute implants that can be tuned for vectorial and spatiotemporal delivery of biological agents and facilitation of target tissue genesis for diverse surgical scenarios and regenerative medicine approaches. It also underscores the potential to develop physical therapy protocols to maximize tissue genesis via the implant's mechanoactive properties.

SIGNIFICANCE

In the past 2 centuries, the periosteum, a niche for stem cells and super-smart biological material, has been used empirically in surgery to repair tissues as diverse as trachea and bone. In the past 25 years, the number of articles indexed in PubMed for the keywords "periosteum and tissue engineering" and "periosteum and regenerative medicine" has burgeoned. Yet the biggest limitation to the prescriptive use of periosteum is lack of easy access, giving impetus to the development of periosteum substitutes. Recent studies have opened up the possibility to bank periosteal tissues (e.g., from the femoral neck during routine resection for implantation of hip replacements). This study used an interdisciplinary, quantitative approach to assess tissue genesis in modular periosteum substitute implants, with the aim to provide translational strategies for regenerative medicine and tissue engineering.

Cell Sheet-Based Tissue Engineering for Organizing Anisotropic Tissue Constructs Produced Using Microfabricated Thermoresponsive Substrates

In some native tissues, appropriate microstructures, including orientation of the cell/extracellular matrix, provide specific mechanical and biological functions. For example, skeletal muscle is made of oriented myofibers that is responsible for the mechanical function. Native artery and myocardial tissues are organized three-dimensionally by stacking sheet-like tissues of aligned cells. Therefore, to construct any kind of complex tissue, the microstructures of cells such as myotubes, smooth muscle cells, and cardiomyocytes also need to be organized three-dimensionally just as in the native tissues of the body. Cell sheet-based tissue engineering allows the production of scaffold-free engineered tissues through a layer-by-layer construction technique. Recently, using microfabricated thermoresponsive substrates, aligned cells are being harvested as single continuous cell sheets. The cell sheets act as anisotropic tissue units to build three-dimensional tissue constructs with the appropriate anisotropy. This cell sheet-based technology is straightforward and has the potential to engineer a wide variety of complex tissues. In addition, due to the scaffold-free cell-dense environment, the physical and biological cell-cell interactions of these cell sheet constructs exhibit unique cell behaviors. These advantages will provide important clues to enable the production of well-organized tissues that closely mimic the structure and function of native tissues, required for the future of tissue engineering.

Osteogenic Differentiation Evaluation of an Engineered Extracellular Matrix Based Tissue Sheet for Potential Periosteum Replacement

Due to the indispensable role of periosteum in bone defect healing and regeneration, a promising method to enhance osteogenesis of bone grafts by using an engineered biomimetic periosteum would be highly beneficial. The stromal microenvironment of periosteum is composed of various highly organized extracellular matrix (ECM) fibers, so an aligned natural ECM sheet, derived from the human dermal fibroblast cell sheet, may be advantageous when applied for artificial periosteum fabrication. Human mesenchymal stem cells (hMSCs) have been used to replace the osteoprogenitor cell population in native periosteum due to hMSCs' great osteogenic potential and fast in vitro expansion capacity. The objective of this work is to investigate if the natural ECM sheet and the substrate alignment can promote in vitro osteogenesis of hMSCs. The conventional cell culture substrates collagen I-coated polydimethylsiloxane (PDMS) and tissue culture plastic (TCP) were used as controls. It was found that the ECM sheet significantly increased alkaline phosphatase activity and calcium deposition. The enhanced osteogenic potential was further confirmed by increased bone-specific gene expression. The ECM sheet can bind significantly higher amounts of growth factors including ANG-1, TGF-β1, bFGF, and VEGF, as well as calcium phosphate nanoparticles, which contributed to high osteogenesis of the hMSCs on ECM sheet. However, the alignment of the substrates did not show significant influence on osteogenic activity and growth factor binding. These results demonstrated the great potential of hMSC-seeded ECM sheet as a biomimetic periosteum to improve critical sized bone regeneration.

Absolute polarity determination of teeth cementum by phase sensitive second harmonic generation microscopy

The absolute sign of local polarity in relation to the biological growth direction has been investigated for teeth cementum using phase sensitive second harmonic generation microscopy (PS-SHGM) and a crystal of 2-cyclooctylamino-5-nitropyridine (COANP) as a nonlinear optic (NLO) reference material. A second harmonic generation (SHG) response was found in two directions of cementum: radial (acellular extrinsic fibers that are oriented more or less perpendicular to the root surface) and circumferential (cellular intrinsic fibers that are oriented more or less parallel to the surface). A mono-polar state was demonstrated for acellular extrinsic cementum. However, along the different parts of cementum in circumferential direction, two corresponding domains were observed featuring an opposite sign of polarity indicative for a bi-polar microscopic state of cellular intrinsic cementum. The phase information showed that the orientation of radial collagen fibrils of cementum is regularly organized with the donor (D) groups pointing to the surface. Circumferential collagen molecules feature orientational disorder and are oriented up and down in random manner showing acceptor or donor groups at the surface of cementum. Considering that the cementum continues to grow in thickness throughout life, we can conclude that the cementum is growing circumferentially in two opposite directions and radially in one direction. A Markov chain type model for polarity formation in the direction of growth predicts D-groups preferably appearing at the fiber front.

Two dimensional nanosheets as conductive, flexible elements in biomaterials

Two dimensional nanosheets have great potential as conductive and/or flexible elements in biomaterials.

Recent development of temperature-responsive surfaces and their application for cell sheet engineering

Cell sheet engineering, which fabricates sheet-like tissues without biodegradable scaffolds, has been proposed as a novel approach for tissue engineering. Cells have been cultured and proliferate to confluence on a temperature-responsive cell culture surface at 37°C. By decreasing temperature to 20°C, an intact cell sheet can be harvested from the culture surface without enzymatic treatment. This new approach enables cells to keep their cell–cell junction, cell surface proteins and extracellular matrix. Therefore, recovered cell sheet can be easily not only transplanted to host tissue, but also constructed a three-dimensional (3D) tissue by layering cell sheets. Moreover, cell sheet manipulation technology and bioreactor have been combined with the cell sheet technology to fabricate a complex and functional 3D tissue in vitro. So far, cell sheet technology has been applied in regenerative medicine for several tissues, and a number of clinical studies have been performed. In this review, recent advances in the preparation of temperature-responsive cell culture surface, the fabrication of organ-like tissue and the clinical application of cell sheet engineering are summarized and discussed.

Stretchable and micropatterned membrane for osteogenic differentation of stem cells

Stem cells have emerged as potentially useful cells for regenerative medicine applications. To fully harness this potential, it is important to develop in vitro cell culture platforms with spatially regulated mechanical, chemical, and biological cues to induce the differentiation of stem cells. In this study, a cell culture platform was constructed that used polydopamine (PDA)-coated parafilm. The modified parafilm supports cell attachment and proliferation. In addition, because of the superb plasticity and ductility of the parafilm, it can be easily micropatterned to regulate the spatial arrangements of cells, and can exert different mechanical tensions. Specifically, we constructed a PDA-coated parafilm with grooved micropatterns to induce the osteogenic differentiation of stem cells. Adipose-derived mesenchymal stem cells that were cultured on the PDA-coated parafilm exhibited significantly higher osteogenic commitment in response to mechanical and spatial cues compared to the ones without stretch. Our findings may open new opportunities for inducing osteogenesis of stem cells in vitro using the platform that combines mechanical and spatial cues.

Periosteum-mimetic structures made from freestanding microgrooved nanosheets

A "sticker-like" PLGA nanosheet with microgrooved patterns is developed through a facile combination of spin coating and micropatterning techniques. The resulting microgrooved PLGA nanosheets can be physically adhered on flat or porous surfaces with excellent stability in aqueous environments and can harness the spatial arrangements of cells, which make it a promising candidate for generating biomimic periosteum for bone regenerative applications.

Periosteal thickness and cellularity in mid-diaphyseal cross-sections from human femora and tibiae of aged donors

Due to lack of access in healthy patients, the structural properties underlying the inherent regenerative power and advanced material properties of the human periosteum are not well understood. Periosteum comprises a cellular cambium layer directly apposing the outer surface of bone and an outer fibrous layer encompassed by the surrounding soft tissues. As a first step to elucidating the structural and cellular characteristics of periosteum in human bone, the current study aims to measure cambium and fibrous layer thickness as well as cambium cellularity in human femora and tibiae of aged donors. The major and minor centroidal axes (CA) serve as automated reference points in cross-sections of cadaveric mid-diaphyseal femora and tibiae. Based on the results of this study, within a given individual, the cambium layer of the major CA of the tibia is significantly thicker and more cellular than the respective layer of the femur. These significant intraindividual differences do not translate to significant interindividual differences. Further, mid-diaphyseal periosteal measures including cambium and fibrous layer thickness and cellularity do not correlate significantly with age or body mass. Finally, qualitative observations of periosteum in amputated and contralateral or proximal long bones of the lower extremity show stark changes in layer organization, thickness, and cellularity. In a translational context, these novel data, though inherently limited by availability and accessibility of human mid-diaphyseal periosteum tissue, provide important reference values for the use of periosteum in the context of facilitated healing and regeneration of tissue.

Inter-dependent tissue growth and Turing patterning in a model for long bone development

The development of long bones requires a sophisticated spatial organization of cellular signalling, proliferation, and differentiation programs. How such spatial organization emerges on the growing long bone domain is still unresolved. Based on the reported biochemical interactions we developed a regulatory model for the core signalling factors IHH, PTCH1, and PTHrP and included two cell types, proliferating/resting chondrocytes and (pre-)hypertrophic chondrocytes. We show that the reported IHH-PTCH1 interaction gives rise to a Schnakenberg-type Turing kinetics, and that inclusion of PTHrP is important to achieve robust patterning when coupling patterning and tissue dynamics. The model reproduces relevant spatiotemporal gene expression patterns, as well as a number of relevant mutant phenotypes. In summary, we propose that a ligand-receptor based Turing mechanism may control the emergence of patterns during long bone development, with PTHrP as an important mediator to confer patterning robustness when the sensitive Turing system is coupled to the dynamics of a growing and differentiating tissue. We have previously shown that ligand-receptor based Turing mechanisms can also result from BMP-receptor, SHH-receptor, and GDNF-receptor interactions, and that these reproduce the wildtype and mutant patterns during digit formation in limbs and branching morphogenesis in lung and kidneys. Receptor-ligand interactions may thus constitute a general mechanism to generate Turing patterns in nature.

Electrospun fibers as a scaffolding platform for bone tissue repair

The purpose of the study is to investigate the effects of electrospun fiber diameter and orientation on differentiation and ECM organization of bone marrow stromal cells (BMSCs), in attempt to provide rationale for fabrication of a periosteum mimetic for bone defect repair. Cellular growth, differentiation, and ECM organization were analyzed on PLGA-based random and aligned fibers using fluorescent microscopy, gene analyses, electron scanning microscopy (SEM), and multiphoton laser scanning microscopy (MPLSM). BMSCs on aligned fibers had a reduced number of ALP+ colony at Day 10 as compared to the random fibers of the same size. However, the ALP+ area in the aligned fibers increased to a similar level as the random fibers at Day 21 following stimulation with osteogenic media. Compared with the random fibers, BMSCs on the aligned fibers showed a higher expression of OSX and RUNX2. Analyses of ECM on decellularized spun fibers showed highly organized ECM arranged according to the orientation of the spun fibers, with a broad size distribution of collagen fibers in a range of 40-2.4 μm. Taken together, our data support the use of submicron-sized electrospun fibers for engineering of oriented fibrous tissue mimetic, such as periosteum, for guided bone repair and reconstruction.

Enhanced osteogenesis by a biomimic pseudo-periosteum-involved tissue engineering strategy

Elaborating a bone replacement using tissue-engineering strategies for bone repair seems to be a promising remedy. However, previous platforms are limited in constructing three-dimensional porous scaffolds and neglected the critical importance of periosteum (a pivotal source of osteogenic cells for bone regeneration). We report here an innovative method using the periosteum as a template to replicate its exquisite morphologies onto the surfaces of biomaterials. The precise topographic cues (grooved micropatterns) on the surface of collagen membrane inherited from the periosteum effectively directed cell alignment as the way of natural periosteum. Besides, we placed the stem-cell and endothelial-cell-laden collagen membrane (pseudo-periosteum) onto a three-dimensional porous scaffold. The pseudo-periosteum-covered scaffolds showed remarkable osteogenesis when compared with the pseudo-periosteum-free scaffolds, indicating the significant importance of pseudo-periosteum on bone regeneration. This study gives a novel concept for the construction of bone tissue engineering scaffold and may provide new insight for periosteum research.

The use of anisotropic cell sheets to control orientation during the self-organization of 3D muscle tissue

In some parts of native tissues, the orientation of cells and/or extracellular matrixes is well organized. We know that because anisotropy produces important tissue functions, an appropriate anisotropy needs to be designed to biomimetically construct complex tissue. Here, we show the unique features of anisotropic myoblast sheets for organizing the three-dimensional (3D) orientation of myoblasts and myotubes. Utilizing a micropatterned thermoresponsive surface, human skeletal muscle myoblasts were aligned on the surface, and manipulated as a single anisotropic cell sheet by reducing the culture temperature. Consequently, layering of anisotropic myoblast sheets using gelatin gel allowed 3D myotube constructs to be built up with the desired anisotropy. We also discovered a surprising myoblast behavior. An anisotropic cell sheet placed on top of other cell sheets in fabricating thick tissue was able to change the cell orientation in several layered cell sheets underneath. This self-organization is believed to provide the uniqueness required in designing 3D cell orientation architecture for reconstructed muscle tissue.

Intelligent Surfaces for Cell and Tissue Delivery

Cell transplantation remains a powerful approach for promising numerous biomedical applications to promote tissue regeneration. Therefore, smart delivery systems of therapeutic cells, as well as therapeutic oligonucleotides and proteins, are required. Although cells have been conventionally delivered by direct injection to target sites, a number of clinical studies showed a limitation due to poor cell retention and survival at the sites, resulting in insufficient effect on tissue/organ repair. Therefore, at present, numerous delivery strategies have been developed, and a variety of polymeric materials play important roles. For example, encapsulation in semi-permeable membrane made from biocompatible polymers (e.g. alginate-poly(l-lysine)-alginate) allows xenograft islets to be delivered in vivo without immune suppression. With progress in tissue engineering, scaffold-based cell/tissue delivery reached the mainstream for regenerating damaged tissues. Various kinds of scaffolds have been fabricated from natural and synthetic polymers, such as collagen or poly(l-lactic-co-glycolic acid), and allowed to provide appropriate nutritional conditions and spatial organization for cell growth. Whereas these scaffolds produce reliable architectures to design cell/tissue delivery, scaffold-free cell/tissue delivery also has opened up a new class technology in the field of regenerative medicine. Thermo-responsive poly(N-isopropylacrylamide)-grafted surfaces allow one to fabricate tissue-like cell monolayers, “cell sheets”, and deliver the cell-dense tissue with associated extra-cellular matrix (ECM) to damaged sites without scaffold implantation. The chapter focuses on unique cell/tissue delivery techniques using the intelligent surfaces. This technology has already been applied to human clinical studies for tissue regeneration, and microfabricated thermo-responsive surfaces are further developing for delivering more complex tissue.

Periosteum, bone's "smart" bounding membrane, exhibits direction-dependent permeability

The periosteum serves as bone's bounding membrane, exhibits hallmarks of semipermeable epithelial barrier membranes, and contains mechanically sensitive progenitor cells capable of generating bone. The current paucity of data regarding the periosteum's permeability and bidirectional transport properties provided the impetus for the current study. In ovine femur and tibia samples, the periosteum's hydraulic permeability coefficient, k, was calculated using Darcy's Law and a custom-designed permeability tester to apply controlled, volumetric flow of phosphate-buffered saline through periosteum samples. Based on these data, ovine periosteum demonstrates mechanically responsive and directionally dependent (anisotropic) permeability properties. At baseline flow rates comparable to interstitial fluid flow (0.5 µL/s), permeability is low and does not exhibit anisotropy. In contrast, at high flow rates comparable to those prevailing during traumatic injury, femoral periosteum exhibits an order of magnitude higher permeability compared to baseline flow rates. In addition, at high flow rates permeability exhibits significant directional dependence, with permeability higher in the bone to muscle direction than vice versa. Furthermore, compared to periosteum in which the intrinsic tension (pre-stress) is maintained, free relaxation of the tibial periosteum after resection significantly increases its permeability in both flow directions. Hence, the structure and mechanical stress state of periosteum influences its role as bone's bounding membrane. During periods of homeostasis, periosteum may serve as a barrier membrane on the outer surface of bone, allowing for equal albeit low quiescent molecular communication between tissue compartments including bone and muscle. In contrast, increases in pressure and baseline flow rates within the periosteum resulting from injury, trauma, and/or disease may result in a significant increase in periosteum permeability and consequently in increased molecular communication between tissue compartments. Elucidation of the periosteum's permeability properties is key to understanding periosteal mechanobiology in bone health and healing, as well as to elucidate periosteum structure and function as a smart biomaterial that allows bidirectional and mechanically responsive fluid transport.

Elucidating multiscale periosteal mechanobiology: a key to unlocking the smart properties and regenerative capacity of the periosteum?

The periosteum, a thin, fibrous tissue layer covering most bones, resides in a dynamic, mechanically loaded environment. The periosteum also provides a niche for mesenchymal stem cells. The mechanics of periosteum vary greatly between species and anatomical locations, indicating the specialized role of periosteum as bone's bounding membrane. Furthermore, periosteum exhibits stress-state-dependent mechanical and material properties, hallmarks of a smart material. This review discusses what is known about the multiscale mechanical and material properties of the periosteum as well as their potential effect on the mechanosensitive progenitor cells within the tissue. Furthermore, this review addresses open questions and barriers to understanding periosteum's multiscale structure-function relationships. Knowledge of the smart material properties of the periosteum will maximize the translation of periosteum and substitute periosteum to regenerative medicine, facilitate the development of biomimetic tissue-engineered periosteum for use in instances where the native periosteum is lacking or damaged, and provide inspiration for a new class of smart, advanced materials.

Elucidating multiscale periosteal mechanobiology: a key to unlocking the smart properties and regenerative capacity of the periosteum?

The periosteum, a thin, fibrous tissue layer covering most bones, resides in a dynamic, mechanically loaded environment. The periosteum also provides a niche for mesenchymal stem cells. The mechanics of periosteum vary greatly between species and anatomical locations, indicating the specialized role of periosteum as bone's bounding membrane. Furthermore, periosteum exhibits stress-state-dependent mechanical and material properties, hallmarks of a smart material. This review discusses what is known about the multiscale mechanical and material properties of the periosteum as well as their potential effect on the mechanosensitive progenitor cells within the tissue. Furthermore, this review addresses open questions and barriers to understanding periosteum's multiscale structure-function relationships. Knowledge of the smart material properties of the periosteum will maximize the translation of periosteum and substitute periosteum to regenerative medicine, facilitate the development of biomimetic tissue-engineered periosteum for use in instances where the native periosteum is lacking or damaged, and provide inspiration for a new class of smart, advanced materials.

Concise review: the periosteum: tapping into a reservoir of clinically useful progenitor cells

Elucidation of the periosteum and its regenerative potential has become a hot topic in orthopedics. Yet few review articles address the unique features of periosteum-derived cells, particularly in light of translational therapies and engineering solutions inspired by the periosteum's remarkable regenerative capacity. This review strives to define periosteum-derived cells in light of cumulative research in the field; in addition, it addresses clinical translation of current insights, hurdles to advancement, and open questions in the field. First, we examine the periosteal niche and its inhabitant cells and the key characteristics of these cells in the context of mesenchymal stem cells and their relevance for clinical translation. We compare periosteum-derived cells with those derived from the marrow niche in in vivo studies, addressing commonalities as well as features unique to periosteum cells that make them potentially ideal candidates for clinical application. Thereafter, we review the differentiation and tissue-building properties of periosteum cells in vitro, evaluating their efficacy in comparison with marrow-derived cells. Finally, we address a new concept of banking periosteum and periosteum-derived cells as a novel alternative to currently available autogenic umbilical blood and perinatal tissue sources of stem cells for today's population of aging adults who were "born too early" to bank their own perinatal tissues. Elucidating similarities and differences inherent to multipotent cells from distinct tissue niches and their differentiation and tissue regeneration capacities will facilitate the use of such cells and their translation to regenerative medicine.

Sequential use of human-derived medium supplements favours cardiovascular tissue engineering

For clinical application of tissue engineering strategies, the use of animal-derived serum in culture medium is not recommended, because it can evoke immune responses in patients. We previously observed that human platelet-lysate (PL) is favourable for cell expansion, but generates weaker tissue as compared to culture in foetal bovine serum (FBS). We investigated if human serum (HS) is a better human supplement to increase tissue strength. Cells were isolated from venous grafts of 10 patients and expanded in media supplemented with PL or HS, to determine proliferation rates and expression of genes related to collagen production and maturation. Zymography was used to assess protease expression. Collagen contraction assays were used as a two-dimensional (2D) model for matrix contraction. As a prove of principle, 3D tissue culture and tensile testing was performed for two patients, to determine tissue strength. Cell proliferation was lower in HS-supplemented medium than in PL medium. The HS cells produced less active matrix metallo-proteinase 2 (MMP2) and showed increased matrix contraction as indicated by gel contraction assays and 3D-tissue culture. Tensile testing showed increased strength for tissues cultured in HS when compared to PL. This effect was more pronounced if cells were sequentially cultured in PL, followed by tissue culture in HS. These data suggest that sequential use of PL and HS as substitutes for FBS in culture medium for cardiovascular tissue engineering results in improved cell proliferation and tissue mechanical properties, as compared to use of PL or HS apart.

Anisotropic cell sheets for constructing three-dimensional tissue with well-organized cell orientation

Normal human dermal fibroblasts were aligned on micropatterned thermoresponsive surfaces simply by one-pot cell seeding. After they proliferated with maintaining their orientation, anisotropic cell sheets were harvested by reducing temperature to 20 °C. Surprisingly, the cell sheets showed different shrinking rates between vertical and parallel sides of the cell alignment (aspect ratio: approx. 3: 1), because actin fibers in the cell sheets were oriented with the same direction. The control of cell alignment provided not only a physical anisotropy but also biological impacts to the cell sheet. Vascular endothelial growth factor (VEGF) secreted by aligned fibroblasts was increased significantly, whereas transforming growth factor-β1 (TGF-β1) expression was the same level in anisotropic cell sheets as cell sheets having random cell orientations. Furthermore, although the amount of deposited type Ⅰ collagen was different non-significantly onto between cell sheets with and without controlled cell alignment, collagen deposited onto fibroblasts sheets with cell alignment also showed anisotropy, verified by a fluorescence imaging analysis. The physical and biological anisotropies of cell sheets were potentially useful to construct biomimetic tissues that were organized by aligned cells and/or extracellular matrix (ECM) including collagen in cell sheet-based regenerative medicine. Furthermore, due to the unique thermoresponsive property, the anisotropic cell sheets were successfully manipulated using a gelatin-coated plunger and were layered with maintaining their cell alignment. The combined use of the anisotropic cell sheet and cell sheet manipulation technique promises to create complex tissue that requires the three-dimensional control of their anisotropies, as one of the next-generation cell sheet technologies.