Emulating native periosteum cell population and subsequent paracrine factor production to promote tissue engineered periosteum-mediated allograft healing

Harmonizing Thickness and Permeability in Bone Tissue Engineering: A Novel Silk Fibroin Membrane Inspired by Spider Silk Dynamics

Guided bone regeneration gathers significant interest in the realm of bone tissue engineering; however, the interplay between membrane thickness and permeability continues to pose a challenge that can be addressed by the water-collecting mechanism of spider silk, where water droplets efficiently move from smooth filaments to rough conical nodules. Inspired by the natural design of spider silk, an innovative silk fibroin membrane is developed featuring directional fluid transportation via harmoniously integrating a smooth, dense layer with a rough, loose layer; conical microchannels are engineered in the smooth and compact layer. Consequently, double-layered membranes with cone-shaped microporous passageways (CSMP-DSF membrane) are designed for in situ bone repair. Through extensive in vitro testing, it is noted that the CSMP-DSF membrane guides liquid flow from the compact layer's surface to the loose layer, enabling rapid diffusion. Remarkably, the CSMP-DSF membrane demonstrates superior mechanical properties and resistance to bacterial adhesion. When applied in vivo, the CSMP-DSF membrane achieves results on par with the commercial Bio-Gide collagen membranes. This innovative integration of a cross-thickness wetting gradient structure offers a novel solution, harmonizing the often-conflicting requirements of material transport, mechanical strength, and barrier effectiveness, while also addressing issues related to tissue engineering scaffold perfusion.

Mechanically enhanced and osteobioactive synthetic periosteum via development of poly(ε-caprolactone)/microtantalum composite

Periosteum, the thin layer covering adjacent to bone containing specific architecture, is important for functional bone regeneration and remodeling. Synthetic periosteum investigated presently lacks the resemblance of natural periosteum, suffering from poor mechanical strength and cell attachment. Here, we report a newly-developed biomimetic film to function as synthetic periosteum. Based on poly(ε-caprolactone) (PCL), where surface wettability of the synthetic periosteum is enhanced by microtantalum (mTa) particle blending and after a cold drawing process, further obtains topographical anisotropy without any involvement of solvent. This new blend shows mechanical enhancement over pure PCL, with yield stress and elastic strain approaching the natural periosteum. A distinct degradation mechanism is proposed for the blend, and by seeding with mouse calvarial preosteoblasts, cell proliferation is promoted on surface of the drawn PCL but delayed on the mTa-blended PCL. However, cell mineralization is accelerated on the mTa-blended surface. This is less on the drawn PCL. The synergistical integration of cellular proliferation, alignment and osteogenic enhancement suggest that the cold drawn PCL/Ta blend has unique potential for developing into a synthetic periosteum and other tissue-engineering products.

From Free Tissue Transfer to Hydrogels: A Brief Review of the Application of the Periosteum in Bone Regeneration

The periosteum is a thin layer of connective tissue covering bone. It is an essential component for bone development and fracture healing. There has been considerable research exploring the application of the periosteum in bone regeneration since the 19th century. An increasing number of studies are focusing on periosteal progenitor cells found within the periosteum and the use of hydrogels as scaffold materials for periosteum engineering and guided bone development. Here, we provide an overview of the research investigating the use of the periosteum for bone repair, with consideration given to the anatomy and function of the periosteum, the importance of the cambium layer, the culture of periosteal progenitor cells, periosteum-induced ossification, periosteal perfusion, periosteum engineering, scaffold vascularization, and hydrogel-based synthetic periostea.

Clinical Potential of Mesenchymal Stem Cell-Derived Exosomes in Bone Regeneration

Bone metabolism is regulated by osteoblasts, osteoclasts, osteocytes, and stem cells. Pathologies such as osteoporosis, osteoarthritis, osteonecrosis, and traumatic fractures require effective treatments that favor bone formation and regeneration. Among these, cell therapy based on mesenchymal stem cells (MSC) has been proposed. MSC are osteoprogenitors, but their regenerative activity depends in part on their paracrine properties. These are mainly mediated by extracellular vesicle (EV) secretion. EV modulates regenerative processes such as inflammation, angiogenesis, cell proliferation, migration, and differentiation. Thus, MSC-EV are currently an important tool for the development of cell-free therapies in regenerative medicine. This review describes the current knowledge of the effects of MSC-EV in the different phases of bone regeneration. MSC-EV has been used by intravenous injection, directly or in combination with different types of biomaterials, in preclinical models of bone diseases. They have shown great clinical potential in regenerative medicine applied to bone. These findings should be confirmed through standardization of protocols, a better understanding of the mechanisms of action, and appropriate clinical trials. All that will allow the translation of such cell-free therapy to human clinic applications.

Prediction Criteria for the Formation of Refracture after Union of a Long Bone Fracture on the Basis of Hemodynamic Changes in the Tissues of the Area of Damage

We studied hemodynamic changes in the area of leg bone fracture and determined the prognostic criteria for refracture formation after achieved union. In Wistar rats (n=18), shin bone fracture with external fixation of the fragments was modeled. The union was formed 35 days after osteosynthesis, the device was removed at this term. In 5 cases, a refracture was formed after the termination of fixation. Hemodynamics and local temperature in the tissues in the area of injury were recorded before the start of the experiment and on days 21 and 35 of fixation. In rats with refracture after union, the blood circulation in the area of damage was characterized by a pronounced hypertonicity of the arteries of both large and small diameters, obstruction of venous outflow, and local hyperthermia. This hemodynamics in tissues in the area of damage can serve as an informative criterion for predicting the course of reparative osteogenesis.

Biomimicking design of artificial periosteum for promoting bone healing

Background

Periosteum is a vascularized tissue membrane covering the bone surface and plays a decisive role in bone reconstruction process after fracture. Various artificial periosteum has been developed to assist the allografts or bionic bone scaffolds in accelerating bone healing. Recently, the biomimicking design of artificial periosteum has attracted increasing attention due to the recapitulation of the natural extracellular microenvironment of the periosteum and has presented unique capacity to modulate the cell fates and ultimately enhance the bone formation and improve neovascularization.

Methods

A systematic literature search is performed and relevant findings in biomimicking design of artificial periosteum have been reviewed and cited.

Results

We give a systematical overview of current development of biomimicking design of artificial periosteum. We first summarize the universal strategies for designing biomimicking artificial periosteum including biochemical biomimicry and biophysical biomimicry aspects. We then discuss three types of novel versatile biomimicking artificial periosteum including physical-chemical combined artificial periosteum, heterogeneous structured biomimicking periosteum, and healing phase-targeting biomimicking periosteum. Finally, we comment on the potential implications and prospects in the future design of biomimicking artificial periosteum.

Conclusion

This review summarizes the preparation strategies of biomimicking artificial periosteum in recent years with a discussion of material selection, animal model adoption, biophysical and biochemical cues to regulate the cell fates as well as three types of latest developed versatile biomimicking artificial periosteum. In future, integration of innervation, osteochondral regeneration, and osteoimmunomodulation, should be taken into consideration when fabricating multifunctional artificial periosteum.

The Translational Potential of this Article: This study provides a holistic view on the design strategy and the therapeutic potential of biomimicking artificial periosteum to promote bone healing. It is hoped to open a new avenue of artificial periosteum design with biomimicking considerations and reposition of the current strategy for accelerated bone healing.

Progress of Periosteal Osteogenesis: The Prospect of In Vivo Bioreactor

Repairing large segment bone defects is still a clinical challenge. Bone tissue prefabrication shows great translational potentials and has been gradually accepted clinically. Existing bone reconstruction strategies, including autologous periosteal graft, allogeneic periosteal transplantation, xenogeneic periosteal transplantation, and periosteal cell tissue engineering, are all clinically valuable treatments and have made significant progress in research. Herein, we reviewed the research progress of these techniques and briefly explained the relationship among in vivo microenvironment, mechanical force, and periosteum osteogenesis. Moreover, we also highlighted the importance of the critical role of periosteum in osteogenesis and explained current challenges and future perspective.

Semiparametric mixed-effects model for analysis of non-invasive longitudinal hemodynamic responses during bone graft healing

When dealing with longitudinal data, linear mixed-effects models (LMMs) are often used by researchers. However, LMMs are not always the most adequate models, especially if we expect a nonlinear relationship between the outcome and a continuous covariate. To allow for more flexibility, we propose the use of a semiparametric mixed-effects model to evaluate the overall treatment effect on the hemodynamic responses during bone graft healing and build a prediction model for the healing process. The model relies on a closed-form expectation–maximization algorithm, where the unknown nonlinear function is estimated using a Lasso-type procedure. Using this model, we were able to estimate the effect of time for individual mice in each group in a nonparametric fashion and the effect of the treatment while accounting for correlation between observations due to the repeated measurements. The treatment effect was found to be statistically significant, with the autograft group having higher total hemoglobin concentration than the allograft group.

Encapsulation of Primary Salivary Gland Acinar Cell Clusters and Intercalated Ducts (AIDUCs) within Matrix Metalloproteinase (MMP)-Degradable Hydrogels to Maintain Tissue Structure and Function

Progress in the development of salivary gland regenerative strategies is limited by poor maintenance of the secretory function of salivary gland cells (SGCs) in vitro. To reduce the precipitous loss of secretory function, a modified approach to isolate intact acinar cell clusters and intercalated ducts (AIDUCs), rather than commonly used single cell suspension, is investigated. This isolation approach yields AIDUCs that maintain many of the cell-cell and cell-matrix interactions of intact glands. Encapsulation of AIDUCs in matrix metalloproteinase (MMP)-degradable PEG hydrogels promotes self-assembly into salivary gland mimetics (SGm) with acinar-like structure. Expression of Mist1, a transcription factor associated with secretory function, is detectable throughout the in vitro culture period up to 14 days. Immunohistochemistry also confirms expression of acinar cell markers (NKCC1, PIP and AQP5), duct cell markers (K7 and K5), and myoepithelial cell markers (SMA). Robust carbachol and ATP-stimulated calcium flux is observed within the SGm for up to 14 days after encapsulation, indicating that secretory function is maintained. Though some acinar-to-ductal metaplasia is observed within SGm, it is reduced compared to previous reports. In conclusion, cell-cell interactions maintained within AIDUCs together with the hydrogel microenvironment may be a promising platform for salivary gland regenerative strategies.

Tissue Engineered Neurovascularization Strategies for Craniofacial Tissue Regeneration

Craniofacial tissue injuries, diseases, and defects, including those within bone, dental, and periodontal tissues and salivary glands, impact an estimated 1 billion patients globally. Craniofacial tissue dysfunction significantly reduces quality of life, and successful repair of damaged tissues remains a significant challenge. Blood vessels and nerves are colocalized within craniofacial tissues and act synergistically during tissue regeneration. Therefore, the success of craniofacial regenerative approaches is predicated on successful recruitment, regeneration, or integration of both vascularization and innervation. Tissue engineering strategies have been widely used to encourage vascularization and, more recently, to improve innervation through host tissue recruitment or prevascularization/innervation of engineered tissues. However, current scaffold designs and cell or growth factor delivery approaches often fail to synergistically coordinate both vascularization and innervation to orchestrate successful tissue regeneration. Additionally, tissue engineering approaches are typically investigated separately for vascularization and innervation. Since both tissues act in concert to improve craniofacial tissue regeneration outcomes, a revised approach for development of engineered materials is required. This review aims to provide an overview of neurovascularization in craniofacial tissues and strategies to target either process thus far. Finally, key design principles are described for engineering approaches that will support both vascularization and innervation for successful craniofacial tissue regeneration.

Biomimetic three-layered membranes comprising (poly)-ε-caprolactone, collagen and mineralized collagen for guided bone regeneration

The distinct structural properties and osteogenic capacity are important aspects to be taken into account when developing guided bone regeneration membranes. Herein, inspired by the structure and function of natural periosteum, we designed and fabricated using electrospinning a fibrous membrane comprising (poly)--ε-caprolactone (PCL), collagen-I (Col) and mineralized Col (MC). The three-layer membranes, having PCL as the outer layer, PCL/Col as the middle layer and PCL/Col/MC in different ratios (5/2.5/2.5 (PCM-1); 3.3/3.3/3.3 (PCM-2); 4/4/4 (PCM-3) (%, w/w/w)) as the inner layer, were produced. The physiochemical properties of the different layers were investigated and a good integration between the layers was observed. The three-layered membranes showed tensile properties in the range of those of natural periosteum. Moreover, the membranes exhibited excellent water absorption capability without changes of the thickness. In vitro experiments showed that the inner layer of the membranes supported attachment, proliferation, ingrowth and osteogenic differentiation of human bone marrow-derived stromal cells. In particular cells cultured on PCM-2 exhibited a significantly higher expression of osteogenesis-related proteins. The three-layered membranes successfully supported new bone formation inside a critical-size cranial defect in rats, with PCM-3 being the most efficient. The membranes developed here are promising candidates for guided bone regeneration applications.

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.

A low-temperature-printed hierarchical porous sponge-like scaffold that promotes cell-material interaction and modulates paracrine activity of MSCs for vascularized bone regeneration

Mesenchymal stem cells (MSCs) secrete paracrine trophic factors that are beneficial for tissue regeneration. In this study, a sponge-like scaffold with hierarchical and interconnected pores was developed using low-temperature deposition modeling (LDM) printing. Its effects on the cellular behavior, especially on the paracrine secretion patterns of MSCs, were comprehensively investigated. We found that compared with the scaffolds printed via the fused deposition modeling (FDM) technique, the LDM-printed sponges enhanced the adhesion, retention, survival, and ingrowth of MSCs and promoted cell-material interactions. Moreover, the paracrine functions of the cultured MSCs on the LDM-printed sponges were improved, with significant secretion of upregulated immunomodulatory, angiogenic, and osteogenic factors. MSCs on the LDM-printed sponges exert beneficial paracrine effects on multiple regenerative processes, including macrophage polarization, tube formation, and osteogenesis, verifying the enhanced immunomodulatory, angiogenic, and osteogenic potential. Further protein function assays indicated that focal adhesion kinase (FAK), downstream AKT, and yes-associated-protein (YAP) signaling might participate in the required mechanotransductive pathways, through which the hierarchical porous structures stimulated the paracrine effects of MSCs. In a rat distal femoral defect model, the MSC-laden LDM-printed sponges significantly promoted vascularized bone regeneration. The results of the present study demonstrate that the hierarchical porous biomimetic sponges prepared via LDM printing have potential applications in tissue engineering based on their cell-material interaction promotion and MSC paracrine function modulation effects. Furthermore, our findings suggest that the optimization of biomaterial properties to direct the paracrine signaling of MSCs would enhance tissue regeneration.

Matrix metalloproteinase (MMP)-degradable tissue engineered periosteum coordinates allograft healing via early stage recruitment and support of host neurovasculature

Despite serving as the clinical "gold standard" treatment for critical size bone defects, decellularized allografts suffer from long-term failure rates of ~60% due to the absence of the periosteum. Stem and osteoprogenitor cells within the periosteum orchestrate autograft healing through host cell recruitment, which initiates the regenerative process. To emulate periosteum-mediated healing, tissue engineering approaches have been utilized with mixed outcomes. While vascularization has been widely established as critical for bone regeneration, innervation was recently identified to be spatiotemporally regulated together with vascularization and similarly indispensable to bone healing. Notwithstanding, there are no known approaches that have focused on periosteal matrix cues to coordinate host vessel and/or axon recruitment. Here, we investigated the influence of hydrogel degradation mechanism, i.e. hydrolytic or enzymatic (cell-dictated), on tissue engineered periosteum (TEP)-modified allograft healing, especially host vessel/nerve recruitment and integration. Matrix metalloproteinase (MMP)-degradable hydrogels supported endothelial cell migration from encapsulated spheroids whereas no migration was observed in hydrolytically degradable hydrogels in vitro, which correlated with increased neurovascularization in vivo. Specifically, ~2.45 and 1.84-fold, and ~3.48 and 2.58-fold greater vessel and nerve densities with high levels of vessel and nerve co-localization was observed using MMP degradable TEP (MMP-TEP) -modified allografts versus unmodified and hydrolytically degradable TEP (Hydro-TEP)-modified allografts, respectively, at 3 weeks post-surgery. MMP-TEP-modified allografts exhibited greater longitudinal graft-localized vascularization and endochondral ossification, along with 4-fold and 2-fold greater maximum torques versus unmodified and Hydro-TEP-modified allografts after 9 weeks, respectively, which was comparable to that of autografts. In summary, our results demonstrated that the MMP-TEP coordinated allograft healing via early stage recruitment and support of host neurovasculature.

Spatial frequency domain imaging for the longitudinal monitoring of vascularization during mouse femoral graft healing

Allograft is the current gold standard for treating critical-sized bone defects. However, allograft healing is usually compromised partially due to poor host-mediated vascularization. In the efforts towards developing new methods to enhance allograft healing, a non-terminal technique for monitoring the vascularization is needed in pre-clinical mouse models. In this study, we developed a non-invasive instrument based on spatial frequency domain imaging (SFDI) for longitudinal monitoring of the mouse femoral graft healing. SFDI technique provided total hemoglobin concentration (THC) and oxygen saturation (StO2) of the graft and the surrounding soft tissues. SFDI measurements were performed from 1 day before to 44 days after graft transplantation. Autograft, another type of bone graft with higher vascularization potential was also measured as a comparison to allograft. For both grafts, the overall temporal changes of the measured THC agreed with the physiological expectations of vascularization timeline during bone healing. A significantly greater increase in THC was observed in the autograft group compared to the allograft group, which agreed with the expectation that allografts have more compromised vascularization.

Characterization of Tissue-Engineered Human Periosteum and Allograft Bone Constructs: The Potential of Periosteum in Bone Regenerative Medicine

Delayed-union or non-union between a host bone and a graft is problematic in clinical treatment of segmental bone defects in orthopedic cases. Based on a preliminary study of human periosteum allografts from this laboratory, the present work has extensively investigated the use of human cadaveric tissue-engineered periosteum-allograft constructs as an approach to healing such serious orthopedic surgical situations. In this current report, human cadaveric periosteum-wrapped bone allografts and counterpart controls without periosteum were implanted subcutaneously in athymic mice (nu/nu) for 10, 20, and, for the first time, 40 weeks. Specimens were then harvested and assessed by histological and gene expression analyses. Compared to controls, the presence of new bone formation and resorption in periosteum-allograft constructs was indicated in both histology and gene expression results over 40 weeks of implantation. Of several genes also examined for the first time, RANKL and SOST expression levels increased in a statistically significant manner, data suggesting that bone formation and the presence of increasing numbers of osteocytes in bone matrices had increased with time. The tissue-engineering strategy described in this study provides a possible means of improving delayed-union or non-union at the healing sites of segmental bone defects or bone fractures. The potential of periosteum and its resident cells could thereby be utilized effectively in tissue-engineering methods and tissue regenerative medicine.

A comprehensive review of mouse diaphyseal femur fracture models

Complications related to treatment of long bone fractures still stand as a major challenge for orthopaedic surgeons. Elucidation of the mechanisms of bone healing and development, and the subsequent alteration of these mechanisms to improve outcomes, typically requires animal models as an intermediary between in vitro and human clinical studies. Murine models are some of the most commonly used in translational research, and mouse fracture models are particularly diverse, offering a wide variety of customization with distinct benefits and limitations depending on the study. This review critically examines three common femur fracture models in the mouse, namely cortical hole, 3-point fracture (Einhorn), and segmental bone defect. We lay out the general procedure for execution of each model, evaluate the practical implications and important advantages/disadvantages of each and describe recent innovations. Furthermore, we explore the applications that each model is best adapted for in the context of the current state of murine orthopaedic research.

Nanocomposites drug delivery systems for the healing of bone fractures

The skeletal system is fundamental for the structure and support of the body consisting of bones, cartilage, and connective tissues. Poor fracture healing is a chief clinical problem leading to disability, extended hospital stays and huge financial liability. Even though most fractures are cured using standard clinical methods, about 10% of fractures are delayed or non-union. Despite decades of progress, the bone-targeted delivery system is still restricted due to the distinctive anatomical bone features. Recently, various novel nanocomposite systems have been designed for the cell-specific targeting of bone, enhancing drug solubility, improving drug stability and inhibiting drug degradation so that it can reach its target site without being removed in the systemic circulation. Such targeting systems could consist of biological compounds i.e. bone marrow stem cells (BMSc), growth factors, RNAi, parathyroid hormone or synthetic compounds, i.e. bisphosphonates (BPs) and calcium phosphate cement. Hydrogels and nanoparticles are also being employed for fracture healing. In this review, we discussed the normal mechanism of bone healing and all the possible drug delivery systems being employed for the healing of the bone fracture.

Advances in the Masquelet technique: Myeloid-derived suppressor cells promote angiogenesis in PMMA-induced membranes

The periosteum plays a critical role in bone formation and defect reconstruction. The concept of tissue engineering in the periosteum has been suggested to solve the clinical problems related to bone defect repair. Insertion of polymethyl methacrylate (PMMA) bone cement can induce the autologous generation of a tissue-engineered periosteum and has been considered as a promising strategy for bone defect reconstruction. The PMMA-induced membrane is a crucial element in the reconstruction of bone defects, especially for angiogenesis, but its biological mechanism remains elusive. Here, a PMMA-induced membrane model was established using a femoral critically sized defect in mice. We identified myeloid-derived suppressor cells (MDSCs) as a regulatory component of induced membrane vascularization. The increased number of MDSCs was markedly linked to increased membrane thickness and capillary density. Importantly, the results of an in vitro coculture assay indicated that MDSCs of the induced membrane further facilitated the angiogenic capacity of human umbilical vein endothelial cells (HUVECs) by upregulating the expression of VEGFA, Ang2 and HIF-1α. Furthermore, signaling pathway blockade results suggested that STAT3 activation is involved in the upregulation of VEGFA, Ang2 and HIF-1α expression in induced membrane MDSCs. Our findings provide new insights into the mechanism of angiogenesis in the PMMA-induced membrane and confirm the key signaling molecules of MDSCs in induced membrane angiogenesis. Based on these results, this strategy may become a new therapy for the treatment of large bone defects in the future. STATEMENT OF SIGNIFICANCE: In this study, we established an autologous tissue-engineered periosteum - PMMA-induced membrane, which was formed by the foreign body reaction to PMMA bone cement. The induced membrane establishes a blood supply for the large bone defect healing. After investigation, our study discovered the critical cell type in the formation and angiogenesis processes of the induced membrane, myeloid-derived suppressor cells (MDSCs). We revealed that MDSCs of the induced membrane promote the angiogenesis of endothelial cells through the expression of VEGFA, Ang2 and HIF-1α, which was upregulated by the activation of STAT3 signaling. Our findings clarified the beneficial effect of MDSCs in the angiogenesis of bone repair, and offered an additional target for the study of foreign body reactions to bone repair materials.

In vitro biocompatibility and biomechanics study of novel, Microscopy Aided Designed and ManufacturEd (MADAME) materials emulating natural tissue weaves and their intrinsic gradients

This study conducted biomechanical and biocompatibility tests of textiles and textile composites, created using recursive logic to emulate the properties of natural tissue weaves and their intrinsic mechanical stiffness gradients. Two sets of samples were created, first to test feasibility on textile samples designed as periosteum substitutes with elastane fibers mimicking periosteum's endogenous elastin and nylon fibers substituting for collagen, and then on composites comprising other combinations of suture materials before and after sterilization. In the first part, the bulk tensile mechanical stiffness of elastane-nylon textiles were tuned through respective fiber composition and orientation, i.e., aligned with and orthogonal to loading direction. Cell culture biocompatibility studies revealed no significant differences in proliferation rates of embryonic murine stem cells seeded on textiles compared to collagen membrane controls. Until the 15th day of culture, cells were rarely observed in direct contact with the elastane fibers, similar to previous observations with elastomeric sheets used in periosteum substitute implants. In the second part of the study textile samples were created from FDA-approved medical sutures comprising silk, expanded polytetrafluoroethylene, and polybutester. Biocompatibility and mechanical stiffness were assessed as a function of sterilization/disinfection mode (steam, ethylene oxide, and serial disinfection with ethanol). Cell proliferation rates did not differ significantly from controls, except for silk-suture containing textiles, which showed bacterial contamination and no viable cells after 15 days' culture for all sterilization methods. Sterilization had mixed (mostly not significant) effects on textile stiffness, except for the case of polybutester suture-based textiles that showed a significant increase in stiffness with ethylene oxide sterilization. In general, all textile combinations exhibited significantly higher stiffness than periosteum. Textiles comprising medical sutures of different stiffnesses arranged in engineered patterns offer a novel means to achieve mechanical gradients in medical device materials, emulating those of nature's own.

Rat sinus mucosa- and periosteum-derived exosomes accelerate osteogenesis

Guided bone regeneration (GBR) is commonly used for alveolar bone augmentation. The paracrine mechanism in the field of bone tissue engineering has been emphasized in recent years and exosomes are considered to have the potential of promoting osteogenesis. We aimed to study the influence of sinus mucosa and periosteum on bone regeneration through paracrine stimulation, especially via exosomes, and compare the differences between them. Here, we report that conditioned medium (CM) from sinus mucosa-derived cells (SMCs) and periosteum-derived cells (PCs) and the isolated exosomes enhanced the proliferation, migration and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BM-MSCs) in vitro. A rat model of femoral bone defects was used to demonstrate that the exosomes derived from SMCs (SMC-Exos) and PCs (PC-Exos) can accelerate bone formation in vivo. Furthermore, we present a preliminary discussion of the possible functional components involved in the effects of SMC-Exos and PC-Exos on bone regeneration. In conclusion, these results demonstrated that the sinus mucosa and periosteum can accelerate osteogenesis through paracrine effects and the exosomes play important roles in this process.

Temporal blood flow changes measured by diffuse correlation tomography predict murine femoral graft healing

Blood flow changes during bone graft healing have the potential to provide important information about graft success, as the nutrients, oxygen, circulating cells and growth factors essential for integration are delivered by blood. However, longitudinal monitoring of blood flow changes during graft healing has been a challenge due to limitations in current techniques. To this end, non-invasive diffuse correlation tomography (DCT) was investigated to enable longitudinal monitoring of three-dimensional blood flow changes in deep tissue. Specific to this study, longitudinal blood flow changes were utilized to predict healing outcomes of common interventions for massive bone defects using a common mouse femoral defect model. Weekly blood flow changes were non-invasively measured using a diffuse correlation tomography system for 9 weeks in three types of grafts: autografts (N = 7), allografts (N = 6) and tissue-engineered allografts (N = 6). Healing outcomes were quantified using an established torsion testing method 9 weeks after transplantation. Analysis of the spatial and temporal blood flow reveals that major differences among the three groups were captured in weeks 1-5 after graft transplantation. A multivariate model to predict maximum torque by relative blood flow changes over 5 weeks after graft transplantation was built using partial least squares regression. The results reveal lower bone strength correlates with greater cumulative blood flow over an extended period of time (i.e., 1-5 weeks). The current research demonstrates that DCT-measured blood flow changes after graft transplantation can be utilized to predict long-term healing outcomes in a mouse femoral graft model.

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.

Development of controlled drug delivery systems for bone fracture-targeted therapeutic delivery: A review

Impaired fracture healing is a major clinical problem that can lead to patient disability, prolonged hospitalization, and significant financial burden. Although the majority of fractures heal using standard clinical practices, approximately 10% suffer from delayed unions or non-unions. A wide range of factors contribute to the risk for nonunions including internal factors, such as patient age, gender, and comorbidities, and external factors, such as the location and extent of injury. Current clinical approaches to treat nonunions include bone grafts and low-intensity pulsed ultrasound (LIPUS), which realizes clinical success only to select patients due to limitations including donor morbidities (grafts) and necessity of fracture reduction (LIPUS), respectively. To date, therapeutic approaches for bone regeneration rely heavily on protein-based growth factors such as INFUSE, an FDA-approved scaffold for delivery of bone morphogenetic protein 2 (BMP-2). Small molecule modulators and RNAi therapeutics are under development to circumvent challenges associated with traditional growth factors. While preclinical studies has shown promise, drug delivery has become a major hurdle stalling clinical translation. Therefore, this review overviews current therapies employed to stimulate fracture healing pre-clinically and clinically, including a focus on drug delivery systems for growth factors, parathyroid hormone (PTH), small molecules, and RNAi therapeutics, as well as recent advances and future promise of fracture-targeted drug delivery.

Preparation and Evaluation of Tibia- and Calvarium-Derived Decellularized Periosteum Scaffolds

The periosteum plays a key role in bone regeneration and an artificial bionic material is urgently required. The periostea on the tibia and skull differ with respect to the types of cells, microstructure, and components, leading to different biological functions and biomechanical properties. We aimed to prepare decellularized periosteum scaffolds derived from different origins and evaluate their angiogenic and osteogenic activities. Histological assessment of α-smooth muscle actin, bone morphogenetic protein-2, and alkaline phosphatase in tibial and calvarial periosteum tissues provided preliminary information on their differing angiogenic and osteogenic properties. We developed decellularization protocols to completely remove the periosteum cellular components and for good maintenance of the hierarchical multilayer structures and components of the extracellular matrix (ECM) with no cytotoxicity. Moreover, using a chicken egg chorioallantoic membrane assay and a nude mouse implantation model, we found that tibia-derived periosteum ECM had superior osteogenic activity and calvarium-derived ECM had good angiogenic activity. The preliminary mechanisms of differing activities were then evaluated by osteogenesis- and angiogenesis-related gene expression in human umbilical vein endothelial cell- and MC-3T3 cell-seeded ECM scaffolds. Thus, this study provides periosteum biomaterials that are derived from specific tissues and have different functional properties and structures, for use in bone regeneration.

Inorganic Strengthened Hydrogel Membrane as Regenerative Periosteum

Periosteum plays the pivotal role in neomineralization, vascularization and protection during bone tissue regeneration. However, many artificial periosteum focused only on protection and lacked of the osteogenesis and angiogenesis functional capacity. In this study, we developed a novelty inorganic strengthened gelatin hydrogel membrane via inorganic and organic co-cross-linked double network as artificial periosteum for enhancing the durable angiogenesis and osteogenesis in bone reconstruction. Mesoporous bioactive glass nanoparticles (MBGNs) chemically modified with photo-cross-linkable gelatin derivative (GelMA) were further incorporated into GelMA to fabricate an organic/inorganic co-cross-linked hydrogel membrane (GelMA-G-MBGNs). The GelMA-G-MBGNs hydrogel membrane displayed better mechanical property, durable degradation time, pH stable, biomineralization and long-term ion release. In vitro study demonstrated that, when compared with GelMA or GelMA/MBGNs, the GelMA-G-MBGN membrane significantly promoted osteogenic differentiation while maintaining stable local pH, which is conducive to cell adhesion and proliferation. Finally, the GelMA-G-MBGN membrane shows a superior artificial periosteum with superior capacity in angiogenesis and osteogenesis for accelerating new and mature lamellar bone formation in rat calvarial critical size defect. This co-cross-linked hydrogel membrane implied a promising strategy for the development of advanced periosteum biomaterials with excellent handle and bone repairing properties.

Three dimensional printed calcium phosphate and poly(caprolactone) composites with improved mechanical properties and preserved microstructure

Biphasic calcium phosphate scaffolds formed via three dimensional (3D) printing technology to exhibit porosity and chemical resorbability to promote osseointegration often lack the strength and toughness required to withstand loading in bone tissue engineering applications. Herein, sintering and CaP:poly(caprolactone) (PCL) composite formation were explored to improve 3D printed scaffold strength and toughness. Hydroxyapatite and α-tricalcium phosphate (α-TCP) biphasic calcium powders were printed using phosphoric acid binder, which generated monetite and hydroxyapatite scaffolds. Upon sintering, evolution of β-TCP was observed along with an increase in flexural strength and modulus but no effect on fracture toughness was observed. Furthermore, scaffold porosity increased with sintering. Additionally, two techniques of PCL composite formation were employed: postprint precipitation and 3D print codeposition to further augment scaffold mechanical properties. While both techniques significantly improved flexural strength, flexural modulus, and fracture toughness under most conditions explored, precipitation yielded more substantial increases in these properties, which is attributed to better continuity of the PCL phase. However, precipitation also compromised surface porosity due to PCL passivation of the calcium phosphate surface, which may subsequently hinder scaffold integration and bone regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 663-672, 2018.

Investigation of osteogenic activity of primary rabbit periosteal cells stimulated by multi-axial tensile strain

Periosteum-derived cells was indicated to respond to mechanical force and have stem cell potential capable of differentiating into multiple tissue. Investigation of osteogenic activity under mechanical stimulation is important to understand the therapeutic conditions of fracture healing. In this work, a cell culture platform was developed for respectively providing isotropic and anisotropic axial strain. Primary rabbit periosteal cells were isolated and cultured in the chamber. Multi-axial tensile strain was received and osteogenic activity was investigated by mRNA expressions of CBFA1 and OPN. The highest mRNA expression was found in moderate strain (5-8%) under anisotropic axial strain. These results provided important foundation for further in vivo studies and development of tailor-made stretching rehabilitation equipment.

Construction of versatile multilayered composite nanoparticles from a customized nanogel template

We present a highly adaptable design platform for multi-responsive, multilayered composite nanoparticles (MC-NPs) with fine-tunable functional layers. A flexible disulfide-linked nanogel template is obtained by a controlled in-situ gelation method, enabling a high degree of control over each successive layer. From this template, we optimize “smart” biomaterials with biofunctional surfaces, tunable drug release kinetics, and magnetic or pH-responsive functionality, fabricated into MC-NPs for targeted drug release and periosteum-mimetic structures for controlled rhBMP-2 release towards bone tissue formation in-vivo. Such a versatile platform for the design of MC-NPs is a powerful tool that shows considerable therapeutic potential in clinical fields such as oncology and orthopedics.

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A highly adaptable design platform for multi-responsive, multilayered composite nanoparticles.

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A flexible disulfide-linked nanogel template is obtained by a controlled in-situ gelation method.

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Sequential assembly of multilayered NPs with a nanogel template, porous silica shell, pH-responsive PAA layer, and hydroxyapatite coating.

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The ability to finely tune the structure and function of each layer.

[Research progress of the role of periosteum in distraction osteogenesis]

Objective

To review the research progress of the role of periosteum in distraction osteogenesis.

Methods

The related domestic and foreign literature about the role of periosteum in distraction osteogenesis in recent years was extensively reviewed, summarized, and the mechanism and influencing factors of periosteum during traction and osteogenesis were analyzed.

Results

The periosteum is rich in all kinds of cells (mesenchymal stem cells, osteoblasts, etc.), microvessel and various growth factors, which are necessary for the formation of new bone. It can promote the formation of new bone in the process of traction osteogenesis significantly.

Conclusion

The periosteum plays an important role in the progress of distraction osteogenesis.

Controlled and sustained delivery of siRNA/NPs from hydrogels expedites bone fracture healing

Despite great potential, delivery remains as the most significant barrier to the widespread use of siRNA therapeutics. siRNA has delivery limitations due to susceptibility to RNase degradation, low cellular uptake, and poor tissue-specific localization. Here, we report the development of a hybrid nanoparticle (NP)/hydrogel system that overcomes these challenges. Hydrogels provide localized and sustained delivery via controlled release of entrapped siRNA/NP complexes while NPs protect and enable efficient cytosolic accumulation of siRNA. To demonstrate therapeutic efficacy, regenerative siRNA against WW domain-containing E3 ubiquitin protein ligase 1 (Wwp1) complexed with NP were entrapped within poly(ethylene glycol) (PEG)-based hydrogels and implanted at sites of murine mid-diaphyseal femur fractures. Results showed localization of hydrogels and controlled release of siRNA/NPs at fractures for 28 days, a timeframe over which fracture healing occurs. siRNA/NP sustained delivery from hydrogels resulted in significant Wwp1 silencing at fracture callus compared to untreated controls. Fractures treated with siRNA/NP hydrogels exhibited accelerated bone formation and significantly increased biomechanical strength. This NP/hydrogel siRNA delivery system has outstanding therapeutic promise to augment fracture healing. Owing to the structural similarities of siRNA, the development of the hydrogel platform for in vivo siRNA delivery has myriad therapeutic possibilities in orthopaedics and beyond.

Encapsulation of primary salivary gland cells in enzymatically degradable poly(ethylene glycol) hydrogels promotes acinar cell characteristics

Radiation therapy for head and neck cancers leads to permanent xerostomia due to the loss of secretory acinar cells in the salivary glands. Regenerative treatments utilizing primary submandibular gland (SMG) cells show modest improvements in salivary secretory function, but there is limited evidence of salivary gland regeneration. We have recently shown that poly(ethylene glycol) (PEG) hydrogels can support the survival and proliferation of SMG cells as multicellular spheres in vitro. To further develop this approach for cell-based salivary gland regeneration, we have investigated how different modes of PEG hydrogel degradation affect the proliferation, cell-specific gene expression, and epithelial morphology within encapsulated salivary gland spheres. Comparison of non-degradable, hydrolytically-degradable, matrix metalloproteinase (MMP)-degradable, and mixed mode-degradable hydrogels showed that hydrogel degradation by any mechanism is required for significant proliferation of encapsulated cells. The expression of acinar phenotypic markers Aqp5 and Nkcc1 was increased in hydrogels that are MMP-degradable compared with other hydrogel compositions. However, expression of secretory acinar proteins Mist1 and Pip was not maintained to the same extent as phenotypic markers, suggesting changes in cell function upon encapsulation. Nevertheless, MMP- and mixed mode-degradability promoted organization of polarized cell types forming tight junctions and expression of the basement membrane proteins laminin and collagen IV within encapsulated SMG spheres. This work demonstrates that cellularly remodeled hydrogels can promote proliferation and gland-like organization by encapsulated salivary gland cells as well as maintenance of acinar cell characteristics required for regenerative approaches. Investigation is required to identify approaches to further enhance acinar secretory properties.

STATEMENT OF SIGNIFICANCE

Regenerative strategies to replace damaged salivary glands require the function and organization of acinar cells. Hydrogel-based approaches have shown promise to control cell function and phenotype. However, little is known about how specific parameters, such as the mechanism of hydrogel degradation (e.g., hydrolytic or enzymatic), influence the viability, proliferation, organization, and phenotype of salivary gland cells. In this work, it is shown that hydrogel-encapsulated primary salivary gland cell proliferation is dependent upon hydrogel degradation. Hydrogels crosslinked with enzymatically degradable peptides promoted the expression of critical acinar cell markers, which are typically downregulated in primary cultures. Furthermore, salivary gland cells encapsulated in enzymatically- but not hydrolytically-degradable hydrogels displayed highly organized and polarized salivary gland cell markers, which mimics characteristics found in native gland tissue. In sum, results indicate that salivary gland cells respond to cellularly remodeled hydrogels, resulting in self-assembly and organization akin to acini substructures of the salivary gland.

Notch activation enhances mesenchymal stem cell sheet osteogenic potential by inhibition of cellular senescence

Our previous studies have confirmed the therapeutic effects of mesenchymal stem cell (MSC) monolayer sheet transplantation on allograft repair. A limiting factor in their application is the loss of MSC multi-potency as a result of high density sheet culture-induced senescence. In the study reported in this article, we tested whether Notch activation could be used to prevent or delay sheet culture-induced cell aging. Our results showed that, during in vitro long-term (5-day) cell sheet culture, MSCs progressively lose their progenitor characteristics. In contrast, Notch activation by Jagged1 in MSC sheet culture showed reduced cellular senescence and cell cycle arrest compared with control MSCs without Notch activation. Importantly, knockdown of Notch target gene Hes1 totally blocked the inhibition effect of Jagged1 on cellular senescence. Finally, the in vivo allograft transplantation data showed a significant enhanced callus formation and biomechanical properties in Notch activation cultured long-term sheet groups when compared with long-term cultured sheet without Notch activation. Our results suggest that Notch activation by Jagged1 could be used to overcome the stem cell aging caused by high density sheet culture, thereby increasing the therapeutic potential of MSC sheets for tissue regeneration.

[FGF-2/PELA/BMP-2 microcapsule scaffold promotes osteogenic differentiation of rat periosteum-derived stem cells in vitro]

OBJECTIVE

To observe the effect of a microencapsule scaffold capable of sustained release of fibroblast growth factor-2 (FGF-2) and bone morphogenetic protein-2 (BMP-2) in promoting the osteogenic differentiation of rat periosteum-derived stem cells (PDSCs) in vitro.

METHODS

PDSCs from 4-week-old SD rats, after identification of the surface markers using flow cytometry, were induced to differentiate into osteoblast, chondroblast, and adipocyte lineages. The differentiated cells were verified by staining with Alizarin red, toluidine blue, alcian blue, oil red O and by immunofluorescence assay. FGF-2/PELA/BMP-2, FGF-2/PELA, PELA/BMP-2 and PELA microcapsules were prepared, examined for surface morphologies using scanning electron microscopy (SEM), and tested for controlled release of FGF-2 and BMP-2 using ELISA. The third passage of PDSCs were cultured in the presence of the aqueous extracts of one of the 4 materials, and alkaline phosphatase (AKP) activity in the culture media was detected at 7 and 14 days of culture; the expression levels of osteogenesis-related genes were quantified with quantitative real-time PCR (qRT-PCR). The osteogenic differentiation ability of the PDSCs cultured with the extracts was compared.

RESULTS

The PDSCs, which expressed mesenchymal stem cell surface markers, were shown to have osteogenic, chondrogenic and adipogenic differentiation potentials. The cells cultured with the extract of FGF-2/PELA/BMP-2 microcapsules showed the highest AKP activity at 7 and 14 days of culture, and their expression levels of OCN and RunX-2 mRNA were the highest among the 4 groups; RunX-2 expression reached its peak level on day 14, and OCN mRNA expression level increased progressively as the culture time extended.

CONCLUSION

FGF-2/PELA/BMP-2 biomimetic controlled release microcapsules preserve the cytokine activities and are capable of promoting the osteogenic differentiation of rat PDSCs.

Combined delivery of FGF-2, TGF-β1, and adipose-derived stem cells from an engineered periosteum to a critical-sized mouse femur defect

Critical-sized long bone defects suffer from complications including impaired healing and non-union due to substandard healing and integration of devitalized bone allograft. Removal of the periosteum contributes to the limited healing of bone allografts. Restoring a periosteum on bone allografts may provide improved allograft healing and integration. This article reports a polysaccharide-based tissue engineered periosteum that delivers basic fibroblast growth factor (FGF-2), transforming growth factor-β1 (TGF-β1), and adipose-derived mesenchymal stem cells (ASCs) to a critical-sized mouse femur defect. The tissue engineered periosteum was evaluated for improving bone allograft healing and incorporation by locally delivering FGF-2, TGF-β1, and supporting ASCs transplantation. ASCs were successfully delivered and longitudinally tracked at the defect site for at least 7 days post operation with delivered FGF-2 and TGF-β1 showing a mitogenic effect on the ASCs. At 6 weeks post implantation, data showed a non-significant increase in normalized bone callus volume. However, union ratio analysis showed a significant inhibition in allograft incorporation, confirmed by histological analysis, due to loosening of the nanofiber coating from the allograft surface. Ultimately, this investigation shows our tissue engineered periosteum can deliver FGF-2, TGF-β1, and ASCs to a mouse critical-sized femur defect and further optimization may yield improved bone allograft healing. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 900-911, 2017.

Non-invasive diffuse correlation tomography reveals spatial and temporal blood flow differences in murine bone grafting approaches

Longitudinal blood flow during murine bone graft healing was monitored non-invasively using diffuse correlation tomography. The system utilized spatially dense data from a scanning set-up, non-linear reconstruction, and micro-CT anatomical information. Weekly in vivo measurements were performed. Blood flow changes in autografts, which heal successfully, were localized to graft regions and consistent across mice. Poor healing allografts showed heterogeneous blood flow elevation and high inter-subject variabilities. Allografts with tissue-engineered periosteum showed responses intermediate to both autografts and allografts, consistent with healing observed. These findings suggest that spatiotemporal blood flow changes can be utilized to differentiate the degree of bone graft healing.

"Over-inlay" block graft and differential morphometry: a novel block graft model to study bone regeneration and host-to-graft interfaces in rats

PURPOSE

The aim of this study was to present new a model that allows the study of the bone healing process, with an emphasis on the biological behavior of different graft-to-host interfaces. A standardized "over-inlay" surgical technique combined with a differential histomorphometric analysis is presented in order to optimize the use of critical-size calvarial defects in pre-clinical testing.

METHODS

Critical-size defects were created into the parietal bone of 8 male Wistar rats. Deproteinized bovine bone (DBBM) blocks were inserted into the defects, so that part of the block was included within the calvarial thickness and part exceeded the calvarial height (an "over-inlay" graft). All animals were sacrificed at 1 or 3 months. Histomorphometric and immunohistochemical evaluation was carried out within distinct regions of interest (ROIs): the areas adjacent to the native bone (BA), the periosteal area (PA) and the central area (CA).

RESULTS

The animals healed without complications. Differential morphometry allowed the examination of the tissue composition within distinct regions: the BA presented consistent amounts of new bone formation (NB), which increased over time (24.53%±1.26% at 1 month; 37.73%±0.39% at 3 months), thus suggesting that this area makes a substantial contribution toward NB. The PA was mainly composed of fibrous tissue (71.16%±8.06% and 78.30%±2.67%, respectively), while the CA showed high amounts of DBBM at both time points (78.30%±2.67% and 74.68%±1.07%, respectively), demonstrating a slow remodeling process. Blood vessels revealed a progressive migration from the interface with native bone toward the central area of the graft. Osterix-positive cells observed at 1 month within the PA suggested that the periosteum was a source of osteoprogenitor elements. Alkaline phosphatase data on matrix deposition confirmed this observation.

CONCLUSIONS

The present model allowed for a standardized investigation of distinct graft-to-host interfaces both at vertically augmented and inlay-augmented sites, thus possibly limiting the number of animals required for pre-clinical investigations.

Non-Invasive Monitoring of Temporal and Spatial Blood Flow during Bone Graft Healing Using Diffuse Correlation Spectroscopy

Vascular infiltration and associated alterations in microvascular blood flow are critical for complete bone graft healing. Therefore, real-time, longitudinal measurement of blood flow has the potential to successfully predict graft healing outcomes. Herein, we non-invasively measure longitudinal blood flow changes in bone autografts and allografts using diffuse correlation spectroscopy in a murine femoral segmental defect model. Blood flow was measured at several positions proximal and distal to the graft site before implantation and every week post-implantation for a total of 9 weeks (autograft n = 7 and allograft n = 10). Measurements of the ipsilateral leg with the graft were compared with those of the intact contralateral control leg. Both autografts and allografts exhibited an initial increase in blood flow followed by a gradual return to baseline levels. Blood flow elevation lasted up to 2 weeks in autografts, but this duration varied from 2 to 6 weeks in allografts depending on the spatial location of the measurement. Intact contralateral control leg blood flow remained at baseline levels throughout the 9 weeks in the autograft group; however, in the allograft group, blood flow followed a similar trend to the graft leg. Blood flow difference between the graft and contralateral legs (ΔrBF), a parameter defined to estimate graft-specific changes, was elevated at 1–2 weeks for the autograft group, and at 2–4 weeks for the allograft group at the proximal and the central locations. However, distal to the graft, the allograft group exhibited significantly greater ΔrBF than the autograft group at 3 weeks post-surgery (p < 0.05). These spatial and temporal differences in blood flow supports established trends of delayed healing in allografts versus autografts.

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.

Non-contact scanning diffuse correlation tomography system for three-dimensional blood flow imaging in a murine bone graft model

A non-contact galvanometer-based optical scanning system for diffuse correlation tomography was developed for monitoring bone graft healing in a murine femur model. A linear image reconstruction algorithm for diffuse correlation tomography was tested using finite-element method based simulated data and experimental data from a femur or a tube suspended in a homogeneous liquid phantom. Finally, the non-contact system was utilized to monitor in vivo blood flow changes prior to and one week after bone graft transplantation within murine femurs. Localized blood flow changes were observed in three mice, demonstrating a potential for quantification of longitudinal blood flow associated with bone graft healing.