Synthesis of a tissue-engineered periosteum with acellular dermal matrix and cultured mesenchymal stem cells

Acellular dermal matrices in reconstructive surgery; history, current implications and future perspectives for surgeons

Large-scale defects of body in the reconstructive surgical practice, and the helplessness of their repair with autologous tissues, have been an important factor in the development of artificial biological products for the temporary, definitive, or staged repair of these defects. A major advance in the field of plastic and other reconstructive surgery in this regard has been the introduction and successful use of acellular dermal matrices (ADMs). In recent years, not only the type of tissue from which ADMs are produced, product range, diversity and areas of use have increased, but their use in reconstructive fields, especially in post oncologic breast surgery, has become highly regarded and this has favored ADMs to be a potential cornerstone in specific and well-defined surgical fields in future. It is essential that reconstructive surgeons become familiar with some of the ADM's as well as the advantages and limitations to their use. This review not only provides basic science and clinical evidence of the current use of ADMs in wide range of surgical fields but also targets to keep them as an important backdrop in the armamentarium of reconstructive surgeons. Brief considerations of possible future directions for ADMs are also conducted in the end.

Tailoring photobiomodulation to enhance tissue regeneration

Photobiomodulation (PBM), the use of biocompatible tissue-penetrating light to interact with intracellular chromophores to modulate the fates of cells and tissues, has emerged as a promising non-invasive approach to enhancing tissue regeneration. Unlike photodynamic or photothermal therapies that require the use of photothermal agents or photosensitizers, PBM treatment does not need external agents. With its non-harmful nature, PBM has demonstrated efficacy in enhancing molecular secretions and cellular functions relevant to tissue regeneration. The utilization of low-level light from various sources in PBM targets cytochrome c oxidase, leading to increased synthesis of adenosine triphosphate, induction of growth factor secretion, activation of signaling pathways, and promotion of direct or indirect gene expression. When integrated with stem cell populations, bioactive molecules or nanoparticles, or biomaterial scaffolds, PBM proves effective in significantly improving tissue regeneration. This review consolidates findings from in vitro, in vivo, and human clinical outcomes of both PBM alone and PBM-combined therapies in tissue regeneration applications. It encompasses the background of PBM invention, optimization of PBM parameters (such as wavelength, irradiation, and exposure time), and understanding of the mechanisms for PBM to enhance tissue regeneration. The comprehensive exploration concludes with insights into future directions and perspectives for the tissue regeneration applications of PBM.

Dual Factor-Loaded Artificial Periosteum Accelerates Bone Regeneration

In the clinic, inactivation of osteosarcoma using microwave ablation would damage the periosteum, resulting in frequent postoperative complications. Therefore, the development of an artificial periosteum is crucial for postoperative healing. In this study, we prepared an artificial periosteum using silk fibroin (SF) loaded with stromal cell-derived factor-1α (SDF-1α) and calcitonin gene-related peptide (CGRP) to accelerate bone remodeling after the microwave ablation of osteosarcoma. The prepared artificial periosteum showed a sustained release of SDF-1α and CGRP after 14 days of immersion. In vitro culture of rat periosteal stem cells (rPDSCs) demonstrated that the artificial periosteum is favorable for cell recruitment, the activity of alkaline phosphatase, and bone-related gene expression. Furthermore, the artificial periosteum improved the tube formation and angiogenesis-related gene expression of human umbilical vein endothelial cells (HUVECs). In an animal study, the periosteum in the femur of a rabbit was inactivated through microwave ablation and then removed. The damaged periosteum was replaced with the as-prepared artificial periosteum and favored bone regeneration. In all, the designed dual-factor-loaded artificial periosteum is a promising strategy to replace the damaged periosteum in the therapy of osteosarcoma for a better bone-rebuilding process.

Periosteum Containing Implicit Stem Cells: A Progressive Source of Inspiration for Bone Tissue Regeneration

The periosteum is known as the thin connective tissue covering most bone surfaces. Its extrusive bone regeneration capacity was confirmed from the very first century-old studies. Recently, pluripotent stem cells in the periosteum with unique physiological properties were unveiled. Existing in dynamic contexts and regulated by complex molecular networks, periosteal stem cells emerge as having strong capabilities of proliferation and multipotential differentiation. Through continuous exploration of studies, we are now starting to acquire more insight into the great potential of the periosteum in bone formation and repair in situ or ectopically. It is undeniable that the periosteum is developing further into a more promising strategy to be harnessed in bone tissue regeneration. Here, we summarized the development and structure of the periosteum, cell markers, and the biological features of periosteal stem cells. Then, we reviewed their pivotal role in bone repair and the underlying molecular regulation. The understanding of periosteum-related cellular and molecular content will help enhance future research efforts and application transformation of the periosteum.

Accumulative Rolling Mg/PLLA Composite Membrane with Lamellar Heterostructure for Enhanced Bacteria Inhibition and Rapid Bone Regeneration

Developing composite materials with optimized mechanics, degradation, and bioactivity for bone regeneration has long been a crucial mission. Herein, a multifunctional Mg/Poly-l-lactic acid (Mg/PLLA) composite membrane based on the "materials plain" concept through the accumulative rolling (AR) method is proposed. Results show that at a rolling ratio of 75%, the comprehensive mechanical properties of the membrane in the rolling direction are self-reinforced significantly (elongation at break ≈53.2%, tensile strength ≈104.0 MPa, Young's modulus ≈2.13 GPa). This enhancement is attributed to the directional arrangement and increased crystallization of PLLA molecular chains, as demonstrated by SAXS and DSC results. Furthermore, the AR composite membrane presents a lamellar heterostructure, which not only avoids the accumulation of Mg microparticles (MgMPs) but also regulates the degradation rate. Through the contribution of bioactive MgMPs and their photothermal effect synergistically, the membrane effectively eliminates bacterial infection and accelerates vascularized bone regeneration both in vitro and in vivo. Notably, the membrane exhibits outstanding rat skull bone regeneration performance in only 4 weeks, surpassing most literature reports. In short, this work develops a composite membrane with a "one stone, four birds" effect, opening an efficient avenue toward high-performance orthopedic materials.

4D Printing of Personalized-Tunable Biomimetic Periosteum with Anisotropic Microstructure for Accelerated Vascularization and Bone Healing

An ideal biomimetic periosteum is expected to wrap various bone surfaces to orchestrate an optimal microenvironment for bone regeneration, including facilitating local vascularization, recruiting osteoblasts, and mineralizing the extracellular matrix (ECM). To mimic the role of the natural periosteum in promoting bone repair, a 4D printing technique to inlay aligned cell sheets on shape-shifting hydrogel is used, containing biophysical signals and spatially adjustable physical properties, for the first time. The outer hydrogel layer endows the biomimetic periosteum with the ability to digitally coordinate its 3D geometry to match the specific macroscopic bone shape to maintain a bone healing microenvironment. The inner aligned human mesenchymal stem cells (hMSCs) layer not only promotes the migration and angiogenesis of co-cultured cells but also exhibits excellent osteogenic differentiation properties. In vivo experiments show that apart from morphing preset shapes as physical barriers, the aligned biomimetic periosteum can actively facilitate local angiogenesis and early-stage osteogenesis. Altogether, this present work provides a novel route to construct a personalized biomimetic periosteum with anisotropic microstructure by introducing a tunable shape to maintain the bone reconstruction microenvironment and this strategy can be extended to repair sophisticated bone defects.

Characterization and potential of periosteum-derived cells: an overview

As a thin fibrous layer covering the bone surface, the periosteum plays a significant role in bone physiology during growth, development and remodeling. Over the past several decades, the periosteum has received considerable scientific attention as a source of mesenchymal stem cells (MSCs). Periosteum-derived cells (PDCs) have emerged as a promising strategy for tissue engineering due to their chondrogenic, osteogenic and adipogenic differentiation capacities. Starting from the history of PDCs, the present review provides an overview of their characterization and the procedures used for their isolation. This study also summarizes the chondrogenic, osteogenic, and adipogenic abilities of PDCs, serving as a reference about their potential therapeutic applications in various clinical scenarios, with particular emphasis on the comparison with other common sources of MSCs. As techniques continue to develop, a comprehensive analysis of the characterization and regulation of PDCs can be conducted, further demonstrating their role in tissue engineering. PDCs present promising potentials in terms of their osteogenic, chondrogenic, and adipogenic capacities. Further studies should focus on exploring their utility under multiple clinical scenarios to confirm their comparative benefit over other commonly used sources of MSCs.

Periosteum: Functional Anatomy and Clinical Application

Periosteum is a connective tissue that envelopes the outer surface of bones and is tightly bound to the underlying bone by Sharpey’s fibers. It is composed of two layers, the outer fibrous layer and the inner cambium layer. The periosteum is densely vascularised and contains an osteoprogenitor niche that serves as a repository for bone-forming cells, which makes it an essential bone-regenerating tissue and has immensely contributed to fracture healing. Due to the high vascularity of inner cambium layer of the periosteum, periosteal transplantation has been widely used in the management of bone defects and fracture by orthopedic surgeons. Nevertheless, the use of periosteal graft in the management of bone defect is limited due to its contracted nature after being harvested. This review summarizes the current state of knowledge about the structure of periosteum, and how periosteal transplantation have been used in clinical practices, with special reference on its expansion.

Current strategies in biomaterial-based periosteum scaffolds to promote bone regeneration: A review

The role of periosteum rich in a variety of bone cells and growth factors in the treatment of bone defects has gradually been discovered. However, due to the limited number of healthy transplantable periosteum, there are still major challenges in the clinical treatment of critical-size bone defects. Various techniques for preparing biomimetic periosteal scaffolds that are similar in composition and structure to natural periosteal scaffold have gradually emerged. This article reviews the current preparation methods of biomimetic periosteal scaffolds based on various biomaterials, which are mainly divided into natural periosteal materials and various polymer biomaterials. Several preparation methods of biomimetic periosteal scaffolds with different principles are listed, their strengths and weaknesses are also discussed. It aims to provide a more systematic perspective for the preparation of biomimetic periosteal scaffolds in the future.

Construction of biomimetic cell-sheet-engineered periosteum with a double cell sheet to repair calvarial defects of rats

Background

The periosteum plays a crucial role in the development and injury healing process of bone. The purpose of this study was to construct a biomimetic periosteum with a double cell sheet for bone tissue regeneration.

Methods

In vitro, the human amniotic mesenchymal stem cells (hAMSCs) sheet was first fabricated by adding 50 ​μg/ml ascorbic acid to the cell sheet induction medium. Characterization of the hAMSCs sheet was tested by general observation, microscopic observation, live/dead staining, scanning electron microscopy (SEM) and hematoxylin and eosin (HE) staining. Afterwards, the osteogenic cell sheet and vascular cell sheet were constructed and evaluated by general observation, alkaline phosphatase (ALP) staining, Alizarin Red S staining, SEM, live/dead staining and CD31 immunofluorescent staining for characterization. Then, we prepared the double cell sheet. In vivo, rat calvarial defect model was introduced to verify the regeneration of bone defects treated by different methods. Calvarial defects (diameter: 4 ​mm) were created of Sprague–Dawley rats. The rats were randomly divided into 4 groups: the control group, the osteogenic cell sheet group, the vascular cell sheet group and the double cell sheet group. Macroscopic, micro-CT and histological evaluations of the regenerated bone were performed to assess the treatment results at 8 weeks and 12 weeks after surgery.

Results

In vitro, hAMSCs sheet was successfully prepared. The hAMSCs sheet consisted of a large number of live hAMSCs and abundant extracellular matrix (ECM) that secreted by hAMSCs, as evidenced by macroscopic/microscopic observation, live/dead staining, SEM and HE staining. Besides, the osteogenic cell sheet and the vascular cell sheet were successfully prepared, which were verified by general observation, ALP staining, Alizarin Red S staining, SEM and CD31 immunofluorescent staining. In vivo, the macroscopic observation and micro-CT results both demonstrated that the double cell sheet group had better effect on bone regeneration than other groups. In addition, histological assessments indicated that large amounts of new bone had formed in the calvarial defects and more mature collagen in the double cell sheet group.

Conclusion

The double cell sheet could promote to repair calvarial defects of rats and accelerate bone regeneration.

The translational potential of this article

We successfully constructed a biomimetic cell-sheet-engineered periosteum with a double cell sheet by a simple, low-cost and effective method. This biomimetic periosteum may be a promising therapeutic strategy for the treatment of bone defects, which may be used in clinic in the future.

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.

Periosteum and development of the tissue-engineered periosteum for guided bone regeneration

Background

Periosteum plays a significant role in bone formation and regeneration by storing progenitor cells, and also acts as a source of local growth factors and a scaffold for recruiting cells and other growth factors. Recently, tissue-engineered periosteum has been studied extensively and shown to be important for osteogenesis and chondrogenesis. Using biomimetic methods for artificial periosteum synthesis, membranous tissues with similar function and structure to native periosteum are produced that significantly improve the efficacy of bone grafting and scaffold engineering, and can serve as direct replacements for native periosteum. Many problems involving bone defects can be solved by preparation of idealized periosteum from materials with different properties using various techniques.

Methods

This review summarizes the significance of periosteum for osteogenesis and chondrogenesis from the aspects of periosteum tissue structure, osteogenesis performance, clinical application, and development of periosteum tissue engineering. The advantages and disadvantages of different tissue engineering methods are also summarized.

Results

The fast-developing field of periosteum tissue engineering is aimed toward synthesis of bionic periosteum that can ensure or accelerate the repair of bone defects. Artificial periosteum materials can be similar to natural periosteum in both structure and function, and have good therapeutic potential. Induction of periosteum tissue regeneration and bone regeneration by biomimetic periosteum is the ideal process for bone repair.

Conclusions

Periosteum is essential for bone formation and regeneration, and it is indispensable in bone repair. Achieving personalized structure and composition in the construction of tissue engineering periosteum is in accordance with the design concept of both universality and emphasis on individual differences and ensures the combination of commonness and individuality, which are expected to meet the clinical needs of bone repair more effectively.

The translational potential of this article

To better understand the role of periosteum in bone repair, clarify the present research situation of periosteum and tissue engineering periosteum, and determine the development and optimization direction of tissue engineering periosteum in the future. It is hoped that periosteum tissue engineering will play a greater role in meeting the clinical needs of bone repair in the future, and makes it possible to achieve optimization of bone tissue therapy.

Construction of developmentally inspired periosteum-like tissue for bone regeneration

The periosteum, a highly vascularized thin tissue, has excellent osteogenic and bone regenerative abilities. The generation of periosteum-mimicking tissue has become a novel strategy for bone defect repair and regeneration, especially in critical-sized bone defects caused by trauma and bone tumor resection. Here, we utilized a bone morphogenetic protein-2 (BMP-2)-loaded scaffold to create periosteum-like tissue (PT) in vivo, mimicking the mesenchymal condensation during native long bone development. We found that BMP-2-induced endochondral ossification plays an indispensable role in the construction of PTs. Moreover, we confirmed that BMP-2-induced PTs exhibit a similar architecture to the periosteum and harbor abundant functional periosteum-like tissue-derived cells (PTDCs), blood vessels, and osteochondral progenitor cells. Interestingly, we found that the addition of chondroitin sulfate (CS), an essential component of the extracellular matrix (ECM), could further increase the abundance and enhance the function of recruited PTDCs from the PTs and finally increase the regenerative capacity of the PTs in autologous transplantation assays, even in old mice. This novel biomimetic strategy for generating PT through in vivo endochondral ossification deserves further clinical translation.

Use of confocal microscopy imaging for in vitro assessment of adipose-derived mesenchymal stromal cells seeding on acellular dermal matrices: 3D reconstruction based on collagen autofluorescence

Background

Both mesenchymal stromal cells (MSCs) and acellular dermal matrices (ADMs) represent fascinating therapeutic tools in the wound healing scenario. Strategies aimed at combining these two treatment modalities are currently under investigation. Moreover, scarcity of quantitative, nondestructive techniques for quality assessment of engineered tissues poses great limitations in regenerative medicine and collagen autofluorescence‐based imaging techniques are acquiring great importance in this setting.

Objective

Our goals were to assess the in vitro interactions between ADSCs and ADMs and to analyze extracellular‐matrix production.

Methods

Adipose‐derived MSCs (ADSC) were plated on 8‐mm punch biopsies of a commercially available ADM (Integra®). Conventional histology with hematoxylin‐eosin staining, environmental scanning electron microscopy, and confocal‐laser scanning microscopy were used to obtain imaging of ADSC‐seeded ADMs. Collagen production by ADSCs was quantified by mean fluorescence intensity (MFI), expressed in terms of positive pixels/field, obtained through ImageJ software processing of three‐dimensional projections from confocal scanning images. Control conditions included: fibroblast‐seeded ADM, ADSC‐ and fibroblast‐induced scaffolds, and Integra® alone.

Results

ADSCs were efficiently seeded on Integra® and were perfectly incorporated in the pores of the scaffold. Collagen production was revealed to be significantly higher when ADSCs were seeded on ADM rather than in all other control conditions. Collagen autofluorescence was efficiently used as a surrogate marker of ECM production.

Conclusions

Combined therapies based on MSCs and collagenic ADMs are promising therapeutic options for chronic wounds. Not only ADSCs can be efficiently seeded on ADMs, but ADMs also seem to potentiate their regenerative properties, as highlightable from fluorescence confocal imaging.

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.

Biomimetic, Stiff, and Adhesive Periosteum with Osteogenic-Angiogenic Coupling Effect for Bone Regeneration

Current periosteal grafts have limitations related to low mechanical strength, tissue adhesiveness, and poor osteogenesis and angiogenesis potential. Here, a periosteum mimicking bone aid (PMBA) with similar structure and function to natural periosteum is developed by electrospinning photocrosslinkable methacrylated gelatin (GelMA), l-arginine-based unsaturated poly(ester amide) (Arg-UPEA), and methacrylated hydroxyapatite nanoparticles (nHAMA). Such combination of materials enhances the material mechanical strength, favors the tissue adhesion, and guarantees the sustained activation of nitric oxide-cyclic guanosine monophosphate (NO-cGMP) signaling pathway, with well-coordinated osteogenic-angiogenic coupling effect for accelerated bone regeneration. This work presents a proof-of-concept demonstration of thoroughly considering the progression of implant biomaterials: that is, the initial material components (i.e., GelMA, Arg-UPEA, and nHAMA) equip the scaffold with suitable structure and function, while its degradation products (i.e., Ca²⁺ and l-arginine) are involved in long-term mediation of physiological activities. It is envisioned that the strategy will inspire the design of high-performance bioscaffolds toward bone and periosteum tissue engineering.

Nanoscaled Bionic Periosteum Orchestrating the Osteogenic Microenvironment for Sequential Bone Regeneration

Periosteum orchestrates bone repair. Previously developed artificial periosteum was mainly focusing on materials modification to simply enhance bone formation, but few were attempting to make the artificial periosteum fit different bone repair stages. Here, we constructed a functionalized periosteum, which was composed of an electrospun scaffold grafted with leptin receptor antibody (LepR-a) and BMP2-loaded hollow MnO₂ (h-MnO₂) nanoparticles through a polydopamine (PDA)-assisted technique. The bionic periosteum showed suitable mechanical properties and favorable biocompatibility. It effectively recruited skeletal stem cells (SSCs) through antigen-antibody interactions, as in in vitro cell adhesion tests, we observed that more SSCs attached to the LepR-a-grafted periosteum compared to the control group. In vivo, the LepR-a-grafted periosteum covered on the cranial defect in Prx1-Cre/ERT2, -EGFP mice recruited more Prx1-EGFP cells to the fracture site compared to control groups at post-surgery day 3, 7, and 14. Co-staining with Sp7 indicated that most of the recruited Prx1-EGFP cells underwent osteogenic lineage commitment. Sustained BMP2 release from h-MnO₂ promoted osteogenesis by accelerating the osteogenic differentiation of recruited SSCs, as demonstrated by alkaline phosphatase (ALP) and alizarin red staining (ARS) in vitro and microcomputed tomography (micro-CT) in vivo. Interestingly, we also observed the growth of osteogenic coupled capillaries (CD31^hiEmcn^hi) in the bone repair site, which might be induced by increased platelet-derived growth factor-BB (PDGF-BB) in the regenerative microenvironment subsequent to SSCs' differentiation. Taken together, the findings from this study indicate that the multifunctionalized periosteum efficiently recruited and motivated the SSCs in vivo and orchestrated the osteogenic microenvironment for bone repair in a sequence manner. Thus, the construction of the bionic periosteum to couple with natural bone regeneration stages has been demonstrated to be effective in facilitating bone healing.

A porcine acellular dermal matrix induces human fibroblasts to secrete hyaluronic acid by activating JAK2/STAT3 signalling

Human facial skin undergoes continuous ageing over a lifespan. At present, facial skin rejuvenation is mainly achieved by injecting filling materials. However, conventional materials lack long-term beneficial effects and can only rejuvenate the skin temporarily by physical filling. To overcome this shortcoming, this study developed a porcine acellular dermal matrix with a porous three-dimensional scaffold structure and containing natural growth factors (3D-GF-PADM). The average size of the 3D-GF-PADM particles was 33.415 μm, and the dynamic viscosity and elastic modulus were within ranges suitable for clinical applications. Our study revealed that the 3D-GF-PADM exhibited an extremely low α-gal epitope number (3.15 ± 0.84 × 10¹¹/mg) and DNA content, and no immunotoxicity, but contained abundant TGF-β1, VEGF and other growth factors. More importantly, this 3D-GF-PADM actively induced the synthesis of hyaluronic acid by fibroblasts of the host skin. Study at the molecular level further demonstrated that the 3D-GF-PADM activated the JAK2/STAT3 pathway, resulting in the upregulation of HAS2 expression, which led to an increase in hyaluronic acid synthesis. Our study developed a novel 3D-GF-PADM that can actively induce hyaluronic acid synthesis, which may be used clinically as a skin filling material to achieve long-term skin rejuvenation.

By activating the JAK2/STAT3 pathway, 3D-GF-PADM induces the production of hyaluronic acid in human fibroblasts.

Programmed Sustained Release of Recombinant Human Bone Morphogenetic Protein-2 and Inorganic Ion Composite Hydrogel as Artificial Periosteum

Recombinant human bone morphogenetic protein-2 (rhBMP-2) and bioceramic are the widely used bioactive factors in treatment of bone defects, but these easily cause side effects because of uncontrollable local concentration. In this study, rhBMP-2 was grafted on the surface of mesoporous bioglass nanoparticles (MBGNs) with an amide bond and then photo-cross-linked together with methacrylate gelatin (GelMA); in this way, a GelMA/MBGNs-rhBMP-2 hydrogel membrane was fabricated to release rhBMP-2 in a controllable program during the early bone regeneration period and then release calcium and silicon ions to keep promoting osteogenesis instead of rhBMP-2 in a long term. In this way, rhBMP-2 can keep releasing for 4 weeks and then the ions keep releasing after 4 weeks; this process is matched to early and late osteogenesis procedures. In vitro study demonstrated that the early release of rhBMP-2 can effectively promote local cell osteogenic differentiation in a short period, and then, the inorganic ions can promote cell adhesion not only in the early stage but also keep promoting osteogenic differentiation for a long period. Finally, the GelMA/MBGNs-rhBMP-2 hydrogel shows a superior capacity in long-term osteogenesis and promoting bone tissue regeneration in rat calvarial critical size defect. This GelMA/MBGNs-rhBMP-2 hydrogel demonstrated a promising strategy for the controllable and safer use of bioactive factors such as rhBMP-2 in artificial periosteum to accelerate bone repairing.

Enhance Mandibular Symphyseal Surface Bone Growth with Autologous Mesenchymal Stem Cell Sheets: An Animal Study

INTRODUCTION

The size and shape of the chin strongly influence facial profile and harmony. The current correction of chin deficiency mostly relies on genioplasty surgery involving osteotomy. To avoid osteotomy, one possible alternative is to enhance bone growth at the mental protuberance area with cell sheet transplantation. This study was undertaken to evaluate the efficacy of this approach in a pig model.

MATERIALS AND METHODS

Five 4-month-old pigs were included for mandibular bone marrow aspiration and MSC isolation. Triple-layer MSC sheets were then fabricated and utilized using culture-expanded MSCs. Four weeks after bone marrow aspiration, subperiosteal pockets were created on the labial symphyseal surface, followed by transplantation of autogenous MSC sheets to one randomly chosen side with the other side (control) receiving no transplantation. Six weeks after the surgery, the pigs were euthanized and the specimens from both sides were collected for computed tomography (CT) and histological and immunohistochemical analysis. Measurements between the experimental and control sides were compared using paired t tests.

RESULTS

MSC sheet fabrication and transplantation were reliably conducted. The labial cortical bone thickness increased significantly with MSC sheet transplantation by an average of 2 mm (p = 0.0001). The average measurements of mineral apposition rate and cell proliferation at the cell sheet side tended to be higher than the control side although the differences did not reach statistical significance (p = 0.1-0.2). Tissue mineral density measurements from CT images and bone volume fraction (BV/TV) measurements from histologic images were identical between the two sides (p > 0.5).

CONCLUSION

These data provide a proof of concept that autologous MSC sheets may be transplanted to the subperiosteal region of the mandibular symphysis to stimulate local surface bone growth.

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Acellular Dermal Matrices: Applications in Plastic Surgery

Modern advances in tissue engineering have transformed the plastic surgeon's management strategies across a wide variety of applications. Comprehension of the fundamentals of biologic constructs is critical to navigating the available armamentarium. It is essential that plastic surgeons become familiar with some of the existing methods for utilizing biologics as well as the advantages and limitations to their use. In this article, the authors describe the basic science of biologics with a focus on acellular dermal matrices (ADMs), and review the recent evidence behind their use for a variety of reconstructive and aesthetic purposes. The review is organized by system and examines the common indications, techniques, and outcomes pertaining to the application of ADMs in select anatomic areas. The final section briefly considers possible future directions for using biologics in plastic and reconstructive surgery.

Decellularized Periosteum-Covered Chitosan Globule Composite for Bone Regeneration in Rabbit Femur Condyle Bone Defects

Critical-sized bone defects are incapable of self-healing and are commonly seen in clinical practice. The authors explore a new treatment for this, decellularized periosteum is applied to chitosan globules (chitosan-DP globules) as a hybrid material. The efficacy of chitosan-DP globules on rabbit femoral condyle bone defects is assessed with biocompatibility, biomechanics, and osteogenic efficiency measurements, and compared with the results of chitosan globules and empty control. No difference in cytotoxicity is observed among chitosan-DP globules, chitosan globules, and the empty control. Chitosan-DP globules possesse a better surface for cell adhesion than did chitosan globules. Chitosan-DP globules demonstrate superior efficiency for osteogenesis in the defect area compared to chitosan globules as per microcomputed tomography examination and push-out testing, with relatively minor histological differences. Both chitosan globule groups show more satisfactory results than those for the empty control. The results implicate chitosan-DP globules as a promising solution for bone defects.

The periosteum-like effect of fresh human amniotic membrane on bone regeneration in a rabbit critical-sized defect model

OBJECTIVE

The purpose of this study was to investigate the effect of fresh human amniotic membrane (FHAM) as a substitute of periosteum to enhance bone regeneration in critical-sized defects.

METHODS

Tibial diaphyseal bone defects were created in forty New Zealand white rabbits and treated with FHAM or left empty. Treatment groups consisted of: FHAM implanted in the place of removed periosteum (FHAMP group); FHFAM implanted to fill the entire defect (FHAMF group) compared to negative control group; empty defect with removing the periosteum (NC group) and positive control group; and empty defect without removing the periosteum (PC group). Bone regeneration was evaluated by radiographic, micro-computed tomography (μ-CT) and histological analyses at 4 and 8weeks post-surgery.

RESULTS

Radiographic and μ-CT analysis demonstrated clearly enhanced new bone formation in positive control group (PC) and FHAMP group compared to negative control group (NC) and FHAMF group. Histological staining exhibited remaining woven bones and cartilage matrix in the FHAMP group, immature lamellar bone with medellury cavity and marrow bone formation in PC group from 4weeks post-operatively. For FHAMF group, a little new bone formation was detected only from 8weeks post-operatively, and an absence of any sign of healing in NC group at both time points.

CONCLUSION

The results provide that FHAM increases bone regeneration in critical-sized defects when it is implanted in the place of the removed periosteum, but its additive effect does not have the same effect of the natural periosteum.

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.

The Components of Bone and What They Can Teach Us about Regeneration

The problem of bone regeneration has engaged both physicians and scientists since the beginning of medicine. Not only can bone heal itself following most injuries, but when it does, the regenerated tissue is often indistinguishable from healthy bone. Problems arise, however, when bone does not heal properly, or when new tissue is needed, such as when two vertebrae are required to fuse to stabilize adjacent spine segments. Despite centuries of research, such procedures still require improved therapeutic methods to be devised. Autologous bone harvesting and grafting is currently still the accepted benchmark, despite drawbacks for clinicians and patients that include limited amounts, donor site morbidity, and variable quality. The necessity for an alternative to this "gold standard" has given rise to a bone-graft and substitute industry, with its central conundrum: what is the best way to regenerate bone? In this review, we dissect bone anatomy to summarize our current understanding of its constituents. We then look at how various components have been employed to improve bone regeneration. Evolving strategies for bone regeneration are then considered.

Periosteum tissue engineering in an orthotopic in vivo platform

The periosteum plays a critical role in bone homeostasis and regeneration. It contains a vascular component that provides vital blood supply to the cortical bone and an osteogenic niche that acts as a source of bone-forming cells. Periosteal grafts have shown promise in the regeneration of critical size defects, however their limited availability restricts their widespread clinical application. Only a small number of tissue-engineered periosteum constructs (TEPCs) have been reported in the literature. A current challenge in the development of appropriate TEPCs is a lack of pre-clinical models in which they can reliably be evaluated. In this study, we present a novel periosteum tissue engineering concept utilizing a multiphasic scaffold design in combination with different human cell types for periosteal regeneration in an orthotopic in vivo platform. Human endothelial and bone marrow mesenchymal stem cells (BM-MSCs) were used to mirror both the vascular and osteogenic niche respectively. Immunohistochemistry showed that the BM-MSCs maintained their undifferentiated phenotype. The human endothelial cells developed into mature vessels and connected to host vasculature. The addition of an in vitro engineered endothelial network increased vascularization in comparison to cell-free constructs. Altogether, the results showed that the human TEPC (hTEPC) successfully recapitulated the osteogenic and vascular niche of native periosteum, and that the presented orthotopic xenograft model provides a suitable in vivo environment for evaluating scaffold-based tissue engineering concepts exploiting human cells.

Pre-augmentation soft tissue expansion: an overview

OBJECTIVES

The aim of this study was to explore the development of soft tissue expanders, their different types and their potential applications prior to bone augmentation and implant placement.

MATERIAL AND METHODS

A review of pertinent literature was performed using PubMed to comprehend the dynamics of soft tissue expanders and determine the current position of their pre-augmentation applications.

RESULTS

There is promising, albeit preliminary information regarding the benefits of pre-augmentation soft tissue expansion. Findings cannot be generalised due to relatively small sample size.

CONCLUSIONS

Further clinical trials with larger sample sizes and long-term follow-up are needed before soft tissue expanders can be confidently applied in everyday clinical practice.

Development of poly(ethylene glycol) hydrogels for salivary gland tissue engineering applications

More than 40,000 patients are diagnosed with head and neck cancers annually in the United States with the vast majority receiving radiation therapy. Salivary glands are irreparably damaged by radiation therapy resulting in xerostomia, which severely affects patient quality of life. Cell-based therapies have shown some promise in mouse models of radiation-induced xerostomia, but they suffer from insufficient and inconsistent gland regeneration and accompanying secretory function. To aid in the development of regenerative therapies, poly(ethylene glycol) hydrogels were investigated for the encapsulation of primary submandibular gland (SMG) cells for tissue engineering applications. Different methods of hydrogel formation and cell preparation were examined to identify cytocompatible encapsulation conditions for SMG cells. Cell viability was much higher after thiol-ene polymerizations compared with conventional methacrylate polymerizations due to reduced membrane peroxidation and intracellular reactive oxygen species formation. In addition, the formation of multicellular microspheres before encapsulation maximized cell-cell contacts and increased viability of SMG cells over 14-day culture periods. Thiol-ene hydrogel-encapsulated microspheres also promoted SMG proliferation. Lineage tracing was employed to determine the cellular composition of hydrogel-encapsulated microspheres using markers for acinar (Mist1) and duct (Keratin5) cells. Our findings indicate that both acinar and duct cell phenotypes are present throughout the 14 day culture period. However, the acinar:duct cell ratios are reduced over time, likely due to duct cell proliferation. Altogether, permissive encapsulation methods for primary SMG cells have been identified that promote cell viability, proliferation, and maintenance of differentiated salivary gland cell phenotypes, which allows for translation of this approach for salivary gland tissue engineering applications.

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

Emulating autograft healing within the context of decellularized bone allografts has immediate clinical applications in the treatment of critical-sized bone defects. The periosteum, a thin, osteogenic tissue that surrounds bone, houses a heterogenous population of stem cells and osteoprogenitors. There is evidence that periosteum-cell derived paracrine factors, specifically vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP2), orchestrate autograft healing through host cell recruitment and subsequent tissue elaboration. In previous work, we demonstrated that the use of poly(ethylene glycol) (PEG) hydrogels as a tissue engineered (T.E.) periosteum to localize mesenchymal stem cells (MSCs) to the surface of decellularized bone enhances allograft healing and integration. Herein, we utilize a mixed population of 50:50 MSCs and osteoprogenitor cells to better mimic native periosteum cell population and paracrine factor production to further promote allograft healing. This mixed cell population was localized to the surface of decellularized allografts within degradable hydrogels and shown to expedite allograft healing. Specifically, bone callus formation and biomechanical graft-host integration are increased as compared to unmodified allografts. These results demonstrate the dual importance of periosteum-mediated paracrine factors orchestrating host cell recruitment as well as new bone formation while developing clinically translatable strategies for allograft healing and integration.

A modified rabbit ulna defect model for evaluating periosteal substitutes in bone engineering: a pilot study

The present work defines a modified critical size rabbit ulna defect model for bone regeneration in which a non-resorbable barrier membrane was used to separate the radius from the ulna to create a valid model for evaluation of tissue-engineered periosteal substitutes. Eight rabbits divided into two groups were used. Critical defects (15 mm) were made in the ulna completely eliminating periosteum. For group I, defects were filled with a nanohydroxyapatite poly(ester urethane) scaffold soaked in PBS and left as such (group Ia) or wrapped with a tissue-engineered periosteal substitute (group Ib). For group II, an expanded-polytetrafluoroethylene (e-PTFE) (GORE-TEX^®) membrane was inserted around the radius then the defects received either scaffold alone (group IIa) or scaffold wrapped with periosteal substitute (group IIb). Animals were euthanized after 12–16 weeks, and bone regeneration was evaluated by radiography, computed microtomography (μCT), and histology. In the first group, we observed formation of radio-ulnar synostosis irrespective of the treatment. This was completely eliminated upon placement of the e-PTFE (GORE-TEX^®) membrane in the second group of animals. In conclusion, modification of the model using a non-resorbable e-PTFE membrane to isolate the ulna from the radius was a valuable addition allowing for objective evaluation of the tissue-engineered periosteal substitute.

Two dimensional nanosheets as conductive, flexible elements in biomaterials

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

Uncovering the periosteum for skeletal regeneration: the stem cell that lies beneath

The cartilage- and bone-forming properties of the periosteum have long since been recognized. As one of the major sources of skeletal progenitor cells, the periosteum plays a crucial role not only in bone development and growth, but also during bone fracture healing. Aided by the continuous expansion of tools and techniques, we are now starting to acquire more insight into the specific role and regulation of periosteal cells. From a therapeutic point of view, the periosteum has attracted much attention as a cell source for bone tissue engineering purposes. This interest derives not only from the physiological role of the periosteum during bone repair, but is also supported by the unique properties and marked bone-forming potential of expanded periosteum-derived cells. We provide an overview of the current knowledge of periosteal cell biology, focusing on the cellular composition and molecular regulation of this remarkable tissue, as well as the application of periosteum-derived cells in regenerative medicine approaches. This article is part of a Special Issue entitled "Stem Cells and Bone".

Periosteum derived stem cells for regenerative medicine proposals: Boosting current knowledge

Periosteum is a thin fibrous layer that covers most bones. It resides in a dynamic mechanically loaded environment and provides a niche for pluripotent cells and a source for molecular factors that modulate cell behaviour. Elucidating periosteum regenerative potential has become a hot topic in orthopaedics. This review discusses the state of the art of osteochondral tissue engineering rested on periosteum derived progenitor cells (PDPCs) and suggests upcoming research directions. Periosteal cells isolation, characterization and migration in the site of injury, as well as their differentiation, are analysed. Moreover, the role of cell mechanosensing and its contribution to matrix organization, bone microarchitecture and bone stenght is examined. In this regard the role of periostin and its upregulation under mechanical stress in order to preserve PDPC survival and bone tissue integrity is contemplated. The review also summarized the role of the periosteum in the field of dentistry and maxillofacial reconstruction. The involvement of microRNAs in osteoblast differentiation and in endogenous tissue repair is explored as well. Finally the novel concept of a guided bone regeneration based on the use of periosteum itself as a smart material and the realization of constructs able to mimic the extracellular matrix features is talked out. Additionally, since periosteum can differentiate into insulin producing cells it could be a suitable source in allogenic transplantations. That innovative applications would take advantage from investigations aimed to assess PDPC immune privilege.

Engineering vascularized bone grafts by integrating a biomimetic periosteum and β-TCP scaffold

Treatment of large bone defects using synthetic scaffolds remain a challenge mainly due to insufficient vascularization. This study is to engineer a vascularized bone graft by integrating a vascularized biomimetic cell-sheet-engineered periosteum (CSEP) and a biodegradable macroporous beta-tricalcium phosphate (β-TCP) scaffold. We first cultured human mesenchymal stem cells (hMSCs) to form cell sheet and human umbilical vascular endothelial cells (HUVECs) were then seeded on the undifferentiated hMSCs sheet to form vascularized cell sheet for mimicking the fibrous layer of native periosteum. A mineralized hMSCs sheet was cultured to mimic the cambium layer of native periosteum. This mineralized hMSCs sheet was first wrapped onto a cylindrical β-TCP scaffold followed by wrapping the vascularized HUVEC/hMSC sheet, thus generating a biomimetic CSEP on the β-TCP scaffold. A nonperiosteum structural cell sheets-covered β-TCP and plain β-TCP were used as controls. In vitro studies indicate that the undifferentiated hMSCs sheet facilitated HUVECs to form rich capillary-like networks. In vivo studies indicate that the biomimetic CSEP enhanced angiogenesis and functional anastomosis between the in vitro preformed human capillary networks and the mouse host vasculature. MicroCT analysis and osteocalcin staining show that the biomimetic CSEP/β-TCP graft formed more bone matrix compared to the other groups. These results suggest that the CSEP that mimics the cellular components and spatial configuration of periosteum plays a critical role in vascularization and osteogenesis. Our studies suggest that a biomimetic periosteum-covered β-TCP graft is a promising approach for bone regeneration.

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.

Kartogenin induces cartilage-like tissue formation in tendon-bone junction

Tendon–bone junctions (TBJs) are frequently injured, especially in athletic settings. Healing of TBJ injuries is slow and is often repaired with scar tissue formation that compromises normal function. This study explored the feasibility of using kartogenin (KGN), a biocompound, to enhance the healing of injured TBJs. We first determined the effects of KGN on the proliferation and chondrogenic differentiation of rabbit bone marrow stromal cells (BMSCs) and patellar tendon stem/progenitor cells (PTSCs) in vitro. KGN enhanced cell proliferation in both cell types in a concentration-dependent manner and induced chondrogenic differentiation of stem cells, as demonstrated by high expression levels of chondrogenic markers aggrecan, collagen II and Sox-9. Besides, KGN induced the formation of cartilage-like tissues in cell cultures, as observed through the staining of abundant proteoglycans, collagen II and osteocalcin. When injected into intact rat patellar tendons in vivo, KGN induced cartilage-like tissue formation in the injected area. Similarly, when KGN was injected into experimentally injured rat Achilles TBJs, wound healing in the TBJs was enhanced, as evidenced by the formation of extensive cartilage-like tissues. These results suggest that KGN may be used as an effective cell-free clinical therapy to enhance the healing of injured TBJs.

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 effect of mesenchymal stem cells delivered via hydrogel-based tissue engineered periosteum on bone allograft healing

Allografts remain the clinical "gold standard" for treatment of critical sized bone defects despite minimal engraftment and ∼60% long-term failure rates. Therefore, the development of strategies to improve allograft healing and integration are necessary. The periosteum and its associated stem cell population, which are lacking in allografts, coordinate autograft healing. Herein we utilized hydrolytically degradable hydrogels to transplant and localize mesenchymal stem cells (MSCs) to allograft surfaces, creating a periosteum mimetic, termed a 'tissue engineered periosteum'. Our results demonstrated that this tissue engineering approach resulted in increased graft vascularization (∼2.4-fold), endochondral bone formation (∼2.8-fold), and biomechanical strength (1.8-fold), as compared to untreated allografts, over 16 weeks of healing. Despite this enhancement in healing, the process of endochondral ossification was delayed compared to autografts, requiring further modifications for this approach to be clinically acceptable. However, this bottom-up biomaterials approach, the engineered periosteum, can be augmented with alternative cell types, matrix cues, growth factors, and/or other small molecule drugs to expedite the process of ossification.

A sulfated nanofibrous mesh supporting the osteogenic differentiation of periosteum-derived cells

The periosteum is a thin fibrous membrane covering the surface of long bone and is known to play a critical role in bone development and adult bone fracture healing. Loss or damage of the periosteum tissue during traumatic long bone injuries can lead to retarded healing of bone graft-mediated repair. The regenerative potential of periosteum-derived progenitor cells (PDCs) has inspired their use as an alternative to bone marrow-derived mesenchymal stromal cells (MSCs) to augment scaffold-assisted bone repair. In this study, we first demonstrated that PDCs isolated from adult rat long bone exhibited innate advantages over bone marrow-derived MSCs in terms of faster proliferation and more potent osteogenic differentiation upon induction in plastic-adherent culture. Further, we examined the potential of two electrospun nanofibrous meshes, an uncharged regenerated cellulose mesh and a sulfated mesh, to support the attachment and osteogenic differentiation of PDCs. We showed that both nanofibrous meshes were able to support the attachment and proliferation of PDCs and MSCs alike, with the sulfated mesh enabling significantly higher seeding efficiency than the cellulose mesh. Both meshes were also able to support the osteogenic differentiation of adherent PDCs upon induction by osteogenic media, with the sulfated mesh facilitating more potent mineral deposition by adherent PDCs. Our study supports the sulfated nanofibrous mesh as a promising synthetic periosteal membrane for the delivery of exogenous PDCs to augment bone healing.

Interstitial engraftment of adipose-derived stem cells into an acellular dermal matrix results in improved inward angiogenesis and tissue incorporation

Acellular dermal matrices (ADM) are commonly used in reconstructive procedures and rely on host cell invasion to become incorporated into host tissues. We investigated different approaches to adipose-derived stem cells (ASCs) engraftment into ADM to enhance this process. Lewis rat adipose-derived stem cells were isolated and grafted (3.0 × 10(5) cells) to porcine ADM disks (1.5 mm thick × 6 mm diameter) using either passive onlay or interstitial injection seeding techniques. Following incubation, seeding efficiency and seeded cell viability were measured in vitro. In addition, Eighteen Lewis rats underwent subcutaneous placement of ADM disk either as control or seeded with PKH67 labeled ASCs. ADM disks were seeded with ASCs using either onlay or injection techniques. On day 7 and or 14, ADM disks were harvested and analyzed for host cell infiltration. Onlay and injection techniques resulted in unique seeding patterns; however cell seeding efficiency and cell viability were similar. In-vivo studies showed significantly increased host cell infiltration towards the ASCs foci following injection seeding in comparison to control group (p < 0.05). Moreover, regional endothelial cell invasion was significantly greater in ASCs injected grafts in comparison to onlay seeding (p < 0.05). ADM can successfully be engrafted with ASCs. Interstitial engraftment of ASCs into ADM via injection enhances regional infiltration of host cells and angiogenesis, whereas onlay seeding showed relatively broad and superficial cell infiltration. These findings may be applied to improve the incorporation of avascular engineered constructs.

Low-level laser therapy promotes the osteogenic potential of adipose-derived mesenchymal stem cells seeded on an acellular dermal matrix

This study investigates the feasibility of using an adipose-derived mesenchymal stem cell (ASC)-seeded acellular dermal matrix (ADM) along with low-level laser therapy (LLLT) to repair bone defect in athymic nude mice. Critical-sized calvarial defects were treated either with ADM, ADM/LLLT, ADM/ASCs, or ADM/ASCs/LLLT. In micro-computed tomography scans, the ADM/ASCs and the ADM/ASCs/LLLT groups showed remarkable bone formation after 14 days. Additionally, bone regeneration in the ADM/ASCs/LLLT group was obvious at 28 days, but in the ADM/ASCs group at 56 days. Bone mineral density and bone tissue volume in the ADM/ASCs/LLLT group significantly increased after 7 days, but in the ADM/ASCs group after 14 days. Histological analysis revealed that the defects were repaired in the ADM/ASCs and the ADM/ASCs/LLLT group, while the defects in the ADM and the ADM/LLLT groups exhibited few bone islands at 28 and 56 days. The successful seeding of ASCs onto ADM was confirmed, and LLLT enhanced the proliferation and the survival of ASCs at 14 days. Our results indicate that ASC-seeded grafts promote bone regeneration, and the application of LLLT on ASC-seeded ADM results in rapid bone formation. The implantation of an ASC-seeded ADM combined with LLLT may be used effectively for bone regeneration.

Emerging ideas: Engineering the periosteum: revitalizing allografts by mimicking autograft healing

BACKGROUND

To fulfill the need for large volumes, devitalized allografts are used to treat massive bone defects despite a 60%, 10-year postimplantation fracture rate. Allograft healing is inferior to autografts where the periosteum orchestrates remodeling.

HYPOTHESIS

By augmenting allografts with a tissue engineered periosteum consisting of tunable and degradable, poly(ethylene glycol) (PEG) hydrogels for mesenchymal stem cell (MSC) transplantation, the functions critical for periosteum-mediated healing will be identified and emulated.

METHOD OF STUDY

PEG hydrogels will be designed to emulate periosteum-mediated autograft healing to revitalize allografts. We will exploit murine femoral defect models for these approaches. Critical-sized, 5-mm segmental defects will be created and filled with decellularized allograft controls or live autograft controls. Alternatively, defects will be treated with our experimental approaches: decellularized allografts coated with MSCs transplanted via degradable PEG hydrogels to mimic progenitor cell densities and persistence during autograft healing. Healing will be evaluated for 9 weeks using microcomputed tomography, mechanical testing, and histologic analysis. If promising, MSC densities, hydrogel compositions, and genetic methods will be used to isolate critical aspects of engineered periosteum that modulate healing. Finally, hydrogel biochemical characteristics will be altered to initiate MSC and/or host-material interactions to further promote remodeling of allografts.

SIGNIFICANCE

This approach represents a novel tissue engineering strategy whereby degradable, synthetic hydrogels will be exploited to emulate the periosteum. The microenvironment, which will mediate MSC transplantation, will use tunable PEG hydrogels for isolation of critical allograft revitalization factors. In addition, hydrogels will be modified with biochemical cues to further augment allografts to reduce or eliminate revision surgeries associated with allograft failures.

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.