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

Masquelet Inspired in Vivo Engineered Extracellular Matrix as Functional Periosteum for Bone Defect Repair and Reconstruction

The Masquelet technique that combines a foreign body reaction (FBR)-induced vascularized tissue membrane with staged bone grafting for reconstruction of segmental bone defect has gained wide attention in Orthopedic surgery. The success of Masquelet hinges on its ability to promote formation of a "periosteum-like" FBR-induced membrane at the bone defect site. Inspired by Masquelet's technique, here a novel approach is devised to create periosteum mimetics from decellularized extracellular matrix (dECM), engineered in vivo through FBR, for reconstruction of segmental bone defects. The approach involved 3D printing of polylactic acid (PLA) template with desired pattern/architecture, followed by subcutaneous implantation of the template to form tissue, and depolymerization and decellularization to generate dECM with interconnected channels. The dECM matrices produces from the same mice (autologous) or from different mice (allogenic) are used as a functional periosteum for repair of structural bone allograft in a murine segmental bone defect model. This study shows that autologous dECM performed better than allogenic dECM, further permitting local delivery of low dose BMP-2 to enhance allograft incorporation. The success of this current approach can establish a new line of versatile, patient-specific, and periosteum-like autologous dECM for bone regeneration, offering personalized therapeutics to patients with impaired healing.

The Role of the Periosteum in Bone Formation From Adolescence to Old Age

Bone formation is a complex process involving the coordinated activity of many different cell types, including osteoblasts and osteocytes. The periosteum is a dense membrane of connective tissue that covers the outer surface of bones and is essential for the growth, repair, and maintenance of osseous tissue. The present study aims to summarize the contribution of the periosteum in bone formation from adolescence to adulthood and old age. This is a narrative literature review using the PubMed electronic internet database. The search was based on the keyword "periosteal bone formation". Inclusion criteria were preclinical or clinical studies evaluating the role of the periosteum in bone formation. Non-English studies were excluded. The original search provided 126 published papers. After inclusion and exclusion criteria, we finally accepted 20 articles for our current review. After checking the references list of the included studies, 14 more studies were added, leaving 34 studies for the present review. Across the lifespan, periosteal bone formation undergoes dynamic changes. During adolescence, the periosteum is highly osteogenic and actively contributes to rapid bone growth. In adulthood, it plays a role in maintaining bone strength and adapting to mechanical loading. In adulthood, the periosteum continues to provide a source of osteoprogenitor cells, which contribute to the ongoing process of bone remodeling and repair. At more advanced ages, the response of the periosteum to hormones and cytokines in terms of bone formation decreases; however, the power of osteogenetic differentiation of periosteal cells may be preserved.

Pediatric Fracture Remodeling: From Wolff to Wnt

Pediatric fracture remodeling is a complex mechanobiological process in which a team of cells, including osteoclasts, osteoblasts, and osteocytes, responds to cytokine and mechanical signals to synthesize new bone in areas of high stress (concavity of a fracture) and remove older redundant bone in areas of low stress (convexity and medullary canal). Piezo1 mechanoreceptors and other pressure-sensitive membrane proteins perceive and convert mechanical strains into intracellular chemical signals. Cytokines are peptides that bind to cell membrane receptors and influence cell functions. Bone morphogenetic proteins and Wnt are the major osteogenic cytokines. Macrophage colony-stimulating factor and receptor activator of nuclear factor κB ligand (RANKL) are the major osteoclastic cytokines. The combination of mechanical stresses and cytokine concentrations stimulates osteoclasts to resorb bone and osteoblasts to make new bone, resulting in remodeling that restores bone strength and structure.

Regulatory effects of stress release from decellularized periosteum on proliferation, migration, and osteogenic differentiation of periosteum-derived cells

Bone injury is often associated with tears in the periosteum and changes in the internal stress microenvironment of the periosteum. In this study, we investigated the biological effects of periosteal prestress release on periosteum-derived cells (PDCs) and the potential mechanisms of endogenous stem cell recruitment. Decellularized periosteum with natural extracellular matrix (ECM) components was obtained by a combination of physical, chemical, and enzymatic decellularization. The decellularized periosteum removed immunogenicity while retaining the natural network structure and composition of the ECM. The Young's modulus has no significant difference between the periosteum before and after decellularization. The extracted PDCs were further composited with the decellularized periosteum and subjected to 20% stress release. It was found that the proliferative capacity of PDCs seeded on decellularized periosteum was significantly enhanced 6 h after stress release of the periosteum. The cell culture supernatant obtained after periosteal prestress release was able to significantly promote the migration ability of PDCs within 24 h. Enzyme-linked immunosorbnent assay (ELISA) experiments showed that the expression of stroma-derived factor-1α (SDF-1α) and vascular endothelial growth factor (VEGF) in the supernatant increased significantly after 3 h and 12 h of stress release, respectively. Furthermore, periosteal stress release promoted the high expression of osteogenic markers osteocalcin (OCN), osteopontin (OPN), and collagen type I of PDCs. The change in stress environment caused by the release of periosteal prestress was sensed by integrin β1, a mechanoreceptor on the membrane of PDCs, which further stimulated the expression of YAP in the nucleus. These investigations provided a novel method to evaluate the importance of mechanical stimulation in periosteum, which is also of great significance for the design and fabrication of artificial periosteum with mechanical regulation function.

Sequestration and Involucrum: Understanding Bone Necrosis and Revascularization in Pediatric Orthopedics

Sequestration, a condition where a section of bone becomes necrotic due to a loss of vascularity or thrombosis, can be a challenging complication of osteomyelitis. This review explores the pathophysiology of sequestration, highlighting the role of the periosteum in forming involucrum and creeping substitution which facilitate revascularization and bone formation. The authors also discuss the induced membrane technique, a two-stage surgical procedure for cases of failed healing of sequestration. Future directions include the potential use of prophylactic anticoagulation and novel drugs targeting immunocoagulopathy, as well as the development of advanced imaging techniques and single-stage surgical procedures.

Outcome of nonsurgical management of large cyst-like periapical lesions using a modified apical negative pressure irrigation system: a case series study

OBJECTIVE

To assess the effectiveness of a self-constructed modified apical negative pressure irrigation (ANPI) system employing commonly used clinical instruments in nonsurgical root canal therapy (NSRCT) for large cyst-like periapical lesions (LCPLs).

METHODS

From 2017 to 2022, 35 patients diagnosed with LCPLs (5-15 mm) via preoperative clinical and radiographic evaluations of endodontic origin underwent NSRCT combined with ANPI. These patients were subjected to postoperative clinical and radiographic follow-up at 3 months, 6 months, 1 year, 2 years, 3 years, and 4 years, with a CBCT scan specifically conducted at 6-month follow-up. Through the reconstruction of three-dimensional cone beam computed tomography (CBCT) data, an early prognosis was facilitated by monitoring changes in lesion volume. Various treatment predictors-including sex, type of treatment, lesion size, preoperative pain, jaw, type of teeth involved, sealer extrusion, and the number of root canals-were meticulously analyzed. The evaluation of post-treatment outcomes leveraged both clinical observations and radiographic data collected during the follow-up periods. The Kruskal‒Wallis test and one-way ANOVA were also conducted to determine the independent factors influencing treatment outcomes. A significance level of 5% was established.

RESULTS

Thirty-five teeth from 35 patients with a median age of 28 years (range 24-34) were treated; the median follow-up duration was 19 months (range 12-26). The overall success rate was 91.4%, with a median lesion reduction of 77.0% (range 54.2-96.4%) at 6 months. Patients under 30 years of age exhibited a significantly greater success rate than older patients did (100.0% vs. 80.0%, p = 0.037). Other factors, such as sex, jaw, treatment type, preoperative pain, cyst size, tooth location, sealer extrusion, and the number of roots, did not significantly impact treatment outcomes.

CONCLUSIONS

Despite limitations related to the observational case-series study design and relatively small sample size, our findings suggest that utilizing the ANPI in the NSRCT for LCPLs may hold promise. The notably higher success rate in patients younger than 30 years is worth noting.

Characterization of adult human skeletal cells in different tissues reveals a CD90+CD34+ periosteal stem/progenitor population

The periosteum plays a crucial role in bone healing and is an important source of skeletal stem and progenitor cells. Recent studies in mice indicate that diverse populations of skeletal progenitors contribute to growth, homeostasis and healing. Information about the in vivo identity and diversity of skeletal stem and progenitor cells in different compartments of the adult human skeleton is limited. In this study, we compared non-hematopoietic populations in matched tissues from the femoral head and neck of 21 human participants using spectral flow cytometry of freshly isolated cells. High-dimensional clustering analysis indicated significant differences in marker distribution between periosteum, articular cartilage, endosteum and bone marrow populations, and identified populations that were highly enriched or unique to specific tissues. Periosteum-enriched markers included CD90 and CD34. Articular cartilage, which has very poor regenerative potential, showed enrichment of multiple markers, including the PDPN+CD73+CD164+CD146- population previously reported to represent human skeletal stem cells. We further characterized periosteal populations by combining CD90 with other strongly expressed markers. CD90+CD34+ cells sorted directly from periosteum showed significant colony-forming unit fibroblasts (CFU-F) enrichment, rapid expansion, and consistent multi-lineage differentiation of clonal populations in vitro. In situ, CD90+CD34+ cells include a perivascular population in the outer layer of the periosteum and non-perivascular cells closer to the bone surface. CD90+ cells are also highly enriched for CFU-F in bone marrow and endosteum, but not articular cartilage. In conclusion, our study indicates considerable diversity in the non-hematopoietic cell populations in different tissue compartments within the adult human skeleton, and suggests that periosteal progenitor cells reside within the CD90+CD34+ population.

Fracture healing research: Recent insights

Bone has the rare capability of scarless regeneration that enables the complete restoration of the injured bone area. In recent decades, promising new technologies have emerged from basic, translational and clinical research for fracture treatment; however, 5-10 % of all bone fractures still fail to heal successfully or heal in a delayed manner. Several comorbidities and risk factors have been identified which impair bone healing and might lead to delayed bone union or non-union. Therefore, a considerable amount of research has been conducted to elucidate molecular mechanisms of successful and delayed fracture healing to gain further insights into this complex process. One focus of recent research is to investigate the complex interactions of different cell types and the action of progenitor cells during the healing process. Of particular interest is also the identification of patient-specific comorbidities and how these affect fracture healing. In this review, we discuss the recent knowledge about progenitor cells for long bone repair and the influence of comorbidities such as diabetes, postmenopausal osteoporosis, and chronic stress on the healing process. The topic selection for this review was made based on the presented studies at the 2022 annual meeting of the European Calcified Tissue Society (ECTS) in Helsinki.

Site-specific periosteal cells with distinct osteogenic and angiogenic characteristics

OBJECTIVES

This study aimed to investigate the site-specific characteristics of rat mandible periosteal cells (MPCs) and tibia periosteal cells (TPCs) to assess the potential application of periosteal cells (PCs) in bone tissue engineering (BTE).

MATERIALS AND METHODS

MPCs and TPCs were isolated and characterized. The potential of proliferation, migration, osteogenesis and adipogenesis of MPCs and TPCs were evaluated by CCK-8, scratch assay, Transwell assay, alkaline phosphatase staining and activity, Alizarin Red S staining, RT‒qPCR, and Western blot (WB) assays, respectively. Then, these cells were cocultured with human umbilical vein endothelial cells (HUVECs) to investigate their angiogenic capacity, which was assessed by scratch assay, Transwell assay, Matrigel tube formation assay, RT‒qPCR, and WB assays.

RESULTS

MPCs exhibited higher osteogenic potential, higher alkaline phosphatase activity, and more mineralized nodule formation, while TPCs showed a greater capability for proliferation, migration, and adipogenesis. MPCs showed higher expression of angiogenic factors, and the conditioned medium of MPCs accelerated the migration of HUVECs, while MPC- conditioned medium induced the formation of more tubular structure in HUVECs in vitro. These data suggest that compared to TPCs, MPCs exert more consequential proangiogenic effects on HUVECs.

CONCLUSIONS

PCs possess skeletal site-specific differences in biological characteristics. MPCs exhibit more eminent osteogenic and angiogenic potentials, which highlights the potential application of MPCs for BTE.

CLINICAL RELEVANCE

Autologous bone grafting as the main modality for maxillofacial bone defect repair has many limitations. Constituting an important cell type in bone repair and regeneration, MPCs show greater potential for application in BTE, which provides a promising treatment option for maxillofacial bone defect repair.

Sfrp4 is required to maintain Ctsk-lineage periosteal stem cell niche function

We have previously reported that the cortical bone thinning seen in mice lacking the Wnt signaling antagonist Sfrp4 is due in part to impaired periosteal apposition. The periosteum contains cells which function as a reservoir of stem cells and contribute to cortical bone expansion, homeostasis, and repair. However, the local or paracrine factors that govern stem cells within the periosteal niche remain elusive. Cathepsin K (Ctsk), together with additional stem cell surface markers, marks a subset of periosteal stem cells (PSCs) which possess self-renewal ability and inducible multipotency. Sfrp4 is expressed in periosteal Ctsk-lineage cells, and Sfrp4 global deletion decreases the pool of PSCs, impairs their clonal multipotency for differentiation into osteoblasts and chondrocytes and formation of bone organoids. Bulk RNA sequencing analysis of Ctsk-lineage PSCs demonstrated that Sfrp4 deletion down-regulates signaling pathways associated with skeletal development, positive regulation of bone mineralization, and wound healing. Supporting these findings, Sfrp4 deletion hampers the periosteal response to bone injury and impairs Ctsk-lineage periosteal cell recruitment. Ctsk-lineage PSCs express the PTH receptor and PTH treatment increases the % of PSCs, a response not seen in the absence of Sfrp4. Importantly, in the absence of Sfrp4, PTH-dependent increase in cortical thickness and periosteal bone formation is markedly impaired. Thus, this study provides insights into the regulation of a specific population of periosteal cells by a secreted local factor, and shows a central role for Sfrp4 in the regulation of Ctsk-lineage periosteal stem cell differentiation and function.

Analysis of Cellular Crosstalk and Molecular Signal between Periosteum-Derived Precursor Cells and Peripheral Cells During Bone Healing Process Using a Paper-Based Osteogenesis-On-A-Chip Platform

Periosteum-derived progenitor cells (PDPCs) are highly promising cell sources that are indispensable in the bone healing process. Adipose-derived stem cells (ADSCs) are physiologically close to periosteum tissue and release multiple growth factors to promote the bone healing process. Co-culturing PDPCs and ADSCs can construct periosteum-bone tissue microenvironments for the study of cellular crosstalk and molecular signal in the bone healing process. In the current work, a paper-based osteogenesis-on-a-chip platform was successfully developed to provide an in vitro three-dimensional coculture model. The platform was a paper substrate sandwiched between PDPC-hydrogel and ADSC-hydrogel suspensions. Cell secretion could be transferred through the paper substrate from one side to another side. Growth factors including BMP2, TGF-β, POSTN, Wnt proteins, PDGFA, and VEGFA were directly analyzed by a paper-based immunoassay. Cellular crosstalk was studied by protein expression on the paper substrate. Moreover, osteogenesis of PDPCs was investigated by examining the mRNA expressions of PDPCs after culture. Neutralizing and competitive assays were conducted to understand the correlation between growth factors secreted from ADSCs and the osteogenesis of PDPCs. In vitro periosteum-bone tissue microenvironment was established by the paper-based osteogenesis-on-a-chip platform. The proposed approach provides a promising assay of cellular crosstalk and molecular signal in 3D coculture microenvironment that may potentially lead to the development of effective bone regeneration therapy.

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.

Evaluation of the time-dependent osteogenic activity of glycerol incorporated magnesium oxide nanoparticles in induced calvarial defects

Introduction

Magnesium-based biomaterials have been explored for their potential as bone healing materials, as a result of their outstanding biodegradability and biocompatibility. These characteristics make magnesium oxide nanoparticles (MgO NPs) a promising material for treating bone disorders. The purpose of this investigation is to assess the osteogenic activity of newly-developed locally administered glycerol-incorporated MgO NPs (GIMgO NPs) in rabbits' calvarial defects.

Materials and methods

Characterization of GIMgO was done by X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Bilateral calvarial defects were created in eighteen New Zealand Rabbits, of which they were divided into 3 groups with time points corresponding to 2, 4, and 6 weeks postoperatively (n = 6). One defect was implanted with absorbable gel foam impregnated with GIMgO NPs while the other was implanted with gel foam soaked with glycerol (the control). The defects were assessed using histological, Micro-Computed Tomography (Micro-CT), and histometric evaluation.

Results

The characterization of the GIMgO nanogel revealed the presence of MgO NPs and glycerol as well as the formation of the crystalline phase of the MgO NPs within the nanogel sample. The histological and micro-CT analysis showed time-dependent improvement of healing activity in the calvarial defects implanted with GIMgO NPs when compared to the control. Furthermore, the histometric analysis demonstrated a marked increase in the total area of new bone, connective tissue, new bone area and volume in the GIMgO NPs implanted site. Statistically, the amount of new bone formation was more significant at 6 weeks than at 2 and 4 weeks postoperatively in the calvarial defects implanted with GIMgO NPs as compared to the control.

Conclusion

The locally applied GIMgO NPs demonstrated efficacy in promoting bone formation, with more significant effects observed over an extended period. These findings suggest its suitability for clinical use as a therapeutic alternative to enhance bone healing.

Type H blood vessels in coupling angiogenesis-osteogenesis and its application in bone tissue engineering

One specific capillary subtype, termed type H vessel, has been found with unique functional characteristics in coupling angiogenesis with osteogenesis. Researchers have fabricated a variety of tissue engineering scaffolds to enhance bone healing and regeneration through the accumulation of type H vessels. However, only a limited number of reviews discussed the tissue engineering strategies for type H vessel regulation. The object of this review is to summary the current utilizes of bone tissue engineering to regulate type H vessels through various signal pathways including Notch, PDGF-BB, Slit3, HIF-1α, and VEGF signaling. Moreover, we give an insightful overview of recent research progress about the morphological, spatial and age-dependent characteristics of type H blood vessels. Their unique role in tying angiogenesis and osteogenesis together via blood flow, cellular microenvironment, immune system and nervous system are also summarized. This review article would provide an insight into the combination of tissue engineering scaffolds with type H vessels and identify future perspectives for vasculized tissue engineering research.

Clinical effectiveness of periosteal pedicle graft for the management of gingival recession defects-a systematic review and meta-analysis

OBJECTIVE

The purpose of this systematic review and meta-analysis was to evaluate the effectiveness of periosteal pedicle graft (PPG) in terms of root coverage and patient related outcomes. To the best of our knowledge this is the first systematic review with meta-analysis on PPG.

MATERIAL AND METHODS

A comprehensive search was performed using electronic and hand searches upto January 2023. Primary outcomes were Recession depth Reduction (Rec Red), mean root coverage (mRC) and complete root coverage (CRC). Secondary outcomes were gain in width of keratinized gingiva (WKG) and patient reported outcome measures (PROMs). Meta-analysis was performed when possible. The risk bias assessment was done using RevMan5.4.1 and Joanna Briggs institute scale for the included RCTs and case series respectively.

RESULTS

A total of 8 RCTs and 2 case series (538 recession sites) were included based upon the predefined inclusion and exclusion criteria. The follow up period ranged from 6 months to 18 months. Results demonstrated that mRC of PPG + Coronally advanced flap (CAF) was 87.7% for localized gingival recession defects (GRDs) and 84.83% for multiple GRDs. An overall gain in WKG (Weighted Mean =1.49 ± 0.27 mm) was observed among all the included studies in the PPG + CAF group with mean difference (-0.10 (95% CI [-0.52, 0.33], p = 0.66)). Sub-group meta-analysis comparing PPG + CAF with sub-epithelial connective tissue graft (SCTG) + CAF resulted in similar outcomes in terms of Rec Red (0.10 (95% CI [-0.56 to 0.77], p = 0.76)) and gain in WKG (-0.03 (95% CI [-0.25 to 0.18], p = 0.76)). In terms of PROMs systematic review revealed better patient satisfaction with PPG + CAF than SCTG + CAF.

CONCLUSION

PPG + CAF is a viable treatment modality for management of GRDs. The primary and secondary outcomes achieved utilizing PPG + CAF were found to be comparable to other conventional techniques including the gold standard i.e., SCTG.

Bone regeneration in inflammation with aging and cell-based immunomodulatory therapy

Aging of the global population increases the incidence of osteoporosis and associated fragility fractures, significantly impacting patient quality of life and healthcare costs. The acute inflammatory reaction is essential to initiate healing after injury. However, aging is associated with "inflammaging", referring to the presence of systemic low-level chronic inflammation. Chronic inflammation impairs the initiation of bone regeneration in elderly patients. This review examines current knowledge of the bone regeneration process and potential immunomodulatory therapies to facilitate bone healing in inflammaging.Aged macrophages show increased sensitivity and responsiveness to inflammatory signals. While M1 macrophages are activated during the acute inflammatory response, proper resolution of the inflammatory phase involves repolarizing pro-inflammatory M1 macrophages to an anti-inflammatory M2 phenotype associated with tissue regeneration. In aging, persistent chronic inflammation resulting from the failure of M1 to M2 repolarization leads to increased osteoclast activation and decreased osteoblast formation, thus increasing bone resorption and decreasing bone formation during healing.Inflammaging can impair the ability of stem cells to support bone regeneration and contributes to the decline in bone mass and strength that occurs with aging. Therefore, modulating inflammaging is a promising approach for improving bone health in the aging population. Mesenchymal stem cells (MSCs) possess immunomodulatory properties that may benefit bone regeneration in inflammation. Preconditioning MSCs with pro-inflammatory cytokines affects MSCs' secretory profile and osteogenic ability. MSCs cultured under hypoxic conditions show increased proliferation rates and secretion of growth factors. Resolution of inflammation via local delivery of anti-inflammatory cytokines is also a potential therapy for bone regeneration in inflammaging. Scaffolds containing anti-inflammatory cytokines, unaltered MSCs, and genetically modified MSCs can also have therapeutic potential. MSC exosomes can increase the migration of MSCs to the fracture site and enhance osteogenic differentiation and angiogenesis.In conclusion, inflammaging can impair the proper initiation of bone regeneration in the elderly. Modulating inflammaging is a promising approach for improving compromised bone healing in the aging population.

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.

Comparison of perioperative serum osteocrin concentrations between surgical techniques in dogs with cranial cruciate ligament rupture

The cranial cruciate ligament (CCL) rupture is a common orthopedic disease in dogs that is usually managed with tibial plateau leveling osteotomy (TPLO) or extracapsular lateral suture (ECLS). Osteotomy is generally associated with some complications, including nonunion. The periosteum plays an important role in bone growth and remodeling. Osteocrin (OSTN), which was recently identified and is involved in bone formation and differentiation, is produced in the periosteum and osteoblasts. The aimed to investigate whether the concentrations of serum OSTN change before and after stifle surgery in dogs and compare the OSTN concentrations in the two surgical techniques (TPLO: n = 20 vs. ECLS: n = 36). The postoperative serum OSTN concentration in the TPLO group was significantly lower than the preoperative value (p < 0.05), while serum OSTN concentrations differed statistically between the preoperative and suture-removal periods. In contrast, no significant differences were observed in the ECLS group. In conclusion, osteotomy affects serum OSTN concentrations during the perioperative period in dogs, which may be related to periosteal injury.

Micropatterned photothermal double-layer periosteum with angiogenesis-neurogenesis coupling effect for bone regeneration

The abundant neurovascular network in the periosteal fibrous layer is essential for regulating bone homeostasis and repairing bone defects. However, the majority of the current studies only focus on the structure or function, and most of them merely involve osteogenesis and angiogenesis, lacking an in-depth study of periosteal neurogenesis. In this study, a photothermal double-layer biomimetic periosteum with neurovascular coupling was proposed. The outer layer of biomimetic periosteum is a conventional electrospinning membrane to prevent soft tissue invasion, and the inner layer is an oriented nanofiber membrane to promote cell recruitment and angiogenesis. From the perspective of functional bionics, based on the whitlockite (WH) similar to bone composition, we doped Nd (the trivalent form of neodymium element) in it as the inducing element of photothermal response to prepare photothermal whitlockite (Nd@WH). The sustained release of Mg²⁺ in Nd@WH can effectively promote the up-regulation of nerve growth factor (NGF) and vascular endothelial growth factor (VEGF). The release of Ca²⁺ and PO₄ ^3- ions and photothermal osteogenesis jointly promote bone regeneration. Under the combined effect of structure and function, the formation of nerves, blood vessels, and related collagens greatly simulates the microenvironment of extracellular matrix and periosteum regeneration and ultimately promotes bone regeneration. In this study, physical and chemical characterization proved that the bionic periosteum has good flexibility and operability. The in vitro cell experiment and in vivo calvarial defect model verified that PPCL/Nd@WH biomimetic periosteum had excellent bone tissue regeneration function compared with other groups. Finally, PPCL/Nd@WH provides a new idea for the design of bionic periosteum.

The Prrx1eGFP Mouse Labels the Periosteum During Development and a Subpopulation of Osteogenic Periosteal Cells in the Adult

The identity of the cells that form the periosteum during development is controversial with current dogma suggesting these are derived from a Sox9-positive progenitor. Herein, we characterize a newly created Prrx1eGFP reporter transgenic mouse line during limb formation and postnatally. Interestingly, in the embryo Prrx1eGFP-labeled cells become restricted around the Sox9-positive cartilage anlage without themselves becoming Sox9-positive. In the adult, the Prrx1eGFP transgene live labels a subpopulation of cells within the periosteum that are enriched at specific sites, and this population is diminished in aged mice. The green fluorescent protein (GFP)-labeled subpopulation can be isolated using fluorescence-activated cell sorting (FACS) and represents approximately 8% of all isolated periosteal cells. The GFP-labeled subpopulation is significantly more osteogenic than unlabeled, GFP-negative periosteal cells. In addition, the osteogenic and chondrogenic capacity of periosteal cells in vitro can be extended with the addition of fibroblast growth factor (FGF) to the expansion media. We provide evidence to suggest that osteoblasts contributing to cortical bone formation in the embryo originate from Prrx1eGFP-positive cells within the perichondrium, which possibly piggyback on invading vascular cells and secrete new bone matrix. In summary, the Prrx1eGFP mouse is a powerful tool to visualize and isolate periosteal cells and to quantify their properties in the embryo and adult. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Skeletal stem cells: a game changer of skeletal biology and regenerative medicine?

Skeletal stem cells (SSCs) were originally discovered in the bone marrow stroma. They are capable of self-renewal and multilineage differentiation into osteoblasts, chondrocytes, adipocytes, and stromal cells. Importantly, these bone marrow SSCs localize in the perivascular region and highly express hematopoietic growth factors to create the hematopoietic stem cell (HSC) niche. Thus, bone marrow SSCs play pivotal roles in orchestrating osteogenesis and hematopoiesis. Besides the bone marrow, recent studies have uncovered diverse SSC populations in the growth plate, perichondrium, periosteum, and calvarial suture at different developmental stages, which exhibit distinct differentiation potential under homeostatic and stress conditions. Therefore, the current consensus is that a panel of region-specific SSCs collaborate to regulate skeletal development, maintenance, and regeneration. Here, we will summarize recent advances of SSCs in long bones and calvaria, with a special emphasis on the evolving concept and methodology in the field. We will also look into the future of this fascinating research area that may ultimately lead to effective treatment of skeletal disorders.

Controlled Release of Bone Morphogenetic Protein-2 Augments the Coupling of Angiogenesis and Osteogenesis for Accelerating Mandibular Defect Repair

Reconstruction of a mandibular defect is challenging, with high expectations for both functional and esthetic results. Bone morphogenetic protein-2 (BMP-2) is an essential growth factor in osteogenesis, but the efficacy of the BMP-2-based strategy on the bone regeneration of mandibular defects has not been well-investigated. In addition, the underlying mechanisms of BMP-2 that drives the bone formation in mandibular defects remain to be clarified. Here, we utilized BMP-2-loaded hydrogel to augment bone formation in a critical-size mandibular defect model in rats. We found that implantation of BMP-2-loaded hydrogel significantly promoted intramembranous ossification within the defect. The region with new bone triggered by BMP-2 harbored abundant CD31+ endomucin+ type H vessels and associated osterix (Osx)+ osteoprogenitor cells. Intriguingly, the new bone comprised large numbers of skeletal stem cells (SSCs) (CD51+ CD200+) and their multi-potent descendants (CD51+ CD105+), which were mainly distributed adjacent to the invaded blood vessels, after implantation of the BMP-2-loaded hydrogel. Meanwhile, BMP-2 further elevated the fraction of CD51+ CD105+ SSC descendants. Overall, the evidence indicates that BMP-2 may recapitulate a close interaction between functional vessels and SSCs. We conclude that BMP-2 augmented coupling of angiogenesis and osteogenesis in a novel and indispensable way to improve bone regeneration in mandibular defects, and warrants clinical investigation and application.

Bone marrow and periosteal skeletal stem/progenitor cells make distinct contributions to bone maintenance and repair

A fundamental question in bone biology concerns the contributions of skeletal stem/progenitor cells (SSCs) in the bone marrow versus the periosteum to bone repair. We found that SSCs in adult bone marrow can be identified based on Lepr^cre and Adiponectin-cre/creER expression while SSCs in adult periosteum can be identified based on Gli1^creERT2 expression. Under steady-state conditions, new bone arose primarily from bone marrow SSCs. After bone injuries, both SSC populations began proliferating but made very different contributions to bone repair. Drill injuries were primarily repaired by LepR⁺/Adiponectin⁺ bone marrow SSCs. Conversely, bicortical fractures were primarily repaired by Gli1⁺ periosteal SSCs, though LepR⁺/Adiponectin⁺ bone marrow cells transiently formed trabecular bone at the fracture site. Gli1⁺ periosteal cells also regenerated LepR⁺ bone marrow stromal cells that expressed hematopoietic niche factors at fracture sites. Different bone injuries are thus repaired by different SSCs, with periosteal cells regenerating bone and marrow stroma after non-stabilized fractures.

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.

In Vivo Bone Tissue Engineering Strategies: Advances and Prospects

Reconstruction of critical-sized bone defects remains a tremendous challenge for surgeons worldwide. Despite the variety of surgical techniques, current clinical strategies for bone defect repair demonstrate significant limitations and drawbacks, including donor-site morbidity, poor anatomical match, insufficient bone volume, bone graft resorption, and rejection. Bone tissue engineering (BTE) has emerged as a novel approach to guided bone tissue regeneration. BTE focuses on in vitro manipulations with seed cells, growth factors and bioactive scaffolds using bioreactors. The successful clinical translation of BTE requires overcoming a number of significant challenges. Currently, insufficient vascularization is the critical limitation for viability of the bone tissue-engineered construct. Furthermore, efficacy and safety of the scaffolds cell-seeding and exogenous growth factors administration are still controversial. The in vivo bioreactor principle (IVB) is an exceptionally promising concept for the in vivo bone tissue regeneration in a predictable patient-specific manner. This concept is based on the self-regenerative capacity of the human body, and combines flap prefabrication and axial vascularization strategies. Multiple experimental studies on in vivo BTE strategies presented in this review demonstrate the efficacy of this approach. Routine clinical application of the in vivo bioreactor principle is the future direction of BTE; however, it requires further investigation for overcoming some significant limitations.

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.

[Experience in using teriparatide for the treatment of postoperative hypoparathyroidism in hemodialysis patients]

The frequency of chronic postoperative hypoparathyroidism after total parathyroidectomy for secondary and tertiary hyperparathyroidism in patients with end-stage renal failure, according to various authors, can reach 20% or more. Prescribing active metabolites of vitamin D and calcium it is not always sufficient for achievement of target goals. This dictates the need for replacement therapy with recombinant parathyroid hormone. Teriparatide is the only drug of this series approved by the American Food and Drug Administration (FDA) and registered in the Russian Federation. However, it is registered as an anabolic anti-osteoporotic drug and is not indicated for the treatment of chronic hypoparathyroidism. The use of teriparatide in postoperative hypoparathyroidism in patients receiving renal replacement therapy with programmed hemodialysis in the Russian Federation has not been previously studied. Data on this issue is also limited in foreign literature. However, it is a potential treatment option for hemodialysis patients with chronic hypoparathyroidism and severe bone disorders. In this article, we present 2 clinical cases of substitution and anabolic therapy with teriparatide in this cohort of patients.

Sfrp4 and the Biology of Cortical Bone

PURPOSE OF REVIEW

Periosteal apposition and endosteal remodeling regulate cortical bone expansion and thickness, both critical determinants of bone strength. Yet, the cellular characteristics and local or paracrine factors that regulate the periosteum and endosteum remain largely elusive. Here we discuss novel insights in cortical bone growth, expansion, and homeostasis, provided by the study of Secreted Frizzled Receptor Protein 4 (Sfrp4), a decoy receptor for Wnt ligands.

RECENT FINDINGS

SFRP4 loss-of function mutations cause Pyle disease, a rare skeletal disorder characterized by cortical bone thinning and increased fragility fractures despite increased trabecular bone density. On the endosteal surface, Sfrp4-mediated repression of non-canonical Wnt signaling regulates endosteal resorption. On the periosteum, Sfrp4 identifies as a critical functional mediator of periosteal stem cell/progenitor expansion and differentiation. Analysis of signaling pathways regulating skeletal stem cells/progenitors provides an opportunity to advance our understanding of the mechanisms involved in cortical bone biology.

Lineage Differentiation Potential of Different Sources of Mesenchymal Stem Cells for Osteoarthritis Knee

Tissue engineering and regenerative medicine (TERM) have paved a way for treating musculoskeletal diseases in a minimally invasive manner. The regenerative medicine cocktail involves the usage of mesenchymal stem/stromal cells (MSCs), either uncultured or culture-expanded cells along with growth factors, cytokines, exosomes, and secretomes to provide a better regenerative milieu in degenerative diseases. The successful regeneration of cartilage depends on the selection of the appropriate source of MSCs, the quality, quantity, and frequency of MSCs to be injected, and the selection of the patient at an appropriate stage of the disease. However, confirmation on the most favorable source of MSCs remains uncertain to clinicians. The lack of knowledge in the current cellular treatment is uncertain in terms of how beneficial MSCs are in the long-term or short-term (resolution of pain) and improved quality of life. Whether MSCs treatments have any superiority, exists due to sources of MSCs utilized in their potential to objectively regenerate the cartilage at the target area. Many questions on source and condition remain unanswered. Hence, in this review, we discuss the lineage differentiation potentials of various sources of MSCs used in the management of knee osteoarthritis and emphasize the role of tissue engineering in cartilage regeneration.

Bone Healing Materials in the Treatment of Recalcitrant Nonunions and Bone Defects

The usual treatment for bone defects and recalcitrant nonunions is an autogenous bone graft. However, due to the limitations in obtaining autogenous bone grafts and the morbidity associated with their procurement, various bone healing materials have been developed in recent years. The three main treatment strategies for bone defects and recalcitrant nonunions are synthetic bone graft substitutes (BGS), BGS combined with bioactive molecules, and BGS and stem cells (cell-based constructs). Regarding BGS, numerous biomaterials have been developed to prepare bone tissue engineering scaffolds, including biometals (titanium, iron, magnesium, zinc), bioceramics (hydroxyapatite (HA)), tricalcium phosphate (TCP), biopolymers (collagen, polylactic acid (PLA), polycaprolactone (PCL)), and biocomposites (HA/MONs@miR-34a composite coating, Bioglass (BG)-based ABVF-BG (antibiotic-releasing bone void filling) putty). Bone tissue engineering scaffolds are temporary implants that promote tissue ingrowth and new bone regeneration. They have been developed to improve bone healing through appropriate designs in terms of geometric, mechanical, and biological performance. Concerning BGS combined with bioactive molecules, one of the most potent osteoinductive growth factors is bone morphogenetic proteins (BMPs). In recent years, several natural (collagen, fibrin, chitosan, hyaluronic acid, gelatin, and alginate) and synthetic polymers (polylactic acid, polyglycolic acid, polylactic-coglycolide, poly(e-caprolactone) (PCL), poly-p-dioxanone, and copolymers consisting of glycolide/trimethylene carbonate) have been investigated as potential support materials for bone tissue engineering. Regarding BGS and stem cells (cell-based constructs), the main strategies are bone marrow stromal cells, adipose-derived mesenchymal cells, periosteum-derived stem cells, and 3D bioprinting of hydrogels and cells or bioactive molecules. Currently, significant research is being performed on the biological treatment of recalcitrant nonunions and bone defects, although its use is still far from being generalized. Further research is needed to investigate the efficacy of biological treatments to solve recalcitrant nonunions and bone defects.

HIF-1α Regulates Osteogenesis of Periosteum-Derived Stem Cells Under Hypoxia Conditions via Modulating POSTN Expression

Periosteum is indispensable in bone repair and is an important source of skeletal stem cells (SSCs) for endogenous bone regeneration. However, there are only a few studies about SSCs in periosteum. The craniomaxillofacial bone regeneration is done under the hypoxia microenvironment, in which HIF-1α plays an important role. The effect of HIF-1α on periosteum-derived stem cells (PDSCs) and the mechanisms of PDSCs activation under hypoxia conditions are unknown. In this study, the calvarial bone defect was established, with the periosteum removed or retained. Results show that the bone regeneration was severely impaired in the periosteum removed group. Moreover, pluripotent PDSCs isolated from the periosteum were positive for mesenchymal stem cell (MSC) markers. To determine the role of HIF-1α, the expression of HIF-1α was knocked down in vivo and in vitro, impairing the bone regeneration or osteogenesis of PDSCs. Furthermore, the knockdown of HIF-1α expression also reduced periostin (POSTN) expression, and recombinant POSTN addition partly rescued the osteogenic inhibition. Finally, to explore the mechanism under POSTN activation, the phosphorylation level of the PI3K/AKT pathway was assessed in transfected PDSCs. The phosphorylation level of PI3K and AKT was enhanced with HIF-1α overexpression and inhibited with HIF-1α knockdown, and the addition of PI3K activator or AKT activator could partly rescue POSTN expression. In conclusion, as a potential target to promote bone repair under the hypoxia microenvironment, HIF-1α can regulate the osteogenic differentiation of PDSCs via the PI3K/AKT/POSTN pathway, which lay a solid foundation for periosteum-based craniomaxillofacial bone regeneration.

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.

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.

Understanding and utilizing textile-based electrostatic flocking for biomedical applications

Electrostatic flocking immobilizes electrical charges to the surface of microfibers from a high voltage-connected electrode and utilizes Coulombic forces to propel microfibers toward an adhesive-coated substrate, leaving a forest of aligned fibers. This traditional textile engineering technique has been used to modify surfaces or to create standalone anisotropic structures. Notably, a small body of evidence validating the use of electrostatic flocking for biomedical applications has emerged over the past several years. Noting the growing interest in utilizing electrostatic flocking in biomedical research, we aim to provide an overview of electrostatic flocking, including the principle, setups, and general and biomedical considerations, and propose a variety of biomedical applications. We begin with an introduction to the development and general applications of electrostatic flocking. Additionally, we introduce and review some of the flocking physics and mathematical considerations. We then discuss how to select, synthesize, and tune the main components (flocking fibers, adhesives, substrates) of electrostatic flocking for biomedical applications. After reviewing the considerations necessary for applying flocking toward biomedical research, we introduce a variety of proposed use cases including bone and skin tissue engineering, wound healing and wound management, and specimen swabbing. Finally, we presented the industrial comments followed by conclusions and future directions. We hope this review article inspires a broad audience of biomedical, material, and physics researchers to apply electrostatic flocking technology to solve a variety of biomedical and materials science problems.

The effect of the platelet-rich plasma on osteogenic potential of the periosteum in an animal bone defect model

Objectives

This study aims to investigate whether plasma-rich plasma (PRP) enhances the osteogenic potential of periosteal grafts used to repair bone defects and maintains both histologically and biomechanically more durable bone tissue.

Materials and methods

A standard bone defect was formed to the left femurs of 54 Sprague-Dawley rats and three groups were formed. In the first group (n=18), no periosteal repair was done for bone defect. In the second group (n=18), periosteal graft tissue was sutured to cover the defect entirely. In the third group (n=18), before periosteal repair, a 1 mL of PRP fibrin was applied into the bone defect. All femoral specimens were compared histologically at four and six weeks and biomechanically by three-point bending test at six weeks after treatment.

Results

In the PRP applied group, healing of the bone defect at four weeks was significantly better than the other groups in terms of histological new bone formation (p<0.05). At six weeks, new bone formation in both of the periosteum preserved groups was superior to the first group (p<0.05, for both). There was no statistically significant difference between the second and third groups at the end of the sixth week in the biomechanical analysis, although both groups were significantly stronger than the first group (p<0.05).

Conclusion

Stimulation of the periosteum with PRP application causes early osteogenic differentiation of precursor cells. Although, at biomechanical basis, PRP application does not create any significant difference, in the recovery of the bone defects at very early period, application of PRP may play a role to accelerate fracture healing and to decrease nonunions.

Osteogenic and Chondrogenic Potential of Periosteum-Derived Mesenchymal Stromal Cells: Do They Hold the Key to the Future?

The periosteum, with its outer fibrous and inner cambium layer, lies in a dynamic environment with a niche of pluripotent stem cells for their reparative needs. The inner cambium layer is rich in mesenchymal progenitors, osteogenic progenitors, osteoblasts, and fibroblasts in a scant collagen matrix environment. Their role in union and remodeling of fracture is well known. However, the periosteum as a source of mesenchymal stem cells has not been explored in detail. Moreover, with the continuous expansion of techniques, newer insights have been acquired into the roles and regulation of these periosteal cells. From a therapeutic standpoint, the periosteum as a source of tissue engineering has gained much attraction. Apart from its role in bone repair, analysis of the bone-forming potential of periosteum-derived stem cells is lacking. Hence, this article elucidates the role of the periosteum as a potential source of mesenchymal stem cells along with their capacity for osteogenic and chondrogenic differentiation for therapeutic application in the future.

Role of FBXW2 in explant cultures of bovine periosteum-derived cells

OBJECTIVE

Bone regeneration is a potential technique for treating osteoporosis. A previous study reported that F-box and WD-40 domain-containing protein 2 (FBXW2) localized with osteocalcin in bovine periosteum after 5 weeks of explant culture. However, the osteoblastic functions of FBXW2 remain unclear. In this study, double-fluorescent immunostaining was used to investigate the potential role of FBXW2 and its relationship with osteocalcin.

RESULTS

At day 0, FBXW2 was expressed in the cambium layer between the bone and periosteum, while osteocalcin was expressed in bone. After explant culture, changes in the periosteum were observed from weeks 1 to 7. At week 1, partial FBXW2 expression was seen with a small amount of osteocalcin. At week 2, a layer of FBXW2 was observed. From weeks 3 to 7, tube-like structures of FBXW and osteocalcin were observed, and periosteum-derived cells were released from the periosteum in areas where no FBXW2 was observed. Bovine periosteum-derived cells can form a three-dimensional cell pellet, because multilayered cell sheets are formed inside of the periosteum in vitro. It is shown that in results FBXW2 is produced in periosteal explants near sites where initial osteogenic activity is observed, suggesting that it may be involved in periosteal osteogenesis.

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

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

Cilia kinases in skeletal development and homeostasis

Primary cilia are dynamic compartments that regulate multiple aspects of cellular signaling. The production, maintenance, and function of cilia involve more than 1000 genes in mammals, and their mutations disrupt the ciliary signaling which manifests in a plethora of pathological conditions-the ciliopathies. Skeletal ciliopathies are genetic disorders affecting the development and homeostasis of the skeleton, and encompass a broad spectrum of pathologies ranging from isolated polydactyly to lethal syndromic dysplasias. The recent advances in forward genetics allowed for the identification of novel regulators of skeletogenesis, and revealed a growing list of ciliary proteins that are critical for signaling pathways implicated in bone physiology. Among these, a group of protein kinases involved in cilia assembly, maintenance, signaling, and disassembly has emerged. In this review, we summarize the functions of cilia kinases in skeletal development and disease, and discuss the available and upcoming treatment options.

Free Periosteal Flaps with Scaffold: An Overlooked Armamentarium for Maxillary and Mandibular Reconstruction

Simple Summary

Head and neck bone reconstruction with revascularized free periosteal flaps and scaffold is an overlooked option in the literature. Aim of the present paper was to systematically analyse the results of maxillary and mandibular reconstruction with this technique. We found a total of 7 studies with 55 patients fitting with our inclusion criteria. The overall rate of complications was 43.7%. The success rate intended as scaffold integration resulted to be 74.5%. Our paper therefore highlighted that maxillary and mandibular reconstruction with revascularized free periosteal flaps and scaffold is a possible alternative in patient unable to bone free flap complex reconstruction, with a success rate higher to that of other secondary options.

Abstract

Introduction: Head and neck bone reconstruction is a challenging surgical scenario. Although several strategies have been described in the literature, bone free flaps (BFFs) have become the preferred technique for large defects. Revascularized free periosteal flaps (FPFs) with support scaffold represents a possible alternative in compromised patient, BFF failure, or relapsing cancers as salvage treatment. However, only few clinical applications in head and neck are reported in literature. Purpose of the study was to systematically analyse the results of functional and oncologic maxillary and mandibular reconstruction with FPF with scaffold. Materials and Methods: A comprehensive review of the dedicated literature was performed according to the PRISMA guidelines searching on Scopus, PubMed/MEDLINE, Cochrane Library, Embase, Researchgate and Google Scholar databases using relevant keywords, phrases and medical subject headings (MeSH) terms. An excursus on the most valuable FPF’ harvesting sites was also carried out. Results: A total of 7 studies with 55 patients were included. Overall, the majority of the patients (n = 54, 98.1%) underwent an FPF reconstruction of the mandibular site. The most used technique was the radial forearm FPF with autologous frozen bone as scaffold (n = 40, 72.7%). The overall rate of complications was 43.7%. The success rate intended as scaffold integration resulted to be 74.5%. Conclusions: Maxillary and mandibular reconstruction with FPF and scaffold is a possible alternative in patient unfit for complex BFF reconstruction and it should be considered as a valid alternative in the sequential salvage surgery for locally advanced cancer. Moreover, it opens future scenarios in head and neck reconstructive surgery, as a promising tool that can be modelled to tailor complex 3D defects, with less morbidities to the donor site.

Mouse Periosteal Cell Culture, in vitro Differentiation, and in vivo Transplantationin Tibial Fractures

The periosteum covering the outer surface of bone contains skeletal stem/progenitor cells that can efficiently form cartilage and bone during bone repair. Several methods have been described to isolate periosteal cells based on bone scraping and/or enzymatic digestion. Here, we describe an explant culture method to isolate periosteum-derived stem/progenitor cells for subsequent in vitro and in vivo analyses. Periosteal cells (PCs) isolated using this protocol express mesenchymal markers, can be expanded in vitro, and exhibit high regenerative potential after in vivo transplantation at a fracture site, suggesting that this protocol can be employed for PC production to use in new cell-based therapies.

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.

Isolation and Culture of Periosteum-Derived Progenitor Cells from Mice

This chapter describes the methods of isolation of mouse periosteal progenitor cells. There are three basic methods utilized. The bone grafting method was developed utilizing the fracture healing process to expand the progenitor populations. Bone capping methods requires enzymatic digestion and purification of cells from the native periosteum, while the Egression/Explant method requires the least manipulation with placement of cortical bone fragments with attached periosteum in a culture dish. Various cell surface antibodies have been employed over the years to characterize periosteum derived progenitor cells, but the most consistent minimal criteria was recommended by the International Society for Cellular Therapy. Confirmation of the multipotent status of these isolated cells can be achieved by differentiation into the three basic mesodermal lineages in vitro.

Postradiation Fractures after Combined Modality Treatment in Extremity Soft Tissue Sarcomas

Soft tissue sarcoma (STS) of the extremities is typically treated with limb-sparing surgery and radiation therapy; with this treatment approach, high local control rates can be achieved. However, postradiation bone fractures, fractures occurring in the prior radiation field with minimal or no trauma, are a serious late complication that occurs in 2–22% of patients who receive surgery and radiation for STS. Multiple risk factors for sustaining a postradiation fracture exist, including high radiation dose, female sex, periosteal stripping, older age, femur location, and chemotherapy administration. The treatment of these pathological fractures can be difficult, with complications including delayed union, nonunion, and infection posing particular challenges. Here, we review the mechanisms, risk factors, and treatment challenges associated with postradiation fractures in STS patients.

Diabetes impairs periosteal progenitor regenerative potential

Diabetics are at increased risk for fracture, and experience severely impaired skeletal healing characterized by delayed union or nonunion of the bone. The periosteum harbors osteochondral progenitors that can differentiate into chondrocytes and osteoblasts, and this connective tissue layer is required for efficient fracture healing. While bone marrow-derived stromal cells have been studied extensively in the context of diabetic skeletal repair and osteogenesis, the effect of diabetes on the periosteum and its ability to contribute to bone regeneration has not yet been explicitly evaluated. Within this study, we utilized an established murine model of type I diabetes to evaluate periosteal cell differentiation capacity, proliferation, and availability under the effect of a diabetic environment. Periosteal cells from diabetic mice were deficient in osteogenic differentiation ability in vitro, and diabetic mice had reduced periosteal populations of mesenchymal progenitors with a corresponding reduction in proliferation capacity following injury. Additionally, fracture callus mineralization and mature osteoblast activity during periosteum-mediated healing was impaired in diabetic mice compared to controls. We propose that the effect of diabetes on periosteal progenitors and their ability to aid in skeletal repair directly impairs fracture healing.

Comparison of the Translational Potential of Human Mesenchymal Progenitor Cells from Different Bone Entities for Autologous 3D Bioprinted Bone Grafts

Reconstruction of segmental bone defects by autologous bone grafting is still the standard of care but presents challenges including anatomical availability and potential donor site morbidity. The process of 3D bioprinting, the application of 3D printing for direct fabrication of living tissue, opens new possibilities for highly personalized tissue implants, making it an appealing alternative to autologous bone grafts. One of the most crucial hurdles for the clinical application of 3D bioprinting is the choice of a suitable cell source, which should be minimally invasive, with high osteogenic potential, with fast, easy expansion. In this study, mesenchymal progenitor cells were isolated from clinically relevant human bone biopsy sites (explant cultures from alveolar bone, iliac crest and fibula; bone marrow aspirates; and periosteal bone shaving from the mastoid) and 3D bioprinted using projection-based stereolithography. Printed constructs were cultivated for 28 days and analyzed regarding their osteogenic potential by assessing viability, mineralization, and gene expression. While viability levels of all cell sources were comparable over the course of the cultivation, cells obtained by periosteal bone shaving showed higher mineralization of the print matrix, with gene expression data suggesting advanced osteogenic differentiation. These results indicate that periosteum-derived cells represent a highly promising cell source for translational bioprinting of bone tissue given their superior osteogenic potential as well as their minimally invasive obtainability.

Bone tissue engineering in the greater omentum with computer-aided design/computer-aided manufacturing scaffolds is enhanced by a periosteum transplant

Aim: This study aimed to evaluate two different vascularized bone flap scaffolds and the impact of two barrier membranes for the reconstruction of critical-size bone defects. Materials & methods: 3D-printed scaffolds of biodegradable calcium phosphate and bioinert titanium were loaded with rhBMP-2 bone marrow aspirate, wrapped by a collagen membrane or a periosteum transplant and implanted into the greater omentum of miniature pigs. Results: Histological evaluation demonstrated significant bone formation within the first 8 weeks in both scaffolds. The periosteum transplant led to enhanced bone formation and a homogenous distribution in the scaffolds. The omentum tissue grew out a robust vascular supply. Conclusion: Endocultivation using 3D-printed scaffolds in the greater omentum is a very promising approach in defect-specific bone tissue regeneration.

Sensory denervation increases potential of bisphosphonates to induce osteonecrosis via disproportionate expression of calcitonin gene-related peptide and substance P

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a serious side effect of systematic administration of bisphosphonates (BPs). Sensory innervation is crucial for bone healing. We established inferior alveolar nerve injury (IANI) and inferior alveolar nerve transection (IANT) models characterized by disorganized periosteum, increased osteoclasts, and unbalanced neuropeptide expression. Zoledronate injection disrupted neuropeptide expression in the IANI and IANT models by decreasing calcitonin gene-related peptide (CGRP) and increasing substance P (SP); associated with this, BRONJ prevalence was significantly higher in the IANT model, followed by the IANI model and the sham control. CGRP treatment significantly reduced BRONJ occurrence, whereas SP administration had the opposite effect. In vitro, RAW 264.7 cells were treated with BPs and then CGRP and/or SP to study changes in zoledronate toxicity; combined application of CGRP and SP decreased zoledronate toxicity, whereas CGRP or SP applied alone showed no effects. These results demonstrate that sensory denervation facilitates the occurrence of BRONJ and that CGRP used therapeutically may prevent BRONJ progression, provided that SP is also present. Further studies are necessary to determine the optimal ratio of CGRP to SP for promoting bone healing and to uncover the mechanism by which CGRP and SP cooperate.