Evidence for multi-fragmentation and mass shedding of boulders on rubble-pile binary asteroid system (65803) Didymos.

Asteroids smaller than 10 km are thought to be rubble piles formed from the reaccumulation of fragments produced in the catastrophic disruption of parent bodies. Ground-based observations reveal that some of these asteroids are today binary systems, in which a smaller secondary orbits a larger primary asteroid. However, how these asteroids became binary systems remains unclear. Here, we report the analysis of boulders on the surface of the stony asteroid (65803) Didymos and its moonlet, Dimorphos, from data collected by the NASA DART mission. The size-frequency distribution of boulders larger than 5 m on Dimorphos and larger than 22.8 m on Didymos confirms that both asteroids are piles of fragments produced in the catastrophic disruption of their progenitors. Dimorphos boulders smaller than 5 m have size best-fit by a Weibull distribution, which we attribute to a multi-phase fragmentation process either occurring during coalescence or during surface evolution. The density per km2 of Dimorphos boulders ≥1 m is 2.3x with respect to the one obtained for (101955) Bennu, while it is 3.0x with respect to (162173) Ryugu. Such values increase once Dimorphos boulders ≥5 m are compared with Bennu (3.5x), Ryugu (3.9x) and (25143) Itokawa (5.1x). This is of interest in the context of asteroid studies because it means that contrarily to the single bodies visited so far, binary systems might be affected by subsequential fragmentation processes that largely increase their block density per km2. Direct comparison between the surface distribution and shapes of the boulders on Didymos and Dimorphos suggest that the latter inherited its material from the former. This finding supports the hypothesis that some asteroid binary systems form through the spin up and mass shedding of a fraction of the primary asteroid.

Fast boulder fracturing by thermal fatigue detected on stony asteroids.

Spacecraft observations revealed that rocks on carbonaceous asteroids, which constitute the most numerous class by composition, can develop millimeter-to-meter-scale fractures due to thermal stresses. However, signatures of this process on the second-most populous group of asteroids, the S-complex, have been poorly constrained. Here, we report observations of boulders' fractures on Dimorphos, which is the moonlet of the S-complex asteroid (65803) Didymos, the target of NASA's Double Asteroid Redirection Test (DART) planetary defense mission. We show that the size-frequency distribution and orientation of the mapped fractures are consistent with formation through thermal fatigue. The fractures' preferential orientation supports that these have originated in situ on Dimorphos boulders and not on Didymos boulders later transferred to Dimorphos. Based on our model of the fracture propagation, we propose that thermal fatigue on rocks exposed on the surface of S-type asteroids can form shallow, horizontally propagating fractures in much shorter timescales (100 kyr) than in the direction normal to the boulder surface (order of Myrs). The presence of boulder fields affected by thermal fracturing on near-Earth asteroid surfaces may contribute to an enhancement in the ejected mass and momentum from kinetic impactors when deflecting asteroids.

The Dimorphos ejecta plume properties revealed by LICIACube.

The Double Asteroid Redirection Test (DART) had an impact with Dimorphos (a satellite of the asteroid Didymos) on 26 September 20221. Ground-based observations showed that the Didymos system brightened by a factor of 8.3 after the impact because of ejecta, returning to the pre-impact brightness 23.7 days afterwards2. Hubble Space Telescope observations made from 15 minutes after impact to 18.5 days after, with a spatial resolution of 2.1 kilometres per pixel, showed a complex evolution of the ejecta3, consistent with other asteroid impact events. The momentum enhancement factor, determined using the measured binary period change4, ranges between 2.2 and 4.9, depending on the assumptions about the mass and density of Dimorphos5. Here we report observations from the LUKE and LEIA instruments on the LICIACube cube satellite, which was deployed 15 days in advance of the impact of DART. Data were taken from 71 seconds before the impact until 320 seconds afterwards. The ejecta plume was a cone with an aperture angle of 140 ± 4 degrees. The inner region of the plume was blue, becoming redder with increasing distance from Dimorphos. The ejecta plume exhibited a complex and inhomogeneous structure, characterized by filaments, dust grains and single or clustered boulders. The ejecta velocities ranged from a few tens of metres per second to about 500 metres per second.

Characterization of the Protein Corona of Three Chairside Hemoderivatives on Melt Electrowritten Polycaprolactone Scaffolds.

In tissue engineering, the relationship between a biomaterial surface and the host's immune response during wound healing is crucial for tissue regeneration. Despite hemoderivative functionalization of biomaterials becoming a common tissue-engineering strategy for enhanced regeneration, the characteristics of the protein-biomaterial interface have not been fully elucidated. This study characterized the interface formed by the adsorbed proteins from various hemoderivatives with pristine and calcium phosphate (CaP)-coated polycaprolactone (PCL) melt electrowritten scaffolds. PCL scaffolds were fabricated by using melt electrospinning writing (MEW). Three hemoderivatives (pure platelet-rich plasma (P-PRP), leucocyte platelet-rich plasma (L-PRP) and injectable platelet-rich fibrin (i-PRF)) and total blood PLASMA (control) were prepared from ovine blood. Hemoderivatives were characterized via SEM/EDX, cross-linking assay, weight loss, pH and protein quantification. The interface between PCL/CaP and hemoderivative was examined via FTIR, XPS and electrophoresis. i-PRF/PCL-CaP (1653 cm-1), PLASMA/PCL-CaP (1652 cm-1) and i-PRF/PCL (1651 cm-1) demonstrated a strong signal at the Amide I region. PLASMA and i-PRF presented similar N1s spectra, with most of the nitrogen involved in N-C=O bonds (≈400 eV). i-PRF resulted in higher adsorption of low molecular weight (LMW) proteins at 60 min, while PLASMA exhibited the lowest adsorption. L-PRP and P-PRP had a similar pattern of protein adsorption. The characteristics of biomaterial interfaces can be customized, thus creating a specific hemoderivative-defined layer on the PCL surface. i-PRF demonstrated a predominant adsorption of LMW proteins. Further investigation of hemoderivative functionalized biomaterials is required to identify the differential protein corona composition, and the resultant immune response and regenerative capacity.

Oral health research funding in relation to disease burden in Australia.

BACKGROUND: This study aims to investigate and compare the major Australian government research funding schemes for oral health science with other disciplines from the burden of disease perspective. METHODS: Major government research funding scheme outcomes were identified. An innovative index of Fair Research Funding (FRF) was developed to examine the extent to which National Health and Medical Research Council funding is aligned with the disease burden. In addition to comparing different diseases, overall governmental research funding for different areas of oral health sciences was explored. RESULTS: Oral disorders with $15 million NHMRC grant funds (2017-2021) and FRF of 10.7 has the lowest and most inequitable amount of Australian government support in relation to disease burden. The share of oral health science in the Australian Research Council and Medical Research Future Fund was very minimal, with $3.43 and $1.88 million respectively. CONCLUSION: Governmental research funding for oral health sciences is inequitable according to the disease burden. More dedicated oral health sciences research funding schemes are essential. Funding for prevention-focused public oral health programmes is a vital requirement towards reducing the inequalities in population oral health.

Inner southern magnetosphere observation of Mercury via SERENA ion sensors in BepiColombo mission.

Mercury's southern inner magnetosphere is an unexplored region as it was not observed by earlier space missions. In October 2021, BepiColombo mission has passed through this region during its first Mercury flyby. Here, we describe the observations of SERENA ion sensors nearby and inside Mercury's magnetosphere. An intermittent high-energy signal, possibly due to an interplanetary magnetic flux rope, has been observed downstream Mercury, together with low energy solar wind. Low energy ions, possibly due to satellite outgassing, were detected outside the magnetosphere. The dayside magnetopause and bow-shock crossing were much closer to the planet than expected, signature of a highly eroded magnetosphere. Different ion populations have been observed inside the magnetosphere, like low latitude boundary layer at magnetopause inbound and partial ring current at dawn close to the planet. These observations are important for understanding the weak magnetosphere behavior so close to the Sun, revealing details never reached before.

Resorbable additively manufactured scaffold imparts dimensional stability to extraskeletally regenerated bone.

Dimensionally stable vertical bone regeneration outside of the existing bony envelope is a major challenge in the field of orofacial surgery. In this study, we demonstrate that a highly porous, resorbable scaffold fabricated using additive manufacturing techniques enables reproducible extra-skeletal bone formation and prevents bone resorption. An additively manufactured medical grade polycaprolactone (mPCL) biphasic scaffold mimicking the architecture of the jaw bone, consisting of a 3D-printed outer shell overlying an inner highly porous melt electrowritten scaffold, was assessed for its ability to support dimensionally stable bone regeneration in an extraskeletal ovine calvarial model. To investigate bone formation capacity (stage 1), 7 different constructs placed under a protective dome were assessed 8 weeks post-implantation: Empty control, Biphasic scaffold with hydrogel (PCL-Gel), PCL-Gel with 75 or 150 µg of BMP-2 (PCL-BMP-75 and PCL-BMP-150), hydrogel only (Gel), Gel containing 75 or 150 µg of BMP-2 (Gel-BMP-75 and Gel-BMP-150). To assess dimensional stability (stage 2), in a separate cohort, 5 animals were similarly implanted with 2 samples of each of the Gel-BMP-150 and PCL-BMP-150 groups, and after 8 weeks of healing, the protective domes were removed and titanium implants were placed in the regenerated bone and allowed to heal for a further 8 weeks. Bone formation and osseointegration were assessed using micro-computed tomography, histology and histomorphometry. In stage 1, enhanced bone formation was found in the BMP-2 containing groups, especially the PCL-BMP constructs whereby regeneration of full bone height was achieved in a reproducible manner. There was no significant bone volume increase with the higher dose of BMP-2. In the dimensional stability assessment (stage 2), after the rtemoval of the protective dome, the biphasic scaffold prevented bone resorption whereas in the absence of the scaffold, the bone previously formed in the hydrogel underwent extensive resorption. This was attributed to the space maintenance properties and dimensional stability of the biphasic scaffold. Titanium implants osseointegrated into the newly formed bone within the biphasic scaffolds. In conclusion, additively manufactured biphasic scaffolds functionalized with BMP-2 facilitated dimensionally stable bone regeneration that supported dental implant osseointegration.

SERENA: Particle Instrument Suite for Determining the Sun-Mercury Interaction from BepiColombo.

The ESA-JAXA BepiColombo mission to Mercury will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric particle dynamics at Mercury as well as their interactions with solar wind, solar radiation, and interplanetary dust. The particle instrument suite SERENA (Search for Exospheric Refilling and Emitted Natural Abundances) is flying in space on-board the BepiColombo Mercury Planetary Orbiter (MPO) and is the only instrument for ion and neutral particle detection aboard the MPO. It comprises four independent sensors: ELENA for neutral particle flow detection, Strofio for neutral gas detection, PICAM for planetary ions observations, and MIPA, mostly for solar wind ion measurements. SERENA is managed by a System Control Unit located inside the ELENA box. In the present paper the scientific goals of this suite are described, and then the four units are detailed, as well as their major features and calibration results. Finally, the SERENA operational activities are shown during the orbital path around Mercury, with also some reference to the activities planned during the long cruise phase.

Developing a prototype for integrated dental and diabetes care: understanding needs and priorities.

BACKGROUND: Periodontal treatment may be a useful adjunct to medical management of diabetes; however, oral health has not been integrated into multidisciplinary diabetes care in Australia. This study aimed to understand the needs of patients and staff at a diabetes clinic to inform a prototype of integrated dental and diabetes care. METHODS: Quantitative and qualitative data were collected from patients and staff at West Moreton Diabetes Clinic (WMDC) between September-October 2019. Clinical information, survey responses and dental screening results were analysed for 41 patients. Semi-structured interviews were held with six patients and a focus group with seven staff. RESULTS: Most patients (83%) had not seen a dentist in the previous year. Of the 37 patients with remaining natural teeth, 84% required periodontal assessment and 46% had multiple carious lesions. Unmet treatment needs and rates of access were similar for private and public dental patients. Staff and patients reported high levels of support for incorporation of dental care at WMDC. CONCLUSIONS: Integrating oral health into diabetes management is well-supported by patients and staff to address significant unmet dental needs for both public and private dental patients. Incorporating dental screening/services within diabetes clinics may increase uptake and improve awareness of its importance in diabetes management.

An overview of decellularisation techniques of native tissues and tissue engineered products for bone, ligament and tendon regeneration.

Decellularised tissues and organs have been successfully used in a variety of tissue engineering/regenerative medicine applications. Because of the complexity of each tissue (size, porosity, extracellular matrix (ECM) composition etc.), there is no standardised protocol and the decellularisation methods vary widely, thus leading to heterogeneous outcomes. Physical, chemical, and enzymatic methods have been developed and optimised for each specific application and this review describes the most common strategies utilised to achieve decellularisation of soft and hard tissues. While removal of the DNA is the primary goal of decellularisation, it is generally achieved at the expense of ECM preservation due to the harsh chemical or enzymatic processing conditions. As denaturation of the native ECM has been associated with undesired host responses, decellularisation conditions aimed at effectively achieving simultaneous DNA removal and minimal ECM damage will be highlighted. Additionally, the utilisation of decellularised matrices in regenerative medicine is explored, as are the most recent strategies implemented to circumvent challenges in this field. In summary, this review focusses on the latest advancements and future perspectives in the utilisation of natural ECM for the decoration of synthetic porous scaffolds.

Periodontal Tissue Engineering with a Multiphasic Construct and Cell Sheets.

This study reports on scaffold-based periodontal tissue engineering in a large preclinical animal model. A biphasic scaffold consisting of bone and periodontal ligament compartments manufactured by melt and solution electrospinning, respectively, was used for the delivery of in vitro matured cell sheets from 3 sources: gingival cells (GCs), bone marrow-derived mesenchymal stromal cells (Bm-MSCs), and periodontal ligament cells (PDLCs). The construct featured a 3-dimensional fibrous bone compartment with macroscopic pore size, while the periodontal compartment consisted of a flexible porous membrane for cell sheet delivery. The regenerative performance of the constructs was radiographically and histologically assessed in surgically created periodontal defects in sheep following 5 and 10 wk of healing. Histologic observation demonstrated that the constructs maintained their shape and volume throughout the entirety of the in vivo study and were well integrated with the surrounding tissue. There was also excellent tissue integration between the bone and periodontal ligament compartments as well as the tooth root interface, enabling the attachment of periodontal ligament fibers into newly formed cementum and bone. Bone coverage along the root surface increased between weeks 5 and 10 in the Bm-MSC and PDLC groups. At week 10, the micro-computed tomography results showed that the PDLC group had greater bone fill as compared with the empty scaffold, while the GC group had less bone than the 3 other groups (control, Bm-MSC, and PDLC). Periodontal regeneration, as measured by histologically verified new bone and cementum formation with obliquely inserted periodontal ligament fibers, increased between 5 and 10 wk for the empty, Bm-MSC, and PDLC groups, while the GC group was inferior to the Bm-MSC and PDLC groups at 10 wk. This study demonstrates that periodontal regeneration can be achieved via the utilization of a multiphasic construct, with Bm-MSCs and PDLCs obtaining superior results as compared with GC-derived cell sheets.

Pro-osteogenic properties of hydrophilic and hydrophobic titanium surfaces: Crosstalk between signalling pathways in in vivo models.

BACKGROUND: It is now generally accepted that the response to a particular signal, such as the surgical trauma following implant placement, is not the result of a single linear signalling pathway, but rather reflects pathway integration, which can occur at multiple levels. Although it is well documented that both SLA and SLActive surfaces are able to promote bone formation and osseointegration, it is still unclear which are the key signalling pathways involved and how surface hydrophilicity/hydrophobicity might affect pathway integration. OBJECTIVE: To combine gene and protein data from in vivo studies applying titanium hydrophobic (Sandblasting, Large-grit, Acid-etching, SLA) and hydrophilic (SLActive) surfaces to understand the molecular mechanisms responsible for the pro-osteogenic properties of these surfaces. METHODS: The Kyoto Encyclopedia of Genes and Genomes (KEGG® ) pathway database and the Ingenuity® Pathway Analysis (IPA® ) software were applied to the genomic and proteomic data of previous in vivo studies applying SLA and SLActive surfaces, with the specific aim to focus on bone formation-related signalling pathways. While gene data were derived from a human study on osseointegration, protein data originated from a preclinical study in rabbits. Data were available for the 4, 7 and 14 days of healing periods. RESULTS: Both genomic and proteomic data showed that the osteogenesis process takes place mainly at 7 and 14 days of healing on both SLA and SLActive surfaces. Surface hydrophilicity enhances bone formation at multiple levels, by directly promoting an earlier expression of pathways involved in cell proliferation and osteoblast precursor differentiation (eg, mitogen-activated protein kinase, phosphoinositide-3 kinase-AKT, Wnt, Notch, transforming growth factor-ß), but also by positively regulating angiogenesis, bone mineralization and bone remodelling. CONCLUSION: This study combined, for the first time, different 'omics' outputs to get new insights on the molecular mechanisms behind the influence of surface hydrophilicity on osseointegration/bone formation. Specific signalling pathways, such as Wnt, vascular endothelial growth factor and mitogen-activated protein kinase, were identified as differentially modulated by titanium surface hydrophilicity both at a genomic and proteomic level. These findings may be used in the future to monitor/predict the bone formation/osseointegration process, or as a screening tool towards the manufacture of new pro-osteogenic implant surfaces. In order to take into account the full complexity and interplay of cell signalling during bone formation, powerful bioinformatics tools integrating different 'omics' data and predicting signalling pathways trends should be applied by future studies.

Osteonecrosis of the jaws: a 14-year retrospective survey of hospital admissions.

BACKGROUND: Osteonecrosis of the jaw (ONJ) is a serious complication of both radiation and antiresorptive therapies. This study aimed to determine how many patients have been treated for medication-related osteonecrosis of the jaws (MRONJ) and osteoradionecrosis (ORN), and whether the number of diagnoses has decreased over time with improved awareness and preventative measures. METHODS: Medical records at the Royal Brisbane and Women's Hospital, Gold Coast University Hospital and Robina Hospital were reviewed to identify patients diagnosed with MRONJ and ORN between January 2003 and May 2017. Data on patient demographics, year of admission and primary disease were analysed. RESULTS: Two hundred and thirty-eight patients were diagnosed with ONJ, of which 74.4% were ORN and 25.6% were MRONJ. Tongue (24.6%), floor of mouth (17.3%) and tonsillar (15.1%) squamous cell carcinomas were the most common primary diseases associated with ORN, with a strong male predominance (80%). Of patients diagnosed with MRONJ, 52.5% were taking low-dose antiresorptives for osteoporosis (44.2%), rheumatoid arthritis (4.6%) or Paget's disease (3.3%), while 47.5% were oncology patients receiving high-dose antiresorptives. CONCLUSIONS: The number of patients diagnosed with MRONJ and ORN has trended upwards since 2003. ORN affected three times more patients than MRONJ, and patients on low-dose antiresorptives accounted for over half of the MRONJ cases.

Risk factors for medication-related osteonecrosis of the jaws: A systematic review.

The purpose of this study was to identify the patient populations at risk of medication-related osteonecrosis of the jaw (MRONJ) and determine which medical and dental comorbidities are significant risk factors for this disease. An electronic search of Embase, MEDLINE, Cochrane Central Register of Controlled Trials, WHO International Clinical Trials Registry Platform and ProQuest Dissertations and Theses Global was conducted to identify all human studies that reported risk factors for MRONJ. Only a qualitative analysis was performed due to significant heterogeneity in the collected data. The search strategy identified 2872 records, of which 219 studies were eligible for inclusion. A total of 4106 patients with MRONJ were identified, 39 different systemic diseases were implicated, and 14 medical and 11 dental risk factors were reported, although no statistical analysis of the significance of each of these factors was possible. The clinical reach of MRONJ may be wider than anticipated, and more data on the significance of each potential risk factor are needed to guide the identification and management of at-risk patients.

Melatonin as a pro-osteogenic agent in oral implantology: a systematic review of histomorphometric outcomes in animals and quality evaluation using ARRIVE guidelines.

The aim of this review was to evaluate the outcomes of preclinical trials that assessed the use of melatonin as a pro-osteogenic agent in the field of oral implantology. Melatonin is a hormone that has been shown to have beneficial antioxidant and bone-metabolic effects. A number of experimental studies have analysed its effect in promoting osseointegration around dental implants in animals. A bibliographic search in PubMed, Scopus and EBSCOhost was performed. Animal studies that quantitatively analysed the pro-osteogenic effect of melatonin were included. Quality assessment of the included studies was performed using the ARRIVE guidelines. Eight studies met the inclusion criteria. The experimental animals used were dogs, rabbits and rats. Melatonin was used in a lyophilized powdered form, an injectable form or as a dipping solution. Six of the eight studies included showed a statistically significant positive effect of melatonin on bone-implant contact and various other histomorphometric parameters. The ARRIVE criteria were generally well reported by the included studies (17.5 ± 1.60/24), although several criteria (including randomization and blinding) were poorly documented, with most of the studies showing a high/unclear risk of bias. The majority of the studies included showed a statistically significant positive effect of melatonin on bone formation around implants. However, the clinical significance of this effect was unclear given the high/unclear risk of bias in the majority of included studies. Given the limited amount of data available, further research should be conducted to evaluate the clinical potential of this pineal hormone in clinically relevant situations, such as compromised sites or patients.

Tissue engineered periodontal products.

Attainment of periodontal regeneration is a significant clinical goal in the management of advanced periodontal defects arising from periodontitis. Over the past 30 years numerous techniques and materials have been introduced and evaluated clinically and have included guided tissue regeneration, bone grafting materials, growth and other biological factors and gene therapy. With the exception of gene therapy, all have undergone evaluation in humans. All of the products have shown efficacy in promoting periodontal regeneration in animal models but the results in humans remain variable and equivocal concerning attaining complete biological regeneration of damaged periodontal structures. In the early 2000s, the concept of tissue engineering was proposed as a new paradigm for periodontal regeneration based on molecular and cell biology. At this time, tissue engineering was a new and emerging field. Now, 14 years later we revisit the concept of tissue engineering for the periodontium and assess how far we have come, where we are currently situated and what needs to be done in the future to make this concept a reality. In this review, we cover some of the precursor products, which led to our current position in periodontal tissue engineering. The basic concepts of tissue engineering with special emphasis on periodontal tissue engineering products is discussed including the use of mesenchymal stem cells in bioscaffolds and the emerging field of cell sheet technology. Finally, we look into the future to consider what CAD/CAM technology and nanotechnology will have to offer.

Induced Pluripotent Stem Cells: A New Frontier for Stem Cells in Dentistry.

Induced pluripotent stem cells (iPSCs) are the newest member of a growing list of stem cell populations that hold great potential for use in cell-based treatment approaches in the dental field. This review summarizes the dental tissues that have successfully been utilized to generate iPSC lines, as well as the potential uses of iPSCs for tissue regeneration in different dental applications. While iPSCs display great promise in a number of dental applications, there are safety concerns with these cells that need to be addressed before they can be used in clinical settings. This review outlines some of the apprehensions to the use of iPSCs clinically, and it details approaches that are being employed to ensure the safety and efficacy of these cells. One of the major approaches being investigated is the differentiation of iPSCs prior to use in patients. iPSCs have successfully been differentiated into a wide range of cells and tissue types. This review focuses on 2 differentiation approaches-the differentiation of iPSCs into mesenchymal stem cells and the differentiation of iPSCs into osteoprogenitor cells. Both these resulting populations of cells are particularly relevant to the dental field.

Three-Dimensional Bioprinting for Regenerative Dentistry and Craniofacial Tissue Engineering.

Craniofacial tissues are organized with complex 3-dimensional (3D) architectures. Mimicking such 3D complexity and the multicellular interactions naturally occurring in craniofacial structures represents one of the greatest challenges in regenerative dentistry. Three-dimensional bioprinting of tissues and biological structures has been proposed as a promising alternative to address some of these key challenges. It enables precise manufacture of various biomaterials with complex 3D architectures, while being compatible with multiple cell sources and being customizable to patient-specific needs. This review describes different 3D bioprinting methods and summarizes how different classes of biomaterials (polymer hydrogels, ceramics, composites, and cell aggregates) may be used for 3D biomanufacturing of scaffolds, as well as craniofacial tissue analogs. While the fabrication of scaffolds upon which cells attach, migrate, and proliferate is already in use, printing of all the components that form a tissue (living cells and matrix materials together) to produce tissue constructs is still in its early stages. In summary, this review seeks to highlight some of the key advantages of 3D bioprinting technology for the regeneration of craniofacial structures. Additionally, it stimulates progress on the development of strategies that will promote the translation of craniofacial tissue engineering from the laboratory bench to the chair side.

Decellularized periodontal ligament cell sheets with recellularization potential.

The periodontal ligament is the key tissue facilitating periodontal regeneration. This study aimed to fabricate decellularized human periodontal ligament cell sheets for subsequent periodontal tissue engineering applications. The decellularization protocol involved the transfer of intact human periodontal ligament cell sheets onto melt electrospun polycaprolactone membranes and subsequent bi-directional perfusion with NH4OH/Triton X-100 and DNase solutions. The protocol was shown to remove 92% of DNA content. The structural integrity of the decellularized cell sheets was confirmed by a collagen quantification assay, immunostaining of human collagen type I and fibronectin, and scanning electron microscopy. ELISA was used to demonstrate the presence of residual basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and hepatocyte growth factor (HGF) in the decellularized cell sheet constructs. The decellularized cell sheets were shown to have the ability to support recellularization by allogenic human periodontal ligament cells. This study describes the fabrication of decellularized periodontal ligament cell sheets that retain an intact extracellular matrix and resident growth factors and can support repopulation by allogenic cells. The decellularized hPDL cell sheet concept has the potential to be utilized in future "off-the-shelf" periodontal tissue engineering strategies.

Multiphasic scaffolds for periodontal tissue engineering.

For a successful clinical outcome, periodontal regeneration requires the coordinated response of multiple soft and hard tissues (periodontal ligament, gingiva, cementum, and bone) during the wound-healing process. Tissue-engineered constructs for regeneration of the periodontium must be of a complex 3-dimensional shape and adequate size and demonstrate biomechanical stability over time. A critical requirement is the ability to promote the formation of functional periodontal attachment between regenerated alveolar bone, and newly formed cementum on the root surface. This review outlines the current advances in multiphasic scaffold fabrication and how these scaffolds can be combined with cell- and growth factor-based approaches to form tissue-engineered constructs capable of recapitulating the complex temporal and spatial wound-healing events that will lead to predictable periodontal regeneration. This can be achieved through a variety of approaches, with promising strategies characterized by the use of scaffolds that can deliver and stabilize cells capable of cementogenesis onto the root surface, provide biomechanical cues that encourage perpendicular alignment of periodontal fibers to the root surface, and provide osteogenic cues and appropriate space to facilitate bone regeneration. Progress on the development of multiphasic constructs for periodontal tissue engineering is in the early stages of development, and these constructs need to be tested in large animal models and, ultimately, human clinical trials.