What do COVID-19 Tweets Reveal about Public Engagement with Nature of Science?

Using the social media platform Twitter, this study explores public reference to "scientific method(s)" in tweets specifically pertaining to COVID-19 posted between January and June 2020. The study focuses on three research questions: When did reference to scientific methods peak, which aspects of nature of science (NOS) do these tweets address, and the extent to which Twitter users' sentiments provide useful information about their attitudes towards the scientific method. COVID-19 tweets were mined and queried using "scientific method(s)" as a keyword. A content analysis using the Family Resemblance Approach (FRA) to NOS and a non-computational sentiment analysis were conducted on the obtained data set. The findings revealed that tweets using science method(s) peaked most during the months of April and May, as more information was being communicated about promising treatments and vaccine development. Most tweets were assigned multiple FRA categories. The sentiment analysis revealed that attitude towards the scientific method was predominantly supportive. Discussion of three events that were observed in clusters of tweets provided additional context. The paper concludes by noting the methodological affordances and limitations of applying the FRA for identifying NOS-related content in Twitter environments and underscoring the potential of targeted NOS messaging in promoting informed discussions about NOS in the public sphere.

An antioxidant stabilized, chemically cross-linked UHMWPE with superior toughness.

Chemical cross-linking of ultrahigh molecular weight polyethylene (UHMWPE) using an organic peroxide followed by high temperature melting results in a large increase in toughness accompanied by a decrease in cross-link density, which, surprisingly does not compromise the wear resistance. We compared the mechanical properties and wear behavior of a vitamin E blended, chemically cross-linked and high temperature melted UHMWPE produced by ram extrusion (PRX HTM) to those measured with the clinically available 100-kGy irradiated and melted UHMWPE (CISM 100). We also assessed the local biocompatibility of PRX-HTM in rabbit subcutaneous pouch and osteochondral defect models. The ultimate tensile strength and pin-on-disc wear rate were similar to CISM 100; whereas the elongation-at-break and impact toughness were much higher with PRX-HTM. The stress intensity factor range at crack inception was also higher with PRX-HTM. Accelerated aging did not result in any measurable oxidation or changes in mechanical properties. Hip simulator wear rate of acetabular liners made with PRX-HTM was 0.3 ± 0.4 mg/million-cycle, similar to that reported for CISM 100 liners. The wear particles were largely spherical with a number-averaged particle size of 0.95 µm with ~75% of particles below 1 µm. The subcutaneous and osteochondral rabbit implantations showed no histological differences between PRX-HTM and the control CISM 100. Pre-clinical wear, mechanical, and biocompatibility testing of PRX HTM showed feasibility for the use of this material as a total joint arthroplasty implant bearing surface. This process has the potential of eliminating the additional step of radiation cross-linking by combining consolidation and cross-linking while improving toughness. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1945-1952, 2019.

Residual Byproducts of Peroxide Crosslinked Vitamin E-Blended Ultrahigh Molecular Weight Polyethylene.

BACKGROUND: Wear resistance of ultrahigh molecular weight polyethylene (UHMWPE) is improved via ionizing radiation crosslinking and subsequent high temperature melting for improved toughness. Our group has previously reported that crosslinking can also be achieved chemically using organic peroxides. However, volatile peroxide byproducts are generated during consolidation. The purpose of this study was to quantify elution of volatile peroxide byproducts from UHMWPE before and after in vivo implantation, and to determine their effects on local tissues. METHODS: We prepared crosslinked UHMWPE samples with 5 times the nominal concentration of peroxide needed for improved wear resistance. Control samples (not crosslinked), crosslinked samples, and crosslinked high temperature melting samples were implanted subcutaneously in New Zealand white rabbits for 28 days. Fourier-transform infrared spectroscopy (FTIR) was used to quantify elution of residual peroxide byproducts, and biocompatibility was determined via histological analysis of periprosthetic tissues. RESULTS: Fourier-transform infrared spectroscopy demonstrated elution of residual peroxide byproducts in vivo. No histological differences were observed between tissues in contact with any of the 3 groups of implants; tissues were characterized by fibrosis and a synovial-like lining for all groups. CONCLUSION: UHMWPE chemically crosslinked with very high concentration of organic peroxide did not show any detrimental changes to surrounding subcutaneous tissues, further demonstrating feasibility of crosslinking UHMWPE with a peroxide, rather than irradiation, for the potential use of the material as a bearing surface for joint arthroplasty.

Effects of vitamin E-diffused highly cross-linked UHMWPE particles on inflammation, apoptosis and immune response against S. aureus.

Particle-induced osteolysis and periprosthetic joint infection (PJI) are closely associated with periprosthetic tissue immune function. The objective of this study was to determine the effects of polyethylene particles on inflammation and response against S. aureus. Effects that vitamin E-diffused cross-linked UHMWPE (VE-PE) particles had on apoptosis, inflammation, and bactericidal activities compared to virgin cross-linked UHMWPE (control PE) particles were examined. Murine RAW 264.7 macrophages exposed to VE-PE particles in vitro were less apoptotic, secreted less tumor necrosis factor (TNF)-α, and responded more effectively against lipopolysaccharide or S. aureus compared to control PE particles. Implantation of VE-PE particles in murine calvaria in vivo caused less reactive oxygen species generation, less apoptosis, and less osteolysis compared to control PE particles. Implantation of PE particles in mice calvaria for 28 days, followed by inoculation with S. aureus in the same site where PE particles were implanted, demonstrated enhanced S. aureus clearance in the VE-PE group at day 33 after inoculation. These findings indicate that VE-PE particles might be less inflammatory and might preserve innate immunity of local tissue, allowing for enhanced clearance of bacteria.

Chondrogenesis by bone marrow-derived mesenchymal stem cells grown in chondrocyte-conditioned medium for auricular reconstruction.

Bone marrow-derived mesenchymal stem cells (BMSCs) can be obtained by minimally invasive means and would be a favourable source for cell-based cartilage regeneration. However, controlling the differentiation of the BMSCs towards the desired chondrogenic pathway has been a challenge hampering their application. The major aim of the present study was to determine if conditioned medium collected from cultured auricular chondrocytes could promote chondrogenic differentiation of BMSCs. Auricular chondrocytes were isolated and grown in BMSC standard culture medium (SM) that was collected and used as chondrocyte-conditioned medium (CCM). The BMSCs were expanded in either CCM or SM for three passages. Cells were seeded onto fibrous collagen scaffolds and precultured for 2 weeks with or without transforming growth factor-beta 3 (TGF-ß3). After preculture, constructs were implanted subcutaneously in nude mice for 6 and 12 weeks and evaluated with real-time polymerase chain reaction, histology, immunohistochemistry and biochemistry. Real-time polymerase chain reaction results showed upregulation of COL2A1 in the constructs cultured in CCM compared with those in SM. After 12 weeks in vivo, abundant neocartilage formation was observed in the implants that had been cultured in CCM, with or without TGF-ß3. In contrast, very little cartilage matrix formation was observed within the SM groups, regardless of the presence of TGF-ß3. Osteogenesis was only observed in the SM group with TGF-ß3. In conclusion, CCM even had a stronger influence on chondrogenesis than the supplementation of the standard culture medium with TGF-ß3, without signs of endochondral ossification. Efficient chondrogenic differentiation of BMSCs could provide a promising alternative cell population for auricular regeneration. Copyright © 2016 John Wiley & Sons, Ltd.

Articular cartilage generation applying PEG-LA-DM/PEGDM copolymer hydrogels.

BACKGROUND: Injuries to the human native cartilage tissue are particularly problematic because cartilage has little to no ability to heal or regenerate itself. Employing a tissue engineering strategy that combines suitable cell sources and biomimetic hydrogels could be a promising alternative to achieve cartilage regeneration. However, the weak mechanical properties may be the major drawback to use fully degradable hydrogels. Besides, most of the fully degradable hydrogels degrade too fast to permit enough extracellular matrix (ECM) production for neocartilage formation. In this study, we demonstrated the feasibility of neocartilage regeneration using swine articular chondrocytes photoencapsualted into poly (ethylene glycol) dimethacrylate (PEGDM) copolymer hydrogels composed of different degradation profiles: degradable (PEG-LA-DM) and nondegradable (PEGDM) macromers in molar ratios of 50/50, 60/40, 70/30, 80/20, and 90/10. METHODS: Articular chondrocytes were isolated enzymatically from juvenile Yorkshire swine cartilage. 6 × 10(7) cells cells were added to each milliliter of macromer/photoinitiator (I2959) solution. Nonpolymerized gel containing the cells (100 µL) was placed in cylindrical molds (4.5 mm diameter × 6.5 mm in height). The macromer/photoinitiator/chondrocyte solutions were polymerized using ultraviolet (365 nm) light at 10 mW/cm(2) for 10 mins. Also, an articular cartilaginous ring model was used to examine the capacity of the engineered cartilage to integrate with native cartilage. Samples in the pilot study were collected at 6 weeks. Samples in the long-term experimental groups (60/40 and 70/30) were implanted into nude mice subcutaneously and harvested at 6, 12 and 18 weeks. Additionally, cylindrical constructs that were not implanted used as time zero controls. All of the harvested specimens were examined grossly and analyzed histologically and biochemically. RESULTS: Histologically, the neocartilage formed in the photochemically crosslinked gels resembled native articular cartilage with chondrocytes in lacunae and surrounded by new ECM. Increases in total DNA, glycosaminoglycan, and hydroxyproline were observed over the time periods studied. The neocartilage integrated with existing native cartilage. CONCLUSIONS: Articular cartilage generation was achieved using swine articular chondrocytes photoencapsulated in copolymer PEGDM hydrogels, and the neocartilage tissue had the ability to integrate with existing adjacent native cartilage.

Ear-Shaped Stable Auricular Cartilage Engineered from Extensively Expanded Chondrocytes in an Immunocompetent Experimental Animal Model.

Advancement of engineered ear in clinical practice is limited by several challenges. The complex, largely unsupported, three-dimensional auricular neocartilage structure is difficult to maintain. Neocartilage formation is challenging in an immunocompetent host due to active inflammatory and immunological responses. The large number of autologous chondrogenic cells required for engineering an adult human-sized ear presents an additional challenge because primary chondrocytes rapidly dedifferentiate during in vitro culture. The objective of this study was to engineer a stable, human ear-shaped cartilage in an immunocompetent animal model using expanded chondrocytes. The impact of basic fibroblast growth factor (bFGF) supplementation on achieving clinically relevant expansion of primary sheep chondrocytes by in vitro culture was determined. Chondrocytes expanded in standard medium were either combined with cryopreserved, primary passage 0 chondrocytes at the time of scaffold seeding or used alone as control. Disk and human ear-shaped scaffolds were made from porous collagen; ear scaffolds had an embedded, supporting titanium wire framework. Autologous chondrocyte-seeded scaffolds were implanted subcutaneously in sheep after 2 weeks of in vitro incubation. The quality of the resulting neocartilage and its stability and retention of the original ear size and shape were evaluated at 6, 12, and 20 weeks postimplantation. Neocartilage produced from chondrocytes that were expanded in the presence of bFGF was superior, and its quality improved with increased implantation time. In addition to characteristic morphological cartilage features, its glycosaminoglycan content was high and marked elastin fiber formation was present. The overall shape of engineered ears was preserved at 20 weeks postimplantation, and the dimensional changes did not exceed 10%. The wire frame within the engineered ear was able to withstand mechanical forces during wound healing and neocartilage maturation and prevented shrinkage and distortion. This is the first demonstration of a stable, ear-shaped elastic cartilage engineered from auricular chondrocytes that underwent clinical-scale expansion in an immunocompetent animal over an extended period of time.

Biological reaction to polyethylene particles in a murine calvarial model is highly influenced by age.

Particle-induced osteolysis is driven by multiple factors including bone metabolism, inflammation, and age. The objective of this study was to determine the influence of age on polyethylene (PE) particle-induced osteolysis in a murine calvarial model comparing 2-month-old (young) versus 24-month-old (old) mice. After PE particle implantation, calvaria were assessed at days (D) 3, D7, D14, and D21 via chemoluminescent imaging for inflammation (L-012 probe). In addition micro-computed tomography (micro-CT) and histomorphometry end points addressed the bone reaction. Inflammation peaked at D7 in young mice and D14 in old mice. Using micro-CT, a nadir of mature bone was recorded at D7 for young mice, versus D21 for old mice. Besides, regenerating bone peaked at distinct timepoints: D7 for young mice versus D21 for old mice. In the young mice group, the histomorphometric findings correlated with micro-CT regenerating bone findings at D7, associated with ample osteoïd deposition. No osteoïd could be histologically quantified in the old mice group at D7. This study demonstrated that the biological reaction to polyethylene particles is highly influenced by age.

Conditions for seeding and promoting neo-auricular cartilage formation in a fibrous collagen scaffold.

BACKGROUND: Carved autologous costal cartilage and porous polyethylene implants (Medpor) are the most common approaches for total ear reconstruction, but these approaches may have inconsistent cosmetic outcomes, a high risk of extrusion, or other surgical complications. Engineering ear cartilage to emulate native auricular tissue is an appealing approach, but often the cell-seeded scaffolds are susceptible to shrinkage and architectural changes when placed in vivo. The aim of this study was to assess the most favorable conditions for in vitro pre-culture of cell-seeded type I collagen scaffolds prior to in vivo implantation. METHODS: Sheep auricular chondrocytes were seeded into this type I collagen scaffold. The cell-seeded constructs were cultured in either static or dynamic conditions for two days or two weeks and then implanted into nude mice for another six weeks. The harvested constructs were evaluated histologically, immunohistochemically, and biochemically. RESULTS: Robust neo-cartilage formation was found in these collagen scaffolds seeded with auricular chondrocytes, which was comparable to native cartilage morphologically, histologically, and biochemically. Culture under dynamic conditions prior to implantation improved the neo-cartilage formation histologically and biochemically. CONCLUSION: Dynamic culture of this cell-seeded fibrous collagen material could permit predictable engineered auricular cartilage and a promising approach for external ear reconstruction.

Osteochondral defect repair using a polyvinyl alcohol-polyacrylic acid (PVA-PAAc) hydrogel.

Poly(vinyl alcohol) (PVA) hydrogels can be candidates for articular cartilage repair due to their high water content. We synthesized a PVA-poly(acrylic acid) (PAAc) hydrogel formulation and determined its ability to function as a treatment option for condylar osteochondral (OC) defects in a New Zealand white rabbit (NZWR) model for 12 weeks and 24 weeks. In addition to hydrogel OC implants, tensile bar-shaped hydrogels were also implanted subcutaneously to evaluate changes in mechanical properties as a function of in vivo duration. There were no statistically significant differences (p > 0.05) in the water content measured in the OC hydrogel implant that was harvested after 12 weeks and 24 weeks, and non-implanted controls. There were no statistically significant differences (p > 0.05) in the break stress, strain at break or modulus of the tensile bars either between groups. Histological analysis of the OC defect, synovial capsule and fibrous tissue around the tensile bars determined hydrogel biocompatibility. Twelve-week hydrogels were found to be in situ flush with the articular cartilage; meniscal tissue demonstrated an intact surface. Twenty-four week hydrogels protruded from the defect site due to lack of integration with subchondral tissue, causing fibrillation to the meniscal surface. Condylar micro-CT scans ruled out osteolysis and bone cysts of the subchondral bone, and no PVA-PAAc hydrogel contents were found in the synovial fluid. The PVA-PAAc hydrogel was determined to be fully biocompatible, maintained its properties over time, and performed well at the 12 week time point. Physical fixation of the PVA-PAAc hydrogel to the subchondral bone is required to ensure long-term performance of hydrogel plugs for OC defect repair.

Vitamin E-diffused highly cross-linked UHMWPE particles induce less osteolysis compared to highly cross-linked virgin UHMWPE particles in vivo.

Recent in vitro findings suggest that UHMWPE wear particles containing vitamin E (VE) may have reduced biologic activity and decreased osteolytic potential. We hypothesized that particles from VE-stabilized, radiation cross-linked UHMWPE would cause less osteolysis in a murine calvarial bone model when compared to virgin gamma irradiated cross-linked UHMWPE. Groups received equal amount of particulate debris overlaying the calvarium for 10 days. Calvarial bone was examined using high resolution micro-CT and histomorphometric analyses. There was a statistically significant difference between virgin (12.2%±8%) and VE-UHMWPE (3%±1.4%) groups in regards to bone resorption (P=0.005) and inflammatory fibrous tissue overlaying the calvaria (0.48 vs. 0.20, P<0.0001). These results suggest that VE-UHMWPE particles have reduced osteolytic potential in vivo when compared to virgin UHMWPE.

Ovine model for auricular reconstruction: porous polyethylene implants.

OBJECTIVES: We developed a large animal model for auricular reconstruction with engineered cartilage frameworks and evaluated the performance of porous polyethylene auricular implants in this model. METHODS: Eighteen high-density porous polyethylene auricular frameworks were implanted subcutaneously in the infra-auricular areas of 9 sheep. The implants were harvested 17 weeks later for gross and histologic examination. The perioperative and postoperative courses were carefully documented. RESULTS: Five implants became exposed, and 2 implants needed to be removed at 7 weeks. Additionally, 1 infected implant was removed at 2 weeks. Seromas developed in 2 implants because of drain failures and were drained successfully during the first postoperative week. There were no other surgical site complications. The remaining 10 implants had an acceptable cosmetic appearance at 17 weeks. CONCLUSIONS: The perioperative complication rate in the ovine porous polyethylene auricular implant model was higher than that reported for auricular reconstructions in humans. The implant exposures were likely caused by ischemia and excessive stress on the thin overlying skin, because vascularized flap coverage was not used. The histologic findings were comparable to the results reported for other animal models. This large animal model is appropriate for auricular reconstruction experiments, including engineered constructs.

Successful creation of tissue-engineered autologous auricular cartilage in an immunocompetent large animal model.

Tissue-engineered cartilage has historically been an attractive alternative treatment option for auricular reconstruction. However, the ability to reliably generate autologous auricular neocartilage in an immunocompetent preclinical model should first be established. The objectives of this study were to demonstrate engineered autologous auricular cartilage in the immunologically aggressive subcutaneous environment of an immunocompetent animal model, and to determine the impact of in vitro culture duration of chondrocyte-seeded constructs on the quality of neocartilage maturation in vivo. Auricular cartilage was harvested from eight adult sheep; chondrocytes were isolated, expanded in vitro, and seeded onto fibrous collagen scaffolds. Constructs were cultured in vitro for 2, 6, and 12 weeks, and then implanted autologously in sheep and in control nude mice for 6 and 12 weeks. Explanted tissue was stained with hematoxylin and eosin, safranin O, toluidine blue, collagen type II, and elastin. DNA and glycosaminoglycans (GAGs) were quantified. The quality of cartilage engineered in sheep decreased with prolonged in vitro culture time. Superior cartilage formation was demonstrated after 2 weeks of in vitro culture; the neocartilage quality improved with increased implantation time. In nude mice, neocartilage resembled native sheep auricular cartilage regardless of the in vitro culture length, with the exception of elastin expression. The DNA quantification was similar in all engineered and native cartilage (p>0.1). All cartilage engineered in sheep had significantly less GAG than native cartilage (p<0.02); significantly more GAG was observed with increased implantation time (p<0.02). In mice, the GAG content was similar to that of native cartilage and became significantly higher with increased in vitro or in vivo durations (p<0.02). Autologous auricular cartilage was successfully engineered in the subcutaneous environment of an ovine model using expanded chondrocytes seeded on a fibrous collagen scaffold after a 2-week in vitro culture period.

Sesamoidectomy for hallux sesamoid fractures.

BACKGROUND: Hallux sesamoid fractures are challenging to treat. Symptomatic nonunion is a common problem after nonoperative treatment. Surgical fixation of the fracture can result in successful union, but is technically challenging and can be associated with prolonged return to activities (RTA). Sesamoidectomy is an alternative surgical option that may provide reliable outcomes and allow an earlier RTA in athletes. The purpose of this case-series study was to evaluate a cohort of athletic patients with a hallucal sesamoid fracture treated with sesamoidectomy. METHODS: A total of 24 patients with 24 sesamoid fractures that failed to respond to nonoperative measures were treated surgically with sesamoidectomy. Patients' age, level of activity, fractured bone, surgical approach, time required to RTA, and postoperative complications were recorded. Pre- and postoperative pain was assessed with a visual analog scale ranging from zero (no pain) to 10 (intense pain). Five patients were classified as elite athletes playing at an intercollegiate level and 19 were classified as active individuals performing an athletic activity at least three times per week. The mean patient age was 32.2 ± 10.4 (range, 17 to 54) years. The 24 patients were reviewed at a mean follow-up of 35 ± 21 (range, 8 to 70) months. RESULTS: A total of 22/24 patients (91.6%) returned to activities at a mean time of 11.6 ± 3.87 (range, 8 to 24) weeks. Mean preoperative pain level was 6.2 ± 1.4 and the pain level improved after treatment to a mean of 0.7 ± 1. One patient developed a symptomatic hallux valgus deformity after the resection of the medial sesamoid. CONCLUSIONS: This case series demonstrates good results after sesamoidectomy for sesamoid fractures in athletic individuals with reliable pain relief and RTA within 11.6 weeks. Progressive hallux valgus remains a concern after medial sesamoidectomy, with an incidence of 1 in 24 cases in this study.

Properties of cartilage engineered from elderly human chondrocytes for articular surface repair.

Numerous studies on engineering cartilage utilizing chondrocytes from juvenile animal sources have been reported. However, there are many unknown aspects of engineering cartilage using human chondrocytes-especially from middle-aged or elderly adults-which are critical for clinical application of tissue engineering in the field of orthopedic surgery. The primary aim of this study was to engineer neocartilage tissue from 50-60-year-old human chondrocytes in comparison to engineered cartilage made from juvenile swine chondrocytes (JSCs). Articular chondrocytes from middle-aged, nonarthritic humans and juvenile swine were isolated and placed in culture for expansion. The chondrocytes (passage 1) were mixed in fibrin gel at 40-60×10(6) cells/mL until polymerization. Cells/nodule constructs and devitalized cartilage-cells/hydrogel-devitalized cartilage constructs (three-layered model) were implanted into subcutaneous pockets of nude mice for 12, 18, and 24 weeks. The specimens were evaluated histologically, biochemically, and biomechanically. This allowed for direct comparison of the cartilage engineered from human versus swine cells. Histological analysis demonstrated that samples engineered utilizing chondrocytes from middle-aged adults accumulated basophilic, sulfated glycosaminoglycans (sGAG), and abundant type II collagen around the cells in a manner similar to that seen in samples engineered using JSCs at all time points. Biochemical analysis revealed that samples made with human cells had about 40%-60% of the amount hydroxyproline of native human cartilage, a trend parallel to that observed in the specimens made with swine chondrocytes. The amount of sGAG in the human chondrocyte specimens was about one-and-a-half times the amount in native human cartilage, whereas the amount in the samples made with swine chondrocytes was always less than native cartilage. The biomechanical analysis revealed that the stiffness and tensile of samples made with human cells were in a pattern similar to that seen with swine chondrocytes. This study demonstrates that chondrogenesis using articular chondrocytes from middle-aged adults can be achieved in a predictable and reliable manner similar to that shown in studies using cells from juvenile animals and can form the basis of engineering cartilage with degradable scaffolds in this patient population.

The tissue-engineered auricle: past, present, and future.

The reconstruction, repair, and regeneration of the external auricular framework continue to be one of the greatest challenges in the field of tissue engineering. To replace like with like, we should emulate the native structure and composition of auricular cartilage by combining a suitable chondrogenic cell source with an appropriate scaffold under optimal in vitro and in vivo conditions. Due to the fact that a suitable and reliable substitute for auricular cartilage has yet to be engineered, hand-carved autologous costal cartilage grafts and ear-shaped porous polyethylene implants are the current treatment modalities for auricular reconstruction. However, over the last decade, significant advances have been made in the field of regenerative medicine and tissue engineering. A variety of scaffolds and innovative approaches have been investigated as alternatives to using autologous carved costal cartilage or porous polyethylene implants. A review of recent developments and the current state of the art and science is presented, focusing on scaffolds, cell sources, seeding densities, and mechanical characteristics of tissue-engineered auricular cartilage.

Implant-assisted meniscal repair in vivo using a chondrocyte-seeded flexible PLGA scaffold.

A cell-based engineered construct can be used for healing of intractable meniscal lesions. Our aims were to assess the culture conditions (static versus dynamic oscillation) and the healing capacity of the chondrocyte-seeded flexible implants in a heterotopic mouse model. Swine articular chondrocytes were labeled with PKH 26 or DiI dye and seeded onto a flexible PLGA scaffold using dynamic oscillating conditions for 24 h. Half of cell-seeded scaffolds were cultured in the same dynamic conditions, while the remaining scaffolds were cultured statically. After 7 days, scaffolds were placed between swine meniscal discs and were implanted subcutaneously in nude mice for 6 weeks. Additional constructs for assessing in vivo cell tracking were implanted for 12 weeks. Live/dead assays demonstrated labeled chondrocytes attached throughout the scaffold in both culture conditions. DNA measurements showed no significant difference between the culture conditions. A continuous fibro-cartilaginous healing tissue was observed between meniscal discs in all 12 dynamically cultured constructs and 9 of 11 statically cultured ones. There was no evidence of meniscal healing using acellular scaffold as well as in meniscal constructs lacking an implant. Both PKH 26- and DiI-labeled cells were identified along the healing interface. We conclude the chondrocyte-seeded flexible PLGA implants induce healing of meniscal discs in nude mice. Culture conditions after seeding have no apparent effects on healing.

Chondrogenic priming adipose-mesenchymal stem cells for cartilage tissue regeneration.

PURPOSE: Chondrocytes lose their ability to produce cartilaginous matrix during multiplication in culture through repeated passages, resulting in inferior tissue phenotype. To overcome the limited amount of primary chondrocytes, we aimed to determine the optimal culture condition for in vitro/in vivo cartilage regeneration using human adipose-derived mesenchymal stem cells (AMSCs). METHODS: To evaluate the effects exerted by the chondrocytic culture condition on AMSC, we utilized chondrocyte conditioned medium (CM) and/or co-culture methods to prime and differentiate AMSCs. We evaluated ultimate in vivo engineered cartilage with primed AMSCs with that of chondrocytes. To examine the link between conditioned factors and proliferation/differentiation, cell cycle progression of AMSCs were examined using 5-ethynyl-2'-deoxyuridine (EdU), and gene expression was monitored. RESULTS: We report that AMSCs can be stimulated to become chondrogenic cells when expanded with chondrocyte CM. Polymeric scaffolds co-seeded with CM- expanded AMSCs and primary chondrocytes resulted in in vivo cartilaginous tissues with similar biochemical content to constructs seeded with chondrocytes alone. CONCLUSION: These results indicate that chondrocyte CM consists of suitable morphogenetic factors that induce the chondrogenic priming of AMSCs for cartilage tissue engineering.

Engineering ear constructs with a composite scaffold to maintain dimensions.

Engineered cartilage composed of a patient's own cells can become a feasible option for auricular reconstruction. However, distortion and shrinkage of ear-shaped constructs during scaffold degradation and neocartilage maturation in vivo have hindered the field. Scaffolds made of synthetic polymers often generate degradation products that cause an inflammatory reaction and negatively affect neocartilage formation in vivo. Porous collagen, a natural material, is a promising candidate; however, it cannot withstand the contractile forces exerted by skin and surrounding tissue during normal wound healing. We hypothesised that a permanent support in the form of a coiled wire embedded into a porous collagen scaffold will maintain the construct's size and ear-specific shape. Half-sized human adult ear-shaped fibrous collagen scaffolds with and without embedded coiled titanium wire were seeded with sheep auricular chondrocytes, cultured in vitro for up to 2 weeks, and implanted subcutaneously on the backs of nude mice. After 6 weeks, the dimensional changes in all implants with wire support were minimal (2.0% in length and 4.1% in width), whereas significant reduction in size occurred in the constructs without embedded wire (14.4% in length and 16.5% in width). No gross distortion occurred over the in vivo study period. There were no adverse effects on neocartilage formation from the embedded wire. Histologically, mature neocartilage extracellular matrix was observed throughout all implants. The amount of DNA, glycosaminoglycan, and hydroxyproline in the engineered cartilage were similar to that of native sheep ear cartilage. The embedded wire support was essential for avoiding shrinkage of the ear-shaped porous collagen constructs.