A challenge for tissue engineering is producing three-dimensional (3D), vascularized cellular constructs of clinically relevant size, shape and structural integrity. We present an integrated tissue-organ printer (ITOP) that can fabricate stable, human-scale tissue constructs of any shape. Mechanical stability is achieved by printing cell-laden hydrogels together with biodegradable polymers in integrated patterns and anchored on sacrificial hydrogels. The correct shape of the tissue construct is achieved by representing clinical imaging data as a computer model of the anatomical defect and translating the model into a program that controls the motions of the printer nozzles, which dispense cells to discrete locations. The incorporation of microchannels into the tissue constructs facilitates diffusion of nutrients to printed cells, thereby overcoming the diffusion limit of 100-200 μm for cell survival in engineered tissues. We demonstrate capabilities of the ITOP by fabricating mandible and calvarial bone, cartilage and skeletal muscle. Future development of the ITOP is being directed to the production of tissues for human applications and to the building of more complex tissues and solid organs.
Stress urinary incontinence (SUI) is likelier to develop following a first pregnancy and delivery. Although retrospective epidemiological studies suggest an increased risk from both pregnancy and vaginal delivery, few cohort studies have estimated the long-term risk of SUI. This longitudinal cohort study examined the influence of SUI, beginning in a first pregnancy or puerperal period, on the risk of SUI symptoms 12 years later in 241 primiparous women entered consecutively into the trial in 1989 when seen for their first delivery. The 12-year incidence of SUI was based on 146 women lacking SUI for at least 3 months after delivery. By 12 years after the first delivery, 201 women had had 1-5 further pregnancies, and 187 had had 1-4 additional deliveries.The prevalence of SUI 12 years after the first delivery was 42%, and about 5% of women had SUI on a daily basis. Nearly 9% of women in the study reported hygienic problems or social discomfort resulting from SUI. The 12-year incidence of SUI was 30%. Any degree of SUI at 12 years was significantly more prevalent in women whose SUI began during the first pregnancy or within 3 months after giving birth, compared to women without SUI for at least the first 3 puerperal months. More than half of women whose SUI began during or after the first pregnancy but remitted by 3 months postpartum had SUI when assessed after 12 years. The risk of SUI 12 years after the first delivery was increased in women with higher body mass indices, but decreased in women who breast fed their infants for 6 months or longer and also in those having cesarean section at the first delivery. None of the women had undergone surgery for SUI. Training of the pelvic floor muscles did not lessen its prevalence.These findings show that, when SUI begins during the first pregnancy and especially the first delivery, the risk of symptoms 12 years later is significantly increased. Women who are obese before their first pregnancy and delivery appear to be especially at risk, whereas cesarean delivery may protect again long-lasting SUI in premenopausal women. GYNECOLOGYVolume 62, Number 5 OBSTETRICAL AND GYNECOLOGICAL SURVEY
Stem cells capable of differentiating to multiple lineages may be valuable for therapy. We report the isolation of human and rodent amniotic fluid-derived stem (AFS) cells that express embryonic and adult stem cell markers. Undifferentiated AFS cells expand extensively without feeders, double in 36 h and are not tumorigenic. Lines maintained for over 250 population doublings retained long telomeres and a normal karyotype. AFS cells are broadly multipotent. Clonal human lines verified by retroviral marking were induced to differentiate into cell types representing each embryonic germ layer, including cells of adipogenic, osteogenic, myogenic, endothelial, neuronal and hepatic lineages. Examples of differentiated cells derived from human AFS cells and displaying specialized functions include neuronal lineage cells secreting the neurotransmitter L-glutamate or expressing G-protein-gated inwardly rectifying potassium channels, hepatic lineage cells producing urea, and osteogenic lineage cells forming tissue-engineered bone.
Although three-dimensional (3D) bioprinting technology has gained much attention in the field of tissue engineering, there are still several significant engineering challenges to overcome, including lack of bioink with biocompatibility and printability. Here, we show a bioink created from silk fibroin (SF) for digital light processing (DLP) 3D bioprinting in tissue engineering applications. The SF-based bioink (Sil-MA) was produced by a methacrylation process using glycidyl methacrylate (GMA) during the fabrication of SF solution. The mechanical and rheological properties of Sil-MA hydrogel proved to be outstanding in experimental testing and can be modulated by varying the Sil-MA contents. This Sil-MA bioink allowed us to build highly complex organ structures, including the heart, vessel, brain, trachea and ear with excellent structural stability and reliable biocompatibility. Sil-MA bioink is well-suited for use in DLP printing process and could be applied to tissue and organ engineering depending on the specific biological requirements.
Stem cells obtained from amniotic fluid show high proliferative capacity in culture and multilineage differentiation potential. Because of the lack of significant immunogenicity and the ability of the amniotic fluid-derived stem (AFS) cells to modulate the inflammatory response, we investigated whether they could augment wound healing in a mouse model of skin regeneration. We used bioprinting technology to treat full-thickness skin wounds in nu/nu mice. AFS cells and bone marrow-derived mesenchymal stem cells (MSCs) were resuspended in fibrin-collagen gel and “printed” over the wound site. At days 0, 7, and 14, AFS cell- and MSC-driven wound closure and re-epithelialization were significantly greater than closure and re-epithelalization in wounds treated by fibrin-collagen gel only. Histological examination showed increased microvessel density and capillary diameters in the AFS cell-treated wounds compared with the MSC-treated wounds, whereas the skin treated only with gel showed the lowest amount of microvessels. However, tracking of fluorescently labeled AFS ceils and MSCs revealed that the cells remained transiently and did not permanently integrate in the tissue. These observations suggest that the increased wound closure rates and angiogenesis may be due to delivery of secreted trophic factors, rather than direct cell-cell interactions. Accordingly, we performed proteomic analysis, which showed that AFS cells secreted a number of growth factors at concentrations higher than those of MSCs. In parallel, we showed that AFS cell-conditioned media induced endothelial cell migration in vitro. Taken together our results indicate that bioprinting AFS cells could be an effective treatment for large-scale wounds and burns.
Biofabrication is an evolving research field that has recently received significant attention. In particular, the adoption of Biofabrication concepts within the field of Tissue Engineering and Regenerative Medicine has grown tremendously, and has been accompanied by a growing inconsistency in terminology. This article aims at clarifying the position of Biofabrication as a research field with a special focus on its relation to and application for Tissue Engineering and Regenerative Medicine. Within this context, we propose a refined working definition of Biofabrication, including Bioprinting and Bioassembly as complementary strategies within Biofabrication.
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