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Welcome to The Visible Embryo, a comprehensive educational resource on human development from conception to birth.

The Visible Embryo provides visual references for changes in fetal development throughout pregnancy and can be navigated via fetal development or maternal changes.

The National Institutes of Child Health and Human Development awarded Phase I and Phase II Small Business Innovative Research Grants to develop The Visible Embryo. Initally designed to evaluate the internet as a teaching tool for first year medical students, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than one million visitors each month.

Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

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Pregnancy Timeline by SemestersDevelopmental TimelineFertilizationFirst TrimesterSecond TrimesterThird TrimesterFirst Thin Layer of Skin AppearsEnd of Embryonic PeriodEnd of Embryonic PeriodFemale Reproductive SystemBeginning Cerebral HemispheresA Four Chambered HeartFirst Detectable Brain WavesThe Appearance of SomitesBasic Brain Structure in PlaceHeartbeat can be detectedHeartbeat can be detectedFinger and toe prints appearFinger and toe prints appearFetal sexual organs visibleBrown fat surrounds lymphatic systemBone marrow starts making blood cellsBone marrow starts making blood cellsInner Ear Bones HardenSensory brain waves begin to activateSensory brain waves begin to activateFetal liver is producing blood cellsBrain convolutions beginBrain convolutions beginImmune system beginningWhite fat begins to be madeHead may position into pelvisWhite fat begins to be madePeriod of rapid brain growthFull TermHead may position into pelvisImmune system beginningLungs begin to produce surfactant
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development

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Home | Pregnancy Timeline | News Alerts |News Archive May 27, 2015

(ABOVE: Mouse retina) Stem cell-derived photoreceptor cells were
injected into this retina, assting the animal to improved eyesight.
Image Credit: University of Toronto





Hydrogels boost stem cells to heal brains

Researchers have engineered 'hydrogels' to hold stem cells for transplant into damaged brain and eyes of mice. The transplanted cells helped reverse blindness and help mice recover from stroke.

University of Toronto (U of T) scientists and engineers have made a breakthrough — transplanting stem cells within a gel-like material. Led by U of T professors Molly Shoichet, Derek van der Kooy and Cindi Morshead at the Donnelly Centre for Cellular and Biomolecular Research, the method encases stem cells for transplant within a "hydrogel". The work was published in Stem Cell Reports, official scientific journal of the International Society for Stem Cell Research.

Stem cells hold great promise for therapy as they can turn into any cell type in the body. This includes the potential to generate replacement tissues and organs. While scientists are great at growing stem cells in a lab dish, once placed in the body these cells have trouble thriving.

Shoichet is a bioengineer who recently won the prestigious L'Oreal-UNESCO for Women in Science Award. Along with her team, she created the hydrogel several years ago in order to hold cells together during transplantation.

"This study shows that hydrogels do more than just hold stem cells together. The gels directly promote stem cell survival during tissue integration, bringing stem-cell based therapy closer to reality" says Shoichet.

In one part of the study the team injecting encapsulated photoreceptors, grown from stem cells, into the eyes of blind mice. Photoreceptors are the light sensing cells of the eye. The hydrogel increased stem cell survival and integration enabling mice to regain partial vision. "After cell transplantation, our measurements showed that mice with previously no visual function regained approximately 15% of their pupillary response. Their eyes are beginning to detect light and respond appropriately," says Dr. Brian Ballios, an engineer and expert in stem cell biology and regenerative medicine for retinal degenerative disease who led this part of the study.

In another part of the study, Dr. Michael Cooke, injected the stem cells into the brains of mice who had recently suffered strokes. "Within weeks after transplantation, we started seeing improvements in the mice's motor coordination," says Cooke. His team now wants to carry out similar experiments in rats, whose larger brains are better suited for behavioral tests.

The biogel material has only two components — methylcellulose that holds the cells together, and hyaluronan which keeps the cells alive. "Through this physical blend of two materials we are getting the best of both worlds," says Shoichet.

Because the hydrogel boosted cell survival in the eye and the brain, it could potentially be used for transplants in many different body sites. Once cells are delivered, the gel dissolves to be reabsorbed by the body within a few weeks.


•An injectable biomaterial improves rod survival/integration into adult retina

•The same material improves neural stem cell distribution/survival into adult brain

•Functional repair is demonstrated after cell transplantation in both retina and brain

•Hyaluronan-CD44 interaction is implicated in the pro-survival effect on stem cell progeny

The utility of stem cells and their progeny in adult transplantation models has been limited by poor survival and integration. We designed an injectable and bioresorbable hydrogel blend of hyaluronan and methylcellulose (HAMC) and tested it with two cell types in two animal models, thereby gaining an understanding of its general applicability for enhanced cell distribution, survival, integration, and functional repair relative to conventional cell delivery in saline. HAMC improves cell survival and integration of retinal stem cell (RSC)-derived rods in the retina. The pro-survival mechanism of HAMC is ascribed to the interaction of the CD44 receptor with HA. Transient disruption of the retinal outer limiting membrane, combined with HAMC delivery, results in significantly improved rod survival and visual function. HAMC also improves the distribution, viability, and functional repair of neural stem and progenitor cells (NSCs). The HAMC delivery system improves cell transplantation efficacy in two CNS models, suggesting broad applicability.

This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/)

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