Combining Umbilical Cord Cells with Hyaluronic Acid Improves Heart Repair After a Heart Attack


Umbilical cord blood cells have an advantage over bone marrow or peripheral blood cells in that aging, systemic inflammation, and stress or damage caused by cell processing procedures can potentially compromise and diminish the regenerative capability of these cells. This problem is particularly acute in the case of treating patients who have recently suffered a heart attack, since transplanted cells experience a rather hostile environment that kills off most cells. Additionally, blood flow through the heart tends to wash out infused cells, which further decreases any regenerative activities the cells might have otherwise exerted.

With this in mind, Patrick Hsieh and his colleagues at the Academia Sinica, in Taipei, Taiwan tested if ability of human cord blood mononuclear cells (CB-MNCs) injected into the heart in combination with a hyaluronan (HA) hydrogel could extend the regenerative abilities of these cells in a pig model. HA is a common component of connective tissue, and, in general, it is very well tolerated by patients and implanted cells. Furthermore, it has the added bonus of shielding cells from a hostile environment and preventing them from being washed out of the heart.

Hsieh used a total of 34 minipigs and divided them into five different groups. One group was the sham operation group in which minipigs received surgical incisions but no heart attack was induced. The second group had heart attacks surgically induced and received infusions of normal saline solutions. The third group of minipigs also experienced heart attacks, and had HA injected into the heart walls. The fourth group also suffered heart attacks and received injections of human umbilical cord stem cells into their heart walls. The fifth group experienced heart attacks and received injections of both HA and human umbilical cord blood cells. The animals were kept and examined two months after surgery.

Two months after the surgery, the minipigs that received injections of human umbilical cord blood cells plus HA showed the highest left ventricle ejection fraction (51.32% ± 0.81%). This is significant when compared to 42.87% ± 0.97%, for the group that received injections of normal saline, 44.2% ± 0.63% for the group that received injections of HA alone, and 46.17% ± 0.39% for the group that received injections of umbilical cord blood cells only. Additionally, hearts from minipigs that received cord blood cells plus HA improved the systolic and diastolic function significantly better than the other experimental groups. Injections of either cord blood cells alone or in combination with HA significantly decreased the scar area and promoted the formation of new blood vessels in the infarcted region. In general, this study suggests that combined infusion of umbilical cord blood cells and HA improves the function of the heart after a heart attack and might prove to be a promising treatment option of heart attack patients.

This is a preclinical study, but it is a preclinical study in a larger animal model system. Umbilical cord blood cells have a demonstrated ability to induce healing in the heart after a heart attack. However, the combination of these cells with HA almost certainly significantly increases cell retention in the heart, thereby significantly improving cardiac performance, and preventing cardiac remodeling. Therefore, using healthy cells donated from another source to replace damaged or moribund cells may be a better option to treat a heart patient and repair their sick heart.

This work appeared in Stem Cells Trans Med November 2015, doi: 10.5966/sctm.2015-0092

Stem Cell Treatments to Repair Cartilage Defects in the Knee


Erosions of the cartilage that covers the surfaces at the ends of our leg bones has motivated several laboratories to undertake clinical studies to test new techniques to heal lost cartilage, particularly at the knee. Many of these techniques have their share of drawbacks and advantages, but the number of clinical trials to deal with cartilage lesions of the knee are increasing. Unfortunately, more work remains to be done, but much more is known about several of these techniques than before. This article will summarize many of these techniques.

Microfracture is a procedure in which several small holes are drilled into the end of the bone to enhance the migration of mesenchymal stem cells from the bone marrow to the site of the cartilage defect. These MSCs then differentiate into chondrocytes and make cartilage that fills the lesion with new cartilage. Unfortunately, the cartilage made in these cases is fibrocartilage and not hyaline cartilage. Fibrocartilage lacks the biomechanical strength and durability of hyaline cartilage and it typically deteriorates 18-24 months after surgery. When used to treat large lesions, 20-50% of all cases develop intralesional osteophytes and the sclerotic bone increases the failure rate of autologous chrondrocyte implantation 3-7X. Thus microfractionation is only performed under very specific conditions and only in young patients, since this technique does not work in older patients.

Microfracture

Autologous Chondrocyte Implantation or ACI uses a full-thickness punch biopsy from a low-weight-bearing region of the joint taken during an arthroscopic surgery. This biopsy contains chondrocytes that are grown in cell culture to a population of about 12-48 million chondrocytes, which are troweled into the lesion during a second arthroscopic surgery. Clinical trials have established that ACI is safe and effective for large knee lesions. Peterson and others and Minas and others have established that even after 10 years, patients who have been treated with ACI show good relief of pain and increased knee function.

In the Peterson study, questionnaires were sent to 341 patients. 224 of 341 patients replied to the questionnaires, and of these respondents, 74% of the patients reported their status as better or the same as the previous years 10-20 years after the procedure (mean, 12.8 years).  92% were satisfied and would have ACI again.  Knee function and pain levels were significantly better after the procedure than before.  From this study, Peterson and others concluded that ACI is an effective and durable solution for the treatment of large full-thickness cartilage and osteochondral lesions of the knee-joint, and that the clinical and functional outcomes remain high even 10 to 20 years after the implantation.

Minas and others analyzed data from 210 patients treated with ACI who were followed for more than 10 years. ACI provided durable outcomes with a survivorship of 71% at 10 years and improved function in 75% of patients with symptomatic cartilage defects of the knee at a minimum of 10 years after surgery. A history of prior marrow stimulation as well as the treatment of very large defects was associated with an increased risk of failure.
In comparison studies by Bentley and others, ACI produced superior results to mosaicplasty (osteochondral transplantation or cylinders of bone drilled form low-weight-bearing parts of the knee that are implanted in a mosaic fashion into the knee).  In the Bentley study, 10 of 58 ACI patients had failed grafts after 10 years, but 23 of 42 mosaicplasty patients had failed cartilage repair.  According to studies by Based and others, and Saris and others, ACI is also superior to microfractionation in the repair of large cartilage lesions (>3 cubic cm), but seems to provide the same outcomes as microfracture for smaller lesions, according to Knudsen and others.  There are drawbacks to ACI.  The tissue flap used to seal the cartilage implant sometimes becomes pathologically enlarged.  Other materials have been used to seal the patch, such as hyaluronic acid, or collagen types I and III, but the use of these materials increases the expense of the procedure and the likelihood that the immune system will response to the covering.  Also, ACI outcomes vary to such an extent that the procedure is simply too unstandardized at the present time to be used consistently in the clinic.

Autologous Cartilage Implantation

In an attempt to standardize ACI, several orthopedic surgeons have tried to add a supportive scaffold of some sort to the chondrocytes harvested from the patient’s body.  Several studies in tissue culture have shown that chondrocytes not only divide better, but also keep their identities as chondrocytes better in a three-dimensional matrix (see Grigolo et al, Biomaterials (2002) 23: 1187-1195 and Caron et al, Osteoarthritis Cartilage (2012) 20; 1170-1178).  Therefore, ACI has given way to MACI or Matrix-Induced Autologous Chondrocyte Implantation, which seeds the chondrocytes on an absorbable porcine-derived mixed collagen (type I and III) prior to implantation.  The implant is then secured into the debrided cartilage lesion by means of a fibrin cover.

Several case studies have shown that MACI has substantial promise, but individual case studies are the weakest evidence available.  To prove its superiority over ACI or microfracture surgery, MACI must be compared in controlled studies.  In the few studies that have been conducted, the superiority of MACI remains unproven to date.  Patients who received MACI or ACI showed similar clinical outcomes in two studies (Bartlett and others, Journal of Bone and Joint Surgery (2005) 87: 640-645; and Zeifang et al, American Journal of Sports Medicine (2010) 38: 924-933), although those who received MACI showed a significantly lower tendency for the graft to enlarge.  MACI is clearly superior to microfracture surgery (Basad, et al., Knee Surgery, Sports Traumatology and Arthroscopy (2010) 18: 519-527), but longer-term studies are needed to establish the superiority of MACI over other treatment options.

A slight variation of the MACI theme is to embed the chondrocytes in a gel-like material called hyaluronic acid (HA).  HA-embedded chondrocytes have been shown to promote the formation of hyaline cartilage in patients (Maracci et al., Clinical Orthopedics and Related Research (2005) 435: 96-105).  Even though the outcomes are superior for patients treated with HA-MACI, the recovery period is longer (Kon E, et al., American Journal of Sports Science (2011) 39: 2549-2567).  MACI is available in Europe but not the US to date.  FDA approval is supposedly pending.  Long-term follow-up studies are required to establish the efficacy of this procedure.

Future prospects for treating knee cartilage lesions include culturing collagen-seeded chondrocytes for a longer period of time than the three days normally used for MACI.  During these longer culture periods, the seeded chondrocytes mature, and make their own scaffolds, which ensure higher-quality cartilage and better chondrocyte engraftment (see Khan IM and others, European Cell Materials (2008) 16: 26-39).  Alternatively, joint cartilage responds to stress by undergoing cell proliferating and increasing in density.  This response is due to the production of growth factors such as Transforming Growth Factor-β1 and -β3 (TGF-β1 and TGF-β3).  This motivated some enterprising tissue engineers to use recombinant forms of these growth factors to grow cartilage in bioreactors under high-stress conditions.  Such a strategy has given rise to NeoCart, a tissue-engineered product that has gone through Phase I and II trials and has been shown in two-year follow-up studies to be safe and more effective than microfracture surgery (Crawford DC and others, Journal of Bone and Joint Surgery, American Volume. 2012 Jun 6;94(11):979-89 and Crawford DC, and others, Am J Sports Med. 2009 Jul;37(7):1334-43).

Mesenchymal stem cells (MSCs) from bone marrow and other sites have also been used to successfully treat cartilage lesions.  These types of treatments are less expensive than ACI and MACI, and do not require two surgeries as do ACI and MACI.  The studies that have been published using a patient’s own MSCs have been largely positive, although some pain associated with the site of the bone marrow aspiration is a minor side effect (see Centeno and others, Pain Physician (2008) 11:343-353; Emadedin, et al., Arch Iran Med (2012) 15: 422-428; Wong RL, et al., Arthroscopy (2013) 29: 2020-2028).  Fat-based MSCs have been tested as potential cartilage-healers in elderly patients (Koh YG, et al., Knee Surgery, Sports Traumatology, and Arthroscopy (Dec 2013, published on-line ahead of print date).  While these initial results look promising,, fat-based, MSCs have only just begun to be tested for their ability to regenerate cartilage.  Fat-based MSCs show different properties than their bone-marrow counterparts, and it is by no means guaranteed that fat-based MSCs can regenerate cartilage as well as MSCs from bone marrow.

Fresh cartilage grafts from donors (aka – cartilage allografts) use transplanted cartilage that has been freshly collected from a donor.  Fresh cartilage allografts have had positive benefits for young, active patients and the grafts have lasted 1-25 years (Gross AE, et al., Clinical Orthopedics and Related Research (2008) 466: 1863-1870).  Particulate cartilage allografts takes minced cartilage and lightly digests it with enzymes to liberate some of the cartilage-synthesizing chondrocytes, and then pats this material into the cartilage lesion, where it is secured with a fibrin glue plug.  The cartilage provides an excellent matrix for the synthesis of new cartilage, and the chondrocytes make new cartilage while seeded onto this cartilage scaffold.  Clinical experience with this technique includes a two-year follow-up in which MRI evidence showed good filling of the lesions (Bonner KF, Daner W, and Yao JQ, Journal of Knee Surgery 2010 23: 109-114 and Farr J, et al., Journal of Knee Surgery 2012 25: 23-29).  A variation on this technique uses a harvested hyaline cartilage plug that is glued into an absorbable scaffold before transplantation into the cartilage lesion.  This procedure had the same safety profile as microfracture surgery, but resulted in better clinical outcomes, high quality cartilage, and fewer adverse side effects (Cole JB et al., American Journal of Sports Medicine 2011 39: 1170-1179).  A clinical trial that tested this procedure remains uncompleted after the company suspended the trial because of conflicts with the FDA (Clinical Trial NCT00881023).

AMIC or Autologous Matrix-Induced Chondrogenesis is a cell-free treatment option in which the cartilage lesion is cleaned and filled subjected to microfracture, after which the lesion is filled with a mixed collagen matrix that is glued or stitched to the cartilage lesion.  The MSCs released by the microfracture procedure now move into a scaffold-laden cartilage lesion that induces the formation of hyaline cartilage.  This technique appears to aid the filling of full-thickness cartilage defects, and follow-up examinations have revealed that after 5 years, patients showed substantial improvements in knee function, pain relief and MRI analyses of knee cartilage showed high-quality cartilage in repaired lesion (Kusano T, et al., Knee Surgery, Sports Traumatology, and Arthroscopy 2012 20: 2109-2115; Gille J, et al., Archives of Orthopedic Trauma Surgery 2013 133: 87-93; Gille J, et al., Knee Surgery, Sports Traumatology, and Arthroscopy 2010 18: 1456-1464).

These are just a few of the new treatments of cartilage lesions of the knee and other joints.  As you can see, all of this will lead to greater repair of knee lesions and it is all being done without embryonic stem cells or destroying embryos.

Human Infra-patellar Fat Pad-Derived Stromal Cells Show Great Cartilage-Making Potential, Which is Enhanced By Connective Tissue Components


With age and overuse, our knees wear out and we sometimes need an artificial one. The cartilage shock absorber at the ends of our bones simply does not regenerate very well, and this results in large problems when we get older.

Is there an effective way to regenerate cartilage? Stem cells do have the ability to make cartilage, but finding the right stem cell and delivering enough of them to make a difference remains a challenge.

To that end, Tang-Yuan Chu and his colleagues from Tzu Chi University and the Buddhist Tzu Chi General Hospital in Hualien, Taiwan have discovered that stem cells from the fat pad that surrounds the knee appear to be one of the best sources of cartilage-making cells for the knee.

The infra-patellar fat pad or IFP contains a stem cell population called infra-patellar fat pad-derived stromal cells or IFPSCs. These IFPSCs were isolated by Chu and his colleagues from patients who were undergoing arthroscopic surgery. When Chu and others grew these cells in culture, the IFPSCs grew robustly for two weeks. The culture protocol was a standard one and no special requirements were required. In fact, after two weeks, the IFPSCs grew to more than 10 million cells on the third passage.

When the ability of IFPSCs to form cartilage-making cells (chondrocytes) were compared with mesenchymal stem cells from bone marrow, fat and umbilical cord connective tissue (Wharton’s jelly), the IFPSCs showed a clear superiority to these other cells types, and differentiated into chondrocytes quite effectively.

Next, Chu and his crew cultured the IFPSCs on a material called hyaluronic acid (HA). HA is a common component of the synovial fluid that helps lubricate our larger joints and in connective tissue, and basement membranes upon which epithelial cells sit.

Hyaluronic Acid

When grown on 25% HA, the IFPSCs were better at making bone or fat than IFPSCs grown on no HA. Furthermore, when grown on 25% HA, IFPSCs showed a four-fold increase in their ability to form chondrocytes. The HA also did not affect the ability of the cells to divide.

In conclusions, these IFPSCs seem to possess a strong potential to differentiate into chondrocytes and regenerate cartilage. Also, this ability is augmented in a growth environment of 25% HA. Certainly some preclinical trials with laboratory animal are due. Wouldn’t you say?

Source: Dah-Ching Ding; Kun-Chi Wu; Hsiang-Lan Chou; Wei-Ting Hung; Hwan-Wun Liu; Tang-Yuan Chu. Human infra-patellar fat pad-derived stromal cells have more potent differentiation capacity than other mesenchymal cells and can be enhanced by hyaluronan.  Cell Transplantation, http://dx.doi.org/10.3727/096368914X681937.

A Step Towards Making Customized Blood Vessels


Johns Hopkins University scientists have directed stem cells to form networks of new blood vessels, and successfully transplanted those laboratory-made blood vessels into laboratory mice.

The stem cells in this experiment were made by reprogramming ordinary cells. Thus this new technique could potentially be used to make blood vessels that are genetically matched to individual patients and have a very low chance of being rejected by the patient’s immune system.

“In demonstrating the ability to rebuild a microvascular bed in a clinically relevant manner, we have made an important step toward the construction of blood vessels for therapeutic use,” said Sharon Gerecht, associate professor in the Johns Hopkins University Department of Chemical and Biomolecular Engineering, Physical Sciences-Oncology Center and Institute for NanoBioTechnology. “Our findings could yield more effective treatments for patients afflicted with burns, diabetic complications and other conditions in which vasculature function is compromised.”

Gerecht’s research group and others have previously grown blood vessels in the laboratory using stem cells, but there are problems with using these blood vessels in human patients. For example, in a paper published by Gerecht’s group in Stem Cells Translational Medicine earlier this year (Stem Cells Trans Med April 2013 vol. 2 no. 4 297-306), ECFCs or endothelial colony-forming cells from human umbilical cords were grown and used to make networks of blood vessels in culture. Those blood vessels were then embedded in blocks of “hyaluronic acid.” Hyaluronic acid is a component of human connective tissue, and when the ECFCs were embedded into it, they were then placed on the skin of mice that had received third-degree burns. On day 3 following transplantation, white blood cells called macrophages degraded the hyaluronic acid gel rather quickly. Between days 5–7, the mouse’s blood vessels infiltrated the implant and connected with the human blood vessels in the wound area. The growth of the human blood vessels peaked at day 7 and then decreased by the end of the proliferation stage. As the wound reached the remodeling period during the second week after transplantation, the blood vessels, including the transplanted human vessels generally regressed, and a few microvessels, wrapped by mouse smooth muscle cells and with a vessel area less than 200 square micrometers (including the human ones), remained in the healed wound.

This is a fascinating experiment, but making blood vessels this way is a heck of a lot of work, and even though the umbilical cord ECFCs are less likely to be rejected by the immune system of the patient, the chances of immune system rejection are still present. is there a better way?

In this current study, Gerecht and her team tried to streamline the new growth process. Where other experiments used chemical cues to differentiate stem cells into the desired cell type, Sravanti Kusuma in Gerecht’s laboratory devised a way to instruct stem cells to exclusively form the two cell types required for blood vessel construction (smooth muscle cells and endothelial cells).

According to Kusuma, “It makes the process quicker and more robust if you don’t have to sort through a lot of cells you don’t need to find the ones you do, or grow two batches of cells,”

Derivation of EVCs from hPSCs. (A) Schema for self-assembled vascular derivatives. (i) hPSCs are differentiated toward EVCs that can be matured into functional ECs and pericytes. (ii) Derived EVCs are embedded within a synthetic HA matrix that facilitates self-organization into vascular networks. (B) VEcad expression in day 12 differentiated hiPSC-MR31 and hESC-H9 cell lines comparing the three differentiation conditions tested (flow cytometry analysis; n = 3). (C and D) Flow cytometry plots (n = 3) of EVC derivatives assessing the expression of pluripotent markers TRA-1-60 and TRA-1-81 (C) and CD105 and CD146 (D). (E) EVC differentiation efficiency from hPSC lines per 1 million input hPSCs. (F) Flow cytometry plots (n = 3) of EVC derivatives assessing expression of VEcad double-labeled with CD105 or PDGFRβ. (Left) Isotype controls. (G) Quantitative RT-PCR analysis of EC and perivascular marker expression by EVCs and sorted VEcad+ and VEcad− cells. # denotes not detected. Data are normalized to EVCs of each specific hPSC type. (H) Flow cytometry plots (n = 3) of hematopoietic marker CD45 (hiPSC-BC1). (I) Quantitative RT-PCR of H9-EVCs for the expression of SMMHC and peripherin, compared with undifferentiated cells (d0) and mature derivatives (13, 37). Isotype controls for flow cytometry are in gray. Flow cytometry results shown are typical of the independent experiments. *P < 0.05; **P < 0.01; ***P < 0.001
Derivation of EVCs from hPSCs. (A) Schema for self-assembled vascular derivatives. (i) hPSCs are differentiated toward EVCs that can be matured into functional ECs and pericytes. (ii) Derived EVCs are embedded within a synthetic HA matrix that facilitates self-organization into vascular networks. (B) VEcad expression in day 12 differentiated hiPSC-MR31 and hESC-H9 cell lines comparing the three differentiation conditions tested (flow cytometry analysis; n = 3). (C and D) Flow cytometry plots (n = 3) of EVC derivatives assessing the expression of pluripotent markers TRA-1-60 and TRA-1-81 (C) and CD105 and CD146 (D). (E) EVC differentiation efficiency from hPSC lines per 1 million input hPSCs. (F) Flow cytometry plots (n = 3) of EVC derivatives assessing expression of VEcad double-labeled with CD105 or PDGFRβ. (Left) Isotype controls. (G) Quantitative RT-PCR analysis of EC and perivascular marker expression by EVCs and sorted VEcad+ and VEcad− cells. # denotes not detected. Data are normalized to EVCs of each specific hPSC type. (H) Flow cytometry plots (n = 3) of hematopoietic marker CD45 (hiPSC-BC1). (I) Quantitative RT-PCR of H9-EVCs for the expression of SMMHC and peripherin, compared with undifferentiated cells (d0) and mature derivatives (13, 37). Isotype controls for flow cytometry are in gray. Flow cytometry results shown are typical of the independent experiments. *P < 0.05; **P < 0.01; ***P < 0.001

Another difference from previous experiments was the use of induced pluripotent stem cells rather than bone marrow-derived endothelial precursor cells or umbilical cord-derived endothelial colony-forming cells. Gerecht’s team collaborated with Linzhao Cheng from the Institute for Cell Engineering to co-opt her expertise with induced pluripotent stem cells (iPSCs), which are made from adult cells and are de-differentiated through genetic engineering techniques to become embryonic-like stem cells.

Cheng said that this experiment is “an elegant use of human induced pluripotent stem cells that can form multiple cell types within one kind of tissue or organ and have the same genetic background [as the patient].” Cheng continued” “In addition to being able to form blood cells and neural cells as previously shown, blood-derived human induced pluripotent stem cells can also form multiple types of vascular network cells.”

To grow blood vessels, Cheng, Gerecht and others placed the stem cells into a scaffolding made of hydrogel (hyaluronic acid and water). This hydrogel was full of chemical cues that directed the cells to differentiate in to endothelial and smooth muscle cells and form a network of blood vessels. This constitutes the first time human blood vessels had been made from human pluripotent stem cells in a synthetic material.

Self-assembly of EVCs to multicellular networks in a 3D matrix. (A) Network formation from BC1-EVCs in collagen (i) and HA hydrogels (ii). (B) Sorted VEcad+ and VEcad− cells encapsulated within collagen gels were unable to form networks. (Insert) Example of a cell with typical stellate morphology, with phalloidin in green and nuclei in blue. (Scale bars: 100 μm.) (C) Vacuole formation was observed after one day as evidenced by light microscopy (LM) (i) and confocal images (ii) of vacuole vital stain, FM4-64, in red and nuclei in blue. (Scale bar: 10 μm.) (D) On day 2, network formation with enlarged lumen (i and ii) and cell sprouting (iii and iv) were visualized by LM images (i and iii) and confocal images (ii and iv) of FM4-64 in red and nuclei in blue. (Scale bars: 10 μm in i and iii; 20 μm in ii; 50 μm in iv.) (E) On day 3, complex networks were observed with enlarged and open lumen, as indicated by confocal z-stacks and orthogonal sections of FM4-64 in red and nuclei in blue. (Scale bar: 20 μm.) (F) After 3 d, multilayered structures were also detected, as demonstrated by a 3D projection image of NG2 (green), phalloidin (red), and nuclei (blue) showing NG2+ pericytes integrated onto hollow structures. Images shown are typical of the independent experiment. (Scale bars: 50 µm.)
Self-assembly of EVCs to multicellular networks in a 3D matrix. (A) Network formation from BC1-EVCs in collagen (i) and HA hydrogels (ii). (B) Sorted VEcad+ and VEcad− cells encapsulated within collagen gels were unable to form networks. (Insert) Example of a cell with typical stellate morphology, with phalloidin in green and nuclei in blue. (Scale bars: 100 μm.) (C) Vacuole formation was observed after one day as evidenced by light microscopy (LM) (i) and confocal images (ii) of vacuole vital stain, FM4-64, in red and nuclei in blue. (Scale bar: 10 μm.) (D) On day 2, network formation with enlarged lumen (i and ii) and cell sprouting (iii and iv) were visualized by LM images (i and iii) and confocal images (ii and iv) of FM4-64 in red and nuclei in blue. (Scale bars: 10 μm in i and iii; 20 μm in ii; 50 μm in iv.) (E) On day 3, complex networks were observed with enlarged and open lumen, as indicated by confocal z-stacks and orthogonal sections of FM4-64 in red and nuclei in blue. (Scale bar: 20 μm.) (F) After 3 d, multilayered structures were also detected, as demonstrated by a 3D projection image of NG2 (green), phalloidin (red), and nuclei (blue) showing NG2+ pericytes integrated onto hollow structures. Images shown are typical of the independent experiment. (Scale bars: 50 µm.)

While these networks of blood vessels looked like the real thing, would they work within a living creature? The answer that question, Gerecht and her group transplanted them into mice. After two weeks the lab-grown blood vessels had integrated with the mouse’s own blood vessels and the hydrogel had dissolved and been degraded. “That these vessels survive and function inside a living animal is a crucial step in getting them to medical application,” Kusama said.

An important follow-up to these experiments is to examine the three-dimensional structure of these blood vessels to determine if truly have all the characteristics of human blood vessels that can deliver blood to damaged tissues and help those tissues recover from injury or trauma.