The production of the spider silk

The structure of the silk fibre has two components , a crystalline one incorporated in the semi - amorphous region . The crystalline section contains poly – ( Gly – Ala ) , and poly – Ala nano – domains , filling in 50 % of the volume . The weak Hydrogen bonds have the functionality to link the nano – domains , in 10 – 15 % of the volume . The overall fibre is a natural block copolymer , with the elastic capacity from 500 % to 1000 % , and with the tensile strength in the GPa magnitude .

The Araneidae , a garden spider , weaves the two - dimensional web to capture insects . The web silk for this spider does not break when the insect attaches . The retraction time of the extended web spiral is small , so that the silk does not attach to unwanted elements . The silk coated naturally with a hydroscopic glue , has increased elasticity . The researchers analyse the natural phenomenon , both in the absence , and in the presence of fluid . Figure 1 summarises two experiments , a and b , conducted with the same setup , in the laboratory . The stretching curve is red , and the retraction curve is blue .

Figure 1 . The force spectra of the silk web molecules for The Araneidae ( the orb – weaving spider ) .
Copyright ( 2003 ) Nature Publishing Group

The natural method to produce silk has yet many unknowns for the researchers . The spider silk produced naturally is in limited volume . A method to produce hand - made silk , similar to the spider silk , with lower tensile strength , is from the transgenic silk worms, and from the milk of the transgenic goats .

A suitable match between the material properties of biomaterials and the ones of the cardiac tissue may be improved . A scaffold may be electrospun with the silk solution , with or without the addition of extra cellular matrix solution .

References :

Becker N . , Oroudjev E . , Mutz S . , Cleveland J . P . , Hansma P . K . , Hayashi C . Y . , Makarov D . E . , Hansma H . G . ( 2003 ) “ Molecular nanosprings in spider capture – silk threads ” , Nature Materials , 2 , 278 - 283 .

The longitudinal monitoring for the myocardium

The imaging techniques , in suitable parameters , provide the connection between the cell therapies and the clinical procedure . The longitudinal monitoring provides information about the functioning mechanism of the reprogrammed cells in the in vivo environment . The review presents the imaging techniques that are able to explain the cause for the limited restoration process of the cell therapies in the cardiac tissue .

The human body contains approximately 3 , 7 × 10¹³ cells . The heart contains 6 × 10⁹ cells , in 300 grams ( figure 1 ) . The damage of the heart does not lead automatically to the regeneration of the full functional capacity . The scar formation and the inflammatory signals may not be enough to have a full regeneration of the cardiac tissue . The regenerative medicine enhances the healing mechanisms of the body with the cell therapy .

Figure 1 . The number of cells in the parts of the human body .
Copyright ( 2014 ) Katie Vicari / Nature Publishing Group

The minimum number of injected cells that is detectable by the imaging techniques is in the range of 10⁴ - 10⁶ cells . The heart contains 2 × 10⁷ cells in one gram of tissue , in the left ventricle . The fused positron emission tomography ( PET ) - computed tomography ( CT ) image of the porcine heart is an example for the technique ( figure 2 ) . The long arrows point to the trajectory of the thoracotomy . T is the inserted tube . The short arrows point to the 10⁸ human mesenchymal stem cells , injected in the left ventricle ( LV ) . The %ID / g is the percentage of the uptake by the injected human cells in one gram of porcine cardiac tissue .

Figure 2 . The PET - CT imaging of the expression for the reporter gene in the porcine myocardium .
Copyright ( 2009 ) RSNA

The results of a porcine model for the myocardial infarction identifies as the time for the maximum proliferation at an interval of 33 - 35 days after the injection of the mesenchymal stem cells in the myocardium .

The injected cells are not tracked in vivo if they are not labelled in vitro . The nanoparticles , as the exogeneous label , provide a strong contrast in a short acquisition time , but it is unreliable in the long - term monitoring . The incorporation process of reporter genes labels indirectly the target cell . The reporter gene in the nucleus creates reporter proteins secreted in the cytoplasm . The imaging technique detects the reporter proteins . The ideal cell label stays inside the target cells for a long time , is non - toxic , is in a concentration that is stoichiometric related to the number of target cells , and clears the system rapidly after the apoptosis of the target cells .

The challenges of the imaging techniques are the label dilution , and the cell tracking . The label dilution should remain inside the tracked cells until the apoptosis , but sometimes the dilution transfers to the host cells . The long - term tracking of the implanted cells through the imaging techniques has the challenge to quantify the number of cells from the initial implantation procedure that are alive , and the number of cells that proliferate , in the spatial and the temporal dimension .

The infarcted myocardium is trully regenerated with the aid from the cell therapies when the viable cardiac tissue in the infarct area has the volume increased , the fiber architecture is integer in structure , and the regenerated myocardium has synchronous contraction with the host .

References :

Naumova A . V . , Modo M . , Moore A . , Murry C . E . , Frank J . A . ( 2014 ) “ Clinical imaging in regenerative medicine ” , Nature Biotechnology , 32 ( 8 ) , 804 - 818 .

Willmann J . K . , Paulmurugan R . , Rodriguez - Porcel M . , Stein W . , Brinton T . J . , Connolly A . J . , Nielsen C . H . , Lutz A . M . , Lyons J . , Ikeno F . , Suzuki Y . , Rosenberg J . , Chen I . Y . , Wu J . C . , Yeung A . C . , Yock P . , Robbins R . C . , Gambhir S . S . ( 2009 ) “ Imaging gene expression in human mesenchymal stem cells : from small to large animals ” , Radiology - Radiological Society of North America , 252 ( 1 ) , 117 - 127 .

The engineering of complex tissue structures

The laboratory of transplantation biology for regenerative medicine at The University of Gothenburg in Sweden . The research group lead by Professor Suchitra Sumitran – Holgersson designed the first engineered vein succesfully transplanted in the hepatic portal circulation of a 10 - year old female , in 2012 . A donated nine centimeters long iliac vein was used in the study . The cells of the donor were cleared from the three dimensional structure of the vein . The stem cells from the bone marrow of the patient were cultured in the laboratory . The differentiated endothelial and smooth muscle cells grew and divided onto the vessel . There was no need for using immunisuppressives .

Professor Holgersson presented her three future research directions in the talk given at Ted^x in 2012 . Her research team redesiged blood vessels and the trachea , and would continue with complicated organs as the liver and the larynx . Two human organs were thrown away , and Professor Holgersson considered they should be recycled : the placenta as filling material in face cheeks and thighs , and the amniotic membrane for wrapping around areas requiring skin grafts . The animal organ , for example the pig heart , was recycled and redesigned , with the challenging task to meet the in vivo requirements .

References :

Olausson M . , Patil P . B . , Kuna V . K . , Chougule P . , Hernandez N . , Methe K . , Kullberg – Lindh C . , Borg H . , Ejnell H . , Sumitran – Holgersson S . ( 2012 ) “ Transplantation of an allogeneic vein bioengineered with autologous stem cells: a proof - of - concept study ” , The Lancet , 380 ( 9838 ) , 230 – 237 .

Cardiomyocytes for myocardial regeneration

The pumping mechanism of the heart is adjusted by the network of coronary arteries and cardiac veins . Myocardial infarction ocurs when the blood supply is disrupted . In the progressive form , this may lead to heart failure .

The repopulation of the scar is achieved through various methods . One of them is to use autologous bone marrow cells . Another strategy is to differentiate the cardiac progenitor cells ( CPC ) . A third direction is to use cardiomyocytes ( CMs ) derived from human embryonic stem cells ( hESC ) , hESCs cardiac progenitor cells ( hESC - CPC ) , human pluripotent stem cells ( hPSCs ) , or human induced pluripotent stem cells ( hiPSCs ) for the transplantation in the myocardium .

The review paper Concise review : reprogramming strategies for cardiovascular regenerative medicine : from induced pluripotent stem cells to direct reprogramming analyses more than a hundred papers . Three reprogramming strategies for the myocardial regeneration are brought in discussion ( figure 1 ) : the iPSCs technology , the partially reprogramming method and the direct set of approaches .

Figure 1 . The CMs derived from the iPSC ( top ) , the partial reprogramming ( middle ) , and the direct reprogramming technology ( below ) .

The hESCs represent the first reliable source for cardiomyocytes in vitro . The immune rejection , and the patient – or disease – specific hESCs are two challenges for the clinical allogeneic cell transplantation .

The hESCs and hiPSCs may generate beating cardiomyocytes in an inefficient method . The canonical Wnt pathway uses hiPSCs and small molecules in a more efficient signaling strategy .

Cardiomyocytes are partially reprogrammed from the iPSCs through a technology developed in 2006 . It takes a few months to differentiate the colonies of hiPSCs into the cardiac lineage . The use of partially reprogrammed cells reduces the length of time for the process to 11 – 12 days . There are also challenges for reaching the clinical practice ( figure 2 ) . Some of them are : the phenotypic heterogeneity of the differentiating CMs , the tumorigenic risk , and the poor in – vivo survival .

Figure 2 . The phases and challenges of the partially reprogrammed iPSCs method towards clinical practice .

The process of direct reprogramming of fibroblasts into induced cardiomyocyte cells ( iCMs ) is epigenetically stable . It is achieved through various combinations : by adding the Hand2 to the Gata4 , Mef2c and Tbx5 combination of transcription factors ; by using myocardin , and a combination of the Mef2c and Tbx5 transcription factors ; through a combination of a Janus inhibitor and four microRNAs ; by mixing two microRNAs and four transcription factors . The challenges of the myocardial regeneration are reduced through the deliver of reprogramming factors directly to the cardiac tissue .

Progress in the regeneration therapy is achieved if further studies are performed on early stages of myocardial infarction , if the stem cells delivered in – vivo generate efficiently new myocardium , and if the newly developed myocardium has suitable performance for the patient .