Weaving for heart valve tissue engineering.

Weaving is a resourceful technology which offers a large selection of solutions that are readily adaptable for tissue engineering (TE) of artificial heart valves (HV). The different ways that the yarns are interlaced in this technique could be used to produce complex architectures, such as the three-layer architecture of the leaflets. Once the assembly is complete, growth of cells in the scaffold would occur in the orientation of the yarn, enabling the deposition of extra cellular matrixes proteins in an oriented manner. Weaving technology is a rapidly evolving field that, first, needs to be understood, and then explored by tissue engineers, so that it could be used to create efficient scaffolds. Similarly, the textile engineers need to gain a basic understanding of key structural and mechanical aspects of the heart valve. The aim of this review is to provide the platform for joining these two fields and to enable cooperative research efforts. Moreover, examples of woven medical products and patents as well as related publication are discussed in this review, nevertheless due to the large, and continuously growing volume of data, only the aspects strictly associated with HVTE lay in the scope of this paper.

Valve Tissue Engineering with Living Absorbable Threads.

Tissue engineering (TE) depends on the population of scaffolds with appropriate cells, arranged in a specific physiological direction using a variety of techniques. Here, a novel technique of creating "living threads" is described based on thin (poly(ε-caprolactone) fibers of different diameters (23-243 µm). The fibers readily attract human mesenchymal stem cells (MSCs), which are firmly adhered. These versatile fibers can be used to produce dimensional shapes identical in shape to the cup-like structure of a normal human valve, while preserving the specific orientation of both the cells and the fibers. The MSCs on leaflets and the cells cultured in flask shown similar epitopes expression when analyzed by fluorescence activated cell sorting. Together, these characteristics have important functional implications as living absorbable fibers can be a valuable resource in TE of living tissues, including heart valves.

Alginate for cardiac regeneration: From seaweed to clinical trials.

Heart failure is a growing endemic in the aging Western population with a prevalence of over 20 million people worldwide1. Existing heart failure therapies are unable to reverse heart failure and do not address its fundamental cause, the loss of cardiomyocytes2. In order to induce myocardial regeneration for the myocardium and the heart valve, facilitate self-repair, improve tissue salvage, reduce or reverse the adverse-remodeling and ultimately achieve long-term functional stabilization and improvement in the heart function, novel strategies for therapeutic regeneration are being developed which are aiming to compensate for the insufficient and low intrinsic regenerative ability of the adult heart3. Similarly, valve replacement with mechanical or biological substitutes meets numerous hurdles. New approaches using multicellular approaches and new material are extensively studied. Most of those strategies depend on biomaterials that help to achieve functional integrated vasculogenesis and myogenesis in the heart/tissue. Especially for failed heart valve function a number of therapeutic approaches are common from corrective intervention to complete replacement4. However the complexity of the heart valve tissue and its high physical exposure has led to a variety of approaches, however therapeutic regeneration needs to be established. Beside other approaches alginate has been identified as one building block to achieve therapeutic regeneration. Alginate is a versatile and adaptable biomaterial that has found numerous biomedical applications which include wound healing, drug delivery and tissue engineering. Due to its biologically favorable properties including the ease of gelation and its biocompatibility, alginate-based hydrogels have been considered a particularly attractive material for the application in cardiac regeneration and valve replacement techniques. Here, we review current applications of alginate in cardiac regeneration as well as perspectives for the alginate-dependent, cardiac regeneration strategies.

Knitting for heart valve tissue engineering.

Knitting is a versatile technology which offers a large portfolio of products and solutions of interest in heart valve (HV) tissue engineering (TE). One of the main advantages of knitting is its ability to construct complex shapes and structures by precisely assembling the yarns in the desired position. With this in mind, knitting could be employed to construct a HV scaffold that closely resembles the authentic valve. This has the potential to reproduce the anisotropic structure that is characteristic of the heart valve with the yarns, in particular the 3-layered architecture of the leaflets. These yarns can provide oriented growth of cells lengthwise and consequently enable the deposition of extracellular matrix (ECM) proteins in an oriented manner. This technique, therefore, has a potential to provide a functional knitted scaffold, but to achieve that textile engineers need to gain a basic understanding of structural and mechanical aspects of the heart valve and in addition, tissue engineers must acquire the knowledge of tools and capacities that are essential in knitting technology. The aim of this review is to provide a platform to consolidate these two fields as well as to enable an efficient communication and cooperation among these two research areas.

Adaptation of a commonly used, chemically defined medium for human embryonic stem cells to stable isotope labeling with amino acids in cell culture.

Metabolic labeling with stable isotopes is a prominent technique for comparative quantitative proteomics, and stable isotope labeling with amino acids in cell culture (SILAC) is the most commonly used approach. SILAC is, however, traditionally limited to simple tissue culture regimens and only rarely employed in the context of complex culturing conditions as those required for human embryonic stem cells (hESCs). Classic hESC culture is based on the use of mouse embryonic fibroblasts (MEFs) as a feeder layer, and as a result, possible xenogeneic contamination, contribution of unlabeled amino acids by the feeders, interlaboratory variability of MEF preparation, and the overall complexity of the culture system are all of concern in conjunction with SILAC. We demonstrate a feeder-free SILAC culture system based on a customized version of a commonly used, chemically defined hESC medium developed by Ludwig et al. and commercially available as mTeSR1 [mTeSR1 is a trade mark of WiCell (Madison, WI) licensed to STEMCELL Technologies (Vancouver, Canada)]. This medium, together with adjustments to the culturing protocol, facilitates reproducible labeling that is easily scalable to the protein amounts required by proteomic work flows. It greatly enhances the usability of quantitative proteomics as a tool for the study of mechanisms underlying hESCs differentiation and self-renewal. Associated data have been deposited to the ProteomeXchange with the identifier PXD000151.

Organ weaving: woven threads and sheets as a step towards a new strategy for artificial organ development.

The concept of "organ weaving" is presented, a fabrication technique that can be an attractive option for the development of artificial tissues and organs. "Living threads" are created by immersing threads that are soaked in a CaCl(2) solution into a sodium-alginate-loaded cell suspension bath, encapsulating the cells and creating a bio-friendly, easily manageable starting material for building up larger scaffold structures. Such living threads have the advantage of being a particularly mild culturing medium for mammalian cells, protecting the cells during subsequent processing steps from dehydration and other rapid changes in the chemistry of the surrounding environment. Connecting different types of threads into 3D objects gives unique opportunities to address tissue engineering challenges.

"One cell-one well": a new approach to inkjet printing single cell microarrays.

A new approach to prepare arrays of sessile droplets of living single cell cultures using a liquid hydrophobic barrier prevents the samples from dehydrating, and allows for spatially addressable arrays for statistical quantitative single cell studies. By carefully advancing a thin layer of mineral oil on the substrate over the droplets during the printing, dehydration of the droplets can be prevented, and the vitality of the cells can be maintained. The net result of this confluence of submerged cell culturing and inkjet printing is facile access to spatially addressable arrays of isolated single cells on surfaces. Such single cell arrays may be particularly useful as high-throughput tools in the rapidly emerging "omics" fields of cell biology.

A practical approach to the development of inkjet printable functional ionogels-bendable, foldable, transparent, and conductive electrode materials.

Ionic liquid gels, or ionogels, are semi-conductive, flexible materials, offering a host of tunable physical properties, gaining an increasing level of scientific interest. One of the challenges of this emerging category of materials is that the structure-process-property relationships are still empirically driven. In this study, a simple, practical approach is laid out to prepare standardized libraries of these materials, for the purpose of selecting transparent, flexible conductive formulations that can be dispensed using inkjet printing. The net result of this was the optimization of a PEG-DMA ionogel formulation exhibiting an optical transparency that was greater than 94% from near-UV to near-IR from a 150 µm thick films, and a resistivity of 12.4 Ω · m.

Laser printing mediated cell patterning.

An approach for complex cell patterning, using laser printing, is described allowing essentially any cellular image or pattern to be rapidly fabricated.

Microarrays of over 2000 hydrogels--identification of substrates for cellular trapping and thermally triggered release.

In this paper we describe an approach whereby over 2000 individual polymers were synthesized, in situ, on a microscope slide using inkjet printing. Subsequent biological analysis of the entire library allowed the rapid identification of specific polymers with the desired properties. Herein we demonstrate how this array of new materials could be used for the identification of polymers that allow cellular adherence, proliferation and then mild thermal release, for multiple cell lines, including mouse embryonic stem (mES) cells. The optimal, identified hydrogels were successfully scaled-up and demonstrated excellent cell viability after thermal detachment for all cell lines tested. We believe that this approach offers an avenue to the discovery of a specific thermal release polymer for every cell line.

Inkjet fabrication of polymer microarrays and grids--solving the evaporation problem.

Polymer microarrays, consisting of either discrete features or a matrix of inter-crossed lines were directly fabricated in situ by inkjet printing individual monomers and initiator solutions in organic solvents through a film of oil, thereby allowing the rapid generation of a broad range of co-polymers, while solving the problem of selective monomer evaporation.

Inkjet fabrication of hydrogel microarrays using in situ nanolitre-scale polymerisation.

Polymer hydrogel microarrays were fabricated by inkjet printing of monomers and initiator, allowing up to 1800 individual polymer features to be printed on a single glass slide.