Elastomeric Tissue Research Articles

Effects of Dynamic Suit Orthoses on the Spatio-Temporal Gait Parameters in Children with Cerebral Palsy: A Systematic Review.

Dynamic suit orthoses (DSO) are currently used as a complementary treatment method in children with Cerebral Palsy (cwCP). The aim of this review was to assess the effects of interventions with DSO on the altered spatio-temporal gait parameters (STGPs) in cwCP. An electronic search was conducted in the Web of Science, Scopus, PEDro, Cochrane Library, MEDLINE/PubMed, and CINAHL databases up to July 2021. We included a total of 12 studies, which showed great heterogeneity in terms of design type, sample size, and intervention performed (two employed a Therasuit, three employed the Adeli suit, three employed Theratogs, one employed elastomeric tissue dynamic orthosis, one employed a full-body suit, one employed external belt orthosis, and one employed dynamic orthosis composed of trousers and T-shirt). The Cochrane collaboration’s tool and the Checklist for Measuring Study Quality were used to assess the risk of bias and the methodological quality of the studies. It was variable according to the Checklist for Measuring Study Quality, and it oscillated between eight and 23. The studies of higher methodological quality showed significant post-intervention changes in walking speed (which is the most widely evaluated parameter), cadence, stride length, and step length symmetry. Although the evidence is limited, the intervention with DSO combined with a programme of training/physical therapy seems to have positive effects on the STGPs in cwCP, with the functional improvements that it entails. Despite the immediate effect after one session, a number of sessions between 18 and 60 is recommended to obtain optimum results. Future studies should measure all STGPs, and not only the main ones, such as gait speed, in order to draw more accurate conclusions on the functional improvement of gait after the use of this type of intervention.

Bone Marrow Mononuclear Cell Preseeding on Bioresorbable Elastomeric Tissue Engineered Heart Valves for Transcatheter Pulmonary Valve Replacement: A Word of Caution

Objective: Initially developed for inoperable cases, transcatheter valve replacement (TVR) is being extended to lower-risk and younger patients. Tissue engineering aims at solving the degenerative ...

Engineering Citric Acid-Based Porous Scaffolds for Bone Regeneration.

Tissue engineering aims to develop scaffolds that are biocompatible and mimic the mechanical and biological properties of the target tissue as closely as possible. Here, we describe the fabrication and characterization of a biodegradable, elastomeric porous scaffold: poly(1,8-octanediol-co-citric acid) (POC) incorporated with nanoscale hydroxyapatite (HA). While this chapter focuses on the scaffold's potential for bone regeneration, POC can also be used in other tissue engineering applications requiring an elastomeric implant. Because of the relative ease with which POC can be synthesized, its mechanical properties can be tailored to mimic the structure and function of the target elastomeric tissue for enhanced tissue regeneration.

Investigation of the high-strain rate (shock and ballistic) response of the elastomeric tissue simulant Perma-Gel®

For both ethical and practical reasons accurate tissue simulant materials are essential for ballistic testing applications. A wide variety of different materials have been previously adopted for such roles, ranging from gelatin to ballistics soap. However, while often well characterised quasi-statically, there is typically a paucity of information on the high strain-rate response of such materials in the literature. Here, building on previous studies by the authors on other tissue analogues, equation-of-state data for the elastomeric epithelial/muscular simulant material Perma-Gel® is presented, along with results from a series of ballistic tests designed to illustrate its impact-related behaviour. Comparison of both hydrodynamic and ballistic behaviour to that of comparable epithelial tissues/analogues (Sylgard® and porcine muscle tissue) has provided an insight into the applicability of both Perma-Gel® and, more generally, monolithic simulants for ballistic testing purposes. Of particular note was an apparent link between the high strain-rate compressibility (evidenced in the Hugoniot relationship in the Us-up plane) and subsequent ballistic response of these materials. Overall, work conducted in this study highlighted the importance of fully characterising tissue analogues – with particular emphasis on the requirement to understand the behaviour of such analogues under impact as part of a system as well as individually.

Evaluation of a Light Activated and Elastomeric Tissue Sealant for Vascular Surgery

Objectives: Tissue adhesives (TA) and sealants may offer advantages over sutures during surgery, particularly in the reduction of operative time and procedural simplification, improving patient safety and faster recovery. However, commercially available TA still show limitations such as low adhesive strength and sealing performance, limited control over activation and poor biocompatibility. GB02 is a novel light activated sealant developed by Gecko Biomedical (Paris, France) that aims to fill this unmet clinical need. In this study the performance of GB02 for sutureless closure of vascular incisions is compared with commercially available sealants.

Patterned, tubular scaffolds mimic longitudinal and radial mechanics of the neonatal trachea

Tracheal damage, abnormality or absence can result from the growth of tumors or from Congenital High Airway Obstruction Syndrome. No optimal or routine treatment has been established for tracheal repair, despite numerous attempts with natural and artificial prostheses. The fetal trachea is comprised of cartilaginous rings connected by an elastomeric tissue. In an effort to design an engineered trachea replacement, we have synthesized 2-hydroxyethyl methacrylate hydrogels with moduli of 67±3.1kPa (soft) and 13.0±1.8MPa (hard). Given the criteria for longitudinal extensibility and lateral rigidity applied during respiration, we evaluated a series of patterned hydrogels with different sizes of hard and soft segments to mimic fetal tracheas. A 1:2 ratio of soft:hard segments resulted in a construct capable of 11.0±1% extension within the elastic range. Tubular constructs with this ratio required similar load/length for cyclic compression as ovine trachea samples. Achieving biomimetic mechanical properties in a trachea replacement may be essential for achieving normal respiration in recipient patients. Statement of SignificanceFetal abnormalities or tumors can result in tracheal absence or damage. Despite numerous attempts with natural and artificial replacements, there is still no routine treatment for tracheal repair. The literature recognizes the importance of tracheal lateral rigidity and longitudinal extensibility for normal respiration. Achieving closely matched mechanical properties may provide proper function and help decrease implant fibrosis and subsequent occlusion. In this study, we evaluated the mechanics of a series of patterned, tubular hydrogels with different ratios of hard and soft segments to mimic alternating cartilage and ligament sections in fetal tracheas. We compared our results to that of sheep trachea. This is the first report to assess both radial rigidity and longitudinal extensibility in an engineered trachea construct.

Elastomeric Cell-Laden Nanocomposite Microfibers for Engineering Complex Tissues

Biomaterials-based three dimensional scaffolds with tunable elasticity hold promise in replacing failed organs resulting from injuries, aging, and diseases by providing a suitable cellular microenvironment to facilitate regeneration of damaged tissues. However, controlled presentation of biological signals with tunable tissue mechanics and architecture remain a bottleneck that needs to be addressed to engineer functional artificial tissues. Nanocomposite hydrogels that promote cells adhesion and demonstrate tunable viscoelastic properties could mimic key properties and structures of native tissue. We have developed elastomeric fiber shaped cellular constructs from poly(ethylene glycol) diacrylate, silicate nanoparticles, and gelatin methacrylate via ionic and covalent crosslinking. By controlling the interactions between nanoparticles and polymers, nanocomposite hydrogels with tunable mechanical and degradation properties are fabricated. By encapsulating multiple cell types in these cellular constructs, we demonstrate materials-based control of cell spreading, survival, and proliferation. As a proof-of-concept, we assembled the hydrogel microfibers to obtain multicellular elastomeric tissue constructs. These elastic microfibers may serve as model systems to explore the effect of mechanical stress on cell–matrix interactions. Moreover, such elastomeric hydrogel fibers can be used to engineer scaffold structures, fabric sheets, bundles, or as building blocks for 3D tissue construction.

Robust and Semi‐Interpenetrating Hydrogels from Poly(ethylene glycol) and Collagen for Elastomeric Tissue Scaffolds

Here we present an injectable PEG/collagen hydrogel system with robust networks for use as elastomeric tissue scaffolds. Covalently crosslinked PEG and physically crosslinked collagen form semi-interpenetrating networks. The mechanical strength of the hydrogels depends predominantely on the PEG concentration but the incorporation of collagen into the PEG network enhances hydrogel viscoelasticity, elongation, and also cell adhesion properties. Experimental data show that this hydrogel system exhibits tunable mechanical properties that can be further developed. The hydrogels allow cell adhesion and proliferation in vitro. The results support the prospect of a robust and semi-interpenetrating biomaterial for elastomeric tissue scaffolds applications.

Local Tissue Geometry Determines Contractile Force Generation of Engineered Muscle Networks

The field of skeletal muscle tissue engineering is currently hampered by the lack of methods to form large muscle constructs composed of dense, aligned, and mature myofibers and limited understanding of structure-function relationships in developing muscle tissues. In our previous studies, engineered muscle sheets with elliptical pores ("muscle networks") were fabricated by casting cells and fibrin gel inside elastomeric tissue molds with staggered hexagonal posts. In these networks, alignment of cells around the elliptical pores followed the local distribution of tissue strains that were generated by cell-mediated compaction of fibrin gel against the hexagonal posts. The goal of this study was to assess how systematic variations in pore elongation affect the morphology and contractile function of muscle networks. We found that in muscle networks with more elongated pores the force production of individual myofibers was not altered, but the myofiber alignment and efficiency of myofiber formation were significantly increased yielding an increase in the total contractile force despite a decrease in the total tissue volume. Beyond a certain pore length, increase in generated contractile force was mainly contributed by more efficient myofiber formation rather than enhanced myofiber alignment. Collectively, these studies show that changes in local tissue geometry can exert both direct structural and indirect myogenic effects on the functional output of engineered muscle. Different hydrogel formulations and pore geometries will be explored in the future to further augment contractile function of engineered muscle networks and promote their use for basic structure-function studies in vitro and, eventually, for efficient muscle repair in vivo.

Functional characterization of human coronary artery smooth muscle cells under cyclic mechanical strain in a degradable polyurethane scaffold

There are few synthetic elastomeric biomaterials that simultaneously provide the required biological conditioning and the ability to translate biomechanical stimuli to vascular smooth muscle cells (VSMCs). Biomechanical stresses are important physiological elements that regulate VSMC function, and polyurethane elastomers are a class of materials capable of facilitating the translation of stress induced biomechanics. In this study, human coronary artery smooth muscle cells (hCASMCs), which were seeded into a porous degradable polar/hydrophobic/ionic (D-PHI) polyurethane scaffold, were subjected to uniaxial cyclic mechanical strain (CMS) over a span of four weeks using a customized bioreactor. The distribution, proliferation and contractile protein expression of hCASMCs in the scaffold were then analyzed and compared to those grown under static conditions. Four weeks of CMS, applied to the elastomeric scaffold, resulted in statistically greater DNA mass, more cell area coverage and a better distribution of cells deeper within the scaffold construct. Furthermore, CMS samples demonstrated improved tensile mechanical properties following four weeks of culture, suggesting the generation of more extracellular matrix within the polyurethane constructs. The expression of smooth muscle α-actin, calponin and smooth muscle myosin heavy chain and the absence of Ki-67+ cells in both static and CMS cultures, throughout the 4 weeks, suggest that hCASMCs retained their contractile character on these biomaterials. The study highlights the importance of implementing physiologically-relevant biomechanical stimuli in the development of synthetic elastomeric tissue engineering scaffolds.

Ultraviolet light crosslinking of poly(trimethylene carbonate) for elastomeric tissue engineering scaffolds

A practical method of photocrosslinking high molecular weight poly(trimethylene carbonate)(PTMC) is presented. Flexible, elastomeric and biodegradable networks could be readily prepared by UV irradiating PTMC films containing pentaerythritol triacrylate (PETA) and a photoinitiator. The network characteristics, mechanical properties, wettability, and in vitro enzymatic erosion of the photocrosslinked PTMC films were investigated. Densely crosslinked networks with gel contents up to 98% could be obtained in this manner. Upon photocrosslinking, flexible and tough networks with excellent elastomeric properties were obtained. To illustrate the ease with which the properties of the networks can be tailored, blends of PTMC with mPEG-PTMC or with PTMC-PCL-PTMC were also photocrosslinked. The wettability and the enzymatic erosion rate of the networks could be tuned by blending with block copolymers. Tissue engineering scaffolds were also fabricated using these flexible photocrosslinkable materials. After crosslinking, the fabricated PTMC-based scaffolds showed inter-connected pores and extensive microporosity. Human mesenchymal stem cell (hMSC) culturing studies showed that the photocrosslinked scaffolds prepared from PTMC and PTMC/PTMC-PCL-PTMC blends are well-suited for tissue engineering applications.

Magnetic Resonance Imaging Evaluation of Remodeling by Cardiac Elastomeric Tissue Scaffold Biomaterials in a Rat Model of Myocardial Infarction

Grafting of elastomeric biomaterial scaffolds may offer a radical strategy for the prevention of heart failure after myocardial infarction by increasing efficacy of stem cell delivery as well as acting as mechanical restraint devices to constrain scar expansion. Biomaterials can be partially optimized in vitro, but their in vivo performance is most critical and should ideally be monitored serially and noninvasively. We used magnetic resonance imaging (MRI) to assess three scaffold materials with a range of structural moduli equal to or greater than myocardial tissue: poly(glycerol sebacate) (PGS), poly(ethyleneterephathalate)/dimer fatty acid (PED), and TiO(2)-reinforced PED (PED-TiO(2)). Patches, 1 cm in diameter, were grafted onto the hearts of infarcted rats, with biomaterial-free infarcted rat hearts used as controls. MRI was able to determine scaffold size and location on the heart and identified unexpectedly rapid in vivo degradation of the PGS compared with previous in vitro testing. PED patches did not withstand in vivo attachment, but the more rigid PED-TiO(2) material was detrimental to heart function, increasing chamber and scar sizes and reducing ejection fractions compared with controls. In contrast, the mechanically compatible PGS scaffold successfully reduced hypertrophy, giving it potential for limiting excessive postinfarct remodeling. PGS was unable to support systolic function, but it would be suitable for strategies to deliver cardiac stem/progenitor cells, to limit remodeling during the period of functional cellular integration, and to degrade after cell assimilation by the heart. This work has also shown for the first time the value of using MRI as a noninvasive tool for evaluating and optimizing therapeutic biomaterials in vivo.