Hybrid design and prototyping of metamaterials and metasurfaces

Metamaterials are engineered materials conceived and designed to achieve very special or even unique physical properties, which depend on the designed micro or nanostructures, more than on the chemical composition of the raw materials employed for their fabrication. Normally metamaterials are made of periodic repetitions of unit cells or Boolean combinations of lattices or porous building blocks. Metasurfaces are the quasi-two-dimensional version of metamaterials and are generally applied to controlling electromagnetic and acoustic waves reaching them. Metamaterials are mainly created through high-precision additive manufacturing technologies, while metasurfaces are normally obtained using micromanufacturing techniques from the electronics industry and laser patterning methods. Consequently, the potential benefits and industrial applications of multi-scale or hierarchical metastructures, which could be obtained by merging metamaterials and metasurfaces, remain unexplored. Through the innovative combination of 3D CAD modelling resources and specific tools for computational mapping of topographical 2D images this study validates the possibility of texturing the building blocks and unit cells of metamaterials, hence reaching designs with interwoven metamaterials and metasurfaces. These microtextured lattices are additively manufactured, using two-photon polymerisation, to demonstrate the feasibility of bridging the gap between metamaterials and metasurfaces and analyse current challenges and potential applications of these digital materials

Hard Block Degradable Polycarbonate Urethanes : Promising Biomaterials for Electrospun Vascular Prostheses

We report biodegradable thermoplastic polyurethanes for soft tissue engineering applications, where frequently used carboxylic acid ester degradation motifs were substituted with carbonate moieties to achieve superior degradation properties. While the use of carbonates in soft blocks has been reported, their use in hard blocks of thermoplastic polyurethanes is unprecedented. Soft blocks consist of poly(hexamethylene carbonate), and hard blocks combine hexamethylene diisocyanate with the newly synthesized cleavable carbonate chain extender bis(3-hydroxypropylene)carbonate (BHPC), mimicking the motif of poly(trimethylene carbonate) with highly regarded degradation properties. Simultaneously, the mechanical benefits of segmented polyurethanes are exploited. A lower hard block concentration in BHPC-based polymers was more suitable for vascular grafts. Nonacidic degradation products and hard block dependent degradation rates were found. Implantation of BHPC-based electrospun degradable vascular prostheses in a small animal model revealed high patency rates and no signs of aneurysm formations. Specific vascular graft remodeling and only minimal signs of inflammatory reactions were observed.</p

A structural reconsideration : Linear aliphatic or alicyclic hard segments for biodegradable thermoplastic polyurethanes?

Thermoplastic polyurethane elastomers (TPUs) with a biodegradable chain extender and different nonaromatic diisocyanate hard segments were synthesized and tested concerning their thermal, mechanical, and degradation properties and for their processability regarding electrospinning. The design of the TPUs was based on the structural modification of the hard segment using linear aliphatic hexamethylene diisocyanate (HMDI), more rigid alicyclic 4,4′-methylene bis(cyclohexylisocyanate) (H12MDI), 1,3-bis(isocyanatomethyl)cyclohexane (BIMC), or isophorone diisocyanate (IPDI). The soft segment consisted of poly(tetrahydrofuran). Bis(2-hydroxyethyl) terephthalate (BET) was used as chain extender with cleavable ester bonds. Some of the polyurethanes based on alicyclic diisocyanate showed better mechanical performance than the less rigid HMDI-based TPU. The TPU in vitro degradability was tested for 25 days at elevated temperatures in PBS buffer and indicated a bulk erosion process. Electrospinning experiments were conducted and promising results with respect to further applicability of these materials in vascular tissue engineering were obtained.</p

Biocompatibility Assessment of a New Biodegradable Vascular Graft via In Vitro Co-culture Approaches and In Vivo Model

Following the implantation of biodegradable vascular grafts, macrophages and fibroblasts are the major two cell types recruited to the host-biomaterial interface. In-vitro biocompatibility assessment usually involves one cell type, predominantly macrophages. In this study, macrophage and fibroblast mono- and co-cultures, in paracrine and juxtacrine settings, were used to evaluate a new biodegradable thermoplastic polyurethane (TPU) vascular graft. Expanded-polytetrafluoroethylene (ePTFE) grafts served as controls. Pro/anti-inflammatory gene expression of macrophages and cytokines was assessed in vitro and compared to those of an in vivo rat model. Host cell infiltration and the type of proliferated cells was further studied in vivo. TPU grafts revealed superior support in cell attachment, infiltration and proliferation compared with ePTFE grafts. Expression of pro-inflammatory TNF-/IL-1 cytokines was significantly higher in ePTFE, whereas the level of IL-10 was higher in TPU. Initial high expression of pro-inflammatory CCR7 macrophages was noted in TPU, however there was a clear transition from CCR7 to anti-inflammatory CD163 expression in vitro and in vivo only in TPU, confirming superior cell-biomaterial response. The co-culture models, especially the paracrine model, revealed higher fidelity to the immunomodulatory/biocompatibility behavior of degradable TPU grafts in vivo. This study established an exciting approach developing a co-culture model as a tool for biocompatibility evaluation of degradable biomaterials.(VLID)348920