Design, Fabrication, and Application of Mini-Scaffolds for Cell Component in Tissue Engineering

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Advances in the fabrication of biomaterials for gradient tissue engineering

Natural tissues and organs exhibit an array of spatial gradients, from the polar-ized neural tube during embryonic development to the osteochondral interfacepresent at articulating joints. The strong structure–function relationships inthese heterogeneous tissues have sparked intensive research into the develop-ment of methods that can replicate physiological gradients in engineered tis-sues. In this Review, we consider different gradients present in natural tissuesand discuss their critical importance in functional tissue engineering. Using thisbasis, we consolidate the existing fabrication methods into four categories: addi-tive manufacturing, component redistribution, controlled phase changes, andpostmodification. We have illustrated this with recent examples, highlightedprominent trends in thefield, and outlined a set of criteria and perspectives forgradient fabrication

Development of a static bioactive stent prototype and dynamic aneurysm-on-a-chip(TM) model for the treatment of aneurysms

Aneurysms are pockets of blood that collect outside blood vessel walls forming dilatations and leaving arterial walls very prone to rupture. Current treatments include: (1) clipping, and (2) coil embolization, including stent-assisted coiling. While these procedures can be effective, it would be advantageous to design a biologically active stent, modified with magnetic stent coatings, allowing cells to be manipulated to heal the arterial lining. Further, velocity, pressure, and wall shear stresses aid in the disease development of aneurysmal growth, but the shear force mechanisms effecting wound closure is elusive. Due to these factors, there is a definite need to cultivate a new stent device that will aid in healing an aneurysm insitu. To this end, a static bioactive stent device was synthesized. Additionally, to study aneurysm pathogenesis, a lab-on-a-chip device (a dynamic stent device) is the key to discovering the underlying mechanisms of these lesions. A first step to the reality of a true bioactive stent involves the study of cells that can be tested against the biomaterials that constitute the stent itself. The second step is to test particles/cells in a microfluidic environment. Therefore, biocompatability data was collected against PDMS, bacterial nanocellulose (BNC), and magnetic bacterial nanocellulose (MBNC). Preliminary static bioactive stents were synthesized whereby BNC was grown to cover standard nitinol stents. In an offshoot of the original research, a two-dimensional microfluidic model, the Aneurysm-on-a-ChipTM (AOC), was the logical answer to study particle flow within an aneurysm sac - this was the dynamic bioactive stent device. The AOC apparatus can track particles/cells when it is coupled to a particle image velocimetry software (PIV) package. The AOC fluid flow was visualized using standard microscopy techniques with commercial microparticles/cells. Movies were taken during fluid flow experiments and PIV was utilized to monito

Development of multifunctional hybrid scaffolds for massive bone defects filling and regeneration

Despite the growing number of survival cases, due to the increase in cases, the death rate from cancer-related diseases has been increasing over the years. Being less than 0.2% of all cancers, primary bone cancers are extremely unusual and often curable. However, about 50% of these tumors can metastasize, so early intervention is frequently necessary. Tumor or tumor-like resection derived from osteosarcoma usually leads to the creation of large bone defects, which constitute a reconstructive problem. The current standard procedures used to resolve this and other related issues are viable solutions. However, they are far from being ideal, still carrying many risks, and often failing. With the ongoing advances in a variety of theoretical subjects and in manufacturing (namely 3D printing), bone graft substitutes using smart biodegradable scaffolds are revolutionizing bone tissue engineering and regenerative medicine. In addition, despite the numerous options currently available, the scientific consensus is that the ideal bone graft should likely have a hybrid composition. The goal of this thesis is to provide an overall review of the current state-of-the-art on the main concepts associated with chitosan-based 3D scaffolds. Porous scaffolds produced by conventional fabrication techniques, using chemically cross-linked chitosan hydrogel are analysed. Due to its growing popularity, cross-linking agent genipin was selected as a case study. Follows an analysis on the most recent methods of scaffold fabrication reinforced by rapid prototyping techniques (PLA is further examined as printing material). The incorporation of bioactive agents and cells is evaluated in both options. The different factors that influence the properties of each material, the overall performance of the 3D structures, and the most common methods of surface modification are also discussed topics. To finalize, the key aspects that still need improvement and future perspectives for scaffold technology are highlighted.Representando menos de 0,2% de todos os casos de cancro, os cancros ósseos primários são extremamente incomuns e, na maioria das vezes, curáveis, no entanto, cerca de 50% destes tumores podem metastizar e, portanto, uma intervenção precoce é frequentemente necessária. A ressecção de tumores ou de variantes destes geralmente leva à criação de grandes defeitos ósseos que constituem um problema reconstrutivo. Os procedimentos padrões usados atualmente para resolver este e outros problemas relacionados são soluções viáveis, no entanto, ainda longe de serem ideais, constatando-se a presença de diversos riscos e de um elevado rácio de insucesso. Com os contínuos avanços nos demais conteúdos teóricos e em fabricação (nomeadamente impressão 3D), os substitutos de scaffolds (“andaimes”) ósseos recorrendo a suportes biodegradáveis inteligentes têm vindo a revolucionar a engenharia de tecidos ósseos e a medicina regenerativa. Para além disso, apesar das mais diversas opções atualmente disponíveis, o consenso científico é que o scaffold ideal deverá ter uma composição híbrida. Esta tese pretende fornecer uma revisão geral do estado da arte atual acerca dos principais conceitos associados a scaffolds 3D à base de quitosano. São analisados scaffolds porosos produzidos por técnicas convencionais, à base de hidrogel de quitosano reticulado quimicamente. Devido à sua crescente popularidade, o agente de reticulação genipina foi selecionado como estudo de caso. Segue se uma análise relacionada com os métodos mais recentes de fabrico de scaffoldsreforçados por técnicas de prototipagem rápida (PLA é posteriormente examinado como material de impressão). A incorporação de agentes bioativos e células é avaliada em ambas as opções. Os diferentes fatores que influenciam as propriedades de cada material, o desempenho geral da estrutura 3D e os métodos mais comuns de preparação de superfície são também tópicos discutidos. Para finalizar, destacam-se os aspetos ainda sujeitos a aperfeiçoamento e as perspetivas futuras para a tecnologia de scaffolds

3D Bioprinting for Tissue and Organ Fabrication

The field of regenerative medicine has progressed tremendously over the past few decades in its ability to fabricate functional tissue substitutes. Conventional approaches based on scaffolding and microengineering are limited in their capacity of producing tissue constructs with precise biomimetic properties. Three-dimensional (3D) bioprinting technology, on the other hand, promises to bridge the divergence between artificially engineered tissue constructs and native tissues. In a sense, 3D bioprinting offers unprecedented versatility to co-deliver cells and biomaterials with precise control over their compositions, spatial distributions, and architectural accuracy, therefore achieving detailed or even personalized recapitulation of the fine shape, structure, and architecture of target tissues and organs. Here we briefly describe recent progresses of 3D bioprinting technology and associated bioinks suitable for the printing process. We then focus on the applications of this technology in fabrication of biomimetic constructs of several representative tissues and organs, including blood vessel, heart, liver, and cartilage. We finally conclude with future challenges in 3D bioprinting as well as potential solutions for further development.United States. Office of Naval Research. Young Investigator ProgramNational Institutes of Health (U.S.) (Grants EB012597, AR057837, DE021468, HL099073 and R56AI105024)Presidential Early Career Award for Scientists and Engineer

3D bioactive composite scaffolds for bone tissue engineering

Bone is the second most commonly transplanted tissue worldwide, with over four million operations using bone grafts or bone substitute materials annually to treat bone defects. However, significant limitations affect current treatment options and clinical demand for bone grafts continues to rise due to conditions such as trauma, cancer, infection and arthritis. Developing bioactive three-dimensional (3D) scaffolds to support bone regeneration has therefore become a key area of focus within bone tissue engineering (BTE). A variety of materials and manufacturing methods including 3D printing have been used to create novel alternatives to traditional bone grafts. However, individual groups of materials including polymers, ceramics and hydrogels have been unable to fully replicate the properties of bone when used alone. Favourable material properties can be combined and bioactivity improved when groups of materials are used together in composite 3D scaffolds. This review will therefore consider the ideal properties of bioactive composite 3D scaffolds and examine recent use of polymers, hydrogels, metals, ceramics and bio-glasses in BTE. Scaffold fabrication methodology, mechanical performance, biocompatibility, bioactivity, and potential clinical translations will be discussed

A tough act to follow: collagen hydrogel modifications to improve mechanical and growth factor loading capabilities

[EN] Collagen hydrogels are among the most well-studied platforms for drug delivery and in situ tissue engineering, thanks to their low cost, low immunogenicity, versatility, biocompatibility, and similarity to the natural extracellular matrix (ECM). Despite collagen being largely responsible for the tensile properties of native connective tissues, collagen hydrogels have relatively low mechanical properties in the absence of covalent cross-linking. This is particularly problematic when attempting to regenerate stiffer and stronger native tissues such as bone. Furthermore, in contrast to hydrogels based on ECM proteins such as fibronectin, collagen hydrogels do not have any growth factor (GF)-specific binding sites and often cannot sequester physiological (small) amounts of the protein. GF binding and in situ presentation are properties that can aid significantly in the tissue regeneration process by dictating cell fate without causing adverse effects such as malignant tumorigenic tissue growth. To alleviate these issues, researchers have developed several strategies to increase the mechanical properties of collagen hydrogels using physical or chemical modifications. This can expand the applicability of collagen hydrogels to tissues subject to a continuous load. GF delivery has also been explored, mathematically and experimentally, through the development of direct loading, chemical cross-linking, electrostatic interaction, and other carrier systems. This comprehensive article explores the ways in which these parameters, mechanical properties and GF delivery, have been optimized in collagen hydrogel systems and examines their in vitro or in vivo biological effect. This article can, therefore, be a useful tool to streamline future studies in the field, by pointing researchers into the appropriate direction according to their collagen hydrogel design requirements.This work was supported by Medical Research Scotland, EPSRC (through a programme grant EP/P001114/1) and a programme of research funded by the Sir Bobby Charlton Foundation. M.S.S. acknowledges support from a grant from the UK Regenerative Medicine Platform 'Acellular/Smart Materials - 3D Architecture' (MR/R015651/1). The graphical abstract was created using BioRender.com.Sarrigiannidis, S.; Rey, JM.; Dobre, O..; González-García, C.; Dalby, M.; Salmerón Sánchez, M. (2021). A tough act to follow: collagen hydrogel modifications to improve mechanical and growth factor loading capabilities. Materials Today Bio. 10(1):1-22. https://doi.org/10.1016/j.mtbio.2021.10009812210

4D printing: a cutting-edge platform for biomedical applications

Nature's materials have evolved over time to be able to respond to environmental stimuli by generating complex structures that can change their functions in response to distance, time, and direction of stimuli. A number of technical efforts are currently being made to improve printing resolution, shape fidelity, and printing speed to mimic the structural design of natural materials with three-dimensional (3D) printing. Unfortunately, this technology is limited by the fact that printed objects are static and cannot be reshaped dynamically in response to stimuli. In recent years, several smart materials have been developed that can undergo dynamic morphing in response to a stimulus, thus resolving this issue. Four-dimensional (4D) printing refers to a manufacturing process involving additive manufacturing, smart materials, and specific geometries. It has become an essential technology for biomedical engineering and has the potential to create a wide range of useful biomedical products. This paper will discuss the concept of 4D bioprinting and the recent developments in smart matrials, which can be actuated by different stimuli and be exploited to develop biomimetic materials and structures, with significant implications for pharmaceutics and biomedical research, as well as prospects for the future

Design and Assembly Considerations in the Engineering of Vascular Tissue

Native vascular tissue functions are highly dependent on structural organization at the super-cellular, cellular, and sub-cellular spatial scales. We hypothesized that the structure-function relationship of vascular tissues in vivo can be leveraged to engineer vascular tissues in vitro by prescribing the shape of constituent cells and their assembly into organized three-dimensional structures. To this end, we first asked if vascular smooth muscle cell shape influences cellular contractility. We engineered human vascular smooth muscle cells to assume similar shapes to those in elastic and muscular arteries and then measured their contraction while stimulating with endothelin-1. We found that vascular smooth muscle cells with elongated shapes exhibited lower contractile strength but a greater percentage increase in contraction after endothelin-1 stimulation, suggesting that elongated vascular smooth muscle cell shape endows the muscular artery with greater dynamic contractile range. Next, we sought to assemble cells into tissues by employing a three-dimensional cellular patterning strategy based on the folding of porous, thin polymer films. We assembled different three-dimensional endothelial and vascular smooth muscle organizations by patterning two-dimensional poly(lactic-co-glycolic) acid and collagen thin films with cell suspensions at prescribed locations. The films were subsequently folded following Miura-ori geometry guidelines and the matrices were embedded subcutaneously in immunodeficient mice in order to assess the vascularization of the implanted constructs. We found that spatial organization that allowed endothelial and vascular smooth muscle cells to interact adjacent to each other laterally in the same folding plane created the densest vascularized network, suggesting that three-dimensional structural organization of vascular cells can influence the formation of vascularized networks. Taken together, our result shows that functional vascular tissues in vitro can be engineered by encoding structure cues in their design and assembly.Engineering and Applied Science