Computer-aided patterning of PCL microspheres to build modular scaffolds featuring improved strength and neovascularized tissue integration

Abstract

In the past decade, modular scaffolds prepared by assembling biocompatible and biodegradable building blocks (e.g. microspheres) have found promising applications in tissue engineering (TE) towards the repair/regeneration of damaged and impaired tissues. Nevertheless, to date this approach has failed to be transferred to the clinic due to technological limitations regarding microspheres patterning, a crucial issue for the control of scaffold strength, vascularization and integration in vivo. In this work, we propose a robust and reliable approach to address this issue through the fabrication of polycaprolactone (PCL) microsphere-based scaffolds with in-silico designed microarchitectures and high compression moduli. The scaffold fabrication technique consists of four main steps, starting with the manufacture of uniform PCL microspheres by fluidic emulsion technique. In the second step, patterned polydimethylsiloxane (PDMS) moulds were prepared by soft lithography. Then, layers of 500 µm PCL microspheres with geometrically inspired patterns were obtained by casting the microspheres onto PDMS moulds followed by their thermal sintering. Finally, three-dimensional porous scaffolds were built by the alignment, stacking and sintering of multiple (up to six) layers. The so prepared scaffolds showed excellent morphological and microstructural fidelity with respect to the in-silico models, and mechanical compression properties suitable for load bearing TE applications. Designed porosity and pore size features enabled in vitro human endothelial cells adhesion and growth as well as tissue integration and blood vessels invasion in vivo. Our results highlighted the strong impact of spatial patterning of microspheres on modular scaffolds response, and pay the way about the possibility to fabricate in silico-designed structures featuring biomimetic composition and architectures for specific TE purposes.

Review on Bioinspired Design of ECM-Mimicking Scaffolds by Computer-Aided Assembly of Cell-Free and Cell Laden Micro-Modules

“…The addition of channels in a porous scaffold can also promote cell growth and rapid vascularization, thus leading to better outcomes in new tissue formation. Besides, for the regeneration of tissues featuring oriented architectures, such as nerve, muscle, tendon, ligament, and teeth, scaffolds with aligned pores are needed to direct cell alignment and migration [ 13 , 33 , 34 , 35 ]. CAD-AM techniques have revolutionized TE fabrication processes as they use medical imaging combined with virtual models and automated layer-by-layer manufacturing to control the composition and structure of porous scaffolds to meet patient-specific requirements [ 25 , 26 ].…”

“…Building blocks sintering was obtained by chemical reaction, physical reaction, cell-cell interaction, and external driving force [ 96 ]. Bone tissue scaffolds were obtained by heat or the chemical sintering of thermoplastic polymeric microspheres, such as PCL and PLGA [ 13 , 97 ]. Biological sintering, such as that modulated by cells/cells and cells/ECM interlocking, may allow for the better preservation of cellular viability and, therefore, was used to obtain hybrid cell/material constructs from cell laden modules [ 79 , 88 , 98 , 99 ].…”

“…The use of mould patterning or the integration of tissue modules within the skeletal structure of a printed thermoplastic polymer may improve the capability of the scaffolds to sustain mechanical loading. For instance, mould patterning was used to obtain cell-free microsphere-sintered TE scaffolds featuring in silico defined microarchitectures [ 13 , 110 , 111 ]. The developed approach used a replica moulding technique to create arrays of pillars onto PDMS mould that can be used to fix the position of microspheres into a well definite layered configuration [ 13 ].…”

“…Computer-aided design (CAD) and additive manufacturing (AM) have revolutionized the TE field. In fact, these techniques enabled the design and manufacture of porous implantable scaffolds characterized by patient-specific size, shape and geometrical features, reliable microstructural properties, and controlled biomechanical response [ 2 , 3 , 12 , 13 ]. The regenerative potential of these scaffolds was considerably improved by integrating mechanisms of loading and controlled delivery of tissue morphogenic and tissue modulator molecules, such as growth factors (GFs) [ 14 , 15 , 16 , 17 , 18 , 19 , 20 ].…”

A facile one-pot strategy for the preparation of porous polymeric microspheres via UV irradiation-induced polymerization in emulsions

“…Porous polymeric microspheres are a kind of polymer spherical particles with porosity and high crosslinking degrees. With the inherent characteristics of low density, large specific surface area and confined internal space, 1,2 porous polymeric microspheres possess unique absorption and release behaviors, which show broad application prospects in controlled drug release, 3–5 catalyst support, 6 tissue regeneration scaffolds, 7,8 microreactors 9,10 and other fields.…”