Topographically and Chemically Enhanced Textile Polycaprolactone Scaffolds for Tendon and Ligament Tissue Engineering

The use of tissue engineering to address the shortcomings of current procedures for tendons and ligaments is promising, but it requires a suitable scaffold that meets various mechanical, degradation-related, scalability-related, and biological requirements. Macroporous textile scaffolds made from appropriate fiber material have the potential to fulfill the first three requirements. This study aimed to investigate the biocompatibility, sterilizability, and functionalizability of a multilayer braided scaffold. These macroporous scaffolds with dimensions similar to those of the human anterior cruciate ligament consist of fibers with appropriate tensile strength and degradation behavior melt-spun from Polycaprolactone (PCL). Two different cross-sectional geometries resulting in significantly different specific surface areas and morphologies were used at the fiber level, and a Chitosan-graft-PCL (CS-g-PCL) surface modification was applied to the melt-spun substrates for the first time. All scaffolds elicited a positive cell response, and the CS-g-PCL modification provided a platform for incorporating functionalization agents such as drug delivery systems for growth factors, which were successfully released in therapeutically effective quantities. The fiber geometry was found to be a variable that could be manipulated to control the amount released. Therefore, scaled, surface-modified textile scaffolds are a versatile technology that can successfully address the complex requirements of tissue engineering for ligaments and tendons, as well as other structures.

Chemically Crosslinked Amphiphilic Degradable Shape Memory Polymer Nanocomposites with Readily Tuned Physical, Mechanical, and Biological Properties

Facile surgical delivery and stable fixation of synthetic scaffolds play roles just as critically as degradability and bioactivity in ensuring successful scaffold-guided tissue regeneration. Properly engineered shape memory polymers (SMPs) may meet these challenges. Polyhedral oligomeric silsesquioxanes (POSSs) can be covalently integrated with urethane-crosslinked polylactide (PLA) to give high-strength, degradable SMPs around physiological temperatures. To explore their potential for guided bone regeneration, here we tune their hydrophilicity, degradability, cytocompatibility, and osteoconductivity/osteoinductivity by crosslinking star-branched POSS-PLA with hydrophilic polyethylene glycol diisocyanates of different lengths and up to 60 wt % hydroxyapatite (HA). The composites exhibit high compliance, toughness, up to gigapascal storage moduli, and excellent shape recovery (>95%) at safe triggering temperatures. Water swelling ratios and hydrolytic degradation rates positively correlated with the hydrophilic crosslinker lengths, while the negative impact of degradation on the proliferation and osteogenesis of bone marrow stromal cells was mitigated with HA incorporation. Macroporous composites tailored for a rat femoral segmental defect were fabricated, and their ability to stably retain and sustainedly release recombinant osteogenic bone morphogenetic protein-2 and support cell attachment and osteogenesis was demonstrated. These properties combined make these amphiphilic osteoconductive degradable SMPs promising candidates as next-generation synthetic bone grafts.

Integrating Nanosensors into Macroporous Hydrogels for Implantation

Macroporous hydrogels are an attractive platform for implantable sensors because the network of interconnected macropores facilitates tissue integration. Embedded sensing elements, in our case, plasmonic gold nanoparticles, can transduce the presence, absence, and concentration of biochemical markers to the outside. We present here how to integrate such nanosensors into a macroporous hydrogel while preserving the nanosensor functionality in order to produce implantable sensors. We demonstrate that out of four different polymers, the poly(2-hydroxyethyl methacrylate-poly(ethylene glycole)diacrylate copolymer (pHEMA-PEGDA) results in a working sensor. Our approach of incorporating nanosized sensor elements into a hydrogel matrix generally identifies suitable polymers for implantable sensor systems.

Macroporous 3D Scaffold with Self-Fitting Capability for Effectively Repairing Massive Rotator Cuff Tear

The postoperative retear rate of direct repair of massive rotator cuff tear has risen up to 40% because of the dissatisfied tendon-to-bone healing and poor regenerative potential of remnant rotator cuff tissue. A biological scaffold that connects the remnant rotator cuff tissue and bone might be a promising substitute. In the present study, we have developed a macroporous three-dimensional scaffold poly(ester-urethane)urea (PEUU), with self-fitting capability employing thermally induced phase separation (TIPS) technique. The scaffold provides oriented connected macropores for cells migration, and promoted tendon-to-bone healing on the basis of surgical repair. The scaffolds were characterized by scanning electron microscopy, stress-strain test and cell biocompatibility study. In vitro studies exhibited that PEUU scaffold with suitable elastic mechanical properties can better support proliferation and migration of rabbit bone mesenchymal stem cells (RBMSCs). After three months postreconstruction of massive rotator cuff tear in a rabbit model using PEUU scaffold, there was complete regeneration of rotator cuff with physical tendon-to-bone interface and continuous tendon tissue, as observed from histological analysis. Further, biomechanical testing demonstrated that rotator cuff induced by PEUU scaffold had no significant difference as compared to normal rotator cuff. This macroporous, mechanically matched scaffold is potentially suitable for the application in massive rotator cuff repair. In conclusion, this study demonstrates the high efficiency of the macroporous 3D scaffold with self-fitting capability in facilitating rotator cuff regeneration.

Topotactic Fibrillogenesis of Freeze-Cast Microridged Collagen Scaffolds for 3D Cell Culture

Type I collagen is the main component of the extracellular matrix (ECM). In vitro, under a narrow window of physicochemical conditions, type I collagen self-assembles to form complex supramolecular architectures reminiscent of those found in native ECM. Presently, a major challenge in collagen-based biomaterials is to couple the delicate collagen fibrillogenesis events with a controlled shaping process in non-denaturating conditions. In this work, an ice-templating approach promoting the structuration of collagen into macroporous monoliths is used. Instead of common solvent removal procedures, a new topotactic conversion approach yielding self-assembled ordered fibrous materials is implemented. These collagen-only, non-cross-linked scaffolds exhibit uncommon mechanical properties in the wet state, with a Young's modulus of 33 ± 12 kPa, an ultimate tensile stress of 33 ± 6 kPa, and a strain at failure of 105 ± 28%. With the help of the ice-patterned microridge features, normal human dermal fibroblasts and C2C12 murine myoblasts successfully migrate and form highly aligned populations within the resulting three-dimensional (3D) collagen scaffolds. These results open a new pathway to the development of new tissue engineering scaffolds ordered across various organization levels from the molecule to the macropore and are of particular interest for biomedical applications where large-scale 3D cell alignment is needed such as for muscular or nerve reconstruction.

Development of arginine-glycine-aspartate-immobilized 3D printed poly(propylene fumarate) scaffolds for cartilage tissue engineering

Poly(propylene fumarate) (PPF) has known to be a good candidate material for cartilage tissue regeneration because of its excellent mechanical properties during its degradation processes. Here, we describe the potential application of PPF-based materials as 3D printing bioinks to create macroporous cell scaffolds using micro-stereolithography. To improve cell-matrix interaction of seeded human chondrocytes within the PPF-based 3D scaffolds, we immobilized arginine-glycine-aspartate (RGD) peptide onto the PPF scaffolds. We also evaluated various cellular behaviors of the seeded chondrocytes using MTS assay, microscopic and histological analyses. The results indicated that PPF-based biocompatible scaffolds with immobilized RGD peptide could effectively support initial adhesion and proliferation of human chondrocytes. Such a 3D bio-printable scaffold can offer an opportunity to promote cartilage tissue regeneration.

Mechanosensation across borders: fibroblasts inside a macroporous scaffold sense and respond to the mechanical environment beyond the scaffold walls

In tissue defects, cells face distinct mechanical boundary conditions, but how this influences early stages of tissue regeneration remains largely unknown. Biomaterials are used to fill defects but also to provide specific mechanical or geometrical signals. However, they might at the same time shield mechanical information from surrounding tissues that is relevant for tissue functionalisation. This study investigated how fibroblasts in a soft macroporous biomaterial scaffold respond to distinct mechanical environments while they form microtissues. Different boundary stiffnesses counteracting scaffold contraction were provided via a newly developed in vitro setup. Online monitoring over 14 days revealed 3.0 times lower microtissue contraction but 1.6 times higher contraction force for high vs. low stiffness. This difference was significant already after 48 h, a very early stage of microtissue growth. The microtissue's mechanical and geometrical adaptation indicated a collective cellular behaviour and mechanical communication across scaffold pore walls. Surprisingly, the stiffness of the environment influenced cell behaviour even inside macroporous scaffolds where direct cell-cell contacts are hindered. Mechanical communication between cells via traction forces is essential for tissue adaptation to the environment and should not be blocked by rigid biomaterials. Copyright © 2017 John Wiley & Sons, Ltd.

An experimental-numerical investigation on the effects of macroporous scaffold geometry on cell culture parameters

INTRODUCTION

Perfused bioreactors have been demonstrated to be effective in the delivery of nutrients and in the removal of waste products to and from the interior of cell-populated three-dimensional scaffolds. In this paper, a perfused bioreactor hosting a macroporous scaffold provided with a channel is used to investigate transport phenomena and culture parameters on cell growth.

METHODS

MG63 human osteosarcoma cells were seeded on macroporous poly​(ε-caprolactone) scaffolds provided with a channel. The scaffolds were cultured in a perfused bioreactor and in static conditions for 5 days. Cell viability and growth were assessed while the concentration of oxygen, glucose and lactate were measured. An in silico, multiphysics, numerical model was set up to study the fluid dynamics and the mass transport of the nutrients in the perfused bioreactor hosting different scaffold geometries.

RESULTS

The experimental and numerical results indicated that the specific cell metabolic activity in scaffolds cultured under perfusion was 30% greater than scaffolds cultured under static conditions. In addition, the scaffold provided with a channel enabled the shear stress to be controlled, the initial seeding density to be retained, and adequate mass transport and waste removal.

CONCLUSIONS

We show that the macroporous scaffold provided with a channel cultured in a macroscale bioreactor can be a robust reference experimental model system to systematically investigate and assess crucial culture parameters. We also show that such an experimental model system can be employed as a simplified "representative unit" to improve the performance of both perfused culture systems and hollow, fiber-integrated scaffolds for large-scale tissue engineering.

A compressible scaffold for minimally invasive delivery of large intact neuronal networks

Millimeter to centimeter-sized injectable neural scaffolds based on macroporous cryogels are presented. The polymer-scaffolds are made from alginate and carboxymethyl-cellulose by a novel simple one-pot cryosynthesis. They allow surgical sterility by means of autoclaving, and present native laminin as an attachment motive for neural adhesion and neurite development. They are designed to protect an extended, living neuronal network during compression to a small fraction of the original volume in order to enable minimally invasive delivery. The scaffolds behave as a mechanical meta-material: they are soft at the macroscopic scale, enabling injection through narrow-bore tubing and potentially good cellular scaffold integration in soft target tissues such as the brain. At the same time, the scaffold material has a high local Young modulus, allowing protection of the neuronal network during injection. Based on macroscopic and nanomechanical characterization, the generic geometrical and mechanical design rules are presented, enabling macroporous cellular scaffold injectability.