Poly(ε-caprolactone) scaffolds of highly controlled porosity and interconnectivity derived from co-continuous polymer blends: model bead and cell infiltration behavior

A review on the application of chitosan-based polymers in liver tissue engineering

Chitosan-based polymers have enormous structural tendencies to build bioactive materials with novel characteristics, functions, and various applications, mainly in liver tissue engineering (LTE). The specific physicochemical, biological, mechanical, and biodegradation properties give the effective ways to blend these biopolymers with synthetic and natural polymers to fabricate scaffolds matrixes, sponges, and complexes. A variety of natural and synthetic biomaterials, including chitosan (CS), alginate (Alg), collagen (CN), gelatin (GL), hyaluronic acid (HA), hydroxyapatite (HAp), polyethylene glycol (PEG), polycaprolactone (PCL), poly(lactic-co-glycolic) acid (PGLA), polylactic acid (PLA), and silk fibroin gained considerable attention due to their structure-properties relationship. The incorporation of CS within the polymer matrix results in increased mechanical strength and also imparts biological behavior to the designed PU formulations. The significant and growing interest in the LTE sector, this review aims to be a detailed exploration of CS-based polymers biomaterials for LTE. A brief explanation of the sources and extraction, properties, structure, and scope of CS is described in the introduction. After that, a full overview of the liver, its anatomy, issues, hepatocyte transplantation, LTE, and CS LTE applications are discussed.

Biomaterials to enhance stem cell transplantation

The successful transplantation of stem cells has the potential to transform regenerative medicine approaches and open promising avenues to repair, replace, and regenerate diseased, damaged, or aged tissues. However, pre-/post-transplantation issues of poor cell survival, retention, cell fate regulation, and insufficient integration with host tissues constitute significant challenges. The success of stem cell transplantation depends upon the coordinated sequence of stem cell renewal, specific lineage differentiation, assembly, and maintenance of long-term function. Advances in biomaterials can improve pre-/post-transplantation outcomes by integrating biophysiochemical cues and emulating tissue microenvironments. This review highlights leading biomaterials-based approaches for enhancing stem cell transplantation.

Chitosan coatings with distinct innate immune bioactivities differentially stimulate angiogenesis, osteogenesis and chondrogenesis in poly-caprolactone scaffolds with controlled interconnecting pore size

This study tested whether osseous integration into poly (ε-caprolactone) (PCL) bioplastic scaffolds with fully-interconnecting 155 ± 8 μm pores is enhanced by an adhesive, non-inflammatory 99% degree of deacetylation (DDA) chitosan coating (99-PCL), or further incorporation of pro-inflammatory 83% DDA chitosan microparticles (83-99-PCL) to accelerate angiogenesis. New Zealand White rabbit osteochondral knee defects were press-fit with PCL, 99-PCL, 83-99-PCL, or allowed to bleed (drill-only). Between day 1 and 6 weeks of repair, drill-only defects repaired by endochondral ossification, with an 8-fold higher bone volume fraction (BVF) versus initial defects, compared to a 2-fold (99-PCL), 1.1-fold (PCL), or 0.4-fold (83-99-PCL) change in BVF. Hematoma innate immune cells swarmed to 83-99-PCL, elicited angiogenesis throughout the pores and induced slight bone resorption. PCL and 99-PCL pores were variably filled with cartilage or avascular mesenchyme near the bone plate, or angiogenic mesenchyme into which repairing trabecular bone infiltrated up to 1 mm deep. More repair cartilage covered the 99-PCL scaffold (65%) than PCL (18%) or 83-99-PCL (0%) (p < 0.005). We report the novel finding that non-inflammatory chitosan coatings promoted cartilage infiltration into and over a bioplastic scaffold, and were compatible with trabecular bone integration. This study also revealed that in vitro osteogenesis assays have limited ability to predict osseous integration into porous scaffolds, because (1) in vivo, woven bone integrates from the leading edge of regenerating trabecular bone and not from mesenchymal cells adhering to scaffold surfaces, and (2) bioactive coatings that attract inflammatory cells induce bone resorption.

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Porous polycaprolactone scaffolds elicited drawn-out osteochondral wound repair.

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Regenerating trabecular bone only infiltrated angiogenic mesenchyme free of inflammatory cells.

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83% DDA chitosan stimulated sterile inflammatory angiogenesis and trabecular bone resorption.

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99% DDA chitosan coatings promoted chondrogenesis inside and over the PCL articular surface.

Porous Carbonated Hydroxyapatite-Based Paraffin Wax Nanocomposite Scaffold for Bone Tissue Engineering: A Physicochemical Properties and Cell Viability Assay Analysis

Porosity is one of the parameters of scaffold pore structure that must be developed using paraffin wax as a synthetic polymer for making porous bioceramics carbonated hydroxyapatite (CHA). This study fabricated CHA based on abalone mussel shells (Halioitis asinina); CHA/paraffin wax nanocomposite scaffolds were synthesized using paraffin wax with concentration variations of 10, 20, and 30 wt.%. The energy-dispersive X-ray spectroscopy (EDS) results showed that the Ca/P molar ratio of CHA was 1.72, which approaches the natural bone. The addition of paraffin wax in all concentration variation treatments caused the crystallographic properties of the CHA/paraffin wax nanocomposite scaffolds to decrease. The results of pore analysis suggest that the high concentration of paraffin wax in the CHA suspension is involved in the formation of more pores on the surface of the scaffold, but only CHA/paraffin wax 30 wt.% had a scaffold with potential to be used in media with a cellular growth orientation. The micropore analysis was also supported by the cell viability assay results for CHA/paraffin wax 30 wt.% nanocomposite scaffold, where serial doses of scaffold concentrations to mouse osteoblast cells were secure. Overall, based on this analysis, the CHA/paraffin wax scaffold can be a candidate for bone tissue engineering.

Bioceramic hydroxyapatite-based scaffold with a porous structure using honeycomb as a natural polymeric Porogen for bone tissue engineering

Background

The application of bioceramic hydroxyapatite (HA) derived from materials high in calcium to tissue engineering has been of concern, namely scaffold. Scaffold pores allow for cell mobility metabolic processes, and delivery of oxygen and nutrients by blood vessel. Thus, pore architecture affects cell seeding efficiency, cell viability, migration, morphology, cell proliferation, cell differentiation, angiogenesis, mechanical strength of scaffolds, and, eventually, bone formation. Therefore, to improve the efficacy of bone regeneration, several important parameters of the pore architecture of scaffolds must be carefully controlled, including pore size, geometry, orientation, uniformity, interconnectivity, and porosity, which are interrelated and whose coordination affects the effectiveness of bone tissue engineering. The honeycomb (HCB) as natural polymeric porogen is used to pore forming agent of scaffolds. It is unique for fully interconnected and oriented pores of uniform size and high mechanical strength in the direction of the pores. The aim of this study was therefore to evaluate the effect of HCB concentration on macropore structure of the scaffolds.

Methods

Bioceramic hydroxyapatite (HA) was synthesized from abalone mussel shells (Halioitis asinina) using a precipitation method, and HA-based scaffolds were fabricated with honeycomb (HCB) as the porogen agent. Pore structure engineering was successfully carried out using HCB at concentrations of 10, 20, and 30 wt%.

Results

The Energy Dispersive X-Ray Spectroscopy (EDS) analysis revealed that the Ca/P molar ratio of HA was 1.67 (the stoichiometric ratio of HA). The Fourier Transform Infrared Spectroscopy (FTIR) spectra results for porous HA-based scaffolds and synthesized HA showed that no chemical decomposition occurred in the HA-based scaffold fabrication process. The porosity of the scaffold tended to increase when higher concentrations of HCB were added. XRD data show that the HCB was completely degraded from the scaffold material. The cell metabolic activity and morphology of the HA + HCB 30 wt% scaffold enable it to facilitate the attachment of MC3T3E1 cells on its surface.

Conclusion

HCB 30 wt% is the best concentration to fabricate the scaffold corresponding to the criteria for pores structure, crystallographic properties, chemical decomposition process and cell viability for bone tissue engineering.

Morphology, Thermal and Mechanical Properties of Co-Continuous Porous Structure of PLA/PVA Blends by Phase Separation

Poly (lactic acid) (PLA) was blended with poly (vinyl alcohol) (PVA) in the composition of 70/30 (L7V3), 60/40 (L6V4), and 50/50 (L5V5) wt.%. L7V3 exhibits a sea-island morphology, while L6V4 and L5V5 show co-continuous phase morphologies. These polymers exhibited a solitary glass transition temperature, which obeyed the Fox equation. Thereafter, the blends were made porous by an etching process in hot water (35 °C) for 0-7 days, to remove PVA. The maximum etched PVA content of L7V3, L6V4, and L5V5 was 0.5%, 13.4%, and 36.1%, respectively; hence, L5V5 exhibited a co-continuous porous morphology with the porosity of 43.4%, the degree of swelling of 47.5%, and the pore size of 2 µm. The degree of crystallinity of PLA, exposed PLA, and L7V3 showed an insignificant change. L5V5, having the highest porosity, demonstrated the highest increase in the degree of crystallinity of approximately two times, because water induced the crystallization of PLA. The high porosity of L5V5 exhibited an excellent absorption property by increasing absorption energy more than two times, as obtained by micro indention. It had the maximum indentation depth more than 250 µm. Flexural and tensile properties considerably decreased with an increase in the porosity.

Fabrication of PCL Scaffolds by Supercritical CO2 Foaming Based on the Combined Effects of Rheological and Crystallization Properties

Polycaprolactone (PCL) scaffolds have recently been developed via efficient and green supercritical carbon dioxide (scCO₂) melt-state foaming. However, previously reported gas-foamed scaffolds sometimes showed insufficient interconnectivity or pore size for tissue engineering. In this study, we have correlated the thermal and rheological properties of PCL scaffolds with their porous morphology by studying four foamed samples with varied molecular weight (MW), and particularly aimed to clarify the required properties for the fabrication of scaffolds with favorable interconnected macropores. DSC and rheological tests indicate that samples show a delayed crystallization and enhanced complex viscosity with the increasing of MW. After foaming, scaffolds (27 kDa in weight-average molecular weight) show a favorable morphology (pore size = 70–180 μm, porosity = 90% and interconnectivity = 96%), where the lowest melt strength favors the generation of interconnected macropore, and the most rapid crystallization provides proper foamability. The scaffolds (27 kDa) also possess the highest Young’s modulus. More importantly, owing to the sufficient room and favorable material transportation provided by highly interconnected macropores, cells onto the optimized scaffolds (27 kDa) perform vigorous proliferation and superior adhesion and ingrowth, indicating its potential for regeneration applications. Furthermore, our findings provide new insights into the morphological control of porous scaffolds fabricated by scCO₂ foaming, and are highly relevant to a broader community that is focusing on polymer foaming.

Evaluation of scaffold microstructure and comparison of cell seeding methods using micro-computed tomography-based tools

Micro-computed tomography (micro-CT) provides a means to analyse and model three-dimensional (3D) tissue engineering scaffolds. This study proposes a set of micro-CT-based tools firstly for evaluating the microstructure of scaffolds and secondly for comparing different cell seeding methods. The pore size, porosity and pore interconnectivity of supercritical CO2 processed poly(l-lactide-co-ɛ-caprolactone) (PLCL) and PLCL/β-tricalcium phosphate scaffolds were analysed using computational micro-CT models. The models were supplemented with an experimental method, where iron-labelled microspheres were seeded into the scaffolds and micro-CT imaged to assess their infiltration into the scaffolds. After examining the scaffold architecture, human adipose-derived stem cells (hASCs) were seeded into the scaffolds using five different cell seeding methods. Cell viability, number and 3D distribution were evaluated. The distribution of the cells was analysed using micro-CT by labelling the hASCs with ultrasmall paramagnetic iron oxide nanoparticles. Among the tested seeding methods, a forced fluid flow-based technique resulted in an enhanced cell infiltration throughout the scaffolds compared with static seeding. The current study provides an excellent set of tools for the development of scaffolds and for the design of 3D cell culture experiments.

Effects of macropore size in carbonate apatite honeycomb scaffolds on bone regeneration

The pore architecture of scaffolds is a critical factor for angiogenesis and bone regeneration. Although the effects of scaffold macropore size have been investigated, most scaffolds feature macropores with poor uniformity and interconnectivity, and other parameters (e.g., microporosity, chemical composition, and strut thickness) differ among scaffolds. To clarify the threshold of effective macropore size, we fabricated honeycomb scaffolds (HCSs) with distinct macropore (i.e., channel) sizes (~100, ~200, and ~300 μm). The HCSs were composed of AB-type carbonate apatite with ~8.5% carbonate ions, i.e., the same composition as human bone mineral. Their honeycomb architecture displayed uniformly sized and orderly arranged channels with extremely high interconnectivity, and all the HCSs displayed ~100-μm-thick struts and 0.06 cm³ g^-1 of micropore volume. The compressive strengths of HCSs with ~100-, ~200-, and ~300-μm channels were higher than those of reported scaffolds, and decreased with increasing channel size: 62 ± 6, 55 ± 9, and 43 ± 8 MPa, respectively. At four weeks after implantation in rabbit femur bone defects, new bone and blood vessels were formed in all the channels of these HCSs. Notably, the ~300-μm channels were extensively occupied by new bone. We demonstrated that high interconnectivity and uniformity of channels can decrease the threshold of effective macropore size, enabling the scaffolds to maintain high mechanical properties and osteogenic ability and serve as implants for weight-bearing areas.

Medical-grade polycaprolactone scaffolds made by melt electrospinning writing for oral bone regeneration - a pilot study in vitro

BACKGROUND

The spectrum of indications for the use of membranes and scaffolds in the field of oral and maxillofacial surgery includes, amongst others, guided bone regeneration (GBR). Currently available membrane systems face certain disadvantages such as difficult clinical handling, inconsistent degradation, undirected cell growth and a lack of stability that often complicate their application. Therefore, new membranes which can overcome these issues are of great interest in this field.

METHODS

In this pilot study, we investigated polycaprolactone (PCL) scaffolds intended to enhance oral wound healing by means of melt electrospinning writing (MEW), which allowed for three-dimensional (3D) printing of micron scale fibers and very exact fiber placement. A singular set of box-shaped scaffolds of different sizes consisting of medical-grade PCL was examined and the scaffolds' morphology was evaluated via scanning electron microscopy (SEM). Each prototype sample with box sizes of 225 μm, 300 μm, 375 μm, 450 μm and 500 μm was assessed for cytotoxicity and cell growth by seeding each scaffold with human osteoblast-like cell line MG63.

RESULTS

All scaffolds demonstrated good cytocompatibility according to cell viability, protein concentration, and cell number. SEM analysis revealed an exact fiber placement of the MEW scaffolds and the growth of viable MG63 cells on them. For the examined box-shaped scaffolds with pore sizes between 225 μm and 500 μm, a preferred box size for initial osteoblast attachment could not be found.

CONCLUSIONS

These well-defined 3D scaffolds consisting of medical-grade materials optimized for cell attachment and cell growth hold the key to a promising new approach in GBR in oral and maxillofacial surgery.

Biocompatible scaffolds based on natural polymers for regenerative medicine

The chitosan and gelatine are commonly used biopolymers for the tissue engineering applications. In the previous methods for the cryogels synthesis, multistep preparation methods using toxic cross-linking agents such as glutaraldehyde are reported. Here, we present a two-step preparation method of gelatin macroporous cryogels and one-step preparation method of chitosan or gelatin cryogels. The physico-chemical properties of obtained scaffolds were characterized using FTIR, zeta potential, SEM and laser confocal microscopy. Non-toxic and biodegradable cross-linking agents such as oxidized dextran and 1,1,3,3-tetramethoxypropane are utilized. The one-step chitosan cryogels had degradation degree ~2 times higher compared to the cryogels prepared with a two-step method i.e. reduced by borohydride. Scaffolds cross-linked by glutaraldehyde had about 40% viability, whereas nine various compositions of cryogels showed significantly higher viability (~80%) of fibroblast cells in vitro. The cryogels were obtained without using the harmful compounds and therefore can be used straightforward as biocompatible and biodegradable scaffolds for the cell culturing purposes and other biomedical applications.

Cationic osteogenic peptide P15-CSP coatings promote 3-D osteogenesis in poly(epsilon-caprolactone) scaffolds of distinct pore size

P15-CSP is a biomimetic cationic fusion peptide that stimulates osteogenesis and inhibits bacterial biofilm formation when coated on 2-D surfaces. This study tested the hypothesis that P15-CSP coatings enhance 3-D osteogenesis in a porous but otherwise hydrophobic poly-(ɛ-caprolactone) (PCL) scaffold. Scaffolds of 84 µm and 141 µm average pore size were coated or not with Layer-by-Layer polyelectrolytes followed by P15-CSP, seeded with adult primary human mesenchymal stem cells (MSCs), and cultured 10 days in proliferation medium, then 21 days in osteogenic medium. Atomic analyses showed that P15-CSP was successfully captured by LbL. After 2 days of culture, MSCs adhered and spread more on P15-CSP coated pores than PCL-only. At day 10, all constructs contained nonmineralized tissue. At day 31, all constructs became enveloped in a "skin" of tissue that, like 2-D cultures, underwent sporadic mineralization in areas of high cell density that extended into some 141 µm edge pores. By quantitative histomorphometry, 2.5-fold more tissue and biomineral accumulated in edge pores versus inner pores. P15-CSP specifically promoted tissue-scaffold integration, fourfold higher overall biomineralization, and more mineral deposits in the outer 84 µm and inner 141 µm pores than PCL-only (p < 0.05). 3-D Micro-CT revealed asymmetric mineral deposition consistent with histological calcium staining. This study provides proof-of-concept that P15-CSP coatings are osteoconductive in PCL pore surfaces with 3-D topography. Biomineralization deeper than 150 µm from the scaffold edge was optimally attained with the larger 141 µm peptide-coated pores. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2171-2181, 2017.

Polymer Bioprocessing to Fabricate 3D Scaffolds for Tissue Engineering

Traditional methods for polymer processing involve the use of hazardous organic solvents which may compromise the biological function of scaffolds in tissue engineering. Indeed, the toxic effect of them on biological microenvironment has a tremendous impact on cell fate so altering the main activities involved in in vitro tissue formation. To date, extensive researches focus on seeking newer methods for bio-safely processing polymeric biomaterials to be implanted in the human body. Here, we aim at over viewing two approaches based on solvent free or green solvent based processes in order to identify alternative solutions to fabricate bio-inspired scaffolds to be successfully used in regenerative and degenerative medicine.