Pulsating fluid flow affects pre-osteoblast behavior and osteogenic differentiation through production of soluble factors

The intricate mechanism of PLS3 in bone homeostasis and disease

Since our discovery in 2013 that genetic defects in PLS3 lead to bone fragility, the mechanistic details of this process have remained obscure. It has been established that PLS3 variants cause syndromic and nonsyndromic osteoporosis as well as osteoarthritis. PLS3 codes for an actin-bundling protein with a broad pattern of expression. As such, it is puzzling how PLS3 specifically leads to bone-related disease presentation. Our review aims to summarize the current state of knowledge regarding the function of PLS3 in the predominant cell types in the bone tissue, the osteocytes, osteoblasts and osteoclasts. This is related to the role of PLS3 in regulating mechanotransduction, calcium regulation, vesicle trafficking, cell differentiation and mineralization as part of the complex bone pathology presented by PLS3 defects. Considering the consequences of PLS3 defects on multiple aspects of bone tissue metabolism, our review motivates the study of its mechanism in bone diseases which can potentially help in the design of suitable therapy.

Osteogenic Activity on NaOH-Etched Three-Dimensional-Printed Poly-ɛ-Caprolactone Scaffolds in Perfusion or Spinner Flask Bioreactor

Bioreactor systems, for example, spinner flask and perfusion bioreactors, and cell-seeded three-dimensional (3D)-printed scaffolds are used in bone tissue engineering strategies to stimulate cells and produce bone tissue suitable for implantation into the patient. The construction of functional and clinically relevant bone graft using cell-seeded 3D-printed scaffolds within bioreactor systems is still a challenge. Bioreactor parameters, for example, fluid shear stress and nutrient transport, will crucially affect cell function on 3D-printed scaffolds. Therefore, fluid shear stress induced by spinner flask and perfusion bioreactors might differentially affect osteogenic responsiveness of pre-osteoblasts inside 3D-printed scaffolds. We designed and fabricated surface-modified 3D-printed poly-ɛ-caprolactone (PCL) scaffolds, as well as static, spinner flask, and perfusion bioreactors to determine fluid shear stress and osteogenic responsiveness of MC3T3-E1 pre-osteoblasts seeded on the scaffolds in the bioreactors using finite element (FE)-modeling and experiments. FE-modeling was used to quantify wall shear stress (WSS) distribution and magnitude inside 3D-printed PCL scaffolds within spinner flask and perfusion bioreactors. MC3T3-E1 pre-osteoblasts were seeded on NaOH surface-modified 3D-printed PCL scaffolds, and cultured in customized static, spinner flask, and perfusion bioreactors up to 7 days. The scaffolds' physicochemical properties and pre-osteoblast function were assessed experimentally. FE-modeling showed that spinner flask and perfusion bioreactors locally affected WSS distribution and magnitude inside the scaffolds. The WSS distribution was more homogeneous inside scaffolds in perfusion than in spinner flask bioreactors. The average WSS on scaffold-strand surfaces ranged from 0 to 6.5 mPa for spinner flask bioreactors, and from 0 to 4.1 mPa for perfusion bioreactors. Surface modification of scaffolds by NaOH resulted in a surface with a honeycomb-like pattern and increased surface roughness (1.6-fold), but decreased water contact angle (0.3-fold). Both spinner flask and perfusion bioreactors increased cell spreading, proliferation, and distribution throughout the scaffolds. Perfusion, but not spinner flask bioreactors more strongly enhanced collagen (2.2-fold) and calcium deposition (2.1-fold) throughout the scaffolds after 7 days compared with static bioreactors, likely due to uniform WSS-induced mechanical stimulation of the cells revealed by FE-modeling. In conclusion, our findings indicate the importance of using accurate FE models to estimate WSS and determine experimental conditions for designing cell-seeded 3D-printed scaffolds in bioreactor systems. Impact Statement The success of cell-seeded three-dimensional (3D)-printed scaffolds depends on cell stimulation by biomechanical/biochemical factors to produce bone tissue suitable for implantation into the patient. We designed and fabricated surface-modified 3D-printed poly-ɛ-caprolactone (PCL) scaffolds, as well as static, spinner flask, and perfusion bioreactors to determine wall shear stress (WSS) and osteogenic responsiveness of pre-osteoblasts seeded on the scaffolds using finite element (FE)-modeling and experiments. We found that cell-seeded 3D-printed PCL scaffolds within perfusion bioreactors more strongly enhanced osteogenic activity than within spinner flask bioreactors. Our results indicate the importance of using accurate FE-models to estimate WSS and determine experimental conditions for designing cell-seeded 3D-printed scaffolds in bioreactor systems.

Mechanobiology in Cells and Tissues

This Editorial is a comment on the success of the Special Issue "Mechanobiology in Cells and Tissues" published in the International Journal of Molecular Sciences [...].

Sulfated carboxymethyl cellulose and carboxymethyl κ-carrageenan immobilization on 3D-printed poly-ε-caprolactone scaffolds differentially promote pre-osteoblast proliferation and osteogenic activity

The lack of bioactivity in three-dimensional (3D)-printing of poly-є-caprolactone (PCL) scaffolds limits cell-material interactions in bone tissue engineering. This constraint can be overcome by surface-functionalization using glycosaminoglycan-like anionic polysaccharides, e.g., carboxymethyl cellulose (CMC), a plant-based carboxymethylated, unsulfated polysaccharide, and κ-carrageenan, a seaweed-derived sulfated, non-carboxymethylated polysaccharide. The sulfation of CMC and carboxymethylation of κ-carrageenan critically improve their bioactivity. However, whether sulfated carboxymethyl cellulose (SCMC) and carboxymethyl κ-carrageenan (CM-κ-Car) affect the osteogenic differentiation potential of pre-osteoblasts on 3D-scaffolds is still unknown. Here, we aimed to assess the effects of surface-functionalization by SCMC or CM-κ-Car on the physicochemical and mechanical properties of 3D-printed PCL scaffolds, as well as the osteogenic response of pre-osteoblasts. MC3T3-E1 pre-osteoblasts were seeded on 3D-printed PCL scaffolds that were functionalized by CM-κ-Car (PCL/CM-κ-Car) or SCMC (PCL/SCMC), cultured up to 28 days. The scaffolds’ physicochemical and mechanical properties and pre-osteoblast function were assessed experimentally and by finite element (FE) modeling. We found that the surface-functionalization by SCMC and CM-κ-Car did not change the scaffold geometry and structure but decreased the elastic modulus. Furthermore, the scaffold surface roughness and hardness increased and the scaffold became more hydrophilic. The FE modeling results implied resilience up to 2% compression strain, which was below the yield stress for all scaffolds. Surface-functionalization by SCMC decreased Runx2 and Dmp1 expression, while surface-functionalization by CM-κ-Car increased Cox2 expression at day 1. Surface-functionalization by SCMC most strongly enhanced pre-osteoblast proliferation and collagen production, while CM-κ-Car most significantly increased alkaline phosphatase activity and mineralization after 28 days. In conclusion, surface-functionalization by SCMC or CM-κ-Car of 3D-printed PCL-scaffolds enhanced pre-osteoblast proliferation and osteogenic activity, likely due to increased surface roughness and hydrophilicity. Surface-functionalization by SCMC most strongly enhanced cell proliferation, while CM-κ-Car most significantly promoted osteogenic activity, suggesting that surface-functionalization by CM-κ-Car may be more promising, especially in the short-term, for in vivo bone formation.

Biomimetic 3D-printed PCL scaffold containing a high concentration carbonated-nanohydroxyapatite with immobilized-collagen for bone tissue engineering: enhanced bioactivity and physicomechanical characteristics

A challenging approach of three-dimensional (3D)-biomimetic scaffold design for bone tissue engineering is to improve scaffold bioactivity and mechanical properties. We aimed to design and fabricate 3D-polycaprolactone (PCL)-based nanocomposite scaffold containing a high concentration homogeneously distributed carbonated-nanohydroxyapatite (C-nHA)-particles in combination with immobilized-collagen to mimic real bone properties. PCL-scaffolds without/with C-nHA at 30%, 45%, and 60% (wt/wt) were 3D-printed. PCL/C-nHA60%-scaffolds were surface-modified by NaOH-treatment and collagen-immobilization. Physicomechanical and biological properties were investigated experimentally and by finite-element (FE) modeling. Scaffold surface-roughness enhanced by increasing C-nHA (1.7 - 6.1-fold), but decreased by surface-modification (0.6-fold). The contact angle decreased by increasing C-nHA (0.9 - 0.7-fold), and by surface-modification (0.5-fold). The zeta potential decreased by increasing C-nHA (3.2-9.9-fold). Average elastic modulus, compressive strength, and reaction force enhanced by increasing C-nHA and by surface-modification. FE modeling revealed that von Mises stress distribution became less homogeneous by increasing C-nHA, and by surface-modification. Maximal von Mises stress for 2% compression strain in all scaffolds did not exceed yield stress for bulk-material. 3D-printed PCL/C-nHA60% with surface-modification enhanced pre-osteoblast spreading, proliferation, collagen deposition, alkaline phosphatase activity, and mineralization. In conclusion, a novel biomimetic 3D-printed PCL-scaffold containing a high concentration C-nHA with surface-modification was successfully fabricated. It exhibited superior physicomechanical and biological properties, making it a promising biomaterial for bone tissue engineering.