Biology subjects

Hixon, K. R.

Publications and source records attributed to Hixon, K. R..

4 recordsLinked to original sources

bioRxiv2025

Proliferation of Early and Mature Osteoblasts Is Required for Bone Fracture Healing in Mice

Fractures heal by rapid formation of mineralized callus. Essential to this process is proliferation of periosteal cells to supply bone-forming osteoblasts. To better understand the role of cell proliferation in fracture healing, we asked: How is callus composition altered when osteolineage cells proliferation is blocked? Do mature osteoblasts proliferate to contribute to callus formation? First, mice expressing herpes simplex virus-thymidine kinase (HSV-TK) driven by the 3.6Col1a1 promoter were treated with ganciclovir (GCV) to ablate proliferating osteolineage cells for 5 or 10 days. Analysis of callus cells using single-cell RNA-seq revealed that GCV-treated Col1-TK mice had fewer osteoblasts and chondrocytes than control mice, with more myofibroblasts and immune cells, consistent with fibrous nonunion. In controls, 15-30% of callus cells that expressed the early osteoblast markers osterix (OSX) and the late marker osteocalcin (OCN) were in the cell cycle. Next, we targeted proliferating osteoblasts at different stages of differentiation by crossing Osx-CreERT2, Ocn-Cre and Dmp1-CreERT2 mice with novel ROSA-TK mice. Following fracture, each Cre;ROSA-TK mouse line exhibited poorer radiographic healing, decreased callus bone volume and a shift from callus bone to fibrous tissue. We conclude that osteoblasts, often considered post-mitotic, proliferate after fracture to contribute to formation of mineralized callus essential to healing.

physiology↗

bioRxiv2025

Sintering 3D-Printed Hydroxyapatite-Wollastonite Lattices Improve Bioactivity and Mechanical Integrity for Bone Composite Scaffolds

The advancement of bone tissue engineering relies on the development of scaffolds that combine structural integrity with bioactivity. This study introduces a novel composite scaffold integrating three-dimensional (3D) printed hydroxyapatite (HA)-wollastonite (WOL) gyroid lattices with chitosan-gelatin cryogels, designed to fulfill these dual requirements. The HA-WOL lattices were fabricated using digital light processing (DLP) 3D-printing and subjected to optimized thermal treatment cycles demonstrating statistically superior compressive modulus and ultimate strength. This thermal process facilitated the phase transformation of HA-WOL to bioactive {beta}-tricalcium phosphate ({beta}-TCP) and silicocarnotite mixed phases, with MG63 (osteoblast-like) cell culture revealing significantly enhanced viability and biocompatibility. The chitosan-gelatin polymer network was successfully incorporated into the lattice, resulting in a composite scaffold with retained relative swelling capacity, improved mechanical stability, and superior bioactivity compared to cryogel-only constructs. Additional MG63 cell culture studies revealed that the composite scaffold supported cell viability and proliferation into the constructs, demonstrating its potential to conduct tissue regeneration across bone defects. This work highlights the synergistic effects of integrating bioactive ceramics with polymer-based cryogels, offering a promising solution to address bone regeneration in orthopaedic reconstruction. Future research will focus on in vivo validation and optimization of scaffold architecture to further enhance clinical relevance. This study paves the way for next-generation composite scaffolds capable of bridging the gap between mechanical integrity and biological performance in bone regeneration.

bioengineering↗

bioRxiv2024

PoreVision: A Program for Enhancing Efficiency and Accuracy in SEM Pore Analyses

Porous bulk materials are frequently utilized as cell scaffolds in tissue engineering. Previous studies have highlighted the significance of scaffold pore size and pore orientation in influencing cell migration and differentiation. Moreover, there exists a considerable body of research focused on optimizing pore characteristics to enhance scaffold performance. However, current methods for numerical pore characterization typically involve expensive machines or manual size measurements using image manipulation software. In this project, our objective is to develop a user-friendly, versatile, and freely accessible software tool using Python scripting. This tool aims to streamline and objectify pore characterization, thereby accelerating research efforts and providing a standardized framework for researchers working with porous materials. By facilitating quantitative analysis of pore size, shape, and orientation, our software tool will contribute to a more comprehensive understanding of scaffold properties and their impact on cellular behavior. Ultimately, we aim to aid researchers in the field of tissue engineering with a user-friendly tool that enhances the reproducibility and reliability of pore characterization analyses.

bioengineering↗

bioRxiv2020

Ablation of Proliferating Osteoblast Lineage Cells After Fracture Leads to Atrophic Nonunion in a Mouse Model

Nonunion is defined as the permanent failure of a fractured bone to heal, often necessitating surgical intervention. Atrophic nonunions are a subtype that are particularly difficult to treat. Animal models of atrophic nonunion are available; however, these require surgical or radiation-induced trauma to disrupt periosteal healing. These methods are invasive and not representative of many clinical nonunions where osseous regeneration has been arrested by a "failure of biology". We hypothesized that arresting osteoblast cell proliferation after fracture would lead to atrophic nonunion in mice. Using mice that express a thymidine kinase (tk) "suicide gene" driven by the 3.6Col1a1 promoter (Col1-tk), proliferating osteoblast lineage cells can be ablated upon exposure to the nucleoside analog ganciclovir (GCV). Wild-type (WT; control) and Col1-tk littermates were subjected to a full femur fracture and intramedullary fixation at 12 weeks age. We confirmed abundant tk+ cells in fracture callus of Col-tk mice dosed with water or GCV, specifically many osteoblasts, osteocytes, and chondrocytes at the cartilage-bone interface. Histologically, we observed altered callus composition in Col1-tk mice at 2 and 3 weeks post fracture, with significantly less bone and more fibrous tissue. Col1-tk mice, monitored for 12 weeks with in vivo radiographs and microCT scans, had delayed bone bridging and reduced callus size. Following sacrifice, ex vivo microCT and histology demonstrated failed union with residual bone fragments and fibrous tissue in Col1-tk mice. Biomechanical testing demonstrated a failure to recover torsional strength in Col1-tk mice, in contrast to WT. Our data indicates that suppression of proliferating osteoblast-lineage cells for at least 2 weeks after fracture blunts the formation and remodeling of a mineralized callus leading to a functional nonunion. We propose this as a new murine model of atrophic nonunion.

bioengineering↗