# Urine-derived stem cells efficiently assemble into micro-bone organoids supported by decellularized bone matrix microparticles for rapidly repairing bone defects through direct filling and paracrine functions

## TL;DR

Urine-derived stem cells combined with a bone matrix support create micro-bone organoids that rapidly repair bone defects and promote healing through direct and indirect mechanisms.

## Contribution

A novel bone organoid (uBOs) using urine-derived stem cells and decellularized bone matrix microparticles for efficient bone repair.

## Key findings

- uBOs generated from urine-derived stem cells and decellularized bone matrix microparticles show comparable osteogenic potential to bone marrow stem cell-derived organoids.
- uBOs promote rapid bone regeneration in a rat model within 6 weeks through direct filling and paracrine effects.
- uBOs stimulate angiogenesis and osteogenesis, offering a new tissue engineering strategy for bone defect treatment.

## Abstract

The repair of large bone defects remains a significant challenge in orthopedic clinical practice. This study aims to rapidly cultivate a novel type of bone organoids (BOs), namely uBOs (USCs@DBM-MPs derived BOs), by utilizing self-developed highly biomimetic decellularized bone matrix microparticles (DBM-MPs) as the supporting carrier in combination with non-invasively obtained urine-derived stem cells (USCs), and to explore its therapeutic efficacy and biological mechanism. In our vitro experiments confirmed that DBM-MPs exhibit excellent biocompatibility and osteoinductivity, and urine-derived stem cells (USCs) have comparable osteogenic potential to bone marrow stem cells (BMSCs). Furthermore, USCs were loaded onto DBM-MPs for osteogenic directional induction, and a novel bone organoid—uBOs, was successfully generated within 14 days. Meanwhile, compared with bBOs (BMSCs@DBM-MPs derived BOs), uBOs exhibit comparable levels of biological activity, proliferation characteristics, and osteogenic potential. Moreover, uBOs offer the advantages of a broader availability and a non-invasive acquisition process. What is particularly noteworthy is that these uBOs exhibit paracrine functions capable of promoting both angiogenesis and osteogenesis. In-vivo rat femoral condyle defect model, minimally invasive injection of uBOs into the bone defect area achieved rapid bone regeneration within only 6 weeks, perfectly repairing the defect area. The uBOs developed in this study not only as a bone substitute unit for direct filling and repair of bone defects, but also continuously induce angiogenesis and bone fusion at the defect site through their paracrine mechanism, offering a brand-new and efficient tissue engineering strategy for bone defect treatment.

Decellularized bone matrix (DBM) was initially prepared using an independent decellularization system. Subsequently, a novel bone organoid carrier—decellularized bone matrix microparticles (DBM-MPs), characterized by high biomimicry, easy accessibility, and superior osteoinductivity, was constructed via freeze-milling and filtration. Urine-derived stem cells (USCs) with non-invasive, widely available, and sustainable were utilized as the seed cells for bone organoid construction. Furthermore, USCs were loaded onto DBM-MPs for osteogenic directional induction, and a novel bone organoid—uBOs, was successfully generated within 14 days. These uBOs demonstrate paracrine functions capable of stimulating angiogenesis and osteogenesis, and can function as off-the-shelf substitutes to completely fill bone defects and achieve rapid bone repair.Image 1

•USCs supported by DBM-MPs, can efficiently generate novel micro-bone organoids (uBOs).•uBOs can function as off-the-shelf substitutes to completely fill bone defects and achieve rapid bone repair.•uBOs demonstrate paracrine functions capable of stimulating angiogenesis and osteogenesis.

USCs supported by DBM-MPs, can efficiently generate novel micro-bone organoids (uBOs).

uBOs can function as off-the-shelf substitutes to completely fill bone defects and achieve rapid bone repair.

uBOs demonstrate paracrine functions capable of stimulating angiogenesis and osteogenesis.