Foamed surfactant solution as a template for self-setting injectable hydroxyapatite scaffolds for bone regeneration

Minimally invasive orthopedic procedures demand injectable materials that can support bone regeneration. Prior research has shown that injectable scaffolds must balance structural integrity with biocompatibility. It was already known that calcium phosphates are osteoconductive but lack injectability. No prior work had resolved how to create a self-setting foam with sufficient porosity and mechanical strength. This gap motivated the exploration of surfactant-based foaming techniques. Existing studies have demonstrated the role of surfactants in stabilizing foams, but their use in injectable bone grafts remains limited. The challenge lies in achieving rapid setting without compromising cell compatibility. This paper's contribution is a novel approach to scaffold fabrication.

The aim of this work is to develop a fully synthetic injectable scaffold for bone regeneration. The specific problem is the lack of materials that combine injectability with self-setting properties. The motivation stems from the need for minimally invasive surgical options in orthopedics. This study focuses on combining alpha-tricalcium phosphate with a foamed surfactant solution. The goal is to create a scaffold that retains porosity after injection. The study also aims to evaluate the effect of processing parameters on material properties. Another objective is to assess the scaffold's ability to support osteoblastic cell activity. This approach addresses the limitations of current injectable bone graft materials.

The study involved mixing alpha-tricalcium phosphate powder with a foamed polysorbate 80 solution. Polysorbate 80 was selected for its non-ionic surfactant properties and parenteral approval. The foam was prepared by blending the powder and surfactant solution in a controlled manner. The injectability of the foam was tested at various time intervals after mixing. The foam's ability to retain structure post-injection was evaluated using imaging techniques. Mechanical properties were measured using compression tests. The effect of surfactant concentration on foam stability was analyzed. Finally, the scaffold's biocompatibility was assessed using osteoblastic-like cell cultures.

The foam retained its porous structure when injected within 2.5 minutes after mixing. The hydrolysis of alpha-TCP produced a calcium-deficient hydroxyapatite solid foam in situ. The porosity of the foam was influenced by the mixing time and surfactant concentration. Compression tests showed that the foam had sufficient mechanical strength for bone grafting. The surfactant concentration used was below the safe limit for parenteral formulations. Osteoblastic-like cells demonstrated proliferation and differentiation on the pre-set foam. The foam's macroporosity and injectability were maintained during the setting process. These findings suggest the material's potential for minimally invasive bone grafting.

The study demonstrates that a self-setting injectable hydroxyapatite foam can be produced using a surfactant-based approach. The material retains porosity and mechanical strength after injection. The surfactant concentration used was within safe limits for parenteral applications. The foam supports osteoblastic cell activity, indicating biocompatibility. The method allows for rapid setting through alpha-TCP hydrolysis. The foam's properties align with the requirements for bone regeneration materials. This approach offers a step forward in developing injectable scaffolds for orthopedic surgery. The findings suggest potential applications in minimally invasive bone grafting procedures.