A novel and injectable strontium-containing hydroxyapatite bone cement for bone substitution: A systematic evaluation

Restoring bone defects remains a clinical challenge due to limitations in current bone graft materials. While hydroxyapatite (HA) is widely used for its osteoconductive properties, injectable forms with controlled setting times and mechanical strength are still being optimized. Existing bone cements often lack sufficient radiopacity or biocompatibility for long-term osseointegration. Researchers have explored strontium (Sr) incorporation to enhance osteogenic potential without compromising material stability. However, the specific effects of Sr-doped HA cements on stem cell behavior and in vivo integration remain understudied. This gap motivated the development of a new injectable Sr-HA cement formulation. No prior work had resolved the balance between injectability, mechanical strength, and biological compatibility in Sr-containing cements. The field requires materials that maintain structural integrity while promoting bone regeneration without cytotoxic effects. This paper addresses these unresolved questions through a systematic evaluation of a novel Sr-HA cement.

The aim of this research was to develop and evaluate a novel injectable strontium-containing hydroxyapatite (Sr-HA) bone cement for potential use in bone defect reconstruction. The specific problem addressed is the need for a bone cement that combines favorable mechanical properties with biocompatibility and osteogenic potential. The motivation stems from the limitations of current bone graft materials in terms of injectability, setting time, and integration with host bone. The study sought to determine whether Sr-HA cement could offer improved radiopacity and osseointegration while maintaining low cytotoxicity. Researchers focused on optimizing the Sr concentration and liquid composition to achieve desired mechanical and biological outcomes. The study also aimed to assess the impact of Sr-HA cement on stem cell behavior in vitro. Additionally, the researchers evaluated the material's performance in vivo to confirm its suitability for bone substitution. This work provides a systematic assessment of a new bone cement candidate.

The study involved the synthesis of Sr-HA cement using a powder formulation containing 5% strontium and a setting liquid with 5% potassium citrate. The cement composition included hydroxyapatite (HA) and α-tricalcium phosphate (TCP). Researchers tested injectability by measuring the cement's flowability and ease of delivery. Setting times were determined using standard methods for initial and final setting times. Mechanical properties such as compressive strength, maximal load, and maximum bending stress were evaluated using mechanical testing equipment. Radiopacity was assessed using X-ray imaging techniques. Biocompatibility was tested in vitro using periodontal ligament stem cells (DLSCs) and dental pulp stem cells (DPSCs) to evaluate cytotoxicity and osteogenic differentiation. In vivo studies were conducted in maxillary and tibial regions to assess osseointegration. The experimental design included both mechanical and biological assessments to comprehensively evaluate the Sr-HA cement's performance.

The Sr-HA cement demonstrated 100% injectability, indicating its suitability for minimally invasive delivery. The initial setting time was 240 seconds, and the final setting time was 420 seconds, suggesting appropriate handling properties. The cement exhibited a compressive strength of 73.4 MPa, which is comparable to existing bone cements. It also showed favorable maximal load and maximum bending stress values, indicating structural stability. Radiopacity was found to be excellent, which is beneficial for monitoring implant integration. In vitro tests revealed low cytotoxicity for cell proliferation and no significant disruption of osteogenic differentiation in DLSCs and DPSCs. The cement slightly promoted osteogenic differentiation of MC3T3 cells, suggesting potential for osseointegration. In vivo studies confirmed favorable osseointegration with the maxilla and tibia, supporting its suitability for bone substitution.

The findings suggest that the novel Sr-HA cement is a promising candidate for bone substitution due to its favorable mechanical and biological properties. The cement's injectability and setting times indicate practicality for clinical use. The compressive strength and bending stress values support its structural adequacy for bone repair. The excellent radiopacity allows for non-invasive monitoring of integration. Biocompatibility tests showed low cytotoxicity and no disruption of stem cell differentiation. The slight promotion of osteogenic differentiation in MC3T3 cells implies potential for osseointegration without adverse effects on DLSCs and DPSCs. In vivo osseointegration with the maxilla and tibia further supports its suitability for bone defect reconstruction. These results align with the authors' claim that Sr-HA cement is a suitable bone substitution material.