**4. Conclusion**

Nano-particulate calcium phosphate has shown several interesting advantages in biomedical applications because of its biocompatibility and easy preparation process. The DNA condensation characteristic of nano-particulate calcium phosphate makes it a potential choice for gene therapy system applications. Nano-particulate calcium phosphates are able to condense DNA strands, carry them in the blood, deliver the genetic material to target cells, and move them into cells resulting in reasonable transcription.

Therefore, there is a common agreement among most of the works regarding gene delivery application on utilizing the calcium phosphate to deliver the gene into the nucleus; the final target of gene therapy methods. Because of the advantages of the DNA/calcium phosphate complex, it is one of the highly appealing systems currently studied, although it has been used in in-vitro gene delivery for many years already. The translation of its application into clinical therapy methods requires more work.

Researchers need to solve the instability of calcium phosphate in physiological conditions. If calcium phosphate/DNA complexes degrade in the blood circuit, it cannot be used in most of the clinical gene delivery applications. The other problem is the low transfection efficiency, which currently limits the application of the system. There are controversial reports about the transfection efficiency of calcium phosphate/DNA system, mostly because of instability and the complicated nature of calcium phosphate in solution. Once these problems are overcome by adequate novel technologies, the excellent biocompatibility and biodegradability of calcium phosphate remains as a major advantage.
