Fabrication of carrier-structures by laser processing on titanium alloys

The global market for dental and orthopedic implants has grown in recent years due to the ageing of the population. Reports indicate that the number of implant-related surgeries is increasing significantly from year to year. Despite the rapid technological advancement, some dental and orthopedic surgeries are unsuccessful due to implant-related problems such as inflammation or lack of osseointegration. Therefore, further improvements need to be made to the implants to combat these specific problems in order to significantly reduce the number of unsuccessful implant surgeries.
In the present work, laser surface texturing of Ti6Al4V was performed using a femtosecond laser system at high repetition rates to create unique micro-structures on its surface. The influence of laser pulse overlap and laser repetition rates play a major role on structure formation. Laser texturing with a high degree of overlap resulted in melting of the material, leading to the formation of specific micro-structures that can be used as cavities for drug delivery. The reason for melt formation on the surface of Ti alloy is attributed to local heat accumulation at high repetition rates. It was also demonstrated that such structures can be fabricated on materials with low thermal conductivity, which prevent heat dissipation into the bulk of the material.
Laser textured micro-structures serve as a drug- delivery cavities which are to be filled with drugs before the implantation. After the implantation is performed, drugs loaded in the cavities released to prevent bacterial adhesion and biofilm formation on the surface of the implant. In addition, laser texturing also can enhance the wettability of implants and matrix mineralization (bone formation), which was previously observed on laser textured surfaces.
Laser textured titanium alloys have demonstrated to have smaller heat-affected zone (HAZ) compared to nano- or picosecond lasers, which does not affect the mechanical properties of implant. To investigate the change in mechanical properties due to laser texturing, fatigue tests were performed on textured titanium samples with two specific types of micro-structures to be used for drug delivery. Some of the samples were heat treated prior fatigue tests in order to eliminate the residual stresses induced by laser texturing. Fatigue tests revealed that micro-structures have deteriorative effect on mechanical properties of textured samples. Nevertheless, one type of micro-structures is better in terms of mechanical stability.
In addition, laser textured samples were tested on wettability. The results shown that structures are hydrophilic after the fabrication, and with time they become hydrophobic. The reason behind it is found to be chemical alteration of textured sample surfaces.
In general, above stated features suggest that surface texturing of Ti alloys using femtosecond laser direct writing is a promising method for fabrication of functional surfaces which can combat bacterial adhesion and biofilm formation after implantation.