
Additive manufacturing – also known as 3D printing – has come a long way in a relatively short space of time. Invented in the 1980s, and popularised in the 2000s, it is now used across industries as diverse as construction, aviation and product design. Within the medical devices sector, 3D printing is being used to manufacture a broad array of implants and surgical instruments.
All the same, it’d be fair to say that 3D printing has not yet reached its full potential. Despite the maturity of the technology, widespread adoption is still lagging, and not all techniques are successful. In surveys, manufacturers have consistently cited factors like high upfront costs and limited availability of materials as reasons not to proceed.
A new approach, developed by engineers at the University of Florida, could help manufacturers overcome these limitations. The researchers say their technique, known as vapour-induced phaseseparation 3D printing (VIPS-3DP), is simpler and more economical than existing technologies, not to mention more sustainable.
With low upfront investment costs, it can be used to create both single-material and multi-material objects, making it especially well-suited to complex structures with several different parts.

“Due to the ease of adding powder materials of different sizes and compositions to the polymer ink, VIPS-3DP has an advantage over many other 3D printing techniques without specialised equipment,” explains Dr Yong Huang, a professor in the University of Florida’s department of mechanical and aerospace engineering. Although VIPS-3DP could be used across multiple sectors, medical devices manufacturers are especially well positioned to see the benefits. One day, the technology could become the go-to method for manufacturing porous medical implants, such as those used within bone tissue engineering. As Huang adds, 3D printers are also adept at manufacturing ceramic components, common in artificial bones and joints along with dental replacements.
Just a phase
Like many other 3D printing methods, VIPS-3DP is classed as a ‘direct-ink writing’ (DIW) technique, which involves dispensing ‘ink’ out of small nozzles to build up 3D structures layer-by-layer. The ‘ink’ in question is a kind of polymer-based liquid, which needs to solidify rapidly as soon as it’s laid down.
There are several ways of accomplishing this goal, but one way is via so-called ‘phase separation’. In essence, when you separate the ink into two ‘phases’ – one of which contains a concentrated solution of polymers – the newly deposited filaments will begin to solidify. This, in turn, can be achieved through various means. One is using evaporation-based methods, while another is through immersing the polymer solvent in an antisolvent bath.
While these techniques are widely used, they aren’t always optimal. As the researchers detailed in their paper, published in April in the journal Nature Communications, immersion-bath printing can be an arduous process with additional steps needed at the end. Generally speaking, the 3D printing community is looking for something greener, simpler and cheaper.
With that in mind, the researchers tried a new approach: a vaporous non-solvent mist (VIPS-3DP). This technique proved highly successful in tests, leading them to believe that VIPS-3DP has the edge in terms of “printability, process and material selection”.
According to the University of Florida, this technology has now been granted two patents. Its development was supported through funding from federal agencies, including the National Science Foundation and the Department of Energy.
Applications and advantages
So how does VIPS-3DP differ from what manufacturers are using currently? As Huang explains, phase separation techniques may not be new – but VIPS-3DP has some unique features.
“First, the use of non-volatile and recyclable chemical solvents to prepare polymer inks for printing minimises the contamination due to volatile compounds,” he says. “It also enables green manufacturing by solvent recycling.”
Second, because the printing process takes place at room temperature, energy usage is kept to a minimum. You may need to introduce some additional sintering steps after printing (i.e. compacting and solidifying the material), which consume additional energy, but the printing process itself is extremely efficient. This is good news from an environmental standpoint.
Third, and perhaps most importantly, VIPS-3DP is not reserved for polymer printing alone. You can, after all, also use VIPS-3DP to print materials such as ceramics and metals, widely used within the medical devices field.
“VIPS-3DP can be easily expanded beyond the printing of polymeric inks,” is how Huang emphatically puts it. “Colloidal inks of polymer solution-based metallic and ceramic suspensions can be successfully 3D printed in air without the need for auxiliary support.”
In practice, a manufacturer looking to pursue this approach would start by taking the metal or ceramic powder and mixing it with an applicable polymer. They might be looking to create a composite material, in which case the mixture would remain as it is. Alternatively, the polymer would function as a binder, before being removed at the end. (In this instance, the delicate powdered material is known as a ‘green part’ whereas the binding material is known as a ‘brown part’.)
$20.4bn
The size of the global 3D printing market in 2023.
Grand View Research
“The metal or ceramic powders are bound together by the solidified polymer as a green part after printing,” Huang says. “The green part can then go through a sintering process to remove the polymer matrix via thermal debinding. In other words, we heat the green part until the plastic turns into a gas.”
Once the polymer has been removed, meanwhile, the powders are placed in a controlled environment oven. Here, the temperature is raised to approximately two-thirds of their melting point, which allows the particles to fuse together without significantly distorting their printed geometry.
2.7m
The number of 3D printers in use worldwide by 2030.
Statistics
This means VIPS-3DP is a highly versatile technique when it comes to material selection. In their paper, the researchers describe printing “a wide variety” of stainless steel parts, along with copperembedded polymeric structures, nickel-tungsten carbide parts, and several others. In each of these cases, and whatever the degree of complexity, the general methodology is the same.
Pores for thought
Although you can create many different items with VIPS-3DP, the researchers say their technique is especially suitable for crafting porous objects – namely those with tiny holes or gaps within the material. This is an important feature of many implants and tissue scaffolds.
To achieve this you would simply mix a so-called ‘porogen’ material into the ink and remove it after printing. Through placing the printed parts into a coagulation and porogen dissolution bath, you would induce the polymer to fully solidify while the porogen parts are dissolved.
This approach lends itself well to objects with ‘multi-scale porosity’ – in which different parts of the material have different degrees of porousness. According to Huang, this could prove to be a real asset when it comes to manufacturing medical implants.
“Scaffolds made using VIPS-3DP have multi-scale porosity for better osseointegration,” he says. “The VIPS process introduces intra-filament micropores, while the printing conditions tune the lattice structure, adding inter-filament macropores.”
90%
The percentage of the top 50 medical device manufacturers that use 3D printing to create prototypes
Formlabs
In simple terms, when you’re designing a device that needs to integrate with bone, the porosity serves an important end. For one thing, it helps the implant ‘anchor’ onto the bone, while reducing the risk of stress shielding (a reduction in bone density commonly experienced by those with implants). For another thing, it increases the device surface area, which helps promote cell attachment and growth.
Ideally speaking, you would want a mixture of small pores (helpful for bone regeneration and protein absorption) and larger pores (helpful for the growth of new bone cells). However, that level of detail wasn’t possible up till now.
“The multi-scale porosity idea has been favoured to have high levels of bone integration around the porous medical implants,” says Huang. “It provides robust and integrated mechanical anchoring. However, there is no economical manufacturing technology to make such multi-scale porosity medical implants.”
In tests, the researchers printed a lattice structure with a porous top layer and a much denser bottom layer. They found that their printed structures were not toxic to the body’s cells. What’s more, the porous nature of the scaffold enabled significant cell growth and migration into the porous cavities – a definite advantage when designing the next generation of medical implant.
Going forward, the researchers plan on developing a ‘digital twin’ for VIPS-3DP – a virtual model of the technology that looks and functions exactly like its real-world counterpart. This will be useful for running simulations that predict how various manufacturing processes would perform on the factory floor. They also hope to identify more material combinations for VIPS-3DP applications.
“Application-wise,” adds Huang, “the next steps mainly include the adoption of VIPS-3D for medical implant printing and utilisation of printed porous parts for substance storage, material filtering, and similar uses.”
It’s early days for VIPS-3DP, and it remains to be seen what manufacturers will make of it. All the same, the central proposition of the technology is clearly very attractive. Offering manufacturers unprecedented control over the properties of their printed parts, it could yet cut costs and strengthen products, while helping them reduce their environmental footprint.