An engineer for Toyota in Melbourne, Australia, is using his own spare time and money to design and build prosthetic limbs for people who can't afford them.

What's more, he shares his designs on the internet for free so anyone with access to a 3D printer can use them.

Mat Bowtell spent thousands of dollars on 3D printers and software. He crowdfunds the material costs of building prosthetic limbs for those who don't have the means to buy what they need.

And two of the beneficiaries of Bowtell's design skills and generosity are sisters Kalani, three, and Lilli, 12, who both have a condition that meant fingers did not grow on their left hands.

Bowtell's inspirational work for the young girls from Wollongong, who were given new functional hands that can grip objects, was profiled in a TV report by 9 News Melbourne.

"The amount of satisfaction that you get from giving something to somebody for free is so much more than you get if you ever were to make any money from doing so," he told the news channel.

In 2016, Bowtell designed what he calls the "Kinetic Finger", which is "a revolutionary functional prosthetic for partial finger amputees, and the design has been released online under a free license to allow anyone to make it but not sell or profit from it," according to his fundraising page on My Cause.

"This design won me one of nine scholarships to attend and present my design at the Creative Innovation Global 2016 conference in September.

"Traditional finger prosthetics can cost between $2,000 to $5,000, making them inaccessible to most people around the world. My 'Kinetic Finger' can be manufactured for under $1 to bridge that gap. A recipient in Japan was able to play the piano again after 10 years."