  Known for its decentralized and tamper-aware properties, blockchain is
attractive to enhance the infrastructure of systems that have been constrained
by traditionally centralized and vendor-locked environments. Although
blockchain has commonly been used as the operational model behind
cryptocurrency, it has far more foreseeable utilities in domains like
healthcare, where efficient data flow is highly demanded. Particularly,
blockchain and related technologies have been touted as foundational
technologies for addressing healthcare interoperability challenges, such as
promoting effective communications and securing data exchanges across various
healthcare systems. Despite the increasing interests in leveraging blockchain
technology to improve healthcare infrastructures, a major gap in literature is
the lack of available recommendations for concrete architectural styles and
design considerations for creating blockchain-based apps and systems with a
healthcare focus. This research provides two contributions to bridge the gap in
existing research. First, we introduce a pattern sequence for designing
blockchain-based healthcare systems focused on secure and at-scale data
exchange. Our approach adapts traditional software patterns and proposes novel
patterns that take into account both the technical requirements specific to
healthcare systems and the implications of these requirements on naive
blockchain-based solutions. Second, we provide a pattern-oriented reference
architecture using an example application of the pattern sequence for guiding
software developers to design interoperable (on the technical level) healthcare
IT systems atop blockchain-based infrastructures. The reference architecture
focuses on minimizing storage requirements on-chain, preserving the privacy of
sensitive information, facilitating scalable communications, and maximizing
evolvability of the system.
