## 4 SSHies: An Era of Research
### Blockchain and Smart Contracts-Based Techniques in HIE Systems: A Background
The OmniPHR prototype comprises a novel blockchain-based design that optimizes health data replication across computing nodes. The study also demonstrated how the OmniPHR model can integrate distributed data into a unified view of health records, demonstrating its potential for improving healthcare systems. The authors of [45] emphasized the importance of mobile applications and blockchain technology in enhancing data exchange in mobile health applications. The incorporation of open application programming interfaces (APIs) in healthcare can streamline development processes and bolster cross-platform standardization. Additionally, the study underscored the significance of standalone apps that patients can utilize daily with minimal intervention from physicians and clinics. To address data privacy concerns on the blockchain, proxy patterns were employed, while scalability was ensured through system patterns. The proposed system facilitates seamless communication among healthcare providers, insurance providers, and users. Given the widespread use of mobile-based applications, the adoption of a useful application with an open API and enhanced interoperability has the potential to revolutionize the fundamental structure of healthcare delivery. The study conducted by [83] concentrates on transmitting health activity data from wearable and embedded devices to a distributed ledger utilizing the IOTA protocol. The authors advocate for the adoption of masked authenticated messaging (MAM) as a lightweight data transmission protocol over a tamper-proof distributed ledger for the secure broadcasting of sensitive activity data. Furthermore, they developed a system for broadcasting sensor data from wearable devices using MAM. To ensure structural and semantic interoperability, FHIR observations are encoded using logical observation identifiers names and codes (LOINC). Overall, the study underscored the significance of distributed ledger technologies in verifying the authenticity of encrypted activity data. The paper [84] aimed to create a secure and scalable FHIR chain based on blockchain technology, ONC requirements, and a Daap application to share clinical data. The proposed method involves creating a FHIR chain based on key ONC technical requirements such as verifying identity, storing and exchanging data securely, granting permission to access data sources, maintaining consistent data formats, and maintaining modularity. The Dapp securely stores and exchanges data with FHIR-based reference pointers, permits data access with token-based exchange, and maintains modularity using the MVC pattern. However, the Dapp has limitations such as not addressing semantic interoperability, compatibility with legacy systems not supporting FHIR, and control of clinical malpractice. The authors of [46] conducted testing scenarios using HyperLedger Fabric to explore various criteria and use-cases for healthcare applications. The methodology involved identifying key requirements such as security, GDPR compliance, scalability, and flexibility. The testing approach included fault tolerance testing using HyperLedger composer and HyperLedger Fabric, interactive tests, automated unit tests, and automated systems. The study concluded that blockchain is a promising solution for providing transparency, security, and privacy using consensus-driven decentralized data management on top of peer-to-peer distributed computing systems. The authors of [85] proposed, BLOSSOM a method for securing medical patient data using blockchain technology. The proposed solution includes an algorithm for creating a blockchain container, implementing a Medichain class with member functions, a proof of work algorithm for mining blocks, an algorithm for checking the validity of the blockChain using two conditions, a command line interface for interacting with the blockChain, and an algorithm for building a Merkle tree for data availability and traceability.