A Blockchain-Based On-Chain Storage System for Electronic Health Records

A Blockchain-Based On-Chain Storage System for Electronic Health Records

Esha Malavia (1) , Aryan Patankar (2) , Heet Shap (3), Pravin Hole (4) , Prachi Tawde (5) , Satishkumar Varma (6)

1) Information Technology, Dwarkadas J. Sanghvi College of Engineering, Mumbai, India

2) Information Technology, Dwarkadas J. Sanghvi College of Engineering, Mumbai, India

3) Information Technology, Dwarkadas J. Sanghvi College of Engineering, Mumbai, India

4) Information Technology, Dwarkadas J. Sanghvi College of Engineering, Mumbai, India

5) Information Technology, Dwarkadas J. Sanghvi College of Engineering, Mumbai, India

6) Information Technology, Dwarkadas J. Sanghvi College of Engineering, Mumbai, India

Abstract – Hospitals in India face major challenges in securely and efciently sharing patient records due to centralized sys-tems, privacy risks, and poor interoperability. MediChain offers a practical, secure, and scalable solution for healthcare data sharing tailored to Indian hospitals. Scattered medical records, poor system compatibility, and weak consent practices continue to plague hospitals in India, compromising privacy and slowing down care. This paper proposes MediChain, a blockchain-based framework to support secure, transparent, and patient-centered data sharing. Smart contracts manage user registra-tion, access permissions, and immutable audit logs. Sensitive health information remains encrypted off-chain while blockchain anchors metadata for integrity verication. Implementation on Ethereum Sepolia using synthetic Synthea data demonstrated reliable consent management and record anchoring.

Index TermsBlockchain, Encryption, Privacy, Healthcare, Decentralized Systems, Smart Contracts

1. Background and Survey Overview

   Blockchain technology has gained prominence as a robust framework for maintaining secure, decentralized, and tamper-resistant digital records. The healthcare domain, which of-ten suffers from fragmented data repositories and poor sys-tem interoperability, represents a critical application area for blockchain-based electronic health record (EHR) management. Conventional healthcare information systems predominantly depend on centralized databases, exposing them to risks such as data breaches, unauthorized access, and compromised data integrity. By leveraging features such as immutability, distributed consensus, and provenance tracking, blockchain enables reliable and veriable patient record management while eliminating reliance on a single controlling authority [1]

   1. Blockchain Fundamentals

      Blockchain functions as a distributed ledger maintained across multiple network nodes, in which each block contains

      time-stamped transactions that are cryptographically linked to preceding blocks. The use of cryptographic hash functions ensures that any modication to stored data disrupts the integrity of the entire chain, thereby providing strong resis-tance to tampering. Network consensus is achieved through mechanisms such as Proof of Work (PoW), Proof of Stake (PoS), and Byzantine Fault Tolerance (BFT), which enable agreement on the ledger state without reliance on a cen-tralized authority. Owing to these characteristics, blockchain is well suited for applications that demand secure, trustless collaboration among multiple parties, including healthcare data management systems [2]

   2. Types of Blockchain

   Blockchain networks can be broadly categorized into pub-lic, private, consortium, and hybrid architectures based on their governance and access control mechanisms. Public blockchains, such as Ethereum, operate on open participa-tion models where any user can join the network, validate transactions, and view the ledger. While this ensures high transparency and decentralization, public blockchains often face challenges related to scalability, transaction latency, and data privacy, which can limit their suitability for sensitive healthcare applications.

   In contrast, private blockchains restrict network partici-pation to authorized entities and are typically managed by a single organization. This controlled access enables higher transaction throughput, reduced latency, and stronger pri-vacy guarantees, making private blockchains more appropriate for hospital-centric deployments where data condentiality is critical. Consortium blockchains extend this concept by allowing multiple trusted organizations, such as hospitals or healthcare providers, to collectively manage the network. This model balances decentralization and governance, promoting

   interoperability and shared control without exposing data to the public [1]

   Hybrid blockchain systems combine elements of both public and private architectures by maintaining sensitive data and operations within permissioned environments while anchoring selected metadata or verication proofs on public blockchains. This approach enables public veriability and auditability while preserving regulatory compliance and patient privacy. For electronic health record (EHR) management systems, private and consortium blockchains are generally preferred, as they offer better alignment with healthcare regulations, data protection requirements, and operational scalability.

   B

   LOCKCHAIN

   F

   RAME

2. Comparison of works

   Various blockchain frameworks have been developed, each offering different performance characteristics, consensus strategies, and integration exibility.

   TABLE I

   Framework

   Public / Private

   Very

   Permission Type

   Ethereum

   Hyperledger Fabric

   Corda Quorum Polygon

   Private

   Consensus Model

   PoS / PoW PBFT

   Healthcare Suit-ability

   High

   High

   Consortium

   Private Public

   BFT IBFT

   PoS + Layer-2

   High

   Moderate Moderate

   Comparison of Blockchain Frameworks

3. On-Chain vs Off-Chain Storage Models

   Existing EHR blockchain architectures use either full on-chain storage or hybrid off-chain models. On-chain storage provides maximum immutability and audit transparency but is constrained by scalability and gas cost. Off-chain storage solutions such as IPFS store patient data externally, while only hashes or metadata are stored on-chain.

   TABLE II

   Comparison of Storage Approaches

   Feature	On-Chain Storage	Off-Chain Storage
   Immutability	Very High	Moderate
   Cost	High	Low
   Scalability	Low	High
   Security Risk	Minimal	Requires External Trust

4. Applications of Blockchain Across Domains

   Blockchain technology has been widely adopted across di-verse domains including nance, digital identity management, supply chain tracking, energy trading, and government record-keeping. Its decentralized and tamper-resistant characteristics have enabled secure transaction processing, transparent audit-ing, and improved trust across multi-stakeholder systems [3].

   Within the healthcare sector, blockchain has shown signicant potential in applications such as secure electronic health record (EHR) management, automation of insurance claims, verica-tion of pharmaceutical supply chains to prevent counterfeit drugs, and ensuring data integrity in clinical trials [4]. These pratical deployments indicate the increasing maturity and technical feasibility of blockchain-based healthcare solutions. Consequently, they highlight the need for further research and development of fully on-chain EHR systems that can provide enhanced transparency, stronger data integrity guarantees, and improved patient-centric control over medical information [5] [6]

5. Literature Review

   1. Research Gaps

      Despite notable advancements in blockchain-enabled health-care solutions, the majority of existing frameworks continue to adopt hybrid storage architectures in which sensitive patient in-formation is stored off-chain while only hashes or metadata are anchored on the blockchain. Although this approach attempts to address scalability and storage overhead, it introduces con-tinued reliance on centralized or semi-centralized infrastruc-ture, thereby weakening the core decentralization guarantees of blockchain technology. Such dependencies raise concerns related to data privacy, long-term availability, and trust, partic-ularly when off-chain storage providers become compromised or unavailable. Several studies have also highlighted that ne-grained consent enforcement and comprehensive provenance tracking are often implemented in a limited or fragmented manner, reducing transparency and accountability across the entire lifecycle of medical data [7], [8].

      A substantial portion of current research emphasizes con-ceptual architectures or theoretical evaluations rather than fully deployable and rigorously validated systems. This has resulted in a persistent gap between academic contributions and real-world adoption within operational hospital environments [9], [10]. Moreover, experimental validation using authentic and anonymized clinical datasets remains relatively scarce, lim-iting the ability to assess system robustness under practical conditions. Critical performance aspects such as scalability, transaction latency, and operational cost are often evaluated in isolation and not under region-specic workloads. This limita-tion is particularly evident in large, heterogeneous healthcare ecosystems such as those found in India, where infrastructure constraints and high transaction volumes pose additional chal-lenges [4], [11].

      These collective limitations highlight the need for a fully on-chain, patient-centric electronic health record management solution that minimizes dependence on external infrastructure while providing strong guarantees of data integrity, trace-ability, and transparency [12]. Such a system should enable veriable and decentralized access control, enforce patient consent in a systematic manner, and maintain tamper-resistant audit trails that can be independently validated by authorized stakeholders. Recent studies further emphasize that addressing interoperability barriers and deployment challenges is essential

      for achieving large-scale adoption of blockchain-based EHR systems [6], [13]. Addressing these challenges is critical for enabling secure, efcient, and trustworthy healthcare data exchange in real-world clinical environments, thereby improv-ing institutional workows, strengthening patient trust, and supporting long-term healthcare digital transformation [14], [15].

   2. Conclusion on Observations

   A comparative review of existing studies indicates that blockchain technology consistently improves data integrity, immutability, and traceability within healthcare systems. At the same time, the literature highlights several practical lim-itations, including transaction latency, cost efciency, and challenges related to user accessibility. [16] Many proposed solutions remain largely conceptual, with limited implemen-tation or insufcient integration into real hospital infrastruc-tures. These observations underline the need to balance strong technical design with practical clinical usability [17]. The proposed MediChain framework responds to these challenges by implementing a fully decentralized and provenance-aware electronic health record system on the Ethereum Sepolia network. The system is evaluated using synthetic datasets and anonymized patient records from JJ Hospital, thereby narrowing the gap between theoretical research and deployable healthcare solutions.

6. Proposed System

   1. Research Objectives

      MediChain is a blockchain-driven electronic health record management system designed to ensure data provenance, in-tegrity, and transparency without relying on centralized storage infrastructure. The primary objective of this research is to develop a fully on-chain e-healthcare framework that provides tamper-resistant medical data storage by leveraging the inher-ent immutability and cryptographic hashing mechanisms of blockchain technology. The system incorporates provenance awareness to support accountability and transparency by en-abling every operation, including record creation, modication, and access, to be time-stamped and traceable to its originating entity.

      The proposed framework is implemented using the Ethereum Sepolia test network in conjunction with a Next.js-based frontend, enabling seamless interaction between de-ployed smart contracts and the user interface. The system is evaluated using synthetic Synthea datasets as well as anonymized real-world hospital records obtained from JJ Hos-pital to validate design correctness and data traceability. In addition, MediChain adopts blockchain-based authentication mechanisms to achieve decentralized access control, thereby eliminating reliance on conventional usernamepassword au-thentication schemes.

   2. System Architecture

      1. Frontend: The user interface of the proposed system is built using Next.js, a React-based framework that supports

         the development of efcient, responsive, and scalable web applications. For visual styling, Tailwind CSS is employed, enabling a consistent, exible, and professional design while simplifying layout customization.

      2. Blockchain Integration: The system is deployed and tested on the Ethereum Sepolia test network, which serves as a controlled blockchain environment for smart contract execution. Sepolia closely replicates real-world blockchain be-havior while allowing experimentation and validation without the nancial overhead associated with mainnet deployment.

      3. Wallet Integration: MetaMask is integrated as the pri-mary wallet interface to facilitate user authentication and transaction authorization. Through MetaMask, users can se-curely connect their blockchain accounts, approve transactions, and interact directly with the deployed smart contracts in a decentralized manner.

      4. Smart Contracts: The smart contracts forming the core logic of the system are developed and deployed using the Remix IDE, a web-based development platform tailored for Solidity-based applications. These contracts manage health-care record operations, enforce access control policies, and govern transaction execution, ensuring secure and reliable handling of electronic health records [18]

   3. Data Flow

      The system follows a well-dened workow to support the secure storage, modication, and retrieval of healthcare information across the blockchain network.

      1. User Interaction: Users initiate interaction with the system by connecting their MetaMask wallet, which serves as the mechanism for identity verication through blockchain credentials. Once the wallet connection is successfully estab-lished, users are granted the ability to submit new healthcare records, update existing information, or view stored medical data based on their authorized access level.

      2. Data Submission: When healthcare information such as patient medical records or practitionerdetails is entered, the data is transmitted from the frontend interface to the blockchain layer. Each submission generates a transaction that is digitally signed using the users wallet, ensuring authen-ticity, integrity, and secure transmission of the data to the network.

      3. Smart Contract Execution: The signed transaction in-vokes the appropriate smart contract function responsible for processing the requested operation, such as record creation or modication. Upon execution, the healthcare data is recorded on the blockchain in an immutable manner, providing trans-parency and resistance to unauthorized alteration.

      4. Data Retrieval: To access stored information, users interact with the systems frontend, which communicates with the blockchain by invoking relevant smart contract functions. The requested data is then retrieved from the blockchain and presented to the user, ensuring consistent and veriable access to healthcare records.

         TABLE III

         Comparison with Existing Blockchain-based Healthcare Systems

         Reference	Focus Area	Key Contribution	Distinction from MediChain
         Agnal et al., IEEE ICCCT (2025)	Decentralized EMR archi-tecture	Presents a blockchain-driven framework for electronic medical records emphasizing data integrity and system interoperability.	The work remains primarily architecture-centric, while MediChain delivers a fully implemented on-chain system evaluated us-ing anonymized hospital datasets.
         Zilong and Alobaedy, IEEE EECT (2025)	Secure blockchain-based EHR management	Investigates security, scalability, and ac-cess control aspects of blockchain-enabled healthcare data systems.	MediChain enhances this approach by in-tegrating complete on-chain provenance tracking and systematic consent enforce-ment.
         Zhang et al., IEEE IoT Jour-nal (2025)	Comprehensive survey of blockchain in healthcare	Analyzes current blockchain applications, challenges, and emerging research direc-tions across healthcare ecosystems.	While survey-focused, MediChain directly addresses highlighted limitations through a deployable and validated on-chain imple-mentation.
         Kro¨ckel et al., IET Blockchain (2025)	Blockchain adoption and value realization	Examines patient benets, organizational value, and adoption barriers associated with blockchain in healthcare.	MediChain complements this perspective by concentrating on technical execution and decentralized system feasibility.
         Madhumala et al., Springer IC3N (2025)	Efcient healthcare data management using blockchain	Proposes a blockchain-based healthcare framework aimed at improving data security and operational efciency.	In contrast to hybrid storage approaches, MediChain anchors records and provenance directly on-chain without external depen-dencies.
         Patil et al., IEEE AMATHE (2025)	Blockchain-enabled EHR security mechanisms	Implements smart contract-based authoriza-tion to enhance EHR security and stake-holder coordination.	MediChain extends this model by incorpo-rating immutable audit trails and patient-centric consent control.

         Fig. 1. Interaction between users, Next.js interface, and Ethereum smart contracts.

   4. Functionality of Smart Contracts

      The MediChain architecture is derived from provenance-aware blockchain models proposed in earlier research, while simplifying the design into a single-layer, fully on-chain framework. In this architecture, both metadata and pa-tient health records are committed directly to the Ethereum blockchain, eliminating reliance on external storage layers and ensuring consistent provenance and integrity guarantees.

      1. Components:

         1. User Interface Layer (Next.js Frontend): The user interface layer is implemented using Next.js 14, a React-based framework that supports server-side rendering and API integration. MetaMask is incorporated to enable cryptographic authentication and secure transaction signing. The frontend provides role-specic dashboards that allow patients to upload records and view provenance information, doctors to request and access authorized records, and administrators to perform ledger auditing and monitoring activities.

         2. Blockchain Layer (Ethereum Sepolia): The blockchain layer constitutes the core logic of MediChain and is implemented through Solidity-based smart contracts deployed on the Ethereum Sepolia test network. This layer manages user role registration, health record lifecycle operations, and provenance tracking. Role mappings for patients, doctors, and administrators are maintained to enforce access control policies, while health records are created, updated, and retrieved directly on-chain. In addition, every transaction event is recorded to preserve lineage and traceability. All transactions are immutably stored on the blockchain, with data represented as keyvalue pairs in the form of a record identier mapped to a hashed representation of patient data. Provenance information links each modication to its previous state using block timestamps and sender addresses, enabling complete traceability of record evolution.

         3. Backend / API Layer (Next.js API Routes): The back-end layer is implemented using Next.js API routes and serves as an intermediary between the frontend and the blockchain network. This layer utilizes the Ethers.js library to interact with blockchain RPC endpoints, facilitating secure read and write operations. It manages user authentication, serializes healthcare data prior to blockchain submission, and handles transaction execution. Additionally, the backend maintains provenance indexing and local caching mechanisms to improve system responsiveness during data visualization and querying.

         4. Data Storage Layer (On-Chain): The data storage layer operates entirely on-chain, where hashed patient data, clinical summaries, and diagnostic results are permanently recorded on the Ethereum ledger. Prior to submission, each data element is processed using the Keccak-256 hashing algorithm to ensure immutability and resistance to tamper-ing. Blockchain metadata, including block numbers, times-tamps, and sender addresses, inherently serves as veriable provenance evidence, allowing the origin and chronological sequence of medical records to be independently validated.

   5. Testing and Network Deployment

      The Ethereum Sepolia test network is utilized as a secure and cost-efcient platform for system deployment and valida-tion. All system operations, including smart contract execu-tion, data storage, and data retrieval processes, are extensively tested within this environment to verify functional correctness, reliability, and security prior to any consideration of mainnet deployment.

   6. Datasets Used

      1. Connecting the Wallet: Users gain access to the system by connecting their MetaMask wallet, which serves as the primary mechanism for authentication. The wallet integration veries user credentials through blockchain-based identity conrmation, enabling secure interaction with the system.

      2. Performing Transactions: Once authenticated, users can submit healthcare-related information, approve blockchain transactions, and securely store data on the distributed ledger. All transactions are executed through wallet authorization, ensuring integrity and non-repudiation.

      3. Viewing Records: Healthcare records stored on the blockchain are retrieved through smart contract calls and presented to users in a clear and user-friendly interface. This approach ensures seamless access to information while maintaining data consistency and transparency.

      4. Synthea Dataset: Synthetic healthcare data generated using the open-source Synthea simulator is utilized for system evaluation. This dataset is employed to stress-test blockchain storage mechanisms, measure transaction latency, and assess the effectiveness of provenance querying under controlled conditions.

      5. Hospital Dataset: Anonymized patient records obtained from JJ Hospital, Mumbai, are used to evaluate real-world applicability of the proposed system. All personally identi-able information is removed prior to experimentation to ensure privacy compliance, allowing the dataset to be safely used for validating system integration and performance.

7. RESULTS

   The proposed blockchain-based healthcare data manage-ment system was deployed and evaluated on the Ethereum Sepolia test network. Comprehensive testing was conducted to validate system functionality, security properties, and per-formance characteristics under realistic operating conditions.

   1. Functional Validation

      The system successfully demonstrated all essential op-erational capabilities required for electronic health record management. Users were able to add patient medical infor-mation, including basic medical records, health conditions, and prescribed medications, through the frontend interface. Stored healthcare records were accurately retrieved from the blockchain through smart contract interactions, ensuring con-sistency between submitted and fetched data. In addition, authorized users were able to modify specic record attributes, such as health status updates or medication schedules, with

      all changes correctly reected during subsequent retrieval operations.

   2. Security Verication

      Evaluation of system security conrmed the presence of strong protective mechanisms. The inherent immutability of the blockchain ensured that all healthcare records remained re-sistant to unauthorized modication, preserving data integrity. User authentication and transaction approvals were secured through MetaMask wallet integration, which maintained con-dentiality of private keys and prevented unauthorized access. Furthermore, access control policies enforced at the smart contract level ensured that sensitive operations could only be executed by users with appropriate permissions.

   3. Performance Metrics

   Performance analysis conducted on the Sepolia test network indicated that the system operates within acceptable efciency bounds for a blockchain-based healthcare application. The average transaction conrmation time was observed to be approximately 12 seconds, while typical operations incurred gas costs of around 0.00021 ETH. Network latency during peak usage periods remained minimal, generally under 2 seconds, demonstrating stable system responsiveness under testing conditions.

   Acknowledgment

   The authors would like to sincerely thank their project guide for his continuous guidance and support throughout the course of this work. His valuable insights and technical expertise played a signicant role in the successful design, implementa-tion, and evaluation of the blockchain-based healthcare data management system. The authors are also grateful for his consistent encouragement and constructive feedback, which were essential in addressing challenges and achieving the objectives of this project.

8. Conclusion

This work demonstrates the effectiveness of integrating blockchain technology into healthcare data management to enable secure, transparent, and tamper-resistant sharing of medical information. The proposed MediChain framework addresses key challenges in electronic health record systems, including data integrity, privacy preservation, and scalability, through a fully on-chain, provenance-aware design. By lever-aging smart contracts, cryptographic hashing, and decentral-ized access control mechanisms, the system ensures reliable record management without reliance on centralized storage infrastructure.

Experimental evaluation on the Ethereum Sepolia test network conrms the feasibility of the proposed approach under realistic conditions, with acceptable transaction la-tency, low operational cost, and strong security guarantees. While the framework successfully validates the practicality of blockchain-based EHR management, challenges related to sys-tem interoperability, large-scale deployment, and integration

with existing healthcare infrastructure remain. Future work will focus on addressing these limitations through extended real-world testing and optimization, with the objective of improving operational efciency, enhancing patient care, and strengthening the security of sensitive medical data.

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